Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

Below, you can either scroll through the complete list of our annually published material, search for a specific author or term via the free text search, or use the interactive keyword cloud to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.

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  • 2020 • 254 High-velocity water vapor corrosion of Yb-silicate: Sprayed vs. sintered body
    Bakan, E. and Kindelmann, M. and Kunz, W. and Klemm, H. and Vaßen, R.
    Scripta Materialia 178 468-471 (2020)
    The water vapor corrosion of Yb-silicates is of interest to their application as environmental barrier coatings in gas turbine technology. In this study, densified samples from the Yb-silicate powder, as well as plasma-sprayed free-standing Yb-silicate coating were tested at a high-velocity steam rig (T = 1400 °C, v = 90 m/s, PH2O = 0.19 atm) for microstructural comparison. After the test, the measured weight losses of the coatings were larger than that of the densified sample. At the same time, the thicknesses of the corroded scales at the coating surfaces were found to be thicker than that of the sintered sample by a factor of two. © 2019
    view abstractdoi: 10.1016/j.scriptamat.2019.12.019
  • 2020 • 253 An investigation on burner rig testing of environmental barrier coatings for aerospace applications
    Bakan, E. and Mack, D.E. and Lobe, S. and Koch, D. and Vaßen, R.
    Journal of the European Ceramic Society (2020)
    In this study, burner rig testing of Si/Yb2Si2O7 environmental barrier coating protected SiC-based ceramic matrix composites was conducted. Tests were performed at standard conditions as well as with liquid water injection to the flame. Furthermore, the influence of the impingement angle of the flame (45° vs. 90°) on water vapor corrosion was explored. Gas flow rates were adapted in each test to adjust 1250 °C at the sample surface. The comparison of test results showed that water injection advances the corrosion of the Yb2Si2O7 topcoat and the impingement angle affects the size and shape of the corroded area on the sample surface. © 2020 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2020.06.016
  • 2020 • 252 Efficient OER Catalyst with Low Ir Volume Density Obtained by Homogeneous Deposition of Iridium Oxide Nanoparticles on Macroporous Antimony-Doped Tin Oxide Support
    Böhm, D. and Beetz, M. and Schuster, M. and Peters, K. and Hufnagel, A.G. and Döblinger, M. and Böller, B. and Bein, T. and Fattakhova-Rohlfing, D.
    Advanced Functional Materials 30 (2020)
    A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open-porous morphology are synthesized that reach a conductivity of ≈3.6 S cm−1 and are further used as catalyst support. ATO-supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrOx colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO-supported IrO2 nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm−3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A gIr −1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO2-supported IrO2 reference catalyst under the same measurement conditions. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adfm.201906670
  • 2020 • 251 Thermal fatigue behavior of functionally graded W/EUROFER-layer systems using a new test apparatus
    Emmerich, T. and Vaßen, R. and Aktaa, J.
    Fusion Engineering and Design 154 (2020)
    In future fusion reactors tungsten coatings shall protect First Wall components, made of reduced activation ferritic martensitic steel, against the plasma, because of tungsten's favourable thermo-mechanical properties and low sputtering yield. Functionally graded material layers implemented between the coating and the steel substrate, compensate the difference in the coefficient of thermal expansion. By using the vacuum plasma spraying technique several layer systems were successfully produced and tested, among other aspects, in regard to their thermal fatigue behaviour up to 500 thermal cycles in a vacuum furnace. However, higher numbers of thermal cycles are anticipated for future fusion reactors and, therefore, a less time consuming approach for thermal fatigue testing is required. Hence, a new testing apparatus with induction heating and inert gas cooling was built and first thermal fatigue experiments with up to 5000 cycles were carried out on different functionally graded tungsten/steel layers systems. The subsequent investigations of these samples show that the layer systems are stable for the applied number of thermal cycles and their properties are solely determined during their respective coating processes. © 2020
    view abstractdoi: 10.1016/j.fusengdes.2020.111550
  • 2020 • 250 Synthesis of Novel Sulfobetaine Polymers with Differing Dipole Orientations in Their Side Chains, and Their Effects on the Antifouling Properties
    Schönemann, E. and Koc, J. and Aldred, N. and Clare, A.S. and Laschewsky, A. and Rosenhahn, A. and Wischerhoff, E.
    Macromolecular Rapid Communications 41 (2020)
    The impact of the orientation of zwitterionic groups, with respect to the polymer backbone, on the antifouling performance of thin hydrogel films made of polyzwitterions is explored. In an extension of the recent discussion about differences in the behavior of polymeric phosphatidylcholines and choline phosphates, a quasi-isomeric set of three poly(sulfobetaine methacrylate)s is designed for this purpose. The design is based on the established monomer 3-[N-2-(methacryloyloxy)ethyl-N,N-dimethyl]ammonio-propane-1-sulfonate and two novel sulfobetaine methacrylates, in which the positions of the cationic and the ionic groups relative to the polymerizable group, and thus also to the polymer backbone, are altered. The effect of the varied segmental dipole orientation on their water solubility, wetting behavior by water, and fouling resistance is compared. As model systems, the adsorption of the model proteins bovine serum albumin (BSA), fibrinogen, and lysozyme onto films of the various polyzwitterion surfaces is studied, as well as the settlement of a diatom (Navicula perminuta) and barnacle cyprids (Balanus improvisus) as representatives of typical marine fouling communities. The results demonstrate the important role of the zwitterionic group's orientation on the polymer behavior and fouling resistance. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/marc.201900447
  • 2020 • 249 Silicon Oxide Barrier Films Deposited on Polycarbonate Substrates in Pulsed Plasmas
    Shafaei, S. and Yang, L. and Rudolph, M. and Awakowicz, P.
    Plasma Chemistry and Plasma Processing 40 607-623 (2020)
    For many applications of polycarbonate (PC) from packaging to micro-electronics improved barrier properties are necessary. In this contribution, silica thin films were deposited from hexamethyldisiloxane/oxygen (HMDSO/O2) on polycarbonate substrate in three step plasma processes by combining a microwave (MW) surface wave discharge of 2.45 GHz with an optional radio-frequency (RF) bias of 13.56 MHz. The influence of interlayer thickness, HMDSO flow and oxygen to HMDSO ratio on barrier performance for three step-coating processes was investigated. The morphology and surface properties of the coated surface of PC were studied by atomic force microscopy (AFM). The surface topography showed a silica particles distribution on the PC substrate with relatively smooth surface roughness. AFM-QNM provides more insight into the surface morphology and stiffness. The results identify the coating structure for PC film coated with and without bias. High barrier improvement of the deposited films on PC substrates was obtained after plasma silicon coating process with a barrier improvement factor up to 337. It was found that the deposition process is optimal for food packaging applications by using combined MW-RF PECVD technology. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
    view abstractdoi: 10.1007/s11090-019-10049-y
  • 2020 • 248 Thermoregeneration of Plastrons on Superhydrophobic Coatings for Sustained Antifouling Properties
    Simovich, T. and Rosenhahn, A. and Lamb, R.N.
    Advanced Engineering Materials 22 (2020)
    A popular and desirable function of superhydrophobic coatings is their remarkable ability to retain an entrapped layer of air, called a plastron, when submerged underwater. The drawback is that the air layer is short-lived due to solvation into the surrounding liquid. While manipulating the solubility of gases using temperature is a possible approach, it generally requires inefficiently heating large volumes of water. Following the demonstrated ability to maintain air bubbles on superhydrophobic surfaces for drag reduction, this article introduces a novel method of extracting gas from water to replenish and stabilize the plastron on superhydrophobic surfaces for sustained antifouling abilities. This method involves locally heating the liquid surrounding a superhydrophobic coating, reducing gas solubility, and causing the gas to nucleate at the liquid–air interface. The approach requires a relatively low energy input, due to the small volume of locally heated water. With a constant supply of equilibrated water and minimal energy input, the plastron can survive indefinitely without the need for a mechanical delivery of air. The thermoregenerating superhydrophobic samples were shown to exhibit excellent antifouling behavior and inhibited diatom attachment over a period of 5 days. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/adem.201900806
  • 2020 • 247 A flame-retardant phytic-acid-based LbL-coating for cotton using polyvinylamine
    Zilke, O. and Plohl, D. and Opwis, K. and Mayer-Gall, T. and Gutmann, J.S.
    Polymers 12 (2020)
    Phytic acid (PA), as a natural source of phosphorus, was immobilized on cotton (CO) in a layer-by-layer (LbL) approach with polyvinylamine (PVAm) as the oppositely charged electrolyte to create a partly bio-based flame-retardant finish. PVAm was employed as a synthetic nitrogen source with the highest density of amine groups of all polymers. Vertical flame tests revealed a flame-retardant behavior with no afterflame and afterglow time for a coating of 15 bilayers (BL) containing 2% phosphorus and 1.4% nitrogen. The coating achieved a molar P:N ratio of 3:5. Microscale combustion calorimetry (MCC) analyses affirmed the flame test findings by a decrease in peak heat release rate (pkHRR) by more than 60% relative to unfinished CO. Thermogravimetric analyses (TGA) and MCC measurements exhibited a shifted CO peak to lower temperatures indicating proceeding reactions to form an isolating char on the surface. Fourier transform infrared spectroscopy (FTIR) coupled online with a TGA system, allowed the identification of a decreased amount of acrolein, methanol, carbon monoxide and formaldehyde during sample pyrolysis and a higher amount of released water. Thereby the toxicity of released volatiles was reduced. Our results prove that PA enables a different reaction by catalyzing cellulosic dehydration, which results in the formation of a protective char on the surface of the burned fabric. © 2020 by the authors.
    view abstractdoi: 10.3390/POLYM12051202
  • 2019 • 246 Developments in pre- and post-treatment of thin films and their influences on surface topography and coating adhesion strength of cutting tools
    Bathe, T. and Biermann, D.
    Production Engineering 13 751-759 (2019)
    Due to the increased requirements on machining of metallic and non-metallic materials, the pre- and post-treatment of hard thin films has been an important topic in several researches in the past decade. The main improvement in tool properties by a reduction of surface inhomogeneities is reached by an additional mechanical or chemical treatment before and/or after the coating process. Especially the cleaning before coating has to be considered to reduce the amount of debris of the pre-treatment which may negatively effect surface quality after the coating process. The mainly used processes of mechanical treatment to enhance surface topography before and after coating are several machining processes such as abrasive jet machining or drag finishing. This paper introduces a novel process for the pre- and post-treatment of coated cutting tools by elastically bonded diamond grinding wheels. Both the removal rate of surface inhomogeneities, the influence of surface topography before and after coating and the influence of the initial tool surfaces regarding coating adhesion strength were investigated to underline the potential of this pre- and post-treatment. Additionally, a new method for characterizing and describing the number of coating defects and proportion area of coating defects per mm 2 is presented. © 2019, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-019-00921-3
  • 2019 • 245 Surface modification of Ti6Al4V alloy scaffolds manufactured by electron beam melting
    Chudinova, E. and Surmeneva, M. and Koptyug, A. and Loza, K. and Prymak, O. and Epple, M. and Surmenev, R.
    Journal of Physics: Conference Series 1145 (2019)
    In this paper, the results of the surface functionalization of the Ti6Al4V alloy scaffolds with different structures for use as a material for medical implants are presented. Radio frequency magnetron sputtering was used to modify the surface of the porous structures by deposition of the biocompatible hydroxyapatite (HA) coating with the thickness of 86050 nm. The surface morphology, elemental and phase composition of the HA-coated scaffolds were studied. According to energy-dispersive X-ray spectroscopy, the stoichiometric ratio of Ca/P for flat, orthorhombic and cubic scaffolds is 1.65, 1.60, 1.53, respectively, which is close to that of stoichiometric ratio for HA (Ca/P = 1.67). It was revealed that this method of deposition makes it possible to obtain the homogeneous crystalline coating both on the dense sample and in the case of scaffolds of complex geometry with different lattice cell structure. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1145/1/012030
  • 2019 • 244 Effect of mg and si content in aluminum alloys on friction surfacing processing behavior
    Ehrich, J. and Roos, A. and Hanke, S.
    Minerals, Metals and Materials Series 357-363 (2019)
    Friction surfacing (FS) coating layers are generated through severe plastic deformation (SPD) at elevated temperatures (≈0.8 Tmelt). Alloying elements in metals affect heat generation and dynamic recrystallization kinetics during SPD, and therefore require significant adjustments of FS processing conditions. In this study, custom made Aluminum alloys (AA 6060 with additions of 2 and 3.5 wt% Mg, and 6.6, 10.4 and 14.6 wt% Si) were processed by FS. It was found that for the high-Mg Aluminum alloys especially the rotational speeds require a downward adaption to achieve a steady state process. A higher content of Mg results in a reduced rate of thermal softening and more efficient heat generation. With regard to the plasticization behavior during FS, the high amount of hard phases in the high-Si alloys was expected to cause additional friction and increase heat generation. However, as the Si content increases, the process temperatures decrease. Influences of Mg and Si content on material efficiency and coating dimensions were evaluated and discussed. © 2019, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/978-3-030-05864-7_45
  • 2019 • 243 Development of a Surface-Active Coating for Promoted Gas Hydrate Formation
    Filarsky, F. and Schmuck, C. and Schultz, H.J.
    Chemie-Ingenieur-Technik 91 85-91 (2019)
    This work deals with the influences of surface-active coatings made by silanization with an increasing hydrophobicity on methane hydrate formation in view of induction times, gas uptake, and rate of gas consumption. Hydrate formation was performed in a stirred pressure autoclave under stationary and transient conditions in presence of different coatings made from diverse silanes. With increasing carbon chain length of the silanes, promoting effects were observed while using stationary formation conditions. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/cite.201800002
  • 2019 • 242 Surface roughening of Al2O3/Al2O3-ceramic matrix composites by nanosecond laser ablation prior to thermal spraying
    Gatzen, C. and Mack, D.E. and Guillon, O. and Vaßen, R.
    Journal of Laser Applications 31 (2019)
    Al2O3/Al2O3 ceramic matrix composites are candidate materials for high-temperature applications such as gas turbines. As water vapor corrosion of Al2O3/Al2O3-CMC (ceramic matrix composite) is a major issue, the application of suitable environmental barrier coatings is inevitable. An important factor for coating adhesion, especially in thermal spraying, is mechanical interlocking. Therefore, a rough substrate surface is needed. Although it has been proven that laser ablation is a suitable method for surface preparation of metallic substrates, no studies on Al2O3/Al2O3-CMCs are available. Therefore, the suitability of surface preparation of an Al2O3/Al2O3-CMC by laser ablation for use prior to atmospheric plasma spraying was examined. The laser ablation threshold fluence for Al2O3/Al2O3-CMC was determined. The effects of different processing parameters on the surface were studied. Various surface morphologies were obtained, such as cauliflower and honeycomb structures. The samples were characterized by white light interferometry, laser microscopy, and scanning electron microscopy. The obtained surface structures were coated with Gd2Zr2O7. It was found that the adhesion strength of coatings on laser treated samples was drastically increased. © 2019 Laser Institute of America.
    view abstractdoi: 10.2351/1.5080546
  • 2019 • 241 Cold spray deposition of Cr2AlC MAX phase for coatings and bond-coat layers
    Go, T. and Sohn, Y.J. and Mauer, G. and Vaßen, R. and Gonzalez-Julian, J.
    Journal of the European Ceramic Society 39 860-867 (2019)
    Highly pure Cr2AlC powders were synthesized and deposited for the first time by cold spray technology on stainless steel substrates. The Cr2AlC coatings were relative dense, up to 91%, and present high purity (> 98%) since only small traces of Cr2Al, Al2O3 and Cr2O3 were detected by XRD, SEM and EDX. The microstructure of the coatings is homogeneous, although some preferential orientation in the basal plane was observed by XRD pole figures. The adhesion between the coating and the substrate is strong, and compressive residual stresses up to 300 MPa in the coating were determined by XRD. Furthermore, a conventional YSZ Thermal Barrier Coating (TBCs) was deposited by Atmospheric Plasma Spray (APS) on top of the cold sprayed Cr2AlC coating in order to demonstrate the processing feasibility of Cr2AlC MAX phases as a bond-coat layer. © 2018 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2018.11.035
  • 2019 • 240 Encapsulation of sub-micrometer sized zeolites by porous silica – towards a rational design strategy for functional yolk-shells
    Joshi, H. and Schmidt, W. and Schüth, F.
    Microporous and Mesoporous Materials 1-8 (2019)
    Catalysis often requires spatial separation of active centres. In material science this translates to a challenge in the synthesis of such materials, namely core-shells. Yolk-shell materials, a type of core-shell materials, possess a void between the core and shell that can be advantageous in catalysis. Yolk-shell materials with zeolitic core have not been reported extensively, despite their potential applicability in catalysis. This stems from the non-spherical morphology and surface properties of the zeolites, which makes controlled coating without defects difficult. Herein, we report a strategy for the encapsulation of beta zeolite (HBEA) with disordered mesoporous silica shell (HBEA@void@mSiO 2 ). HBEA is chosen as the centre (yolk) due to its cuboidal shape. The process involves creation of two shells, (a) sacrificial shell composed of resorcinol and formaldehyde, and (b) mesoporous silica shell. The result is an organic@inorganic hybrid that is thermally treated to obtain the corresponding hybrid. Polyvinylpyrrolidone (PVP) is an important component of the synthesis which assists in obtaining a uniform coating around the core. Thorough morphological, structural, fractal and textural characterization of this material was performed by electron microscopy, XRD, SAXS and sorption techniques. The hybrid possesses a hierarchical structure with an increasing porosity and spatial isolation of the core by the presence of a void. The siliceous nature of HBEA@void@mSiO 2 also enables a post-synthesis treatment for functional modification with mercaptosilane groups. The synthesis process shown here is highly controllable and has laid a solid foundation for a generalized synthesis strategy to build functional yolk-shell materials based on zeolites. © 2019
    view abstractdoi: 10.1016/j.micromeso.2019.03.013
  • 2019 • 239 Repair of Ni-based single-crystal superalloys using vacuum plasma spray
    Kalfhaus, T. and Schneider, M. and Ruttert, B. and Sebold, D. and Hammerschmidt, T. and Frenzel, J. and Drautz, R. and Theisen, W. and Eggeler, G. and Guillon, O. and Vassen, R.
    Materials and Design 168 (2019)
    Turbine blades in aviation engines and land based gas-turbines are exposed to extreme environments. They suffer damage accumulation associated with creep, oxidation and fatigue loading. Therefore, advanced repair methods are of special interest for the gas-turbine industry. In this study, CMSX-4 powder is sprayed by Vacuum Plasma Spray (VPS) on single-crystalline substrates with similar compositions. The influence of the substrate temperature is investigated altering the temperature of the heating stage between 850 °C to 1000 °C. Different spray parameters were explored to identify their influence on the microstructure. Hot isostatic pressing (HIP) featuring fast quenching rates was used to minimize porosity and to allow for well-defined heat-treatments of the coatings. The microstructure was analysed by orientation imaging scanning electron microscopy (SEM), using electron backscatter diffraction (EBSD). The effects of different processing parameters were analysed regarding their influence on porosity and grain size. The results show that optimized HIP heat-treatments can lead to dense coatings with optimum γ/γ′ microstructure. The interface between the coating and the substrate is oxide free and shows good mechanical integrity. The formation of fine crystalline regions as a result of fast cooling was observed at the single-crystal surface, which resulted in grain growth during heat-treatment in orientations determined by the crystallography of the substrate. © 2019
    view abstractdoi: 10.1016/j.matdes.2019.107656
  • 2019 • 238 Numerical Study on Particle–Gas Interaction Close to the Substrates in Thermal Spray Processes with High-Kinetic and Low-Pressure Conditions
    Mauer, G.
    Journal of Thermal Spray Technology 28 27-39 (2019)
    In thermal spray processes, the interaction between the gas jet and the particulate feedstock can affect the coating build-up mechanisms considerably. In particular under high-kinetic and low-pressure conditions, small particles are subjected to rapid deflection and velocity changes close to the substrate. In this work, numerical studies were carried out to investigate the interaction between gas and particles in the substrate boundary layers (BL). Typical conditions for suspension plasma spraying (SPS), plasma spray-physical vapor deposition (PS-PVD), and aerosol deposition (AD) were taken as a basis. Particular importance was attached to the consideration of rarefaction and compressibility effects on the drag force. Typical Stokes numbers for the different thermal spray processes were calculated and compared. Possible effects on the resulting coating build-up mechanisms and microstructure formation are discussed. The results show that just for larger particles in the SPS process the laminar flow attached to the particles begins to separate so that the drag coefficients have to be corrected. Furthermore, slip effects occur in all the investigated processes and must be considered. The comparison of calculated Stokes numbers with critical values shows that there is a disposition to form columnar microstructures or stacking effects depending on the particle size for PS-PVD and SPS, but not for AD. © 2018, ASM International.
    view abstractdoi: 10.1007/s11666-018-0810-3
  • 2019 • 237 Miniaturization of low cycle fatigue-testing of single crystal superalloys at high temperature for uncoated and coated specimens [Miniaturisierung der Versuchstechnik für Niedrig-Lastwechsel-Ermüdung bei Hochtemperatur an Proben aus einkristallinen Superlegierungen mit und ohne Schutzschichten]
    Meid, C. and Waedt, U. and Subramaniam, A. and Wischek, J. and Bartsch, M. and Terberger, P. and Vaßen, R.
    Materialwissenschaft und Werkstofftechnik 50 777-787 (2019)
    A newly developed miniature specimen and respective fixture for high temperature low cycle fatigue testing of nickel based single crystal superalloys is presented. Miniaturization allows the preparation of test specimens in all main crystallographic orientations of the cubic nickel crystal using laboratory sized material samples and enables excellent utilization of the costly material. The specimen geometry is optimized by means of parameter studies employing numerical calculations such that for the main crystallographic orientations the stress concentration at the fillet between gauge length and specimen head is minimized, and failure is likely to occur within the gauge length. The designed fixture allows easy specimen mounting and provides sufficient support for applying an extensometer for strain measurement. Protective metallic coatings against oxidation can be applied on the specimen by plasma spraying for studying the effect of coatings on the fatigue lifetime. The functionality of the specimen geometry and fixture design for low cycle fatigue testing is demonstrated for temperatures up to 950 °C. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/mawe.201800135
  • 2019 • 236 Resonant Raman scattering characterization of thermally annealed HiPIMS deposited MoSx coatings
    Moldenhauer, H. and Wittig, A. and Kokalj, D. and Stangier, D. and Brümmer, A. and Tillmann, W. and Debus, J.
    Surface and Coatings Technology 377 (2019)
    Raman spectroscopy is used to investigate the structural and tribological properties of HiPIMS sputtered MoSx thin films which were post-growth-annealed at different temperatures. The Raman scattering combined with X-ray diffraction determines a reduction in the residual strain within the MoSx layers with increasing annealing temperature. In the high-temperature annealed coatings a Raman signature at 40 cm−1 emerges, which results from a strengthening of the inter-layer van-der-Waals interaction. This observation indicates that the thermally annealed MoSx thin films become more resistant against shear forces, which is manifested in an increase of the coefficient of friction measured with a ball-on-disc tribometer. The coefficient of friction moreover decreases with lowering the sulfur/molybdenum ratio which, in turn, depends on the substrate and annealing temperatures. Furthermore, a Raman forbidden mode may be exploited to detect stacking faults within the sputtered coatings. Its observation is realized through resonant excitation of an MoS2 exciton at about 633 nm. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2019.124891
  • 2019 • 235 Influence of Ag on antibacterial performance, microstructure and phase transformation of NiTi shape memory alloy coatings
    Momeni, S. and Tillmann, W.
    Vacuum 164 242-245 (2019)
    Shape memory binary NiTi and ternary NiTiAg coatings were deposited by means of magnetron sputtering technique. The results show how simultaneous sputtering of Ag can affect the microstructure, phase transformation behavior and antibacterial properties of NiTi coatings. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.vacuum.2019.02.051
  • 2019 • 234 Minimally Invasive Supervision of Plasma-assisted Dielectric Deposition Processes
    Pohle, D. and Schulz, C. and Oberberg, M. and Awakowicz, P. and Rolfes, I.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications 163-165 (2019)
    This paper introduces a minimally invasive in-situ plasma monitoring concept suited for the challenging conditions in dielectric deposition processes. Based on the so-called stacked planar multipole resonance probe (spMRP), the sensor is placed directly on the plasma-remote side of a dielectric substrate to be coated, thus minimizing its influence on the process. The sensor's electric field penetrates both substrate and deposited dielectric layers and couples into the plasma. This enables an effective supervision of the plasma parameters required for process control at the point of highest interest. The effect of increasing coating thicknesses on the measurement performance is investigated within 3D electromagnetic field simulations. Final measurements in an argon-oxygen plasma depositing aluminium oxide confirm both the general suitability of the proposed concept as well as the insensitivity to additional dielectric coatings. © 2019 IEEE.
    view abstractdoi: 10.1109/IMWS-AMP.2019.8880124
  • 2019 • 233 Impact of Al2O3-40 wt.% TiO2 feedstock powder characteristics on the sprayability, microstructure and mechanical properties of plasma sprayed coatings
    Richter, A. and Berger, L.-M. and Sohn, Y.J. and Conze, S. and Sempf, K. and Vaßen, R.
    Journal of the European Ceramic Society 39 5391-5402 (2019)
    Atmospheric plasma sprayed (APS) Al2O3-TiO2 coatings have found a wide range of industrial application due to their favorable properties, combined with low costs and a high availability. However, the detailed effect of the phase composition and the element distribution of the feedstock powders on the coating properties and the spraying process have only crudely been investigated so far. Here the impact of aluminum titanate (Al2TiO5) on the microstructural features and mechanical properties of Al2O3-40 wt.% TiO2 APS coatings is demonstrated by investigating the detailed phase composition and the distribution of aluminum and titanium in three fused and crushed feedstock powders and the respective coatings. Thereby, a direct influence of Al2TiO5 content on the deposition efficiency, the porosity, the elastic modulus, and the hardness of the coatings is revealed. The results emphasize the need for a more detailed specification of commercial Al2O3-TiO2 feedstock powders to ensure a high reliability of the coating properties. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2019.08.026
  • 2019 • 232 Surface functionalization of titanium with silver nanoparticles
    Sharonova, A. and Surmeneva, M. and Loza, K. and Prymak, O. and Epple, M. and Surmenev, R.
    Journal of Physics: Conference Series 1145 (2019)
    This study aims to investigate the most efficient ways for metallic samples functionalization with silver nanoparticles (AgNPs). Three different techniques of surface functionalization have been used for the coating of titanium metal, i.e. the sessile drop method (evaporation), dip-coating and electrophoretic deposition (EPD). AgNPs stabilized with polyvinylpyrrolidone had a spherical shape and the metallic core diameter, charge and polydispersity index were 70 20 nm, -15 mV and 0.192, respectively. SEM analysis revealed that AgNPs were homogeneously distributed over the entire surface and did not form the particle agglomerates only in case of EPD. Thus, EPD method and spherical AgNPs can be used for further investigation concerning the preparation of biocomposites with antibacterial and bioactive properties. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/1145/1/012032
  • 2019 • 231 Coating damage localization of naval vessels using artificial neural networks
    Thiel, C. and Neumann, K. and Ludwar, F. and Rennings, A. and Doose, J. and Erni, D.
    Ocean Engineering 192 (2019)
    For the localization of coating damages of naval vessels numerical simulation using the FEM software COMSOL Multiphysics were carried out to calculate the corresponding underwater electric potential (UEP) signature. Therefore, we defined said damages at random hull surface positions and used the information provided by the impressed current cathodic protection (ICCP) system, more exactly the cathodic current itself, and the calculated UEP signatures as input parameters to train an artificial neural network (ANN) for predicting the coating damage location. With this deep learning approach, more than 90% of all coating damages are predicted correctly, considering a generic ship model with 50m length, whose hull is divided into 12 different sectors. Even the mere use of ICCP currents as highly aggregated input parameters for the ANN lead to a satisfactory prediction rate over 80% within the predefined sectors, thus providing quite accurate results using minimal amount of data. © 2019 Elsevier Ltd
    view abstractdoi: 10.1016/j.oceaneng.2019.106560
  • 2019 • 230 Influence of plasma nitriding pretreatments on the tribo-mechanical properties of DLC coatings sputtered on AISI H11
    Tillmann, W. and Lopes Dias, N.F. and Stangier, D.
    Surface and Coatings Technology 357 1027-1036 (2019)
    The duplex treatment, consisting of plasma nitriding and the deposition of a DLC coating, was carried out on the hot-work tool steel AISI H11. The coating structure, composed of Cr-based interlayers and a hydrogenated carbon layer, was sputtered on non-nitrided, nitrided, as well as nitrided-repolished AISI H11 steel with an either annealed or quenched and tempered base condition to examine the influence of the pretreatment condition on the tribo-mechanical properties of the DLC coating. Besides the graded hardness profile, plasma nitriding leads to a roughness increase, which affects the microstructure as well as the mechanical properties of the DLC coating. The rougher surface favors a film growth of a carbon layer with larger cluster-like structures. As a result, these DLC coatings exhibit hardness values below 22 GPa, while the coating systems sputtered on substrates with smoother surfaces reach values of approximately 26 GPa and showed a good adherence. The heat treatment condition influences the load-bearing capacity of the nitrided substrate as the higher core hardness enhances the mechanical support of the coating and reaches the highest adhesion class HF1 in the Rockwell C tests. Due to the lower film adhesion and the low hardness of the DLC coatings sputtered on nitrided non-repolished AISI H11, high coefficients of frictions and wear coefficients of up to 0.59 and 3.19 ∗ 10−5 mm3/N∗m were determined in tribometer tests against WC/Co counterparts. In contrast, the nitrided repolished steel exhibits a low coefficient of friction of 0.12 as well as a low wear coefficient of 0.06 ∗ 10−5 mm3/N∗m. Therefore, a repolishing of the nitrided AISI H11 with quenched and tempered base condition ensures the highest load-bearing capability of the substrate as well as an improved friction and wear behavior of the DLC coating. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2018.11.002
  • 2019 • 229 Influence of the etching processes on the adhesion of TiAlN coatings deposited by DCMS, HiPIMS and hybrid techniques on heat treated AISI H11
    Tillmann, W. and Grisales, D. and Stangier, D. and Ben Jebara, I. and Kang, H.
    Surface and Coatings Technology 378 (2019)
    Ensuring a good adhesion of the coatings to the substrate is one of the key points during the manufacturing of machining and forming tools. The nature of the substrate material and the way it is pre-treated and cleaned before the deposition plays an important role in the adhesion of the coatings. The in-situ cleaning processes as plasma etching and metal ion etching have demonstrated to have an influence on the adhesion of different coating/substrate systems. The introduction of HiPIMS technologies for the in-situ cleaning and the deposition of PVD coatings throughout this technique has opened varied opportunities to improve the performance of the coated parts. Systematic and comparative analysis of the influence of plasma etching itself (PE), plasma etching and metal ion etching (PE + MIE), and plasma etching and HiPIMS etching (PE + HiPE) etching processes on the adhesion of the TiAlN to the hot work tool steel AISI H11 has been performed. Additionally, subsequent to the etching processes, TiAlN coatings have been deposited using DCMS, HiPIMS and hybrid (DCMS/HiPIMS) technologies. Residual stresses of the heat treated AISI H11 were evaluated before and after the different etching process as well as after coating's deposition. It has been shown that the etching process affects the growth direction and microstructure of the TiAlN coatings, especially of those deposited by DCMS and hybrid. For instance, DCMS and hybrid TiAlN coatings deposited after PE have the presence of the TiAlN (200) reflection, not evidenced on the coatings deposited after PE + MIE and PE + HiPE. Moreover, hybrid coatings on PE + HiPE have a preferential (220) growth orientation and a (111) orientation when deposited on PE and PE + MIE cleaned substrate. Finally, in order to evaluate the adhesion of the coatings to the substrate, both scratch test and Rockwell C indentation test were used. The coatings deposited on the mere plasma etched (PE) substrate turn out to be the coatings with the highest critical load Lc3 and the lowest HF standards (HF1–HF3). This behaviour is attributed to the conservation of the substrate's surface integrity and the no promotion of surface tensions that can act in detriment of the adhesion of the coating. © 2019 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2019.125075
  • 2019 • 228 Investigation of HVOF-ID spraying with WC-CoCr-155 μm feedstock powder
    Tillmann, W. and Schaak, C. and Hagen, L. and Dildrop, M.
    IOP Conference Series: Materials Science and Engineering 480 (2019)
    High velocity oxygen fuel (HVOF) spraying of WC-Co(Cr) with different chemical compositions, different powder size fractions, and different mean carbide sizes is a well-established research field for outer diameter (OD) applications. These coatings are typically applied as wear protective layers for different types of industries. Current demands for internal diameter (ID) coatings lead to a great interest in HVOF-ID spraying. This field of application necessitates a special spray gun equipment and spray powders with particle size fractions smaller than 20 μm. At the same time, the process control concerning both the spray gun configuration and the use of fine powders leads to new challenges which differ from those of OD HVOF spraying. In this study, HVOF-ID spraying using a WC-CoCr 86-10-4 (-155 μm) feedstock with a mean WC particle size of 400 nm is investigated with respect to the resulting coating properties. A statistical design of experiments (DoE) is utilized to enable a systematic analysis of various process parameter settings along with their interaction on the microstructural characteristics as well as the deposition efficiency (DE). Based on the results, a desirability-based multi-criteria optimization is carried out in order to produce adequate coating properties. The obtained knowledge about the spray system enables to realize dense WC-CoCr coatings with a porosity of approximately 1 %. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/480/1/012008
  • 2019 • 227 Antifouling Properties of Dendritic Polyglycerols against Marine Macrofouling Organisms
    Wanka, R. and Aldred, N. and Finlay, J.A. and Amuthalingam, A. and Clarke, J.L. and Clare, A.S. and Rosenhahn, A.
    Langmuir 35 16568-16575 (2019)
    Dendritic polyglycerols (PGs) were synthesized and postmodified by grafting of poly(ethylene glycol) (PEG) and polypropylene glycol (PPG) diglycidyl ether groups, and their antifouling and fouling-release properties were tested. Coating characterization by spectroscopic ellipsometry, contact angle goniometry, attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and atomic force microscopy showed brushlike morphologies with a high degree of microscale roughness and the ability to absorb large amounts of water within seconds. PGs with three different thicknesses were tested in laboratory assays against settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of zoospores of the alga Ulva linza. Very low coating thicknesses, e.g., 11 nm, reduced the settlement of barnacles, under static conditions, to 2% compared with 55% for an octadecyltrichlorosilane reference surface. In contrast, zoospores of U. linza settled readily but the vast majority were removed by exposure to a shear force of 52 Pa. Both PEG and PPG modification increased the antifouling properties of the PG films, providing a direct comparison of the ultralow fouling properties of all three polymers. Both, the modified and the nonmodified PGs are promising components for incorporation into amphiphilic fouling-resistant coatings. © 2019 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.9b02720
  • 2018 • 226 Water infiltration impact on tensile strength and breaking strain of architectural fabrics
    Asadi, H. and Uhlemann, J. and Stranghöner, N.
    Advances in Structural Engineering 21 2605-2616 (2018)
    Architectural fabrics consist of woven base cloth protected by a coating on both sides. Corrosive liquids or vapours may diffuse through the matrix material and corrosion effects on fibres may lead to substantial reduction in mechanical properties. Tensile strength is of most importance for the safety of a structure and strain properties govern its serviceability. Wetting is one of the main environmental impacts. Due to rain, condensation or snow melting cycles, the membrane gets wet. If the fabric under the coating gets wet and to which amount depends on the condition of the covering coating over the lifetime of the architectural structure and on the wicking properties of the fabric material. Water penetration influences the fabric’s properties. How and to what extent is the field of investigations of this article. The influence of water on the tensile strength and the breaking strain of two common architectural fabrics, polyester (PES)/ polyvinylchloride (PVC) and glass/polytetrafluoroethylene (PTFE), are investigated. Virgin and aged materials are examined. © The Author(s) 2018.
    view abstractdoi: 10.1177/1369433218756005
  • 2018 • 225 Cold gas spraying of Ti-48Al-2Cr-2Nb intermetallic for jet engine applications
    Bakan, E. and Mauer, G. and Sohn, Y.J. and Schwedt, A. and Rackel, M.W. and Riedlberger, F. and Pyczak, F. and Peters, J.O. and Mecklenburg, M. and Gartner, T.M. and Vaßen, R.
    Surface and Coatings Technology (2018)
    The present article describes aspects of the cold gas spray processability of the intermetallic Ti-48Al-2Cr-2Nb (at. %) alloy, which is employed as a structural material in gas turbine engines. The effects of processing parameters, namely, gas pressure, gas temperature, spray distance, as well as the gas atomized feedstock particle size (d50 = 30 and 42 μm, respectively) and phase composition on deposition, were investigated. The results showed that when the highest available gas pressure (40 bar) and temperature (950 °C) were combined with a short spray distance (20 mm), well-adhering coatings could be deposited regardless of the investigated particle size. However, the maximum coating thickness could be achieved was about 30 μm with a deposition efficiency of 1%. Phase composition of the gas atomized feedstock was investigated with HT-XRD and according to the findings, heat treatment of the feedstock under vacuum was carried out. With this treatment, non-equilibrium, disordered α phase of the atomized powder was transformed into an α α2 and γ phase mixture. At the same time, an increase in the hardness and oxygen content of the powder was detected. Swipe test performed with the heat treated powder revealed no improvement in terms of deposition, in fact, the number of adhering particles on the substrate was decreased in comparison with that of the untreated powder. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2018.11.092
  • 2018 • 224 Development of W-coating with functionally graded W/EUROFER-layers for protection of First-Wall materials
    Emmerich, T. and Qu, D. and Vaßen, R. and Aktaa, J.
    Fusion Engineering and Design 128 58-67 (2018)
    To protect First-Wall components, made of reduced activation ferritic martensitic steel, against the plasma of future fusion reactors, tungsten coatings are a feasible option. The difference in coefficient of thermal expansion between the coating and the steel substrate can be compensated using functionally graded material layers. Such layers were successfully produced by vacuum plasma spraying. This technique reduces, however, the hardness of the substrate surface near zone. Modified spraying parameters moderate the hardness loss. The parameters may, though, affect also the layer bonding toughness which is evaluated in this work by four point bending tests. Furthermore, the layers behavior on First-Wall Mock‐ups and under different thermal loads is investigated by finite element simulations. The measurement of the layer adhesion indicates that the layer adhesion decreases only for modified spraying parameters that do not reduce the substrate hardness. It follows also from the toughness calculation that without layer residual stresses the toughness values depend on coating thickness. In regard to the Mock‐up behavior the simulations show that intermediate steps are necessary during heating and cooling to prevent artificial stresses and inelastic deformation. It is, however, not possible to avoid stresses and inelastic deformation completely as they originate from the residual stresses. © 2018
    view abstractdoi: 10.1016/j.fusengdes.2018.01.047
  • 2018 • 223 Tailoring columnar microstructure of axial suspension plasma sprayed TBCs for superior thermal shock performance
    Ganvir, A. and Joshi, S. and Markocsan, N. and Vassen, R.
    Materials and Design 144 192-208 (2018)
    This paper investigates the thermal shock behavior of thermal barrier coatings (TBCs) produced by axial suspension plasma spraying (ASPS). TBCs with different columnar microstructures were subjected to cyclic thermal shock testing in a burner rig. Failure analysis of these TBCs revealed a clear relationship between lifetime and porosity. However, tailoring the microstructure of these TBCs for enhanced durability is challenging due to their inherently wide pore size distribution (ranging from few nanometers up to few tens of micrometers). This study reveals that pores with different length scales play varying roles in influencing TBC durability. Fracture toughness shows a strong correlation with the lifetime of various ASPS TBCs and is found to be the prominent life determining factor. Based on the results, an understanding-based design philosophy for tailoring of the columnar microstructure of ASPS TBCs for enhanced durability under cyclic thermal shock loading is proposed. © 2018 The Authors
    view abstractdoi: 10.1016/j.matdes.2018.02.011
  • 2018 • 222 Thermal cycling testing of TBCs on Cr2AlC MAX phase substrates
    Gonzalez-Julian, J. and Go, T. and Mack, D.E. and Vaßen, R.
    Surface and Coatings Technology 340 17-24 (2018)
    Thermal barrier coatings (TBCs) based on yttria-stabilized zirconia (YSZ) were deposited by Atmospheric Plasma Spray (APS) on highly dense and pure Cr2AlC substrates. The Cr2AlC/YSZ systems were tested under thermal cycling conditions at temperatures between 1100 and 1300 °C testing up to 500 h. The response of the system was excellent due to the strong adhesion between the substrate and the coating, and the formation of an outer and protective layer based on α-Al2O3. The oxide scale is formed due to the diffusion of Al atoms from the crystal structure of the Cr2AlC, followed by the reaction with oxygen in the air. The thickness of the oxide scale was 8.9, 17.6 and 39.7 μm at 1100, 1200 and 1300 °C, respectively, which is rather thick in comparison with the classical superalloy/TBC systems. Cr2AlC/YSZ systems survived without any damage under the severe cycling conditions at 1100 and 1200 °C due to the protective oxide scale layer and the sufficient thermal expansion match between the Cr2AlC, YSZ and α-Al2O3. At 1300 °C and after 268 h of cycling conditions, the system failed due to the formation of a porous carbide layer underneath of the oxide scale. The results are rather promising and confirm the potential of the MAX phases to operate under long term applications of high temperature and oxidizing environments. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2018.02.035
  • 2018 • 221 Microstructural features of dynamic recrystallization in alloy 625 friction surfacing coatings
    Hanke, S. and Sena, I. and Coelho, R.S. and dos Santos, J.F.
    Materials and Manufacturing Processes 33 270-276 (2018)
    In friction surfacing (FS), material is deposited onto a substrate in the plasticized state, using frictional heat and shear stresses. The coating material remains in the solid state and undergoes severe plastic deformation (SPD) at high process temperatures (≈0.8 Tmelt), followed by high cooling rates in the range of 30 K/s. Dynamic recrystallization and the thermal cycle determine the resulting microstructure. In this study, Ni-based alloy 625 was deposited onto 42CrMo4 substrate, suitable, for instance, for repair welding of corrosion protection layers. Alloy 625 is known to undergo discontinuous dynamic recrystallization under SPD, and the resulting grain size depends on the strain rate. The coating microstructure was studied by microscopy and electron backscatter diffraction (EBSD). The coatings exhibit a fully recrystallized microstructure with equiaxed grains (0.5–12 µm) and a low degree of grain average misorientation. Flow lines caused by a localized decrease in grain size and linear alignment of grain boundaries are visible. Grain nucleation and growth were found to be strongly affected by localized shear and nonuniform material flow, resulting in varying amounts of residual strain, twins and low-angle grain boundaries in different regions within a single coating layer’s cross section. FS can be used to study dynamic recrystallization at high temperatures, strains and strain rates, while at the same time materials with a recrystallization grain size sensitive to the strain rate can be used to study the material flow during the process. © 2017 Taylor & Francis.
    view abstractdoi: 10.1080/10426914.2017.1291947
  • 2018 • 220 A method for the in-situ study of solid-state joining techniques using synchrotron radiation - observation of phase transformations in Ti-6Al-4V after friction surfacing
    Hanke, S. and Staron, P. and Fischer, T. and Fitseva, V. and dos Santos, J.F.
    Surface and Coatings Technology 335 355-367 (2018)
    The solid-state deposition process Friction Surfacing (FS) was applied to Ti-6Al-4V alloy on portable welding equipment at a high-energy synchrotron beamline. The heat input and coating thickness were altered by varying the deposition speed. X-ray diffraction was carried out in-situ during the deposition process and the cooling of the coated samples. Phase transformations were evaluated and correlated with thermal cycles determined by thermocouples and an infrared camera. SEM investigation of the coating microstructure was conducted to examine the morphology of the α phase. During FS the coating material is severely deformed and dynamically recrystallized in the β phase state at temperatures > 1300 °C. Small changes in the β grain size were observed within the first 2 s after deposition only. Depending on the cooling rate it transforms into different types of α phase during cooling. Phase transformation rates were found to correlate well with the differences in α morphology. The two faster translational speeds showed transformation rates > 45 vol%/s and a partially martensitic microstructure. When a thick coating is deposited at low translational speed, α → β transformation continues for several seconds after deposition, followed by a slow cooling rate resulting in martensite free coatings containing α m from massive transformation. The potential gain and the deficiencies of this complex in-situ study of a technical process, instead of simplified model experiments, for the understanding of fundamental mechanisms involved in FS are discussed. © 2017
    view abstractdoi: 10.1016/j.surfcoat.2017.12.049
  • 2018 • 219 Advanced crystallographic study of the columnar growth of YZS coatings produced by PS-PVD
    He, W. and Mauer, G. and Schwedt, A. and Guillon, O. and Vaßen, R.
    Journal of the European Ceramic Society 38 2449-2453 (2018)
    In the Plasma Spray-Physical Vapor Deposition (PS-PVD) process, columnar structured coatings are deposited mainly from the vapor phase due to the intensive evaporation of the feedstock powder. This paper highlights the application of electron backscatter diffraction (EBSD) for the characterization of columnar structured ceramic PS-PVD coatings. The growth processes of PS-PVD coatings could be elucidated, developing from small equiaxed crystals to large columnar crystals. Furthermore, the main effect of the torch swing on coating deposition could be the interruption of crystal growth and thus repeated nucleation. This may have a similar effect as slowly rotating the substrate in Electron Beam-Physical Vapor Deposition (EB-PVD). © 2017 Elsevier Ltd
    view abstractdoi: 10.1016/j.jeurceramsoc.2017.12.054
  • 2018 • 218 Adhesion of plasma-deposited silicon oxide barrier layers on PDMS containing polypropylene
    Hoppe, C. and Mitschker, F. and Awakowicz, P. and Kirchheim, D. and Dahlmann, R. and de los Arcos, T. and Grundmeier, G.
    Surface and Coatings Technology 335 25-31 (2018)
    The adhesion of SiOx coatings deposited by plasma-enhanced chemical vapor deposition onto injection-molded polypropylene (PP) was investigated as function of polypropylene surface Si enrichment. The PP was either used in its original state or was modified by a by-mixture with small amounts of polydimethylsiloxane (PDMS) in the extrusion process. The substrates where characterized by X-ray photoelectron spectroscopy, attenuated infrared reflection and time of flight spectroscopy; it was seen that the PP/PDMS substrates showed a Si-enriched top layer about 1 nm thick. The adhesion of the SiOx coatings to the PP/PDMS substrates was greatly enhanced with respect to the non-functionalized PP, which shows that adhesion of plasma-deposited SiOx layers to polymer substrates can be improved without the need to deposit intermediate adhesion layers, and without the need to include a plasma pre-treatment step into the process. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.12.015
  • 2018 • 217 Amphiphilic Alginates for Marine Antifouling Applications
    Jakobi, V. and Schwarze, J. and Finlay, J.A. and Nolte, K.A. and Spöllmann, S. and Becker, H.-W. and Clare, A.S. and Rosenhahn, A.
    Biomacromolecules 19 402-408 (2018)
    Amphiphilic polymers are promising candidates for novel fouling-release coatings for marine applications. We grafted amphiphilic alginates with fluorinated side chains to glass and silicon substrates and characterized the obtained films by contact angle goniometry, spectroscopic ellipsometry, XPS, and ATR-FTIR. The potential to inhibit protein attachment was tested against four different proteins, and intermediate fluorine loadings showed the strongest reduction with respect to hydrophobic, aliphatic controls. A similar trend was observed in dynamic attachment experiments using Navicula perminuta diatoms and settlement experiments with zoospores of the green algae Ulva linza. The results indicate that amphiphilic alginates are promising natural and renewable biomacromolecules that could be included in future protective coating technologies. © 2017 American Chemical Society.
    view abstractdoi: 10.1021/acs.biomac.7b01498
  • 2018 • 216 Improved homogeneity of plasma and coating properties using a lance matrix gas distribution in MW-PECVD
    Kirchheim, D. and Wilski, S. and Jaritz, M. and Mitschker, F. and Oberberg, M. and Trieschmann, J. and Banko, L. and Brochhagen, M. and Schreckenberg, R. and Hopmann, C. and Böke, M. and Benedikt, J. and de los Arcos, T. and Grun...
    Journal of Coatings Technology and Research (2018)
    Plasma reactors for the application of silicon oxide coatings (SiOx) are often customized to optimize the processes regarding substrate properties and targeted functionalities. The design of these reactors is often based on qualitative considerations. This paper evaluates the use of a numerical, free simulation software for continuous mechanical problems (OpenFOAM) as a tool to evaluate reactor design options. As demonstrator for this purpose serves a given reactor for large-area pulsed microwave plasmas with a precursor inlet in the form of a shower ring. Previous results indicate that the shower ring may lead to an inhomogeneity in plasma and coatings properties along the substrate surface. Thus, a new precursor inlet design shall be developed. For this, the distribution of the process gases in the reactor for a variety of gas inlet designs and gas flows was simulated and a design chosen based on the results. The reactor was modified accordingly, and the simulations correlated with experimental results of plasma and coating properties. The results show that, despite many simplifications, a simulation of the neutral gas distribution using an open-access software can be a viable tool to support reactor and process design development. © 2018, American Coatings Association.
    view abstractdoi: 10.1007/s11998-018-0138-4
  • 2018 • 215 Deformation induced degradation of hot-dip aluminized steel
    Lemmens, B. and Springer, H. and Peeters, M. and De Graeve, I. and De Strycker, J. and Raabe, D. and Verbeken, K.
    Materials Science and Engineering A 710 385-391 (2018)
    In this work the fracture and corrosion behaviour of hot-dip aluminized steels is investigated in controlled dipping experiments which allowed to separately study the effects of Si in the Al bath (1–10 wt%) and the intermetallic phase thickness (5–30 µm). The addition of Si had no direct influence on the performance of the coating system for similar thickness values of the IMP seam, which in turn showed to be the dominant factor independent from the amount of Si. Thin intermetallic phase seams (< about 10 µm) exhibited more (about 5–10 per 100 µm interfacial length) but smaller cracks with a fishnet pattern on the outer Al-Si coating, which remained intact and interconnected until a tensile deformation of 15–20%. Thicker intermetallic phase seams resulted in less (about 2 per 100 µm interfacial length) but broader cracks perpendicular to the tensile direction, giving rise to a lamellar pattern on the Al-Si coating, which cracks and uncovers the steel already at strains below 10%, and readily flakes off leaving the steel substrate to accelerated corrosion in chloride environments. Our results indicate that the reduction of the intermetallic phase seam thickness remains the main target to improve the performance of hot-dip aluminized coated steel by combining appropriate Si additions with minimized dipping temperatures and times. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2017.10.094
  • 2018 • 214 Control of the material flow in sheet-bulk metal forming using modifications of the tool surface
    Löffler, M. and Schulte, R. and Freiburg, D. and Biermann, D. and Stangier, D. and Tillmann, W. and Merklein, M.
    International Journal of Material Forming 1-10 (2018)
    Sheet-bulk metal forming (SBMF) processes are characterized by a successive and/or simultaneous occurrence of different load conditions such as the stress and strain states. These conditions influence the material flow and often lead to a reduced geometrical accuracy of the produced components. To improve the product quality, a control of the material flow is required. One suitable approach, the local adaption of tribological conditions by means of surface modifications of tool or workpiece, so-called tailored surfaces. To control the material flow and thus to improve the component accuracy, methods to reduce and to increase friction are needed. The aim of this study is to determine requirements for necessary adaptions of the friction, the identification of tribological mechanisms for different types of tool-sided tailored surfaces as well as the verification of the effectiveness of these surface modifications to improve the results of a specific SBMF process. The numerical analysis of a combined deep drawing and upsetting process revealed that this process is characterized by two areas of varying tribological load conditions. Using a numerical analysis, the friction factor gradient between these two areas was identified as a main influencing factor on the material flow. Based on this finding, Chromium-based hard coatings for the reduction of the friction and high-feed milled surfaces for an increase of the friction were investigated regarding their frictional behaviour. The results of the ring-compression tests revealed that the carbon content and the post treatment of coated tool surfaces are relevant to reduce the friction. The increased profile depth of the milled surfaces was identified as the main influencing factor on the tribological behaviour of this kind of tailored surfaces. The effectiveness of both types of tailored surfaces was verified for the combined deep drawing and upsetting process. © 2018 Springer-Verlag France SAS, part of Springer Nature
    view abstractdoi: 10.1007/s12289-018-1399-2
  • 2018 • 213 Conditions for nucleation and growth in the substrate boundary layer at plasma spray-physical vapor deposition (PS-PVD)
    Mauer, G. and Vaßen, R.
    Surface and Coatings Technology (2018)
    Plasma spray-physical vapor deposition (PS-PVD) is a novel coating process based on plasma spraying. In contrast to conventional methods, deposition can come off not only from liquid splats but also from vapor phase. Moreover, there is the suggestion that also nano-sized clusters can be formed by homogeneous nucleation and contribute to deposition. In this work, the conditions for nucleation and growth of such nano-sized particles in the plasma flow around the substrate under PS-PVD conditions were investigated. A boundary layer kinetics model was coupled to an approach for homogeneous nucleation from supersaturated vapors and primary particle growth by condensation as well as secondary particle formation by coagulation. The results confirm the importance of the boundary layer on the substrate. However, since these particles are relatively small, their contribution to coating deposition is limited. Furthermore, microstructure or crystallographic orientations are unlikely to be affected by this cluster deposition. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2018.06.086
  • 2018 • 212 Systematic Investigation on the Influence of Spray Parameters on the Mechanical Properties of Atmospheric Plasma-Sprayed YSZ Coatings
    Mutter, M. and Mauer, G. and Mücke, R. and Guillon, O. and Vaßen, R.
    Journal of Thermal Spray Technology 1-15 (2018)
    In the atmospheric plasma spray (APS) process, micro-sized ceramic powder is injected into a thermal plasma where it is rapidly heated and propelled toward the substrate. The coating formation is characterized by the subsequent impingement of a large number of more or less molten particles forming the so-called splats and eventually the coating. In this study, a systematic investigation on the influence of selected spray parameters on the coating microstructure and the coating properties was conducted. The investigation thereby comprised the coating porosity, the elastic modulus, and the residual stress evolution within the coating. The melting status of the particles at the impingement on the substrate in combination with the substrate surface condition is crucial for the coating formation. Single splats were collected on mirror-polished substrates for selected spray conditions and evaluated by identifying different types of splats (ideal, distorted, weakly bonded, and partially molten) and their relative fractions. In a previous study, these splat types were evaluated in terms of their effect on the above-mentioned coating properties. The particle melting status, which serves as a measure for the particle spreading behavior, was determined by in-flight particle temperature measurements and correlated to the coating properties. It was found that the gun power and the spray distance have a strong effect on the investigated coating properties, whereas the feed rate and the cooling show minor influence. © 2018 ASM International
    view abstractdoi: 10.1007/s11666-018-0697-z
  • 2018 • 211 Investigation on the oxidation behavior of AlCrVxN thin films by means of synchrotron radiation and influence on the high temperature friction
    Tillmann, W. and Kokalj, D. and Stangier, D. and Paulus, M. and Sternemann, C. and Tolan, M.
    Applied Surface Science 427 511-521 (2018)
    Friction minimization is an important topic which is pursued in research and industry. In addition to the use of lubricants, friction-reducing oxide phases can be utilized which occur during. These oxides are called Magnéli phases and especially vanadium oxides exhibit good friction reducing properties. Thereby, the lubrication effect can be traced back to oxygen deficiencies. AlCrN thin films are being used as coatings for tools which have to withstand high temperatures. A further improvement of AlCrN thin films concerning their friction properties is possible by incorporation of vanadium. This study analyzes the temperature dependent oxidation behavior of magnetron sputtered AlCrVN thin films with different vanadium contents up to 13.5 at.-% by means of X-ray diffraction and X-ray absorption near-edge spectroscopy. Up to 400 °C the coatings show no oxidation. A higher temperature of 700 °C leads to an oxidation and formation of Magnéli phases of the coatings with vanadium contents above 10.7 at.-%. Friction coefficients, measured by ball-on-disk test are correlated with the oxide formation in order to figure out the effect of vanadium oxides. At 700 °C a decrease of the friction coefficient with increasing vanadium content can be observed, due to the formation of VO2, V2O3 and the Magnéli phase V4O7. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.09.029
  • 2018 • 210 In Situ Acoustic Monitoring of Thermal Spray Process Using High-Frequency Impulse Measurements
    Tillmann, W. and Walther, F. and Luo, W. and Haack, M. and Nellesen, J. and Knyazeva, M.
    Journal of Thermal Spray Technology 27 50-58 (2018)
    In order to guarantee their protective function, thermal spray coatings must be free from cracks, which expose the substrate surface to, e.g., corrosive media. Cracks in thermal spray coatings are usually formed because of tensile residual stresses. Most commonly, the crack occurrence is determined after the thermal spraying process by examination of metallographic cross sections of the coating. Recent efforts focus on in situ monitoring of crack formation by means of acoustic emission analysis. However, the acoustic signals related to crack propagation can be absorbed by the noise of the thermal spraying process. In this work, a high-frequency impulse measurement technique was applied to separate different acoustic sources by visualizing the characteristic signal of crack formation via quasi-real-time Fourier analysis. The investigations were carried out on a twin wire arc spraying process, utilizing FeCrBSi as a coating material. The impact of the process parameters on the acoustic emission spectrum was studied. Acoustic emission analysis enables to obtain global and integral information on the formed cracks. The coating morphology and coating defects were inspected using light microscopy on metallographic cross sections. Additionally, the resulting crack patterns were imaged in 3D by means of x-ray microtomography. © 2017, ASM International.
    view abstractdoi: 10.1007/s11666-017-0673-z
  • 2018 • 209 Spray pattern analysis in TWAS using photogrammetry and digital image correlation
    Tillmann, W. and Rademacher, H.G. and Hagen, L. and Abdulgader, M. and El Barad'Ei, M.
    IOP Conference Series: Materials Science and Engineering 373 (2018)
    In terms of arc spraying processes, the spray plume characteristic is mainly affected by the flow characteristic of the atomization gas at the nozzle inlet and intersection point of the wire tips, which in turn affect the particle distribution at the moment of impact when molten spray particles splash onto the substrate. With respect to the route of manufacturing of near net-shaped coatings on complex geometries, the acquisition of the spray patterns is pressingly necessary to determine the produced coating thickness. Within the scope of this study, computer fluid dynamics (CFD) simulations were carried out to determine the distribution of spray particles for different spray parameter settings. The results were evaluated by three-dimensional spray spot analyses using an optical measurement based on photogrammetry and digital image correlation. The optical measurement represents a promising and much faster candidate to measure spray patterns compared to the tactile measurement system but with an equal accuracy. For given nozzle configurations and spray parameter settings, numerous spray patterns were examined to their shape factors, demonstrating the potential of an online analysis, which encompasses a "fast sample loop" and a data processing system to generate a three-dimensional surface of the spray spot profile. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/373/1/012014
  • 2018 • 208 Vacuum plasma spraying of functionally graded tungsten/EUROFER97 coatings for fusion applications
    Vaßen, R. and Rauwald, K.-H. and Guillon, O. and Aktaa, J. and Weber, T. and Back, H.C. and Qu, D. and Gibmeier, J.
    Fusion Engineering and Design 133 148-156 (2018)
    As structural materials for future fusion power plants, reduced activation ferritic martensitic steels as EUROFER97 can be used. Unfortunately, the interaction of the plasma with the steel would result in a limited lifetime, so protective layers are investigated. An excellent protective material is tungsten, as it shows unique properties with respect to low sputtering, high melting points and low activation. However, the mismatch of thermo-physical properties between tungsten and EUROFER97 can lead to large stress levels and even failure. A possible way to overcome this problem is the use of functionally graded material (FGM). The paper will describe the manufacture of these FGMs by vacuum plasma spraying and their characterization. First of all, two different feeding lines have been used to produce the coatings. A major problem lies in different melting points of tungsten and steel. So the particle size distribution has to be adjusted to achieve sufficient melting of both materials during the spray process. In a second step, the feeding rates were optimized to obtain the wanted amount of tungsten and steel phases in the graded structures. In a thermal spray process, the gradient cannot be made continuously, however it has to be applied in a step-wise manner. In this investigation, samples with 3 and 5 different concentrations (excluding the pure steel and tungsten part) have been produced. The microstructures of these layers have been investigated. In addition, hardness was measured and the residual stress state was determined by the hole drilling method. © 2018
    view abstractdoi: 10.1016/j.fusengdes.2018.06.006
  • 2018 • 207 Monte Carlo simulation of column growth in plasma spray physical vapor deposition process
    Wang, P. and He, W. and Mauer, G. and Mücke, R. and Vaßen, R.
    Surface and Coatings Technology 335 188-197 (2018)
    Plasma spray-physical vapor deposition is used to produce columnar microstructure coatings under particular operating parameters. Simulations of the growth of columns were carried out through a two-dimensional Monte Carlo model. The modeling was performed using inclined vapor flux impinging onto a substrate due to shadowing effects. An incoming particle travels along a straight line and attaches itself to already deposited particles. Furthermore, the newly deposited particle will relax to a stable surrounding position along the incoming velocity direction. The modeling results predicted the linking of an oblique vapor flux and column orientation. The numerical simulations were validated in three ways. Firstly, the porosity of simulated columns was predicted and compared to that obtained in the experimental columnar microstructure of coatings. Secondly, the morphology of simulated structures is compared to that of experimental coatings produced by plasma spray physical vapor deposition. Finally, the simulated orientation of columns is compared to the experimental one. © 2017
    view abstractdoi: 10.1016/j.surfcoat.2017.12.023
  • 2018 • 206 Fouling-Release Properties of Dendritic Polyglycerols against Marine Diatoms
    Wanka, R. and Finlay, J.A. and Nolte, K.A. and Koc, J. and Jakobi, V. and Anderson, C. and Clare, A.S. and Gardner, H. and Hunsucker, K.Z. and Swain, G.W. and Rosenhahn, A.
    ACS Applied Materials and Interfaces 10 34965-34973 (2018)
    Dendritic polyglycerols (PGs) were grafted onto surfaces using a ring-opening polymerization reaction, and the fouling-release properties against marine organisms were determined. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, ATR-FTIR, and stability tests in different aqueous media. A high resistance toward the attachment of different proteins was found. The PG coatings with three different thicknesses were tested in a laboratory assay against the diatom Navicula incerta and in a field assay using a rotating disk. Under static conditions, the PG coatings did not inhibit the initial attachment of diatoms, but up to 94% of attached diatoms could be removed from the coatings after exposure to a shear stress of 19 Pa. Fouling release was found to be enhanced if the coatings were sufficiently thick. The excellent fouling-release properties were supported in dynamic field-immersion experiments in which the samples were continually exposed to a shear stress of 0.18 Pa. © 2018 American Chemical Society.
    view abstractdoi: 10.1021/acsami.8b12017
  • 2018 • 205 Conformational study of melamine crosslinkers and spectroscopical comparison of HMMM molecules by practical measurements and quantum chemical calculations
    Wysoglad, J. and Ehlers, J.-E. and Lewe, T. and Dornbusch, M. and Gutmann, J.S.
    Journal of Molecular Structure 1166 456-469 (2018)
    To understand and improve network formation processes and performance properties makes structural molecular studies critically important for the coil-coating industry. Crosslinking agents such as hexamethoxymethylmelamine (HMMM) or less methylated derivatives, e.g. methoxymethylmelamine (MMM), are often added to industrial coating formulations. For molecules with considerably fewer atoms and accordingly less rotational freedom (such as MMM) it is readily accessible to identify principal conformations. Thus, an MMM conformer study is straightforward and serves as orientation concerning HMMM conformer studies. For HMMM molecules an extensive computation method was developed to investigate the conformational distribution average and probably most likely molecular structures. Using the density functional theory (DFT) B3LYP-D3BJ method with Dunning's correlation basis set, calculations were performed to investigate the three-dimensional structural geometries of HMMM (basis set cc-pVDZ) and MMM (basis set cc-pVTZ). Beginning with 1500 conformations for HMMM and using various cut-off filters we focused on final residual 22 conformers for solvent phase calculations and 16 conformers for gas phase calculations. To the best of our knowledge, this is the first time that chemical properties for melamine crosslinkers were presented under consideration of conformational population distribution. Thus, computations of fully optimized structural geometries, energies and vibrational states indicate that preferred structural alignments for the methoxymethyl (MM) group in melamine molecules exist. Nevertheless, we suppose that as a matter of principle the MM group of MMM molecules can easily perform rotations by itself and all conformational structure geometries of MMM will exist. Concerning the MM groups position compared to triazine plane HMMM molecules have two main configurations,”3up-3down” and “4up-2down”, as dominant conformer species. Computations of weighted and averaged IR and Raman spectra of final conformations for HMMM monomers, dimers and trimers at ambient temperature are novel and in good agreement with experiment. Prediction of a final UV–Vis spectrum of top ten Boltzmann-weight and averaged monomeric HMMM conformers is in perfect agreement with practical measurement of commercially available HMMM. © 2018 Elsevier B.V.
    view abstractdoi: 10.1016/j.molstruc.2018.04.069
  • 2017 • 204 Residual stress depth distributions for atmospheric plasma sprayed MnCo1.9Fe0.1O4 spinel layers on crofer steel substrate
    Back, H.C. and Mutter, M. and Gibmeier, J. and Mücke, R. and Vaßen, R.
    Materials Science Forum 905 MSF 174-181 (2017)
    In solid oxide fuel cells (SOFC) for operating temperatures of 800 °C or below, the use of ferritic stainless steel can lead to degradation in cell performance due to chromium migration into the cells at the cathode side [1]. Application of a coating on the ferritic stainless steel interconnect is one option to prevent Cr outward migration through the coating. MnCo1.9Fe0.1O4 (in the following designated as MCF) spinels act as a diffusion barrier and retain high conductivity during operation [2]. Knowledge about the residual stress depth distribution throughout the complete APS coating system is important and can help to optimize the coating process. This implicitly requires reliable residual stress analysis in the coating, the interface region and in the substrate. For residual stress analysis on these specific layered systems diffraction based analysis methods (XRD) using laboratory X-ray sources can only by applied at the very surface. For larger depths sublayer removal is necessary to gain reliable residual stress data. The established method for sublayer removal is electrochemical etching, which fails, since the spinel layer is inert. However, a mechanical layer removal will affect the local residual stress distribution. As an alternative, mechanical residual stress analyses techniques can be applied. Recently, we established an approach to analyse residual stress depth distributions in thick film systems by means of the incremental hole drilling method [5, 6]. In this project, we refined our approach for the application on MCF coatings with a layer thickness between 60 – 125 µm. © 2017 Trans Tech Publications, Switzerland.
    view abstractdoi: 10.4028/
  • 2017 • 203 Yb2Si2O7 Environmental Barrier Coatings Deposited by Various Thermal Spray Techniques: A Preliminary Comparative Study
    Bakan, E. and Marcano, D. and Zhou, D. and Sohn, Y.J. and Mauer, G. and Vaßen, R.
    Journal of Thermal Spray Technology 26 1011-1024 (2017)
    Dense, crack-free, uniform, and well-adhered environmental barrier coatings (EBCs) are required to enhance the environmental durability of silicon (Si)-based ceramic matrix composites in high pressure, high gas velocity combustion atmospheres. This paper represents an assessment of different thermal spray techniques for the deposition of Yb2Si2O7 EBCs. The Yb2Si2O7 coatings were deposited by means of atmospheric plasma spraying (APS), high-velocity oxygen fuel spraying (HVOF), suspension plasma spraying (SPS), and very low-pressure plasma spraying (VLPPS) techniques. The initial feedstock, as well as the deposited coatings, were characterized and compared in terms of their phase composition. The as-sprayed amorphous content, microstructure, and porosity of the coatings were further analyzed. Based on this preliminary investigation, the HVOF process stood out from the other techniques as it enabled the production of vertical crack-free coatings with higher crystallinity in comparison with the APS and SPS techniques in atmospheric conditions. Nevertheless, VLPPS was found to be the preferred process for the deposition of Yb2Si2O7 coatings with desired characteristics in a controlled-atmosphere chamber. © 2017, ASM International.
    view abstractdoi: 10.1007/s11666-017-0574-1
  • 2017 • 202 Ceramic Top Coats of Plasma-Sprayed Thermal Barrier Coatings: Materials, Processes, and Properties
    Bakan, E. and Vaßen, R.
    Journal of Thermal Spray Technology 26 992-1010 (2017)
    The ceramic top coat has a major influence on the performance of the thermal barrier coating systems (TBCs). Yttria-partially-stabilized zirconia (YSZ) is the top coat material frequently used, and the major deposition processes of the YSZ top coat are atmospheric plasma spraying and electron beam physical vapor deposition. Recently, also new thermal spray processes such as suspension plasma spraying or plasma spray-physical vapor deposition have been intensively investigated for TBC top coat deposition. These new processes and particularly the different coating microstructures that can be deposited with them will be reviewed in this article. Furthermore, the properties and the intrinsic–extrinsic degradation mechanisms of the YSZ will be discussed. Following the TBC deposition processes and standard YSZ material, alternative ceramic materials such as perovskites and hexaaluminates will be summarized, while properties of pyrochlores with regard to their crystal structure will be discussed more in detail. The merits of the pyrochlores such as good CMAS resistance as well as their weaknesses, e.g., low fracture toughness, processability issues, will be outlined. © 2017, ASM International.
    view abstractdoi: 10.1007/s11666-017-0597-7
  • 2017 • 201 Fabrication of Oxide Dispersion Strengthened Bond Coats with Low Al2O3 Content
    Bergholz, J. and Pint, B.A. and Unocic, K.A. and Vaßen, R.
    Journal of Thermal Spray Technology 1-12 (2017)
    Nanoscale oxide dispersions have long been used to increase the oxidation and wear resistance of alloys used as bond coatings in thermal barrier coatings. Their manufacturing via mechanical alloying is often accompanied by difficulties regarding their particle size, homogeneous distribution of the oxide dispersions inside the powder, involving considerable costs, due to cold welding of the powder during milling. A significant improvement in this process can be achieved by the use of process control agent (PCA) to achieve the critical balance between cold welding and fracturing, thereby enhancing the process efficiency. In this investigation, the influence of the organic additive stearic acid on the manufacturing process of Al2O3-doped CoNiCrAlY powder was investigated. Powders were fabricated via mechanical alloying at different milling times and PCA concentrations. The results showed a decrease in particle size, without hindering the homogeneous incorporation of the oxide dispersions. Two powders manufactured with 0.5 and 1.0 wt.% PCA were deposited by high velocity oxygen fuel (HVOF) spraying. Results showed that a higher content of elongated particles in the powder with the higher PCA content led to increased surface roughness, porosity and decreased coating thickness, with areas without embedded oxide particles. © 2017 ASM International
    view abstractdoi: 10.1007/s11666-017-0550-9
  • 2017 • 200 Computational homogenisation for thermoviscoplasticity: application to thermally sprayed coatings
    Berthelsen, R. and Denzer, R. and Oppermann, P. and Menzel, A.
    Computational Mechanics 1-28 (2017)
    Metal forming processes require wear-resistant tool surfaces in order to ensure a long life cycle of the expensive tools together with a constant high quality of the produced components. Thermal spraying is a relatively widely applied coating technique for the deposit of wear protection coatings. During these coating processes, heterogeneous coatings are deployed at high temperatures followed by quenching where residual stresses occur which strongly influence the performance of the coated tools. The objective of this article is to discuss and apply a thermo-mechanically coupled simulation framework which captures the heterogeneity of the deposited coating material. Therefore, a two-scale finite element framework for the solution of nonlinear thermo-mechanically coupled problems is elaborated and applied to the simulation of thermoviscoplastic material behaviour including nonlinear thermal softening in a geometrically linearised setting. The finite element framework and material model is demonstrated by means of numerical examples. © 2017 Springer-Verlag GmbH Germany
    view abstractdoi: 10.1007/s00466-017-1436-x
  • 2017 • 199 Characterization of DC magnetron plasma in Ar/Kr/N2 mixture during deposition of (Cr,Al)N coating
    Bobzin, K. and Bagcivan, N. and Theiß, S. and Brugnara, R. and Bibinov, N. and Awakowicz, P.
    Journal of Physics D: Applied Physics 50 (2017)
    doi: 10.1088/1361-6463/aa4ea2
  • 2017 • 198 Fundamental study of an industrial reactive HPPMS (Cr,Al)N process
    Bobzin, K. and Brögelmann, T. and Kruppe, N.C. and Engels, M. and Von Keudell, A. and Hecimovic, A. and Ludwig, Al. and Grochla, D. and Banko, L.
    Journal of Applied Physics 122 (2017)
    In this work, a fundamental investigation of an industrial (Cr,Al)N reactive high power pulsed magnetron sputtering (HPPMS) process is presented. The results will be used to improve the coating development for the addressed application, which is the tool coating for plastics processing industry. Substrate-oriented plasma diagnostics and deposition of the (Cr,Al)N coatings were performed for a variation of the HPPMS pulse frequency with values from f = 300 Hz to f = 2000 Hz at constant average power P = 2.5 kW and pulse length ton = 40 μs. The plasma was investigated using an oscilloscope, an intensified charge coupled device camera, phase-resolved optical emission spectroscopy, and an energy-dispersive mass spectrometer. The coating properties were determined by means of scanning electron microscopy, glow discharge optical emission spectroscopy, cantilever stress sensors, nanoindentation, and synchrotron X-ray diffraction. Regarding the plasma properties, it was found that the average energy within the plasma is nearly constant for the frequency variation. In contrast, the metal to gas ion flux ratio is changed from JM/JG = 0.51 to JM/JG = 0.10 for increasing frequency. Regarding the coating properties, a structure refinement as well as lower residual stresses, higher universal hardness, and a changing crystal orientation from (111) to (200) were observed at higher frequencies. By correlating the plasma and coating properties, it can be concluded that the change in the gas ion to metal ion flux ratio results in a competitive crystal growth of the film, which results in changing coating properties. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4990997
  • 2017 • 197 Hybrid biocomposites based on titania nanotubes and a hydroxyapatite coating deposited by RF-magnetron sputtering: Surface topography, structure, and mechanical properties
    Chernozem, R.V. and Surmeneva, M.A. and Krause, B. and Baumbach, T. and Ignatov, V.P. and Tyurin, A.I. and Loza, K. and Epple, M. and Surmenev, R.A.
    Applied Surface Science 426 229-237 (2017)
    In this study, biocomposites based on porous titanium oxide structures and a calcium phosphate (CaP) or hydroxyapatite (HA) coating are described and prepared. Nanotubes (NTs) with different pore dimensions were processed using anodic oxidation of Ti substrates in a NH4F-containing electrolyte solution at anodization voltages of 30 and 60 V with a DC power supply. The external diameters of the nanotubes prepared at 30 V and 60 V were 53 ± 10 and 98 ± 16 nm, respectively. RF-magnetron sputtering of the HA target in a single deposition run was performed to prepare a coating on the surface of TiO2 NTs prepared at 30 and 60 V. The thickness of the CaP coating deposited on the mirror-polished Si substrate in the same deposition run with TiO2 NTs was determined by optical ellipsometry (SE) 95 ± 5 nm. Uncoated and CaP-coated NTs were annealed at 500 °C in air. Afterwards, the presence of TiO2 (anatase) was observed. The scanning electron microscopy (SEM), X-ray diffraction (XRD), photoelectron spectroscopy (XPS) and nanoindentation results revealed the influence that the NT dimensions had on the CaP coating deposition process. The tubular surfaces of the NTs were completely coated with the HA coating when prepared at 30 V, and no homogeneous CaP coating was observed when prepared at 60 V. The XRD patterns show peaks assigned to crystalline HA only for the coated TiO2 NTs prepared at 30 V. High-resolution XPS spectra show binding energies (BE) of Ca 2p, P 2p and O 1s core-levels corresponding to HA and amorphous calcium phosphate on TiO2 NTs prepared at 30 V and 60 V, respectively. Fabrication of TiO2 NTs results in a significant decrease to the elastic modulus and nanohardness compared to the Ti substrate. The porous structure of the NTs causes an increase in the elastic strain to failure of the coating (H/E) and the parameter used to describe the resistance of the material to plastic deformation (H3/E2) at the nanoscale level compared to the Ti substrate. Furthermore, only the HA coating on the NTs exhibits a significantly increased H/E ratio and H3/E2 factor compared to the NTs and Ti substrate. Increases in resistance to penetration for the indenter were also observed for HA-coated TiO2 NTs prepared at 30 V compared to uncoated and CaP-coated NTs prepared at 60 V. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.07.199
  • 2017 • 196 A Unified Interdisciplinary Approach to Design Antibacterial Coatings for Fast Silver Release
    El Arrassi, A. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Köller, M. and Ludwig, Al. and Tschulik, K.
    ChemElectroChem (2017)
    The increasing number of surgical treatments performed per year requires novel approaches to inhibit implant-associated infections, caused by multi-antibiotic resistant bacteria. Silver ions (Ag+) are known for their effective antimicrobial activity. Therefore, a system that efficiently and locally releases the minimum required amount of Ag+ directly after the surgical treatment is in high demand. Herein we study electrochemically, microbiologically, microscopically and spectroscopically sacrificial Ag anode coatings for antibacterial implant applications. It is found that Ag dot arrays deposited on noble metals (Pd, Ir) release Ag+ much faster than continuous Ag thin films. The Ag+ release qualitatively scales with the difference of standard potentials between Ag and the noble metal. Furthermore, with higher numbers of Ag dots, the total amount of released Ag+ increases, while the release efficiency declines. Notably, an efficient killing of Staphylococcus aureus bacteria was seen for coatings containing as little as 23ng of Ag per mm2. Thus, the use of sacrificial Ag anodes as highly efficient antibacterial coating materials is evaluated. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/celc.201700247
  • 2017 • 195 Catalytic Oxidation of Soot Spray-Coated Lithium Zirconate in a Plate Reactor
    Emmerich, T. and Lotz, K. and Sliozberg, K. and Schuhmann, W. and Muhler, M.
    Chemie-Ingenieur-Technik 89 263-269 (2017)
    A plate reactor was designed to investigate the catalytic soot oxidation applying glass ceramic plates coated with lithium zirconate. The results are compared to the corresponding powder catalysts in thermogravimetric experiments. The deposition of soot by spray coating resulted in an intimate contact mode equivalent to the mortaring preparation of the tight contact powder samples. In the presence of lithium ions the soot oxidation temperature was decreased significantly both in the thermobalance and in the plate reactor. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/cite.201600118
  • 2017 • 194 Dependence of the optical constants and the performance in the SPREE gas measurement on the thickness of doped tin oxide over coatings
    Fischer, D. and Hertwig, A. and Beck, U. and Negendank, D. and Lohse, V. and Kormunda, M. and Esser, N.
    Applied Surface Science 421 480-486 (2017)
    In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29-56. nm, the second was iron doped on gold/glass substrate with 1.6-6.3. nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6. nm to 5.1. nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3. nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much. © 2016.
    view abstractdoi: 10.1016/j.apsusc.2016.11.188
  • 2017 • 193 Influence of rotational speed on process characteristics in friction surfacing of Ti-6Al-4V
    Fitseva, V. and Hanke, S. and dos Santos, J.F.
    Materials and Manufacturing Processes 32 557-563 (2017)
    Friction surfacing process is employed to deposit metallic coatings, whereby similar and dissimilar material combinations can be realized. The process can be applied as a local repair technology, or the coating material can locally modify the surfaces. One advantage of this process is that the coatings are deposited in solid state without reaching the melting range of materials, thereby avoiding dilution with the substrate. The involved severe plastic deformation under high temperatures alters the microstructure of the coating material, leaving it fully dynamically recrystallized. The current work focuses on deposition of Ti-6Al-4V coatings. For that material, the process parameter rotational speed plays a major role in the material’s response during processing. Two different regimes with a threshold at 2000 min−1exist, upon which the flow behavior of Ti-6Al-4V significantly differs, affecting among others the coating dimensions. Microstructural analysis reveals that the material is deformed in a high temperature β phase, and the high cooling rates (46.4 Ks−1) lead to martensitic transformation. The β grain size differs in the low and high rotational speed regimes. This study shows that metallurgical processes play an important role in friction surfacing, since they influence all relevant process characteristics, including microstructure, material efficiency and process forces. © 2017 Taylor & Francis.
    view abstractdoi: 10.1080/10426914.2016.1257799
  • 2017 • 192 Study of stability of microstructure and residual strain after thermal loading of plasma sprayed YSZ by through surface neutron scanning
    Gibmeier, J. and Back, H.C. and Mutter, M. and Vollert, F. and Rebelo-Kornmeier, J. and Mücke, R. and Vaßen, R.
    Physica B: Condensed Matter (2017)
    Yttria stabilized zirconia (YSZ) is often applied as thermal barrier coating on metal parts as e.g. turbine blades made of nickel base super alloys. The coating process in combination with the preconditioning of the substrate material induces characteristic residual stress distributions in the coating system consisting of topcoat, bondcoat and the substrate material. Knowledge about the residual stress depth distribution in the coating and at the interfaces down to the substrate material is essential for the assessment of the mechanical integrity and the reliability of the coating. In this regard the stability of the microstructure and the residual stresses is of particular interest; hence this forms the scope of our investigations. Yttria (8 wt.%) stabilized zirconia with a NiCoCrAlY bondcoat was deposited by atmospheric plasma spraying (APS) at different spray conditions on a nickel base super alloy substrate material. The coatings were subjected to different heat-treatment processes, i.e. static aging and cyclic thermal loadings. Through surface scanning using neutron diffraction was carried out for the as sprayed condition and for the thermally loaded samples. Based on the measured diffraction data the stability of the microstructure (phases) and the residual strain/stresses through the depths of the coating system were assessed. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.physb.2017.12.014
  • 2017 • 191 Transparent, mediator- and membrane-free enzymatic fuel cell based on nanostructured chemically modified indium tin oxide electrodes
    González-Arribas, E. and Bobrowski, T. and Di Bari, C. and Sliozberg, K. and Ludwig, R. and Toscano, M.D. and De Lacey, A.L. and Pita, M. and Schuhmann, W. and Shleev, S.
    Biosensors and Bioelectronics 97 46-52 (2017)
    We detail a mediator- and membrane-free enzymatic glucose/oxygen biofuel cell based on transparent and nanostructured conducting supports. Chemically modified indium tin oxide nanoparticle modified electrodes were used to substantially increase the active surface area without significantly compromising transparency. Two different procedures for surface nanostructuring were employed, viz. spray-coating and drop-coating. The spray-coated biodevice showed superior characteristics as compared to the drop-coated enzymatic fuel cell, as a result of the higher nanostructured surface area as confirmed by electrochemical characterisation, as well as scanning electron and atomic force microscopy. Subsequent chemical modification with silanes, followed by the immobilisation of either cellobiose dehydrogenase from Corynascus thermophiles or bilirubin oxidase from Myrothecium verrucaria, were performed to obtain the bioanodes and biocathodes, respectively. The optimised biodevice exhibited an OCV of 0.67 V and power output of up to 1.4 µW/cm2 at an operating voltage of 0.35 V. This is considered a significant step forward in the field of glucose/oxygen membrane- and mediator-free, transparent enzymatic fuel cells. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.bios.2017.05.040
  • 2017 • 190 Sand-blasting treatment as a way to improve the adhesion strength of hydroxyapatite coating on titanium implant
    Grubova, I. and Priamushko, T. and Surmeneva, M. and Korneva, O. and Epple, M. and Prymak, O. and Surmenev, R.
    Journal of Physics: Conference Series 830 (2017)
    In the current study, the effect of corundum particle sizes (50 and 250-320 μm) used for sand-blasting on the structure, roughness, wettability, mechanical properties, and adhesion of radio frequency magnetron hydroxyapatite coating deposited on treated titanium substrate is studied. Morphology analysis revealed that pretreatment uniformly deforms the surface and induces the formation of pits, which size depends linearly on the grit size. The deposited coatings (Ca/P was in a range of 1.75-1.79) are homogeneous and repeat the relief of the substrate (mean roughness Ra is 1.9±0.1 (250-320 μm) and 0.8±0.1 μm (50 μm)). Texture coefficient calculations revealed the predominant (002) growth texture of hydroxyapatite coatings. The resistance of the coating to plastic deformation and the surface hardening were significantly higher for coatings formed on sand blasted with particle size of 50 μm. Scratch test have shown the significant improvement of wear resistance and lower friction coefficient of coatings for smoother samples. Dynamic contact angle measurements revealed the hydrophilic properties of the hydroxyapatite coating. Thus, sand-blasting of titanium with corundum powder having the size of 50 μm prior to the deposition of RF magnetron coating is recommended for the medical applications intended to improve the bonding between the substrate and coating.
    view abstractdoi: 10.1088/1742-6596/830/1/012109
  • 2017 • 189 Investigations on the Nature of Ceramic Deposits in Plasma Spray–Physical Vapor Deposition
    He, W. and Mauer, G. and Gindrat, M. and Wäger, R. and Vaßen, R.
    Journal of Thermal Spray Technology 26 83-92 (2017)
    In Plasma Spray–Physical Vapor Deposition (PS-PVD) process, major fractions of the feedstock powder can be evaporated so that coatings are deposited mainly from the vapor phase. In this work, Computational Fluid Dynamics (CFD) results indicate that such evaporation occurs significantly in the plasma torch nozzle and even nucleation and condensation of zirconia is highly possible there. Experimental work has been performed to investigate the nature of the deposits in the PS-PVD process, in particular coatings from condensate vapor and nano-sized clusters produced at two spraying distances of 1000 mm and 400 mm. At long spraying distance, columns in the coatings have pyramidal tops and very sharp faceted microstructures. When the spraying distance is reduced to 400 mm, the tops of columns become relatively flat and a faceted structure is not recognizable. XRD patterns show obvious preferred orientations of (110) and (002) in the coatings sprayed at 400 mm but only limited texture in the coatings sprayed at 1000 mm. Meanwhile, a non-line of sight coating was also investigated, which gives an example for pure vapor deposition. Based on these analyses, a vapor and cluster depositions are suggested to further explain the formation mechanisms of high-quality columnar-structured PS-PVD thermal barrier coatings which have already shown excellent performance in cyclic lifetime test. © 2016, ASM International.
    view abstractdoi: 10.1007/s11666-016-0513-6
  • 2017 • 188 Isothermal and cyclic oxidation behavior of free standing MCrAlY coatings manufactured by high-velocity atmospheric plasma spraying
    Hejrani, E. and Sebold, D. and Nowak, W.J. and Mauer, G. and Naumenko, D. and Vaßen, R. and Quadakkers, W.J.
    Surface and Coatings Technology 313 191-201 (2017)
    In the present paper the high temperature oxidation behavior of a free standing NiCoCrAlY coating produced by high-velocity atmospheric plasma spraying (HV-APS) is investigated and compared with that produced by conventional low pressure plasma spraying (LPPS). Isothermal thermogravimetric experiments at 1000 and 1100 °C in synthetic air revealed a lower oxidation rate of the HV-APS than the LPPS coating. Both coatings formed oxide scales based on alpha alumina, however, in the LPPS coating incorporation of coarse mixed Y/Al-oxide pegs into the scale occurred, increasing the oxidation rate by providing short circuit paths for oxygen diffusion probably due to higher diffusivities in the mixed oxide and/or along the interfaces between mixed oxide and alumina. In the HV-APS coatings most of the yttrium was tied-up in sub-μm Y-containing oxide particles and only minor amounts of mixed Y/Al oxide precipitates were found in the alumina surface scale. Cyclic air oxidation tests at 1100 °C revealed a lower oxidation rate and better scale adherence for the HV-APS coating. The results thus show that HV-APS is a promising method for the processing of MCrAlY coatings. The specific yttrium distribution in form of fine oxide precipitates in the HV-APS material prevents the formation of deleterious Y-rich oxide pegs and promotes formation of a slowly growing, protective alumina scale with excellent adherence. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.01.081
  • 2017 • 187 Effect of test atmosphere composition on high-temperature oxidation behaviour of CoNiCrAlY coatings produced from conventional and ODS powders
    Huang, T. and Bergholz, J. and Mauer, G. and Vassen, R. and Naumenko, D. and Quadakkers, W.J.
    Materials at High Temperatures 1-11 (2017)
    The oxidation behaviour of free-standing CoNiCrAlY coatings produced by low-pressure plasma spraying using conventional powder and oxide dispersion strengthened (ODS) powder containing 2 wt. % Al-oxide dispersion was investigated. Thermogravimetric experiments at 1100 °C in Ar-20%O2 and Ar-4%H2-2%H2O showed lower oxidation rates of the ODS than the conventional coating. In the latter material the scale growth was enhanced by extensive Y-incorporation of Y/Al-mixed oxide precipitates in the scale and apparently by Y-segregation to oxide grain boundaries. In the ODS coating the alumina dispersion bonded Y in the form of Y-aluminate thereby effectively suppressing scale ‘overdoping’. SEM/EBSD studies of all alumina scales revealed a columnar grain structure with the lateral grain size increasing approximately linearly with depth from the oxide/gas interface. For both coatings the alumina scale growth was slower in Ar–H2–H2O than in Ar–O2. The result is believed to be related to a lower oxygen potential gradient and to slower grain boundary diffusion in the scale forming in H2/H2O containing gas. © 2017 Informa UK Limited, trading as Taylor & Francis Group
    view abstractdoi: 10.1080/09603409.2017.1389422
  • 2017 • 186 Influence of residual stress on the adhesion and surface morphology of PECVD-coated polypropylene
    Jaritz, M. and Hopmann, C. and Behm, H. and Kirchheim, D. and Wilski, S. and Grochla, D. and Banko, L. and Ludwig, Al. and Böke, M. and Winter, J. and Bahre, H. and Dahlmann, R.
    Journal of Physics D: Applied Physics 50 (2017)
    The properties of plasma-enhanced chemical vapour deposition (PECVD) coatings on polymer materials depend to some extent on the surface and material properties of the substrate. Here, isotactic polypropylene (PP) substrates are coated with silicon oxide (SiOx) films. Plasmas for the deposition of SiOx are energetic and oxidative due to the high amount of oxygen in the gas mixture. Residual stress measurements using single Si cantilever stress sensors showed that these coatings contain high compressive stress. To investigate the influence of the plasma and the coatings, residual stress, silicon organic (SiOCH) coatings with different thicknesses between the PP and the SiOx coating are used as a means to protect the substrate from the oxidative SiOx coating process. Pull-off tests are performed to analyse differences in the adhesion of these coating systems. It could be shown that the adhesion of the PECVD coatings on PP depends on the coatings' residual stress. In a PP/SiOCH/SiOx-multilayer system the residual stress can be significantly reduced by increasing the thickness of the SiOCH coating, resulting in enhanced adhesion. © 2017 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aa8798
  • 2017 • 185 Transport mechanisms through PE-CVD coatings: Influence of temperature, coating properties and defects on permeation of water vapour
    Kirchheim, D. and Jaritz, M. and Mitschker, F. and Gebhard, M. and Brochhagen, M. and Hopmann, C. and Böke, M. and Devi, A. and Awakowicz, P. and Dahlmann, R.
    Journal of Physics D: Applied Physics 50 (2017)
    doi: 10.1088/1361-6463/aa511c
  • 2017 • 184 Influence of plasma electrolytic oxidation coatings on fatigue performance of AZ31 Mg alloy
    Klein, M. and Lu, X. and Blawert, C. and Kainer, K.U. and Zheludkevich, M.L. and Walther, F.
    Materials and Corrosion 68 50-57 (2017)
    Magnesium and its alloys are attractive for lightweight construction, but suffer often from poor corrosion resistance. Plasma electrolytic oxidation is a promising surface treatment to overcome these limitations. Recently, introduction of particles to the PEO electrolyte has been explored as new strategy to provide a wider range of compositions and new functionalities for PEO coatings. However, this surface treatment can have negative impact on the fatigue strength. In the present study, the influence of PEO coatings with and without particle addition on the corrosion fatigue behavior of AZ31 Mg alloy is investigated. The corrosion fatigue behavior is investigated in load increase tests and constant amplitude tests in 0.5% NaCl solutions. Results are correlated with the corrosion behavior evaluated in polarization and electrochemical impedance spectroscopy measurements. Corrosion tests show significant improvement of the corrosion resistances of PEO-coated specimens. However, the uncoated material exhibits the highest corrosion fatigue strength, whereas a reduction of 7% for the PEO-coated specimen without particles and 27% for the PEO-coated specimen with particles is found. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/maco.201609088
  • 2017 • 183 Gradual modification of ITO particle's crystal structure and optical properties by pulsed UV laser irradiation in a free liquid jet
    Lau, M. and Straube, T. and Aggarwal, A.V. and Hagemann, U. and De Oliveira Viestel, B. and Hartmann, N. and Textor, T. and Lutz, H. and Gutmann, J.S. and Barcikowski, S.
    Dalton Transactions 46 6039-6048 (2017)
    Indium tin oxide (ITO) particle coatings are known for high transparency in the visible, good conductive properties and near-infrared absorption. These properties depend on ITO particle's stoichiometric composition, defects and size. Here we present a method to gradually change ITO particle's optical properties by a simple and controlled laser irradiation process. The defined irradiation process and controlled energy dose input allows one to engineer the absorption and transmission of coatings made from these particles. We investigate the role of the surrounding solvent, influence of laser fluence and the specific energy dose targeting modification of the ITO particle's morphology and chemistry by stepwise laser irradiation in a free liquid jet. TEM, SEM, EDX, XPS, XRD and Raman are used to elucidate the structural, morphological and chemical changes of the laser-induced ITO particles. On the basis of these results the observed modification of the optical properties is tentatively attributed to chemical changes, e.g. laser-induced defects or partial reduction. © 2017 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c7dt00010c
  • 2017 • 182 Lifetime and failure modes of plasma sprayed thermal barrier coatings in thermal gradient rig tests with simultaneous CMAS injection
    Mack, D.E. and Wobst, T. and Jarligo, M.O.D. and Sebold, D. and Vaßen, R.
    Surface and Coatings Technology 324 36-47 (2017)
    Degradation of thermal barrier coatings (TBCs) in gas-turbine engines due to calcium–magnesium–aluminosilicate (CMAS) glassy deposits from various sources such as sand, volcanic ash, fly ash, or variable quality fuels has been a tenacious issue during the recent years. This follows from the fact that engines are required to operate under increasingly harsh conditions in all kind of gas turbine applications following the demands for higher efficiency and operational flexibility. While the understanding of the mechanism of CMAS induced degradation of TBCs as well as approaches for mitigation of CMAS attack by means of advanced TBC compositions have grown remarkably, most of the reported results have been obtained from lab testing at isothermal conditions or from evaluation of ex-service components, either. The isothermal tests are not reproducing important thermomechanical effects from service conditions, and it may be hard to figure out the thermal history of the ex-service examples. In this study a burner rig facility has been used for the evaluation of TBC performance, where a thermal gradient is applied across the TBC at cyclic load and CMAS is continuously injected to the combustion environment to simulate the conditions closer to actual service in an engine while allowing control of important degradation limiting parameters. Tests have been performed on the state of the art material YSZ while loading parameters as high temperature dwell time and CMAS deposition rate have been varied. Tests have been evaluated in terms of chemical degradation, failure mode and TBC spallation lifetime by means of SEM, EDS and XRD. Test conditions and relevance to in-service operating conditions are discussed. Major impacts on thermal gradient cycling lifetime and similarities and discrepancies related to reported failure mechanism are reviewed. © 2017
    view abstractdoi: 10.1016/j.surfcoat.2017.04.071
  • 2017 • 181 Functional performance of Gd2Zr2O7/YSZ multi-layered thermal barrier coatings deposited by suspension plasma spray
    Mahade, S. and Curry, N. and Björklund, S. and Markocsan, N. and Nylén, P. and Vaßen, R.
    Surface and Coatings Technology 318 208-216 (2017)
    7-8. wt.% yttria stabilized zirconia (YSZ) is the standard ceramic top coat material used in gas turbines to insulate the underlying metallic substrate. However, at higher temperatures (>. 1200. C), phase stability and sintering becomes an issue for YSZ. At these temperatures, YSZ is also susceptible to CMAS (calcium magnesium alumino silicates) infiltration. New ceramic materials such as pyrochlores have thus been proposed due to their excellent properties such as lower thermal conductivity and better CMAS attack resistance compared to YSZ. However, pyrochlores have inferior thermo mechanical properties compared to YSZ. Therefore, double-layered TBCs with YSZ as the intermediate layer and pyrochlore as the top ceramic layer have been proposed. In this study, double layer TBC comprising gadolinium zirconate (GZ)/YSZ and triple layer TBC (GZdense/GZ/YSZ) comprising relatively denser GZ top layer on GZ/YSZ were deposited by suspension plasma spray. Also, single layer 8YSZ TBC was suspension plasma sprayed to compare its functional performance with the multi-layered TBCs. Cross sections and top surface morphology of as sprayed TBCs were analyzed by scanning electron microscopy (SEM). XRD analysis was done to identify phases formed in the top surface of as sprayed TBCs. Porosity measurements were made using water intrusion and image analysis methods. Thermal diffusivity of the as sprayed TBCs was measured using laser flash analysis and thermal conductivity of the TBCs was calculated. The multi-layered GZ/YSZ TBCs were shown to have lower thermal conductivity than the single layer YSZ. The as sprayed TBCs were also subjected to thermal cyclic testing at 1300. C. The double and triple layer TBCs had a longer thermal cyclic life compared to YSZ. The thermo cycled samples were analyzed by SEM. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.12.062
  • 2017 • 180 Erosion Performance of Gadolinium Zirconate-Based Thermal Barrier Coatings Processed by Suspension Plasma Spray
    Mahade, S. and Curry, N. and Björklund, S. and Markocsan, N. and Nylén, P. and Vaßen, R.
    Journal of Thermal Spray Technology 26 108-115 (2017)
    7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM. © 2016, ASM International.
    view abstractdoi: 10.1007/s11666-016-0479-4
  • 2017 • 179 Impact of processing conditions and feedstock characteristics on thermally sprayed MCrAlY bondcoat properties
    Mauer, G. and Sebold, D. and Vaßen, R. and Hejrani, E. and Naumenko, D. and Quadakkers, W.J.
    Surface and Coatings Technology 318 114-121 (2017)
    One of the options to manufacture MCrAlY bondcoats (M. =Co, Ni) for thermal barrier coating systems is High Velocity Oxy-Fuel spraying (HVOF). In this work, particle diagnostics were applied to investigate the impact of processing conditions and feedstock characteristics on the relevant bondcoat properties. The results showed that compromises must be made on the oxygen/fuel ratio, spray distance, and particle size distribution to strike a balance between low oxidation and dense microstructures.These limitations initiated the development of the High Velocity Atmospheric Plasma Spray process (HV-APS) as a further alternative process. In this work, HV-APS process parameters were developed for a three cathode torch in combination with a 5. mm diameter high speed nozzle. A one-dimensional calculation of the expansion through this nozzle to atmospheric pressure yielded supersonic conditions with a Mach number of 1.84. The calculated plasma temperatures at the nozzle exit and in the expanded jet are 8400. K and slightly above 5200. K, respectively, which is low compared to conventional APS processes. A very fine powder with a median particle size of 18. μm was identified to be most suitable. Although the spray conditions were relatively cold, reasonable deposition efficiencies up to 61% and rather dense coatings were achieved using this feedstock. The as-sprayed porosity was ≈. 2% which was reduced by the subsequent vacuum heat treatment to <. 1%. The oxygen content determined by chemical analysis for a sample sprayed at a spray distance of 100. mm was 0.41. ±. 0.04. wt%.Moreover, reference samples were manufactured by Low Pressure Plasma Spraying (LPPS). The oxidation behavior was compared in isothermal and cyclic oxidation tests. The oxidation rates of the HV-APS coatings were found to be significantly lower than those of LPPS coatings. The thermally grown oxide scale showed less yttrium incorporation and better adherence in case of HV-APS. The latter is suggested to be related to a unique new distribution of Y-rich nano-sized oxide precipitates. The cyclic oxidation test confirmed the better oxidation resistance of the HV-APS coatings. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.08.079
  • 2017 • 178 Recent developments in plasma spray processes for applications in energy technology
    Mauer, G. and Jarligo, M.O. and Marcano, D. and Rezanka, S. and Zhou, D. and Vaßen, R.
    IOP Conference Series: Materials Science and Engineering 181 (2017)
    This work focuses on recent developments of plasma spray processes with respect to specific demands in energy technology. High Velocity Atmospheric Plasma Spraying (HV-APS) is a novel variant of plasma spraying devoted to materials which are prone to oxidation or decomposition. It is shown how this process can be used for metallic bondcoats in thermal barrier coating systems. Furthermore, Suspension Plasma Spraying (SPS) is a new method to process submicron-sized feedstock powders which are not sufficiently flowable to feed them in dry state. SPS is presently promoted by the development of novel torch concepts with axial feedstock injection. An example for a columnar structured double layer thermal barrier coating is given. Finally, Plasma Spray-Physical Vapor Deposition (PS-PVD) is a novel technology operating in controlled atmosphere at low pressure and high plasma power. At such condition, vaporization even of high-melting oxide ceramics is possible enabling the formation of columnar structured, strain tolerant coatings with low thermal conductivity. Applying different conditions, the deposition is still dominated by liquid splats. Such process is termed Low Pressure Plasma Spraying-Thin Film (LPPS-TF). Two examples of applications are gas-tight and highly ionic and electronic conductive electrolyte and membrane layers which were deposited on porous metallic substrates. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/181/1/012001
  • 2017 • 177 Monitoring and Improving the Reliability of Plasma Spray Processes
    Mauer, G. and Rauwald, K.-H. and Mücke, R. and Vaßen, R.
    Journal of Thermal Spray Technology 26 799-810 (2017)
    Monitoring and improving of process reliability are prevalent issues in thermal spray technology. They are intended to accomplish specific quality characteristics by controlling the process. For this, implicit approaches are in demand to rapidly conclude on relevant coating properties, i.e., they are not directly measured, but it is assumed that the monitored variables are in fact suggestive for them. Such monitoring can be performed in situ (during the running process) instead of measuring coating characteristics explicitly (directly) and ex situ (after the process). Implicit approaches can be based on extrinsic variables (set from outside) as well as on intrinsic parameters (internal, not directly adjustable) having specific advantages and disadvantages, each. In this work, the effects of atmospheric plasma spray process variables are systemized in process schemes. On this basis, different approaches to contribute to improved process reliability are described and assessed paying particular attention to in-flight particle diagnostics. Finally, a new test applying spray bead analysis is introduced and first results are presented. © 2017, ASM International.
    view abstractdoi: 10.1007/s11666-017-0559-0
  • 2017 • 176 Thermally induced age hardening in tough Ta-Al-N coatings via spinodal decomposition
    Mikula, M. and Sangiovanni, D.G. and Plašienka, D. and Roch, T. and Čaplovičová, M. and Truchlý, M. and Satrapinskyy, L. and Bystrický, R. and Tonhauzerová, D. and Vlčková, D. and Kúš, P.
    Journal of Applied Physics 121 (2017)
    We combine experiments and ab initio density functional theory calculations to investigate the evolution in structural and mechanical properties of TaAlN coatings as a function of the annealing temperature T. Formation of coherent cubic TaN- and AlN-rich nanometer-size domains, occurring during the initial stage of thermally induced phase separation within cubic NaCl-type (B1) TaAlN solid solutions, yields a monotonic increase in hardness from 29 GPa (as deposited coatings) up to a maximum of 35 GPa (+17%) reached after annealing at 1000 °C. Further thermal treatment at T &gt; 1000 °C leads to the transformation of metastable cubic domains into stable hexagonal TaNx and wurtzite AlN phases, thus resulting in hardness reductions. A comparison of our results with those reported in the literature reveals that TaAlN coatings are at least as hard while considerably less stiff (lower elastic moduli) than TiAlN coatings, thus indicating a substantial increase in toughness achieved upon replacing Ti with Ta in the host lattice. Present findings suggest that cubic TaAlN solid solutions are promising candidates for applications in protective coatings possessing both high-temperature hardness and toughness. © 2017 Author(s).
    view abstractdoi: 10.1063/1.4981534
  • 2017 • 175 Performance of mobile NMR for non-destructive analyses of existing concrete structures - Influencing factors
    Orlowsky, J.
    High Tech Concrete: Where Technology and Engineering Meet - Proceedings of the 2017 fib Symposium 1299-1306 (2017)
    The maintenance of existing concrete structures gains increasing importance. New challenges within this topic are the durability modelling of conservation measures and the timing of renewing them. One necessary step for the solution of these new challenges are needs-oriented non-destructive testing methods. For the first time, ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of relevant parameters directly on the building site. By positioning the NMR sensor on a lift analysing of the amplitudes and relaxation times can be done at different depths/positions inside the concrete cover. The determined parameters are: Ingress, distribution and transport of water as well as other liquids at the concrete surface (up to 25 mm depth beginning at the concrete surface) and effectiveness of concrete coatings including thickness of different coating layers. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. This has been done in the frame of a wide test program. Firstly, influences from temperature changes and tilting of the sensor are discussed in the present paper. Afterwards results concerning the steel reinforcement influence on the investigations are named and a practical solution to consider the determined shift of the profile towards the steel is presented. © Springer International Publishing AG 2018.
    view abstractdoi: 10.1007/978-3-319-59471-2-150
  • 2017 • 174 Investigation of the resistance of open-column-structured PS-PVD TBCs to erosive and high-temperature corrosive attack
    Rezanka, S. and Mack, D.E. and Mauer, G. and Sebold, D. and Guillon, O. and Vaßen, R.
    Surface and Coatings Technology 324 222-235 (2017)
    In modern gas turbines, highly loaded components are internally cooled and furthermore covered with thermal barrier coatings (TBCs) to withstand the harsh operating conditions with temperatures exceeding the application limit of such coatings. Under realistic operating conditions, siliceous minerals, of a calcium-magnesium-aluminum-silicate (CMAS) composition, are ingested into the turbine and deposited on the TBCs. Besides erosion, this also leads to degradation by chemical interaction. The plasma spray-physical vapor deposition (PS-PVD) process is an advanced method for manufacturing TBCs, which fills the gap between traditional thermal spray processes and electron beam physical vapor deposition (EB-PVD). Due to the unique plasma conditions, coatings with columnar microstructures exhibiting high strain tolerance can be created. However, because of the high amount of open porosity the resistance of such structures to CMAS and erosion attack was expected to be low. In the present work, PS-PVD TBCs were investigated in a burner rig facility under thermal gradient cycling conditions and simultaneous CMAS attack. The interactions of the PS-PVD-deposited YSZ and the CMAS melt were studied by means of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) and compared to EB-PVD coatings. Additionally, the resistance of PS-PVD TBCs to erosion is compared to APS TBCs by means of room temperature tests according to ASTM G76-13. © 2017
    view abstractdoi: 10.1016/j.surfcoat.2017.05.003
  • 2017 • 173 A coated inclusion-based homogenization scheme for viscoelastic composites with interphases
    Schöneich, M. and Dinzart, F. and Sabar, H. and Berbenni, S. and Stommel, M.
    Mechanics of Materials 105 89-98 (2017)
    A coated inclusion-based homogenization scheme is developed for three-phase viscoelastic composites in the Laplace–Carson domain. The interphase between inclusion and matrix is considered as a coating in a composite-like inclusion and shows altered viscoelastic behavior compared to the matrix. The strain concentration equations between the viscoelastic inclusion and the viscoelastic coating are derived with two different models: the double inclusion (denoted DI) model, and the reconsidered double inclusion (RDI) model. Then, the homogenization scheme is based on a modified Mori–Tanaka scheme for three-phase viscoelastic composites, which is validated with the exact analytical formulation in the case of spherical composite inclusions and isotropic behaviors for all constituents. The comparison of the proposed coated inclusion-based homogenization scheme based on the RDI model with the exact analytical solution shows a significant improvement compared to the one based on the DI model in the prediction of effective properties for composites with interphases. Finally, considering experimental dynamic mechanical analyses (DMA) in the frequency domain for a carbon-black filled styrene butadiene rubber from the literature, the effective viscoelastic behavior is estimated with a good accuracy in terms of the storage and loss moduli for different volume fractions of composite inclusions. © 2016
    view abstractdoi: 10.1016/j.mechmat.2016.11.009
  • 2017 • 172 Effects of substrate roughness and spray-angle on deposition behavior of cold-sprayed Inconel 718
    Singh, R. and Rauwald, K.-H. and Wessel, E. and Mauer, G. and Schruefer, S. and Barth, A. and Wilson, S. and Vassen, R.
    Surface and Coatings Technology 319 249-259 (2017)
    In this study, Inconel 718 powder particles were successfully cold-sprayed on Inconel 718 substrate by using nitrogen gas for a repair application of aero engine components. The effects of substrate roughness and spray-angle on the deposition behavior of Inconel 718 particles were investigated. It has been found that the deposition behavior of Inconel 718 powder on Inconel 718 substrates is highly influenced by substrate surface roughness. Single powder particle interaction with substrates of different roughness showed that plastic deformation and interfacial material mixing is higher if powder particles interact with substrates of higher roughness. Consequently, substrates with lower roughness demonstrated many abnormalities (e.g. cracks, peeling-off) during the deposition. Substrate roughness is limited to influence the deposition efficiency of the first few layers. Besides, it is also observed that particle deformation and coating quality are significantly affected by the spray-angle because of asymmetric deformation of the particle due to additional tangential momentum. Moreover, it is observed that deposition efficiency is reduced with a decrease in spray-angle, while the coating porosity and coating roughness show an inverse trend. Furthermore, the effects of three input parameters, namely substrate preparation, spray angle and stand-off distance, on four outputs (responses), such as thickness, roughness, porosity and Vickers-hardness of the coating were studied using non-linear statistical regression analysis. The above mentioned four outputs were found to be significantly dependent on substrate preparation and spray-angle. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.03.072
  • 2017 • 171 Alkaline fuel cell with nitride membrane
    Sun, S.-H. and Pilaski, M. and Wartmann, J. and Letzkus, F. and Funke, B. and Dura, G. and Heinzel, A.
    Proceedings of SPIE - The International Society for Optical Engineering 10246 (2017)
    The aim of this work is to fabricate patterned nitride membranes with Si-MEMS-technology as a platform to build up new membrane-electrode-assemblies (MEA) for alkaline fuel cell applications. Two 6-inch wafer processes based on chemical vapor deposition (CVD) were developed for the fabrication of separated nitride membranes with a nitride thickness up to 1 μm. The mechanical stability of the perforated nitride membrane has been adjusted in both processes either by embedding of subsequent ion implantation step or by optimizing the deposition process parameters. A nearly 100% yield of separated membranes of each deposition process was achieved with layer thickness from 150 nm to 1 μm and micro-channel pattern width of 1μm at a pitch of 3 μm. The process for membrane coating with electrolyte materials could be verified to build up MEA. Uniform membrane coating with channel filling was achieved after the optimization of speed controlled dip-coating method and the selection of dimethylsulfoxide (DMSO) as electrolyte solvent. Finally, silver as conductive material was defined for printing a conductive layer onto the MEA by Ink-Technology. With the established IR-thermography setup, characterizations of MEAs in terms of catalytic conversion were performed successfully. The results of this work show promise for build up a platform on wafer-level for high throughput experiments. © 2017 SPIE.
    view abstractdoi: 10.1117/12.2265689
  • 2017 • 170 RF magnetron sputtering of a hydroxyapatite target: A comparison study on polytetrafluorethylene and titanium substrates
    Surmenev, R.A. and Surmeneva, M.A. and Grubova, I.Y. and Chernozem, R.V. and Krause, B. and Baumbach, T. and Loza, K. and Epple, M.
    Applied Surface Science 414 335-344 (2017)
    A pure hydroxyapatite (HA) target was used to prepare the biocompatible coating of HA on the surface of a polytetrafluorethylene (PTFE) substrate, which was placed on the same substrate holder with technically pure titanium (Ti) in the single deposition runs by radio-frequency (RF) magnetron sputtering. The XPS, XRD and FTIR analyses of the obtained surfaces showed that for all substrates, instead of the HA coating deposition, the coating of a mixture of calcium carbonate and calcium fluoride was grown. According to SEM investigations, the surface of PTFE was etched, and the surface topography of uncoated Ti was preserved after the depositions. The FTIR results reveal no phosphate bonds; only calcium tracks were observed in the EDX-spectra on the surface of the coated PTFE substrates. Phosphate oxide (V), which originated from the target, could be removed using a vacuum pump system, or no phosphate-containing bonds could be formed on the substrate surface because of the severe substrate bombardment process, which prevented the HA coating deposition. The observed results may be connected with the surface re-sputtering effect of the growing film by high-energy negatively charged ions (most probably oxygen or fluorine), which are accelerated in the cathode dark sheath. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2017.04.090
  • 2017 • 169 Incorporation of silver nanoparticles into magnetron-sputtered calcium phosphate layers on titanium as an antibacterial coating
    Surmeneva, M.A. and Sharonova, A.A. and Chernousova, S. and Prymak, O. and Loza, K. and Tkachev, M.S. and Shulepov, I.A. and Epple, M. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 156 104-113 (2017)
    A three-layer system of nanocrystalline hydroxyapatite (first layer; 1000 nm thick), silver nanoparticles (second layer; 1.5 μg Ag cm−2) and calcium phosphate (third layer, either 150 or 1000 nm thick) on titanium was prepared by a combination of electrophoretic deposition of silver nanoparticles and the deposition of calcium phosphate by radio frequency magnetron sputtering. Scanning electron microscopy showed that the silver nanoparticles were evenly distributed over the surface. The adhesion of multilayered coating on the substrate was evaluated using the scratch test method. The resistance to cracking and delamination indicated that the multilayered coating has good resistance to contact damage. The release of silver ions from the hydroxyapatite/silver nanoparticle/calcium phosphate system into the phosphate-buffered saline (PBS) solution was measured by atomic absorption spectroscopy (AAS). Approximately one-third of the incorporated silver was released after 3 days immersion into PBS, indicating a total release time of the order of weeks. There were no signs of cracks on the surface of the coating after immersion after various periods, indicating the excellent mechanical stability of the multilayered coating in the physiological environment. An antimicrobial effect against Escherichia coli was found for a 150 nm thick outer layer of the calcium phosphate using a semi-quantitative turbidity test. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2017.05.016
  • 2017 • 168 Self-sharpening-effect of nickel-diamond coatings sprayed by HVOF
    Tillmann, W. and Brinkhoff, A. and Schaak, C. and Zajaczkowski, J.
    IOP Conference Series: Materials Science and Engineering 181 (2017)
    The durability of stone working and drilling tools is an increasingly significant requirement in industrial applications. These tools are mainly produced by brazing diamond metal matrix composites inserts to the tool body. These inserts are produced by sintering diamonds and metal powder (e.g. nickel). If the wear is too high, the diamonds will break out of the metal matrix and other diamonds will be uncovered. This effect is called self-sharpening. But diamonds are difficult to handle because of their thermal sensitivity. Due to their high thermal influence, manufacturing costs, and complicate route of manufacturing (first sintering, then brazing), there is a great need for alternative production methods for such tools. One alternative to produce wear-resistant and self-sharpening coatings are thermal spray processes as examined in this paper. An advantage of thermal spray processes is their smaller thermal influence on the diamond, due to the short dwelling time in the flame. To reduce the thermal influence during spraying, nickel coated diamonds were used in the HVOF-process (high velocity oxygen fuel process). The wear resistance was subsequently investigated by means of a standardized ball-on-disc test. Furthermore, a SEM (scanning electron microscope) was used to gain information about the wear-mechanism and the self-sharpening effect of the coating. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/181/1/012016
  • 2017 • 167 Influence of Si content on mechanical and tribological properties of TiAlSiN PVD coatings at elevated temperatures
    Tillmann, W. and Dildrop, M.
    Surface and Coatings Technology 321 448-454 (2017)
    TiN- and CrN-based binary or ternary coatings have been used for many years in order to extend the service life of machining tools. The increasing demands in the metalworking industry require more efficient coating systems. According to recent studies, silicon offers promising opportunities to positively influence the characteristics of thin titanium or chromium-based coatings. The nanocomposite TiAlSiN presents a high hardness and a fine grain structure. Furthermore, by adding silicon, the oxidation resistance as well as the tribological properties can be increased and improved. In this study, TiAlSiN coatings with different Si contents (0–10.9 at%) were produced by means of magnetron sputtering. In order to test the possibility to sputter pure, low conductive silicon targets, different sputter and bias modes were tested. The ratios of the other coating elements were kept constant while varying the silicon content inside the PVD coatings. Nitrided steel samples (AISI H11) were used as substrate materials. The influence of the Si content on the tribomechanical properties of TiAlSiN were analyzed. The analyses focused on the coatings with a silicon content of 5–10 at% due to the change of the coating morphology within this range. The coating morphology and different chemical compositions of the silicon-doped coatings were investigated by means of scanning electron microscopy and EDX analyses. Phase analyses were conducted and residual stresses were measured by means of X-ray diffraction. The hardness and Young's modulus of the PVD coatings were investigated using nanoindentation. Furthermore, scratch tests were performed in order to characterize the adhesion between the substrate and the coating. Finally, high temperature tribometer tests were executed to determine the wear resistance of the TiAlSiN coatings at room temperature as well as at elevated temperatures (500 °C, 800 °C). © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.05.014
  • 2017 • 166 Influence of bias voltage and sputter mode on the coating properties of TiAlSiN: Einfluss der Biasspannung und des Sputtermodus auf die Schichteigenschaften von TiAlSiN
    Tillmann, W. and Dildrop, M.
    Materialwissenschaft und Werkstofftechnik 48 855-861 (2017)
    Silicon offers promising opportunities to improve the characteristics of thin coatings. By adding silicon to TiAlN, the oxidation resistance as well as the tribological properties can be increased and improved. To analyze the influence of the silicon content on the coating properties of TiAlSiN, it is necessary to keep the ratio of the other coating elements constant by using the right target configuration. Within this study, TiAlSiN coatings were deposited on hot work steel AISI H11 by using magnetron sputtering (Cemecon CC800/9 sinox ML). This steel was previously plasma nitrided to increase the hardness and hence the carrying load of the substrate, avoiding shell egg effect during the analysis. Different sputter modes were used to analyze the possibility to produce TiAlSiN by utilizing a pure low conductive silicon target. The bias voltages were systematically varied to see their influence on the structure and chemical compositions of the coating which were investigated by means of scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Furthermore, the roughness of the surface of the coatings was measured by an optical three-dimensional surface analyzer. The results of this study serve as a basis for further investigations regarding the variation of the silicon content of TiAlSiN coatings. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/mawe.201600731
  • 2017 • 165 A Study on the Tribological Behavior of Vanadium-Doped Arc Sprayed Coatings
    Tillmann, W. and Hagen, L. and Kokalj, D. and Paulus, M. and Tolan, M.
    Journal of Thermal Spray Technology 26 503-516 (2017)
    The formation of thin reactive films in sliding contacts under elevated temperature provides enhanced tribological properties since the formation of Magnéli phases leads to the ability of self-lubricating behavior. This phenomenon was studied for vanadium-doped coating systems which were produced using CVD and PVD technology. Vanadium-containing arc sprayed coatings were not widely examined so far. The aim of this study was to characterize Fe-V coatings deposited by the Twin Wire Arc Spraying process with respect to their oxidation behavior at elevated temperatures and to correlate the formation of oxides to the tribological properties. Dry sliding experiments were performed in the temperature range between 25 and 750 °C. The Fe-V coating possesses a reduced coefficient of friction and wear coefficient (k) at 650 and 750 °C, which were significant lower when compared to conventional Fe-based coatings. The evolution of oxide phases was identified in situ by x-ray diffraction for the investigated temperature range. Further oxidation of (pre-oxidized) arc sprayed Fe-V coatings, as verified by differential thermal analysis and thermo-gravimetric analysis, starts at about 500 °C. © 2017 ASM International
    view abstractdoi: 10.1007/s11666-017-0524-y
  • 2017 • 164 Investigation on the Tribological Behavior of Arc-Sprayed and Hammer-Peened Coatings Using Tungsten Carbide Cored Wires
    Tillmann, W. and Hagen, L. and Schröder, P.
    Journal of Thermal Spray Technology 26 229-242 (2017)
    Due to their outstanding properties, WC-W2C iron-based cermet coatings are widely used in the field of wear protection. Regarding commonly used WC-W2C reinforced coating systems, it has been reported that their tribological behavior is mainly determined by the carbide grain size fraction. Although the manufacturing route for arc-sprayed WC-W2C cermet coatings is in an advanced state, there is still a lack of knowledge concerning the performance of cored wires with tungsten carbides as filling material and their related coating properties when post-treatment processes are used such as machine hammer peening (MHP). A major objective was to characterize WC-W2C FeCMnSi coatings, deposited with different carbide grain size fractions as a filling using cored wires, with respect to their tribological behavior. Moreover, deposits derived from cored wires with a different amount of hard phases are investigated. According to this, polished MHP surfaces are compared to as-sprayed and polished samples by means of metallographic investigations. With the use of ball-on-disk and dry rubber wheel tests, dry sliding and rolling wear effects on a microscopic level are scrutinized. It has been shown that the MHP process leads to a densification of the microstructure formation. For dry sliding experiments, the MHP coatings obtain lower wear resistances, but lower coefficients of friction than the conventional coatings. In view of abrasion tests, the MHP coatings possess an improved wear resistance. Strain hardening effects at the subsurface area were revealed by the mechanical response using nanoindentation. However, the MHP process has caused a cracking of embedded carbides, which favor breakouts, leading to advanced third-body wear. © 2016, ASM International.
    view abstractdoi: 10.1007/s11666-016-0447-z
  • 2017 • 163 Investigation of the influence of the vanadium content on the high temperature tribo-mechanical properties of DC magnetron sputtered AlCrVN thin films
    Tillmann, W. and Kokalj, D. and Stangier, D. and Paulus, M. and Sternemann, C. and Tolan, M.
    Surface and Coatings Technology 328 172-181 (2017)
    The forming of high-strength steels or new aluminum alloys leads to a steady increase of the load of tools and coatings. One approach is to positively influence the manufacturing process by using thin solid films with self-lubricating features, provided by oxides at high temperatures with low decohesion energies. For the purpose of this study, AlCrN provides the matrix, while vanadium oxides are used to enhance the frictional and wear properties. However, it is not yet clear which minimum amount of vanadium has to be incorporated in DC magnetron sputtered AlCrN coatings to improve the tribological behavior. Therefore, in this study, AlCrVN coatings are synthesized with an increasing vanadium content by means of reactive DC magnetron sputtering. Additionally, a vanadium-free AlCrN coating is used as reference for the tribo-mechanical investigations. The coatings were synthesized up to a vanadium content of 13.5 at.-% and no phase change could be detected by means of x-ray diffraction. Moreover, no hexagonal AlN phase, which reduces the mechanical properties and the oxidation resistance, was formed. In contrast to the vanadium-free coating, the hardness of the coatings containing vanadium is slightly reduced. The coating with the smallest vanadium content shows the highest hardness of all analyzed coatings. A heat treatment at 400 °C does not lead to any significant changes with respect to mechanical properties, but at 700 °C hardness, modulus of elasticity and critical load decreased for all coatings, indicating a significant change in mechanical properties. The ball-on-disc test at room-temperature, 400 °C, and 700 °C shows the highest wear coefficient for the coating with the lowest vanadium content, due to the poor adhesion of the coating, although this coating shows the highest H/E-ratio. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.08.046
  • 2017 • 162 Embedment of eutectic tungsten carbides in arc sprayed steel coatings
    Tillmann, W. and Hagen, L. and Kokalj, D.
    Surface and Coatings Technology 331 153-162 (2017)
    Tungsten carbide reinforced deposits have already evolved into a predominant coating system in order to protect stressed surfaces against wear. Among thermal spraying processes, due to a high deposition rate, arc spraying is a promising process to manufacture cost-saving, wear resistant coatings. However, inherent process characteristics prevailing in arc spraying as well as the utilization of tungsten carbides, as a filling for cored wires, could lead to undesirable phase evolutions, which in turn provoke the degradation of the mechanical properties. The embedment of tungsten carbides into the surrounding metallic matrix is affected by metallurgical interactions with molten spray particles. Within the scope of this study, an external injection of tungsten carbides was applied in order to analyze the embedment of tungsten carbides in arc sprayed low alloyed steel. Accordingly, metallographic investigations were carried out, which address the reactive layer at the interface of embedded tungsten carbides to the surrounded iron-based matrix. Microstructural characteristics such as mechanical properties and phase composition were scrutinized by means of nanoindentation, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. It was found that the embedment of tungsten carbides, which have been externally injected into the arc burning zone, differs from that obtained from deposits produced with the use of cored wire with tungsten carbide as filling. Thus, externally injected tungsten carbides are less inclined to form eta carbides due to dissolution, which again results in differences in the mechanical properties across the reactive layer. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.10.044
  • 2017 • 161 Robot based deposition of WC-Co HVOF coatings on HSS cutting tools as a substitution for solid cemented carbide cutting tools
    Tillmann, W. and Schaak, C. and Biermann, D. and Aßmuth, R. and Goeke, S.
    IOP Conference Series: Materials Science and Engineering 181 (2017)
    Cemented carbide (hard metal) cutting tools are the first choice to machine hard materials or to conduct high performance cutting processes. Main advantages of cemented carbide cutting tools are their high wear resistance (hardness) and good high temperature strength. In contrast, cemented carbide cutting tools are characterized by a low toughness and generate higher production costs, especially due to limited resources. Usually, cemented carbide cutting tools are produced by means of powder metallurgical processes. Compared to conventional manufacturing routes, these processes are more expensive and only a limited number of geometries can be realized. Furthermore, post-processing and preparing the cutting edges in order to achieve high performance tools is often required. In the present paper, an alternative method to substitute solid cemented carbide cutting tools is presented. Cutting tools made of conventional high speed steels (HSS) were coated with thick WC-Co (88/12) layers by means of thermal spraying (HVOF). The challenge is to obtain a dense, homogenous, and near-net-shape coating on the flanks and the cutting edge. For this purpose, different coating strategies were realized using an industrial robot. The coating properties were subsequently investigated. After this initial step, the surfaces of the cutting tools were ground and selected cutting edges were prepared by means of wet abrasive jet machining to achieve a smooth and round micro shape. Machining tests were conducted with these coated, ground and prepared cutting tools. The occurring wear phenomena were analyzed and compared to conventional HSS cutting tools. Overall, the results of the experiments proved that the coating withstands mechanical stresses during machining. In the conducted experiments, the coated cutting tools showed less wear than conventional HSS cutting tools. With respect to the initial wear resistance, additional benefits can be obtained by preparing the cutting edge by means of wet abrasive jet machining. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/181/1/012011
  • 2017 • 160 Influence of the WC grain size on the properties of PVD/HVOF duplex coatings
    Tillmann, W. and Stangier, D. and Hagen, L. and Schröder, P. and Krabiell, M.
    Surface and Coatings Technology 328 326-334 (2017)
    Duplex coatings are an innovative approach to further improve cemented carbide surfaces in terms of tribo-mechanical properties by depositing a thin Physical Vapor Deposition (PVD) layer on top of the High Velocity Oxygen Fuel (HVOF) sprayed coating. Within this investigation, AISI M3 steel substrates were primarily coated with three different WC-12Co feedstock powders by means of HVOF spraying. The agglomerate size of all powders was constant (− 45 + 15 μm), the WC grain size was varied from conventional (carbide size 2.5 μm) over fine (carbide size 1 μm) to nanosized (carbide size 0.1 μm) carbides. Subsequently, the samples were polished prior to the deposition of a CrAlN PVD coating by means of magnetron sputtering. The aim is to evaluate the influence of the WC grain size on the CrAlN/WC-12Co duplex coating properties. It was shown that a smaller carbide grain size influences the microstructure of the CrAlN coating and causes a finer crystalline structure. Furthermore, higher compressive residual stresses occur in the duplex interlayer and the top layer when using nanosized carbides. Moreover, nanosized carbides in the HVOF coating are favorable in terms of layer adhesion, which was analyzed by means of HRC indent test and scratch test. Further enhancements are the increase in hardness and the reduction in roughness which was directly influenced by the WC grain size. Considering the obtained results, it is to conclude that a reduction of the interlayer WC grain size improves the performance of CrAlN/WC-12Co duplex coatings. © 2017 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2017.08.064
  • 2017 • 159 Mechanisms of oxygen permeation through plastic films and barrier coatings
    Wilski, S. and Wipperfürth, J. and Jaritz, M. and Kirchheim, D. and Mitschker, F. and Awakowicz, P. and Dahlmann, R. and Hopmann, C.
    Journal of Physics D: Applied Physics 50 (2017)
    Oxygen and water vapour permeation through plastic films in food packaging or other applications with high demands on permeation are prevented by inorganic barrier films. Most of the permeation occurs through small defects (&lt;3 μm) in the barrier coating. The defects were visualized by etching with reactive oxygen in a capacitively coupled plasma and subsequent SEM imaging. In this work, defects in SiOx-coatings deposited by plasma-enhanced chemical vapour deposition on polyethylene terephthalate (PET) are investigated and the mass transport through the polymer is simulated in a 3D approach. Calculations of single defects showed that there is no linear correlation between the defect area and the resulting permeability. The influence of adjacent defects in different distances was observed and led to flow reduction functions depending on the defect spacing and defect area. A critical defect spacing where no interaction between defects occurs was found and compared to other findings. According to the superposition principle, the permeability of single defects was added up and compared to experimentally determined oxygen permeation. The results showed the same trend of decreasing permeability with decreasing defect densities. © 2017 IOP Publishing Ltd.
    view abstractdoi: 10.1088/1361-6463/aa8525
  • 2017 • 158 Mechanical properties of AlXFeY intermetallics in Al-base coatings on steel 22MnB5 and resulting wear mechanisms at press-hardening tool steel surfaces
    Windmann, M. and Röttger, A. and Hahn, I. and Theisen, W.
    Surface and Coatings Technology 321 321-327 (2017)
    Hard and brittle intermetallic AlXFeY phases formed in the Al-base coating applied on high-strength steel 22MnB5 promote strong wear of press-hardening tools during forming and quenching (approx. 800–100 °C). In this study, bulk materials of the intermetallic phases Al13Fe4, Al5Fe2, Al2Fe, and AlFe were produced by remelting stoichiometric powder mixtures. These were then used for mechanical and wear investigations. We found that the dominating wear mechanisms on the tool steel surfaces are strongly influenced by the temperature and depend on the mechanical properties of the respective intermetallic phases. Phases of type Al13Fe4, Al5Fe2, and Al2Fe possess a high hardness of 850–1090 HV0.5 and a low fracture toughness of 0.9–1.6 MPa √ m at room temperature, whereas the AlFe phase has a much lower hardness (520 HV0.5) and a higher fracture toughness (26 MPa √ m ). The hardness of all phases decreases with increasing temperature. At high temperatures (500–800 °C), the intermetallic phases lead mainly to adhesive wear of the tool steel surfaces. At lower temperatures, also abrasive wear occurs due to delamination of hard and brittle intermetallic particles. We found that abrasive wear of the tool steel surface could be decreased by adapting the phase composition in the Al-base coating. © 2017
    view abstractdoi: 10.1016/j.surfcoat.2017.04.075
  • 2016 • 157 Electrophoretic deposition of ligand-free platinum nanoparticles on neural electrodes affects their impedance in vitro and in vivo with no negative effect on reactive gliosis
    Angelov, S.D. and Koenen, S. and Jakobi, J. and Heissler, H.E. and Alam, M. and Schwabe, K. and Barcikowski, S. and Krauss, J.K.
    Journal of Nanobiotechnology 14 (2016)
    Background: Electrodes for neural stimulation and recording are used for the treatment of neurological disorders. Their features critically depend on impedance and interaction with brain tissue. The effect of surface modification on electrode impedance was examined in vitro and in vivo after intracranial implantation in rats. Electrodes coated by electrophoretic deposition with platinum nanoparticles (NP; <10 and 50 nm) as well as uncoated references were implanted into the rat's subthalamic nucleus. After postoperative recovery, rats were electrostimulated for 3 weeks. Impedance was measured before implantation, after recovery and then weekly during stimulation. Finally, local field potential was recorded and tissue-to-implant reaction was immunohistochemically studied. Results: Coating with NP significantly increased electrode's impedance in vitro. Postoperatively, the impedance of all electrodes was temporarily further increased. This effect was lowest for the electrodes coated with particles <10 nm, which also showed the most stable impedance dynamics during stimulation for 3 weeks and the lowest total power of local field potential during neuronal activity recording. Histological analysis revealed that NP-coating did not affect glial reactions or neural cell-count. Conclusions: Coating with NP <10 nm may improve electrode's impedance stability without affecting biocompatibility. Increased impedance after NP-coating may improve neural recording due to better signal-to-noise ratio. © 2016 Angelov et al.
    view abstractdoi: 10.1186/s12951-015-0154-9
  • 2016 • 156 Finite element simulation of coating-induced heat transfer: application to thermal spraying processes
    Berthelsen, R. and Tomath, D. and Denzer, R. and Menzel, A.
    Meccanica 51 291-307 (2016)
    Thermal spraying is a widely applied coating technique. The optimisation of the thermal spraying process with respect to temperature or temperature induced residual stress states requires a numerical framework for the simulation of the coating itself as well as of the quenching procedure after the application of additional material. This work presents a finite element framework for the simulation of mass deposition due to coating by means of thermal spraying combined with the simulation of nonlinear heat transfer of a rigid heat conductor. The approach of handling the dynamic problem size is highlighted with focus on the thermodynamical consistency of the derived model. With the framework implemented, numerical examples are employed and material parameters are fitted to experimental data of steel as well as of tungsten-carbide–cobalt-coating. © 2015, Springer Science+Business Media Dordrecht.
    view abstractdoi: 10.1007/s11012-015-0236-7
  • 2016 • 155 High-temperature stability and interfacial reactions of Ti and TiN thin films on Al2O3 and ZrO2
    Brust, S. and Röttger, A. and Theisen, W.
    Surface and Coatings Technology 307 47-55 (2016)
    Metallic thin films are used in many applications to modify ceramic surfaces. However, during subsequent processing, chemical interactions may change the properties of the coating. In addition, differences in thermal expansion can lead to delamination of the coating. In this study, titanium and titanium nitride thin films were deposited via physical and chemical vapor deposition (PVD and CVD, respectively) on alumina- and yttria-stabilised zirconia substrates, before being heat-treated at 1200 °C or 1500 °C in static argon atmosphere and analysed via SEM, EDS and XRD to investigate the effect of temperature on the thin films. It was shown that the chemical interactions between TiN and both Al2O3 and ZrO2 are weak. However, partial delamination of the TiN coating on alumina was observed after both annealing temperatures. The TiN coating on zirconia remained adherent. In contrast, the Ti coatings underwent a transformation to cubic TiO on both oxide substrates. This was due to partial reduction of the ZrO2 to ZrO2 − x and dissolution of the Al2O3, which leads to a Ti3Al0.9O1.1 interlayer. The TiO coating which formed remained adherent on the alumina at both annealing temperatures, but delaminated from the ZrO2 substrate after annealing at 1500 °C. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.08.060
  • 2016 • 154 Are Mo2BC nanocrystalline coatings damage resistant? Insights from comparative tension experiments
    Djaziri, S. and Gleich, S. and Bolvardi, H. and Kirchlechner, C. and Hans, M. and Scheu, C. and Schneider, J.M. and Dehm, G.
    Surface and Coatings Technology 289 213-218 (2016)
    Mo2BC nanocrystalline coatings were deposited on Cu substrates to compare their mechanical performance with bench-mark TiAlN, and pure Mo, Al and Al2O3 reference coatings. The Mo2BC coatings were characterized by X-ray diffraction and transmission electron microscopy to analyze the microstructure. In order to study the damage behavior, the coatings were subjected to uniaxial tensile loading and the crack spacing with increasing strain was monitored using optical and scanning electron microscopy. Based on crack density measurements, the Mo2BC coatings were found to be significantly less prone to cracking than the bench-mark TiAlN coatings. The higher resistance to cracking arises from the electronic structure of the Mo2BC nanolaminates, which imparts moderate ductility to the deformation behavior. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.02.010
  • 2016 • 153 Synthesis and structure of strontium ferrite nanowires and nanotubes of high aspect ratio
    Ebrahimi, F. and Ashrafizadeh, F. and Bakhshi, S.R. and Farle, M.
    Journal of Sol-Gel Science and Technology 77 708-717 (2016)
    Abstract: Strontium hexaferrite nanowires and nanotubes were synthesized in porous anodic aluminum oxide templates. Different solution-based synthesis techniques (spin coating, vacuum suction, and dip coating) were investigated. Strontium ferrite nanopowders were also synthesized by a similar sol–gel process. The morphology, structure, and composition of the embedded hexaferrite nanostructures were examined by field emission scanning electron microscope, X-ray diffraction, and transmission electron microscopy. Strontium ferrite wires with Fe/Sr ratios from 10 to 12 under different annealing temperatures of 500–700 °C were studied. The results showed that dip coating could produce fine and uniform strontium ferrite nanowires. The ratio of Fe/Sr of 11 and a calcination temperature of 650 °C were found to be optimum conditions. The produced material may be of importance for novel microwave-frequency nanoscale devices. Graphical Abstract: [Figure not available: see fulltext.] © 2015, Springer Science+Business Media New York.
    view abstractdoi: 10.1007/s10971-015-3902-2
  • 2016 • 152 The role of process temperature and rotational speed in the microstructure evolution of Ti-6Al-4V friction surfacing coatings
    Fitseva, V. and Hanke, S. and Santos, J.F.D. and Stemmer, P. and Gleising, B.
    Materials and Design 110 112-123 (2016)
    Friction surfacing is a solid state technique for depositing metallic coatings. Coating materials are thermo-mechanically processed at high temperatures during deposition. The high degree of deformation involved leads to a dynamically recrystallised fine grained microstructure. For Ti-6Al-4V, the microstructure and mechanical properties of coatings generated by friction surfacing have not been studied yet. The current work focuses on investigating effects of rotational speed on microstructure, grain size evolution and mechanical properties of the coating material. Various rotational speeds in a wide range, exceeding the range of deformation used in many other severe plastic deformation processes, were used to generate Ti-6Al-4V coatings by friction surfacing. Their influence on the thermal cycle and consequently on microstructure formation was revealed. The β grain size is related to the rotational speed and thermal cycle. Grain refinement at low rotational speed was observed, while higher rotational speeds and corresponding increase in maximum temperature led to grain coarsening. Although the peak temperature dominates the grain size evolution, dynamic recrystallisation during friction surfacing counteracts this effect, reducing the grain size by one order of magnitude. The coatings exhibit a hardness ascent about 15% due to martensite formation, high dislocation density and oxide precipitations. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2016.07.132
  • 2016 • 151 Fabrication and physico-mechanical properties of thin magnetron sputter deposited silver-containing hydroxyapatite films
    Ivanova, A.A. and Surmeneva, M.A. and Tyurin, A.I. and Pirozhkova, T.S. and Shuvarin, I.A. and Prymak, O. and Epple, M. and Chaikina, M.V. and Surmenev, R.A.
    Applied Surface Science 360 929-935 (2016)
    As a measure of the prevention of implant associated infections, a number of strategies have been recently applied. Silver-containing materials possessing antibacterial activity as expected might have wide applications in orthopedics and dentistry. The present work focuses on the physico-chemical characterization of silver-containing hydroxyapatite (Ag-HA) coating obtained by radio frequency (RF) magnetron sputtering. Mechanochemically synthesized Ag-HA powder (Ca10-xAgx(PO4)6(OH)2-x, x = 1.5) was used as a precursor for sputtering target preparation. Morphology, composition, crystallinity, physico-mechanical features (Young's modulus and nanohardness) of the deposited Ag-HA coatings were investigated. The sputtering of the nanostructured multicomponent target at the applied process conditions allowed to deposit crystalline Ag-HA coating which was confirmed by XRD and FTIR data. The SEM results revealed the formation of the coating with the grain morphology and columnar cross-section structure. The EDX analysis confirmed that Ag-HA coating contained Ca, P, O and Ag with the Ca/P ratio of 1.6 ± 0.1. The evolution of the mechanical properties allowed to conclude that addition of silver to HA film caused increase of the coating nanohardness and elastic modulus compared with those of pure HA thin films deposited under the same deposition conditions. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2015.11.087
  • 2016 • 150 Experimental and numerical analysis of tribological effective surfaces for forming tools in Sheet-Bulk Metal Forming
    Kersting, P. and Gröbel, D. and Merklein, M. and Sieczkarek, P. and Wernicke, S. and Tekkaya, A.E. and Krebs, E. and Freiburg, D. and Biermann, D. and Weikert, T. and Tremmel, S. and Stangier, D. and Tillmann, W. and Matthias, S....
    Production Engineering 10 37-50 (2016)
    Sheet-Bulk Metal Forming (SBMF) allows the manufacture of complex parts with integrated functional form elements, such as teeth and thickened areas. Therefore, bulk forming operations are applied to sheets with initial thicknesses of 2 or 3 mm. The design and functionality of the tools are as important as the process itself. Therefore, the working group "Tools" of the Transregional Collaborative Research Centre on Sheet-Bulk Metal Forming (CRC/TR73) focuses on the optimization of the technical tool design. By varying topographies or applying tailored coatings, the friction behavior is changed to achieve a better form filling and to reduce process forces during the forming operations. In this paper, the potential of different tailored surfaces is validated by simulations and experimental studies. The tribological behavior of 14 surface microstructures is evaluated using a half-space model in order to select structures suitable for application. Those were characterized experimentally by ring-compression and pin-extrusion tests. The determined friction factors were used in a forming simulation to predict the form filling of small cavities in a flow forming operation. Furthermore, special attention is paid to the utilization of the anisotropic behavior of specific structures. The results were validated by an incremental gear forming process. © 2016, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-015-0651-6
  • 2016 • 149 Atomic-layer-controlled deposition of TEMAZ/O2-ZrO2 oxidation resistance inner surface coatings for solid oxide fuel cells
    Keuter, T. and Mauer, G. and Vondahlen, F. and Iskandar, R. and Menzler, N.H. and Vaßen, R.
    Surface and Coatings Technology 288 211-220 (2016)
    Solid oxide fuel cells (SOFCs) directly convert the chemical energy of fuels into electrical energy with high efficiency. Under certain conditions oxygen can diffuse to the Ni/8 mol% Y2O3-doped ZrO2 substrate of anode-supported SOFCs, then the nickel re-oxidizes, leading to cracks in the electrolyte and cell failure thus limiting the durability of SOFCs. In order to improve the stability of SOFCs with respect to oxidation, the inner surface of the porous substrate is coated with a ZrO2 oxidation resistance layer using atomic layer deposition (ALD) with the precursors tetrakis(ethylmethylamino)zirconium (TEMAZ) and molecular oxygen. This TEMAZ/O2-ZrO2 ALD process has not yet been reported in the literature and hence, the development of the process is described in this paper. The inner surface of the porous substrate is coated with ZrO2 and the film thickness is compared with theoretical predictions, verifying the ALD model. Furthermore, the coating depth can be estimated using a simple analytical equation. The ALD ZrO2 film protects the nickel in the substrate against oxidation for at least 17 re-oxidation/re-reduction cycles. The ZrO2 inner surface coating is a highly promising candidate for enhancing the resistance of SOFCs to re-oxidation because of the excellent oxidation resistance and good cycling stability of the film. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.01.026
  • 2016 • 148 Preparation of pulsed DC magnetron deposited Fe-doped SnO2 coatings
    Kormunda, M. and Fischer, D. and Hertwig, A. and Beck, U. and Sebik, M. and Esser, N.
    Physica Status Solidi (A) Applications and Materials Science 213 2303-2309 (2016)
    Iron-doped SnO2 coatings were deposited in a 50 kHz DC-pulsed magnetron sputtering discharge. The pulses had a duration of 4 μs in selected gas mixtures from pure argon up to 60% of oxygen at a constant total pressure of 0.2 Pa. A single target of SnO2 with Fe inset was used. The mass spectrometry study detected the gas-related ions Ar+, O2 + and O+, where the last one becomes the dominant positive ion at higher oxygen contents. Atomic oxygen ions had a higher energy as it resulted from the collision-caused dissociation on the target surface. The tin-related species were detected as Sn+ and SnO+. SnO2 + species were not detected. The deposition rate decreased by using gas mixtures with oxygen as well as the corresponding amount of Sn-related species in the plasma. The increase of oxygen also increased significantly the sheet resistance of the films. The XPS study showed that the iron concentration decreased by using additional oxygen. But the O/Sn ratio in the coatings was constant, contrary to the increased FeO/Fe ratio in the films. An additional analysis of the coatings by spectroscopic ellipsometry has shown a dependence of the polarizability and the permittivity on the amount of oxygen used during the deposition. In contrast, the study has found no such dependence for the absorption of the layers. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/pssa.201532882
  • 2016 • 147 Residual Analysis in Generalized Function-on-Scalar Regression for an HVOF Spraying Process
    Kuhnt, S. and Rehage, A. and Becker-Emden, C. and Tillmann, W. and Hussong, B.
    Quality and Reliability Engineering International 32 2139-2150 (2016)
    The coating of materials plays an important role in various fields of engineering. Essential properties such as wear protection can be improved by a suitable coating technique. One of these techniques is high-velocity oxygen-fuel spraying. A drawback of high-velocity oxygen-fuel spraying is that it lacks reproducibility due to effects which are hard to measure directly. However, coating powder particles are observable over time during their flight towards the material and contain valuable information about the state of the process. Because of their smooth nature, measures of temperature and velocity can be assumed as target variables in generalized function-on-scalar regression. We propose methods to perform residual analysis in this framework aiming at the detection of individual residual functions which deviate from the majority of residuals. These methods help to detect anomalies in the process and hence improve the estimators. Functional target variables result in functional residuals whose analysis is barely explored. One reason might be that ordinary residual plots should be inspected at each observed point in time. We circumvent this infeasible procedure by the use of functional depths that help to identify unusual residuals and thereby gain deeper insight of the data-generating process. In a simulation study, we find that a good depth for detecting trend outliers is the h-modal depth as long as the link function is chosen correctly. In case of shape outliers rFUNTA pseudo-depth performs well. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1002/qre.2018
  • 2016 • 146 Effect of Residual Stress on the Wear Resistance of Thermal Spray Coatings
    Luo, W. and Selvadurai, U. and Tillmann, W.
    Journal of Thermal Spray Technology 25 321-330 (2016)
    The wear resistance of thermal spray coatings mainly depends on coating properties such as the microstructure, hardness, and porosity, as well as on the residual stress in the coating. The residual stress is induced by a variety of influences e.g., temperature gradients, difference of the thermal expansion coefficient of the coating/substrate materials, and the geometry of the components. To investigate the residual stress, the impulse excitation technique was employed to measure the Young’s and shear moduli. The residual stress was determined by the hole-drilling method and x-ray diffraction. Pin-on-Disk and Pin-on-Tube tests were used to investigate the wear behavior. After the wear tests, the wear volume was measured by means of a 3D-profilometer. The results show that the value of the residual stress can be modified by varying the coating thickness and the substrate geometry. The compressive stress in the HVOF-sprayed WC-Co coatings has a significant positive influence on the wear resistance whereas the tensile stress has a negative effect. © 2015, ASM International.
    view abstractdoi: 10.1007/s11666-015-0309-0
  • 2016 • 145 Assessing biofouling resistance of a polyamide reverse osmosis membrane surface-modified with a zwitterionic polymer
    Marré Tirado, M.L. and Bass, M. and Piatkovsky, M. and Ulbricht, M. and Herzberg, M. and Freger, V.
    Journal of Membrane Science 520 490-498 (2016)
    Desalination and water treatment by reverse osmosis (RO) can highly increase clean water supply in today's world. However, biofouling of polyamide (PA) RO membranes is a serious obstacle for a wider use of this technology. One of the promising ways of biofouling control is membranes surface modification with zwitterionic polymers. A number of published works showed that zwitterionic coatings can improve the resistance of PA membranes to the initial bacteria adhesion, however no long-term experiments with real treated water effluents were conducted. In this work a commercial PA RO membrane was surface-modified with a zwitterionic polymer and its resistance to biofouling was tested in both short-term bacteria adhesion experiments and longer filtration tests conducted using real treated wastewater effluents, spiked with a small level of nutrients. The obtained results showed that, initially, there was a clear improvement in the biofouling resistance of the modified membranes and their permeation flux remained stable, in contrast to the non-modified counterpart. However, eventually, the permeabilities of the two membranes declined to a similar degree. The results indicate that antifouling coatings might not promise a better membrane performance in long term. The analysis of the biofilms grown on the pristine and the modified membranes suggested that adaptation capabilities of biofilms overcame the favorable changes in surface properties of the membrane achieved by the modification. The presented results emphasized the importance of long-term filtration experiments as an ultimate test for assessing biofouling resistance of the modified desalination membranes. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.memsci.2016.07.027
  • 2016 • 144 Toughness enhancement in highly NbN-alloyed Ti-Al-N hard coatings
    Mikula, M. and Plašienka, D. and Sangiovanni, D.G. and Sahul, M. and Roch, T. and Truchlý, M. and Gregor, M. and Čaplovič, L. and Plecenik, A. and Kúš, P.
    Acta Materialia 121 59-67 (2016)
    Obtaining high hardness combined with enhanced toughness represents one of the current challenges in material design of hard ceramic protective coatings. In this work, we combine experimental and ab initio density functional theory (DFT) analysis of the mechanical properties of Ti-Al-Nb-N coatings to validate the results of previous theoretical investigations predicting enhanced toughness in TiAlN-based systems highly alloyed (&gt;25 at. %) with nitrides of pentavalent VB group elements Nb, Ta, and V. As-deposited Ti1-x-yAlxNbyN coatings (y = 0 ÷ 0.61) exhibit single phase cubic sodium chloride (B1) structure identified as TiAl(Nb)N solid solutions. The highest hardness, ∼32.5 ± 2 GPa, and the highest Young's modulus, ∼442 GPa, are obtained in Nb-free Ti0.46Al0.54N exhibiting pronounced 111 growth-orientation. Additions of Nb in the coatings promote texture evolution toward 200. Nanoindentation measurements demonstrate that alloying TiAlN with NbN yields significantly decreased elastic stiffness, from 442 to ∼358 ÷ 389 GPa, while the hardness remains approximately constant (between 28 ± 2 and 31 ± 3 GPa) for all Nb contents. DFT calculations and electronic structure analyses reveal that alloying dramatically reduces shear resistances due to enhanced d-d second-neighbor metallic bonding while retaining strong metal-N bonds which change from being primarily ionic (TiAlN) to more covalent (TiAlNbN) in nature. Overall, Nb substitutions are found to improve ductility of TiAlN-based alloys at the cost of slight losses in hardness, equating to enhanced toughness. © 2016 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2016.08.084
  • 2016 • 143 Composite cavitation resistant PVD coatings based on NiTi thin films
    Momeni, S. and Tillmann, W. and Pohl, M.
    Materials and Design 110 830-838 (2016)
    As a protective coating, TiCN hard PVD coating was deposited on magnetron sputtered NiTi thin films under various coating architectures. The microstructure, composition, mechanical properties, tribological performance as well as the cavitation resistance of deposited coatings were analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nanoindentation, ball–on-disc, scratch test, three dimensional (3D) optical microscopy, and the standard ultrasonic cavitation test (ASTM G 32). The obtained results revealed that under a specific coating architecture, the superelasticity of NiTi can be combined with high hardness and wear resistance of TiCN coatings. As a consequence of the combination of these properties, the composite NiTi based coatings are capable of presenting remarkable cavitation resistance and tribological performance. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.matdes.2016.08.054
  • 2016 • 142 Investigations on the Initial Stress Evolution During Atmospheric Plasma Spraying of YSZ by In Situ Curvature Measurement
    Mutter, M. and Mauer, G. and Mücke, R. and Vaßen, R. and Back, H.C. and Gibmeier, J.
    Journal of Thermal Spray Technology 25 672-683 (2016)
    The residual stresses within plasma-sprayed coatings are an important factor that can influence the lifetime as well as the performance in operation. The investigation of stresses evolving during deposition and post-deposition cooling for atmospheric plasma spraying of yttria-stabilized zirconia coatings using in situ measurement of the samples curvature is a powerful tool for identifying the factors that contribute to stress generation. Under various spray conditions, the first deposition pass leads to a significantly larger increase in samples curvature than the subsequent passes. It is shown in this work that the amount of curvature change at the onset of spraying is significantly influenced by the spray conditions, as well as by the substrate material. More information on the origin of this steep curvature increase at the onset of spraying was obtained by single splat experiments, which yielded information on the splat bonding behavior under various conditions. A comparison of the compressive yield strength for different substrate materials indicated the influence of substrate residual stress relaxation. Residual stress measurements using the incremental hole-drilling method and x-ray diffraction confirmed that the coating deposition affects the substrate residual stress level. The yield strength data were combined with the substrate near-surface temperature during deposition, obtained by finite element simulations, and with the measured residual stress-profile. This revealed that residual stress relaxation is the key factor for the initial curvature increase. © 2016, ASM International.
    view abstractdoi: 10.1007/s11666-016-0398-4
  • 2016 • 141 Probabilistic lifetime model for atmospherically plasma sprayed thermal barrier coating systems
    Nordhorn, C. and Mücke, R. and Mack, D.E. and Vaßen, R.
    Mechanics of Materials 93 199-208 (2016)
    Calculations of atmospherically plasma sprayed thermal barrier coating durability were facilitated by the development of a numerical lifetime model including probabilistic fracture mechanical analyses of thermally induced topcoat stress field evolutions. The stress distributions were determined in finite element analyses taking into account oxide scale growth and topcoat sintering as transient degradation effects. The influence of interface microstructure was investigated by implementing two different interface approximation functions. Subsequent fracture mechanical analyses of subcritical crack growth were performed at numerous different and permanently assigned abstract crack positions. A comparison of the transient energy release rate to its critical value, which depends on crack length and therefore position, results in statistical distributions of system lifetime as a function of simulated thermal cycling conditions. The model was calibrated by presetting an experimental lifetime distribution which was determined in thermal cycling experiments performed at a burner rig facility. The associated cycle-dependent calibration parameter reflects the effect of fracture toughness increase for increasing crack lengths. Experimental reference values for system lifetime were found to be reproduced by the lifetime model. The stress field inversion directly correlated to oxide scale growth rate was identified as the main failure mechanism. The expectation values and standard deviations of the calculated lifetime distributions were found to be in accordance to the experimentally obtained lifetime data and the data scattering typically observed in thermal cycling. © 2015 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.mechmat.2015.11.002
  • 2016 • 140 Analyzing of Coatings on Steel - Reinforced Concrete Elements by Mobile NMR
    Orlowsky, J.
    Archives of Civil Engineering 62 65-82 (2016)
    A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first time ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of these important parameters on the building site. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as well as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating leading to identical results. © 2016 Polish Academy of Sciences.
    view abstractdoi: 10.1515/ace-2015-0052
  • 2016 • 139 Influence of Machine Hammer Peening on the Tribological Behavior and the Residual Stresses of Wear Resistant Thermally Sprayed Coatings
    Rausch, S. and Wiederkehr, P. and Biermann, D. and Zabel, A. and Selvadurai, U. and Hagen, L. and Tillmann, W.
    Procedia CIRP 45 275-278 (2016)
    WC-W2C iron based cermet coatings are widely used in the field of wear protection. In surface engineering, machine hammer peening (MHP) is a novel surface treatment technology, which enhances the surface properties, especially for surfaces in tribological contact. In this study, the wear behavior of peened WC-W2C FeCrCMnSi arc sprayed coatings is characterized and compared to conventional coatings under as-sprayed conditions. The resulting strain hardening effects were measured by mechanical response using nanoindentation. In addition, residual stresses at the surfaces were determined using X-ray diffraction and the sin2ψ method. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.
    view abstractdoi: 10.1016/j.procir.2016.02.059
  • 2016 • 138 Wear behavior of tribologically optimized tool surfaces for incremental forming processes
    Sieczkarek, P. and Wernicke, S. and Gies, S. and Tekkaya, A.E. and Krebs, E. and Wiederkehr, P. and Biermann, D. and Tillmann, W. and Stangier, D.
    Tribology International 104 64-72 (2016)
    The mechanical wear behavior of forming tools is the limiting factor during an incremental gear-forming process. These forming tools with a simply shaped geometry are exposed to high forming forces. Additionally, the necessary workpiece chambering, which is characteristic for this incremental process restricts the dimensioning of the tools. Thereby, the geometrical design of the forming tools is limited, which leads to a decreased lifetime. Functional structures on the tool surfaces can influence the occurring loading and wear behavior by reducing the contact area, the supply of lubricant pockets, and by a controlled influence and adjustment of the occurring material flow. For the extension of the tool's lifetime, different surface concepts and combinations with CrAlN PVD-coatings are investigated. To offer conditions with a high tool load, the investigations are focused on an incremental gear forming process with a simple one-wedge forming tool. The results show abrasive and adhesive wear characteristics, as well as outbreaks, and crack formations. The crack propagation on the flank leads to a chipping of the tool tip, hence limiting the tool life. Compared to the reference tool, a surface structure combined with a PVD-coating provides a significant increase of the tool life of 84%. © 2016 Elsevier Ltd
    view abstractdoi: 10.1016/j.triboint.2016.08.028
  • 2016 • 137 The detachment behavior of polycarbonate on thin films above the glass transition temperature
    Tillmann, W. and Hagen, L. and Hoffmann, F. and Dildrop, M. and Wibbeke, A. and Schöppner, V. and Resonnek, V. and Pohl, M. and Krumm, C. and Tiller, J.C. and Paulus, M. and Sternemann, C.
    Polymer Engineering and Science 56 786-797 (2016)
    When producing mono-axially stretched films made of amorphous polycarbonate, a self-reinforcement is generated due to the stretching process. This leads to an increase of the strength and stiffness. The mono-axial stretching process is conducted at temperatures above the glass transition temperature, whereas better mechanical properties are obtained at higher stretching temperatures. However, the film tends to adhere to the rolls, especially at temperatures from 10°C above the glass transition temperature. The rolls of the mono-axial stretching unit are made of an induction hardened and polished quenched and tempered steel 1.7225 – 42CrMo4. This work reports on the investigation of the detachment behavior of polycarbonate on different coatings as a function of the temperature and contact time. The main intention is to find a suitable coating on which the polycarbonate film adheres only slightly at temperatures clearly exceeding the glass transition temperature. POLYM. ENG. SCI., 56:786–797, 2016. © 2016 Society of Plastics Engineers. © 2016 Society of Plastics Engineers
    view abstractdoi: 10.1002/pen.24307
  • 2016 • 136 X-ray diffraction (XRD)-studies on the temperature dependent interface reactions on hafnium, zirconium, and nickel coated monocrystalline diamonds used in grinding segments for stone and concrete machining
    Tillmann, W. and Tolan, M. and Pinho Ferreira, M. and Paulus, M. and Becke, M. and Stangier, D.
    Materialwissenschaft und Werkstofftechnik 47 1193-1201 (2016)
    Diamond impregnated metal matrix composites are the state of the art solution for the machining of mineral materials. The type of interface reactions between the metal matrix and diamond surface has an essential influence on the tool performance and durability. To improve the diamond retention, the diamonds can be coated by physical vapour deposition with metallic materials, which enforce interface reactions. Hence, this paper focuses on the investigation of the interfacial area on metal-coated monocrystalline diamonds. Hafnium and zirconium, both known as carbide forming elements, are used as coating materials. The third coating, which is used to determine its catalytic influences when applied as a physical vapour deposition (PVD)-layer, is nickel. Additionally, the coated diamond samples were heat-treated to investigate the starting point of the formation of new phases. X-ray diffraction-analyses revealed the assumed carbide formation on hafnium and zirconium coated samples. The formation temperature was identified between 800 °C and 1000 °C for hafnium and zirconium coatings. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstractdoi: 10.1002/mawe.201600713
  • 2016 • 135 Tribological development of TiCN coatings by adjusting the flowing rate of reactive gases
    Tillmann, W. and Momeni, S.
    Journal of Physics and Chemistry of Solids 90 45-53 (2016)
    TiCN coatings were deposited by means of direct current magnetron sputtering of Ti targets in presence of N2 and C2H2 reactive gases. The microstructure, composition, mechanical and tribological properties of the deposited thin films were analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nanoindentation, ball-on-disc, scratch test, and three dimensional (3D) optical microscopy. The obtained results presents a reproducible processing route for tailoring microstructure, mechanical and tribological behavior of TiCN coatings by controlling flowing rate of the reactive gases. © 2015 Elsevier Ltd.
    view abstractdoi: 10.1016/j.jpcs.2015.11.009
  • 2016 • 134 Influence of PVD-coating technology and pretreatments on residual stresses for sheet-bulk metal forming tools
    Tillmann, W. and Stangier, D. and Denkena, B. and Grove, T. and Lucas, H.
    Production Engineering 10 17-24 (2016)
    Residual stresses in the substrate material are significantly influencing the performance of PVD-coated parts and tools which are exposed to high forces. Especially for forming operations, such as sheet-bulk metal forming, during which normal contact pressures of 1.4 GPa can occur, the reduction of friction and, at the same time, the wear protection by means of thin Cr-based coatings are essential. To ensure a long service life of forming tool and tool coating, each step of the substrate pre-treatment, as well as the magnetron-sputtering process, has to be coordinated and compatible. Therefore, polished as well as nitrided samples consisting of high-speed steel (AISI M3:2) are exposed to a sequence of plasma-based pre-treatments prior to depositing a CrAlN coating. Hardness and Young’s modulus of the substrate and the coating are analysed by means of nanoindentation. To determine the adhesion between coating and substrate, scratch tests are conducted and analysed using a scanning electron microscope. For each step, the residual stresses are determined using sin2ψ measurements, which are correlated to the mechanical properties. A plasma-nitriding process before the CrAlN coating induces high compressive residual stresses into the sample subsurface and at the same time increases the hardness of the surface. This results in higher critical loads during the scratch tests and therefore a better adhesion of the coating on the substrate. © 2015, German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-015-0653-4
  • 2016 • 133 Surface investigation and tribological mechanism of a sulfate-based lubricant deposited on zinc-coated steel sheets
    Timma, C. and Lostak, T. and Janssen, S. and Flock, J. and Mayer, C.
    Applied Surface Science 390 784-794 (2016)
    Phosphatation is a well-known technique to improve friction and wear behaviour of zinc coated steel, but has a variety of economic and ecologic limitations. In this study an alternative coating based on ammonium sulfate ((NH4)2SO4) is applied on skin-passed hot-dip galvanized steel sheets in order to investigate its surface chemical and tribological behaviour in a Pin-on-Disk Tribometer. Raman- and X-ray photoelectron spectroscopic results revealed a formation of ammonium zinc sulfate ((NH4)2Zn(SO4)2 * xH2O) on the surface, which is primarily located in the skin-passed areas of the steel material. Sulfate coated samples exhibited a superior friction behaviour in Pin-on-Disk Tests using squalane as a model substance for oil-like lubricated conditions and a formation of a thin lubrication film is obtained in the wear track. Squalane acts as a carrier substance for ammonium zinc sulfate, leading to an effective lubrication film in the wear track. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.apsusc.2016.09.002
  • 2016 • 132 The 2016 Thermal Spray Roadmap
    Vardelle, A. and Moreau, C. and Akedo, J. and Ashrafizadeh, H. and Berndt, C.C. and Berghaus, J.O. and Boulos, M. and Brogan, J. and Bourtsalas, A.C. and Dolatabadi, A. and Dorfman, M. and Eden, T.J. and Fauchais, P. and Fisher, G...
    Journal of Thermal Spray Technology 25 1376-1440 (2016)
    Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications. © 2016, ASM International.
    view abstractdoi: 10.1007/s11666-016-0473-x
  • 2016 • 131 Aging of atmospherically plasma sprayed chromium evaporation barriers
    Vaßen, R. and Grünwald, N. and Marcano, D. and Menzler, N.H. and Mücke, R. and Sebold, D. and Sohn, Y.J. and Guillon, O.
    Surface and Coatings Technology 291 115-122 (2016)
    Chromium evaporation barriers are frequently used in solid oxide fuel cells to protect the porous cathode from chromium poisoning. Volatile chromium species are generated at the operation temperature of about 600-900 °C in a humid atmosphere for chromia scale forming steels as interconnect materials. In order to reduce this effect, barrier coatings are applied, often by atmospheric plasma spraying. However, also in these coatings microstructural changes as densification and in parallel formation of large pores have been observed. In order to clarify these mechanisms plasma sprayed Mn1.0 Co1.9Fe0.1O4 ("MCF") are deposited on ferritic steels and furthermore coated with a perovskite based contact layer as used in stack build-up. These coatings are annealed in air up to 1000 h and the microstructural changes and bending of the samples are studied. The results show increasing bending with increasing aging time. High temperature curvature measurements indicate that the amount of bending is not significantly dependent on temperature. As an explanation the creep deformation of the substrate/coating system at high temperatures due to compressive stress levels in the coating is given. The origin of the stress is related to phase changes in combination with the oxidation of the coatings. In addition, interdiffusion and densification processes are discussed. © 2016 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2016.02.005
  • 2016 • 130 Antifouling and Antibacterial Multifunctional Polyzwitterion/Enzyme Coating on Silicone Catheter Material Prepared by Electrostatic Layer-by-Layer Assembly
    Vaterrodt, A. and Thallinger, B. and Daumann, K. and Koch, D. and Guebitz, G.M. and Ulbricht, M.
    Langmuir 32 1347-1359 (2016)
    The formation of bacterial biofilms on indwelling medical devices generally causes high risks for adverse complications such as catheter-associated urinary tract infections. In this work, a strategy for synthesizing innovative coatings of poly(dimethylsiloxane) (PDMS) catheter material, using layer-by-layer assembly with three novel functional polymeric building blocks, is reported, i.e., an antifouling copolymer with zwitterionic and quaternary ammonium side groups, a contact biocidal derivative of that polymer with octyl groups, and the antibacterial hydrogen peroxide (H2O2) producing enzyme cellobiose dehydrogenase (CDH). CDH oxidizes oligosaccharides by transferring electrons to oxygen, resulting in the production of H2O2. The design and synthesis of random copolymers which combine segments that have antifouling properties by zwitterionic groups and can be used for electrostatically driven layer-by-layer (LbL) assembly at the same time were based on the atom-transfer radical polymerization of dimethylaminoethyl methacrylate and subsequent partial sulfobetainization with 1,3-propane sultone followed by quaternization with methyl iodide only or octyl bromide and thereafter methyl iodide. The alternating multilayer systems were formed by consecutive adsorption of the novel polycations with up to 50% zwitterionic groups and of poly(styrenesulfonate) as the polyanion. Due to its negative charge, enzyme CDH was also firmly embedded as a polyanionic layer in the multilayer system. This LbL coating procedure was first performed on prefunctionalized silicon wafers and studied in detail with ellipsometry as well as contact angle (CA) and zetapotential (ZP) measurements before it was transferred to prefunctionalized PDMS and analyzed by CA and ZP measurements as well as atomic force microscopy. The coatings comprising six layers were stable and yielded a more neutral and hydrophilic surface than did PDMS, the polycation with 50% zwitterionic groups having the largest effect. Enzyme activity was found to be dependent on the depth of embedment in the multilayer coating. Depending on the used polymeric building block, up to a 60% reduction in the amount of adhering bacteria and clear evidence for killed bacteria due to the antimicrobial functionality of the coating could be confirmed. Overall, this work demonstrates the feasibility of an easy to perform and shape-independent method for preparing an antifouling and antimicrobial coating for the significant reduction of biofilm formation and thus reducing the risk of acquiring infections by using urinary catheters. © 2016 American Chemical Society.
    view abstractdoi: 10.1021/acs.langmuir.5b04303
  • 2016 • 129 Removal of oxides and brittle coating constituents at the surface of coated hot-forming 22MnB5 steel for a laser welding process with aluminum alloys
    Windmann, M. and Röttger, A. and Kügler, H. and Theisen, W.
    Surface and Coatings Technology 285 153-160 (2016)
    The surface of a press-hardened steel 22MnB5 coated with Al-base (AlSi10Fe3) and Zn-base (ZnNi10) was conditioned by a pulse laser and by sandblasting to remove undesirable oxides and brittle phases. Oxides formed on coating surfaces counteract the wettability of welding filler during a welding or brazing process. Furthermore, welding and brazing joints of 22MnB5 coated with aluminum alloys failed along the brittle intermetallic phases in the coating under a low mechanical load. Treated 22MnB5 surfaces were analyzed microscopically, and the phase compositions were investigated by synchrotron diffraction measurements. It was found that brittle phases could be locally removed by laser ablation; however, high laser energies led to remelting and oxidation of the coating surface. In contrast, sandblasting homogenously removed oxides and brittle intermetallic phases. Surface-treated 22MnB5 steel sheets were joined to AA6016 aluminum sheets by laser welding, and the strength of the weldment was determined by tensile tests. The measured mechanical strength of the aluminum/steel joints was 210-230. MPa. Failure of the weldments under tensile loading occurred within the aluminum sheet, away from the steel surface/welding filler interface if brittle coating components and oxides were removed homogenously. © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2015.11.037
  • 2016 • 128 Effect of Plasma Enthalpy on the Structure of La2Zr2O7 Coatings Prepared by Suspension Plasma Spraying
    Zotov, N. and Guignard, A. and Mauer, G. and Vaßen, R.
    Journal of the American Ceramic Society 99 1086-1091 (2016)
    La2Zr2O7 coatings, prepared by suspension plasma spraying, have been studied by X-ray diffraction (XRD) as a function of torch power. Rietveld refinements of high-resolution XRD data show that with increasing plasma temperature (as a result of the increasing torch power), the La2Zr2O7 coatings remain cation ordered but progressively anion disordered. © 2015 The American Ceramic Society.
    view abstractdoi: 10.1111/jace.14058
  • 2015 • 127 Chemical vapor deposition and analysis of thermally insulating ZrO2 layers on injection molds
    Atakan, B. and Khlopyanova, V. and Mausberg, S. and Mumme, F. and Kandzia, A. and Pflitsch, C.
    Physica Status Solidi (C) Current Topics in Solid State Physics 12 878-885 (2015)
    High quality injection molding requires a precise control of cooling rates. Thermal barrier coating (TBC) of zirconia with a thickness of 20-40 μm on polished stainless steel molds could provide the necessary insulating effect. This paper presents results of zirconia deposition on stainless steel substrates using chemical vapor deposition (CVD) aiming to provide the process parameters for the deposition of uniform zirconia films with such a thickness. The deposition was performed with zirconium (IV) acetylacetonate (Zr(C<inf>5</inf>H<inf>7</inf>O<inf>2</inf>)<inf>4</inf>) as precursor and synthetic air as co-reactant, which allows deposition at temperatures below 600 °C. The experiments were carried out in a hot-wall reactor at pressures between 7.5 mbar and 500 mbar and in a temperature range from 450 °C to 600 °C. Important growth parameters were characterized and growth rates between 1 and 2.5 μm/h were achieved. Thick and well adhering zirconia layers of 38 μm could be produced on steel within 40 h. The transient heat transfer rate upon contact with a hot surface was also evaluated experimentally with the thickest coatings. These exhibit a good TBC performance. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/pssc.201510033
  • 2015 • 126 Porosity-Property Relationships of Plasma-Sprayed Gd2Zr2O7/YSZ Thermal Barrier Coatings
    Bakan, E. and Mack, D.E. and Mauer, G. and Mücke, R. and Vaßen, R.
    Journal of the American Ceramic Society 98 2647-2654 (2015)
    During the past decade, gadolinium zirconate (Gd<inf>2</inf>Zr<inf>2</inf>O<inf>7</inf>, GZO) has attracted interest as an alternative material to partially yttria-stabilized zirconia (YSZ) for thermal barrier coatings (TBCs). Despite the well-known benefits of GZO, such as lower thermal conductivity and superior temperature capability compared to YSZ, processing of GZO via atmospheric plasma spraying (APS) still remains a challenge. Here, we report on APS experiments which were performed to investigate the influence of processing on GZO microstructure and lifetime of GZO/YSZ double-layer TBCs. Different microstructures of GZO were produced and characterized in terms of porosity, stoichiometry, Young′s modulus, and their effects on the lifetime of YSZ/GZO double-layer TBCs were discussed. Particle diagnostics were utilized for the optimization of the process parameters with respect to different microstructures of GZO and stoichiometry. It was found that both cumulative porosity of GZO and pore size distribution, which alter the Young′s modulus significantly, govern the lifetime of double layers. In addition, it was shown that the deviation in GZO stoichiometry due to gadolinia evaporation in the investigated range does not display any critical effect on lifetime. © 2015 The American Ceramic Society.
    view abstractdoi: 10.1111/jace.13611
  • 2015 • 125 An approach for transparent and electrically conducting coatings: A transparent plastic varnish with nanoparticulate magnetic additives
    Beck, G. and Barcikowski, S. and Chakravadhanula, V.S.K. and Comesaña-Hermo, M. and Deng, M. and Farle, M. and Hilgendorff, M. and Jakobi, J. and Janek, J. and Kienle, L. and Mogwitz, B. and Schubert, T. and Stiemke, F.
    Thin Solid Films 595 96-107 (2015)
    For the purpose of preparing TCCs (= transparent and electrical conducting coatings), metallic and ferromagnetic nano-additives were dispersed into a transparent varnish and the obtained dispersions were coated on transparent plastic substrates. During hardening of the dispersion the magnetic nano-additives were aligned by a magnetic field. The resulting coatings have electrical pathways along lines of nano-additive chains and are highly transparent in the areas between the lines. Therefore, the electrical conductivity is anisotropic, and it depends on the alignment of the nano-additives (i.e. on the distance between the nano-additives within the chains and the length of the lines) as well as on the thickness of an oxide and/or solvent shell around the nano-additives. The transparency depends also on the alignment and here especially on the thickness and the distance between the formed lines. The quality of the alignment in turn, depends on the magnetic properties and on the size of the particles. We used commercial plastic varnishes, which form electrically isolating (≥ 10− 12 S/m) and transparent (about 90% transparency) coatings, and the following magnetic additives: Co-, Fe-, CoPt3, CoPt3@Au- and Fe@Au-nanoparticles as well as CoNi-nanowires. Coatings with Fe@Au-nanoparticles show the best results in terms of the electrical conductivity (10− 5 S/m–10− 6 S/m) at transparencies above 70%. Furthermore, in addition to the magnetic nano-additives, transparent additives (Al2O3-particles) and non-magnetic, but better conducting additives (carbon-nanotubes) were added to the varnish to increase the transparency and the electrical conductivity, respectively. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.tsf.2015.10.059
  • 2015 • 124 Influence of surface modifications on friction, using high-feed milling and wear resistant PVD-coating for sheet-metal forming tools
    Biermann, D. and Freiburg, D. and Hense, R. and Tillmann, W. and Stangier, D.
    Key Engineering Materials 639 275-282 (2015)
    Increasing technological requirements, as well as the demand for an efficient production demands high performance materials and enhanced manufacturing processes. The development of a new manufacturing process, sheet-bulk metal forming (SBMF), is one approach to produce lightweight forming parts with an increased number of functional properties while, at the same time, combining the advantages of sheet and bulk metal forming. For SBMF processes, the specific adjustment of the friction between tool and workpiece for a specifically designed material flow, which is called tailored friction, is of great importance. The reduction of friction is essential in order to ensure a homogeneous forming zone. However, a higher friction can be used to control the material flow to increase the local thickness of the work piece for additional functional integration. This paper shows the development of surface structures for SBMF tools by means of high-feed milling. Process parameters like the tilt angle or the feed are varied to influence the surface parameters of the structures, which results in different tribological properties of the forming tool. The structured surfaces are subsequently coated with a wear resistant CrAlN coating, processed by a magnetron-sputtering process (PVD) to enhance the lifetime and performance of the forming tool. Finally, a ring compressing test is used to investigate the tribological behavior of the coated structures. © 2015 Trans Tech Publications, Switzerland.
    view abstractdoi: 10.4028/
  • 2015 • 123 Cavitation-resistant NiTi coatings produced by low-pressure plasma spraying (LPPS)
    Bitzer, M. and Rauhut, N. and Mauer, G. and Bram, M. and Vaßen, R. and Buchkremer, H.-P. and Stöver, D. and Pohl, M.
    Wear 328-329 369-377 (2015)
    Cavitation is a severe wear mechanism in technical applications where parts are in contact with rapidly flowing liquids. Examples are turbine blades in hydropower plants or pump components. Coating exposed surfaces with wear-resistant materials is an effective measure for extending lifetime in the case of cavitation attack. NiTi is an attractive material for such coatings considering its clearly pronounced damping behavior based on its pseudoelastic properties. A promising processing route for coating net-shaped components with NiTi is low-pressure plasma spraying (LPPS). In the present work, NiTi layers were produced by LPPS, starting from pre-alloyed NiTi powder. Cavitation resistance was investigated in relation to LPPS parameters, layer thickness and specific surface treatment. Increased cavitation resistance was demonstrated compared to UTP 730, an established cavitation protection material. The study was accompanied by comprehensive characterization of microstructure and phase transformation behavior of the NiTi coatings. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2015.03.003
  • 2015 • 122 Phenolated Oleic Acid Based Polybenzoxazine Derivatives as Corrosion Protection Layers
    Bələnucə, B. and Raicopol, M. and Maljusch, A. and Garea, S. and Hanganu, A. and Schuhmann, W. and Andronescu, C.
    ChemPlusChem 80 1170-1177 (2015)
    Benzoxazine derivatives were synthesized using phenolated methyl oleate and either aniline, 1,6-diaminohexane, or 4,4′-diaminodiphenylmethane, respectively, as amine components. Polymerization of the benzoxazine derivatives led to the formation of hydrophobic and dense coatings on Zn-Mg-Al alloy coated steel sheets for passive corrosion protection. The polybenzoxazine coatings which are formed by crosslinking during a heat-treatment step invoked a substantial anodic shift of the open-circuit potential as well as the breakthrough potential in potentiodynamic measurements. The proposed polybenzoxazine derivatives pave the way for a new type of passive polymer protection system based on sustainably obtained precursor components. Copyright © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstractdoi: 10.1002/cplu.201500092
  • 2015 • 121 Friction surfacing of Ti-6Al-4V: Process characteristics and deposition behaviour at various rotational speeds
    Fitseva, V. and Krohn, H. and Hanke, S. and dos Santos, J.F.
    Surface and Coatings Technology 278 56-63 (2015)
    By the process of friction surfacing, coatings are generated from metallic materials at temperatures below their melting range. The high degree of deformation while depositing leads to grain refinement in the microstructure, which has a positive effect on the mechanical properties of the layer. The applicability of the process has been described for a large number of materials. The deposition of Ti-6Al-4V has been reported in one publication but was not systematically studied. Therefore, the main aims of the present work are to define the process parameter fields for the deposition of Ti-6Al-4V leading to flash and defect free coatings and associate them with geometric features of the deposited layer.This investigation has shown that Ti-6Al-4V coatings can be effectively deposited onto a Ti-6Al-4V substrate by friction surfacing. A wide range of process parameters was established in which coatings of high quality have been obtained. The consumption rate control has been implemented as an efficient mode for the deposition of Ti-6Al-4V coatings. Temperature measurements at the coating interface have been accomplished showing that the coating material has been deformed in the β-phase. Furthermore, the homogeneity of the coating surface has been established to be a function of the rotational speed. The coatings exhibited a defect-free bond at the interface with the substrate. Two process parameter ranges with respect to the flash formation have been established. One of them enables flash-free coatings and the other generates coatings with flash formation on the retreating side, which can be controlled by the rotational and deposition speeds. Moreover, an increase in the rotational speed has been shown to lead to an increase in the coating thickness and width as well as an increase in the deposition efficiency up to 39 %. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2015.07.039
  • 2015 • 120 Correlation between surface properties and wettability of multi-scale structured biocompatible surfaces
    Gorodzha, S.N. and Surmeneva, M.A. and Prymak, O. and Wittmar, A. and Ulbricht, M. and Epple, M. and Teresov, A. and Koval, N. and Surmenev, R.A.
    IOP Conference Series: Materials Science and Engineering 98 (2015)
    The influence of surface properties of radio-frequency (RF) magnetron deposited hydroxyapatite (HA) and Si-containing HA coatings on wettability was studied. The composition and morphology of the coatings fabricated on titanium (Ti) were characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). The surface wettability was studied using contact angle analysis. Different geometric parameters of acid-etched (AE) and pulse electron beam (PEB)-treated Ti substrates and silicate content in the HA films resulted in the different morphology of the coatings at micro- and nano- length scales. Water contact angles for the HA coated Ti samples were evaluated as a combined effect of micro roughness of the substrate and nano-roughness of the HA films resulting in higher water contact angles compared with acid-etched (AE) or pulse electron beam (PEB) treated Ti substrates. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/98/1/012026
  • 2015 • 119 The effect of patterned titanium substrates on the properties of silver-doped hydroxyapatite coatings
    Grubova, I.Y. and Surmeneva, M.A. and Ivanova, A.A. and Kravchuk, K. and Prymak, O. and Epple, M. and Buck, V. and Surmenev, R.A.
    Surface and Coatings Technology 276 595-601 (2015)
    This paper reports the effect of substrate nano/micro-structure design on the grain size, mechanical properties and surface wettability of nanostructured radio frequency (RF) magnetron sputter-deposited silver-containing hydroxyapatite (Ag-HA) coatings containing 0.13-0.36. wt.% silver. The results of this study revealed that the Ag-HA coating microstructure could be designed by controlling the pre-treated surface topography of titanium. The nano/micro-patterned surfaces of titanium were prepared by sand-blasting followed by acid-etching. The size of the nano-patterns on the surface of titanium was also affected by the sand-blasting procedure; namely, the lower the pressure was, the larger the size of the nano-structures and the distance between them. The effect of the coating grain size on the surface wettability and physico-mechanical properties of the biocomposites was revealed. The hydrophobic properties were imparted to the rough titanium by a nanostructured Ag-HA coating. Although according to the XRD patterns the coatings were mainly composed of HA, some differences in the morphology were observed. Therefore, the decreased wettability of the Ag-HA coatings could be explained by taking into account the different grain sizes of the films rather than the changes to the surface chemistry. Nanoindentation studies revealed that in the case of the Ag-HA-coated samples, smaller grains resulted in significantly higher nanohardness and Young's modulus. © 2015 Elsevier B.V..
    view abstractdoi: 10.1016/j.surfcoat.2015.06.010
  • 2015 • 118 Sliding wear behaviour of a Cr-base alloy after microstructure alterations induced by friction surfacing
    Hanke, S. and Fischer, A. and dos Santos, J.F.
    Wear 338-339 332-338 (2015)
    Friction surfacing is a method suitable to generate a wide variety of metallic coatings by means of frictional heating and severe shear deformation. It is a solid-state joining method, and therefore may be applied to non-fusion weldable as well as non-deformable brittle materials, as Cr-based alloys are. In the present study coatings of Cr60Ni40 alloy are generated onto Nimonic 80A substrates. Microstructural investigations of the coating material are carried out and compared to the usual cast state. The wear behaviour of the coatings as well as the cast material is examined under reciprocating sliding against 52100 ball bearing steel by means of a ball-on-flat test rig, lubricated with silicone oil to prevent oxidation. In this tribological system, wear takes place by abrasion with microploughing being the predominant submechanism, surface fatigue as well as adhesion by materials transfer of Cr60Ni40 from the flats to the steel balls. White etching layers form on Cr60Ni40 underneath the worn surfaces, which show cracks and delaminations. The amount of wear of all coatings is within the same magnitude compared to the cast state but slightly smaller. This can be explained by the distinctly finer microstructure (grain boundary strengthening) and a high degree of supersaturation of the solid solutions (solid solution strengthening) within the coatings. The results of this study show that it is possible to generate coatings of brittle alloys like Cr60Ni40 by friction surfacing, which show a slightly better wear behaviour under reciprocating sliding. Thus, in combination with a ductile substrate, these coatings are likely to extend the range of applicability of such high-temperature wear and corrosion resistant alloys. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2015.07.010
  • 2015 • 117 Simulation based iterative post-optimization of paths of robot guided thermal spraying
    Hegels, D. and Wiederkehr, T. and Müller, H.
    Robotics and Computer-Integrated Manufacturing 35 1-15 (2015)
    Robot-based thermal spraying is a production process in which an industrial robot guides a spray gun along a path in order to spray molten material onto a workpiece surface to form a coating of desired thickness. This paper is concerned with optimizing a given path of this sort by post-processing. Reasons for doing so are to reduce the thickness error caused by a not sufficiently precise design of the given path, to adapt the path to a changed spray gun or spray technology, to adapt the path to slight incremental changes of the workpiece geometry, or to smooth the path in order to improve its execution by the robot. An approach to post-optimization using the nonlinear conjugate gradient method is presented which employs a high-quality GPGPU-based simulation of the spray process for the evaluation of the coating thickness error and additionally taking care of the kinematic path quality. The number of computationally time-consuming calls of the simulation is kept low by analytically calculating estimates of gradients from a simplified material deposition model. A rigorous experimental evaluation on case studies of the mentioned applications shows that the method efficiently delivers improved paths which reduce the coating error on real free form surfaces considerably, i.e. the squared coating error is below 3.5% of the original value in every case study. © 2015 Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.rcim.2015.02.002
  • 2015 • 116 Hybrid biocomposite with a tunable antibacterial activity and bioactivity based on RF magnetron sputter deposited coating and silver nanoparticles
    Ivanova, A.A. and Surmenev, R.A. and Surmeneva, M.A. and Mukhametkaliyev, T. and Loza, K. and Prymak, O. and Epple, M.
    Applied Surface Science 329 212-218 (2015)
    In this work, we describe fabrication techniques used to prepare a multifunctional biocomposite based on a hydroxyapatite (HA) coating and silver nanoparticles (AgNPs). AgNPs synthesized by a wet chemical reduction method were deposited on Ti substrates using a dripping/drying method followed by deposition of calcium phosphate (CaP) coating via radio-frequency (RF) magnetron sputter-deposition. The negatively charged silver nanoparticles (zeta potential -21 mV) have a spherical shape with a metallic core diameter of 50 ± 20 nm. The HA coating was deposited as a dense nanocrystalline film over a surface of AgNPs. The RF-magnetron sputter deposition of HA films on the AgNPs layer did not affect the initial content of AgNPs on the substrate surface as well as NPs size and shape. SEM cross-sectional images taken using the backscattering mode revealed a homogeneous layer of AgNPs under the CaP layer. The diffraction patterns from the coatings revealed reflexes of crystalline HA and silver. The concentration of Ag ions released from the biocomposites after 7 days of immersion in phosphate and acetate buffers was estimated. The obtained results revealed that the amount of silver in the solutions was 0.27 ± 0.02 μg mL-1 and 0.54 ± 0.02 μg mL-1 for the phosphate and acetate buffers, respectively, which corresponded well with the minimum inhibitory concentration range known for silver ions in literature. Thus, this work establishes a new route to prepare a biocompatible layer using embedded AgNPs to achieve a local antibacterial effect. © 2015 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2014.12.153
  • 2015 • 115 Deposition and characterization of single magnetron deposited Fe:SnOx coatings
    Kormunda, M. and Fischer, D. and Hertwig, A. and Beck, U. and Sebik, M. and Pavlik, J. and Esser, N.
    Thin Solid Films 595 200-208 (2015)
    Coatings deposited bymagnetron co-sputtering froma single RF magnetronwith a ceramic SnO2 target with iron inset in argon plasma were studied. Themass spectra of the process identified Sn+ and SnO+ species as the dominant species sputtered fromthe target, but no SnO2 + specieswere detected. The dominant positive ions in argon plasma are Ar+ species. The only detected negative ions were O-. Sputtered neutral tin related species were not detected. Iron related species were also not detected because their concentration is below the detection limit. The concentration of iron dopant in the tin oxide coatings was controlled by the RF bias applied on the substrate holder while the discharge pressure also has some influence. The iron concentration was in the range from 0.9 at.% up to 19 at.% increasing with the substrate bias while the sheet resistivity decreases. The stoichiometry ratio of O/(Sn+Fe) in the coatings increased from 1.7 up to 2 in dependence on the substrate bias from floating bias (-5 V) up to-120 V of RF self-bias, respectively. The tin in the coatings was mainly bonded in Sn4+ state and iron was mainly in Fe2+ state when other tin bonding states were detected only in a small amounts. Iron bonding states in contrary to elemental compositions of the coatings were not influenced by the RF bias applied on the substrate. The coatings showed high transparency in the visible spectral range. However, an increased metallic behavior could be detected by using a higher RF bias for the deposition. The X-ray diffraction patterns and electron microscopy pictures made on the coatings confirmed the presence of an amorphous phase. © 2015 Published by Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2015.11.009
  • 2015 • 114 Copper-based nanostructured coatings for low-temperature brazing applications
    Lehmert, B. and Janczak-Rusch, J. and Pigozzi, G. and Zuraw, P. and La Mattina, F. and Wojarski, L. and Tillmann, W. and Jeurgens, L.P.H.
    Materials Transactions 56 1015-1018 (2015)
    This feasibility study demonstrates the possibility to apply nanostructured filler materials for novel low-temperature brazing applications by exploiting the size-dependent melting behavior of metals and alloys when confined to the nano-scale regime. As an example, a copper-based nanostructured brazing filler is presented, which allows metal brazing of coated Ti-6Al-4V components at 750°C, much below the bulk melting point of copper (1083°C). The copper-based nanostructured brazing fillers can be produced in the form of coatings and free-standing brazing foils. The nano-confinement of Cu is abrogated after brazing and, consequently, the brazed joints can be operated well above their reduced brazing temperatures. © 2015 The Japan Institute of Metals and Materials.
    view abstractdoi: 10.2320/matertrans.MI201419
  • 2015 • 113 Monitoring Local Strain in a Thermal Barrier Coating System Under Thermal Mechanical Gas Turbine Operating Conditions
    Manero, A., II and Sofronsky, S. and Knipe, K. and Meid, C. and Wischek, J. and Okasinski, J. and Almer, J. and Karlsson, A.M. and Raghavan, S. and Bartsch, M.
    JOM 67 1528-1539 (2015)
    Advances in aircraft and land-based turbine engines have been increasing the extreme loading conditions on traditional engine components and have incited the need for improved performance with the use of protective coatings. These protective coatings shield the load-bearing super alloy blades from the high-temperature combustion gases by creating a thermal gradient over their thickness. This addition extends the life and performance of blades. A more complete understanding of the behavior, failure mechanics, and life expectancy for turbine blades and their coatings is needed to enhance and validate simulation models. As new thermal-barrier-coated materials and deposition methods are developed, strides to effectively test, evaluate, and prepare the technology for industry deployment are of paramount interest. Coupling the experience and expertise of researchers at the University of Central Florida, The German Aerospace Center, and Cleveland State University with the world-class synchrotron x-ray beam at the Advanced Photon Source in Argonne National Laboratory, the synergistic collaboration has yielded previously unseen measurements to look inside the coating layer system for in situ strain measurements during representative service loading. These findings quantify the in situ strain response on multilayer thermal barrier coatings and shed light on the elastic and nonelastic properties of the layers and the role of mechanical load and internal cooling variations on the response. The article discusses the experimental configuration and development of equipment to perform in situ strain measurements on multilayer thin coatings and provides an overview of the achievements thus far. © 2015, The Minerals, Metals & Materials Society.
    view abstractdoi: 10.1007/s11837-015-1399-3
  • 2015 • 112 Comparison of thermal barrier coating stresses via high energy X-rays and piezospectroscopy
    Manero, A., II and Sofronsky, S., II and Knipe, K. and Lacdao, C. and Smith, M. and Meid, C. and Wischek, J. and Okasinksi, J. and Almer, J. and Karlsson, A.M. and Bartsch, M. and Raghavan, S.
    53rd AIAA Aerospace Sciences Meeting (2015)
    Thermal Barrier Coatings (TBC) have been instrumental in advancing the performance and efficiency of turbine engines over the last decades. The use of high temperature ceramics has allowed increased temperatures by way of protecting the load bearing blade substrate and extending its lifetime. Today there continues to exist the need to understand the behavior of the TBC to extend the life and performance of both the TBC and the underlying substrate blades. In this study, the TBC was examined by the use of optical spectroscopy and synchrotron X-Ray di?raction to understand the strain and stress experienced by each of the layers in the coating. Raman and Photoluminescence spectroscopy were employed to examine the thermally grown oxide layer (TGO) and the ceramic top coat and to identify the influence of variations in temperature distribution. X-Ray di?raction measurements were conducted at the Advanced Photon Source, at Argonne National Laboratory allowing the in-situ investigation of variation in loading conditions including a representative flight cycle. A pre-aged specimen was used for di?raction measurements for a more mature oxide layer. Optical spectroscopy measurements provided high resolution stress maps of the oxide scale. The results from this study provide a more complete understanding as to the behavior of the TBC and its development through the lifetime, and can serve to validate and further the development numerical models. © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
    view abstractdoi: 10.2514/6.2015-0874
  • 2015 • 111 Effects of Feedstock Decomposition and Evaporation on the Composition of Suspension Plasma-Sprayed Coatings
    Mauer, G. and Schlegel, N. and Guignard, A. and Vaßen, R. and Guillon, O.
    Journal of Thermal Spray Technology 24 1187-1194 (2015)
    Emerging new applications and growing demands of plasma-sprayed coatings have initiated the development of new plasma spray processes. One of them is suspension plasma spraying (SPS). The use of liquid feedstock such as suspensions yields higher flexibility compared to the conventional atmospheric plasma spray processes as even submicron-to nano-sized particles can be processed. This allows achieving particular microstructural features, e.g., porous segmented or columnar-structured thermal barrier coatings. To exploit the potentials of such novel plasma spray processes, the plasma-feedstock interaction must be understood better. In this study, decomposition and evaporation of feedstock material during SPS were investigated, since particular difficulties can occur with respect to stoichiometry and phase composition of the deposits. Plasma conditions were analyzed by optical emission spectroscopy (OES). Experimental results are given, namely for gadolinium zirconate and for lanthanum strontium cobalt ferrite deposition. Moreover, the applied OES approach is validated by comparison with the simpler actinometry method. © 2015, ASM International.
    view abstractdoi: 10.1007/s11666-015-0250-2
  • 2015 • 110 Spectroscopic and Microscopic Investigations of Degradation Processes in Polymer Surface-Near Regions during the Deposition of SiOx Films
    Mitschker, F. and Dietrich, J. and Ozkaya, B., Dr. and De los Arcos, T., Dr. and Giner, I., Dr. and Awakowicz, P., Prof. and Grundmeier, G., Prof.
    Plasma Processes and Polymers 12 1002-1009 (2015)
    Atomic oxygen densities and fluences in a microwave plasma are determined by means of optical emission spectroscopy for different oxygen to hexamethyldisiloxane (HMDSO) ratios during deposition of SiO<inf>x</inf> and SiO<inf>x</inf>C<inf>y</inf>H<inf>z</inf> like coatings on molecularly defined organic surfaces. The plasma coatings are deposited on octadecanethiol self-assembled monolayers that serve as a sensor layer. They are used for tracing the interfacial changes induced during plasma deposition as a function of the O<inf>2</inf> to HMDSO ratio and absolutely quantified atomic oxygen fluence. The interfacial chemical changes are monitored by means of polarization modulation IR reflection-absorption spectroscopy. The data reveal that significant oxidative degradation of the sensor layer is reached for exposure to an atomic oxygen fluence of 1.0 · 1022 m-2. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/ppap.201500085
  • 2015 • 109 Thin hydroxyapatite coating on AZ91D magnesium alloy fabricated via RF-magnetron sputtering
    Mukhametkaliyev, T.M. and Surmeneva, M.A. and Mueller, M. and Prymak, O. and Epple, M. and Surmenev, R.A.
    IOP Conference Series: Materials Science and Engineering 98 (2015)
    In this study the morphology, composition, structure and wettability of radiofrequency (RF) magnetron sputter-deposited hydroxyapatite (HA) coating deposited on the surface of AZ91D magnesium alloy were investigated. The results revealed that the fabricated coating is uniform, homogeneous with the structure of the stoichiometric HA. The deposition of the HA coating did not change significantly the surface wettability of the bare alloy, however water contact angle dynamics in the case of the HA coated substrates revealed a lower rate of a droplet spreading over the surface. © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1757-899X/98/1/012027
  • 2015 • 108 Structure of Biocompatible Coatings Produced from Hydroxyapatite Nanoparticles by Detonation Spraying
    Nosenko, V. and Strutynska, N. and Vorona, I. and Zatovsky, I. and Dzhagan, V. and Lemishko, S. and Epple, M. and Prymak, O. and Baran, N. and Ishchenko, S. and Slobodyanik, N. and Prylutskyy, Y. and Klyui, N. and Temchenko, V.
    Nanoscale Research Letters 10 1-7 (2015)
    Detonation-produced hydroxyapatite coatings were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Raman spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. The source material for detonation spraying was a B-type carbonated hydroxyapatite powder. The coatings consisted of tetracalcium phosphate and apatite. The ratio depended slightly on the degree of crystallinity of the initial powder and processing parameters of the coating preparation. The tetracalcium phosphate phase was homogeneous; the apatite phase contained defects localized on the sixfold axis and consisted of hydroxyapatite and oxyapatite. Technological factors contributing to the transformation of hydroxyapatite powder structure during coating formation by detonation spraying are discussed. © 2015, Nosenko et al.
    view abstractdoi: 10.1186/s11671-015-1160-4
  • 2015 • 107 Cycling Performance of a Columnar-Structured Complex Perovskite in a Temperature Gradient Test
    Schlegel, N. and Sebold, D. and Sohn, Y.J. and Mauer, G. and Vaßen, R.
    Journal of Thermal Spray Technology 24 1205-1212 (2015)
    To increase the efficiency of turbines for the power generation and the aircraft industry, advanced thermal barrier coatings (TBCs) are required. They need to be long-term stable at temperatures higher than 1200 °C. Nowadays, yttria partially stabilized zirconia (YSZ) is applied as standard TBC material. But its long-term application at temperatures higher than 1200 °C leads to detrimental phase changes and sintering effects. Therefore, new materials have to be investigated, for example, complex perovskites. They provide high melting points, high thermal expansion coefficients and thermal conductivities of approx. 2.0 W/(m K). In this work, the complex perovskite La(Al1/4Mg1/2Ta1/4)O3 (LAMT) was investigated. It was deposited by the suspension plasma spraying (SPS) process, resulting in a columnar microstructure of the coating. The coatings were tested in thermal cycling gradient tests and they show excellent results, even though some phase decomposition was found. © 2015, ASM International.
    view abstractdoi: 10.1007/s11666-015-0254-y
  • 2015 • 106 On the role of zinc on the formation and growth of intermetallic phases during interdiffusion between steel and aluminium alloys
    Springer, H. and Szczepaniak, A. and Raabe, D.
    Acta Materialia 96 203-211 (2015)
    The effect of Zn - both within Al and as a coating on steel - on the intermetallic phase formation and growth was systematically studied in controlled experiments, simulating the interfacial reactions taking place in dissimilar solid/solid and solid/liquid joining procedures. Independent from the reaction temperature, the addition of 1.05 at.% Zn (2.5 wt.%) to Al had no effect on the reaction layers' build-up with the η phase (Al<inf>5</inf>Fe<inf>2</inf>) as the dominant component, but accelerated their parabolic growth up to a factor of 13. While Zn-coatings on steel were found to be beneficial for the regular and even formation of intermetallic reaction zones in solid/liquid joining procedures, their role in solid-state processes was found to be more complex and, if no countermeasures are taken, extremely detrimental to the joint properties. Possible reasons for the Zn-induced growth acceleration are discussed, as well as consequences for possible optimisation steps for reducing harmful effects of Zn in dissimilar joints between Al alloys and steel. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstractdoi: 10.1016/j.actamat.2015.06.028
  • 2015 • 105 Nano-hydroxyapatite-coated metal-ceramic composite of iron-tricalcium phosphate: Improving the surface wettability, adhesion and proliferation of mesenchymal stem cells in vitro
    Surmeneva, M.A. and Kleinhans, C. and Vacun, G. and Kluger, P.J. and Schönhaar, V. and Müller, M. and Hein, S.B. and Wittmar, A. and Ulbricht, M. and Prymak, O. and Oehr, C. and Surmenev, R.A.
    Colloids and Surfaces B: Biointerfaces 135 386-393 (2015)
    Thin radio-frequency magnetron sputter deposited nano-hydroxyapatite (HA) films were prepared on the surface of a Fe-tricalcium phosphate (Fe-TCP) bioceramic composite, which was obtained using a conventional powder injection moulding technique. The obtained nano-hydroxyapatite coated Fe-TCP biocomposites (nano-HA-Fe-TCP) were studied with respect to their chemical and phase composition, surface morphology, water contact angle, surface free energy and hysteresis. The deposition process resulted in a homogeneous, single-phase HA coating. The ability of the surface to support adhesion and the proliferation of human mesenchymal stem cells (hMSCs) was studied using biological short-term tests in vitro. The surface of the uncoated Fe-TCP bioceramic composite showed an initial cell attachment after 24 h of seeding, but adhesion, proliferation and growth did not persist during 14 days of culture. However, the HA-Fe-TCP surfaces allowed cell adhesion, and proliferation during 14 days. The deposition of the nano-HA films on the Fe-TCP surface resulted in higher surface energy, improved hydrophilicity and biocompatibility compared with the surface of the uncoated Fe-TCP. Furthermore, it is suggested that an increase in the polar component of the surface energy was responsible for the enhanced cell adhesion and proliferation in the case of the nano-HA-Fe-TCP biocomposites. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.colsurfb.2015.07.057
  • 2015 • 104 Wear behavior of bio-inspired and technologically structured HVOF sprayed NiCrBSiFe coatings
    Tillmann, W. and Hagen, L. and Stangier, D. and Laemmerhirt, I.-A. and Biermann, D. and Kersting, P. and Krebs, E.
    Surface and Coatings Technology 280 16-26 (2015)
    Surface modification by means of textured structures can largely enhance the tribological and wear behavior of components and tools under various environmental conditions. Continuous developments in machining processes, such as the micromilling technology, can be used to manufacture fine-scaled structures on hardened steel tool surfaces. Thus, the adjusted friction behavior, which can affect the tendency of a material to adhere to the surface, is compensated by the small number of contact points between the friction partner and the surface. Accordingly, anisotropic friction properties of such structures can lead to a locally different wear behavior. In this study, a NiCrBSiFe self-fluxing alloy is thermally sprayed onto specimens made of AISI M2 high-speed steel (HSS). Technological and bionic surface structures were applied on thermally sprayed and laser remelted substrates. Based on ball-on-disk tests, the coefficient of friction was determined and compared for different high velocity oxy fuel (HVOF) sprayed NiCrBSiFe coatings and surface textures. These experiments show that functional structures can reduce the coefficient of friction. The bio-inspired surface shows a friction reduction of approximately 35% compared to the as-sprayed and polished sample, and a reduction of 25% when compared to the remelted and smoothened surface. Moreover, the analyzed surface conditions lead to a different wear behavior than the bio-inspired structure, which possesses areas with a reduced oxidational wear and less adhesion when compared to the other surface conditions. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2015.08.055
  • 2015 • 103 Thermally sprayed finestructured WC-12Co coatings finished by ball burnishing and grinding as an innovative approach to protect forming tools against wear
    Tillmann, W. and Hollingsworth, P. and Baumann, I. and Hiegemann, L. and Weddeling, C. and Tekkaya, A.E. and Rausch, S. and Biermann, D.
    Surface and Coatings Technology 268 134-141 (2015)
    The forming of high-strength steel sheets offers novel possibilities to produce lightweight structural parts with a high stiffness for the aircraft and automotive industries. However, the employment of such sheet materials leads to intense wear and thus reduces the lifetime of forming tools. At the same time, the requirements concerning their performance, their geometrical complexity, and their shape accuracy have been significantly increased. To counteract this problem, the tools are either treated by different thermo-chemical processes (e.g. hardening, nitriding) or are coated using thin film techniques such as PVD or CVD. In this study, thermal spraying is presented as a cost efficient and more flexible approach to protect the surface of forming tools against wear. For this purpose, planar samples as well as cylindrical deep drawing dies were coated by means of the high velocity oxy-fuel (HVOF) flame spraying technique, utilizing a fine WC-12Co powder (agglomerate size 2-10. μm) with a carbide size of 400. nm. Prior to the coating operation, a comprehensive parameter optimization was performed based on the statistical design of experiments (DOE) to achieve coatings with improved mechanical and tribological properties. The planar samples were used to ascertain the sliding and rolling wear behavior within two standardized test methods (Ball-on-Disc and Taber Abraser tests). The coated dies were smoothened by ball burnishing as well as grinding and afterwards evaluated within the deep drawing of high strength (HC380LA) steel sheets. In addition, the results were compared to those achieved with an uncoated conventional cold work steel die, which is commonly employed for this operation. In contrast to the cold work steel, both coated dies, the ball burnished as well as the ground die, showed a significantly better wear performance after the forming of 10,000 parts. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2014.06.039
  • 2015 • 102 Tribological investigation of bionic and micro-structured functional surfaces
    Tillmann, W. and Stangier, D. and Hagen, L. and Biermann, D. and Kersting, P. and Krebs, E.
    Materialwissenschaft und Werkstofftechnik 46 1096-1104 (2015)
    An established concept adjusting tribological properties and for increasing the wear resistance is presented by coatings. In addition to the material adaption of surfaces, there are efforts of applying structures on tool active parts in order to allow a further adjustment on the property profile. For this reason, the presented article investigates the influence of bionic and technologically textured surfaces on the friction and wear behavior with and without near-net shaped wear-resistant PVD coatings. Based on the example of nature, a honeycombed surface structure discovered on the head of scarab beetles as well as a dimple structure optimized for the manufacturing time were transferred on HSS steel by means of micro-milling. The analyses focus on the influence of the surface structures, the effects of PVD coatings and their interactions on the friction and wear behavior. The investigations show that the tribological properties depend on each surface structure and the material pairing. Both the technological and the bionic structures show a reduction of the friction coefficient in combination with the material pairing 100Cr6 and WCCo compared to polished samples. Furthermore, it is shown that the CrAlN coating has no influence on the friction behavior, but rather leads to the desired increase in the wear resistance. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201500434
  • 2015 • 101 Large scale Molecular Dynamics simulation of microstructure formation during thermal spraying of pure copper
    Wang, T. and Begau, C. and Sutmann, G. and Hartmaier, A.
    Surface and Coatings Technology 280 72-80 (2015)
    Thermal spray processes are widely used for the manufacture of advanced coating systems, e.g. metallic coatings for wear and corrosion protection. The desired coating properties are closely related to the microstructure, which is highly influenced by the processing parameters, such as temperature, size and velocity of the sprayed particles. In this paper, large scale Molecular Dynamics simulations are conducted to investigate the microstructure formation mechanisms during the spraying process of hot nano-particles onto a substrate at room temperature using pure copper as a benchmark material representing for a wider class of face-centered-cubic metals. To evaluate the influence of processing parameters on the coating morphology, a number of simulations are performed in which the initial temperature, size and velocity of copper particles are systematically varied in order to investigate the thermal and microstructural evolution during impaction. Two distinct types of microstructural formation mechanisms, resulting in different coating morphologies, are observed in the present investigation, which are either governed by plastic deformation or by the process of melting and subsequent solidification. Furthermore, a thermodynamically motivated model as a function of the particle temperature and velocity is developed, which predicts the microstructural mechanisms observed in the simulations. The results provide an elementary insight into the microstructure formation mechanisms on an atomistic scale, which can serve as basic input for continuum modeling of thermal spray process. © 2015 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2015.08.034
  • 2015 • 100 Evolution of microstructure and mechanical properties of coated Co-base superalloys during heat treatment and thermal exposure
    Webler, R. and Ziener, M. and Neumeier, S. and Terberger, P.J. and Vaßen, R. and Göken, M.
    Materials Science and Engineering A 628 374-381 (2015)
    New γ'-strengthened Co-base superalloys show an interesting potential for high temperature applications. However, protective coatings are needed as for Ni-base superalloys to ensure sufficient oxidation and corrosion resistance. Therefore the properties of a commercial coating on a multinary new γ'-strengthened Co-base superalloy have been studied. Especially the influence of the coating process on the substrate also after long term annealing is discussed. It was found that the highly deformed areas at the coating-substrate interface indicated by a high local misorientation and caused by the sandblasting process led to a recrystallization of the interdiffusion zone during the age hardening heat treatment. A chemical gradient of γ and γ' promoting elements was found in the interdiffusion zone causing a change in hardness as measured by nanoindentation. Depending on the composition two separate recrystallized regions formed in the interdiffusion zone, one with single phase γ-(Co,Ni) and the other with a cellular two phase microstructure of discontinuously grown γ and γ'. © 2015 Elsevier B.V.
    view abstractdoi: 10.1016/j.msea.2015.01.060
  • 2015 • 99 Detection of elevated regions in surface images from laser beam melting processes
    Zur Jacobsmuhlen, J. and Kleszczynski, S. and Witt, G. and Merhof, D.
    IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society 1270-1275 (2015)
    Laser Beam Melting (LBM) is a promising Additive Manufacturing technology that allows the layer-based production of complex metallic components suitable for industrial applications. Widespread application of LBM is hindered by a lack of quality management and process control. Elevated regions in produced layers pose a major risk to process stability as collisions between the powder coating mechanism and the part may occur, which cause damages to either one or even both. We train a classifier-based detector for elevated regions in laser exposure result images. For this purpose we acquire two high resolution layer images: one after laser exposure and another one after powder deposition for the next layer. Ground truth labels for critical regions are obtained from analysis of the latter, where elevated regions are not covered by powder. We compute dense descriptors (HOG, DAISY, LBP) on the surface image after laser exposure and compare their predictive power. The top five descriptor configurations are used to optimize parameters of Random Forest, Support Vector Machine and Stochastic Gradient Descent (SGD) classifiers. We validate the detectors with optimized parameters using cross-validation on 281 images from three build jobs. Using a DAISY descriptor with a SGD classifier we achieve a F1-score of 0.670. The presented method enables detection of elevated regions before powder coating is performed and can be extended to other surface inspection tasks in LBM layer images. Detection results can be used to assess LBM process parameters with respect to process stability during process design and for quality management in production. © 2015 IEEE.
    view abstractdoi: 10.1109/IECON.2015.7392275
  • 2014 • 98 Tribological and mechanical properties of Ti/TiAlN/TiAlCN nanoscale multilayer PVD coatings deposited on AISI H11 hot work tool steel
    Al-Bukhaiti, M.A. and Al-Hatab, K.A. and Tillmann, W. and Hoffmann, F. and Sprute, T.
    Applied Surface Science 318 180-190 (2014)
    A new [Ti/TiAlN/TiAlCN]5 multilayer coatings were deposited onto polished substrate AISI H11 (DIN 1.2343) steel by an industrial magnetron sputtering device. The tribological performance of the coated system was investigated by a ball-on-disk tribometer against 100Cr6 steel and Al2O3 balls. The friction coefficients and specific wear rates were measured at various normal loads (2, 5, 8, and 10 N) and sliding velocities (0.2, 0.4, and 0.8 m/s) in ambient air and dry conditions. The phase structure, composition, wear tracks morphologies, hardness, and film/substrate adhesion of the coatings were characterized by light-microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), 3D-surface analyzer, nanoindentation, and scratch tests. Results showed that the deposited coatings showed low wear rates in the scale of 10-15 m3/N m, low friction coefficients against 100Cr6 and Al2O3 balls in the range of 0.25-0.37, and good hardness in the range of 17-20 GPa. Results also revealed that the friction coefficients and disc wear rates decrease and increase, respectively with the increase in normal load and sliding velocity for both coating/Al2O3 and coating/100Cr6 sliding system. Compared with the uncoated-H11 substrate, the deposited coating exhibited superior tribological and mechanical properties. The dominant wear mechanism was abrasive wear for coating/Al2O3 pair, while for coating/100Cr6 pair, a combination of mild adhesive wear, severe adhesive wear, and abrasive wear (extensive plowing) were the dominant wear mechanisms at different applied normal loads. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2014.03.026
  • 2014 • 97 A Shape-adaptive, Antibacterial-coating of immobilized Quaternary-ammonium compounds tethered on hyperbranched polyurea and its mechanism of action
    Asri, L.A.T.W. and Crismaru, M. and Roest, S. and Chen, Y. and Ivashenko, O. and Rudolf, P. and Tiller, J.C. and Van Der Mei, H.C. and Loontjens, T.J.A. and Busscher, H.J.
    Advanced Functional Materials 24 346-355 (2014)
    Quaternary-ammonium-compounds are potent cationic antimicrobials used in everyday consumer products. Surface-immobilized, quaternary-ammonium-compounds create an antimicrobial contact-killing coating. We describe the preparation of a shape-adaptive, contact-killing coating by tethering quaternary-ammonium- compounds onto hyperbranched polyurea coatings, able to kill adhering bacteria by partially enveloping them. Even after extensive washing, coatings caused high contact-killing of Staphylococcus epidermidis, both in culture-based assays and through confocal-laser-scanning-microscopic examination of the membrane-damage of adhering bacteria. In culture-based assays, at a challenge of 1600 CFU/cm2, contact-killing was &gt;99.99%. The working-mechanism of dissolved quaternary-ammonium-compounds is based on their interdigitation in bacterial membranes, but it is difficult to envisage how immobilized quaternary-ammonium-molecules can exert such a mechanism of action. Staphylococcal adhesion forces to hyperbranched quaternary-ammonium coatings were extremely high, indicating that quaternary-ammonium-molecules on hyperbranched polyurea partially envelope adhering bacteria upon contact. These lethally strong adhesion forces upon adhering bacteria then cause removal of membrane lipids and eventually lead to bacterial death. Shape-adaptive, hyperbranched polyurea with quaternary ammonium compounds. The preparation of AB2 monomers and the covalently attached hyperbranched polyurea coatings with polyethyleneimine covalently coupled to hyperbranched polyurea coatings. The coatings demonstrate high contact-killing efficacies toward adhering staphylococci, without any demonstrable leaching of antibacterial compounds. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adfm.201301686
  • 2014 • 96 CrN/AlN nanolaminate coatings deposited via high power pulsed and middle frequency pulsed magnetron sputtering
    Bagcivan, N. and Bobzin, K. and Ludwig, Al. and Grochla, D. and Brugnara, R.H.
    Thin Solid Films 572 153-160 (2014)
    Nanolaminate coatings based on transition metal nitrides such as CrN, AlN and TiN deposited via physical vapor deposition (PVD) have shown great advantage as protective coatings on tools and components subject to high loads in tribological applications. By varying the individual layer materials and their thicknesses it is possible to optimize the coating properties, e.g. hardness, Young's modulus and thermal stability. One way for further improvement of coating properties is the use of advanced PVD technologies. High power pulsed magnetron sputtering (HPPMS) is an advancement of pulsed magnetron sputtering (MS). The use of HPPMS allows a better control of the energetic bombardment of the substrate due to the higher ionization degree of metallic species. It provides an opportunity to influence chemical and mechanical properties by varying the process parameters. The present work deals with the development of CrN/AlN nanolaminate coatings in an industrial scale unit by using two different PVD technologies. Therefore, HPPMS and mfMS (middle frequency magnetron sputtering) technologies were used. The bilayer period Λ, i.e. the thickness of a CrN/AlN double layer, was varied between 6.2nm and 47.8 nm by varying the rotational speed of the substrate holders. In a second step the highest rotational speed was chosen and further HPPMS CrN/AlN coatings were deposited applying different HPPMS pulse lengths (40, 80, 200 μs) at the same mean cathode power and frequency. Thickness, morphology, roughness and phase composition of the coatings were analyzed by means of scanning electron microscopy (SEM), confocal laser microscopy, and X-ray diffraction (XRD), respectively. The chemical composition was determined using glow discharge optical emission spectroscopy (GDOES). Detailed characterization of the nanolaminate was conducted by transmission electron microscopy (TEM). The hardness and the Young's modulus were analyzed by nanoindentation measurements. The residual stress was determined via Si microcantilever curvature measurements. The phase analysis revealed the formation of h-Cr2N, c-CrN and c-AlN mixed phases for the mfMS CrN/AlN coatings, whereas the HPPMS coatings exhibited only cubic phases (c-CrN, c-AlN). A hardness of 31.0 GPa was measured for the HPPMS coating with a bilayer period of 6.2 nm. The decrease of the HPPMS pulse length at constant mean power leads to a considerable increase of the cathode current on the Cr and Al target associated with an increased ion flux towards the substrate. Furthermore, it was observed that the deposition rate of HPPMS CrN/AlN decreases with shorter pulse lengths, so that a CrN/AlN coating with a bilayer period of 2.9 nm, a high hardness of 40.8 GPa and a high compressive stress (- 4.37 GPa) was achieved using a short pulse length of 40 μs. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.tsf.2014.06.058
  • 2014 • 95 Optimization of guide pads for the BTA deep hole drilling of high alloyed steels by microfinishing
    Biermann, D. and Abrahams, H. and Goeke, S.
    Production Engineering 8 33-40 (2014)
    The boring and trepanning association deep hole drilling of materials with a high tendency to adhesion, such as high alloyed-steels, is characterized by a poor surface quality of the bore hole. Material particles adhere to the guide pads that are positioned on the circumference of the drill head and that are normally responsible for the outstanding workpiece quality. In order to prevent this mechanism the guide pads were coated with an innovative amorphous and tetrahedral bonded (ta-C)-coating. This coating has a reduced friction coefficient of 0.1 against steel and a hardness coefficient of about 7,000 HV. To use the benefits of this ta-C-coating the pre- and the after-treatment of the uncoated carbide substrate and ta-C-coated guide pads are essential. For these process steps a microfinishing process was carried out as an alternative to the conventional treatment by polishing and brushing. The microfinishing of the uncoated guide pads effects a smooth surface that is necessary for an optimum bonding strength of the ta-C-coating at the carbide substrate. Furthermore the chamfer edge in the lead-in-area is rounded which reduces the mechanical load at this specific area during the process. The finishing process of the coated guide pads reduces the coating defects and improves the friction coefficient. Thus, the wear behavior of the guide pads is improved because of the better friction conditions during the drilling process of high alloyed steels. © 2013 German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-013-0505-z
  • 2014 • 94 Effect of cutting edge preparation of coated tools on their performance in milling various materials
    Bouzakis, K.D. and Bouzakis, E. and Kombogiannis, S. and Makrimallakis, S. and Skordaris, G. and Michailidis, N. and Charalampous, P. and Paraskevopoulou, R. and M'Saoubi, R. and Aurich, J.C. and Barthelmä, F. and Biermann, D. an...
    CIRP Journal of Manufacturing Science and Technology 7 264-273 (2014)
    The cutting edges of coated tools are commonly treated in separate production steps during tool manufacturing. Various methods can be employed, focusing on the cutting edge strengthening by its rounding or by more complicated geometries including chamfer and optimized tool wedge radius and angles. The efficiency of diverse cutting edge preparations on the wear behaviour of coated tools, in milling different materials, was investigated in the framework of a cooperative project of the Scientific Committee "Cutting" of the International Academy for Production Engineering (CIRP). In this activity twenty academic and industrial partners were involved according to a predefined project plan. © 2014 CIRP.
    view abstractdoi: 10.1016/j.cirpj.2014.05.003
  • 2014 • 93 Development and analysis of microstructures for the transplantation of thermally sprayed coatings
    Freiburg, D. and Biermann, D. and Peuker, A. and Kersting, P. and Maier, H.-J. and Möhwald, K. and Knödler, P. and Otten, M.
    Procedia CIRP 14 245-250 (2014)
    Thermally sprayed coatings and tribological surfaces are a point of interest in many industrial sectors. They are used for better wear resistance of lightweight materials or for oil retention on surfaces. Lightweight materials are often used in the automotive industry as a weight-saving solution in the production of engine blocks. For this, it is necessary to coat the cylinder liners to ensure wear resistance. In most cases, the coating is sprayed directly onto the surface. Previous research has shown that it is possible to transfer these coatings inversely onto other surfaces [1]. This was achieved with plasma sprayed coatings which were transplanted onto pressure-casted surfaces. These transplanted surfaces exhibited better adhesive strength, smoother surfaces, and lower form deviation compared to directly coated surfaces. Additionally, it was shown that even microstructures of a surface coated by plasma spraying can be transferred to pressure-casted surfaces. This paper presents the development and micromilling of different microstructures for transferring thermally sprayed coatings onto pressure-casted surfaces. In the development process, microstructures with different shapes and aspect ratios as well as thin tribological surfaces are designed in order to evaluate the advantages and limitations of the transplantation process. In subsequent experiments, the micromilling process and a simulation of the coating transplantation are presented and analyzed. © 2014 Published by Elsevier B.V.
    view abstractdoi: 10.1016/j.procir.2014.03.054
  • 2014 • 92 Photocatalytic and antimicrobial Ag/ZnO nanocomposites for functionalization of textile fabrics
    Ibǎnescu, M. and Muşat, V. and Textor, T. and Badilita, V. and Mahltig, B.
    Journal of Alloys and Compounds 610 244-249 (2014)
    The utilization of ZnO nanoparticles with photocatalytic and antimicrobial activity for textile treatment has received much attention in recent years. Since silver is a well-known but more expensive antibacterial material, it is of interest to study the extent to which a small amount of silver increases the photocatalytic and antimicrobial activity of the less expensive zinc oxide nanoparticles. This paper reports on the preparation of Ag/ZnO composite nanoparticles by reducing silver on the surface of commercial ZnO nanoparticles dispersed in isopropanol. Crystalline structure, particle size and band gap energy of as-prepared composite nanoparticles were investigated by X-ray diffraction and UV-Vis absorption measurements. Long term stable sols of ZnO and Ag/ZnO nanoparticles were prepared and applied as liquid coating agent for textile treatment, in combination with inorganic-organic hybrid polymer binder sols prepared from the precursors 3-glycidyloxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS). The coating process was carried out on cotton fabrics and cotton/polyester blended fabrics using the pad-dry-cure method. The photocatalytic activity of the nanoparticles, as prepared or applied on textile fabrics, was studied through the degradation of the dye methylene blue (MB) in water under the UV irradiation. The antimicrobial activity of the nanoparticles applied on textile fabrics, was tested against the Gram-negative bacterium Escherichia coli and Gram-positive Micrococcus luteus. © 2014 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jallcom.2014.04.138
  • 2014 • 91 Synchrotron XRD measurements mapping internal strains of thermal barrier coatings during thermal gradient mechanical fatigue loading
    Knipe, K. and Manero, A.C., II and Sofronsky, S. and Okasinski, J. and Almer, J. and Wischek, J. and Meid, C. and Karlsson, A. and Bartsch, M. and Raghavan, S., Prof.
    Proceedings of the ASME Turbo Expo 6 (2014)
    An understanding of the high temperature mechanics experienced in Thermal Barrier Coatings (TBC) during cycling conditions would be highly beneficial to extending the lifespan of the coatings. This study will present results obtained using synchrotron x-rays to measure depth resolved strains in the various layers of TBCs under thermal mechanical loading and a superposed thermal gradient. Tubular specimens, coated with Yttria Stabilized Zirconia (YSZ) and an aluminum containing nickel alloy as a bond coat both through Electron Beam - Physical Vapor Deposition (EB-PVD), were subjected to external heating and controlled internal cooling generating a thermal gradient across the specimen's wall. Temperatures at the external surface were in excess of 1000°C. Throughout high temperature testing, 2-D high-resolution XRD strain measurements are taken at various locations through the entire depth of the coating layers. Across the YSZ a strain gradient was observed showing higher compressive strain at the interface to the bond coat than towards the surface. This behavior can be attributed to the specific microstructure of the EB-PVD-coating, which reveals higher porosity at the outer surface than at the interface to the bond coat, resulting in a lower in plane modulus near the surface. This location at the interface displays the most significant variation due to applied load at room temperature with this effect diminishing at elevated uniform temperatures. During thermal cycling with a thermal gradient and mechanical loading, the bond coat strain moves from a highly tensile state at room temperature to an initially compressive state at high temperature before relaxing to zero during the high temperature hold. The results of these experiments give insight into previously unseen material behavior at high temperature which can be used to develop an increased understanding of various failure modes and their causes. Copyright © 2014 by ASME.
    view abstractdoi: 10.1115/GT2014-26919
  • 2014 • 90 Macroinitiator-mediated photoreactive coating of membrane surfaces with antifouling hydrogel layers
    Lei, J. and Ulbricht, M.
    Journal of Membrane Science 455 207-218 (2014)
    Applying a hydrophilic layer to the membrane surface is one common strategy to control membrane fouling. This work focuses on hydrophilic membrane coating materials synthesized from poly(ethylene glycol) (PEG)-based hydrogels and application of thin hydrogel layers from such polymers on the surface of composite polyamide nanofiltration membranes. The approach of using macroinitiator-mediated synthesis cum anchoring of a hydrogel layer on the membrane was explored to reduce or avoid homopolymerization in bulk solution and prevent delamination of the antifouling layer from membrane surface. Cationic macroinitiators were based on poly(2-dimethylamino-ethyl methacrylate-co-2-hydroxyethyl methacrylate) obtained by radical copolymerization and comprised photoinitiator side groups linked to the poly(2-hydroxyethyl methacrylate) segments. Adsorption of the macroinitiator to the membrane surface and preparation of hydrogel coatings on polyamide composite membranes via photo-initiated in situ graft and cross-linking copolymerization were studied in detail. The modification degree and its effect on the membrane properties was characterized with respect to membrane chemistry by ATR-IR spectroscopy, surface charge by zeta potential, surface wettability by contact angle, and with respect to pure water permeability and salt rejection. The propensity to protein fouling was also investigated. The results indicate that hydrogel modified membranes have an improved fouling resistance compared to pristine membranes, and that this approach has the potential to become a generic approach for a controlled surface functionalization using a simple two-step protocol. © 2014.
    view abstractdoi: 10.1016/j.memsci.2013.12.059
  • 2014 • 89 Plasma Spraying of Ceramics with Particular Difficulties in Processing
    Mauer, G. and Schlegel, N. and Guignard, A. and Jarligo, M.O. and Rezanka, S. and Hospach, A. and Vaßen, R.
    Journal of Thermal Spray Technology 24 30-37 (2014)
    Emerging new applications and growing demands of plasma-sprayed coatings initiate the development of new materials. Regarding ceramics, often complex compositions are employed to achieve advanced material properties, e.g., high thermal stability, low thermal conductivity, high electronic and ionic conductivity as well as specific thermo-mechanical properties and microstructures. Such materials however, often involve particular difficulties in processing by plasma spraying. The inhomogeneous dissociation and evaporation behavior of individual constituents can lead to changes of the chemical composition and the formation of secondary phases in the deposited coatings. Hence, undesired effects on the coating characteristics are encountered. In this work, examples of such challenging materials are investigated, namely pyrochlores applied for thermal barrier coatings as well as perovskites for gas separation membranes. In particular, new plasma spray processes like suspension plasma spraying and plasma spray-physical vapor deposition are considered. In some cases, plasma diagnostics are applied to analyze the processing conditions. © 2014, ASM International.
    view abstractdoi: 10.1007/s11666-014-0149-3
  • 2014 • 88 Deposition and oxidation of oxide-dispersed CoNiCrAlY bondcoats
    Okada, M. and Vassen, R. and Karger, M. and Sebold, D. and Mack, D. and Jarligo, M.O. and Bozza, F.
    Journal of Thermal Spray Technology 23 147-153 (2014)
    CoNiCrAlY powder and nano-size alumina powder were milled by a high-energy-attrition ball-mill, and an oxide-dispersed powder was produced with a mixed structure of metal and alumina in each particle. The oxide-dispersed bond coat powder was deposited by HVOF. Pores, however, were observed in the coating since the alumina was deposited without sufficient melting. Isothermal oxidation tests were carried out for the bond coat specimens at a temperature of 1373 K up to 1000 h in air. As a result, oxidation proceeded inside the coating, since oxygen penetrated through pores formed in the dispersed alumina. However, the authors find that another deposition using higher power levels led to a bond coat without pores. A commercially available oxide-dispersed CoNiCrAlY powder was also deposited by HVOF and VPS, and isothermal oxidation tests were performed. The analysis clarifies that the HVOF bond coat exhibited the thinnest thermally grown oxide than those of the VPS bond coat and conventional metallic bond coat. Furnace cycling tests were conducted using the specimens with an additional ceramic thermal-barrier coating. The specimen with the bond coat sprayed by VPS using commercial oxide-dispersed powder showed almost same number of cycles to delamination compared with the specimen with the conventional metal bond coat. © 2013 ASM International.
    view abstractdoi: 10.1007/s11666-013-0037-2
  • 2014 • 87 Five-axis grinding of wear-resistant, thermally sprayed coatings on free-formed surfaces
    Rausch, S. and Biermann, D. and Kersting, P.
    Production Engineering 8 423-429 (2014)
    The abrasive wear resistance of tribologically stressed free-formed surfaces can be increased with thermally sprayed tungsten carbide coatings. In order to improve the surface topographies and shape accuracies, the workpieces must be finished prior to industrial application. A suitable machining process is NC grinding on five-axis machining centres using abrasive mounted points. However, the high hardness of the applied coatings and the small diameter of the utilized tools pose a great challenge for the process design. In this paper both, the results of fundamental investigations on the grinding of tungsten carbide coatings as well as a process optimization for the finishing of a coated forming tool are presented. This includes the heat transfer into the coating and the tool wear during the grinding process as well as the wear behaviour of the coating in dependence of the generated surface topography. In order to achieve a smooth surface, elastic-bonded diamond tools were used during polishing in a multi-stage machining process. © 2014 German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-014-0537-z
  • 2014 • 86 Columnar-Structured Mg-Al-Spinel Thermal Barrier Coatings (TBCs) by Suspension Plasma Spraying (SPS)
    Schlegel, N. and Ebert, S. and Mauer, G. and Vaßen, R.
    Journal of Thermal Spray Technology 24 144-151 (2014)
    The suspension plasma spraying (SPS) process has been developed to permit the feeding of sub-micrometer-sized powder into the plasma plume. In contrast to electron beam-physical vapor deposition and plasma spray-physical vapor deposition, SPS enables the cost-efficient deposition of columnar-structured coatings. Due to their strain tolerance, these coatings play an important role in the field of thermal barrier coatings (TBCs). In addition to the cost-efficient process, attention was turned to the TBC material. Nowadays, yttria partially stabilized zirconia (YSZ) is used as standard TBC material. However, its long-term application at temperatures higher than 1200 °C is problematic. At these high temperatures, phase transitions and sintering effects lead to the degradation of the TBC system. To overcome those deficits of YSZ, Mg-Al-spinel was chosen as TBC material. Even though it has a lower melting point (~2135 °C) and a higher thermal conductivity (~2.5 W/m/K) than YSZ, Mg-Al-spinel provides phase stability at high temperatures in contrast to YSZ. The Mg-Al-spinel deposition by SPS resulted in columnar-structured coatings, which have been tested for their thermal cycling lifetime. Furthermore, the influence of substrate cooling during the spraying process on thermal cycling behavior, phase composition, and stoichiometry of the Mg-Al-spinel has been investigated. © 2014, ASM International.
    view abstractdoi: 10.1007/s11666-014-0138-6
  • 2014 • 85 Simulation of grinding processes using finite element analysis and geometric simulation of individual grains
    Siebrecht, T. and Biermann, D. and Ludwig, H. and Rausch, S. and Kersting, P. and Blum, H. and Rademacher, A.
    Production Engineering 8 345-353 (2014)
    The wear-resistance of sheet metal forming tools can be increased by thermally sprayed coatings. However, without further treatment, the high roughness of the coatings leads to poor qualities of the deep drawn sheet surfaces. In order to increase the surface quality of deep drawing tools, grinding on machining centers is a suitable solution. Due to the varying engagement situations of the grinding tools on free-formed surfaces, the process forces vary as well, resulting in inaccuracies of the ground surface shape. The grinding process can be optimized by means of a simulative prediction of the occurring forces. In this paper, a geometric-kinematic simulation coupled with a finite element analysis is presented. Considering the influence of individual grains, an additional approximation to the resulting topography of the ground surface is possible. By using constructive solid geometry and dexel modeling techniques, multiple grains can be simulated with the geometric-kinematic approach simultaneously. The process forces are predicted with the finite element method based on an elasto-plastic material model. Single grain engagement experiments were conducted to validate the simulation results. © 2014 German Academic Society for Production Engineering (WGP).
    view abstractdoi: 10.1007/s11740-013-0524-9
  • 2014 • 84 Influence of substrate pre-treatments on residual stresses and tribo-mechanical properties of TiAlN-based PVD coatings
    Sprute, T. and Tillmann, W. and Grisales, D. and Selvadurai, U. and Fischer, G.
    Surface and Coatings Technology 260 369-379 (2014)
    Residual stresses in the substrate and in the PVD coating have a significant influence on the coating adhesion and lifespan of machining as well as forming tools. Therefore, the understanding and control of the system's residual stresses will lead to a better performance of the coated components. Moreover, although investigations were conducted in the field of stress analysis of PVD coatings, they do not focus on interdependencies of residual stresses in the substrate and in the coating. In this investigation, three different metallographically prepared substrates were used. SiC grinding, diamond grinding, and SiC grinding and plasma nitriding preparations were selected, due to the substantial differences in their final residual stress states. Additionally, a Ti/TiAlN multilayer coating and a reference TiAlN monolayer were deposited on each pre-treated substrate. Their initial and final residual stress states were measured by means of X-ray diffraction. In addition to the residual stress analyses, tribo-mechanical tests, such as nano-indentation, ball-on-disc, and scratch tests were performed in order to correlate the results with these residual stress states. © 2014 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2014.08.075
  • 2014 • 83 Sol-Gel deposited thermographic phosphors as possible thermal history coatings
    Stenders, D. and Karadagli, I. and Pflitsch, C. and Atakan, B.
    IET Conference Publications 2014 (2014)
    In many engineering applications surface temperatures have to be measured accurately. Sometimes the maximum temperature reached by a surface within its lifetime is even more important than its actual temperature. In order to obtain information about such maximum temperatures, so called temperature history sensors can be applied. One idea to obtain such information, which is followed in the actual work, is to deposit doped oxides with phosphorescence properties which are depending on the crystal structure of the host oxide. Thus, if the crystal structure is changing at a certain temperature, this change could also be detected by a simple phosphorescence lifetime measurement afterwards. In the present work, two materials were investigated. Yttria doped with terbium and europium and alumina doped with europium. Both materials were deposited as thin films with the sol gel technique using a newly developed automated spray coating set-up. The samples were heated twice: once for calcination at a given temperature and then a second time by annealing them at different temperatures. After each of the two treatments the phosphorescence lifetimes were investigated. The first procedure is intrinsic for the production of phosphorescing material. The second annealing simulates the high temperature treatment within an application. It is found that the phosphorescence lifetime is changed in most cases, when the second annealing temperature is higher than the first calcination temperature. Thus, a certain design or alignment of the detected maximum temperature is possible. For the doped yttria, the lifetimes increase by ca. 20% after the second treatment at higher temperatures, while for doped alumina a reduction of the lifetimes by more than 50% is observed. In total this may be a promising way for obtaining adjustable temperature history sensors.
    view abstractdoi: 10.1049/cp.2014.0537
  • 2014 • 82 Metal matrix composites deposition in twin wire arc spraying utilizing an external powder injection composition
    Tillmann, W. and Abdulgader, M. and Hagen, L. and Nellesen, J.
    Journal of Thermal Spray Technology 23 40-50 (2014)
    The powder injection parameters, the location of the injection port, as well as the metal matrix composites are important features, which determine the deposition efficiency and embedding behavior of hard materials in the surrounding matrix of the twin wire arc-spraying process. This study investigates the applicability of external powder injection and aims to determine whether the powder injection parameters, the location, and the material combination (composition of the matrix as well as hard material) need to be specifically tailored. Therefore, the position of the injection port in relation to the arc zone was altered along the spraying axis and perpendicular to the arc. The axial position of the injection port determines the thermal activation of the injected powder. An injection behind the arc, close to the nozzle outlet, seems to enhance the thermal activation. The optimal injection positions of different hard materials in combination with zinc-, nickel- and iron-based matrices were found to be closer to the arc zone utilizing a high-speed camera system. The powder size, the mass of the particle, the carrier gas flow, and the electric insulation of the hard material affect the perpendicular position of the radial injection port. These findings show that the local powder injection, the wetting behavior of particles in the realm of the molten pool as well as the atomization behavior of the molten pool all affect the embedding behavior of the hard material in the surrounded metallic matrix. Hardness measurement by means of nanoindentation and EDX analysis along transition zones were utilized to estimate the bonding strength. The observation of a diffusion zone indicates a strong metallurgical bonding for boron carbides embedded in steel matrix. © 2013 ASM International.
    view abstractdoi: 10.1007/s11666-013-0044-3
  • 2014 • 81 Wear analysis of thermal spray coatings on 3D surfaces
    Tillmann, W. and Luo, W. and Selvadurai, U.
    Journal of Thermal Spray Technology 23 245-251 (2014)
    Even though the application of thermal spray coatings on complex geometries gained a greater interest in the last decade, the effect of different geometrical features on the wear behavior is still ill-defined. In this study, the wear resistance of FTC-FeCSiMn coated 3D surfaces was investigated. The wear test was carried out by means of two innovative testing procedures. The first test is a Pin-on-Tubes test where the rotating motion is realized by a lathe chuck. The specimens in the second test were fixed on the table and a robot arm operated the pin. This wear test was applied on specimens with concave or convex surfaces. The residual stresses, which were determined by means of an incremental hole-drilling method, show a dependency on the substrate geometry. The obtained stresses were put in relation to the different radii. After the wear test, a 3D-profilometer determined the wear volume and the sections of the coatings were characterized by a scanning electron microscope. The results indicate that the wear resistance is strongly influenced by the geometry of the substrate. © 2013 ASM International.
    view abstractdoi: 10.1007/s11666-013-9983-y
  • 2014 • 80 Efficient Large-Scale Coating Microstructure Formation Using Realistic CFD Models
    Wiederkehr, T. and Müller, H.
    Journal of Thermal Spray Technology 24 283-295 (2014)
    For the understanding of physical effects during the formation of thermally sprayed coating layers and the deduction of the macroscopic properties of a coating, microstructure modeling and simulation techniques play an important role. In this contribution, a coupled simulation framework consisting of a detailed, CFD-based single splat simulation, and a large-scale coating build-up simulation is presented that is capable to compute large-scale, three-dimensional, porous microstructures by sequential drop impingement of more than 10,000 individual particles on multicore workstation hardware. Due to the geometry-based coupling of the two simulations, the deformation, cooling, and solidification of every particle is sensitive to the hit surface area and thereby pores develop naturally in the model. The single splat simulation employs the highly parallel Lattice-Boltzmann method, which is well suited for GPU-acceleration. In order to save splat calculations, the coating simulation includes a database-driven approach that re-uses already computed splats for similar underground shapes at the randomly chosen impact sites. For a fast database search, three different methods of efficient pre-selection of candidates are described and compared against each other. © 2014, ASM International.
    view abstractdoi: 10.1007/s11666-014-0194-y
  • 2014 • 79 Evaluation of pulsed laser ablation in liquids generated gold nanoparticles as novel transfection tools: Efficiency and cytotoxicity
    Willenbrock, S. and Durán, M.C. and Barchanski, A. and Barcikowski, S. and Feige, K. and Nolte, I. and Murua Escobar, H.
    Proceedings of SPIE - The International Society for Optical Engineering 8972 (2014)
    Varying transfection efficiencies and cytotoxicity are crucial aspects in cell manipulation. The utilization of gold nanoparticles (AuNP) has lately attracted special interest to enhance transfection efficiency. Conventional AuNP are usually generated by chemical reactions or gas pyrolysis requiring often cell-toxic stabilizers or coatings to conserve their characteristics. Alternatively, stabilizer- and coating-free, highly pure, colloidal AuNP can be generated by pulsed laser ablation in liquids (PLAL). Mammalian cells were transfected efficiently by addition of PLAL-AuNP, but data systematically evaluating the cell-toxic potential are lacking. Herein, the transfection efficiency and cytotoxicity of PLAL AuNP was evaluated by transfection of a mammalian cell line with a recombinant HMGB1/GFP DNA expression vector. Different methods were compared using two sizes of PLAL-AuNP, commercialized AuNP, two magnetic NP-based protocols and a conventional transfection reagent (FuGENE HD; FHD). PLAL-AuNP were generated using a Spitfire Pro femtosecond laser system delivering 120 fs laser pulses at a wavelength of 800 nm focusing the fs-laser beam on a 99.99% pure gold target placed in ddH2O. Transfection efficiencies were analyzed after 24h using fluorescence microscopy and flow cytometry. Toxicity was assessed measuring cell proliferation and percentage of necrotic, propidium iodide positive cells (PI %). The addition of PLAL-AuNP significantly enhanced transfection efficiencies (FHD: 31 %; PLAL-AuNP size-1: 46 %; size-2: 50 %) with increased PI% but no reduced cell proliferation. Commercial AuNP-transfection showed significantly lower efficiency (23 %), slightly increased PI % and reduced cell proliferation. Magnetic NP based methods were less effective but showing also lowest cytotoxicity. In conclusion, addition of PLAL-AuNP provides a novel tool for transfection efficiency enhancement with acceptable cytotoxic side-effects. © 2014 SPIE.
    view abstractdoi: 10.1117/12.2038453
  • 2013 • 78 Improvement of wear resistant thermally sprayed coatings by microfinishing
    Biermann, D. and Goeke, S. and Tillmann, W. and Nebel, J.
    CIRP Annals - Manufacturing Technology 62 559-562 (2013)
    To increase the wear resistance of tribologically highly stressed slide faces, thermally sprayed coatings based on tungsten carbide are widely used. In addition to the technological progress in powder metallurgy and coating technology, an improved preparation of the substrate surface increases the fatigue resistance of the coated workpieces. Surfaces machined by short-stroke honing instead of the commonly used abrasive blasting process, show a significantly enhanced interface between the surface and the coating. In addition, the use of diamond as hard cutting material enables the wear resistant coating to be honed and a high surface quality to be generated. © 2013 CIRP.
    view abstractdoi: 10.1016/j.cirp.2013.03.023
  • 2013 • 77 New coating systems for temperature monitoring in turning processes
    Biermann, D. and Kirschner, M. and Pantke, K. and Tillmann, W. and Herper, J.
    Surface and Coatings Technology 215 376-380 (2013)
    High temperature loads in cutting processes can cause high tool wear and damages in the subsurface zone of the workpiece. Especially, the interaction between different cutting parameters affects the thermal loads in the cutting zone. Hence, the knowledge of temperatures in cutting processes is an important factor, and it is the main focus of current investigations. Therefore, this paper deals with an in-process monitoring system for the resulting temperatures in a turning process. In contrast to the investigations performed hitherto, this research deals with a new tool sensor system for temperature measurement. This sensor system is realized by a PVD coating of a Nickel and a Nickel-Chromium layer on the rake face of cutting inserts. On the junction points of this layer system, three thermocouples are deposited. The development of the coating system and the resulting measurement is shown. Additionally, the results are discussed in comparison to thermal imaging system and conventional thermocouples. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2012.08.086
  • 2013 • 76 Failure mechanisms of magnesia alumina spinel abradable coatings under thermal cyclic loading
    Ebert, S. and Mücke, R. and Mack, D. and Vaßen, R. and Stöver, D. and Wobst, T. and Gebhard, S.
    Journal of the European Ceramic Society 33 3335-3343 (2013)
    Abradable coatings have been used in low- and high-pressure sections of jet engine compressors for more than 40 years. Today, they are also used in the high-pressure turbine of jet engines and are gaining more interest for applications in industrial gas turbines. They minimise the clearance between the rotating blade tips and the stationary liners. Aside from being abradable, the coatings have to be mechanically stable and withstand high thermo-mechanical loadings. A typical material used in engines today is yttria-stabilised zirconia (YSZ). This material advantageously combines a suitable thermal conductivity with a high thermal expansion coefficient, but shows a temperature capability limited to 1200 °C in long-term applications. Typical abradable coating thicknesses are above 1. mm. With increasing coating thickness and limited cooling efficiency leading to high surface temperatures, there is a risk of premature failure. As a result, new ceramic materials have been developed with better high-temperature capability. The present work investigates an atmospheric plasma sprayed ceramic double-layer coating system composed of 7YSZ as an intermediate layer and magnesia alumina spinel as a top layer. This double-layer system was sprayed onto disc-shaped Inconel 738 superalloy substrates, which were coated with a vacuum plasma sprayed MCrAlY bondcoat. The lifetime of the coating system was assessed via thermal gradient cycling testing with surface temperatures above 1400 °C. During cycling, the samples showed a typical failure mechanism with exfoliation of thin coating lamellae starting from the coating surface. This failure mechanism was not observed in thermal barrier or abradable coatings in the past. The failure mechanism was analysed and mismatch stress calculations were carried out. © 2013 Elsevier Ltd.
    view abstractdoi: 10.1016/j.jeurceramsoc.2013.06.021
  • 2013 • 75 Design of next generation thermal barrier coatings - Experiments and modelling
    Gupta, M. and Curry, N. and Nylén, P. and Markocsan, N. and Vaßen, R.
    Surface and Coatings Technology 220 20-26 (2013)
    Thermal barrier coating (TBC) systems have been used in the gas turbine industry since the 1980s. The future needs both the air and land based turbine industry involve higher operating temperatures with longer lifetime on the component so as to increase power and efficiency of gas turbines. The aim of this study was to meet these future needs by further development of zirconia coatings. The intention was to design a coating system which could be implemented in industry within the next 3. years. Different morphologies of ceramic topcoat were evaluated; using dual layer systems and polymers to generate porosity. Dysprosia stabilised zirconia was also included in this study as a topcoat material along with the state-of-the-art yttria stabilised zirconia (YSZ). High purity powders were selected in this work. Microstructure was assessed with scanning electron microscope and an in-house developed image analysis routine was used to characterise porosity content. Evaluations were carried out using the laser flash technique to measure thermal conductivity. Lifetime was assessed using thermo-cyclic fatigue testing. Finite element analysis was utilised to evaluate thermal-mechanical material behaviour and to design the morphology of the coating with the help of an artificial coating morphology generator through establishment of relationships between microstructure, thermal conductivity and stiffness. It was shown that the combined empirical and numerical approach is an effective tool for developing high performance coatings. The results show that large globular pores and connected cracks inherited within the coating microstructure result in a coating with best performance. A low thermal conductivity coating with twice the lifetime compared to the industrial standard today was fabricated in this work. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2012.09.015
  • 2013 • 74 Cavitation erosion of Cr60Ni40 coatings generated by friction surfacing
    Hanke, S. and Beyer, M. and Silvonen, A. and dos Santos, J.F. and Fischer, A.
    Wear 301 415-423 (2013)
    CrNi-alloys with high Cr-content generally are quite brittle and, therefore, only available as castings and regarded as neither weldable nor deformable. The process of friction surfacing offers a possibility to generate Cr60Ni40 coatings e.g. on steel or Ni-base substrates. Cavitation tests were carried out using an ultrasonic vibratory test rig (~ASTM G32) with cast specimens and friction surfaced coatings. The coatings show less deformation and smaller disruptions, and wear rates in steady state were found to be three times higher for the cast and heat treated samples than for the coatings, caused by a highly wear resistant Cr-rich phase. The results of this study show that it is possible to generate defect free coatings of Cr60Ni40 with a thickness of about 250. μm by friction surfacing, which under cavitation show a better wear behavior than the cast material. Thus, in combination with a ductile substrate, these coatings are likely to extend the range of applicability of such high-temperature corrosion resistant alloys. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2012.11.016
  • 2013 • 73 Measurement of gain and device performance of a 1050-nm vertical external cavity surface emitting laser
    Haupt, S. and Furitsch, M. and Lindberg, H. and Pietzonka, I. and Strauss, U. and Bacher, G.
    IEEE Journal of Quantum Electronics 49 380-385 (2013)
    In this paper, we measure and analyze the pump power and wavelength dependent gain of an optically pumped infrared 1050-nm vertical external-cavity surface-emitting laser vertical external-cavity surface-emitting laser (VECSEL) developed for an application as a frequency doubled green laser in mobile projectors. Increasing the reflectivity of the chip coating from 3% to 20% for 1050-nm is found to result in a maximal gain of 7.9%, more than twice as high as that of the 3% coating, and in a spectral narrowing of the wavelength-dependent gain as a consequence of the enhanced coupling between the optical field and the quantum well gain medium. From our gain measurements, the wavelength dependent laser threshold can directly be obtained and compared to the VECSEL device characteristics. A very good agreement between the data extracted from the gain measurements and the measured laser threshold in VECSELs with different output mirrors is found. © 1965-2012 IEEE.
    view abstractdoi: 10.1109/JQE.2013.2239958
  • 2013 • 72 Long-term active antimicrobial coatings for surgical sutures based on silver nanoparticles and hyperbranched polylysine
    Ho, C.H. and Odermatt, E.K. and Berndt, I. and Tiller, J.C.
    Journal of Biomaterials Science, Polymer Edition 24 1589-1600 (2013)
    The goal of this study was to develop a long-term active antimicrobial coating for surgical sutures. To this end, two water-insoluble polymeric nanocontainers based on hyperbranched polylysine (HPL), hydrophobically modified by either using glycidyl hexadecyl ether, or a mixture of stearoyl/palmitoyl chloride, were synthesized. Highly stabilized silver nanoparticles (AgNPs, 2-5 nm in size) were generated by dissolving silver nitrate in the modified HPL solutions in toluene followed by reduction with L-ascorbic acid. Poly(glycolic acid)-based surgical sutures were dip-coated with the two different polymeric silver nanocomposites. The coated sutures showed high efficacies of more than 99.5% reduction of adhesion of living Staphylococcus aureus cells onto the surface compared to the uncoated specimen. Silver release experiments were performed on the HPL-AgNP modified sutures by washing them in phosphate buffered saline for a period of 30 days. These coatings showed a constant release of silver ions over more than 30 days. After this period of washing, the sutures retained their high efficacies against bacterial adhesion. Cytotoxicity tests using L929 mouse fibroblast cells showed that the materials are basically non-cytotoxic. © 2013 Taylor and Francis Group, LLC.
    view abstractdoi: 10.1080/09205063.2013.782803
  • 2013 • 71 Physical, chemical and biological properties of micro-arc deposited calcium phosphate coatings on titanium and zirconium-niobium alloy
    Legostaeva, E.V. and Kulyashova, K.S. and Komarova, E.G. and Epple, M. and Sharkeev, Y.P. and Khlusov, I.A.
    Materialwissenschaft und Werkstofftechnik 44 188-197 (2013)
    A comparative investigation of the physical, chemical and biological properties of micro-arc deposited calcium phosphate coatings on titanium and zirconium-niobium substrates was performed. Calcium phosphate coatings on titanium have a higher surface density, porosity and pore size, and a more homogeneous surface topography. Under the same conditions, calcium phosphate coatings on zirconium-niobium have a relief topography, but their surface density, porosity and pore size were all smaller. X-ray diffraction of the coatings showed that the coatings on titanium were X-ray amorphous whereas the coatings on zirconium-niobium consisted of a mixture of crystalline CaZr 4(PO4)6, ZrP2O7, and ZrO2. These differences are due to different electrical and thermophysical characteristics of substrates and passivating films on their surfaces. The coatings were shown to be biocompatible by in-vitro cell culture experiments. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201300107
  • 2013 • 70 Plasma spraying of efficient photoactive TiO2 coatings
    Mauer, G. and Guignard, A. and Vaßen, R.
    Surface and Coatings Technology 220 40-43 (2013)
    In TiO2 coatings for photocatalytic applications or dye-sensitized solar cells, anatase phase with specific rutile content is often preferred to achieve optimum activity. At appropriate process parameters, such phase composition can be obtained by suspension plasma spraying (SPS). However, immediately after deposition, partial transformation to rutile can take place if the substrate temperature is sufficient. Experimental results show that the phase composition has to be balanced with other coating characteristics like microstructure and deposition rate.Another approach to improve the photoactivity of TiO2 is nitrogen doping. It is known that such anionic dopant can create states within the band gap so as to reduce locally the energy barrier of the photoexited electron. Thus, the photoactivity in the range of visible light can be enhanced. TiN addition was investigated to introduce nitrogen in TiO2 coatings directly during SPS. First results are presented. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2012.08.042
  • 2013 • 69 Formation of Silicide Based Oxidation Resistant Coating Over Mo-30 wt% W Alloy
    Paul, B. and Chakraborty, S.P. and Suri, A.K.
    Transactions of the Indian Ceramic Society 72 39-42 (2013)
    Studies were carried out to develop silicide based oxidation resistant coatings over Mo-30W alloy substrate employing halide activated pack cementation coating process. Effect of activator content and temperature on coating was studied. Coated samples were characterized for phase and microstructure evaluation by SEM and EDS. Cyclic oxidation tests on coated alloy were performed at 1000°C up to 50 h. The coating provided enough protection from oxidation. © 2013 Copyright The Indian Ceramic Society.
    view abstractdoi: 10.1080/0371750X.2013.793993
  • 2013 • 68 Oxidation of divalent rare earth phosphors for thermal history sensing
    Rabhiou, A. and Kempf, A. and Heyes, A.
    Sensors and Actuators, B: Chemical 177 124-130 (2013)
    Knowledge of component temperatures under the extreme conditions in industrial prime movers is of great practical importance, but very hard to obtain. Thermal indicating paints offer one possible and practical way, but they have many disadvantages. A novel concept for utilising phosphorescent coatings as thermal history sensors was proposed by Feist et al. [1] in 2007. These phosphor coatings undergo irreversible changes when exposed to high temperatures that affect their photoluminescent emission properties in such a way that off-line analysis of the emission at room temperature can reveal the temperature history of the coating. In this paper, an investigation of the thermally activated oxidation of 2+ ions in phosphors such as BaMgAl10O 17:Eu2+, BaMgAl10O17:Eu 2+, Mn2+ and SrAl14O25:Eu 2+ is reported and used to demonstrate the potential for a phosphorescent thermal history sensor based on a new physical process. Phosphor powders were annealed at temperatures up to 1400 °C, and characterised using photoluminescence spectroscopy. An intensity ratio temperature measurand was defined and it was shown that the dynamic range of a thermal history sensor based on SrAl14O25:Eu2+ could provide a dynamic range extending from 600 °C to 1300 °C. © 2012 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.snb.2012.10.012
  • 2013 • 67 Infiltration of polymer hole-conductor into mesoporous titania structures for solid-state dye-sensitized solar cells
    Rawolle, M. and Sarkar, K. and Niedermeier, M.A. and Schindler, M. and Lellig, P. and Gutmann, J.S. and Moulin, J.-F. and Haese-Seiller, M. and Wochnik, A.S. and Scheu, C. and Müller-Buschbaum, P.
    ACS Applied Materials and Interfaces 5 719-729 (2013)
    The degree of filling of titania nanostructures with a solid hole-conducting material is important for the performance of solid-state dye-sensitized solar cells (ssDSSCs). Different ways to infiltrate the hole-conducting polymer poly(3-hexylthiophene) (P3HT) into titania structures, both granular structures as they are already applied commercially and tailored sponge nanostructures, are investigated. The solar cell performance is compared to the morphology determined with scanning electron microscopy (SEM) and time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS). The granular titania structure, commonly used for ssDSSCs, shows a large distribution of particle and pore sizes, with porosities in the range from 41 to 67%, including even dense parts without pores. In contrast, the tailored sponge nanostructure has well-defined pore sizes of 25 nm with an all-over porosity of 54%. Filling of the titania structures with P3HT by solution casting results in a mesoscopic P3HT overlayer and consequently a bad solar cell performance, even though a filling ratio of 67% is observed. For the infiltration by repeated spin coating, only 57% pore filling is achieved, whereas filling by soaking in the solvent with subsequent spin coating yields filling as high as 84% in the case of the tailored titania sponge structures. The granular titania structure is filled less completely than the well-defined porous structures. The solar cell performance is increased with an increasing filling ratio for these two ways of infiltration. Therefore, filling by soaking in the solvent with subsequent spin coating is proposed. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/am302255c
  • 2013 • 66 Synchrotron X-ray measurement techniques for thermal barrier coated cylindrical samples under thermal gradients
    Siddiqui, S.F. and Knipe, K. and Manero, A. and Meid, C. and Wischek, J. and Okasinski, J. and Almer, J. and Karlsson, A.M. and Bartsch, M. and Raghavan, S.
    Review of Scientific Instruments 84 (2013)
    Measurement techniques to obtain accurate in situ synchrotron strain measurements of thermal barrier coating systems (TBCs) applied to hollow cylindrical specimens are presented in this work. The Electron Beam Physical Vapor Deposition coated specimens with internal cooling were designed to achieve realistic temperature gradients over the TBC coated material such as that occurring in the turbine blades of aeroengines. Effects of the circular cross section on the x-ray diffraction (XRD) measurements in the various layers, including the thermally grown oxide, are investigated using high-energy synchrotron x-rays. Multiple approaches for beam penetration including collection, tangential, and normal to the layers, along with variations in collection parameters are compared for their ability to attain high-resolution XRD data from the internal layers. This study displays the ability to monitor in situ, the response of the internal layers within the TBC, while implementing a thermal gradient across the thickness of the coated sample. The thermal setup maintained coating surface temperatures in the range of operating conditions, while monitoring the substrate cooling, for a controlled thermal gradient. Through variation in measurement location and beam parameters, sufficient intensities are obtained from the internal layers which can be used for depth resolved strain measurements. Results are used to establish the various techniques for obtaining XRD measurements through multi-layered coating systems and their outcomes will pave the way towards goals in achieving realistic in situ testing of these coatings. © 2013 AIP Publishing LLC.
    view abstractdoi: 10.1063/1.4817543
  • 2013 • 65 Innovative tools to improve incremental bulk forming processes
    Sieczkarek, P. and Kwiatkowski, L. and Tekkaya, A.E. and Krebs, E. and Kersting, P. and Tillmann, W. and Herper, J.
    Key Engineering Materials 554-557 1490-1497 (2013)
    Sheet-bulk metal forming is an innovative process with a high potential to generate load-adapted parts with high precision. Bulk forming processes of sheet metals especially require high process forces, resulting in an intense contact pressure and, thus, in a very high abrasive and adhesive wear. As a method to reduce or avoid these common wear phenomena, even hardened or coated tool surfaces are not sufficient. The objective of this paper is to show an improvement of the tool resistance during an incremental forming process by an adapted tool design and the application of structured tool surfaces combined with coatings. For the tool surface the structure of the scarabaeus beetle serves as the basis for a bionic structure. This structure was manufactured by micromilling. Despite the high hardness of the tool material and the complex geometry of the forming tools, very precise patterns were machined successfully using ball-end milling cutters. The combination of bionic structures with coating techniques like physical vapor deposition (PVD) on plasma nitrided tool surfaces is very promising. In this work, the influence of process parameters (workpiece material, lubrication, tool design, stepwise infeed) on the tool resistance during the forming operation was analyzed experimentally. The results of the optimized forming tools were compared to conventional, unstructured, uncoated, and only plasma nitrided forming tools. The different tools were applied to 2 mm thick metal sheets made of aluminum (AlMg3) and steel (nonalloy quality steel DC04). As a result, the process forces could be reduced by a modified shape and surface of the tools. Thus, the lifetime of the tools can be enhanced. Copyright © 2013 Trans Tech Publications Ltd.
    view abstractdoi: 10.4028/
  • 2013 • 64 Star-shaped poly(styrene)-block-Poly(4-vinyl-N-methylpyridiniumiodide) for semipermanent antimicrobial coatings
    Siedenbiedel, F. and Fuchs, A. and Moll, T. and Weide, M. and Breves, R. and Tiller, J.C.
    Macromolecular Bioscience 13 1447-1455 (2013)
    Goal of the present work is to develop an antimicrobial coating that can be applied from an aqueous solution and resists short washing cycles, but can be rinsed off by thorough washing. To this end, a series of star-shaped polystyrene-block-poly(4-vinyl-N-methylpyridinium iodide) polymers are synthesized by anionic polymerization using a core-first approach. The optimal resulting polymers are applied as coatings on glass slides, showing high antimicrobial efficiency against Staphylococcus aureus as well as Escherichia coli. The coatings, characterized by atomic force microscopy and transmission electron microscopy, stay at the surface even after at least 20 flush-like washings with water, and retain their antimicrobial activity. Semipermanent antimicrobial coatings can be achieved by synthesizing 3-arm star-blockcopolymer with an inner poly(styrene)-block and an outer poly(4-vinyl-N-methylpyridiniumiodide)-block. Solubility, antimicrobial activity, and coating stability strongly depend on the block ratios. The coatings can be applied from aqueous solution, withstand flush-like washings and prevent growth of S. aureus and E. coli. Nonetheless, the coatings are removable of by extended rinsing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mabi.201300219
  • 2013 • 63 Preparation of a silicate-containing hydroxyapatite-based coating by magnetron sputtering: Structure and osteoblast-like MG63 cells in vitro study
    Surmeneva, M.A. and Kovtun, A. and Peetsch, A. and Goroja, S.N. and Sharonova, A.A. and Pichugin, V.F. and Grubova, I.Y. and Ivanova, A.A. and Teresov, A.D. and Koval, N.N. and Buck, V. and Wittmar, A. and Ulbricht, M. and Prymak,...
    RSC Advances 3 11240-11246 (2013)
    Silicate-containing hydroxyapatite-based coatings with different structure and calcium/phosphate ratios were prepared by radio-frequency magnetron sputtering on silicon and titanium substrates, respectively. Scanning electron microscopy, X-ray diffraction and IR spectroscopy were used to investigate the effect of the substrate bias on the properties of the silicate-containing hydroxyapatite-based coatings. The deposition rate, composition, and microstructure of the deposited coatings were all controlled by changing the bias voltage from grounded (0 V) to -50 and -100 V. The biocompatibility was assessed by cell culture with human osteoblast-like cells (MG-63 cell line), showing a good biocompatibility and cell growth on the substrates. © 2013 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/c3ra40446c
  • 2013 • 62 Phase and elemental composition of silicon-containing hydroxyapatite-based coatings fabricated by RF-magnetron sputtering for medical implants
    Surmeneva, M.A. and Surmenev, R.A. and Chaikina, M.V. and Kachaev, A.A. and Pichugin, V.F. and Epple, M.
    Inorganic Materials: Applied Research 4 227-235 (2013)
    We studied by X-ray diffraction analysis, IR spectroscopy, and scanning electron microscopy (SEM) the phase composition and the structure of coatings based on silicon-containing hydroxyapatite (Si-HA) deposited by RF-magnetron sputtering. The sputtering target contained two phases (apatite and tricalcium phosphate) and was produced by the ceramic technology from a single-phase mechanically activated powder precursor. The structure of the coating deposited by sputtering from the two-phase target was single phase (hydroxyapatite) and textured in the (002) direction. During deposition, silicate anions partially replaced phosphate ions in the apatite lattice. © Pleiades Publishing, Ltd., 2013.
    view abstractdoi: 10.1134/S2075113313030131
  • 2013 • 61 The structure of an rf-magnetron sputter-deposited silicate-containinghydroxyapatite-based coating investigated by high-resolution techniques
    Surmeneva, M.A. and Chaikina, M.V. and Zaikovskiy, V.I. and Pichugin, V.F. and Buck, V. and Prymak, O. and Epple, M. and Surmenev, R.A.
    Surface and Coatings Technology 218 39-46 (2013)
    A biocompatible nanostructured silicate-containing hydroxyapatite-based (Si-HA) thin coatingwas deposited by radio-frequency (RF) magnetron sputtering on silicon and titanium substrates. The morphology of the Si-HA coating was pore-free, dense and followed the topography of the underlying substrates. Energy-dispersive X-ray spectroscopy (EDX) gave molar Ca/P and Ca/(P+Si) ratios of 1.78 and 1.45, respectively. According to XRD-analysis, the coatingwas nanocrystallinewith a crystallite size in the range of 10-50 nm. The ultrastructure of the coating was analyzed by high-resolution transmission electron spectroscopy (HRTEM) combinedwith fast Fourier transform (FFT) analysis. The average crystallite size calculated by the Rietveld method was in good agreement with the HRTEM results. Moreover, HRTEM-observations indicated the presence of atomic layer misorientations originating from imperfections between the nanocrystals in the coating. The average coating nanohardness (11.6±1.7 GPa) was significantly higher than that of the uncoated Ti substrate (4.0±0.3 GPa), whereas no significant difference between the Young'smodulus of the coating (125±20 GPa) and the substrate (115±10 GPa) was found. Immersion of the coated substrates in simulated body fluid (SBF) led to the deposition of an apatite layer. © 2013 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2012.12.023
  • 2013 • 60 Quality prediction of twin wire Arc sprayed coatings using acoustic Emission Analysis
    Tillmann, W. and Abdulgader, M. and Wang, G. and Zielke, R.
    Journal of Thermal Spray Technology 22 380-390 (2013)
    In this work, acoustic emission analysis is utilized in the twin wire arc spraying (TWAS) process to study the influence of the adjustable process parameters on the simultaneously obtained acoustic signals at the nozzle and at the substrate. The amplitude of recorded signals at the substrate was in general much higher than those recorded at the nozzle. At the substrate side, the amplitude of emitted acoustic signals is dependent on feedstock materials and is higher when using solid wires. The acoustic signals were recorded at the spraying gun for different gas pressures without arc ignition (as dry runs) in order to reveal the effect of the arc on the emitted acoustic signals. A correlation between controllable parameters, the acoustic signals, and the obtained in-flight particle characteristics was observed. This work contributes to the online control of TWAS processes and is one of many proposed publications in the research field of the conducted acoustic emission analysis. © 2012 ASM International.
    view abstractdoi: 10.1007/s11666-012-9861-z
  • 2013 • 59 Tribological comparison of different surface topographies coated with chromium aluminum nitride
    Tillmann, W. and Herper, J. and Laemmerhirt, I.-A.
    Materialwissenschaft und Werkstofftechnik 44 730-735 (2013)
    The reduction of friction and wear is one important goal for the extension of the tool life in many industrial applications. The forming and cutting industries in particular, are very interested in new techniques and surface coating characteristics that will improve the tribological behavior of the tools. Biomimetics is a very promising approach using biological surfaces or phenomena to optimize the properties of engineering components. The "Lotus Effect" is the most famous example, whereby surfaces are made water- and dirt-repellent. Taking a closer look at nature, it can be noticed that many different natural surfaces have perfectly adapted to their environment in order to meet the respective requirements. Extending the use of natural and biological effects to improve the material performance, it was discovered that the skin of many insects has an excellent frictional behavior and thus the potential to be transferred onto technical surfaces. In this paper, the surface structure of a dung beetle (db) was investigated. The main objective was to combine nature-adapted surface patterns with wear-resistant near-netshape PVD-coatings (PVD=physical vapour deposition), in order to improve the tribological properties of a tool surface. The shell of the beetle served as a pattern for the structure of the surfaces. A substrate, composed of high speed steel material, was structured by means of milling prior to the deposition of a chromium aluminum nitride multilayer coating system, using a magnetron sputtering process. The mechanical and tribological properties of the structured and coated surfaces were compared by means of nanoindentation, ball-on-disc-testing, and scanning electron microscopy. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201300183
  • 2013 • 58 Influence of bias voltage on residual stresses and tribological properties of TiAlVN-coatings at elevated temperatures
    Tillmann, W. and Sprute, T. and Hoffmann, F. and Chang, Y.-Y. and Tsai, C.-Y.
    Surface and Coatings Technology 231 122-125 (2013)
    The extension of tool life is a crucial goal for heat resistant forming tools. Therefore, the industry is interested to reduce the friction and wear for these tools. The employment of metals, polymeric composites, and ceramics as solid lubricants increases the production as well as maintenance costs. Thus, the thin film technology and especially new self-lubricating coatings will become increasingly important. Titanium aluminum vanadium nitride as a self-lubricating coating has a high potential to improve the tribological behavior of heat resisting tool surfaces and has good mechanical properties such as a high hardness (more than 40GPa). In this study, TiAlVN coatings were deposited on HS6-5-2C high speed steel substrates by using a magnetron sputtering system. After annealing at 650°C, a V2O5 (Magnéli phase) which adds self-lubricating qualities to the coatings could be detected in the TiAlVN layer. Due to the influence of adhesive and cohesive damage processes, resulting from the residual stress behavior in the layer close to the substrate area, it is critical to measure residual stresses in order to increase the wear resistance. In addition to the phase analyses, residual stress measurements were investigated by means of x-ray diffractometry as well. An experimental method, based on the traditional sin2ψ-method and utilizing a grazing-incidence diffraction geometry was used in order to enhance the irradiation volume of thin film samples. This resulted in a higher intensity for high-angle Bragg peaks than for the Bragg-Brentano geometry. Furthermore, the mechanical and tribological properties of the TiAlVN coatings were characterized at elevated temperatures. The required results were provided by a high temperature ball-on-disk device and a nanoindenter. © 2012 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2012.03.012
  • 2013 • 57 A study of mechanical and tribological properties of self-lubricating TiAlVN coatings at elevated temperatures
    Tillmann, W. and Momeni, S. and Hoffmann, F.
    Tribology International 66 324-329 (2013)
    There are several manufacturing processes, in which the employment of solid lubricants is limited. In addition, ecological damage and higher production costs are further consequences of using such solid lubricants. This work aims at using the great potential of thin film technology to deposit adaptive, self-lubricating coatings as an alternative to conventional solid lubricants. Using magnetron sputtering process several titanium aluminum vanadium nitride coatings (TiAlVN) were developed in this study. These quaternary coatings possess the ability of forming lubricious oxides, known as Magnéli phases, at elevated temperatures, which significantly reduces the friction coefficient and surface wear. © 2013 Elsevier Ltd.
    view abstractdoi: 10.1016/j.triboint.2013.06.007
  • 2013 • 56 Influence of fine powder feedstock (-10 + 2 μm) on the HVOF spraying characteristics, coating morphology, and properties of WC-CoCr 86-10-4
    Tillmann, W. and Nebel, J. and Piotrowski, W.
    Journal of Thermal Spray Technology 22 242-249 (2013)
    The use of fine feedstock powder can extend the feasibility and scope of HVOF coatings to new fields of applications. Especially for the purpose of near-net-shape coatings, these powders facilitate homogeneous layer morphologies, and smooth coating surfaces. However, the small particle sizes also lead to several challenges. One major issue is the in-flight behavior which is distinctly affected by the low mass and relatively large specific surface of the particles. In this paper, the in-flight and coating characteristics of WC-CoCr 86-10-4 (-10 + 2 μm) were investigated. It was determined that the fine powder feedstock shows a high sensitivity to the gas flow, velocity, and temperature of the spray jet. Because of their low mass inertia, their velocity, for example, is actually influenced by local pressure nodes (shock diamonds) in the supersonic flow. Additionally, the relatively large specific surface of the particles promotes partial overheating and degradation. Nevertheless, the morphological and mechanical properties of the sprayed layer are hardly affected. In fact, the coatings feature a superior surface roughness, porosity, hardness, and wear resistance. © 2012 ASM International.
    view abstractdoi: 10.1007/s11666-012-9832-4
  • 2013 • 55 Functionally graded vacuum plasma sprayed and magnetron sputtered tungsten/EUROFER97 interlayers for joints in helium-cooled divertor components
    Weber, T. and Stüber, M. and Ulrich, S. and Vaßen, R. and Basuki, W.W. and Lohmiller, J. and Sittel, W. and Aktaa, J.
    Journal of Nuclear Materials 436 29-39 (2013)
    Two coating technologies, magnetron sputtering and vacuum plasma spraying, have been investigated for their capability in producing functionally graded tungsten/EUROFER97 layers. In a first step, non-graded layers with different mixing ratios were deposited on tungsten substrates and characterized by nanoindentation, macroindentation, X-ray diffraction, transmission, Auger and scanning electron microscopy. The thermal stability of the sprayed layers against heat treatments at 800-1100 °C for 60 min was further analyzed. In a second step, the produced functionally graded layers deposited on tungsten substrates were joined to EUROFER97 bulk-material by diffusion bonding. The bonding and the graded joints were microscopically characterized and exposed to thermal cycles between 20 °C and 650 °C. Results from this study show that both coating technologies are ideal for the synthesis of functionally graded tungsten/EUROFER97 coatings. This is important in providing insights for fture development of joints with functionally graded interlayers. © 2013 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.jnucmat.2013.01.286
  • 2013 • 54 Acquisition and optimization of three-dimensional spray footprint profiles for coating simulations
    Wiederkehr, T. and Müller, H.
    Journal of Thermal Spray Technology 22 1044-1052 (2013)
    For the simulation of thermal spray coating build-up and the prediction of the coating-thickness distribution on given workpieces, an accurate representation of the mass flow emitted from the spray torch is essential. For two-dimensional (2D) simulations, this flow function often is acquired by measuring the coating thickness in cross-sectional profiles of linear spray beads, and for 3D simulations, usually some form of rotationally symmetric normal distribution function is fitted to measured profile data. However, when using free-formed complex workpieces or arbitrary and nonuniform spray paths, more realistic, nonsymmetric, and 3D flow functions are required. We present an approach to acquire accurate and fully 3D flow distribution functions by measuring 3D coating profiles which result from spraying onto a flat surface with a stationary gun, and improving them by means of a developed optimization method that takes more precise cross-sectional measurements into account. This approach thus combines the advantages of the higher accuracy of 2D measurements while fully preserving the 3D characteristics of the measured profile. © 2013 ASM International.
    view abstractdoi: 10.1007/s11666-013-9927-6
  • 2013 • 53 Slippery liquid-infused porous surfaces showing marine antibiofouling properties
    Xiao, L. and Li, J. and Mieszkin, S. and Di Fino, A. and Clare, A.S. and Callow, M.E. and Callow, J.A. and Grunze, M. and Rosenhahn, A. and Levkin, P.A.
    ACS Applied Materials and Interfaces 5 10074-10080 (2013)
    Marine biofouling is a longstanding problem because of the constant challenges placed by various fouling species and increasingly restricted environmental regulations for antifouling coatings. Novel nonbiocidal strategies to control biofouling will necessitate a multifunctional approach to coating design. Here we show that slippery liquid-infused porous surfaces (SLIPSs) provide another possible strategy to obtaining promising antifouling coatings. Microporous butyl methacrylate-ethylene dimethacrylate (BMA-EDMA) surfaces are prepared via UV-initiated free-radical polymerization. Subsequent infusion of fluorocarbon lubricants (Krytox103, Krytox100, and Fluorinert FC-70) into the porous microtexture results in liquid-repellent slippery surfaces. To study the interaction with marine fouling organisms, settlement of zoospores of the alga Ulva linza and cypris larvae of the barnacle Balanus amphitrite is tested in laboratory assays. BMA-EDMA surfaces infused with Krytox103 and Krytox100 exhibit remarkable inhibition of settlement (attachment) of both spores and cyprids to a level comparable to that of a poly(ethylene glycol) (PEG)-terminated self-assembled monolayer. In addition, the adhesion strength of sporelings (young plants) of U. linza is reduced for BMA-EDMA surfaces infused with Krytox103 and Krytox100 compared to pristine (noninfused) BMA-EDMA and BMA-EDMA infused with Fluorinert FC-70. Immersion tests suggest a correlation between the stability of slippery coatings in artificial seawater and fouling resistance efficacy. The results indicate great potential for the application of this concept in fouling-resistant marine coatings. © 2013 American Chemical Society.
    view abstractdoi: 10.1021/am402635p
  • 2012 • 52 SintClad: A new approach for the production of wear-resistant tools
    Blüm, M. and Hill, H. and Moll, H. and Weber, S. and Theisen, W.
    Journal of Materials Engineering and Performance 21 756-763 (2012)
    Tools used in the mineral processing industry are required to feature high wear resistance to facilitate an adequate cost efficiency. These kinds of tools are made of composite materials based on a low-alloyed substrate material and a high-alloyed coating. The coatings can be applied in different ways using production processes like HIP cladding, deposit welding, and composite casting. The article is concerned with the problem of a novel and cost-effective coating alternative: sinter cladding, using the principle of supersolidus liquid-phase sintering (SLPS). Usually SLPS represents a sintering technique, which is used for the compaction of high-alloyed metal powders. However, no recognizable efforts were made to use the SLPSprocess for applying a PM-coating on a bulk substrate material. Sinter cladding for the first time uses SLPS to combine the process of powder compaction with the application of a coating to a solid steel substrate into one single step. Another advantage of the process is the possibility to produce massive bulk coatings with thicknesses exceeding 20 mm. This article is original in the scope of question and investigation methods in terms of microstructure, hardness profiles, EDX measurements, diffusion calculations, and computational thermodynamics. © ASM International.
    view abstractdoi: 10.1007/s11665-012-0199-y
  • 2012 • 51 Cutting with coated tools: Coating technologies, characterization methods and performance optimization
    Bouzakis, K.-D. and Michailidis, N. and Skordaris, G. and Bouzakis, E. and Biermann, D. and M'Saoubi, R.
    CIRP Annals - Manufacturing Technology 61 703-723 (2012)
    Coated tools constitute the majority of the tools applied in material removal processes, rendering the employment of uncoated ones as an exception. A broad growing market of coated cutting tools has been developed. Moreover, numerous material- and manufacturing-engineers have joint their expertise, aiming at developing coatings meeting the needs for processing the most difficult-to-cut materials at the most extreme cutting conditions. The emerging of new workpiece, tool and film materials, the evolution of sophisticated coatings' characterization methods and the continuous need for higher productivity rates, maintain vivid the industrial and scientific interest for further advancing this field. © 2012 CIRP.
    view abstractdoi: 10.1016/j.cirp.2012.05.006
  • 2012 • 50 Synthesis of titanium carbonitride coating layers with star-shaped crystallite morphology
    Garcia, J. and Pitonak, R. and Agudo, L. and Kostka, A.
    Materials Letters 68 71-74 (2012)
    Titanium carbonitride coating layers with star-shaped crystallite morphology were produced by chemical vapor deposition. Crystallites presenting a pentagonal symmetry nucleate at 880 °C and grow perpendicular to the surface by controlling the heating rate of the deposition process. Detailed transmission electron microscopy analyses of star-shaped crystallites along the [110] zone axis showed that each crystallite consists of five tetrahedra separated by (111) twins. A small-angle boundary consisting of edge dislocations forms as a result of elastic stress relaxation in the crystallites. The coatings presented a preferential texture in the direction (110) and an overall composition of Ti(C 0.15 N 0.85). © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.matlet.2011.10.008
  • 2012 • 49 Deposition and characteristics of submicrometer-structured thermal barrier coatings by suspension plasma spraying
    Guignard, A. and Mauer, G. and Vaßen, R. and Stöver, D.
    Journal of Thermal Spray Technology 21 416-424 (2012)
    In the field of thermal barrier coatings (TBCs) for gas turbines, suspension plasma sprayed (SPS) submicrometer-structured coatings often show unique mechanical, thermal, and optical properties compared to conventional atmospheric plasma sprayed ones. They have thus the potential of providing increased TBC performances under severe thermo-mechanical loading. Experimental results showed the capability of SPS to obtain yttria stabilized zirconia coatings with very fine porosity and high density of vertical segmentation cracks, yielding high strain tolerance, and low Young's modulus. The evolution of the coating microstructure and properties during thermal cycling test at very high surface temperature (1400 °C) in our burner rigs and under isothermal annealing was investigated. Results showed that, while segmentation cracks survive, sintering occurs quickly during the first hours of exposure, leading to pore coarsening and stiffening of the coating. In-situ measurements at 1400 °C of the elastic modulus were performed to investigate in more detail the sintering-related stiffening. © ASM International.
    view abstractdoi: 10.1007/s11666-012-9762-1
  • 2012 • 48 The biocompatibility of metal-organic framework coatings: An investigation on the stability of SURMOFs with regard to water and selected cell culture media
    Hanke, M. and Arslan, H.K. and Bauer, S. and Zybaylo, O. and Christophis, C. and Gliemann, H. and Rosenhahn, A. and Wöll, C.
    Langmuir 28 6877-6884 (2012)
    Highly porous thin films based on a [Cu(bdc) 2] n (bdc = benzene-1,4-dicarboxylic acid) metal-organic framework, MOF, grown using liquid-phase epitaxy (LPE) show remarkable stability in pure water as well as in artificial seawater. This opens the possibility to use these highly porous coatings for environmental and life science applications. Here we characterize in detail the stability of these SURMOF 2 thin films under aqueous and cell culture conditions. We find that the material degrades only very slowly in water and artificial seawater (ASW) whereas in typical cell culture media (PBS and DMEM) a rapid dissolution is observed. The release of Cu 2+ ions resulting from the dissolution of the SURMOF 2 in the liquids exhibits no adverse effect on the adhesion of fibroblasts, prototype eukaryotic cells, to the substrate and their subsequent proliferation, thus demonstrating the biocompatibility of SURMOF 2 surface coatings. Thus, the results are an important step toward application of these porous materials as a slow release matrix, for example, for pharmaceuticals and growth factors. © 2012 American Chemical Society.
    view abstractdoi: 10.1021/la300457z
  • 2012 • 47 Correlation of processing route and heat treatment with the abrasive wear resistance of a plastic mold steel
    Hill, H. and Kunze, M. and Heet, C. and Petsch, A. and Weber, S. and Reiter, R. and Giese, P. and Theisen, W. and Wielage, B. and Wesling, V.
    Materialwissenschaft und Werkstofftechnik 43 711-718 (2012)
    The processing of polymers necessitates the use of corrosion and wear resistant tool materials being in direct contact with the feedstock material. Corrosion resistant cold work tool steels, the so called plastic mold steels, are successfully applied here, offering both a good wear and corrosion resistance. The lifetime of this tool depends on the applied heat treatment but also the processing route has a distinct effect on the resulting properties. In this work, different powder metallurgical routes like hot isostatic pressing, build-up welding (plasma transfer arc (PTA)) and thermal spraying (high velocity oxy fuel (HVOF) and atmospheric plasma spraying (APS)) were applied to produce coatings on low-alloyed construction steel. Coatings are compared in relation to the changes in microstructure and the feasibility of an adequate heat treatment. This paper discusses strategies to maximize wear resistance in dependence of heat treatment and the microstructural changes arising from the processing. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201200865
  • 2012 • 46 Decomposition of Ba(Mg 1/3Ta 2/3)O 3 perovskite during atmospheric plasma spraying
    Jarligo, M.O. and Mauer, G. and Sebold, D. and Mack, D.E. and Vaßen, R. and Stöver, D.
    Surface and Coatings Technology 206 2515-2520 (2012)
    Perovskite Ba(Mg 1/3Ta 2/3)O 3, BMT has promising bulk properties (thermal conductivity ~2W/m-K and coefficient of thermal expansion ~11×10 -6/K at 1473K) for thermal barrier coating (TBC) applications at high temperature. However, during atmospheric plasma spraying (APS), such material was found to lose constituents due to the differences of vapor pressures resulting to non-stoichiometric composition of deposited coatings. To investigate the extent of phase decomposition at spray distance and varying electric arc current, different feedstock powders were plasma sprayed into water and collected for chemical, microstructural and phase analyses. When the electric arc current was decreased from 500A to 300A, the decomposition of the powders was reduced and the microstructure of the deposited coatings was improved. The thermal cycling lifetime of the deposited coatings at ~1250°C surface temperature is also higher. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2011.11.003
  • 2012 • 45 Plasma Spray-PVD: Plasma characteristics and impact on coating properties
    Mauer, G. and Vaßen, R.
    Journal of Physics: Conference Series 406 (2012)
    Typical plasma characteristics of the plasma spray-physical vapour deposition (PS-PVD) process were investigated by optical emission spectroscopy. Electron temperatures were determined by Boltzmann plots while temperatures of the heavy species as well as electron densities were obtained by broadening analysis of spectral lines. The results show how the plasma properties and thermodynamic equilibrium conditions are affected by the admixture of hydrogen and the ambient chamber pressure. Some experimental examples of PS-PVD coatings demonstrate the impact on feedstock treatment and deposited microstructures.
    view abstractdoi: 10.1088/1742-6596/406/1/012005
  • 2012 • 44 Improving atmospheric plasma spraying of zirconate thermal barrier coatings based on particle diagnostics
    Mauer, G. and Sebold, D. and Vaßen, R. and Stöver, D.
    Journal of Thermal Spray Technology 21 363-371 (2012)
    Lanthanum zirconate (La 2Zr 2O7) has been proposed as a promising material for thermal barrier coatings. During atmospheric plasma spraying (APS) of La 2Zr 2O7 a considerable amount of a2O3 can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the La 2O 3-ZrO 2 system, in the composition range of pyrochlore structure, the stoichiometric La 2Zr 2O 7 has the highest melting point and other compositions are eutectic. APS experiments were performed with a TriplexPro&trade;-200 plasma torch at different power levels to achieve different degrees of evaporation and thus stoichiometry. For comparison, some investigations on gadolinium zirconate (Gd 2Zr 2O 7) were included, which is less prone to evaporation and formation of non-stoichiometry. Particle temperature distributions were measured by the DPV-2000 diagnostic system. In these distributions, characteristic peaks were detected at specific torch input powers indicating evaporation and solidification processes. Based on this, process parameters can be defined to provide stoichiometric coatings that show good thermal cycling performance. © ASM International.
    view abstractdoi: 10.1007/s11666-011-9706-1
  • 2012 • 43 Damage characterization of thermal barrier coatings by acoustic emission and thermography
    Nies, D. and Rehmer, B. and Skrotzki, B. and Vaßen, R.
    Advanced Engineering Materials 14 790-794 (2012)
    Thermal barrier coatings allow increasing the operating temperature and efficiency of land-, sea-, or air-based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of its lifetime is essential. To assess the lifetime, cyclic tests are conceived to combine thermal loading by heating the surface of the coating with laser irradiation and nondestructive methods for damage determination. Using laser irradiation allows a high reproducibility of the thermal load. The temperature of the sample surface during thermal loading is determined by an infrared-camera which also enables the possibility to detect damage in the coating via thermography. Additionally, four acoustic sensors, attached to the experimental setup, are used to detect damage in the sample and determine the source of acoustic events. Results of acoustic emission correlate well with thermographic images that visualize the formation and evolution of damage through delaminations in the samples. Thermal fatigue tests of thermal barrier coatings (TBCs) by heating the surface with laser irradiation were complemented by nondestructive methods. A comparison is made between results of acoustic emission and thermographic images in order to visualize the formation and evolution of damage through delamination in the samples. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201200107
  • 2012 • 42 Simulation-based prediction of process forces for grinding free-formed surfaces on machining centers
    Rausch, S. and Odendahl, S. and Kersting, P. and Biermann, D. and Zabel, A.
    Procedia CIRP 4 161-165 (2012)
    During the grinding of hard materials using cylindrically and spherically shaped mounted points - like for the machining of complex forming tools with abrasive-wear-resistant coatings - the process force is an important factor influencing the accuracy of the machining outcome. A simulation-based prediction of these forces could be used to adapt the tool path and, thereby, to keep the grinding forces at a low level. In this paper, a simulation system based on the modeling of each grain of the grinding tool and the validation of this simulation model are presented. © 2012 The Authors.
    view abstractdoi: 10.1016/j.procir.2012.10.029
  • 2012 • 41 Grinding of hard-material-coated forming tools on machining centers
    Rausch, S. and Biermann, D.
    Procedia CIRP 1 388-392 (2012)
    In this paper, the grinding of hard-material-coated forming tools on a machining center is presented. The coated materials have to be machined mechanically because of the insufficient surface quality and form errors resulting from the thermal spraying processes. During the fundamental investigations two different tungsten carbide coatings have been machined by applying super abrasive grinding tools consisting of four different bond systems. To identify the suitable grinding tools, the process forces and the surface roughness values have been carried out by a screening design of experiments. © 2012 The Authors.
    view abstractdoi: 10.1016/j.procir.2012.04.069
  • 2012 • 40 Investigation of early degradation processes at coated metals by AC-scanning electrochemical microscopy
    Santana, J.J. and Souto, R.M. and González, S. and Pähler, M. and Schuhmann, W.
    ECS Transactions 41 29-38 (2012)
    Alternating-current scanning electrochemical microscopy (AC-SECM) is employed to characterize the early stages of the degradation reactions occurring in metal-coating systems upon exposure to an aqueous environment. The spatial resolution of the technique results from the measurement of changes in the resistance of the thin electrolyte layer comprised between the tip and the surface of the coating due to variations in the tip-substrate distance. Resistance measurements are conducted at various frequencies of the AC perturbation signal effectively allowing topographic changes to be monitored as a function of time. Furthermore, AC-SECM can be used to determine the tip-substrate distance without the addition of redox mediators to the electrolyte, which might affect the chemical properties of the system. In this way, the effect of chloride ions from the aqueous phase to induce either the heterogeneous absorption of water by the coating, or its accumulation at the metal-substrate interface, has been imaged. ©The Electrochemical Society.
    view abstractdoi: 10.1149/1.3696868
  • 2012 • 39 Improved tool surfaces for incremental bulk forming processes of sheet metals
    Sieczkarek, P. and Kwiatkowski, L. and Tekkaya, A.E. and Krebs, E. and Biermann, D. and Tillmann, W. and Herper, J.
    Key Engineering Materials 504-506 975-980 (2012)
    Sheet-bulk metal forming is a process used to manufacture load-adapted parts with high precision. However, bulk forming of sheet metals requires high forces, and thus tools applied for the operational demand have to withstand very high contact pressures, which lead to high wear and abrasion. The usage of conventional techniques like hardening and coating in order to reinforce the surface resistance are not sufficient enough in this case. In this paper, the tool resistance is improved by applying filigree bionic structures, especially structures adapted from the Scarabaeus beetle to the tool's surface. The structures are realized by micromilling. Despite the high hardness of the tool material, very precise patterns are machined successfully using commercially available ball-end milling cutters. The nature-adapted surface patterns are combined with techniques like plasma nitriding and PVD-coating, leading to a multilayer coating system. The effect of process parameters on the resistance of the tools is analyzed experimentally and compared to a conventional, unstructured, uncoated, only plasma nitrided forming tool. Therefore, the tools are used for an incremental bulk forming process on 2 mm thick metal sheets made of aluminum. The results show that the developed methodology is feasible to reduce the process forces and to improve the durability of the tools.© (2012) Trans Tech Publications.
    view abstractdoi: 10.4028/
  • 2012 • 38 Biocompatible nanostructured coatings based on calcium phosphates prepared by means of rf-magnetron sputtering deposition
    Surmeneva, M. and Surmenev, R. and Pichugin, V. and Ivanova, A. and Grubova, I. and Chaikina, M. and Khlusov, I. and Kovtun, A. and Epple, M.
    Proceedings - 2012 7th International Forum on Strategic Technology, IFOST 2012 (2012)
    The aim of this study was to prevent the problems associated with implants failure. Biocompatible nanostructured thin films of either Si- or Ag-containing non-stoichiometric hydroxyapatite (HA) were deposited by method of radio-frequency (rf) magnetron sputtering. Plates of Ti, Ti6Al4V and 316 L SS were used as substrates. The thin coatings were characterized by EDX, ESEM, XRD, IR spectroscopy, HRTEM, nanoindentation and scratch-test. HRTEM observations of the coatings showed a nanocrystalline structure mixed with amorphous regions. It was found that the morphology, structure and the preferred orientation of the films are greatly affected by the parameters of deposition (rf-power, substrate temperature and voltage bias). The as-deposited modified CaP-based coatings are dense, pore-free and their composition resembles that of the precursor target composition. The Si- and Ag- containing HA coatings had a hardness of 10-12 GPa. A low rf-power (30 W) resulted in amorphous or low crystalline CaP coating structure. An increase in rf-power (> 200 W) induced the coating crystallization. The occurrence of the different structure types is described as function of the bias voltage and temperatures. The negative substrate bias allowed to vary the Ca/P ratio in the range of 1.53 to 4. In vitro biocompatibility assessments of the films using the MG63 osteoblast-like cells indicated excellent cell adherence and surface colonization. Si-containing rf-magnetron films promote osteogenic differentiation of human stromal stem cells in vitro. The coatings are prospective to be used in clinical practice: in stomatology or craniofacial medicine, where the leaching of toxic ions from the substrate is necessary or the initial material surface porosity for a further bone in growth should be preserved. © 2012 IEEE.
    view abstractdoi: 10.1109/IFOST.2012.6357526
  • 2012 • 37 Particle size distribution of the filling powder in cored wires: Its effect on arc behavior, in-flight particle behavior, and splat formation
    Tillmann, W. and Abdulgader, M.
    Journal of Thermal Spray Technology 21 706-718 (2012)
    The filling powder, as a part of the feedstock in cored wires, directly influences the particle formation, in-flight particle behavior, the coating microstructure, and consequently the behavior of the desired coating, produced by twin wire arc spraying (TWAS). In this work, the effect of the particle size distribution of the filling powder in cored wires was studied. The process parameters were changed for different intervals of particle size distributions. Arc fluctuations were measured and found to be higher at smaller particle sizes. The in-flight particles showed a higher velocity when powders with smaller grain sizes were used and higher particle temperature when bigger grain sizes were used. The splats tended to form a regular disk shape in the case of smaller grain sizes. This investigation studied the important effect of using cored wires and the filling powders grain sizes on the TWAS process. © ASM International.
    view abstractdoi: 10.1007/s11666-012-9769-7
  • 2012 • 36 Testing and evaluation of thermal-barrier coatings
    Vaßen, R. and Kagawa, Y. and Subramanian, R. and Zombo, P. and Zhu, D.
    MRS Bulletin 37 911-916 (2012)
    Thermal-barrier coatings are complex systems with properties that largely depend on their specific microstructure. Their properties change during operation, typically leading to degradation. A further difficulty arises from the fact that this degradation also depends on specific loading conditions that can be rather complex. Different laboratory setups are described that simulate, at least partially, the actual loading conditions. In addition, sensing and nondestructive methods are described that are targeted toward reliable operation of a gas-turbine engine with thermal-barrier coated components. © 2012 Materials Research Society.
    view abstractdoi: 10.1557/mrs.2012.235
  • 2012 • 35 Hybrid sol-gel silica films with (TiO 2-CeO 2) binary nanopowders
    Zaharescu, M. and Nicolescu, M. and Gartner, M. and Barau, A. and Predoana, L. and Anastasescu, M. and Stoica, M. and Szekeres, A.
    Journal of Physics: Conference Series 356 (2012)
    In the present work the preparation of hybrid sol-gel silica coatings doped with binary TiO 2-CeO 2 nanopowders was studied. The oxide powder was embedded in the hybrid matrix either by in-situ generation or by previously prepared powder dispersion. The main objective of the work was to establish a correlation between the method of generation of the dopant particles in the system and the properties of the films. The films were deposited on silicon wafer and glass substrates by the 'dip-coating' method and characterized in the as-prepared stage and after annealing at 120 °C. The optical and morphological properties of the films deposited on glass and silicon wafer were determined by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). © Published under licence by IOP Publishing Ltd.
    view abstractdoi: 10.1088/1742-6596/356/1/012018
  • 2011 • 34 Mechanistic Considerations on Contact-Active Antimicrobial Surfaces with Controlled Functional Group Densities
    Bieser, A.M. and Tiller, J.C.
    Macromolecular Bioscience 11 526-534 (2011)
    A series of N-alkyl-N,N-dimethyldeoxyammonium celluloses is synthesized by converting tosyl celluloses with DBA and DDA, respectively. Surface coatings with these water-insoluble derivatives contain well-defined densities of quaternary ammonium functions and nonactive hydrophobic and hydrophilic groups. It is shown that the antimicrobial activity of such surfaces against S. aureus requires a delicate balance between DDA, BDA, and hydrophobic groups. A mechanism is proposed that involves the selective adhesion of anionic phospholipids from the bacterial cell membrane. This so-called phospholipid sponge effect is supported by the fact that all coatings could be deactivated by treatment with SDS or negatively charged phospholipids, but not with neutral phospholipids. The present work strives to gain better insights in the mechanism of surface grafted antimicrobial groups. To this end a series of water-insoluble cellulose derivatives with well-defined ratios of different quaternary ammonium groups and hydrophobic substituents were synthesized and their films were investigated regarding their antimicrobial potential. From the results we propose a new mechanism for such surface grafted biocides, the "phospholipid sponge effect." © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mabi.201000398
  • 2011 • 33 Contact-Active Antimicrobial and Potentially Self-Polishing Coatings Based on Cellulose
    Bieser, A.M. and Thomann, Y. and Tiller, J.C.
    Macromolecular Bioscience 11 111-121 (2011)
    A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase. A stable coating is presented that can kill microbes on contact and is potentially self-polishing only in the presences of these microbes. This is realized by grafting antimicrobial quarternary ammonium groups via polymeric spacers made of poly(2-ethyl-1,3-oxazoline)s on a cellulose backbone. With optimum DS and spacer length, this derivative is indeed contact-active antimicrobial against S. aureus and E. coli and degradable by the enzyme cellulase. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mabi.201000306
  • 2011 • 32 Solid particle erosion of thermal spray and physical vapour deposition thermal barrier coatings
    Cernuschi, F. and Lorenzoni, L. and Capelli, S. and Guardamagna, C. and Karger, M. and Vaßen, R. and von Niessen, K. and Markocsan, N. and Menuey, J. and Giolli, C.
    Wear 271 2909-2918 (2011)
    Thermal barrier coatings (TBC) are used to protect hot path components of gas turbines from hot combustion gases. For a number of decades, in the case of aero engines TBCs are usually deposited by electron beam physical vapour deposition (EB-PVD). EB-PVD coatings have a columnar microstructure that guarantees high strain compliance and better solid particle erosion than PS TBCs. The main drawback of EB-PVD coating is the deposition cost that is higher than that of air plasma sprayed (APS) TBC. The major scientific and technical objective of the UE project TOPPCOAT was the development of improved TBC systems using advanced bonding concepts in combination with additional protective functional coatings. The first specific objective was to use these developments to provide a significant improvement to state-of-the-art APS coatings and hence provide a cost-effective alternative to EB-PVD. In this perspective one standard porous APS, two segmented APS, one EB-PVD and one PS-PVD™ were tested at 700°C in a solid particle erosion jet tester, with EB-PVD and standard porous APS being the two reference systems.Tests were performed at impingement angles of 30° and 90°, representative for particle impingement on trailing and leading edges of gas turbine blades and vanes, respectively. Microquartz was chosen as the erodent being one of the main constituents of sand and fly volcanic ashes. After the end of the tests, the TBC microstructure was investigated using electron microscopy to characterise the failure mechanisms taking place in the TBC.It was found that PS-PVD™ and highly segmented TBCs showed erosion rates comparable or better than EB-PVD samples. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2011.06.013
  • 2011 • 31 Thermal stability of TiAIN/CrN multilayer coatings studied by atom probe tomography
    Choi, P.-P. and Povstugar, I. and Ahn, J.-P. and Kostka, A. and Raabe, D.
    Ultramicroscopy 111 518-523 (2011)
    This study is about the microstructural evolution of TiAlN/CrN multilayers (with a Ti:Al ratio of 0.75:0.25 and average bilayer period of 9 nm) upon thermal treatment. Pulsed laser atom probe analyses were performed in conjunction with transmission electron microscopy and X-ray diffraction. The layers are found to be thermally stable up to 600 °C. At 700 °C TiAlN layers begin to decompose into Ti- and Al-rich nitride layers in the out-of-plane direction. Further increase in temperature to 1000 °C leads to a strong decomposition of the multilayer structure as well as grain coarsening. Layer dissolution and grain coarsening appear to begin at the surface. Domains of AlN and TiCrN larger than 100 nm are found, together with smaller nano-sized AlN precipitates within the TiCrN matrix. Fe and V impurities are detected in the multilayers as well, which diffuse from the steel substrate into the coating along columnar grain boundaries. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.ultramic.2010.11.012
  • 2011 • 30 Cavitation erosion of NiAl-bronze layers generated by friction surfacing
    Hanke, S. and Fischer, A. and Beyer, M. and dos Santos, J.
    Wear 273 32-37 (2011)
    Friction surfacing is a solid-state process, which allows deposition welding at temperatures below the melting range. For this investigation coating layers of NiAl-bronze were deposited by friction surfacing on self-mating substrates, followed by microstructural characterisation. Further, cavitation tests were performed in order to investigate wear resistance. Cavitation erosion mechanisms were analysed by means of optical and electron microscopy. All coatings show incubation periods about twice as long as those of the substrate material, while their average rate of material loss is about one half of that of the substrate. The differences in cavitation erosion resistance are due to more ductile behaviour of the coatings, as well as corrosion increasing the wear of the as-cast material. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.wear.2011.06.002
  • 2011 • 29 On the opening of a class of fatigue cracks due to thermo-mechanical fatigue testing of thermal barrier coatings
    Hernandez, M.T. and Cojocaru, D. and Bartsch, M. and Karlsson, A.M.
    Computational Materials Science 50 2561-2572 (2011)
    The evolution of fatigue cracks observed in thermal barrier coatings (TBCs) subjected to an accelerated test scheme is investigated via numerical simulations. The TBC system consists of a NiCoCrAlY bond coat and partially yttria stabilized zirconia top coat with a thermally grown oxide (TGO) between these two coatings. The cracks of interest evolve in the bond coat parallel and near the interface with the TGO during thermo-mechanical fatigue testing. In their final stage, the cracks lead to partial spallation of the TBC. This study focuses on why the cracks open to their characteristic shape. To this end, finite element simulations are utilized. The crack surface separation is monitored for a range of material properties and oxidation rates. The simulations show that the inelastic response of the bond coat and the oxidation rate of the TGO govern the crack surface separation. Most interestingly, permanent separation of the crack surfaces is caused by a structural ratcheting in the vicinity of the crack. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.commatsci.2011.03.041
  • 2011 • 28 Columnar-structured thermal barrier coatings (TBCs) by thin film low-pressure plasma spraying (LPPS-TF)
    Hospach, A. and Mauer, G. and Vaßen, R. and Stöver, D.
    Journal of Thermal Spray Technology 20 116-120 (2011)
    The very low-pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with coverage of a large area by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low-pressure plasma-spraying processes (LPPS) operating at 5-20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters, it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar-structured TBCs. However, the deposition rate is low, and the line-of-sight nature of the process involves specific restrictions. In this article, the deposition of TBCs by the LPPS-TF process is shown. How the evaporation of the feedstock powder could be improved and to what extent the deposition rates could be increased were investigated. © 2010 ASM International.
    view abstractdoi: 10.1007/s11666-010-9549-1
  • 2011 • 27 Processing and damping properties of sputtered NiTi thin films for tools in machining processes
    Kahleyss, F. and De Miranda, R.L. and Surmann, T. and Zamponi, C. and MacHai, C. and Biermann, D. and Quandt, E.
    Journal of Materials Engineering and Performance 20 500-505 (2011)
    Nowadays, many manufacturing processes require the machining of complex forms with a high aspect ratio or cavities. Tools with a long overhang length are a common method to meet these requirements. Typical examples for this are boring bars for bore-turning and the milling with very long cutters. These tools tend to vibrate strongly due to their slender shape. The stress-induced transformation of austenite to martensite and the distinctive hysteresis loop allow the NiTi shape memory alloys (SMA) to absorb vibration energy. This article describes the innovative approach to dampen process vibrations by coating the tool shafts of cutting tools with long overhang with NiTi thin films. It explores how these thin films can be applied on polished tungsten carbide shafts and how their modal parameters are modified by these coatings. In a further step, this knowledge is used to calculate stability charts of corresponding machining processes. The study reported in this article identified the stabilizing effects of coatings with a thickness of 2-4 lm on milling processes. The minimum stability limit was increased by up to 200%. © ASM International.
    view abstractdoi: 10.1007/s11665-011-9847-x
  • 2011 • 26 Current developments and challenges in thermal barrier coatings
    Mauer, G. and Vaßen, R.
    Surface Engineering 27 477-479 (2011)
    Some of the recent developments and challenges in thermal barrier coatings (TBC) are discussed. A wide flexibility of coating morphologies can be obtained by atmospheric plasma spraying (APS), and the size of microstructural features within the coatings is typically governed by that of the feedstock. By means of suspension plasma spraying (SPS), high segmentation crack densities can be obtained in TBCs while the porosity is maintained at a considerably higher level than by APS. Partially yttria stabilised zirconia (YSZ) with 6 to 8 wt-% yttria content is frequently used as TBC material due to its high thermal expansion coefficient and its relatively good fracture toughness. A strategy to improve the efficiency of gas turbines is abradable TBCs which are widely used in compressors and high-pressure stages. The infiltration of TBC microstructures by thin oxide layers applied by atomic layer chemical vapour deposition can yield improved sintering stability.
    view abstractdoi: 10.1179/1743294411Y.0000000013
  • 2011 • 25 Development of graded Ni-YSZ composite coating on Alloy 690 by Pulsed Laser Deposition technique to reduce hazardous metallic nuclear waste inventory
    Sengupta, P. and Rogalla, D. and Becker, H.W. and Dey, G.K. and Chakraborty, S.
    Journal of Hazardous Materials 192 208-221 (2011)
    Alloy 690 based 'nuclear waste vitrification furnace' components degrade prematurely due to molten glass-alloy interactions at high temperatures and thereby increase the volume of metallic nuclear waste. In order to reduce the waste inventory, compositionally graded Ni-YSZ (Y 2O 3 stabilized ZrO 2) composite coating has been developed on Alloy 690 using Pulsed Laser Deposition technique. Five different thin-films starting with Ni80YSZ20 (Ni 80wt%+YSZ 20wt%), through Ni60YSZ40 (Ni 60wt%+YSZ 40wt%), Ni40YSZ60 (Ni 40wt%+YSZ 60wt%), Ni20YSZ80 (Ni 20wt%+YSZ 80wt%) and Ni0YSZ100 (Ni 0wt%+YSZ 100wt%), were deposited successively on Alloy 690 coupons. Detailed analyses of the thin-films identify them as homogeneous, uniform, pore free and crystalline in nature. A comparative study of coated and uncoated Alloy 690 coupons, exposed to sodium borosilicate melt at 1000°C for 1-6h suggests that the graded composite coating could substantially reduced the chemical interactions between Alloy 690 and borosilicate melt. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.jhazmat.2011.05.006
  • 2011 • 24 Hydrogen quantification of magnetron sputtered hydrogenated amorphous carbon (a-C:H) coatings produced at various bias voltages and their tribological behavior under different humidity levels
    Tillmann, W. and Hoffmann, F. and Momeni, S. and Heller, R.
    Surface and Coatings Technology 206 1705-1710 (2011)
    Hydrogenated amorphous carbon (a-C:H) films have extraordinary tribological properties under dry conditions since the C-atoms at the surface are hydratized and not available for any bonding with the opposing material. Under wet conditions water molecules are weakly absorbed by the a-C:H-coatings so the interaction between the coating surface and the tribological counterpart changes to a dipole-like interaction which is disadvantageous for the tribological performance. According to this, the hydrogen-content plays an important role in the wear and friction behavior of diamond-like carbon (DLC) coatings under different humid conditions.This work focuses on the quantification of the hydrogen content of differently bias a-C:H top layered coating systems and their influence on the tribological behavior under different humidity conditions. By means of a magnetron sputter device DLC-coating systems with an a-C:H-top layer have been deposited at bias voltages between -75 and -200. V. In order to quantify the hydrogen content of the layers Nuclear Reaction Resonance Analysis (NRRA) was used. In combination with the results of the tribological tests under different humid conditions using a ball-on-disk-tester, correlations between the hydrogen content, the bias voltage and the wear and friction performance were made. A clear relationship between the bias voltage and the hydrogen content has been observed, since the values decrease consistently from 27.2. at.% at -75. V to a minimum of 19.9. at.% at -200. V bias voltage. Furthermore the different humidity levels show a strong influence on the tribological performance, while the bias voltage effects mainly the wear and friction results of the samples tested under wet conditions. © 2011 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2011.07.089
  • 2011 • 23 Sliding wear behaviour of diamond-like carbon (DLC) coatings deposited on plasma nitrided steels
    Tillmann, W. and Momeni, S. and Hoffmann, F.
    International Journal of Materials Research 102 1007-1013 (2011)
    A hydrogen-free DLC (diamond-like carbon) coating was deposited with a bias voltage of 150 V on various high and low alloy tool steels to study the effect of the pre-treatment of the steel substrate on the wear behaviour of the DLC coating in sliding contact with uncoated counterparts. The morphology and mechanical properties of the DLC coating as well as the effect of plasma nitriding on the surface roughness and the hardness of the steels were studied in order to perform a correlation with the results of tribology tests. It could be concluded from the results that the plasma nitriding of the high alloy tool steel X210CrW12 leads to a significant decrease in the wear and friction coefficient of the DLC coating. Furthermore, it was found that plasma nitriding of the steel results in a decrease in the wear of uncoated counterparts as well. Finally, the wear mechanisms and failure of DLC coatings deposited on various steels were compared with each other and discussed analytically. © Carl Hanser Verlag GmbH & Co. KG.
    view abstractdoi: 10.3139/146.110547
  • 2011 • 22 Influence of Ti/TiAlN-multilayer designs on their residual stresses and mechanical properties
    Vogli, E. and Tillmann, W. and Selvadurai-Lassl, U. and Fischer, G. and Herper, J.
    Applied Surface Science 257 8550-8557 (2011)
    In this research work, Ti/TiAlN multilayers of various designs were deposited onto substrates pretreated by different etching procedures. The influence of multilayer design and substrate pretreatment on multilayers adhesion, hardness, wear and friction coefficients was systematically analyzed and correlated with residual stresses of these multilayers as well as with residual stresses on the coating-near substrate region, which were analyzed by synchrotron X-ray diffraction at HZB-BESSYII. These investigations show that the adhesion can be improved by a specific etching procedure, which cause increased compressive stress in the coating-near the substrate region. Additionally, it was found, that the multilayer with the thickest ceramic layers has the highest hardness and the lowest wear coefficients as well as the lowest compressive residual stress within studied multilayers. © 2011 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.apsusc.2011.05.013
  • 2011 • 21 TiO 2 coating of high surface area silica gel by chemical vapor deposition of TiCl 4 in a fluidized-bed reactor
    Xia, W. and Mei, B. and Sánchez, M.D. and Strunk, J. and Muhler, M.
    Journal of Nanoscience and Nanotechnology 11 8152-8157 (2011)
    TiO 2 was deposited on high surface area porous silica gel (400 m 2g -1) in a fluidized bed reactor. Chemical vapor deposition was employed for the coating under vacuum conditions with TiCl 4 as precursor. Nitrogen physisorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis spectroscopy were applied to characterize the obtained TiO 2-SiO 2 composites with different Ti loadings up to 5 wt%. Only a slight decrease in the specific surface area was detected at low Ti loadings. At a Ti loading of 2 wt%, TiO 2 was found to be highly dispersed on the SiO 2 surface likely in form of a thin film. At higher Ti loadings, two weak reflections corresponding to anatase TiO 2 were observed in the diffraction patterns indicating the presence of crystalline bulk TiO 2. High resolution XPS clearly distinguished two types of Ti species, i.e., Ti-O-Si at the interface and Ti-O-Ti in bulk TiO 2. The presence of polymeric TiOx species at low Ti loadings was confirmed by a blue shift in the UV-vis spectra as compared to bulk TiO 2. All these results point to a strong interaction between the TiO 2 deposit and the porous SiO 2 substrate especially at low Ti loadings. Copyright © 2011 American Scientific Publishers All rights reserved.
    view abstractdoi: 10.1166/jnn.2011.5107
  • 2010 • 20 Grinding of arc-sprayed tungsten carbide coatings on machining centers - Process configuration and simulation
    Biermann, D. and Mohn, T. and Blum, H. and Kleemann, H.
    Key Engineering Materials 438 115-122 (2010)
    This paper describes the special demands placed on the grinding of arc-sprayed WC-Fe coatings on a conventional machining center. Basic process configuration, experimental results, measurement methods and an approach for a hybrid simulation system are presented. © (2010) Trans Tech Publications.
    view abstractdoi: 10.4028/
  • 2010 • 19 Modified DLC-coated guide pads for BTA deep hole drilling tools
    Biermann, D. and Kessler, N. and Upmeier, T. and Stucky, T.
    Key Engineering Materials 438 195-202 (2010)
    The BTA (Boring and Trepanning Association) deep hole drilling process is commonly used to machine boreholes with a large drilling depth-to-diameter ratio (l/D) and outstanding workpiece quality. The asymmetric tool design leads to a nonzero radial component of the cutting force and the passive force, which are conducted to the borehole wall by so-called guide pads. These guide pads smooth the borehole wall by a forming process and improve the surface quality. Processes, that machine materials with a high adhesion tendency, such as high alloy stainless steel, suffer from poor surface quality in the borehole and the adhesion from the workpiece material on the guide pads. In this paper modified Diamond-Like-Carbon (DLC) coated guide pads for BTA deep hole drilling tools are investigated. The scope of the experiments was the reduction of the adhesion by reducing the friction coefficient of the guide pads, as well as the improvement of the quality of the borehole wall. © (2010) Trans Tech Publications.
    view abstractdoi: 10.4028/
  • 2010 • 18 Thermal-gradient testing of thermal barrier coatings under simultaneous attack by molten glassy deposits and its mitigation
    Drexler, J.M. and Aygun, A. and Li, D. and Vaßen, R. and Steinke, T. and Padture, N.P.
    Surface and Coatings Technology 204 2683-2688 (2010)
    Degradation of thermal barrier coatings (TBCs) in gas-turbine engines by molten calcium-magnesium-aluminosilicate (CMAS) glassy deposits is becoming a pressing issue, as engines are required to operate under increasingly harsh conditions. While new approaches for mitigating CMAS attack of TBCs are starting to emerge, there is a need for appropriate tests for evaluating the efficacy of those approaches. To that end, we present here a new thermal-cycling test for the evaluation of TBC performance, where a thermal gradient is applied across the TBC, with simultaneous injection of CMAS. The conditions simulated in this new test are closer to actual conditions in an engine, as compared to the conventional furnace test without thermal gradient. This new test is applied to a TBC with a new composition designed for mitigating CMAS attack, where the mitigation mechanisms are observed to be similar to those found in the conventional furnace test. However, based on a previously established mechanics model it is shown here that thermal-gradient cyclic testing is essential for evaluating thermomechanical performance of TBCs under attack by CMAS, and that the use of just the conventional furnace test can lead to the underestimation of the TBC performance. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2010.02.026
  • 2010 • 17 Sol-gel deposition of multiply doped thermographic phosphor coatings Al2O3:(Cr3+, M3+) (M = Dy, Tm) for wide range surface temperature measurement application
    Eckert, C. and Pflitsch, C. and Atakan, B.
    Progress in Organic Coatings 68 126-129 (2010)
    A promising method of measuring surface temperatures in harsh environments is the use of thermographic phosphor coatings. There, the surface temperature is evaluated from the phosphorescence decay lifetime following a pulsed laser or flash lamp light excitation. Depending on the used dopant, single doped M3+:α-Al2O3 (M = Cr, Dy, Tm) emit at 694 nm (Cr3+), 488 nm (Dy3+), 584 nm (Dy3+), and 459 nm (Tm3+), respectively. However, the accessible temperature range with a single dopant is limited: for the Cr3+-transition from 293 K up to 900 K, and for the Dy3+ and Tm3+-transitions both from 1073 K up to 1473 K. In the present study a new approach is followed to extend these limitations by co-doping two dopants using the sol-gel method and dip coating of α-Al2O3 thin films. For that application (Dy3+ + Cr3+) co-doped thin α-Al2O3 films and (Tm3+ + Cr3+) co-doped α-Al2O3 films with thicknesses of 4-6 μm were prepared, and the temperature-dependent luminescence properties (emission spectra and lifetimes) were analysed after pulsed laser excitation in the UV (355 nm). The phosphorescence lifetime as a function of temperature were measured between 293 K and 1473 K. A considerably extended range for surface temperature evaluation was established following this new approach by combining different dopants on the molecular level. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.porgcoat.2009.08.021
  • 2010 • 16 Design and characterization of novel wear resistant multilayer CVD coatings with improved adhesion between Al2O3 and Ti(C,N)
    Garcia, J. and Pitonak, R. and Weißenbacher, R. and Köpf, A. and Soldera, F. and Suarez, S. and Miguel, F. and Pinto, H. and Kostka, A. and Mücklich, F.
    Advanced Engineering Materials 12 929-934 (2010)
    Multilayer CVD coatings for high speed cutting applications were designed to achieve high wear and heat resistance during machining of steel alloys. In this work the microstructure and cutting performance of these novel multilayer CVD coatings are investigated and compared with standard CVD multilayer coatings. 3D-FIB tomography is used to characterize the microstructure of the layers, especially the transition between the Ti(C,N) and the Al 2O3 layer. The 3D reconstruction of the surface of the Ti(C,N) layer shows the formation of protruded Ti(C,N) grains with a very particular architecture, which penetrate into the Al2O3 top-layer, providing a mechanical anchoring between both layers. Cemented carbides coated with the novel CVD multilayer present reduced crater and flank wear as well as improved adherence between the Al2O3 top-layer and the Ti(C,N) layer leading to a dramatic improvement of cutting performance. The microstructure and cutting performance of multilayer CVD coatings with a novel transition between the Ti(C,N) and the Al 2O3 layer are investigated. 3D-FIB tomography shows the formation of protruded Ti(C,N) grains with a particular architecture, which penetrate into the Al2O3 top-layer, providing a mechanical anchoring between both layers. Cutting tools coated with the novel CVD multilayer show dramatic improvement of cutting performance, due to reduced crater and flank wear and improved adherence between the Ti(C,N) and the Al 2O3 top-layer. © 2010 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/adem.201000130
  • 2010 • 15 Plasma mediated collagen-I-coating of metal implant materials to improve biocompatibility
    Hauser, J. and Koeller, M. and Bensch, S. and Halfmann, H. and Awakowicz, P. and Steinau, H.-U. and Esenwein, S.
    Journal of Biomedical Materials Research - Part A 94 19-26 (2010)
    This study describes the collagen-I coating of titanium and steel implants via cold low-pressure gas plasma treatment. To analyze the coatings in terms of biocompatibility osteoblast-like osteosarcoma cells and human leukocytes were cultivated on the metal surfaces. Two different implant materials were assessed (Ti6Al4V, X2CrNiMo18) and four different surface properties were evaluated: (a) plasma pretreated and collagen-I coated implant materials; (b) collagen-I dip-coated without plasma pretreatment; (c) plasma treated but not collagen-I coated; (d) standard implant materials served as control. The different coating characteristics were analyzed by scanning electron microscopy (SEM). For adhesion and viability tests calcein-AM staining of the cells and Alamar blue assays were performed. The quantitative analysis was conducted by computer assisted microfluorophotography and spectrometer measurements. SEM analysis revealed that stable collagen-I coatings could not be achieved on the dip-coated steel and titanium alloys. Only due to pretreatment with low-pressure gas plasma a robust deposition of collagen I on the surface could be achieved. The cell viability and cell attachment rate on the plasma pretreated, collagen coated surfaces was significantly (p < 0.017) increased compared to the non coated surfaces. Gas plasma treatment is a feasible method for the deposition of proteins on metal implant materials resulting in an improved biocompatibility in vitro. © 2010 Wiley Periodicals, Inc.
    view abstractdoi: 10.1002/jbm.a.32672
  • 2010 • 14 Metal-free and electrocatalytically active nitrogen-doped carbon nanotubes synthesized by coating with polyaniline
    Jin, C. and Nagaiah, T.C. and Xia, W. and Spliethoff, B. and Wang, S. and Bron, M. and Schuhmann, W. and Muhler, M.
    Nanoscale 2 981-987 (2010)
    Nitrogen doping of multi-walled carbon nanotubes (CNTs) was achieved by the carbonization of a polyaniline (PANI) coating. First, the CNTs were partially oxidized with KMnO4 to obtain oxygen-containing functional groups. Depending on the KMnO4 loading, thin layers of birnessite-type MnO2 (10 wt% and 30 wt%) were obtained by subsequent thermal decomposition. CNT-supported MnO2 was then used for the oxidative polymerization of aniline in acidic solution, and the resulting PANI-coated CNTs were finally heated at 550 °C and 850 °C in inert gas. The samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. A thin layer of carbonized PANI was observed on the CNT surface, and the surface nitrogen concentration of samples prepared from 30% MnO 2 was found to amount to 7.6 at% and 3.8 at% after carbonization at 550 °C and 850 °C, respectively. These CNTs with nitrogen-containing shell were further studied by electrochemical impedance spectroscopy and used as catalysts for the oxygen reduction reaction. The sample synthesized from 30 wt% MnO2 followed by carbonization at 850 °C showed the best electrochemical performance indicating efficient nitrogen doping. © 2010 The Royal Society of Chemistry.
    view abstractdoi: 10.1039/b9nr00405j
  • 2010 • 13 Silver containing sol-gel coatings on polyamide fabrics as antimicrobial finish-description of a technical application process for wash permanent antimicrobial effect
    Mahltig, B. and Textor, T.
    Fibers and Polymers 11 1152-1158 (2010)
    This paper reports on an antimicrobial finishing for polyamide with high washfastness. As antimicrobial agent modified silica sols containing silver components are used as coating agent and are applied to the polyamide fabric by using a semi-industrial procedure. The antimicrobial properties of coated polyamide fabrics are determined against the bacteria E. coli. Significant antimicrobial effects are observed even after 40 washing cycles. The amount of silver on the polyamide fabrics was measured by using ICP-OES. Besides this, samples are investigated by means of UV/Vis-spectroscopy and scanning electron microscopy. Furthermore textile properties as, e. g., air permeability and mechanical properties were measured. Due to high antimicrobial effect and the strong washfastness of this finishing, this reported method could be of high interest for industrial production processes. © 2010 The Korean Fiber Society and Springer Netherlands.
    view abstractdoi: 10.1007/s12221-010-1152-z
  • 2010 • 12 Temporal stability of photothermally fabricated micropatterns in supported phospholipid multilayers
    Mathieu, M. and Schunk, D. and Franzka, S. and Mayer, C. and Hartmann, N.
    Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films 28 953-957 (2010)
    The temporal stability of photothermally fabricated micropatterns in multilayered films of 1,2-dioleoyl-sn-glycero-3-phosphate on surface-oxidized silicon substrates is investigated. Multilayered films are fabricated via spin coating of diluted phospholipid solutions. A focused beam of an Ar+ laser at λ=514 nm and a 1/ e2 spot diameter of 2.5 μm is used to locally remove the coating and fabricate micropatterns. Subsequently, the temporal stability of such patterns at ambient conditions in air and in water is examined using optical microscopy. Generally, these patterns are stable on a time scale of several hours to days, both in air and in water, and hence provide sufficient time for most follow-on experiments. The spin-coated phospholipid films, though, are intrinsically unstable in water. In particular, some hours after immersion in water, dewetting of the film starts to set in. The implications of these results for potential applications are discussed. © 2010 American Vacuum Society.
    view abstractdoi: 10.1116/1.3271156
  • 2010 • 11 Process diagnostics in suspension plasma spraying
    Mauer, G. and Guignard, A. and Vaßen, R. and Stöver, D.
    Surface and Coatings Technology 205 961-966 (2010)
    Benefits and limitations of process diagnostics are investigated for the suspension plasma spraying of yttria-stabilized zirconia thermal barrier coatings. The methods applied were enthalpy probe measurements, optical emission spectroscopy, and in-flight particle diagnostic.It was proved that the plasma characteristics are not affected negatively by the injection of the ethanol based suspension since the combustion of species resulting from ethanol decomposition achieves a gain of plasma enthalpy. Furthermore, the conditions of the suspension injection into the plasma were found to be optimum as a significant content of evaporated powder material could be detected. Regarding the void content and segmentation crack density of the coatings, the in-flight particle diagnostic showed that the spray distance should be dimensioned in a way that the molten particles reach the substrates just before solidification starts. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2010.03.007
  • 2010 • 10 Concept for a phosphorescent thermal history sensor
    Rabhiou, A. and Feist, J. and Kempf, A. and Skinner, S. and Heyes, A.
    Proceedings of the ASME Turbo Expo 3 343-351 (2010)
    The thermal history of hot surfaces is of great practical importance, but very hard to measure. Thermal indicating paints offer one possible and practical way, but they have many disadvantages. A novel concept for the utilisation of phosphorescent coatings as thermal history sensors has been proposed by Feist et al. [1] in 2007. These phosphor coatings undergo irreversible changes when exposed to high temperatures that affect their light emission properties. A subsequent off-line analysis of the emission at room temperature can reveal the temperature history of the coating. In this paper, an investigation of the amorphous-tocrystalline change of Y2SiO5 : Tb is reported and used to provide a proof of concept for a phosphorescent thermal history sensor. The phosphor powder was calcined at different temperatures, and characterised using photoluminescence spectroscopy. A calibration curve was generated from the measurements and is presented and discussed. Copyright © 2010 by ASME.
    view abstractdoi: 10.1115/GT2010-23517
  • 2010 • 9 Nanosols for preparation of antistatic coatings simultaneously yielding water and oil repellent properties for textile treatment
    Textor, T. and Mahltig, B.
    Materials Technology 25 74-80 (2010)
    This paper reports the preparation of novel nanosol coating solutions for textile treatment which allow the application of coatings yielding antistatic and water/oil repellent properties simultaneously. For this, simple SiO 2 sols are modified with both hydrophilic components acting as components responsible for the antistatic properties and with hydrophobic/oleophobic components leading to water and oil repellent properties. Amino-modified alkyltrialkoxysilane N-(2-aminoethyl)-3- aminopropyltrimethoxysilane is used as a hydrophilic component. Alkyl and fluoroalkyl-trialkoxysilanes are evaluated as hydrophobic components. The resulting coating materials will be highly repellent and nevertheless absorb sufficient amount of water guaranteeing antistatic properties. Different coating materials are applied and the repellent properties are investigated by means of contact angle measurements, DuPont test and oil repellence test. Surface resistance is measured to evaluate the antistatic properties and thermogravimetric measurements prove a reversible absorption of humidity of the coating. © 2010 W. S. Maney & Son Ltd.
    view abstractdoi: 10.1179/175355510X12716725525555
  • 2010 • 8 X-ray diffraction residual stress analysis on PVD-multilayer coatings
    Tillmann, W. and Selvadurai-Laßl, U. and Vogli, E. and Fischer, G. and Hoffmann, F.
    Materialwissenschaft und Werkstofftechnik 41 482-488 (2010)
    Hard and wear resistant thin layers provides significant improvements in tools employed in manufacturing industry and are recently of great interest to increase as well as to enhance the tools? performance and lifetime. Ceramic PVD-layers already feature a high hardness combined with a high abrasive wear resistance. However, such layers possess only a limited lifetime due to their low toughness. To increase the toughness as well as the durability of such layers multilayer systems are steadily developed. This research work presents the first results of the influence of the steel substrate pretreatments, multilayer designs and coating process parameters on the properties of two innovative PVD metal-ceramic multilayers, Ti/TiAIN and Cr/CrAIN. It was obviously that the substrate pretreatment and the multilayer design have a large influence on the layer properties and residual stresses. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstractdoi: 10.1002/mawe.201000630
  • 2010 • 7 Improvement of press dies used for the production of diamond composites by means of DUPLEX-PVD-coatings
    Tillmann, W. and Vogli, E. and Momeni, S.
    Surface and Coatings Technology 205 1571-1577 (2010)
    In the machining of hard materials such as glass or stone, cemented carbides have been recently replaced by diamond tools, consisting of a metallic carrier, on to which diamond segments are brazed. One of the most economic ways for the production of diamond segments is the cold compaction of the mixture of a metallic powder and diamond particles. Due to a highly abrasive sliding contact between diamond particles and the die walls, the wear rate of the press dies is very high. As a result of a low lifetime of the press dies, they must be replaced in short time periods. To avoid the costly and time-consuming substitution of the press dies, in this work PVD-coatings were deposited on the inner surface of the pre-plasma nitrided press dies (DUPLEX treatment). Thereby, various high and low alloy tool steels were treated by means of plasma nitriding process. Subsequently, a nanocomposite TiAlN coating (nc-TiAlN) was deposited by means of a high ionization magnetron sputtering device on nitrided and non-nitrided steel substrates. The mechanical and tribological properties of these coating systems were studied by means of several standard tests such as nanoindentation, ball-on-disc and scratch test. The most wear resistant coating system was chosen to employ on the inner surface of the press dies. The wear resistance of the press dies developed in this study was tested under real loading condition during compaction of the mixture of diamond particles and cobalt powder. It was revealed that employing plasma nitrided tool, steels coated with nanocomposite TiAlN decreases the wear rate of the press dies up to 76%. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2010.08.048
  • 2010 • 6 Nanostructured bionic PVD-coatings for forming tools
    Tillmann, W. and Vogli, E. and Herper, J. and Haase, M.
    Key Engineering Materials 438 41-48 (2010)
    It is very important to minimize wear and friction in forming processes in order to avoid adhesion between work piece and tool. For the realization of these requirements, the PVD-coating system CrAlN was deposited and tested on substrates made from high speed steel 1.3343 by means of a reactive sputter process. The coatings were deposited as single- and multilayers with a metallic Crinterlayer. Prior to realizing the appropriate coating design, the substrates were pre-structured. For this purpose natural surfaces were used as a pattern and tested in this research work. The skin of an insect serves as a model and its fine structures were reproduced on the substrate surface by milling. The generated specimens were analyzed with a scanning electron microscope, nanoindenter and ball-on-disc tester to compare the performance of the coating systems. © (2010) Trans Tech Publications.
    view abstractdoi: 10.4028/
  • 2010 • 5 Influence of substrate nitriding on adhesion, friction and wear resistance of DLC (diamond-like carbon)-coatings
    Tillmann, W. and Vogli, E. and Hoffmann, F. and Kemdem, P.
    Key Engineering Materials 438 211-218 (2010)
    Since diamond like carbon layers feature excellent mechanical and tribological behavior under defined environmental circumstances, they are well established in a wide field of industrial and automotive applications in the last decade. However, the pretreatment of the substrate plays also an important role in supporting and enforcing the excellent properties of the coatings. This work analyses the effect of the plasma nitrided cold working steel substrate (80CrV2) on the adhesion, friction and wear resistance of DLC-coatings and compares it to the performance of DLC-coatings applied on a non-hardened substrate material. Therefore the grinded and polished specimens were nitrogen-hardened in an Arc-PVD (Physical Vapor Deposition)-device before the DLC-coating was applied in a Magnetron Sputter-PVD-process. In order to measure the hardness of the thin film coating, a nanoindenter was used. The adhesion was tested with a scratch tester and the wear resistance was measured by using a Ball-on-disc-tester. A 3D-profilometer and a SEM (Scanning Electron Microscope) were utilized to analyze the scratches and wear tracks on the samples. With these results correlations between the substrate nitriding and the mechanical and tribological performance of the DLC-coating were made. © (2010) Trans Tech Publications.
    view abstractdoi: 10.4028/
  • 2010 • 4 Effect of plasma treatment on adhesion of DLC layers to steels
    Tillmann, W. and Vogli, E. and Momeni, S.
    Materials Science Forum 638-642 812-817 (2010)
    Diamond like carbon layers play a key role in industrial applications. However the layers quality deteriorates often due to insufficient interfacial adhesion. In this research work a prior plasma treatment of steel substrates was employed aimed to improve the interfacial adhesion of DLC-layers to steel substrates. Three different kinds of steels were employed and their microstructures as well as their compositions before and after plasma treatment were analyzed. The interfacial adhesion of DLC layers on the non-nitrided and nitrided steels was observed and the influence of the steel microstructure on the interfacial adhesion was studied. © (2010) Trans Tech Publications.
    view abstractdoi: 10.4028/
  • 2010 • 3 Overview on advanced thermal barrier coatings
    Vaßen, R. and Jarligo, M.O. and Steinke, T. and Mack, D.E. and Stöver, D.
    Surface and Coatings Technology 205 938-942 (2010)
    During the last decade a number of ceramic materials, mostly oxides have been suggested as new thermal barrier coating (TBC) materials. These new compositions have to compete with the state-of-the-art TBC material yttria stabilized zirconia (YSZ) which turns out to be difficult due to its unique properties. On the other hand YSZ has certain shortcomings especially its limited temperature capability above 1200 °C which necessitates its substitution in advanced gas turbines.In the paper an overview is tried on different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates. Literature results and also results from our own investigations will be presented and compared to the requirements. Finally, the double-layer concept, a method to overcome the limited toughness of new TBC materials, will be discussed. © 2010 Elsevier B.V.
    view abstractdoi: 10.1016/j.surfcoat.2010.08.151
  • 2010 • 2 Microstructure and wear properties of novel sintered cold work steel and related particle reinforced composite materials
    Weber, S. and Li, J.R. and Theisen, W.
    Materials Science and Technology 26 1494-1502 (2010)
    In the field of wear resistant materials it is known, that for certain applications steel based composites produced by powder metallurgy are beneficial due to a higher wear resistance compared to conventional cast materials. Early developments of these high wear resistant MMC were dependent on hot isostatic pressing but latest experimental findings nowadays also allow for a production by liquid phase sintering. Several materials systems have already been investigated which, however, lack of a sufficient hardness in the as sintered state. Especially for wear resistant coatings it would be beneficial to avoid a separate hardening of a coated component. The low hardness in the as sintered state is related to the transformation kinetics of the metallic matrix of the coating materials, typically leading to a comparatively soft pearlitic microstructure, if the cooling rate is too low. The use of a nickel alloyed PM cold work steel as matrix material avoids this restriction, as the formation of pearlite and bainite is delayed significantly, improving the hardenability of the steel. Adding coarse hard particles of chromium carbide (Cr 3C2), aluminium zirconium oxide (AlZrO) or titanium carbide (TiC) to the steel powder, composite materials with a high abrasive wear resistance can be obtained by liquid phase sintering. The development of these materials, supported by thermodynamic calculations, is presented here together with results of the microstructural investigation and wear tests. © 2010 Institute of Materials, Minerals and Mining.
    view abstractdoi: 10.1179/026708309X12506933872982
  • 2010 • 1 An image morphing method for 3D reconstruction and FE-analysis of pore networks in thermal spray coatings
    Wiederkehr, T. and Klusemann, B. and Gies, D. and Müller, H. and Svendsen, B.
    Computational Materials Science 47 881-889 (2010)
    Using thermal spraying various surface coatings consisting of different material compositions can be manufactured. Besides different solid phases the resulting coating microstructure often contains a non-negligible amount of pores altering their mechanical properties. A common practice to analyze the porosity and composition of a coating is to create cross section images using standard light microscopy equipment or a scanning electron microscope. In this paper a method is presented to construct a three-dimensional multiphase model of the coating from a number of such cross section images by means of an image morphing technique. The resulting model can then be used for visualization purposes or further analysis e.g. within a finite element simulation. The described method has been applied to the construction of a finite element model of a porous coating sample which is used in a compaction simulation to determine its behavior in a rolling process. The required cross section images were obtained using a successive grinding and microscopy procedure. The material behavior of the porous material is modeled by using a modified Johnson-Cook material model formulation for an elasto-viscoplastic material. Comparison of 2D and 3D-simulation results are shown. © 2009 Elsevier B.V. All rights reserved.
    view abstractdoi: 10.1016/j.commatsci.2009.11.019