Dr.-Ing. Marina Macias Barrientos


TU Dortmund University

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  • Biomineralization, dissolution and cellular studies of silicate bioceramics prepared from eggshell and rice husk
    Choudhary, R. and Venkatraman, S.K. and Bulygina, I. and Senatov, F. and Kaloshkin, S. and Anisimova, N. and Kiselevskiy, M. and Knyazeva, M. and Kukui, D. and Walther, F. and Swamiappan, S.
    Materials Science and Engineering C 118 (2021)
    The current investigation aims to replace the synthetic starting materials with biowaste to synthesize and explore three different silicate bioceramics. Pure silica from rice husk was extracted by decomposition of rice husk in muffle furnace followed by alkali treatment and acid precipitation. Raw eggshell and extracted silica were utilized for the preparation of wollastonite, diopside and forsterite by the solid-state method. The TG-DSC analysis shows that the crystallization temperature of wollastonite, diopside and forsterite was found to be 883 °C, 870 °C and 980 °C, respectively. The phase purity of wollastonite was attained at 1100 °C whereas diopside and forsterite were composed of secondary phases even after calcination at 1250 °C and 1300 °C respectively. All three materials behaved differently when exposed to the physiological environment, as wollastonite exhibited remarkable apatite deposition within 3 days whereas a distinct apatite phase was noticed on the surface of diopside after 2 weeks and forsterite shows the formation of apatite phase after five weeks of immersion. The rapid dissolution of Mg2+ ion from forsterite lowered the leaching of silicate ions into the simulated body fluid leading to poor apatite deposition over its surface. Chemical composition was found to plays a key role in the biomineralization ability of these bioceramics. Hemolysis and Lactate Dehydrogenase (LDH) release assays were performed to evaluate the hemocompatibility of silicate ceramics cultured at different concentrations (62.5, 125, and 250 μg/mL) with red blood cells and mononuclear leucocytes (MLs) of mice. The hemolytic activity of all the tested bioceramics was insignificant (less than 1%). The interaction between diopside and mouse multipotent mesenchymal stromal cells (MMSCs) caused a negligible increase in the number of apoptosis-associated Annexin V-binding cells whereas forsterite and wollastonite induced an increase in the number of the apoptotic cells only at the concentration of 250 μg/mL. The LDH assay did not show statistically significant changes in the proliferation of MMSCs after treatment with the bioceramics at the tested concentrations when compared to control (p > 0.05). This finding showed that the death of a part of cells during the first 24 h of incubation did not prevent the proliferation of MMSCs incubated with diopside, forsterite and wollastonite for 72 h. © 2020 Elsevier B.V.
    view abstract10.1016/j.msec.2020.111456
  • Electron beam powder bed fusion of γ‐titanium aluminide: Effect of processing parameters on part density, surface characteristics and aluminum content
    Moritz, J. and Teschke, M. and Marquardt, A. and Stepien, L. and López, E. and Brückner, F. and Macias Barrientos, M. and Walther, F. and Leyens, C.
    Metals 11 (2021)
    Gamma titanium aluminides are very interesting for their use in high‐performance applications such as aircraft engines due to their low density, high stiffness and favorable hightemperature properties. However, the pronounced brittleness of these intermetallic alloys is a major challenge for their processing through conventional fabrication methods. Additive manufacturing by means of electron beam powder bed fusion (EB‐PBF) significantly improves the processability of titanium aluminides due to the high preheating temperatures and facilitates complex components. The objective of this study was to determine a suitable processing window for EB‐PBF of the TNM‐B1 alloy (Ti‐43.5Al‐4Nb‐1Mo‐0.1B), using an increased aluminum content in the powder raw material to compensate for evaporation losses during the process. Design of experiments was used to evaluate the effect of beam current, scan speed, focus offset, line offset and layer thickness on porosity. Top surface roughness was assessed through laser scanning confocal microscopy. Scanning electron microscopy, electron backscatter diffraction (EBSD) and energydispersive X‐ray spectroscopy (EDX) were used for microstructural investigation and to analyze aluminum loss depending on the volumetric energy density used in EB‐PBF. An optimized process parameter set for achieving part densities of 99.9% and smooth top surfaces was derived. The results regarding microstructures and aluminum evaporation suggest a solidification via the β‐phase. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/met11071093
  • Innovations for the optimal use of weathering steel in steel and composite bridge construction [Innovationen zum optimalen Einsatz des wetterfesten Baustahls im Stahl- und Verbundbrückenbau]
    Ungermann, D. and Hatke, P. and Knyazeva, M. and Walther, F. and Lebelt, P. and Gehrke, J.
    Stahlbau 90 (2021)
    Innovations for the optimal use of weathering steel in steel and composite bridge construction. The research project “Innovations for the optimal use of weathering steel in steel and composite bridge construction” investigated essential aspects for the optimal use of weathering steel in steel and composite bridge construction. In addition to current investigations on the formation of the corrosion-inhibiting surface layer in the current atmosphere, the qualification of two geometry-independent and non-destructive measuring techniques for crack detection underneath the compact surface layer and their verification on real bridge structures was carried out. Furthermore, tests for the optimization of the slip factor of slip-resistant prestressed connections of weathering steel were carried out. Basically, the use of weathering steel offers both economic and ecological advantages compared to organically coated structural steel by the formation of its firmly adhering and corrosion-inhibiting surface layer, especially with regard to the present service life in bridge construction. This article summarises the main research findings to demonstrate the sustainable use and advantages of weathering steel in steel and composite bridge construction under the conditions of use in the current natural atmosphere. © 2021, Ernst und Sohn. All rights reserved.
    view abstract10.1002/stab.202000090
  • Optimization of processing parameters of ultrashort (100 fs-2 ps) pulsed laser shock peening of stainless steel
    Kukreja, L.M. and Hoppius, J.S. and Elango, K. and Macias Barrientos, M. and Pöhl, F. and Walther, F. and Gurevich, E. and Ostendorf, A.
    Journal of Laser Applications 33 (2021)
    The authors optimized the processing parameters of laser shock peening (LSP) of stainless steel, taken as a representative metal, using a Ti:sapphire laser with pulse durations in the range of 100 fs-2 ps. It was found that direct exposure of the metal surface to these laser pulses invariably resulted in the formation of laser induced periodic surface structures (LIPSS) on the metal. If LSP was carried out under an aqueous confinement medium, the stainless steel surface was observed to get oxidized without the protective role of the sacrificial layer. Various sacrificial layers were optimized to prevent LIPSS and surface oxidation to achieve maximum peening efficiency. Attenuation of the laser energy due to filamentation and white light generation in the confinement medium of de-ionized water was studied. It was found that 100 fs laser pulses produced much earlier and longer filamentation than those with a pulse duration of 2 ps at the same pulse energy of about 1 mJ. The energy lost in the attenuation mechanisms of filamentation and white light generation was found to be about 60% at the laser pulse duration of 100 fs and only about 20% at 2 ps. These effects are explained in terms of self-focusing and self-phase modulation of the laser light. Keeping filamentation-free length of different confinement media, peening efficiency on stainless steel was investigated for 2 ps laser pulses at different laser fluences. It was found that the maximum achievable hardness of stainless steel increased proportionately with acoustic impedance of the used confinement medium. © 2021 Author(s).
    view abstract10.2351/7.0000475
  • Biomimetic scaffold fabricated with a mammalian trabecular bone template
    Bulygina, I. and Senatov, F. and Choudhary, R. and Kolesnikov, E. and Kaloshkin, S. and Scholz, R. and Knyazeva, M. and Walther, F. and Anisimova, N. and Kiselevskiy, M.
    Polymer Degradation and Stability 172 (2020)
    This study proposes the method of ultra-high molecular weight polyethylene (UHMWPE) biomimetic scaffold fabrication. Anisotropy is considered to be a distinctive feature of native bone but basically only a 3D-fabricated scaffold structure may be anisotropic, while 3D-printing is not applicable to UHMWPE. We proposed a novel method that suggested a template of native mammalian bone to be used as a negative for UHMWPE scaffold fabrication. This method allows direct replication of the bone's structural features on the micro- and macro-scale. Bone scaffolds obtained using the specified method showed anisotropic structure; the pores' average proportions for scaffold and bone were 770 and 470, and 700 and 500 μm, respectively. According to SEM and CT investigations, the scaffolds' macro- and microstructure mimicked the native bone architecture; this feature distinguishes the proposed method from the other UHMWPE scaffold fabrication techniques. The combination of the hydrophilic surface and the nanorelief affected the adhesion and proliferation of cells: the adhesion of multipotent mesenchymal stromal cells (MMSC) amounted to 40% after 4 h; the proliferation of MMSC was 75% after 48 h. The proposed novel method of fabricating biomimetic scaffolds can be used to obtain bone implants of the complex microstructure and anisotropy from high-melt viscosity polymers which cannot be 3D-printed to be further applied in bone reconstruction. The FT-IR analysis confirmed the occurrence of carboxyl oxidation when the surface of UHMWPE sample was treated with chromic acid. The oxidation index (OI) of the samples was found in the order of etching in chromic acid > sterilization > hot moulding respectively. It can be suggested that the oxidative degradation of UHMWPE can be reduced by optimizing manufacturing conditions and further selection of an appropriate processing method. © 2020 Elsevier Ltd
    view abstract10.1016/j.polymdegradstab.2020.109076
  • Biomimetic UHMWPE/HA scaffolds with rhBMP-2 and erythropoietin for reconstructive surgery
    Senatov, F. and Amanbek, G. and Orlova, P. and Bartov, M. and Grunina, T. and Kolesnikov, E. and Maksimkin, A. and Kaloshkin, S. and Poponova, M. and Nikitin, K. and Krivozubov, M. and Strukova, N. and Manskikh, V. and Anisimova, N. and Kiselevskiy, M. and Scholz, R. and Knyazeva, M. and Walther, F. and Lunin, V. and Gromov, A. and Karyagina, A.
    Materials Science and Engineering C 111 (2020)
    A promising direction for the replacement of expanded bone defects is the development of bioimplants based on synthetic biocompatible materials impregnated with growth factors that stimulate bone remodeling. Novel biomimetic highly porous ultra-high molecular weight polyethylene (UHMWPE)/40% hydroxyapatite (HA) scaffold for reconstructive surgery with the porosity of 85 ± 1% vol. and a diameter of pores in the range of 50–800 μm was developed. The manufacturing process allowed the formation of trabecular-like architecture without additional solvents and thermo-oxidative degradation. Biomimetic UHMWPE/HA scaffold was biocompatible and provided effective tissue ingrowth on a model of critical-sized cranial defects in mice. The combined use of UHMWPE/HA with Bone Morphogenetic Protein-2 (BMP-2) demonstrated intensive mineralized bone formation as early as 3 weeks after surgery. The addition of erythropoietin (EPO) significantly enhanced angiogenesis in newly formed tissues. The effect of EPO of bacterial origin on bone tissue defect healing was demonstrated for the first time. The developed biomimetic highly porous UHMWPE/HA scaffold can be used separately or in combination with rhBMP-2 and EPO for reconstructive surgery to solve the problems associated with difference between implant architecture and trabecular bone, low osteointegration and bioinertness. © 2020 Elsevier B.V.
    view abstract10.1016/j.msec.2020.110750
  • Effect of phase formation due to holding time of vacuum brazed AISI 304L/NiCrSiB joints on corrosion fatigue properties
    Otto, J.L. and Penyaz, M. and Schmiedt-Kalenborn, A. and Knyazeva, M. and Ivannikov, A. and Kalin, B. and Walther, F.
    Journal of Materials Research and Technology 9 (2020)
    Whether in turbine components or exhaust gas heat exchangers, vacuum-brazed nickel-based joints are subjected to varying cyclical loads during their applications, often in corrosive environments. The microstructure of the brazed seam, which is determined by the alloy composition and the brazing process parameters, is essential for the service life. In this experimental study a modified BNi-5a foil was produced and used to braze cylindrical AISI 304L butt joints with two different holding times. Using energy dispersive spectroscopy analyses, a direct correlation of the element distribution at the brazing seam with the holding time was detected as a result of diffusion processes. Individual phases were identified, and it could be shown that the longer holding time led to a reduction of borides and silicides as well as to a more even microhardness curve through the seam. The effect of the microstructure on the corrosion fatigue properties was evaluated using multiple amplitude tests by a stepwise increase of the maximum stress amplitude in synthetic exhaust gas condensate. Thereby, improved corrosion fatigue and cyclic deformation behaviors were achieved for the more homogeneous microstructure. Afterwards, topography analyses of the fracture surfaces enabled an understanding of microstructure-dependent damage mechanisms including fatigue crack initiation and propagation. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
    view abstract10.1016/j.jmrt.2020.07.047
  • Erratum to “Service life characterization of orthopedic implant material made of ultra-high molecular weight polyethylene under physiological conditions” [J. Mech. Behav. Biomed. Mater. 104 2020 103617, 1–8] (Journal of the Mechanical Behavior of Biomedical Materials (2020) 104, (S1751616119314122), (10.1016/j.jmbbm.2020.103617))
    Wegner, N. and Scholz, R. and Knyazeva, M. and Walther, F.
    Journal of the Mechanical Behavior of Biomedical Materials 109 (2020)
    The following abstract was missing in the published article. The publisher apologizes for the error. Abstract Due to the demographic change and progress in medical care, the world is facing a particularly strong trend towards an aging population. This trend is accompanied by increasing bone and joint diseases, which often require reconstruction with biomaterials. While the wear behavior of joint implants is well known and has been broadly researched, little attention has been paid to the mechanical stability of orthopedic bone prosthetics such as hydroxyapatite, calcium sulfate, tri-calcium phosphate ceramics, bioactive glasses, or polymer-based substitutes. Biocompatibility is often tested in vivo while there is a general lack of standardized in vitro test methods to determine their mechanical long-term stability, especially under service-relevant cyclic loading, simulating physiological dynamic stresses and environment. Since damage mechanisms change during dynamic loading compared to quasi-static loading, the material can endure lower loads and thus, the characterization under dynamic loading conditions plays an important role. This study represents a validation of a previously developed in vitro short-term method for the characterization of service life of bone prosthetic materials by determining material reaction during cyclic loading in a biomimetic test setup. The investigations were performed on ultra-high molecular weight polyethylene (UHMWPE) as an exemplary prosthetic material. The results confirm the hypotheses previously made and validate the applicability of the short-term method. Furthermore, the strong influence of human body conditions on the mechanical fatigue properties could be shown. In addition to the time-efficient determination of the service life, the advantage of this short-term method is the use of a standardized experimental setup and a standardized sample geometry, ensuring it can be applied to almost any other biomaterial. © 2020 Elsevier Ltd
    view abstract10.1016/j.jmbbm.2020.103828
  • Impact of forsterite addition on mechanical and biological properties of composites
    Choudhary, R. and Venkatraman, S.K. and Bulygina, I. and Chatterjee, A. and Abraham, J. and Senatov, F. and Kaloshkin, S. and Ilyasov, A. and Abakumov, M. and Knyazeva, M. and Kukui, D. and Walther, F. and Swamiappan, S.
    Journal of Asian Ceramic Societies 8 (2020)
    The objective of designing a biocompatible and mechanically stable scaffold for hard tissue regeneration was achieved by fabricating diopside/forsterite composites. Superior mechanical strength, slow degradation, excellent antibacterial activity and good cell viability were attained with the increase in forsterite ratio in the composites whereas apatite deposition ability got enhanced as the diopside content was increased. The variation in the rate of apatite deposition on the surface of composites exhibited different surface topography such as nano-structured interconnected fibrous network and globular morphology. The scaffolds after one-month immersion in a physiological environment exhibited good Young’s modulus and compressive strength. Clear and distinguishable prevention of bacterial growth confirms that composites have the potential to inhibit microbial colony formation of nine different clinical pathogens. The composite containing major diopside content was more effective toward S. aureus while the growth of E. coli was inhibited more by the composite containing a higher ratio of forsterite. The interaction of composites with MG-63 cells showed an enhancement in cell viability as the content of forsterite was increased. MTS assay confirmed the cytocompatibility of samples with negligible toxicity effects. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of The Korean Ceramic Society and The Ceramic Society of Japan.
    view abstract10.1080/21870764.2020.1807695
  • Innovationen zum optimalen Einsatz des wetterfesten Baustahls im Stahl- und Verbundbrückenbau
    Ungermann, D. and Hatke, P. and Knyazeva, M. and Walther, F. and Lebelt, P. and Gehrke, J.
    Stahlbau (2020)
    Innovations for the optimal use of weathering steel in steel and composite bridge construction. The research project “Innovations for the optimal use of weathering steel in steel and composite bridge construction” investigated essential aspects for the optimal use of weathering steel in steel and composite bridge construction. In addition to current investigations on the formation of the corrosion-inhibiting surface layer in the current atmosphere, the qualification of two geometry-independent and non-destructive measuring techniques for crack detection underneath the compact surface layer and their verification on real bridge structures was carried out. Furthermore, tests for the optimization of the slip factor of slip-resistant prestressed connections of weathering steel were carried out. Basically, the use of weathering steel offers both economic and ecological advantages compared to organically coated structural steel by the formation of its firmly adhering and corrosion-inhibiting surface layer, especially with regard to the present service life in bridge construction. This article summarises the main research findings to demonstrate the sustainable use and advantages of weathering steel in steel and composite bridge construction under the conditions of use in the current natural atmosphere. , Ernst und Sohn. All rights reserved.
    view abstract10.1002/stab.202000090
  • Service life characterization of orthopedic implant material made of ultra-high molecular weight polyethylene under physiological conditions
    Wegner, N. and Scholz, R. and Knyazeva, M. and Walther, F.
    Journal of the Mechanical Behavior of Biomedical Materials 104 (2020)
    view abstract10.1016/j.jmbbm.2020.103617
  • Balancing purification and ultrastructure of naturally derived bone blocks for bone regeneration: Report of the purification effort of two bone blocks
    Barbeck, M. and Jung, O. and Xiong, X. and Krastev, R. and Korzinskas, T. and Najman, S. and Radenkovic, M. and Wegner, N. and Knyazeva, M. and Walther, F.
    Materials 12 (2019)
    The present publication reports the purification effort of two natural bone blocks, that is, an allogeneic bone block (maxgraft®, botiss biomaterials GmbH, Zossen, Germany) and a xenogeneic block (SMARTBONE®, IBI S.A., Mezzovico-Vira, Switzerland) in addition to previously published results based on histology. Furthermore, specialized scanning electron microscopy (SEM) and in vitro analyses (XTT, BrdU, LDH) for testing of the cytocompatibility based on ISO 10993-5/-12 have been conducted. The microscopic analyses showed that both bone blocks possess a trabecular structure with a lamellar subarrangement. In the case of the xenogeneic bone block, only minor remnants of collagenous structures were found, while in contrast high amounts of collagen were found associated with the allogeneic bone matrix. Furthermore, only island-like remnants of the polymer coating in case of the xenogeneic bone substitute seemed to be detectable. Finally, no remaining cells or cellular remnants were found in both bone blocks. The in vitro analyses showed that both bone blocks are biocompatible. Altogether, the purification level of both bone blocks seems to be favorable for bone tissue regeneration without the risk for inflammatory responses or graft rejection. Moreover, the analysis of the maxgraft® bone block showed that the underlying purification process allows for preserving not only the calcified bone matrix but also high amounts of the intertrabecular collagen matrix. © 2019 by the authors.
    view abstract10.3390/ma12193234
  • Non-destructive testing derived parameters for microstructure-based residual service life assessment of aging metallic materials in nuclear engineering
    Acosta, R. and Boller, C. and Starke, P. and Jamrozy, M. and Knyazeva, M. and Walther, F. and Heckmann, K. and Sievers, J. and Schopf, T. and Weihe, S.
    Materialpruefung/Materials Testing 61 (2019)
    Metallic components in nuclear engineering are exposed to extensive loads such as pressurization and temperature changes which can affect the properties of the material significantly depending on the load spectrum applied. In view of developing a procedure to evaluate the residual service life of metallic components in nuclear power plants aged during service, metastable austenitic steel AISI 347 (German designation: X6CrNiNb18-10) has been considered as an example. To this purpose, total strain-controlled fatigue tests were carried out under different environmental conditions and monitored by continuously measuring thermometric, resistometric, electromagnetic and electrochemical parameters. These parameters provide an information gain in terms of material characterization when compared to conventional strain measurements. Based on these parameters, the short time evaluation procedure StrainLife has been developed, which allows the determination of local S-N curves with a significantly reduced effort as compared with traditional procedures. This method has been implemented into the structural simulation program PROST for the integrity assessment of the components while considering local fatigue properties. This very effective method allows for the determination of local fatigue properties including the strain-specific local scatter of the metallic microstructure properties of the material which has not been possible by traditional means. © Carl Hanser Verlag GmbH & Co. KG
    view abstract10.3139/120.111417
  • Development of biomimetic in vitro fatigue assessment for UHMWPE implant materials
    Scholz, R. and Knyazeva, M. and Porchetta, D. and Wegner, N. and Senatov, F. and Salimon, A. and Kaloshkin, S. and Walther, F.
    Journal of the Mechanical Behavior of Biomedical Materials 85 (2018)
    An important research goal in the field of biomaterials lies in the progressive amendment of in vivo tests with suitable in vitro experiments. Such approaches are gaining more significance nowadays because of an increasing demand on life sciences and the ethical issues bound to the sacrifice of animals for the sake of scientific research. Another advantage of transferring the experiments to the in vitro field is the possibility of accurately control the boundary conditions and experimental parameters in order to reduce the need of validation tests involving animals. With the aim to reduce the amount of needed in vivo studies for this cause, a short-time in vitro test procedure using instrumented load increase tests with superimposed environmental loading has been developed at TUD to assess the mechanical long-term durability of ultra-high molecular weight polyethylene (UHMWPE) under fatigue loading in a biological environment. © 2018 Elsevier Ltd
    view abstract10.1016/j.jmbbm.2018.05.034
  • 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 (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 abstract10.1007/s11666-017-0673-z
  • Micro-magnetic and microstructural characterization of wear progress on case-hardened 16MnCr5 gear wheels
    Knyazeva, M. and Vasquez, J.R. and Gondecki, L. and Weibring, M. and Pöhl, F. and Kipp, M. and Tenberge, P. and Theisen, W. and Walther, F. and Biermann, D.
    Materials 11 (2018)
    The evaluation of wear progress of gear tooth flanks made of 16MnCr5 was performed using non-destructive micro-magnetic testing, specifically Barkhausen noise (BN) and incremental permeability (IP). Based on the physical interaction of the microstructure with the magnetic field, the micro-magnetic characterization allowed the analysis of changes of microstructure caused by wear, including phase transformation and development of residual stresses. Due to wide parameter variation and application of bandpass filter frequencies of micro-magnetic signals, it was possible to indicate and separate the main damage mechanisms considering the wear development. It could be shown that the maximum amplitude of BN correlates directly with the profile form deviation and increases with the progress of wear. Surface investigations via optical and scanning electron microscopy indicated strong surface fatigue wear with micro-pitting and micro-cracks, evident in cross-section after 3 × 105 cycles. The result of fatigue on the surface layer was the decrease of residual compression stresses, which was indicated by means of coercivity by BN-analysis. The different topographies of the surfaces, characterized via confocal white light microscopy, were also reflected in maximum BN-amplitude. Using complementary microscopic characterization in the cross-section, a strong correlation between micro-magnetic parameters and microstructure was confirmed and wear progress was characterized in dependence of depth under the wear surface. The phase transformation of retained austenite into martensite according to wear development, measured by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) was also detected by micro-magnetic testing by IP-analysis. © 2018 by the authors.
    view abstract10.3390/ma11112290
  • On femtosecond laser shock peening of stainless steel AISI 316
    Hoppius, J.S. and Kukreja, L.M. and Knyazeva, M. and Pöhl, F. and Walther, F. and Ostendorf, A. and Gurevich, E.L.
    Applied Surface Science 435 (2018)
    In this paper we report on the competition in metal surface hardening between the femtosecond shock peening on the one hand, and formation of laser-induced periodic surface structures (LIPSS) and surface oxidation on the other hand. Peening of the stainless steel AISI 316 due to shock loading induced by femtosecond laser ablation was successfully demonstrated. However, for some range of processing parameters, surface erosion due to LIPSS and oxidation seems to dominate over the peening effect. Strategies to increase the peening efficiency are discussed. © 2017 Elsevier B.V.
    view abstract10.1016/j.apsusc.2017.11.145
  • Duplex Steels. Part II: Carbides and Nitrides
    Knyazeva, M. and Pohl, M.
    Metallography, Microstructure, and Analysis 2 (2013)
    view abstract10.1007/s13632-013-0088-2
  • Duplex Steels: Part I: Genesis, Formation, Structure
    Knyazeva, M. and Pohl, M.
    Metallography, Microstructure, and Analysis 2 (2013)
    The ferritic-austenitic duplex steels are equipped with a mechanical-technological combination of properties, which is advantageous compared to the features of stainless completely ferritic or completely austenite steels. The duplex steels crystallize by fully ferritic or ferritic-austenite solidification with the austenite precipitation due to the solid solution reactions during the further cooling. To adjust the ferrite-austenite ratio, the steels must be heat treated by temperatures above the field of precipitation stability, followed by water quenching. The temperature and the time of the heat treatment effect the element distribution according to their higher solubility in the ferritic or austenitic phases. The typical microstructure of the duplex stainless steels can only be realized due to deformation and recrystallisation processing. © 2013 Springer Science+Business Media New York and ASM International.
    view abstract10.1007/s13632-013-0066-8
  • acoustical measurements

  • corrosion

  • cracks

  • damage analysis

  • ferrite

  • metal surfaces

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