Prof. Dr.-Ing. Marion Bartsch

Institute of Materials Research, Experimental and Numerical Methods
Ruhr-Universität Bochum/German Aerospace Center DLR

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  • Method for conducting in situ high-temperature digital image correlation with simultaneous synchrotron measurements under thermomechanical conditions
    Rossmann, L. and Sarley, B. and Hernandez, J. and Kenesei, P. and Köster, A. and Wischek, J. and Almer, J. and Maurel, V. and Bartsch, M. and Raghavan, S.
    Review of Scientific Instruments 91 (2020)
    This work presents a novel method of obtaining in situ strain measurements at high temperature by simultaneous digital image correlation (DIC), which provides the total strain on the specimen surface, and synchrotron x-ray diffraction (XRD), which provides lattice strains of crystalline materials. DIC at high temperature requires specialized techniques to overcome the effects of increased blackbody radiation that would otherwise overexpose the images. The technique presented herein is unique in that it can be used with a sample enclosed in an infrared heater, remotely and simultaneously with synchrotron XRD measurements. The heater included a window for camera access, and the light of the heater lamps is used as illumination. High-temperature paint is used to apply a random speckle pattern to the sample to allow the tracking of displacements and the calculation of the DIC strains. An inexpensive blue theatrical gel filter is used to block interfering visible and infrared light at high temperatures. This technique successfully produces properly exposed images at 870 °C and is expected to perform similarly at higher temperatures. The average strains measured by DIC were validated by an analytical calculation of the theoretical strain. Simultaneous DIC and XRD strain measurements of Inconel 718 (IN718) tensile test specimens were performed under thermal and mechanical loads and evaluated. This approach uses the fact that with DIC, the total strain is measured, including plastic strain, while with XRD, only elastic strain is captured. The observed differences were discussed with respect to the effective deformation mechanisms. © 2020 Author(s).
    view abstract10.1063/1.5124496
  • Recent Progress in Local Characterization of Damage Evolution in Thermal Barrier Coating Under Thermal Cycling
    Maurel, V. and Mahfouz, L. and Guipont, V. and Marchand, B. and Gaslain, F. and Koster, A. and Dennstedt, A. and Bartsch, M. and Coudon, F.
    Minerals, Metals and Materials Series (2020)
    Thermal barrier coating (TBC) systems are currently often tested by thermal cycling with or without temperature gradient on cylinder coupons. As a major drawback, edge effect associated with this geometry induces large scatter in TBC life at spallation. Thus, we promote the use of a laser shock to induce an artificial defect located at the top-coat/oxide interface. This method enables firstly to monitor damage evolution by means of non-destructive methods from this defect during thermal cycling at homogeneous temperature and for burner rig testing with superposed thermal gradient across the TBC. Secondly, by the knowledge of artificial defect location, an accurate 3D reconstruction of the crack tip was performed based on serial sectioning by focus ion beam and viewing by scanning electron microscopy. Founded on these observations, a sensitivity analysis of the measurement uncertainties with respect to the energy release rate of propagating cracks and to the process zone where damage elaborates is proposed. © 2020, The Minerals, Metals & Materials Society.
    view abstract10.1007/978-3-030-51834-9_80
  • Effect of heat treatment on the high temperature fatigue life of single crystalline nickel base superalloy additively manufactured by means of selective electron beam melting
    Meid, C. and Dennstedt, A. and Ramsperger, M. and Pistor, J. and Ruttert, B. and Lopez-Galilea, I. and Theisen, W. and Körner, C. and Bartsch, M.
    Scripta Materialia 168 (2019)
    The high temperature low cycle fatigue behavior of specimens manufactured from a single crystalline nickel base superalloy processed by selective electron beam melting (SEBM) has been investigated with respect to the effect of different heat treatments. The fatigue lifetime of heat treated material was significantly higher than that of as-built material. Applying hot isostatic pressing (HIP) with an integrated heat treatment resulted in even longer fatigue life. Lifetime limiting crack initiation occurred at interfaces of melting layers, at micro-porosity generated during solidification or, in HIP treated samples, at precipitates which formed at the location of collapsed pores. © 2019 Elsevier Ltd
    view abstract10.1016/j.scriptamat.2019.05.002
  • 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 (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 abstract10.1002/mawe.201800135
  • Stress-induced formation of TCP phases during high temperature low cycle fatigue loading of the single-crystal Ni-base superalloy ERBO/1
    Meid, C. and Eggeler, M. and Watermeyer, P. and Kostka, A. and Hammerschmidt, T. and Drautz, R. and Eggeler, G. and Bartsch, M.
    Acta Materialia 168 (2019)
    The microstructural evolution in the single crystal Ni-base superalloy ERBO/1 (CMSX 4 type) is investigated after load controlled low cycle fatigue (LCF) at 950 °C (load-ratio: 0.6, tensile stress range: 420–740 MPa, test frequency: 0.25 Hz, fatigue rupture life: about 1000 - 3000 cycles). Bulk topologically close packed (TCP) phase particles precipitated and were analyzed by three-dimensional focus ion beam slice and view imaging and analytical transmission electron microscopy. The particles did not precipitate homogenously but at locations with enhanced levels of local stresses/strains, such as isolated γ-channels subjected to cross channel stresses, shear bands and in front of micro cracks. The influence of stress/strain is furthermore apparent in the spatial arrangement and the shape of the TCP phase particles. Only μ-phase TCP particles were found by electron diffraction. Results of a structure-map analysis suggest that most of these TCP particles observed after LCF testing would not precipitate in thermodynamic equilibrium. In order to rationalize this effect, the atomic volume was analyzed that transition-metal (TM) elements take in unary fcc and in unary μ-phase crystal structures and found that all TM elements except Zr and V take a larger volume in a unary μ phase than in a unary fcc phase. This trend is in line with the observed localized precipitation of TCP phases that are rich in Ni and other late TM elements. The experimental and theoretical findings suggest consistently that formation of TCP particles in LCF tests is considerably influenced by the local tensile stress/strain states. © 2019 Acta Materialia Inc.
    view abstract10.1016/j.actamat.2019.02.022
  • Three-Dimensional Characterization of Cracks in a Columnar Thermal Barrier Coating System for Gas Turbine Applications
    Dennstedt, A. and Gaslain, F. and Bartsch, M. and Guipont, V. and Maurel, V.
    Integrating Materials and Manufacturing Innovation 8 (2019)
    Thermal barrier coatings (TBC) are multilayered systems comprising a metallic oxidation protection layer or so-called bond coat, a ceramic topcoat, and a thermally grown aluminum oxide developing at the interface. The coating systems fail typically by delamination cracking near this interface, which has a complex three-dimensional morphology influencing the crack path. This study combines laser shock adhesion test to introduce an artificial interfacial crack, known in size and location, and focused ion beam coupled with scanning electron microscopy 3D serial sectioning tomography. Methods for proper segmentation of cracks and adjacent materials and quantitative evaluation of the complex crack system are proposed and applied for analyzing the crack tip region. Finally, derived from the three-dimensional segmentation, a finite element model has been achieved and used for thermal analysis highlighting the crucial role of local damage on thermal conductivity of the TBC. © 2019, The Minerals, Metals & Materials Society.
    view abstract10.1007/s40192-019-00150-7
  • Effect of porosity and eutectics on the high-temperature low-cycle fatigue performance of a nickel-base single-crystal superalloy
    Ruttert, B. and Meid, C. and Mujica Roncery, L. and Lopez-Galilea, I. and Bartsch, M. and Theisen, W.
    Scripta Materialia 155 (2018)
    This work investigates the separate influence of porosity and γ/γ′-eutectics on the low-cycle fatigue life of a single-crystal Ni-base superalloy at high temperatures. A conventional vacuum furnace heat-treatment but also integrated heat-treatments in a hot isostatic press are applied to produce different material variants of the same alloy. High-resolution electron microscopy revealed that both pores and γ/γ′-eutectics act as crack starters, thus initiating early failure. Moreover, the results indicate that remaining γ/γ′-eutectics can weaken the fatigue resistance even more than pores. Furthermore, the results confirm the beneficial effect of proper integrated hot isostatic pressing heat-treatments on the fatigue performance. © 2018
    view abstract10.1016/j.scriptamat.2018.06.036
  • Method for conducting in situ high temperature DIC with simultaneous synchrotron measurements under thermomechanical load
    Rossmann, L. and Sarley, B. and Hernandez, J. and Kenesei, P. and Almer, J. and Wischek, J. and Bartsch, M. and Kösterk, A. and Maurel, V. and Raghavan, S.
    AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2018 (2018)
    This work presents a novel method of obtaining in situ strain measurements at high temperature by simultaneous digital image correlation (DIC), which provides global strain, and synchrotron x-ray diffraction (XRD), which provides lattice strains. Digital image correlation at high temperature requires specialized techniques to overcome the effects of increased black body radiation that would otherwise overexpose the images. The technique presented herein is unique in that it can be used with a sample enclosed in an infrared heater that cannot be illuminated with additional lighting. A small hole was drilled into the heater to serve as a window for the camera, and the light of the heater lamps is used as illumination. High-temperature paint is used to apply a speckle pattern to the sample to allow the tracking of displacements and the calculation of strains. An inexpensive blue theatrical gel filter is used to block the orange, red, and infrared light at high temperatures. This technique successfully produces properly exposed sample images at 870 ◦C; this temperature was determined by the requirements of the experiment, not a limitation of the technique. Another feature of this method is that the camera is controlled remotely, allowing focusing and image capture during synchrotron XRD measurements. The results were validated by an analytical calculation of the theoretical strain. Simultaneous DIC and XRD measurements of Inconel 718 (IN718) were taken under thermal and mechanical loads. The combination of global and lattice strains can provide important information on the anisotropy of the material. © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
    view abstract10.2514/6.2018-1375
  • Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing
    Körner, C. and Ramsperger, M. and Meid, C. and Bürger, D. and Wollgramm, P. and Bartsch, M. and Eggeler, G.
    Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science (2018)
    Currently, additive manufacturing (AM) experiences significant attention in nearly all industrial sectors. AM is already well established in fields such as medicine or spare part production. Nevertheless, processing of high-performance nickel-based superalloys and especially single crystalline alloys such as CMSX-4® is challenging due to the difficulty of intense crack formation. Selective electron beam melting (SEBM) takes place at high process temperatures (~ 1000 °C) and under vacuum conditions. Current work has demonstrated processing of CMSX-4® without crack formation. In addition, by using appropriate AM scan strategies, even single crystals (SX SEBM CMSX-4®) develop directly from the powder bed. In this contribution, we investigate the mechanical properties of SX SEBM CMSX-4® prepared by SEBM in the as-built condition and after heat treatment. The focus is on hardness, strength, low cycle fatigue, and creep properties. These properties are compared with conventional cast and heat-treated material. © 2018 The Author(s)
    view abstract10.1007/s11661-018-4762-5
  • Piezospectroscopic evaluation and damage identification for thermal barrier coatings subjected to simulated engine environments
    Manero, A. and Selimov, A. and Fouliard, Q. and Knipe, K. and Wischek, J. and Meid, C. and Karlsson, A.M. and Bartsch, M. and Raghavan, S.
    Surface and Coatings Technology 323 (2017)
    The application of high temperature ceramic coatings has enabled aircraft and power generation turbines to run at higher inlet temperatures for greater efficiency. Their use extends the lifetime of the superalloy blades that bear thermal gradients and mechanical loads during operation. In this work, ex-situ photo-luminescence spectroscopy was conducted to investigate the stresses within the thermally grown oxide of a thermal barrier coated tubular sample following complex realistic conditions, such as induced thermal gradients, and long duration aging. The resulting high spatial resolution stress contour maps highlight the development of the thermally grown oxide in response to the complex conditions. The outcomes highlight both the role of the aging process and the oxide growth's influence on the stress profile which varies spatially across the specimen. The results further provide early detection of micro-damaged zones in the oxide layer nondestructively. Improving the understanding of the coating system's response to loading conditions will allow for more accurate system modeling and early detection and monitoring of damage zones, which is critical for improving efficiency and longevity of aircraft and power generation turbines. © 2016 Elsevier B.V.
    view abstract10.1016/j.surfcoat.2016.09.057
  • Special Issue: Recent developments in thermo-mechanical fatigue
    Klingelhöffer, H. and Affeldt, E. and Bache, M. and Bartsch, M. and Beck, T. and Christ, H.J. and Fedelich, B. and Hähner, P. and Holdsworth, S.R. and Lang, K.-H. and McGaw, M. and Olbricht, J. and Remy, L. and Skrotzki, B. and Stekovich, S.
    International Journal of Fatigue 99 (2017)
    view abstract10.1016/j.ijfatigue.2017.02.002
  • The three-dimensional structure of flexible resorcinol-formaldehyde aerogels investigated by means of holotomography
    Tannert, R. and Schwan, M. and Rege, A. and Eggeler, M. and da Silva, J.C. and Bartsch, M. and Milow, B. and Itskov, M. and Ratke, L.
    Journal of Sol-Gel Science and Technology (2017)
    Abstract: Organic aerogels based on resorcinol-formaldehyde gels display remarkable properties due to their pronounced nanoporosity. Therefore, studies towards the understanding of their structure-property-relationship are of high value for the design of improved materials. X-ray tomography is a technique that has been used for the structural elucidation of porous materials, but so far no highly resolved three-dimensional structures of resorcinol-formaldehyde gels have been obtained under the classical absorption-based experimental X-ray setup. This paper reports on the successful analysis of a superflexible resorcinol-formaldehyde aerogel using zoom holotomography that yielded images with an unprecedented resolution in the sub-micrometer range. The preparation of suitable powder from monolithic superflexible resorcinol-formaldehyde, the experimental conditions for tomography, and data-processing to obtain a 3D-image of the dried gel sample are described. Macropores above ca. 75 nm could be identified and visualized. They were shown to adopt almost spherical shape and to display a low connectivity. A quantitative analysis of the pore space revealed that most of the identified pores are small macropores (diameter < 0.5 µm), yet most pore volume is located in larger macropores of 1–4 µm diameter. Graphical Abstract: [InlineMediaObject not available: see fulltext.] © 2017 Springer Science+Business Media New York
    view abstract10.1007/s10971-017-4363-6
  • 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 abstract10.2514/6.2015-0874
  • Correlations between microstructure and room temperature tensile behavior of a duplex TNB alloy for systematically heat treated samples
    Kabir, M.R. and Bartsch, M. and Chernova, L. and Kelm, K. and Wischek, J.
    Materials Science and Engineering A 635 (2015)
    The mechanical properties of TiAl alloys are very sensitive to the inherent microstructure. For an in-depth understanding of microstructural influences on mechanical properties a duplex type TNB (Nb-containing TiAl) alloy has been investigated. For varying the microstructure of this alloy controlled heat treatments (HT) have been performed with eight distinct maximum temperatures, ranging from 1230. °C to 1300. °C with a 10. °C temperature increment. The series of annealing processes resulted in duplex microstructures with a gradual change of the ratio of globular grains and lamellar colonies, keeping the global chemical composition unchanged. Microstructure of each sample was characterized using SEM and TEM before and after mechanical testing to correlate the morphology and microstructure features to the tensile properties. Quantitative data analysis from these results revealed how the evolution of duplex microstructures influences the room temperature tensile properties: i.e. the elastic stiffness, room temperature ductility, work hardening, fracture stress, and fracture strain. The results are discussed with respect to deformation mechanisms as understood from the tensile test results and fracture surface investigations. From the observed correlations between microstructure and properties an optimized constellation of globular and lamellar microstructure for relevant properties can be predicted. Furthermore, the required heat-treatment window for properties targeted can be defined. © 2015 Elsevier B.V.
    view abstract10.1016/j.msea.2015.03.041
  • 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 (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 abstract10.1007/s11837-015-1399-3
  • Synchrotron X-Ray Diffraction Measurements Mapping Internal Strains of Thermal Barrier Coatings During Thermal Gradient Mechanical Fatigue Loading
    Knipe, K. and Manero, A. C. and Sofronsky, S. and Okasinski, J. and Almer, J. and Wischek, J. and Meid, C. and Karlsson, A. and Bartsch, M. and Raghavan, S.
    Journal of Engineering for Gas Turbines and Power-transactions of the Asme 137 (2015)
    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 degrees C. Throughout high temperature testing, 2D 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 toward 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.
    view abstract10.1115/1.4029480
  • Strain response of thermal barrier coatings captured under extreme engine environments through synchrotron X-ray diffraction
    Knipe, K. and Manero II, A. and Siddiqui, S.F. and Meid, C. and Wischek, J. and Okasinski, J. and Almer, J. and Karlsson, A.M. and Bartsch, M. and Raghavan, S.
    Nature Communications 5 (2014)
    The mechanical behaviour of thermal barrier coatings in operation holds the key to understanding durability of jet engine turbine blades. Here we report the results from experiments that monitor strains in the layers of a coating subjected to thermal gradients and mechanical loads representing extreme engine environments. Hollow cylindrical specimens, with electron beam physical vapour deposited coatings, were tested with internal cooling and external heating under various controlled conditions. High-energy synchrotron X-ray measurements captured the in situ strain response through the depth of each layer, revealing the link between these conditions and the evolution of local strains. Results of this study demonstrate that variations in these conditions create corresponding trends in depth-resolved strains with the largest effects displayed at or near the interface with the bond coat. With larger temperature drops across the coating, significant strain gradients are seen, which can contribute to failure modes occurring within the layer adjacent to the interface. © 2014 Macmillan Publishers Limited. All rights reserved.
    view abstract10.1038/ncomms5559
  • 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 abstract10.1115/GT2014-26919
  • Combined experimental and numerical approach for linking microstructure and mechanical properties on different length scales for near γ-TiAl alloys
    Kabir, M.R. and Bartsch, M. and Chernova, L. and Schneider, J. and Kelm, K.
    Materials Science Forum 750 (2013)
    At room temperature the macroscopic tensile behavior of TiAl alloys is extremely microstructure sensitive. In general the microstructures of TiAl alloys are heterogeneous at micro and meso scale. The materials micromechanisms that occur at different length scale have to be linked for a proper understanding of the macroscopic response. In order to explore those micromechanisms, methodologies combining advanced experimental and computational analysis have been proposed. Linking microstructure and properties using a two-scale numerical model we are able to explain the stress-strain and hardening behavior of this alloy. © (2013) Trans Tech Publications, Switzerland.
    view abstract10.4028/www.scientific.net/MSF.750.76
  • 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 abstract10.1063/1.4817543
  • Numerical and experimental investigation on lap shear fracture of Al/CFRP laminates
    Naghipour, P. and Schulze, K. and Hausmann, J. and Bartsch, M.
    Composites Science and Technology 72 (2012)
    This paper presents a new approach to numerically investigate the lap shear fracture of a hybrid laminate made of Carbon Fibre Reinforced Plastic (CFRP) and metal foil plies (e.g. aluminium), validated by corresponding experiments. The numerical Finite Element (FE) model of the hybrid laminate, subjected to lap shear fracture, is composed of five laminas with alternating metal/CFRP layers with cohesive elements lying within Al/CFRP interface. In the FE model, individual CFRP laminas are assumed as an orthotropic homogenized continuum under plane stress, and aluminium facesheets are modelled as an elastic-plastic continuum. The Al/CFRP interface is represented via quadratic cohesive elements, the constitutive law of which is an exponentially decaying law representing the degrading behaviour of the interface (implemented as user element in ABAQUS). The numerical model captures the experimentally obtained results with minimal error, and predicts the failure modes successfully. The influence of specimen geometry (e.g. overlap length, total length, and total width) on lap shear fracture response is analyzed in detail in this study, too, in order to confirm the specimen design for the test, as there is still no corresponding test standard for hybrid laminates. © 2012 Elsevier Ltd.
    view abstract10.1016/j.compscitech.2012.07.012
  • Effect of HIP parameters on the micro-structural evolution of a single crystal Ni-based superalloy
    Lopez-Galilea, I. and Huth, S. and Bartsch, M. and Theisen, W.
    Advanced Materials Research 278 (2011)
    For reducing the porosity of single crystal (SX) nickel-based superalloys, Hot Isostatic Pressing (HIP) is used. High pressures of about 100-170 MPa lead to local deformation, which close the pores. However, since HIP also requires high temperatures (1000-12007deg;C) it has a pronounced effect on the microstructure and the local distribution of elements. This contribution analyses the effect of different HIP treatments on both the microstructure and the segregation of the SX superalloy LEK94 in the as-precipitation-hardened state. In addition, the effects of rapid or slow cooling are analyzed. To distinguish the effect of pressure from those of temperature, the HIPed samples are compared with specimens annealed at atmospheric pressure. © (2011) Trans Tech Publications, Switzerland.
    view abstract10.4028/www.scientific.net/AMR.278.72
  • Modelling Shear Fracture of Hybrid CFRP/Ti Laminates with Cohesive Elements; Effects of Geometry and Material Properties
    Naghipour, P. and Bartsch, M. and Hausmann, J. and Schulze, K.
    Supplemental Proceedings: Materials Fabrication, Properties, Characterization, and Modeling 2 (2011)
    The hybrid laminate made of Carbon Fibre Reinforced Plastic (CFRP) and metal foil plies (e.g. titanium) is being investigated numerically to be considered for future stiffer applications in aerospace industry. The numerical FE model of the hybrid laminate, subjected to lap shear fracture, is composed of a CFRP core embedded in between two titanium layers with cohesive elements lying within CFRP/Ti interface. In the FE model, the CFRP laminate is assumed as an orthotropic homogenized continuum under plane stress, and titanium facesheets are modelled as an elastic-plastic continuum. The constitutive law for the quadratic CFRP/Ti interface elements, implemented as User Element in ABAQUS, is an exponentially decaying law representing the degrading behaviour of the interface. The influence of geometry (e.g. overlap length and total length), and interface cohesive properties on the lap shear fracture response are analyzed in detail in this study. The numerical result will later be validated through related experiments. © 2011 The Minerals, Metals & Materials Society.
    view abstract10.1002/9781118062142.ch47
  • 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 (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 abstract10.1016/j.commatsci.2011.03.041
  • Simulation and experimental validation of mixed mode delamination in multidirectional CF/PEEK laminates under fatigue loading
    Naghipour, P. and Bartsch, M. and Voggenreiter, H.
    International Journal of Solids and Structures 48 (2011)
    Cyclic mixed mode delamination in multidirectional composite laminates subjected to high cycle fatigue loading has been investigated by numerical simulations and cyclic mixed mode bending experiments. The numerical model includes lamina and interface elements. The description of the delamination crack growth rate is based on the cyclic degradation of bilinear interface elements linking the evolution of the damage variable with the delamination crack growth rate. The constitutive cyclic damage model is calibrated by means of mixed mode fatigue experiments and reproduces the experimental results successfully and with minor error. It is concluded that only with implementing a cyclic damage variable in the cohesive interface element the experimentally observed crack growth and stiffness degradation can be captured properly. Scanning electron microscopy of fracture surfaces after cyclic loading revealed that abrasion of crack bridging surface roughness is the main microscopical cause of weakening and degradation of the interface. © 2010 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.ijsolstr.2010.12.012
  • Effect of fiber angle orientation and stacking sequence on mixed mode fracture toughness of carbon fiber reinforced plastics: Numerical and experimental investigations
    Naghipour, P. and Bartsch, M. and Chernova, L. and Hausmann, J. and Voggenreiter, H.
    Materials Science and Engineering A 527 (2010)
    This paper focuses on the effect of fiber orientation and stacking sequence on the progressive mixed mode delamination failure in composite laminates using fracture experiments and finite element (FE) simulations. Every laminate is modelled numerically combining damageable layers with defined fiber orientations and cohesive zone interface elements, subjected to mixed mode bending. The numerical simulations are then calibrated and validated through experiments, conducted following standardized mixed mode delamination tests. The numerical model is able to successfully capture the experimentally observed effects of fiber angle orientations and variable stacking sequences on the global load-displacement response and mixed mode inter-laminar fracture toughness of the various laminates. For better understanding of the failure mechanism, fracture surfaces of laminates with different stacking sequences are also studied using scanning electron microscopy (SEM). © 2009 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.msea.2009.07.069
  • Effects of annealing on the microstructure and the mechanical properties of EB-PVD thermal barrier coatings
    Zotov, N. and Bartsch, M. and Chernova, L. and Schmidt, D.A. and Havenith, M. and Eggeler, G.
    Surface and Coatings Technology 205 (2010)
    The effects of thermal annealing at 1000°C in air on the microstructure and the mechanical properties (Young's modulus and hardness) of thermal barrier coatings consisting of a 4mol% Y2O3 partially stabilized ZrO2 top coat and a NiCoCrAlY bond coat, deposited by electron beam physical vapour deposition on nickel-based superalloy IN 625, have been investigated using X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), image analysis and nanoindentation. During annealing, the ceramic top coat undergoes sintering and recrystallization. These processes lead to stress relaxation, an increase of the intra-columnar porosity and the number of large pores as measured by image analysis of SEM micrographs. An increase of the grain size of the γ-phase in the bond coat, accompanied by changes in the morphology of γ-grains with annealing time, is also observed. Correlations between these microstructural changes in the top coat and the bond coat and their mechanical properties are established and discussed. © 2010 Elsevier B.V.
    view abstract10.1016/j.surfcoat.2010.07.008
  • Numerical investigation of room-temperature deformation behavior of a duplex type γtiAl alloy using a multi-scale modeling approach
    Kabir, M.R. and Chernova, L. and Bartsch, M.
    Acta Materialia 58 (2010)
    Room-temperature deformation of a niobium-rich TiAl alloy with duplex microstructure has been numerically investigated. The model links the microstructural features at micro- and meso-scale by the two-level (FE 2) multi-scale approach. The deformation mechanisms of the considered phases were described in the micro-mechanical crystal-plasticity model. Initial material parameters for the model were taken from the literature and validated using tensile experiments at macro-scale. For the niobium-rich TiAl alloy further adaptation of the crystal plasticity parameters is proposed. Based on these model parameters, the influences of the grain orientation, grain size, and texture on the global mechanical behavior have been investigated. The contributions of crystal deformation modes (slips and dislocations in the phases) to the mechanical response are also analyzed. The results enable a quantitative prediction of relationships between microstructure and mechanical behavior on global and local scale, including an assessment of possible crack initiation sites. The model can be used for microstructure optimization to obtain better material properties. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.actamat.2010.06.058
  • carbon fibers

  • coatings

  • fracture

  • mechanical properties

  • microstructure

  • numerical methods

  • scanning electron microscopy

  • x-ray diffraction

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