TY - JOUR A1 - Epishin, A. A1 - Fedelich, Bernard A1 - Nolze, Gert A1 - Schriever, Sina A1 - Feldmann, Titus A1 - Farzik Ijaz, M. A1 - Viguier, B. A1 - Poquillon, D. A1 - Le Bouar, Y. A1 - Ruffini, A. A1 - Finel, A. T1 - Creep of single crystals of nickel-based superalloys at ultra-high homologous temperature JF - Metallurgical and materials transactions A N2 - The creep behavior of single crystals of the nickel-based superalloy CMSX-4 was investigated at 1288 °C, which is the temperature of the hot isostatic pressing treatment applied to this superalloy in the industry. It was found that at this super-solvus temperature, where no gammaPrime-strengthening occurs, the superalloy is very soft and rapidly deforms under stresses between 4 and 16 MPa. The creep resistance was found to be very anisotropic, e.g., the creep rate of [001] crystals was about 11 times higher than that of a [111] crystal. The specimens of different orientations also showed a very different necking behavior. The reduction of the cross-sectional area psi of [001] crystals reached nearly 100 pct, while for a [111] crystal psi = 62 pct. The EBSD analysis of deformed specimens showed that despite such a large local strain the [001] crystals did not recrystallize, while a less deformed [111] crystal totally recrystallized within the necking zone. The recrystallization degree was found to be correlated with deformation behavior as well as with dwell time at high temperature. From the analysis of the obtained results (creep anisotropy, stress dependence of the creep rate, traces of shear deformation, and TEM observations), it was concluded that the main strain contribution resulted from <01-1>{111} octahedral slip. T2 - 3rd European Conference on Superalloys (‘Eurosuperalloys 2018’) CY - Oxford, UK DA - 9.9.2018 KW - Single-crystal KW - Superalloy KW - Creep KW - Isostatic hot pressing (HIP) PY - 2018 DO - https://doi.org/10.1007/s11661-018-4729-6 SN - 1073-5623 SN - 1543-1940 VL - 49A IS - 9 SP - 3973 EP - 3987 PB - Springer Sciences & Business Media CY - New York, NY AN - OPUS4-45660 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. I. A1 - Fedelich, Bernard A1 - Viguier, B. A1 - Schriever, Sina A1 - Svetlov, I. L. A1 - Petrushin, N. V. A1 - Saillard, R. A1 - Proietti, A. A1 - Poquillon, D. A1 - Chyrkin, A. T1 - Creep of single-crystals of nickel-base γ-alloy at temperatures between 1150 °C and 1288 °C JF - Materials Science & Engineering A N2 - A γ-analogue of the superalloy CMSX-4 that does not contain the strengthening γ′ -phase and only consists of the γ-solid solution of nickel has been designed, solidified as single-crystals of different orientations, and tested under creep conditions in the temperature range between 1150 and 1288 °C. The tests have revealed a very high creep anisotropy of this alloy, as was previously found for CMSX-4 at supersolvus temperature of 1288 °C. This creep anisotropy could be explained by the dominance of 〈011〉{111} octahedral slip. Furthermore, the analysis of the creep data has yielded a high value of the creep activation energy, Qc≈442 kJ/mol, which correlates with the high activation energy of Re diffusion in Ni. This supports the hypothesis that dislocation motion in the γ-matrix of Re-containing superalloys is controlled by the diffusion of the Re atoms segregating at the dislocation core. The Norton stress exponent n is close to 5, which is a typical value for pure metals and their alloys. The absence of γ′ -reprecipitation after high-temperature creep tests facilitates microstructural investigations. It has been shown by EBSD that creep deformation results in an increasing misorientation of the existing low angle boundaries. In addition, according to TEM, new low angle boundaries appear due to reactions of the a/2 〈011〉 mobile dislocations and knitting of new networks. KW - Nickel alloys KW - Single-crystals KW - Creep KW - Electron microscopy KW - Deformation mechanisms PY - 2021 DO - https://doi.org/10.1016/j.msea.2021.141880 SN - 0921-5093 VL - 825 SP - 1 EP - 13 PB - Elsevier CY - Amsterdam AN - OPUS4-53132 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Fedelich, Bernard ED - Cailletaud, G. ED - Cormier, J. ED - Eggeler, G. ED - Maurel, V. ED - Nazé, L. T1 - Crystal plasticity models: dislocation based T2 - Nickel base single Crystals across length scales N2 - The large number of TEM investigations and the regular microstructure of single-crystal nickel-base superalloys has boosted the development of a number of physically motivated constitutive laws. In contrast to the more phenomenological models discussed in the next chapter, these models use dislocation densities as internal variables. Obvious advantages are that the computed densities can be compared to TEM observations and the Deformation mechanisms can be easier translated into mathematical equations. KW - Nickel-base superalloys KW - Creep KW - Plasticity PY - 2022 SN - 978-0-12-819357-0 SP - 401 EP - 427 PB - Elsevier Inc. ET - 1 AN - OPUS4-53436 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard A1 - Feldmann, Titus A1 - Charmi, Amir A1 - Epishin, A. T1 - Simulation of pore shrinkage with crystal plasticity and dislocation transport N2 - Single crystal superalloys usually contain pores of sizes 5-10 micro-m after casting and heat treatment. These pores can be reduced under compression by combined creep and diffusion in a subsequent treatment called Hot Isostatic Pressing (HIP). The paper presents a methodology to simulate pore shrinkage under HIP conditions in two dimensions (2D). At the scale of the pores, which is also the scale of the sub-grains (<50 micro-m) the dislocation sources cannot be assumed to be homogeneously distributed. Thus, the applicability of classical crystal plasticity is questionable. In this case, the transport of dislocations under an applied stress from the location where they are nucleated must be explicitly modelled. This is done by solving the transport equations for the dislocation densities and the elasticity equations in 2D. The dislocations are assumed to be nucleated at Low Angle Boundaries. They glide or climb through the sub-grains with a stress dependent velocity. The transport equations are solved by the Flux-Corrected Transport method, which belongs to the predictor-corrector class of algorithms. In the first step, an artificial diffusion is introduced, which suppresses spurious oscillations of the solution. In a second step, the solution is corrected in such a way that no additional extremes appear and that the extremes do not grow. The algorithm is validated by simulating the transport of simple distributions with a constant velocity field. With the dislocation velocities and the computed dislocation densities, the inelastic shear rate at the slip system level is computed by integrating the Orowan equation. In the 2D-setting, three slip systems are considered. The contributions of these slip systems are summed up to obtain the total inelastic strain rate. Dislocation glide and climb and the coupling of climb with vacancies diffusion are considered. The resolution of the equilibrium equations from the inelastic strains turned out to be prone to numerical instabilities. As an alternative, the stresses are directly computed from the distribution of geometrically necessary dislocations following the method presented in. The resulting boundary value problem is solved by the Least-Square Finite Element method. Examples of simulations are presented for a representative region under creep tension and for a pore shrinking under external pressure. T2 - International Conference on Material Modelling, ICMM 6 CY - Lund, Sweden DA - 26.06.2019 KW - Superalloy KW - Pores KW - Creep KW - Dislocations PY - 2019 AN - OPUS4-48488 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard A1 - Epishin, A. A1 - Nolze, Gert A1 - Schriever, Sina A1 - Feldmann, Titus A1 - Ijaz, M. A1 - Viguier, B. A1 - Poquillon, D. A1 - Le Bouar, Y. A1 - Ruffini, A. A1 - Finel, A. T1 - Creep of single-crystals of nickel-base superalloys at ultra-high homologous temperature N2 - The creep behavior of single-crystals of the nickel-base superalloy CMSX-4 was investigated at 1288°C, which is the temperature of the hot isostatic pressing (HIP) treatment applied to this superalloy in the industry. It was found that at this super-solvus temperature, where no Gamma’-strengthening occurs, the superalloy is very soft and rapidly deforms under stresses between 4 and 16 MPa. The creep resistance was found to be very anisotropic, e.g. the creep rate of [001] crystals was about 11 times higher than that of a [111] crystal. The specimens of different orientations also showed a very different necking behavior. The reduction of the cross-section area psi of [001] crystals reached nearly 100%, while for a [111] crystal psi=62%. The EBSD analysis of deformed specimens showed that despite such a large local strain the [001] crystals didn’t not recrystallize, while a less deformed [111] crystal totally recrystallized within the necking zone. From the shape of deformed specimens and TEM investigations it was concluded that the main strain contribution resulted from <011> {111} octahedral slip. T2 - EuroSuperalloys 2018 CY - Oxford, UK DA - 09.09.2018 KW - Nickel-base superalloys KW - Single-crystals KW - Creep PY - 2018 AN - OPUS4-45989 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard A1 - Kindrachuk, Vitaliy A1 - Becker, M. T1 - Simulation of non-isothermal mechanical tests on a single crystal nickel-basis superalloy N2 - Gas turbines are widely used for a variety of purposes including power generation, compression or as jet engines in aircrafts. The critical components of a gas turbine are the high-pressure turbine blades which operate under severe conditions. These include thermo-mechanical loadings over temperatures ranging from room temperature up to 1100°C. While a large number of constitutive models for single crystals have been proposed, most applications are restricted to special loading scenarios, temperature range and deformation mechanisms. In particular, a number of models are focused on pure creep. Only a few papers consider application of both creep and fatigue. Applications of the constitutive models to long-term stress relaxation are even scarcer. The new model assumes deformation-induced softening and can properly reproduce the viscous behavior at different time scales. The model has been calibrated with the uniaxial tests at 800°C and 950°C in [001], [011] and [111] specimens of a nickel-basis superalloy. The predicted creep, short- and long-term relaxation and cyclic tests are in reasonable agreement with the experimental observations. T2 - Eigth International Conference on Low Cycle Fatigue CY - Dresden, Germany DA - 27.06.2017 KW - Constitutive law KW - Superalloy KW - Single crystal KW - Creep KW - Low cycle fatigue PY - 2017 AN - OPUS4-40923 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard A1 - Epishin, A. A1 - Link, T. A1 - Klingelhöffer, Hellmuth A1 - Künecke, Georgia A1 - Portella, Pedro Dolabella ED - Huron, E.S. ED - Reed, R.C. ED - Hardy, M.C. ED - Mills, M.J. ED - Montero, R.E. ED - Portella, Pedro Dolabella ED - Telesman, J. T1 - Rafting during high temperature deformation in a single crystal superalloy: experiments and modeling T2 - Superalloys 2012 - 12th International symposium on superalloys (Proceedings) T2 - Superalloys 2012 - 12th International symposium on superalloys CY - Seven, Springs, PA, USA DA - 2012-09-09 KW - Creep KW - Single crystal KW - Rafting KW - Modeling KW - CMSX-4 KW - Low-cycle-fatigue PY - 2012 SP - 491 EP - 500 PB - Wiley AN - OPUS4-26842 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fedelich, Bernard A1 - Epishin, A. A1 - Link, T. A1 - Klingelhöffer, Hellmuth A1 - Künecke, Georgia A1 - Portella, Pedro Dolabella T1 - Experimental characterization and mechanical modeling of creep induced rafting in superalloys JF - Computational materials science N2 - A constitutive model has been developed for the high temperature mechanical behavior of single crystal superalloys, including rafting and its consequences. The flow stress depends on the γ channel width via the Orowan stress. An evolution equation for channel widening during high temperature straining has been derived and calibrated with measurements. Therein, rafting is assumed to be driven by the relaxation of internal stresses. The model is able to represent the mechanical softening at high stresses consecutive to rafting. The model has been applied to simulate rafting during uniaxial creep in several crystal orientations, in notched specimens as well as in cyclically loaded specimens. KW - Single crystal KW - Superalloys KW - Rafting KW - Creep KW - Viscoplasticity KW - Constitutive law PY - 2012 DO - https://doi.org/10.1016/j.commatsci.2012.05.071 SN - 0927-0256 VL - 64 SP - 2 EP - 6 PB - Elsevier CY - Amsterdam AN - OPUS4-26401 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard A1 - Epishin, A. A1 - Link, T. A1 - Klingelhöffer, Hellmuth A1 - Portella, Pedro Dolabella A1 - Skrotzki, Birgit ED - Maruyama, K. ED - Abe, F. ED - Igarashi, M. ED - Kishida, K. ED - Suzuki, M. ED - Yoshimi, K. T1 - Implementation of creep induced rafting into mechanical modelling of superalloys T2 - 12th International conference on creep and fracture of engineering materials and structures (Proceedings) T2 - 12th International conference on creep and fracture of engineering materials and structures CY - Kyoto, Japan DA - 2012-05-27 KW - Single-crystal nickel-base superalloys KW - Microstructural degradation KW - Creep KW - Modelling KW - Rafting PY - 2012 SP - 1 EP - 4(?) AN - OPUS4-27564 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fedelich, Bernard A1 - Künecke, Georgia A1 - Epishin, A. A1 - Link, T. A1 - Portella, Pedro Dolabella T1 - Constitutive modelling of creep degradation due to rafting in single-crystalline Ni-base superalloys JF - Materials science and engineering A N2 - A constitutive model for the mechanical behaviour of single-crystalline superalloys at high temperatures has been developed. The model relies on the slip system theory and is able to predict rafting and its influence on plastic flow. The kinetics of rafting are assumed to be driven by the reduction of the internal stresses represented by the macroscopic back-stress. The rafting effect is incorporated in the model through the dependence of the Orowan stress on the channel width. The model has been validated for the alloy CMSX-4 at 950 °C. The rafting part of the model has been calibrated by measurements of the channel widths after several levels of creep strains and for several loads. KW - Single crystal superalloy KW - Creep KW - Rafting KW - Constitutive modelling KW - Viscoplasticity PY - 2009 DO - https://doi.org/10.1016/j.msea.2008.04.089 SN - 0921-5093 SN - 1873-4936 VL - 510-511 SP - 273 EP - 277 PB - Elsevier CY - Amsterdam AN - OPUS4-19353 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Fedelich, Bernard A1 - Künecke, Georgia A1 - Epishin, Alexander T1 - Modelling of rafting and its influence in Ni-base superalloys T2 - Materials for Advanced Power Engineering 2006 : Proceedings of the 8th Liège Conference T2 - 8th Liège Conference "Materials for Advanced Power Engineering 2006" CY - Liege, Belgium DA - 2006-01-01 KW - Superalloys KW - Modelling KW - Rafting KW - Creep KW - Single crystals PY - 2006 SN - 3-89336-436-6 N1 - Serientitel: Schriften des Forschungszentrums Jülich - Reihe Energietechnik / Energy Technology – Series title: Schriften des Forschungszentrums Jülich - Reihe Energietechnik / Energy Technology IS - 53 SP - 475 EP - 484 PB - Forschungszentrum Jülich CY - Jülich AN - OPUS4-13983 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard A1 - Owen, J. ED - Bell, R. ED - Merati, A. ED - M. Nganbe, ED - Tyson, B. ED - Wang, X. T1 - Creep damage by multiple cavity growth controlled by grain boundary diffusion T2 - ICF12 - 12th International conference on fracture (Proceedings) T2 - ICF12 - 12th International Conference on Fracture CY - Ottawa, Canada DA - 2009-07-12 KW - Grain boundary cavitation KW - Hochtemperatur KW - Kriechen KW - Schädigung KW - Korngrenzenporosität KW - High temperature KW - Creep KW - Damage PY - 2009 SP - 1 EP - 10 AN - OPUS4-20623 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Fedelich, Bernard A1 - Vöse, Markus ED - Klingbeil, D. ED - Vormwald, M. ED - Eulitz, K.-G. T1 - Modeling of creep damage by multiple cavity growth on grain boundaries T2 - 18th European conference on fracture (ECF 18) - Fracture of materials and structures from micro to macro scale (Proceedings) T2 - 18th European conference on fracture (ECF 18) - Fracture of materials and structures from micro to macro scale CY - Dresden, Germany DA - 2010-08-30 KW - Creep KW - Cavities KW - Grain boundary KW - Damage PY - 2010 SN - 978-3-00-031802-3 SP - 1 EP - 8 AN - OPUS4-22269 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Feldmann, Titus A1 - Fedelich, Bernard A1 - Epishin, A. T1 - Simulation of Hot Isostatic Pressing in a Single-Crystal Ni Base Superalloy with the Theory of Continuously Distributed Dislocations Combined with Vacancy Diffusion JF - Advanced Engineering Materials N2 - Single-crystal components made of nickel base superalloys contain pores after casting and homogenization heat treatment. Hot isostatic pressing (HIP), which is carried above the γ' -solvus temperature of the alloy, is industrially applied to reduce porosity. A modeling of HIP based on continuously distributed dislocations is developed in a 2D setting. Glide and climb of straight-edge dislocations, as well as vacancy diffusion, are the deformation mechanisms taken into account. Thereby, dislocation glide is controlled by dragging a cloud of large atoms, and climb is controlled by vacancy diffusion. Relying on previous investigations of the creep behavior at HIP temperatures, it is assumed that new dislocations are nucleated at low-angle boundaries (LAB) and move through subgrains until they either reach the opposite LABs or react with other dislocations and annihilate. Vacancies are created at the pore surface and diffuse through the alloy until they are either consumed by climbing dislocations or disappear at the LABs. The field equations are solved by finite elements. It is shown that pore shrinking is mostly controlled by vacancy diffusion as the shear stresses at the LABs are too low to nucleate a sufficient amount of dislocations. KW - Nickel-base superalloys KW - HIP KW - Dislocation KW - Creep KW - Model PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-542309 DO - https://doi.org/10.1002/adem.202101341 VL - 2022 PB - Wiley AN - OPUS4-54230 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Grützner, Stefan A1 - Fedelich, Bernard A1 - Rehmer, Birgit A1 - Buchholz, B. ED - Clark, G. ED - Wang, C.H. T1 - Material modelling and lifetime prediction of Ni-base gas turbine blades under TMF conditions T2 - Fatigue 2014 - 11th International Fatigue Congress N2 - Under cyclic thermomechanical loading conditions, various damage mechanisms such as strain accumulation, creep cavitation, ageing, fatigue surface cracking etc. may take place in the material of a gas turbine blade. Depending on the loading conditions, all these effects can contribute to reduce the lifetime of the component. Subject of the present work is the development of a material model to describe the mechanical effects mentioned above, as well as the development of a lifetime model able to discriminate the different damage mechanisms. T2 - Fatigue 2014 - 11th International Fatigue Congress CY - Melbourne, Australia DA - 2014-03-02 KW - Creep KW - Fatigue KW - Ni-base superalloy KW - Oxidation damage KW - Ratcheting KW - Strain induced ageing KW - Viscoplastic PY - 2014 DO - https://doi.org/10.4028/www.scientific.net/AMR.891-892.1277 N1 - Serientitel: Advances materials research – Series title: Advances materials research VL - 891-892 IS - XXX. Thermomechanical Fatigue SP - 1277 EP - 1282 AN - OPUS4-30721 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Grützner, Stefan A1 - Rehmer, Birgit A1 - Fedelich, Bernard A1 - Mosquera Feijoo, Maria T1 - Deformation modeling and lifetime prediction of Ni-base gas turbine blade alloys under TMF-conditions T2 - ASME Turbo Expo 2014 - GT2014 - Turbine technical conference and exposition (Proceedings) N2 - Under cyclic thermomechanical loading conditions, various effects such as strain accumulation, creep damage, ageing, fatigue etc. may occur in the material of a gas turbine blade. Depending on the loading conditions, all these effects contribute to reduce the lifetime of the component. Subject of the present work is the development of a lifetime model able to discriminate between the different damage mechanisms, as well as the development of a material model to describe the mentioned effects and thus providing the input data for lifetime prediction. T2 - ASME Turbo Expo 2014 - GT2014 CY - Düsseldorf, Germany DA - 16.06.2014 KW - Ni-base super alloy KW - Viscoplastic KW - Ratcheting KW - Creep KW - Strain induced ageing KW - Fatigue KW - Oxidation damage PY - 2014 SN - 978-0-7918-4576-9 SP - GT2014-26332, 1-7 AN - OPUS4-30962 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kianinejad, Kaveh A1 - Darvishi Kamachali, Reza A1 - Khedkar, Abhinav A1 - Manzoni, Anna A1 - Agudo Jácome, Leonardo A1 - Schriever, Sina A1 - Saliwan Neumann, romeo A1 - Megahed, Sandra A1 - Heinze, Christoph A1 - Kamrani, Sepideh A1 - Fedelich, Bernard T1 - Creep anisotropy of additively manufactured Inconel-738LC: Combined experiments and microstructure-based modeling JF - Materials Science and Engineering: A N2 - The current lack of quantitative knowledge on processing-microstructure–property relationships is one of the major bottlenecks in today’s rapidly expanding field of additive manufacturing. This is centrally rooted in the nature of the processing, leading to complex microstructural features. Experimentally-guided modeling can offer reliable solutions for the safe application of additively manufactured materials. In this work, we combine a set of systematic experiments and modeling to address creep anisotropy and its correlation with microstructural characteristics in laser-based powder bed fusion (PBF-LB/M) additively manufactured Inconel-738LC (IN738LC). Three sample orientations (with the tensile axis parallel, perpendicular, and 45° tilted, relative to the building direction) are crept at 850 °C, accompanied by electron backscatter secondary diffraction (EBSD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. A crystal plasticity (CP) model for Ni-base superalloys, capable of modeling different types of slip systems, is developed and combined with various polycrystalline representative volume elements (RVEs) built on the experimental measurements. Besides our experiments, we verify our modeling framework on electron beam powder bed fusion (PBF-EB/M) additively manufactured Inconel-738LC. The results of our simulations show that while the crystallographic texture alone cannot explain the observed creep anisotropy, the superlattice extrinsic stacking faults (SESF) and related microtwinning slip systems play major roles as active deformation mechanisms. We confirm this using TEM investigations, revealing evidence of SESFs in crept specimens. We also show that the elongated grain morphology can result in higher creep rates, especially in the specimens with a tilted tensile axis. KW - Additive manufactured Ni-base superalloys KW - Creep KW - Crystal plasticity KW - Superlattice extrinsic stacking faults PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-601576 DO - https://doi.org/10.1016/j.msea.2024.146690 SN - 0921-5093 VL - 907 SP - 1 EP - 16 PB - Elsevier B.V. AN - OPUS4-60157 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kindrachuk, Vitaliy A1 - Fedelich, Bernard A1 - Becker, M. ED - Beck, T. ED - Charkaluk, E. T1 - Constitutive modelling of viscoplastic deformation in single crystal nickel-basis superalloys subjected to cyclic and creep loadings at high-temperatures T2 - Eighth International Conference on Low Cycle Fatigue N2 - Gas turbines are widely used for a variety of purposes including power generation, compression or as jet engines in aircrafts. The critical components of a gas turbine are the high-pressure turbine blades which operate under severe conditions. These include thermo-mechanical loadings over temperatures ranging from room temperature up to 1100°C. While a large number of constitutive models for single crystals have been proposed, most applications are restricted to special loading scenarios, temperature range and deformation mechanisms. In particular, a number of models are focused on pure creep. Only a few papers consider application of both creep and fatigue. Applications of the constitutive models to long-term stress relaxation are even scarcer. The new model assumes deformation-induced softening and can properly reproduce the viscous behavior at different time scales. The model has been calibrated with the uniaxial tests at 800°C and 950°C in [001], [011] and [111] specimens of a nickel-basis superalloy. The predicted creep, short- and long-term relaxation and cyclic tests are in reasonable agreement with the experimental observations. T2 - Eighth International Conference on Low Cycle Fatigue (LCF8) CY - Dresden, Germany DA - 27.06.2017 KW - Constitutive law KW - Single crystal KW - Superalloy KW - Creep KW - Low cycle fatigue PY - 2017 SP - 371 EP - 376 PB - DVM e.V. CY - Berlin AN - OPUS4-40928 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Link, T. A1 - Epishin, A. A1 - Fedelich, Bernard T1 - Inhomogeneity of misfit stresses in nickel-base superalloys: Effect on propagation of matrix dislocatiion loops JF - The philosophical magazine N2 - It is shown experimentally that, during annealing and creep under low applied stresses, matrix dislocation loops frequently cross-glide. The periodic length of the zigzag dislocations deposited in the interfaces is equal to that of the γ/γ'-microstructure. Initially, the zigzag dislocations move in the (001) interface by a combination of glide and climb but then they stop near the γ'-edges and align along (100). Reactions of such dislocations lead to the formation of square interfacial networks consisting of (100) oriented edge dislocations. The complex dislocation movement is explained by the inhomogeneity of the misfit stresses between γ- and γ'-lattices. The tensile components of the stress tensor drive the dislocations through the channel, whereas the shear components near the γ'-edges cause the zigzag movement and the (100) alignment. The total effect is the most efficient relaxation of the misfit stresses. The results are relevant, especially for single-crystal superalloys of the newest generations, which have an increased γ/γ'-misfit due to the high level of refractory elements. KW - Superalloy KW - Creep KW - Dislocation KW - Misfit stress PY - 2009 DO - https://doi.org/10.1080/14786430902877810 SN - 1478-6435 SN - 0031-8086 VL - 89 IS - 13 SP - 1141 EP - 1159 PB - Taylor & Francis CY - London AN - OPUS4-19522 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vöse, Markus A1 - Otto, F. A1 - Fedelich, Bernard A1 - Eggeler, G. T1 - Micromechanical investigations and modelling of a copper-antimony-alloy under creep conditions JF - Mechanics of materials N2 - In many practical applications, creep damage is the limiting factor of a component’s lifetime. A micromechanical model of creep induced grain boundary damage is proposed, which allows for the simulation of creep damage in a polycrystal within the framework of finite element analysis. The model considers grain boundary cavitation and sliding according to a micromechanically motivated cohesive zone model while creep deformation of the grains is described following the slip system theory. The model can be applied to idealised polycrystalline structures, such as a Voronoi tessellation or, like demonstrated here, to real grain structures of miniature creep specimens. Creep tests with pure Cu single crystals and with a coarse-grained polycrystalline Cu-1 wt.% Sb alloy at 823 K have been performed and used to calibrate the polycrystal model. The grain structure of the polycrystalline Cu–Sb specimens has been revealed by the EBSD method. Extensive grain boundary sliding and cavitation has been observed in the crept specimens. Grain boundary sliding has been found to promote wedge-type damage at grain boundary triple junctions and to contribute significantly to the total creep strain. Furthermore, the assumed stress sensitivity of the models grain boundary cavity nucleation rate strongly influences the development of wedge-type damage. KW - Creep KW - Damage KW - Copper–Antimony-Alloy KW - Grain boundary cavitation KW - Grain boundary sliding KW - Micromechanical model PY - 2014 DO - https://doi.org/10.1016/j.mechmat.2013.09.013 SN - 0167-6636 SN - 1872-7743 VL - 69 IS - 1 SP - 41 EP - 62 PB - Elsevier Ltd. CY - Amsterdam AN - OPUS4-29396 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -