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 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 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 - JOUR A1 - Ruffini, A. A1 - Le Bouar, Y. A1 - Finel, A. A1 - Epishin, A. I. A1 - Fedelich, Bernard A1 - Feldmann, Titus A1 - Viguier, B. A1 - Poquillon, D. T1 - Dislocations interacting with a pore in an elastically anisotropic single crystal nickel-base superalloy during hot isostatic pressing N2 - The formation of pores in CMSX-4 nickel based superalloys is detrimental to the service life of the material. A way to avoid the problem is to treat the superalloys under Hot Isostatic Pressing (HIP), which enables a large volume fraction of pores to be annihilated. This paper aims to understand the contribution of plastic activity related to the gliding of dislocations on the pore annihilation. Simulations based on a phase-field model of dislocation are performed and make it possible to consider the strong anisotropy of the CMSX-4 under HIP conditions in conjunction to the strong elastic heterogeneity introduced by the pore. For pores with a radius of few micrometers, it is shown that edge parts of dislocation lines that present an extra half atomic plane oriented towards the pore are stacked above and under it in the direction which is perpendicular to their slip-planes, causing an increase of the number of dislocation along the four octahedral directions of the FCC single crystal which intersect the pore center. Results are streamlined within the isotropic elastic theory of dislocations. Effects of elastic anisotropy and dislocation reactions are also investigated in order to specify what would be the dislocation configuration around a pore in CMSX-4 under HIP conditions. Notably, the elastic anisotropy is shown to significantly modify the arrangement of dislocations close to the pore equator. Simulations also allow for the characterization of pore/dislocation interactions when dislocations are involved in Low Angle Boundaries as experimentally observed. KW - HIP KW - Superalloys KW - Dislocation KW - Pore KW - Phase-field PY - 2022 DO - https://doi.org/10.1016/j.commatsci.2021.111118 SN - 0927-0256 VL - 204 SP - 1 EP - 14 PB - Elsevier CY - Amsterdam AN - OPUS4-54220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. A1 - Camin, B. A1 - Hansen, L. A1 - Chyrkin, A. A1 - Nolze, Gert T1 - Synchrotron Sub-μ X-ray Tomography of Kirkendall Porosity in a Diffusion Couple of Nickel-Base Superalloy and Nickel after Annealing at 1250 °C N2 - Kirkendall porosity that forms during interdiffusion in a diffusion couple of nickel-base superalloy CMSX-10 with pure nickel is investigated. The diffusion experiments are conducted at a temperature of 1250 °C, where the strengthening ƴ'-phase ist partially dissolved. The porosity is studied by X-ray sub-μ tomography with a spatial resolution of about 0.35³ μm³ at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. It is found that depending on the distance from the interface the Kirkendall pores take different shapes: octahedral, rounded pyramidal, drop shaped, dendritic, pear shaped, and joint shapes. Such a variety of pore morphologies indicates a complex multistage process of porosity nucleation and growth under vacancy supersaturation of different degrees. The experimental findings are interpreted on the basis of the results of diffusion modeling. It is shown that the kinetics of porosity growth is essentially influenced by the dissolution of the ƴ'-phase. KW - Diffusion KW - Nickel alloys KW - Porous materials KW - Synchrotron radiations KW - Three-dimensional tomographies PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-521476 DO - https://doi.org/10.1002/adem.202001220 VL - 23 IS - 4 SP - 1220 PB - Wiley Online Library AN - OPUS4-52147 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Treninkov, I. A. A1 - Petrushin, N. V. A1 - Epishin, A. I. A1 - Svetlov, I. L. A1 - Nolze, Gert A1 - Elyutin, E. S. T1 - Experimental Determination of Temperature Dependence of Structural–Phase Parameters of Nickel-Based Superalloy N2 - The temperature dependences of the periods of the crystal lattices of the γ and γ' phases, their dimensional mismatch (misfit), and volume fraction of the γ' phase of an experimental single-crystal hightemperature nickel-based alloy have been determined by X-ray diffraction analysis in the temperature range of 18–1150°C. The temperature ranges in which intense changes in the structural and phase characteristics of the alloy under study take place have been determined. KW - X-ray diffraction analysis KW - High temperatures KW - Nickel-based superalloys KW - Single crystal KW - Crystal lattice period PY - 2022 DO - https://doi.org/10.1134/s2075113322010373 SN - 2075-1133 VL - 13 IS - 1 SP - 171 EP - 178 PB - Springer Science + Business Media CY - Dordrecht AN - OPUS4-54466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Petrushin, N. V. A1 - Epishin, A. I. A1 - Svetlov, I. L. A1 - Nolze, Gert A1 - Elyutin, E. S. A1 - Solov'ev, A. E. T1 - Influence of the Sign of the γ/γ' Misfit on the Structure and Creep Strength of Single Crystals of Nickel-Based Superalloys N2 - Using the method of directional solidification, single crystals of experimental nickel-based superalloys with negative, zero, and positive γ/γ' misfits are obtained. The γ' solvus, solidus, and liquidus temperatures of the alloys are determined, and the microstructures of the alloys after directional solidification, heat treatment, and creep tests are investigated. Creep tests are performed at temperatures of 800 and 1000°C. It is found that single crystals of the alloy with a negative γ/γ' misfit have the highest creep resistance and lifetime (the crystal lattice period of the γ' phase is smaller than that of the γ matrix). KW - Nickel-based superalloys KW - Single crystal KW - Creep KW - Creep strength KW - Microstructure, γ/γ' misfit PY - 2023 DO - https://doi.org/10.1134/s207511332301029x SN - 2075-1133 VL - 14 IS - 1 SP - 13 EP - 22 AN - OPUS4-59505 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Malakhov, A. A1 - Epishin, A. A1 - Denisov, I. A1 - Saikov, I. A1 - Nolze, Gert T1 - Morphology and Structure of Brass–Invar Weld Interface after Explosive Welding N2 - This paper presents the results of a study of the morphology and structure at the weld interface in a brass–Invar bimetal, which belongs to the class of so-called thermostatic bimetals, or thermobimetals. The structure of the brass–Invar weld interface was analyzed using optical microscopy and scanning electron microscopy (SEM), with the use of energy-dispersive X-ray (EDX) spectrometry and back-scattered electron diffraction (BSE) to identify the phases. The distribution of the crystallographic orientation of the grains at the weld interface was obtained using an e-Flash HR electron back-scatter diffraction (EBSD) detector and a forward-scatter detector (FSD). The results of the study indicated that the weld interface had the wavy structure typical of explosive welding. The wave crests and troughs showed the presence of melted zones consisting of a disordered Cu–Zn–Fe–Ni solid solution and undissolved Invar particles. The pattern quality map showed that the structure of brass and Invar after explosive welding consisted of grains that were strongly elongated towards the area of the highest intensive plastic flow. In addition, numerous deformation twins, dislocation accumulations and shear bands were observed. Thus, based on the results of this study, the mechanism of Cu–Zn–Fe–Ni structure formation can be proposed. KW - Explosive welding KW - Thermobimetal KW - Grain structure KW - Brass KW - Invar PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-565964 DO - https://doi.org/10.3390/ma15238587 SN - 1996-1944 VL - 15 IS - 23 SP - 1 EP - 10 PB - MDPI AN - OPUS4-56596 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. A1 - Chyrkin, A. A1 - Nolze, Gert A1 - Midtlyng, Jan A1 - Mayer, H. M. A1 - Petrushin, N. A1 - Reimers, W. T1 - Interdiffusion in the Face-Centered Cubic Phase of the Co-Al-W-Ta System Between 1090 and 1240 °C N2 - Interdiffusion of Al, W, Ta and Co in a Co-base alloy at temperatures between 1090 and 1240 °C has been investigated. The interdiffusion coefficients were found to be close to those reported for these elements in Ni-base alloys. Combining the diffusion simulation software DICTRA with the Ni-base diffusion databases TCNi5 and MobNi3, the interdiffusion profiles of Co, Al W, and Ta were modeled for Co9Al8W2Ta/Co diffusion couples annealed at different temperatures and for different times. The results show that interdiffusion in the Co-Al-W-Ta alloys can be modeled reasonably well using the available commercial databases for thermodynamics and kinetics of Ni-base systems. KW - Alloys KW - Interdiffusion KW - Modeling PY - 2018 DO - https://doi.org/10.1007/s11669-018-0620-9 VL - 39 IS - 2 SP - 176 EP - 185 PB - Springer AN - OPUS4-44463 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Chyrkin, A. A1 - Epishin, A. A1 - Pillai, R. A1 - Link, T. A1 - Nolze, Gert A1 - Quaddaker, W. J. T1 - Modeling interdiffusion processes in CMSX-10/Ni diffusion couple N2 - A diffusion couple between directionally solidified nickel and the single crystal Ni-base superalloy CMSX-10 was produced by hot pressing in vacuum. The diffusion couples were heat treated at temperatures between 1050 and 1250 °C. The exposed samples were characterized by SEM/EBSD/EPMA. The interdiffusion results in dissolution of the c¢-Ni3 Al in the superalloy and in growth of nickel grains towards CMSX-10. Rapid diffusion of aluminum from the superalloy into pure nickel leads to a significant formation of pores in the superalloy. The interdiffusion processes were modelled using the finite-element simulation software DICTRA with the databases TCNi5 and MobNi2, tailored specially for Ni-base superalloys. The effect of alloying elements on the interdiffusion profiles is discussed in terms of alloy thermodynamics. The calculated element concentration profiles are in good agreement with the EPMA measurements. The interdiffusion modeling correctly predicts the shapes of the concentration profiles, e.g. kinks on the Al and Ti profiles in the vicinity of the original interface in the joint. The calculation predicts with reasonable accuracy the extent and the location of the Kirkendall porosity. KW - Chemical potential KW - Diffusion KW - EBSD KW - Composition profiles KW - DICTRA modeling KW - Electron probe microanalysis KW - EPMA PY - 2016 DO - https://doi.org/10.1007/s11669-015-0444-9 SN - 1547-7037 VL - 37 IS - 2 SP - 201 EP - 211 PB - Springer AN - OPUS4-35776 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. I. A1 - Nolze, Gert A1 - Malakhov, A. Yu. A1 - Pervukhina, O. L. T1 - Investigation of the Structure of Interfaces Between Metals and Alloys Joined by Explosion Welding N2 - The structure of interfaces in Fe20Cr6Al/Cu, titanium/steel and brass/Invar bimetals obtained by explosion welding from sheet components with a thickness of 1 and 4, 25 and 5, 12 and 8 mm, respectively, was studied using analytical methods of scanning electron microscopy. The wave dimensions (length/height) were approximately 200/50 μm for Fe20Cr6Al/Cu, 700/70 μm for titanium/steel and 350/100 μm for brass/Invar. At the micron scale, mutual penetration of the welded components into each other (trans-interface diffusion) was not detected. In the iron-based plate of Fe20Cr6Al/Cu bimetal, a strong texture and cracks, which are a critical defect, were formed as a result of severe plastic deformation. Less pronounced textures were revealed in the components of titanium/steel bimetal. In titanium/steel bimetal, Laves phase particles Fe2Ti were found near the welded interface, while in brass/Invar bimetal, local contact melting was observed. However, the particles Fe2Ti and local melting areas are not critical defects, as they do not cause unacceptable deterioration in the adhesive strength of the welded joints, which was confirmed by a high shear strength of 500-570 MPa for the brass/Invar bimetal. KW - EBSD KW - Welding KW - Interface PY - 2025 DO - https://doi.org/10.1007/s11665-025-12660-x SN - 1059-9495 SP - 1 EP - 11 PB - Springer Science and Business Media LLC AN - OPUS4-64732 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Svetlov, I. L. A1 - Epishin, A. I. A1 - Petrushin, N. V. A1 - Gerstein, G. A1 - Nolze, Gert A1 - Maier, H. J. T1 - Creep of Directionally Solidified Eutectics Ni/Ni3 Al–NbC under Thermal Cycling N2 - A nickel-based eutectic alloy with a γ/γ'-NbC structure was directionally solidified with a planar front. The specimens were tested for creep under sawtooth thermal cycling in the temperature range from 600 to 1100°C. It has been established that the lifetime under the conditions of thermal cycling is about five times shorter than it is predicted by the linear damage accumulation rule on the basis of results of isothermal creep tests. Faster creep under thermal cycling is caused by the rapid coarsening of the γ/γ' microstructure due to the periodic partial dissolution and reprecipitation of the γ' phase in heating and cooling half-cycles. KW - High temperature nickel-based eutectic alloys KW - γ/γ' matrix KW - Carbide phase NbC KW - In-situ composites KW - Creep under thermal cycling PY - 2022 DO - https://doi.org/10.1134/S2075113322040347 SN - 2075-1133 VL - 13 IS - 4 SP - 1099 EP - 1108 PB - Springer Science + Business Media CY - Dordrecht AN - OPUS4-55163 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Midtlyng, Jan A1 - Epishin, A. I. A1 - Petrushin, N. V. A1 - Link, T. A1 - Nolze, Gert A1 - Svetlov, I. L. A1 - Reimers, W. T1 - Creep behavior of a γ΄-strengthened Co-base alloy with zero γ/γ΄-lattice misfit at 800 °C, 196 MPa N2 - Deformation and structural behavior of an experimental γ΄-strengthened Co-base alloy during creep at 800 °C and 196 MPa have been investigated. The characteristic features of this alloy are zero γ/γ΄-lattice misfit and a fine γ/γ΄-microstructure. In the initial condition, the γ΄-precipitates in this alloy are small (size of about 100 nm), have polyhedral morphology, and are separated by the very narrow c-channels (width of about 10 nm). The tests performed up to about 1% creep strain (about 500 h creep time) gave creep curves with a slow constant strain rate and without an apparent transient creep, typical for superalloys with nonzero misfit. In this initial stage of creep, entering of the narrow γ-channels by dislocations is blocked by a strong Orowan force. The micromechanism of creep was identified as an octahedral glide of h011i superdislocations simultaneously in two phases, γ and γ΄. The γ/γ΄-microstructure with zero misfit shows no rafting but rapidly coarsens isotropically. It is concluded that zero misfit is beneficial at the initial stages of the creep but is unfavourable for longterm creep because of the continuous microstructural coarsening. KW - Co-Basis-Legierung KW - Gitterfehlpassung KW - Kriechen KW - Ausscheidung PY - 2017 DO - https://doi.org/10.1557/jmr.2017.424 SN - 0884-2914 SN - 2044-5326 VL - 32 IS - 24 SP - 4466 EP - 4474 PB - Cambridge Univ. Press CY - Cambridge AN - OPUS4-44027 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. A1 - Petrushin, N. A1 - Gerstein, G. A1 - Maier, J. A1 - Nolze, Gert T1 - Investigation of the gamma'-strengthened quaternary co-based alloys Co-Al-W-Ta N2 - The alloying system Co-Al-W-Ta is comprehensively investigated in the vicinity of the compositional point Co-9Al-10W-2Ta, at. pct. These investigations provided a large amount of quantitative information, which can be used for alloy development, namely, the compositional dependences of the The alloying system Co-Al-W-Ta is comprehensively investigated in the vicinity of the compositional point Co-9Al-10W-2Ta, at. pct. These investigations provided a large amount of quantitative information, which can be used for alloy development, namely, the compositional dependences of the γ‘-solvus, solidus, and liquidus temperatures; fraction of the extrinsic phases after casting; the compositional dependence of the γ/γ‘-lattice misfit; the element partitioning between γ- and γ‘-phases; and the two Phase compositional area γ/γ‘ in the Co-rich part of the Co-Al-W-Ta phase diagram at 900°C. It is shown that additions of Ta elevate the γ‘-solvus temperature and increase the γ/γ‘-lattice misfit, but adding more than about 3 at. pct Ta results in a large amount of undissolvable extrinsic phases. Additionally, two Co-Al-W-Ta alloys with lower content of W were developed and solidified as [001] single crystals for mechanical testing in a temperature range between 20 and 1200°C. These tests included measurement of the Young modulus, tensile tests with constant strain rate, and stress rupture tests. It was found that at temperatures up to about 750°C the ultimate tensile strength of Co-Al-Ta-W alloys can be at the same level or even higher than of Ni-based superalloys. KW - Cobald based alloy KW - Microstructur KW - Segregation PY - 2018 DO - https://doi.org/10.1007/s11661-018-4756-3 SN - 1543-1940 SN - 1073-5623 VL - 49A IS - 9 SP - 4042 EP - 4057 PB - Springer Sciences & Business Media CY - New York, NY AN - OPUS4-45395 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yukhvid, V. A1 - Gorshkov, V. A1 - Miloserdov, P. A1 - Skachkova, N. A1 - Alymov, M. I. A1 - Nolze, Gert A1 - Epishin, A. T1 - Synthesis of Molybdenum and Niobium Mono- and Binary Silicides by the Method of SHS-Metallurgy N2 - The process of self-propagating high-temperature synthesis of the Mo–Nb–Si silicides from the powder mixtures has been investigated. Based on performed experiments, the composition of powder mixtures as well as technological parameters are proposed which provide the synthesis of monosilicides MoSi₂, NbSi₂, and binary silicides Mo₁-хNbxSi₂ with different ratios of Nb/Mo by adding different contents of MoO₃ and Nb₂O₅. Microstructure and phase compositions of the obtained silicide ingots are characterized by scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and backscatter electron diffraction. KW - Synthesis KW - EBSD KW - XRD PY - 2016 DO - https://doi.org/10.1002/adem.201600334 SN - 1438-1656 SN - 1527-2648 SP - 1 EP - 6 PB - Wiley-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-37209 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Petrushin, N. A1 - Hvatzkiy, K. A1 - Gerasimov, V. A1 - Link, T. A1 - Epishin, A. A1 - Nolze, Gert A1 - Gerstein, G. T1 - A single-crystal co-base superalloy strengthened by gamma' precipitates: structure and mechanical properties N2 - An experimental Co-base superalloy was designed from the Ni-base system by exchange of Ni and Co concentrations. The alloy consist of a Co-matrix (γ phase) strengthened by cuboidal precipitates Co3(Al,X) (γ' phase). The γ'-solvus temperature is 1?005?°C. [001] single crystals of this alloy were solidified and tested for tension at different temperatures up to 1?000?°C. It was found that the Co-base alloy has a much lower yield stress than a corresponding Ni-base alloy, but a much higher ductility. The partitioning behaviour of the alloying elements in the Co-base alloy and the deformation mechanisms were investigated by scanning and transmission electron microscopy. KW - Microstructure KW - Precipitation KW - Stress PY - 2015 DO - https://doi.org/10.1002/adem.201500088 SN - 1438-1656 VL - 17 IS - 6 SP - 755 EP - 760 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-34474 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Link, T. A1 - Epishin, Alexander A1 - Klaus, M. A1 - Brückner, Udo A1 - Reznicek, A. T1 - (100) Dislocations in nickel-base superalloys: Formation and role in creep deformation N2 - α(1 0 0) Dislocations are observed in nickel-base superalloys after creep deformation at high temperatures and low stresses. They are formed in the γ/γ´ interfaces by a three step mechanism. First, primary dislocations with Burgers vector α/2(1 0 1) and 60° character are left behind in the interfaces when dislocation loops glide through the γ channels. The 60° dislocations move into edge orientation and react forming secondary dislocations α/2(1 1 0). In the third step, new primary dislocations are knit into the already existing meshes of primary and secondary dislocations, which results in hexagonal misfit dislocation networks consisting of secondary dislocations α/2(1 1 0) and tertiary dislocations α(1 0 0), both of edge type. This self-organisation process is explained by dislocation theory and crystallography. Creep deformation accelerates when the α(1 0 0) interfacial dislocations enter the γ´ phase. During their climb towards the opposite interface, they attain a characteristic rectangular shape. This shape and the importance of the α(1 0 0) super dislocations for creep deformation are discussed. KW - Superalloys KW - Creep KW - Dislocation reactions KW - Dislocation theory KW - Deformation mechanisms PY - 2005 SN - 0921-5093 SN - 1873-4936 VL - 405 IS - 1-2 SP - 254 EP - 265 PB - Elsevier CY - Amsterdam AN - OPUS4-11968 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Epishin, A. I. A1 - Petrushin, N. V. A1 - Svetlov, I. L. A1 - Nolze, Gert T1 - Model for Forecasting Temperature Dependence of γ/γ' Misfit in Heat-Resistant Nickel Alloys N2 - An analytical model for forecasting the temperature dependence of γ/γ' misfit in heat-resistant nickel alloys is proposed. The model accounts for the concentration dependences of the periods of crystalline lattices of the γ and γ' phases (Vegard law), thermal expansion of the γ and γ' lattices, and dissolution of the γ' phase at high temperatures. Adequacy of calculations of misfit is confirmed by comparison with the results of measurements using methods of X-ray and neutron diffraction. The model is applied for development of a nickel alloy with positive misfit. KW - Heat-resistant nickel alloys KW - Dimensional mismatch of crystalline lattice periods (misfit) KW - Microstructure evolution PY - 2022 DO - https://doi.org/10.1134/S2075113322010105 SN - 2075-1133 VL - 13 IS - 1 SP - 7 EP - 16 PB - Springer AN - OPUS4-54379 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 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 - 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 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 - 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 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 - Epishin, A. A1 - Link, T. A1 - Klingelhöffer, Hellmuth A1 - Fedelich, Bernard A1 - Brückner, Udo A1 - Portella, Pedro Dolabella T1 - New technique for characterization of microstructural degradation under creep: Application to the nickel-base superalloy CMSX-4 N2 - A new experimental technique (repeated load annealing of flat wedge shaped specimens) was proposed for characterization of microstructural degradation under creep conditions. This technique was applied to investigate the microstructural degradation of the nickel-base superalloy CMSX-4 in a wide range of temperatures and stress levels. The results obtained allowed to describe analytically the kinetics of rafting, which is important to predict the reduction of fatigue lifetime and yield stress. KW - Microstructural degradation KW - Nickel-base superalloys KW - Rafting PY - 2009 DO - https://doi.org/10.1016/j.msea.2008.04.135 SN - 0921-5093 SN - 1873-4936 VL - 510-511 SP - 262 EP - 265 PB - Elsevier CY - Amsterdam AN - OPUS4-19354 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -