The Experts below are selected from a list of 207 Experts worldwide ranked by ideXlab platform
U Messerschmidt - One of the best experts on this subject based on the ideXlab platform.
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friction mechanism of Dislocation Motion in icosahedral al pd mn quasicrystals
Philosophical Magazine, 1999Co-Authors: U Messerschmidt, M Bartsch, Michael Feuerbacher, B Geyer, K UrbanAbstract:Abstract Results from the literature and unpublished ones of the present authors are summarized which are relevant to the mechanisms governing the mobility of Dislocations in icosahedral Al-Pd-Mn quasicrystals. These results concern macroscopic deformation tests, conventional transmission electron microscopy, in situ straining experiments in a transmission electron microscope, and computer simulation experiments. These experiments can best be interpreted by assuming that the Dislocation Motion is controlled by the thermally activated overcoming of Mackay-type clusters. The present paper gives an estimate of the activation volume of this process. It turns out that the activation volume of overcoming the clusters individually is one order of magnitude smaller than the experimentally observed one. The experimental observations can be interpreted in a consistent way in terms of the Labusch-Schwarz theory of solution hardening in crystals, which considers the interpenetrating clusters as ‘extended’ obstacles, ...
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recombination enhanced Dislocation Motion in sige and ge
Physica Status Solidi (a), 1999Co-Authors: Ichiro Yonenaga, M Werner, M Bartsch, U Messerschmidt, E R WernerAbstract:In-situstraining experiments on Dislocation Motion in Ge and Si–5 at% Ge alloy single crystals are performed in a high voltage transmission electron microscope. In comparison with previous results by other methods, the Dislocation velocities are found to be enhanced due to a recombination enhancement owing to the excess carrier injection by the electron beam. The reduction in the activation energy of Dislocation Motion is ascribed to the recombination-assisted kink formation. The kink migration energy is estimated to be 0.7 eV in Ge and 1.5 eV in SiGe.
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transition of mechanisms controlling the Dislocation Motion in cubic zro2 below 700 c
Acta Materialia, 1998Co-Authors: Bernd Baufeld, M Bartsch, B. V. Petukhov, U MesserschmidtAbstract:Abstract For cubic ZrO2 single crystals deformed in 〈112〉 direction, new experimental data are presented on the flow stress and its strain rate sensitivity as well as on the Dislocation densities and the distances between glide obstacles along the Dislocations. A model is proposed to describe the strong variation of the parameters of the plastic deformation below 1000 K. It assumes that the mechanisms controlling the Dislocation Motion change from the pinning by localized obstacles above a transition temperature, e.g. small precipitates or jogs, to the overcoming of the Peierls relief at lower temperatures. The model is in agreement with most of the experimental observations.
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in situ observation of Dislocation Motion in icosahedral al pd mn single quasicrystals
Philosophical Magazine Letters, 1995Co-Authors: M Wollgarten, U Messerschmidt, M Bartschs, Michael Feuerbacher, R Rosenfeld, M Beyss, K UrbanAbstract:Abstract The plastic deformation of icosahedral Al-Pd-Mn single quasicrystals has been studied by in situ straining experiments in a high-voltage electron microscope at elevated temperatures. The results provide the first direct evidence for Dislocation Motion in quasicrystals. The Dislocation velocity, for an applied stress of 390 MPa, was determined as 7×10−7ms−1. It was found that the Dislocation Motion takes place in planes which are perpendicular to threefold and fivefold lattice directions.
Vasily V Bulatov - One of the best experts on this subject based on the ideXlab platform.
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quantum effects on Dislocation Motion from ring polymer molecular dynamics
arXiv: Materials Science, 2018Co-Authors: Mark Asta, Rodrigo Freitas, Vasily V BulatovAbstract:Quantum Motion of atoms known as zero-point vibration was recently proposed to explain a long-standing discrepancy between theoretically computed and experimentally measured low-temperature plastic strength of iron and possibly other metals with high atomic masses. This finding challenges the traditional notion that quantum Motion of atoms is relatively unimportant in solids comprised of heavy atoms. Here we report quantum dynamic simulations of quantum effects on Dislocation Motion within the exact formalism of Ring-Polymer Molecular Dynamics (RPMD). To extend the reach of quantum atomistic simulations to length and time scales relevant for extended defects in materials, we implemented RPMD in the open-source code LAMMPS thus making the RPMD method widely available to the community. We use our RPMD/LAMMPS approach for direct calculations of Dislocation mobility and its effects on the yield strength of α-iron. Our simulation results establish that quantum effects are noticeable at temperatures below 50 K but account for only a modest (≈13% at T = 0 K) overall reduction in the Peierls barrier, at variance with the factor of two reduction predicted earlier based on the more approximate framework of harmonic transition state theory. Our results confirm that zero-point vibrations provide ample additional agitation for atomic Motion that increases with decreasing temperature, however its enhancing effect on Dislocation mobility is largely offset by an increase in the effective atom size, an effect known as quantum dispersion that has not been accounted for in the previous calculations. Large ring-polymer molecular dynamics can accurately simulate quantum effects on Dislocation Motion. A team led by Rodrigo Freitas at the University of California, Berkeley and Lawrence Livermore National Laboratory, U.S.A., investigated the effect of atomic quantum Motion on the Peirels stress, i.e., the low-temperature resistance to Dislocation Motion. While classical molecular dynamics yielded the expected overestimation of the Peirels stress compared to experiments, ring-polymer molecular dynamics on 150,000 atoms using parallel computing showed a smaller discrepancy between simulations and experiments. This indicated that earlier quantum corrections overestimated the agitation effect of zero-point-vibrations and downplayed the effect of atomic neighbor confinement. Implementing efficient ring-polymer molecular dynamics can help us study extended defects in materials, while accurately accounting for quantum corrections to atom dynamics.
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dynamic transitions from smooth to rough to twinning in Dislocation Motion
Nature Materials, 2004Co-Authors: Jaime Marian, Vasily V BulatovAbstract:The Motion of Dislocations in response to stress dictates the mechanical behaviour of materials. However, it is not yet possible to directly observe Dislocation Motion experimentally at the atomic level. Here, we present the first observations of the long-hypothesized kink-pair mechanism in action using atomistic simulations of Dislocation Motion in iron. In a striking deviation from the classical picture, Dislocation Motion at high strain rates becomes rough, resulting in spontaneous self-pinning and production of large quantities of debris. Then, at still higher strain rates, the Dislocation stops abruptly and emits a twin plate that immediately takes over as the dominant mode of plastic deformation. These observations challenge the applicability of the Peierls threshold concept to the three-dimensional Motion of screw Dislocations at high strain rates, and suggest a new interpretation of plastic strength and microstructure of shocked metals.
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kinetic monte carlo modeling of Dislocation Motion in bcc metals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: Vasily V Bulatov, Ali S. ArgonAbstract:Abstract We present a kinetic Monte Carlo (kMC) simulation method for modeling screw Dislocation Motion in BCC metals on the micron–second scales, using inputs from atomistic simulations of core mechanisms on the angstrom–picosecond scale. The simulations use atomistic input such as double-kink nucleation energy and kink mobility, include linear elastic (Peach–Koehler) interactions between Dislocation segments, and predict overall Dislocation velocity at different temperature and stress states. In addition, an important mechanism, namely, the spontaneous superjog growth and debris loop nucleation, is identified in the kMC simulation as an important factor controlling the Dislocation Motion in the high stress and medium temperature regime.
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parameter free modelling of Dislocation Motion the case of silicon
Philosophical Magazine, 2001Co-Authors: Vasily V Bulatov, Ali S. Argon, J F Justo, Thomas J Lenosky, M De Koning, Diaz T De La RubiaAbstract:Abstract In silicon and other materials with a high Peierls potential. Dislocation Motion takes place by nucleation and propagation of kink pairs. The rates of these unit processes are complex unknown functions of interatomic interactions in the Dislocation core, stress and temperature. This work is an attempt to develop a quantitative physical description of Dislocation Motion in silicon based on understanding of the core structure and the energetics of core mechanisms of mobility. Atomistic simulations reveal multiple and complex kink mechanisms of Dislocation translation; however, this complexity can be rationalized through the analysis of a straight kink-free Dislocation, based on symmetry-breaking arguments. Further reduction is achieved by observing that the energetics of kink mechanisms is scaled by a single parameter, the energy required to break a bond in the core. To obtain accurate values of this energy we perform density functional calculations that lead us to conclude that the low mobility of...
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Kinetic Monte Carlo modeling of Dislocation Motion in BCC metals
Materials Science and Engineering A, 2001Co-Authors: Wei Cai, Sidney Yip, Vasily V Bulatov, Ali S. ArgonAbstract:We present a kinetic Monte Carlo (kMC) simulation method for modeling screw Dislocation Motion in BCC metals on the micron-second scales, using inputs from atomistic simulations of core mechanisms on the angstrom-picosecond scale. The simulations use atomistic input such as double-kink nucleation energy and kink mobility, include linear elastic (Peach-Koehler) interactions between Dislocation segments, and predict overall Dislocation velocity at different temperature and stress states. In addition, an important mechanism, namely, the spontaneous superjog growth and debris loop nucleation, is identified in the kMC simulation as an important factor controlling the Dislocation Motion in the high stress and medium temperature regime. ?? 2001 Elsevier Science B.V. All rights reserved.
Hajime Okumura - One of the best experts on this subject based on the ideXlab platform.
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pinning of recombination enhanced Dislocation Motion in 4h sic role of cu and eh1 complex
Applied Physics Letters, 2010Co-Authors: Bin Chen, Hirofumi Matsuhata, Takashi Sekiguchi, Takasumi Ohyanagi, Akimasa Kinoshita, Hajime OkumuraAbstract:We report on the pinning of recombination-enhanced Dislocation Motion in 4H–SiC by the implantation of Cu. The Cu was found to be preferentially gettered at basal plane Dislocations (BPDs). Both EH1 and Z1/2 center were detected in 4H–SiC by cathodoluminescence. It was noticed that the EH1 has high luminescence intensity at the central part of the BPDs, while the Z1/2 does not. The complex of Cu and EH1 is regarded to be the cause for the pinning effect. The possible reason for the pinning is discussed.
M Bartsch - One of the best experts on this subject based on the ideXlab platform.
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friction mechanism of Dislocation Motion in icosahedral al pd mn quasicrystals
Philosophical Magazine, 1999Co-Authors: U Messerschmidt, M Bartsch, Michael Feuerbacher, B Geyer, K UrbanAbstract:Abstract Results from the literature and unpublished ones of the present authors are summarized which are relevant to the mechanisms governing the mobility of Dislocations in icosahedral Al-Pd-Mn quasicrystals. These results concern macroscopic deformation tests, conventional transmission electron microscopy, in situ straining experiments in a transmission electron microscope, and computer simulation experiments. These experiments can best be interpreted by assuming that the Dislocation Motion is controlled by the thermally activated overcoming of Mackay-type clusters. The present paper gives an estimate of the activation volume of this process. It turns out that the activation volume of overcoming the clusters individually is one order of magnitude smaller than the experimentally observed one. The experimental observations can be interpreted in a consistent way in terms of the Labusch-Schwarz theory of solution hardening in crystals, which considers the interpenetrating clusters as ‘extended’ obstacles, ...
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recombination enhanced Dislocation Motion in sige and ge
Physica Status Solidi (a), 1999Co-Authors: Ichiro Yonenaga, M Werner, M Bartsch, U Messerschmidt, E R WernerAbstract:In-situstraining experiments on Dislocation Motion in Ge and Si–5 at% Ge alloy single crystals are performed in a high voltage transmission electron microscope. In comparison with previous results by other methods, the Dislocation velocities are found to be enhanced due to a recombination enhancement owing to the excess carrier injection by the electron beam. The reduction in the activation energy of Dislocation Motion is ascribed to the recombination-assisted kink formation. The kink migration energy is estimated to be 0.7 eV in Ge and 1.5 eV in SiGe.
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transition of mechanisms controlling the Dislocation Motion in cubic zro2 below 700 c
Acta Materialia, 1998Co-Authors: Bernd Baufeld, M Bartsch, B. V. Petukhov, U MesserschmidtAbstract:Abstract For cubic ZrO2 single crystals deformed in 〈112〉 direction, new experimental data are presented on the flow stress and its strain rate sensitivity as well as on the Dislocation densities and the distances between glide obstacles along the Dislocations. A model is proposed to describe the strong variation of the parameters of the plastic deformation below 1000 K. It assumes that the mechanisms controlling the Dislocation Motion change from the pinning by localized obstacles above a transition temperature, e.g. small precipitates or jogs, to the overcoming of the Peierls relief at lower temperatures. The model is in agreement with most of the experimental observations.
Bin Chen - One of the best experts on this subject based on the ideXlab platform.
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pinning of recombination enhanced Dislocation Motion in 4h sic role of cu and eh1 complex
Applied Physics Letters, 2010Co-Authors: Bin Chen, Hirofumi Matsuhata, Takashi Sekiguchi, Takasumi Ohyanagi, Akimasa Kinoshita, Hajime OkumuraAbstract:We report on the pinning of recombination-enhanced Dislocation Motion in 4H–SiC by the implantation of Cu. The Cu was found to be preferentially gettered at basal plane Dislocations (BPDs). Both EH1 and Z1/2 center were detected in 4H–SiC by cathodoluminescence. It was noticed that the EH1 has high luminescence intensity at the central part of the BPDs, while the Z1/2 does not. The complex of Cu and EH1 is regarded to be the cause for the pinning effect. The possible reason for the pinning is discussed.