scholarly journals Kink pair production and dislocation motion

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
S. P. Fitzgerald
2001 ◽  
Vol 677 ◽  
Author(s):  
Guofeng Wang ◽  
Alejandro Strachan ◽  
Tahir ÇaǦin ◽  
Willam A. Goddard

We study the structure and formation energy of kinks in 1/2a<111> screw dislocation in metallic Ta Embedded Atom Model Force Field parameterized using quantum mechanical computations. We studied a/3<112> kinks using a simulation cell containing four dislocations in a quadrupole arrangement. We impose periodic boundary conditions in the directions perpendicular to [111] and fixed boundaries in the [111] direction. We find that two, energetically equivalent, core configurations for the 1/2a<111> dislocation lead to 8 distinguishable single kinks and 16 kink pairs. The different mismatches of core configurations along [111] direction cause variations in kink formation energy. The lowest formation energy of a kink pair is determined to be 0.73 eV. The geometric features of such kink pair have been studied with the help of structural analysis of the atomistic model. We also compare the activation energy for dislocation motion via the double kink mechanism with the activation energy for a rigid dislocation motion from a dipole annihilation simulation. We find that the migration energy for dislocation motion via double kink formation is 0.016 eV/b, which is less than the quarter of the migration energy associated with the kink free motion of a straight dislocation, 0.073 eV/b.


2009 ◽  
Vol 11 (3) ◽  
pp. 733-739 ◽  
Author(s):  
Song Yu ◽  
Chong-Yu Wang ◽  
Tao Yu

1998 ◽  
Vol 552 ◽  
Author(s):  
M. Hirscher ◽  
D. Schaible

ABSTRACTHigh-purity stoichiometric NiAl single crystals have been prepared by crucible-free inductive zone melting and afterwards well annealed at temperatures below 1200 K. Internal friction measurements of torsionally deformed single crystals show two relaxation maxima at 500 and 800 K which anneal during the measurement. The first maximum can be assigned to the dislocation motion by kinkpair formation and the annealing to pinning of these dislocations by interstitial impurity atoms. The second maximum is attributed to the Snoek-Köster relaxation of dislocations in the presence of mobile interstitial impurity atoms and the annealing to the pinning of dislocations by vacancies. The kink-pair formation enthalpy in NiAl was estimated.


2021 ◽  
Vol 8 ◽  
Author(s):  
Xinran Zhou ◽  
Jaime Marian

In this work we present simulations of thermally-activated screw dislocation motion in Nb-Ta-V alloys for two distinct scenarios, one where kink propagation is solely driven by chemical energy changes, i.e., thermodynamic energy differences, and another one where a migration barrier of 1.0 eV is added to such changes. The simulations have been performed using a kinetic Monte Carlo model for screw dislocation kinetics modified for complex lattice-level chemical environments. At low stresses, we find that dislocation motion in the case with no barrier is controlled by long waiting times due to slow nucleation rates and extremely fast kink propagation. Conversely, at high stress, the distribution of sampled time steps for both kink-pair nucleation and kink propagation events are comparable, resulting in continuous motion and faster velocities. In the case of the 1.0-eV kink propagation energy barrier, at low stresses kink motion becomes the rate-limiting step, leading to slow dynamics and large kink lateral pileups, while at high stresses both kink pair nucleation and kink propagation coexist on similar time scales. In the end, dislocation velocities differ by more than four orders of magnitude between both scenarios, emphasizing the need to have accurate calculations of kink energy barriers in the complex chemical environments inherent to these alloys.


2020 ◽  
Vol 11 (1) ◽  
Author(s):  
K. Srivastava ◽  
D. Weygand ◽  
D. Caillard ◽  
P. Gumbsch

Abstract Work hardening in bcc single crystals at low homologous temperature shows a strong orientation-dependent hardening for high symmetry loading, which is not captured by classical dislocation density based models. We demonstrate here that the high activation barrier for screw dislocation glide motion in tungsten results in repulsive interactions between screw dislocations, and triggers dislocation motion at applied loading conditions where it is not expected. In situ transmission electron microscopy and atomistically informed discrete dislocation dynamics simulations confirm coupled dislocation motion and vanishing obstacle strength for repulsive screw dislocations, compatible with the kink pair mechanism of dislocation motion in the thermally activated (low temperature) regime. We implement this additional contribution to plastic strain in a modified crystal plasticity framework and show that it can explain the extended work hardening regime observed for [100] oriented tungsten single crystal. This may contribute to better understanding the increase in ductility of highly deformed bcc metals.


2009 ◽  
Vol 1185 ◽  
Author(s):  
Andreas S. Schneider ◽  
Blythe G. Clark ◽  
Carl P. Frick ◽  
Eduard Arzt

AbstractCompression tests with varying loading rates were performed on [001] and [235] oriented small-scale bcc Mo and Nb pillars to determine the contribution of thermally activated screw dislocation motion during deformation. Calculated activation volumes were shown to be in the range of 2 - 9 b3 and by further examination were found to decrease with pillar diameter. This suggests that the kink-pair nucleation of screw dislocations is enhanced by surface effects in the micron and submicron range.


Author(s):  
E. R. Kimmel ◽  
H. L. Anthony ◽  
W. Scheithauer

The strengthening effect at high temperature produced by a dispersed oxide phase in a metal matrix is seemingly dependent on at least two major contributors: oxide particle size and spatial distribution, and stability of the worked microstructure. These two are strongly interrelated. The stability of the microstructure is produced by polygonization of the worked structure forming low angle cell boundaries which become anchored by the dispersed oxide particles. The effect of the particles on strength is therefore twofold, in that they stabilize the worked microstructure and also hinder dislocation motion during loading.


1981 ◽  
Vol 42 (C5) ◽  
pp. C5-67-C5-72
Author(s):  
S. Okuda ◽  
H. Mizubayashi ◽  
N. Kuramochi ◽  
S. Amano ◽  
M. Shimada ◽  
...  

1987 ◽  
Vol 48 (C8) ◽  
pp. C8-113-C8-117
Author(s):  
H.-J. KAUFMANN ◽  
P. P. PAL-VAL ◽  
V. M. CHERNOV ◽  
D. A. KAMAJEV

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