[1] Dislocation dynamics simulations of dislocation interactions and stresses in thin films

R S Fertig III and S P Baker

The dislocation interactions that stop threading dislocations (threads) during relaxation at increasing applied strains in single-crystal thin films are investigated using large-scale three-dimensional dislocation dynamics simulations. Threads were observed to stop via interactions with both threads and misfit dislocations (misfits). Both types of interactions were shown to depend on stress inhomogeneity. Low-stress regions enabled threads to stop in weak thread–misfit interactions even at high average film stresses. Threads were also concentrated in low-stress regions, which facilitated their interaction with other threads. Threads accumulated in thread–thread interactions, and stopped only temporarily in thread–misfit interactions. The mean free path for dislocation motion is shown to be accurately predicted from details of the inhomogeneous stress state arising from the applied strain and the misfit structure. These behaviors are analyzed to present a more complete picture of film strength, strain hardening and relaxation.

[2] Comparing grain boundary energies in face centered cubic metals: Al, Au, Cu and Ni

E A Holm et al

The energy of 388 grain boundaries in Al, Au, Cu and Ni were calculated using atomistic simulations. Grain boundary energies in different elements are strongly correlated. Consistent with a dislocation model for grain boundary structure, the boundary energy scales with the shear modulus. Boundaries with substantial stacking fault character scale with the stacking fault energy. There is more scatter in the data for Al, which has a high stacking fault energy, than for the low stacking fault energy elements.

Title: Collective motion of atoms in grain boundary migration of a  bcc metal

Authors: L Zhou, N Zhou, and G Song

Bibliographic details: Philosophical Magazine, Volume 86, Number 36, 21 December 2006, pp. 5885-5895(11)


Molecular dynamics simulations of grain boundary (GB) migration of a bcc metal, tungsten, have been carried out. The GB is of asymmetrical 〈 110〉 tilt type. Detailed examinations of atomic processes in the migration, show that the GB migration consists mainly of GB dislocation glides. Furthermore, each motion of a GB dislocation involves a cooperative motion of about three atoms on each of the atomic planes perpendicular to the tilt axis, leading to their realignment from the receding grain to the advancing grain. This collective motion is not synchronized in all of the atomic planes, but appears to be in two or three adjacent planes, suggesting a kink mechanism for glides of the GB dislocations.

Notes: In this paper, the authors try to answer two specific questions regarding grain boundary migration in bcc metals using molecular dynamics simulations:

  1. The number of atoms involved in each collective motion (and what determines the number); and,
  2. The relationship between the collective mechanism and grain boundary dislocation mechanism.

There also seems to be indications of grain rotations at around 1.7 nm or so (which is not pursued in this paper). Finally, to answer the questions above–the grain boundary migration is via dislocation glide; each glide is associated with a collective motion of three atoms; further, the glide might also be associated with a kink motion.