Atomistic insights into shear-coupled grain boundary migration in bcc tungsten

Shear-coupled grain boundary (GB), migration is an efficacious plasticity mechanism in nanocrystalline materials. However, the atomistic aspects of this kind of GB motion have received far less attention in bcc metals than that in fcc ones. In this work, we have investigated the shear-coupled migration (SCM) of Sigma 13[100]01 (5) over bar) and Sigma 85[100]07 (6) over bar) GBs in bcc tungsten using atomistic simulations. We demonstrate that the SCM of the two GBs proceeds via the collective glide of GB dislocations along the < 100 > and < 111 > directions, respectively. The magnitudes of the GB migration depend on system lateral dimension, temperature and GB dislocation character. Nudged elastic band calculations in combination with the dynamic simulations give the elementary processes of the SCM and show that the shear strength and thermal resistance of the < 100 > mode GB is much higher than the < 111 > one, consistent with the fact that the < 100 > dislocations are much more difficult to glide than the 1/2 < 111 > dislocations. This conclusion is further supported by the simulation results of GB random walk behavior under the free boundary condition. The present results demonstrate that the atomistic SCM process is fundamentally related to the character of GB dislocations. (C) 2016 Elsevier B.V. All rights reserved.