Uniaxial stress-driven grain boundary migration in Hexagonal Close-packed (HCP) metals: Theory and MD simulations

Stress-driven grain boundary (GB) migration is an important plastic deformation mechanism in nanopolycrystalline metals. Recently, Liu et al. (2014) and Zong et al. (2015) have shown a new mechanism for GB migration in a Hexagonal Close-packed (HCP) bicrystal with 90° GB misorientation under uniaxial stress loading conditions, which is different from shear-coupled GB migration. In real polycrystals, GBs have random orientations. To investigate the effects of GB misorientation and loading directions, we propose a mechanics model for uniaxial stress-driven GB migration in which the GB misorientation varies from 0° to 90°. Two types of imposed uniaxial loadings with loading directions parallel and perpendicular to the GB are considered. The model prediction is compared with that by molecular dynamics (MD) simulations. The results reveal that the uniaxial stress-driven GB migration can only occur in some range of GB misorientation under both loading conditions. The critical strain to trigger the GB migration varies with GB misorientation in a non-monotonic way. The proposed model provides new insights into the GB migration in HCP metals.