Tension-compression asymmetry in uniaxial deformation of a magnesium bicrystal with [(1)over-bar100] symmetric tilt grain boundary

A nanocrystalline metal contains grains that are extremely small, with a high proportion of grain boundary (GB). For understanding of the mechanical properties of nanocrystalline metals, it is indispensable to elucidate the influence of GBs on plastic deformation. In this study, molecular dynamics simulations of uniaxial deformation tests on magnesium bicrystals with [(1) over bar 100] symmetric tilt GBs were performed in order to reveal the role of GBs during the plastic deformation of hexagonal close-packed metals. We found that not only the critical resolved shear stress but also the active deformation mode itself is sensitively dependent on both the misorientation angle between the grains and the loading direction. In particular, ease of nucleation of basal dislocations from the GB could be qualitatively explained by the dependence of the GB energy on the misorientation angle, where dislocation nucleation from the GB is regarded as a process by which GBs accommodate changes in misorientation angle caused by elastic deformation due to an applied load. (C) 2016 Elsevier B.V. All rights reserved.