Role of misorientation angle in twinning and dislocation slip for nano Mg bicrystals with [2-1-10] symmetric tilt grain boundaries under uniaxial compression and tension

摘要

Atomistic modeling is employed to investigate the role of different mechanisms in the plastic response of Mg bicrystal with [2-1-10] symmetric tilt grain boundary (STGB). Excess potential energies for 30 stable STGBs with different misorientation angles are used to different models. The structure of [2-1-10] STGB consists of a base plane and an array of intrinsic grain boundary dislocations (GBDs). The STGB structures varying with the misorientation angle influence the deformation mode, and nucleation and propagation of twins and basal dislocations in the bicrystal models. Uniaxial compression and tension are imposed on 14 bicrystal models containing STGBs under a strain rate of 1 x 10(8) s(-1) at 300 K. For the hcp lattice, non-symmetry of compressive and tensile response is demonstrated. Dislocation nucleation prefers to occur from the GBDs where intrinsic stacking fault facets may nucleate prior to the dislocation emission. Through reaction with (01-11) twin boundary (TB), the basal dislocation from matrix is dissociated into a residual dislocation and a pyramidal dislocation which can glide along the pyramidal plane of twin. While the basal dislocation reacting with (01-13) TB is dissociated into some serrated facets.