The effects of twist angle and loading mode on the deformation behavior of bicrystal copper

Abstract

The effects of twist angle and loading mode on deformation behavior of bicrystal Cu containing symmetric twist grain boundary are investigated by molecular dynamics. Grain boundary dislocation network changes from square-like to ring-like with increasing twist angle. Tensile strength under loading parallel to grain boundary is higher than that under perpendicular loading to grain boundary for the same model, and the larger twist angle is, the larger difference under two loading modes is. Under perpendicular and parallel loadings, initial plastic yield of bicrystal Cu with low angle is triggered by slipping of grain boundary partial dislocations, which results in almost complete dissociation of grain boundary and formation of pillar-like voids inside grains. However, initial plastic yields of bicrystal Cu with higher angle are triggered by explosive collective slipping of short grain boundary partial dislocation and nucleating of new lattice dislocations on grain boundary, respectively, which result in direct splitting of grain boundary and formation of sphere-like voids, respectively. The calculated increase rates of partial dislocation number increase with increasing twist angle, but the increase amplitude is significantly larger under parallel loading. In later stage, void volume of each model is almost the same, but void surface area is significantly different.