On the migration of {3 3 2} <1 1 0> tilt grain boundary in bcc metals and further nucleation of {1 1 2} twin

Abstract

{3 3 2} <1 1 0> tilt grain boundaries (GB) move conservatively under a shear stress by the creation and glide of disconnections. When crystal dislocations interact with the GB they are absorbed and transformed into GB dislocations (GBD). The behaviour of GBDs under shear stress depends on the orientation of the Burgers vector and sense of shear stress. There are two possible scenarios: a) the GBD moves together with the GB in a compensated climb, then plastic deformation is accommodated by shear-coupled GB migration; b) the GBD is sessile because it cannot undergo a compensated climb when interacting with the disconnections. If so, the sessile GBD is the nucleus of a {1 1 2} twin. The nucleation of the twin is produced by the pileup of disconnections at both sides of the GBD. Then, plastic deformation is accommodated by the combination of the motion of the {3 3 2} GB and the growth of {1 1 2} twins inside the grain.