Modelling the motion of twinning dislocations in the HCP metals

Deformation twinning is important for plasticity of the hcp metals, but little is known about the dynamics of the mechanisms that control twin boundary motion. With the exception of the { 1   1   2 ¯   1 } twin, atomic shuffles are required for glide of twinning dislocations and hence boundary movement is temperature-dependent. A computer method has been developed to simulate a step with dislocation character in a boundary with full periodicity in the boundary plane, i.e. along both the direction of the line of the defect and its direction of motion. It may be used to investigate the properties of such interfaces as the defects in them move over large distances. We explain the nature of the method and apply it to study the motion of twinning dislocations in the { 1   1   2 ¯   2 } boundary as a function of applied stress and temperature. A new reaction at the boundary leading to the creation of a (c + a) crystal dislocation and a { 1   1   2 ¯   1 } micro-twin is described.