On the mechanisms of grain boundary migration

Abstract

Grain boundary dislocations and steps may have a major role in migration. The perfect grain boundary dislocations discussed in the present work can have steps at their cores and the step height depends on the dislocation and the boundary concerned. A model for migration is developed and it is correspondingly sensitive to the grain boundary crystallography. The problems of shear and long-range diffusion inherent in this model govern the details of the postulated dislocation processes and diffusion paths. There is direct evidence for migration by both dislocation and step mechanisms from in situ TEM heating experiments. Deformation associated with migrating boundaries in the absence of an external applied stress is interpreted in terms of the dislocation model. Movement of grain boundary dislocations, which are analogous to twinning dislocations, gives deformation and boundary migration. In the dislocation model, diffusion creep and boundary migration are related phenomena at a mechanistic level.