The migration of small angle boundaries

It is shown by transmission electron microscopy that the migration of small angle boundaries occurs by the movement of steps which have a high mobility along the boundaries. A dislocation model for the steps is proposed. According to this model the steps are singularities in the small angle boundary. The steps migrate by short-circuit diffusion of atoms along the core of the dislocation which forms the step. In the parts of the small angle boundary between the steps migrate by volume diffusion. It is shown that coarsening of sub-grains is due to the migration of small angle boundaries.