Molecular dynamics simulations of stress-driven grain boundary migration in bicrystal thin films demonstrated that the grain boundary mobility decreased as the films were made thinner. Examination of the surface morphology proved that this effect was not associated with grain-boundary grooving. The simulation data demonstrated that the grain boundary mobility was a linear function of the inverse thickness. A simple model was presented to explain this effect on the basis of the fundamental mechanism of grain boundary migration: the collective rearrangement of a large group of atoms. A decreasing system size implied that more of the boundary was near to the surface. The presence of the free surface interfered with the collective rearrangement of the atoms during boundary motion, and hence slowed migration. A simple heuristic analysis, based upon this effect, was consistent with the observed functional dependence of boundary mobility upon bicrystal thickness.

A Size Effect in Grain Boundary Migration - a Molecular Dynamics Study of Bicrystal Thin Films. L.Zhou, H.Zhang, D.J.Srolovitz: Acta Materialia, 2005, 53[20], 5273-9