Stress relaxation in a thin film, due to grain-boundary diffusion, was investigated using a new discrete dislocation framework. Discrete dislocations along grain boundaries were nucleated from the free surface, and were then driven to climb by the Peach–Koehler force; with a mobility that was governed by the grain-boundary diffusivity. Application to a planar film/substrate problem with sub-μm scale columnar grains showed that the degree of relaxation depended upon the initial stress and upon the grain aspect-ratio. For thin columnar grains, the relaxation was faster and more effective and the opening displacements along the grain boundary were more uniform. This effect was not captured by current continuum models. When the initial stress was low and the grain size was small, it was necessary to account for variations in the threshold stress, for diffusion among different grain boundaries, in order to achieve realistic results.

Stress Relaxation in Thin Film/Substrate Systems by Grain Boundary Diffusion - a Discrete Dislocation Framework. C.Ayas, E.Van der Giessen: Modelling and Simulation in Materials Science and Engineering, 2009, 17[6], 064007