Large-scale atomistic simulations were performed to study plastic deformation in sub-micron polycrystalline thin films on substrates. The simulations reveal that stresses in the film were relaxed by mass diffusion from the surface into the grain boundary. This leads to formation of a novel material defect referred to as the diffusion wedge. A crack-like stress field was found to develop around the diffusion wedge as the traction along the grain boundary was relaxed and the adhesion between the film and the substrate prohibits strain relaxation close to the interface. The diffusion wedge caused nucleation of dislocations on slip planes parallel to the plane of the film. It was found that the nucleation of such parallel glide dislocations from a diffusion wedge could be described by a critical stress intensity factor similar to the case of a crack. Atomistic simulations of parallel glide dislocations associated with the crack-like grain boundary diffusion wedge represent a significant progress in the theory of diffusional creep in thin films on substrates.

Atomistic and Continuum Studies of Crack-Like Diffusion Wedges and Associated Dislocation Mechanisms in Thin Films on Substrates. M.J.Buehler, A.Hartmaier, H.Gao: Journal of the Mechanics and Physics of Solids, 2003, 51[11-12], 2105-25