Molecular dynamics simulations of fully 3-dimensional model nanocrystalline face-centered cubic microstructures were used to study grain boundary diffusion creep. In order to overcome the limitations which were associated with the relatively short time intervals (typically less than 10-8s) used in such simulations, they were performed at high temperatures where the distinct effect of grain boundary diffusion was clearly identifiable. In order to prevent grain growth, the initial microstructure was chosen to have a uniform grain shape, and a uniform grain size of nm-scale dimensions, and to contain only high-energy grain boundaries which exhibited fast liquid-like self-diffusion. The simulations revealed that, under relatively high tensile stresses, these microstructures exhibited steady-state diffusion creep that was homogeneous; with a strain rate that agreed quantitatively with that given by the Coble-creep formula. The grain-size scaling of Coble creep was found to change from d-3 to d-2 when the grain diameter became of the order of the grain boundary width.

Grain-Boundary Diffusion Creep in Nanocrystalline Palladium by Molecular Dynamics Simulation. V.Yamakov, D.Wolf, S.R.Phillpot, H.Gleiter: Acta Materialia, 2002, 50[1], 61-73