The impact of a grain boundary on the kinetics of diffusion in a concentrated lattice gas was examined quantitatively. In this model, the lattice-gas particles moved via Kawasaki dynamics on the sites of a simple cubic lattice in which a high-diffusivity slab (i.e. grain boundary) was embedded. Their motion was constrained such that multiple occupancy of a site was forbidden. By examining various subsets of particles, it was found that a temporal bias exists and could be explained in terms of approximate rate equations which embody the dynamical inhomogeneity of the system. It was observed that particles tended to migrate toward the grain boundary region for a definite period of time. As it was useful experimentally to relate bulk and grain boundary diffusivities from an analysis of concentration profiles, analogous quantities were identified here which related these diffusivities in the simulations. In particular, by identifying correlations between particle position and site transition frequencies, an accurate analytical model of diffusion kinetics was constructed that was applicable both near to, and far from, grain boundaries. It was found that a volume-weighted diffusivity was not appropriate normal to the boundary due to dynamical correlations.

Monte Carlo and Analytical Modeling of the Effects of Grain Boundaries on Diffusion Kinetics. Y.F.Wang, J.M.Rickman, Y.T.Chou: Acta Materialia, 1996, 44[6], 2505-13