The effect of a grain boundary upon diffusion kinetics in a concentrated lattice-gas was examined quantitatively. In the present model, the lattice-gas particles migrated via Kawasaki dynamics on the sites of a simple cubic lattice in which a high-diffusivity slab (the grain boundary) was embedded. The migration was constrained, in that multiple occupancy of a site was forbidden. By studying various sub-sets of the particles, it was found that a temporal bias existed and could be explained in terms of approximate rate equations which reflected the dynamic inhomogeneity of the system. It was observed that particles tended to migrate towards the grain boundary region for a definite period of time. Because it was experimentally useful to relate bulk and grain-boundary diffusivities by analyzing concentration profiles, analogous quantities were identified here which related the present diffusivities. By identifying correlations between particle positions and site transition frequencies, an accurate analytical model for the diffusion kinetics was constructed that was applicable to points that were near to, or far from, the grain boundaries. It was found that a volume-weighted diffusivity was not suitable, normal to the boundary, due to dynamic correlations.

Y.F.Wang, J.M.Rickman, Y.T.Chou: Acta Materialia, 1996, 44[6], 2505-13