The problem of calculating the long-term limiting effective diffusivity in stable 2-phase polycrystalline material was considered here for the first time. Use was made of a phenomenological model in which the high-diffusivity interphase boundaries were treated as connected coatings of the individual grains. Expressions were derived for the effective diffusivity with segregation. Monte Carlo computer simulations, using lattice-based random walks on a very fine-grained mesh, were used to test the validity of the expressions. It was shown that, for the cases analyzed, the expressions derived for the effective diffusivity were in very good agreement with the results of simulations. The equivalent of the Hart equation for this problem was also derived. The latter equation was always in poor agreement with the simulation results.

The Effective Diffusivity in Polycrystalline Material in the Presence of Interphase Boundaries. I.V.Belova, G.E.Murch: Philosophical Magazine, 2004, 84[1], 17-28