Effective diffusivity of solute in multiphase materials with segregation

The effective diffusion coefficient Deff for solute in a multiphase microstructure in which solute segregation can occur is related to Deff for an isomorphic microstructure in which no segregation occurs. This permits analytical expressions (approximations, bounds, etc.) and methods of numerical calculation for Deff that neglect solute segregation to be applied to systems that exhibit segregation. As an example, exact results are obtained for solute diffusion and segregation to grain boundaries in an idealized polycrystalline microstructure.