Models of nonstationary diffusion over nonequilibrium grain boundaries in nanostructured materials

We propose models of grain-boundary diffusion with a time-dependent diffusion coefficient, which is due to nonequilibrium nature of grain boundaries. It is shown that an increase in the excess energy of nonequilibrium boundaries leads to an increase in the amount of diffusant penetrating into the sample. A generalization of the Fisher solution for the diffusant concentration in the bulk of a grain is obtained; the dependence of the mean concentration of the diffusant is calculated taking into account nonequilibrium diffusion coefficients.