Analysis of Possibilities of Fisher’s Model Development

The possibilities of Fisher’s model development and generalization are considered, as this model in its classical form contradicts some experimental results. Particularly, it does not explain such a phenomenon, observed in Mössbauer studies, as the transfer of grain-boundary diffusing atoms into near-boundary crystallite areas at temperatures when the volume diffusion is admittedly frozen. Different models explaining this phenomenon are briefly reviewed, the greatest attention being paid to a model accounting for the presence of equilibrium-composition near-boundary layers. It is demonstrated that based on the results of grain boundaries investigations one can conclude that at relatively low temperatures (< 0.35 – 0.40 Tm) the diffusant pumping from a grain boundary proceeds much faster than volume diffusion, and possible reasons for that are considered.