Simple transition parameter expression including grain size and intergranular exchange.

A microtrack model approach is utilized to extend the simple William--Comstock (WC) formula to include finite grain size and intergranular exchange. The model assumes microtracks with finite size grains in each microtrack and random phase of grain centers between microtracks. Intergranular exchange is modeled as a mean field. For WC parameters much less than grain size, the model gives a finite transition parameter limit. The effect of exchange is to reduce the transition parameter. [ABSTRACT FROM AUTHOR]