A UNIFIED APPROACH TO GRAIN-BOUNDARY SLIDING IN CREEP AND SUPERPLASTICITY

Rachinger grain boundary sliding is a characteristic of high temperature deformation in both creep when the grain size is large (d > lambda) and superplasticity when the grain size is small (d < lambda), where d and lambda are the grain size and the subgrain size, respectively. An analytical procedure is used to determine the rate equation for Rachinger sliding when d > lambda. Data for superplastic metals are examined to give the rate equation for Rachinger sliding when d < lambda. A unified model is developed for Rachinger sliding at all grain sizes, where the rate of sliding is controlled by the rate of accommodation through intragranular slip. It is demonstrated that the predictions of this model are in good agreement with experimental data under both creep and superplastic conditions.