The role of boundaries during superplastic deformation

Micrograin superplasticity refers to the ability of fine-grained materials (d < 10 mum, where d is the grain size) to exhibit extensive neck-free elon gations during deformation at elevated temperatures (T > 0.5 T-m, where T-m is the melting point). Consideration of recent experimental data regarding the effects of impurities on the characteristics of micrograin superplasti city reveals an important role played by boundaries in superplastic alloys. This role pertains to the ability of boundaries to serve as favorable site s for the accumulation of impurities, i.e. boundary segregation. Evidence i n support of boundary segregation during micrograin superplasticity is revi ewed, with particular emphasis on creep behavior, cavitation, ductility, bo undary sliding and the formation of cavity stringers. Copyright (C) 2001 Jo hn Wiley & Sons, Ltd.