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 elongations 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 superplasticity reveals an important role played by boundaries in superplastic alloys. This role pertains to the ability of boundaries to serve as favorable sites for the accumulation of impurities, i.e. boundary segregation. Evidence in support of boundary segregation during micrograin superplasticity is reviewed, with particular emphasis on creep behavior, cavitation, ductility, boundary sliding and the formation of cavity stringers. Copyright (C) 2001 John Wiley & Sons, Ltd.