Developing superplasticity in ultrafine-grained metals

The processing of bulk metals through the application of severe plastic deformation provides an opportunity for achieving exceptional grain refinement with grain sizes typically lying in the submicrometer or even the nanometer range. Provided these small grains are reasonably stable at elevated temperatures, these ultrafine-grained metals will exhibit excellent superplastic properties when pulled in tension at elevated temperatures. Most ultrafine-grained materials have been produced using either equal-channel angular pressing or high-pressure torsion. This paper examines the results for superplasticity reported to date using metallic alloys processed by equal-channel angular pressing and high-pressure torsion, compares the experimental strain rates with those predicted using the theoretical model for conventional superplastic flow and then demonstrates the feasibility of preparing deformation mechanism maps that provide comprehensive information on the flow mechanisms