Review: achieving superplasticity in metals processed by high-pressure torsion

It is now well established that processing by equal-channel angular pressing (ECAP) leads to grain refinement and produces materials having the potential for exhibiting extensive superplastic flow at elevated temperatures. High-pressure torsion (HPT) is also an effective procedure for refining the grain sizes of polycrystalline metals to the submicrometer or even the nanometer level, and recent results show that this processing method also gives materials that exhibit excellent superplastic characteristics. This report examines the various publications describing superplasticity in metallic alloys processed by HPT. A comprehensive tabulation is presented listing all of the results to date showing true superplastic elongations of at least 400 % after processing by HPT. Examples of superplastic elongations are described for tensile tests conducted using specimens cut from either disk or ring samples. An analysis shows that the flow behavior of various Al and Mg alloys is in good agreement with the predicted flow behavior for conventional superplastic materials.