Achieving superplasticity in ultrafine-grained metals

Superplasticity refers to the ability of some materials to pull out to exceptionally high elongations prior to failure. It is now well established that superplastic flow requires both a high testing temperature and a small grain size that is typically less than ∼10 μm The processing of ultrafine-grained metals with submicrometer grain sizes through the application of severe plastic deformation (SPD) provides an opportunity for achieving excellent superplastic properties in bulk metals provided these small grains are reasonably stable at elevated temperatures. There have been numerous recent developments in the production of superplastic flow in metals processed by SPD and these developments are reviewed in this report. The analysis shows there is an excellent potential for achieving high superplastic elongations in metals processed by SPD, these high elongations often occur at very high strain rates and, in addition, the behaviour of these metals is consistent with the predictions from deformation mechanism maps.