Tensile superplasticity in nanocrystalline materials produced by severe plastic deformation

Tensile superplasticity has been observed in a number of severe plastic deformation (SePD) processed alloys with nanocrystalline microstructure. The observations of superplasticity in nanocrystalline materials are briefly reviewed with emphasis on the aspects that are different from superplasticity in microcrystalline materials. The temperature for onset of superplastic elongation coincides with microstructural instability. The important features include, high strain rate superplasticity in an aluminum alloy, low temperature superplasticity, extensive strain hardening and high flow stresses. A comparison of the experimental results with existing models shows the difference in superplastic deformation kinetics. The deformation mechanisms for microcrystalline materials are not simply scaleable to nanocrystalline range. It is difficult to establish the parameters for deformation mechanism because of grain growth. The observations of low temperature and high strain rate superplasticity in nanocrystalline materials with some unique features opens up new possibilities for scientific and technological advancements.