Room temperature superplaticity in fine/ultrafine grained materials subjected to severe plastic deformation

Abstract

Achieving superplasticity at high temperatures and at very low strain rates is considered to be the most important disadvange of superplastic forming processes. Therefore, it is crucial to achieve superplastic behavior at low temperatures and high strain rates. To do so, it is well known that, high amount of grain refinement in the superplastic material is required. Very recent advances in severe plastic deformation (SPD) techniques based on imposing very high strains to the material provide abnormal grain refinement, and ultrafine-grained (UFG) microstructures can be achived in metallic materials by this manner. Formation of UFG microstructures via SPD methods like equal channel angular pressing (ECAP), high pressure torsion (HPT) and friction stir processing (FSP) bring about superplastic behavior in some classes of alloys even at room temperature (RT) as an extreme example of low temperature superplasticity. This paper overviews the studies aiming to investigate the RT superplasticity in some specific metals and alloys after UFG formation by SPD methods. UFG formation or nanostructuring of the materials by SPD to attain RT superplasticity were analyzed in detail. Also, the parameters affecting the RT superplasticity in different classes of materials and superplastic deformation mechanisms operated at RT superplasticity were explained.