An Overview of the Principles of Low-Temperature Superplasticity in Metallic Materials Processed by Severe Plastic Deformation

Low-temperature superplasticity (LTS) is crucial to reduce manufacturing cost and to enhance the applications of superplastic forming. It is well known that grain refinement is the key point to decrease the temperature at which superplasticity is attained. Therefore, ultrafine-grained (UFG) materials have become attractive for achieving LTS. Severe plastic deformation (SPD) techniques provide abnormal grain refinement, and thus they have been used to achieve LTS in metallic materials. This paper overviews and examines the reports of LTS in the severely-deformed metallic materials. It provides fundamentals of grain refinement via different SPD techniques in various classes of metallic materials including Al-, Mg-, and Ti-based alloys. It also gives a brief summary about the effect of microstructural requirements on LTS with an emphasis on grain size, type and chemical composition of grain boundaries and microstructural alteration during the superplastic deformation. In the last section of the manuscript, the main deformation mechanism of LTS were also explained.