The Contribution of Severe Plastic Deformation to Research on Superplasticity

Superplasticity refers to the ability of some metals, in special testing conditions, to exhibit high elongations of at least 400% before failure. Although this phenomenon appeared initially as a scientific curiosity, it has now become the basis for the large superplastic forming industry which makes significant contributions in many areas including the aerospace and automotive sectors. Early experiments established that superplastic flow requires a small grain size, typically below similar to 10 mu m, and this is generally achieved through appropriate thermomechanical processing. However, the grain sizes achieved in this way are typically of the order of a few micrometers. Recent investigations of the processing of metals through the application of severe plastic deformation (SPD) demonstrated that these techniques provide an opportunity to achieve much smaller grain sizes to the submicrometer or even the nanometer scale and this gives opportunities to develop new investigations of superplastic flow. Accordingly, this overview summarizes some of the major contributions of SPD processing to research in the area of superplasticity with an emphasis on the characteristics of the flow behavior.