Understanding the Concurrent Microstructural Evolution and Its Impact on Superplastic Characteristics: An overview

Extensive studies on experimental constitutive relationship for superplastic deformation of both the ideal equiaxed microstructure and the non-equiaxed microstructure were taken up over a period of more than four decades in the group. While our understanding of microstructure-superplastic flow relationship has grown significantly, there remains a gap between the theoretical modelling, based on steady-state, and the realistic behavior investigated for several materials. The observations made here are also supported by numerous publications by other investigators in the literature, with growing development of not only metals but ceramics, composites, intermetallic compounds and nano-crystalline materials aimed to push superplastic behavior to higher strain rate and lower temperature condition. Here, an attempt is made to list the range of microstructure changes that occur and as such the need to consider the same while evaluating the parameters of constitutive relationship. Some suggestions are provided to minimize the gap between the ideal and real behavior of superplastic flow based on the types of stress-strain curves reported in the superplastic literature and their effect on the nature of stress-strain rate relation. It includes the consideration of effective stress for superplastic deformation, and to incorporate the effects of strain and concurrent microstructure in the experimental constitutive relationship