The Mechanics of Superplastic Deformation and the Assessment of Superplastic Behaviour

Abstract

The significant suggestion of Backofen, Turner and Avery(42) that the basis of superplastic flow is to be found in the strain-rate sensitivity of flow stress is now known to apply equally to structurally as well as environmentally superplastic materials. In this Chapter the nature of the tensile test is first examined briefly. This is followed by a discussion of plastic stability and the rationalization of the phenomenology of superplastic flow in terms of a number of empirical and semi-empirical equations that have been proposed to analyse this mode of deformation. Subsequently the various methods of evaluating strain-rate sensitivity (SRS) in materials being deformed in tension will be described and also compared with other available procedures of determining this flow characteristic. The chapter will conclude with an account of some other specialised techniques, e.g. the examination of grain boundary sliding, of importance in assessing the extent of development of superplastic behaviour.