Microstructural aspects of superplasticity

Abstract

This short review summarizes the contribution of microstructural studies to the present understanding of the deformation mechanisms operating during superplastic deformation. A background summary is included that describes the major features of superplasticity, the relevant deformation theories, and the requirements for successful microstructural studies. However, most of the paper is concentrated on a discussion of the microstructural evidence in the literature on two types of material. The first is a representative group of modern commercial nickel, aluminum, and magnesium alloys. The second is the Zn-Al eutectoid, a member of the well characterized “classical” group of superplastic materials based upon eutectic or eutectoid compositions. The importance of dislocation motion at maximumm is emphasized, both as an accommodation mechanism for grain boundary sliding and directly in response to the applied stress. However, it is shown that, in IN100 and Supral 150, other processes occur simultaneously, including recrystallization and diffusion.