6 - Superplasticity

Abstract

This chapter discusses superplasticity, which is the ability of a polycrystalline material to exhibit very high tensile elongations prior to failure. Since the first observations of this phenomenon, superplasticity has been extensively studied in metals. It is believed that both the arsenic bronzes, used in Turkey in the Bronze Age (2500 BC), and the Damascus steels, utilized from 300 BC to the end of the nineteenth century, were already superplastic materials. One of the most spectacular observations of superplasticity is perhaps of a Bi–Sn alloy that underwent nearly 2000% elongation. The interest in superplasticity has increased due to the recent observations of this phenomenon in a wide range of materials, including some materials, metal matrix composites, and intermetallics that are difficult to form by conventional forming. There are two types of superplastic behavior. The best known and studied, fine-structure Superplasticity (FSS), is briefly discussed in the chapter. The second type, internal stress superplasticity (ISS), refers to the development of Internal stresses in certain materials, which then deform to large tensile strains under relatively low externally applied stresses.