Chapter 6 – Superplasticity

Superplasticity is the ability of a polycrystalline material to exhibit, in a generally isotropic manner, very high tensile elongations prior to failure (T > 0.5 Tm). The first observations of this phenomenon were made as early as 1912. Since then, superplasticity has been extensively studied in metals. It is believed that both the arsenic bronzes used in Turkey during 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 that reported by Pearson in 1934 of a Bi–Sn alloy that underwent nearly 2000% elongation. He also claimed, for the first time, that grain boundary sliding was the main deformation mechanism responsible for superplastic deformation. The interest in superplasticity has increased due to the recent observations of this phenomenon in a wide range of materials, including some materials (such as nanocrystalline materials, ceramics, metal-matrix composites, and intermetallics) that are difficult to form by conventional forming processes. Extensive reviews on superplasticity are available.