Superplasticity is a state in which solid material is deformed well beyond its usual breaking point, usually over 100% during tensile deformation. Such a state is usually achieved at high temperature, typically half the absolute melting point. Example of superplastic materials are silica glass ("molten glass"), chewing gum, and some fine-grained metals
In a state of superplasticity, solid matter can exhibit certain hydrodynamic qualities without becoming an actual liquid.
In metals, superplasticity relies on atomic diffusion and the sliding of grains past each other. As a material is deformed permanently (plastically), it gets thinner. Under superplasticity the stretched material gets thinner in a very uniform manner, rather than forming a "neck" (a local narrowing) which leads to fracture. Also, the formation of internal cavities, which is another cause of early fracture, is inhibited.
Superplasticity is used to form complex objects, by the application of gas pressure or with a tool, and often with the help of dies. Glass blowing is an early example of superplasticity. Aluminum and titanium parts are often superplastically formed for aerospace applications.
External links
FUNDAMENTAL ASPECTS OF SUPERPLASTIC DEFORMATION at the Institute for Metals Superplasticity Problems