superplasticity (rus. сверхпластичность) — a state of crystalline materials which allows them to be deformed well beyond than the usual limits for such materials in the normal state.

Description

The state of superplasticity is characteristic of metals and ceramics with a fine grain size, usually less than 20 microns. In addition to sufficiently fine grains, to reach the state of superplasticity a material requires high homogeneity of distribution over its volume of thermoplastic components which bind grain boundaries during the plastic flow, thus allowing the material to maintain its crystalline structure. For metals, there is still no definite explanation of the initiation mechanism of the superplastic state. It is believed that this mechanism derives from the phenomena of atomic diffusion and sliding of grains against each other. The newly discovered state of superplasticity in coarse-grained iron aluminide is explained by the dynamic grain recrystallisation process.

Superplasticity usually occurs at temperatures above half of the melting point by the absolute scale. When strained, samples in the state of superplasticity, as a rule, do not form a "neck" and are not subject to inertial cavitation, which occurs when samples are destroyed in the normal plasticity state. Many amorphous materials (e.g., glass and plastics) also demonstrate the possibility of significant strain at elevated temperatures but their condition is not related to superplasticity because these materials have no crystalline structure. Their condition is described by the laws of Newtonian fluid behaviour.

Authors

  • Goryacheva Irina G.
  • Shpenеv Alexey G.

Sources

  1. Superplasticity (in Russian) // Online Encyclopedia «Krugosvet», 2001–2009. —www.krugosvet.ru/enc/nauka_i_tehnika/fizika/SVERHPLASTICHNOST.html (reference date: 12.12.2011).
  2. Smirnov O.M., Tsepin M.A. Chumachenko E.N. Superplasticity Materials, Theory, Technology (in Russian). Serie: Synergetics: from past to future. — Мoscow: Komkniga, 2005. — 320 pp.

Contact us