http://en.wikipedia.org/wiki/Superplasticity
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CONCISE DICTIONARY OF MATERIALS SCIENCE. Structure and Characterization of Polycrystalline Materials by Vladimir Novikov писал(а):
Superplasticity. Ability to deform plastically up to nominal strains ≥1000% without noticeable strain hardening. In the course of superplastic deformation (SD), high strain-rate sensitivity (0.2 ≤ m ≤ 0.8) is observed. SD evolves at increased temperatures (0.5–0.7 Tm) and low strain rates (10–4 tο 10–3 s–1,) provided the grain size does not change significantly. The dislocation density inside the grains does not increase in the course of SD, and the grains remain equiaxed. Superplasticity is observed in ultra fine-grained, dual-phase materials or in fine-grained single-phase materials, with or without dispersed second-phase particles. SD is a result of equilibrium between strain hardening due to dislocation multiplication inside grains during plastic deformation, on the one hand, and softening due to the dislocation absorption by the grain boundaries, where dislocations delocalize and annihilate, on the other. This effect of grain boundaries can reveal itself in grain boundary sliding, in ceramics promoted by thin intergranular layers of glassy phases. Superplasticity can also result from dynamic recovery in single-phase materials.
