Advances and applications in high strain rate superplasticity

High strain rate superplasticity (i.e., superplastic behavior at strain rates over 10^-2 s^-l) has been observed in many metallic materials such as aluminum alloys and their matrix composites and it is associated with an ultra-fine grained structure of less than about 3 pm. Its deformation mechanism appears to be different from that in conventional superplastic materials. A new model was considered from the viewpoint of the accommodation mechanism by an accommodation helper such as a liquid or glassy phase. The new mechanism was proposed in which superplasticity was critically controlled by the accommodation helper both to relax the stress concentration resulting from the sliding at grain boundaries and/or interfaces and to limit the build up of internal cavitation and subsequent failure. The possibility of the industrial applications was demonstrated for high-strain-rate superplasticity.