Grain boundary sliding controlled flow and its relevance to superplasticity in metals, alloys, ceramics and intermetallics and strain-rate dependent flow in nanostructured materials

A model that was proposed originally to account for optimal superplasticity in metals and alloys with grain size in the micrometer range and later extended in a few subsequent papers to cover optimal superplastic deformation in ceramics, sub-micrometer-grained and nanostructured materials and intermetallics is described, with an emphasis on the current ideas used in this model and the mathematical procedure used at present (yet to be published in detail) for validating the proposals. The central assumption is that the rate controlling deformation process is confined to high-angle grain/interphase boundary regions that are essential for grain boundary sliding developing to a mesoscopic scale (defined to be of the order of a grain diameter or more) and for superplastic flow setting in. The strain rate equation was validated against experimental observations concerning metals, alloys and ceramics of micrometer- and sub-micrometer grain sizes, nanostructured materials and intermetallics