Superplastic microstructures

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Abstract
The production of fine, stable equiaxed grains, having disordered high angle boundaries, is a prerequisite for superplastic behaviour in crystalline solids. The way that superplastic microstructures can be achieved in pseudo-single-phase and duplex materials by thermomechanical processing is discussed for a number of commercially significant materials. The resulting superplastic deformation characteristics are outlined, as are the factors that influence cavitation during superplastic flow. Alloys based on aluminium, titanium, copper, iron, and nickel are considered, and also aluminium based metal-matrix composites, intermetallic phases, and crystalline ceramic materials. Recent work on markedly enhanced superplastic behaviour in aluminium and copper alloys and in stainless steels is reported, and the similarities between superplasticity in crystalline ceramics and metallic materials is discussed. The development of superplastic microstructures in metal-matrix composites, intermetallic phases, and ceramics has enhanced their formability and their potential as high temperature structural materials. MST/1298