Superplasticity in Nb3Al/Nb in-situ composites

Microstructures of a binary Nb-15.8at%Al alloy ingot were controlled by isothermal forging and heat treatment to produce equiaxed, fine grains of Nb3Al and Nb solid solution (Nb-ss). Nb3Al/Nb-ss, two phase alloy (in-situ composite) is found to exhibit superplasticity especially when one of the constituent phases, Nb-ss is supersaturated. During superplastic deformation Nb-ss transforms to Nb3Al, and Al content in Nb-ss decreases. After superplastic deformation the microstructure consisting of equiaxed grains is left unchanged, although a slight grain growth is observed. It is suggested that stress induced by grain boundary sliding is effectively accommodated through dislocation glide and climb in the soft Nb-ss.