Evolution of microstructures and homogeneity in superplastic deformation

Superplastic deformation of materials having coarse, non-equiaxed and/or non-randomly distributed phases causes microstructural evolution involving grain refinement, transformation to an equiaxed grain shape and/or randomization of phase distribution. It is suggested that the "equilibrium" grain size that will evolve following superplastic flow is determined mainly by the Zener-Hollomon parameter, Z (= ε + ̇ exp (Q/RT); ε + ̇ is the strain rate, T is the absolute temperature of deformation, Q is the activation energy for flow and R is the gas constant). Experimental support for this view is provided.