The evolution of grain size distribution during deformation of superplastic materials

Grain size distribution and its evolution during superplastic deformation have been studied for two materials - ultrahigh carbon steel, which has a two phase microstructure, and a copper alloy, which has a quasi-single phase microstructure. For both materials, the distribution of initial grain sizes is very accurately represented by a lognormal function. As the materials are superplastically deformed, the distributions retain their lognormality throughout the deformation history. The evolution of the parameters characterizing the lognormal distribution (mean and standard deviation) have also been studied and found to vary in a systematic manner. Results can be used to specify the grain size distribution as a function of strain during superplastic deformation and thus should prove useful for computational studies in which grain size distribution is evaluated.