A State Variable Constitutive Model for Superplastic Ti-6Al-4V Based on Grain Size

Abstract

In this work, the superplastic material behavior of Ti-6Al-4V has been correlated with the grain size of the a phase. Because this microstructural state variable is directly observable, the viscoplastic flow kinetics could be determined separately from the state evolution (grain growth). The grain growth rate is the sum of static and deformation enhanced components which have been expressed in terms of current (state) variables rather than the historical quantities of plastic strain or time. In this manner, the grain growth relations are valid for arbitrary deformation rate and temperature paths. The deformation of a tapered rod has been measured and compared with simulation to evaluate the constitutive model.