Unified modelling of the flow behaviour and softening mechanism of a TC6 titanium alloy during hot deformation

In this paper, the flow behaviour and globularization kinetics of a TC6 alloy were investigated by conducting hot compression tests at different temperatures (910-970 degrees C), strain rates (0.01-10.0 s-1) and true strains (0.223, 0.511, 0.916). Scanning electron microscopy (SEM) measurements were performed to evaluate the phase transformation and globularization fraction. Based on the experimental results, a set of internal state variable-based unified viscoplastic constitutive equations was developed to model the flow behaviour and the globularization evolution of the TC6 alloy. The model was fully determined by an optimization method based on genetic algorithm (GA). The results show that the predicted beta phase transformation curve fits the experimental data well, and that the predicted flow stress and globularization fraction of the alpha phase are in good agreement with the experimental data, even at strain rates outside the limits of the model. Furthermore, the flow stress begins to decrease at the onset of the softening mechanism, which occurs at a true strain of approximately 0.05. While an analysis of the predicted variations in the strain hardening rate and strain rate of each phase reveals that the softer beta phase accumulates more overall strain, whereas the strain accumulation in the alpha phase decrease. (C) 2018 Elsevier B.V. All rights reserved.