Superplastic microstructure characteristics and unified constitutive model of TA32 titanium alloy

The superplastic deformation behavior and microstructure characteristics of TA32 titanium alloy were studied at different deformation temperatures (920-960°C) and initial strain rates (1×10-3-3×10-3 s-1). A unified constitutive model was developed and coupled with internal state variables. Results show that TA32 alloy featured steady flow stress and uniform plastic deformability under the dynamic equilibrium between softening and hardening effects. Increasing temperature and strain induced α→β phase transformation and α grain growth. Dislocation accumulation and grain boundary migration formed the dynamic recovery (DRV) and dynamic recrystallization (DRX) mechanisms. Using dislocation density, the proposed unified constitutive model built a quantitative relationship between superplastic flow stress and internal state variables such as grain size, with the correlation coefficient R, average absolute relative error (AARE), and root mean square error (RMSE) between the predicted and experimental stress values being 0.98, 6.91%, and 1.94, respectively. The unified constitutive model could predict well the flow stress and grain size evolution of TA32 titanium alloy during superplastic deformation.