Hot deformation behavior and process parameters optimization of Ti–6Al–7Nb alloy using constitutive modeling and 3D processing map

Abstract

The isothermal compression test for Ti–6Al–7Nb alloy was conducted by using Gleeble-3800 thermal simulator. The hot deformation behavior of Ti–6Al–7Nb alloy was investigated in the deformation temperature ranges of 940–1030 °C and the strain rate ranges of 0.001–10 s−1. Meanwhile, the activation energy of thermal deformation was computed. The results show that the flow stress of Ti–6Al–7Nb alloy increases with increasing the strain rate and decreasing the deformation temperature. The activation energy of thermal deformation for Ti–6Al–7Nb alloy is much greater than that for self-diffusion of α-Ti and β-Ti. Considering the influence of strain on flow stress, the strain-compensated Arrhenius constitutive model of Ti–6Al–7Nb alloy was established. The error analysis shows that the model has higher accuracy, and the correlation coefficient r and average absolute relative error are 0.9879 and 4.11%, respectively. The processing map (PM) of Ti–6Al–7Nb alloy was constructed by the dynamic materials model and Prasad instability criterion. According to PM and microstructural observation, it is found that the main form of instability zone is local flow, and the deformation mechanisms of the stable zone are mainly superplasticity and dynamic recrystallization. The optimal processing parameters of Ti–6Al–7Nb alloy are determined as follows: 960–995 °C/0.01–0.18 s−1 and 1000–1030 °C/0.001–0.01 s−1.