Study on the warm deformation behavior and microstructure evolution of the MDIFed Ti–6Al–4V titanium alloy

The Gleeble-3500 thermal simulator was utilized to perform warm compression experiments on multi-directional isothermal forged (MDIFed) mixed microstructure Ti–6Al–4V titanium alloy with partial ultra-fine grains at the conditions of deformation temperatures ranging from 550 °C to 700 °C, strain rates ranging from 0.001 s−1to 0.1 s−1, with the maximum deformation amount at 50%. The results show that the true stress-strain curve exhibits typical dynamic recrystallization (DRX) characteristics at different deformation conditions. Based on the Arrhenius Model, the constitutive equation of the MDIFedTi-6Al–4V titanium alloy was successfully constructed. The correlation coefficient (R) and average absolute relative error (AARE) values are 0.98341 and 7.01%, respectively, indicating that the Arrhenius Model can well describe the warm deformation behavior of the alloy. Through activation energy spectrum analysis, the average activation energy is approximately 308 kJ/mol. Further, utilizing the dynamic material model (DMM), power dissipation diagrams, instability diagrams, and processing maps were drawn, and the optimal warm processing ranges were determined to be 630 °C–700 °C, 0.001s−1∼0.002s−1and 650 °C–700 °C, 0.06s−1∼0.1s−1. At the same time, the unstable domains were identified to be concentrated in the range of 550 °C–640 °C, 0.03s−1∼0.1s−1. Through the analysis of local misorientation and Schmidt factor in EBSD technology, The results indicate that the deformation mechanism of the MDIFed Ti–6Al–4V titanium alloys is primarily governed by dislocation slip and DRX. The activation of multiple slip systems contributes to the coordination and homogeneity of deformation, thereby enhancing the overall plastic deformation ability of the MDIFed Ti–6Al–4V titanium alloys.