Dynamic Recrystallization Modeling Considering Dynamic Transformation and Behavioral Analysis for a High-Temperature Titanium Alloy during Hot Deformation

Considering the effect of dynamic transformation from the harder alpha phase into the softer beta phase on the decrease in flow stress, the empirical formula of dynamic recrystallization for the near alpha high-temperature titanium alloy during hot deformation was established. The flow stress of the near alpha high-temperature titanium alloy increased rapidly at the initial stage of hot deformation, and then reached peak value and dropped rapidly as the strain increased due to the work hardening and dynamic softening. The volume fraction of dynamic transformation was calculated using the principle of stress balance between work hardening and dynamic softening caused by dynamic recovery, dynamic transformation, and dynamic recrystallization. Through eliminating the effect of dynamic transformation on the flow stress according to the principle of stress balance, the volume fraction of dynamic recrystallization was calculated and an empirical formula based on the Avrami kinetic equation was established. The predicted dynamic recrystallization curve shows an "S" shaped variation and a "slow-fast-slow" growth with increasing strain. The accordance of predicted and experimental results of dynamic recrystallization indicates that the higher temperature and lower strain rate are beneficial in promoting the dynamic recrystallization of the alloy. Low-angle grain boundaries absorbing dislocations and developing into high-angle grain boundaries are the dominant mechanism of the dynamic recrystallization for the near alpha high-temperature titanium alloy during hot deformation.