Effects of recovery and phase transformation on the recrystallization kinetics of Ti-6Al-4V during β-processing

This work unifies the description of microstructure evolution during dynamic and static recrystallization of Ti6Al-4V in a single model. The developed model incorporates the role of dislocation interactions on the phenomenological concepts of dynamic and static recovery, continuous dynamic and static recrystallization, nucleation rate, and grain growth. The beta-grain elongation during hot compression and the role of the deformed prior beta-grain size on the number of potential nucleation sites are considered to visualize the influence of the initial grain size before deformation on the kinetics of static recrystallization. The model is calibrated and validated with experimental data from Ti-6Al-4V samples thermomechanically treated in the beta-domain. Finally, the model is implemented as subroutines into the commercial FEM-based software DEFORMTM 2D. The proposed model accurately predicts I) the flow behavior and grain refinement during supertransus deformation, II) the influence of initial grain size, temperature, and deformation rate on the static recrystallization kinetics, and III) the grain growth kinetics. Simulations of hot forming followed by isothermal heat treatment and continuous cooling show that the Zener drag effect due to the formation of the alpha-phase has a greater influence on the kinetics of beta-recrystallization than the cooling rate itself.