Gleeble-Assisted Investigation and Thermokinetics Simulation of <i>α</i> Phase Isothermal Precipitation during Short-Time Duplex Heat Treatment of Ti-6Al-4V Alloy
Résumé
The precipitation mechanism and kinetics of the secondary alpha phase during short-time duplex heat treatment of the Ti-6Al-4V alloy were investigated. The precipitation kinetics was determined by means of in situ isothermal electrical resistivity tests in a Gleeble thermomechanical testing machine in the temperature range of 600-700 degrees C. The results showed that the higher the aging temperature, the faster the secondary alpha phase precipitation, which obeys the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation with an Avrami parameter n = 1. The precipitation process was also investigated by simulation using the thermokinetic software MatCalc. Results of the simulation on MatCalc indicated that the secondary alpha phase nucleation ended at an earlier stage of the precipitation and that the latter is mainly controlled by the growth of secondary alpha phase precipitates. Increasing the aging temperature resulted in an increase of the precipitate's size with an activation energy of Q = 62 kJ/mol for the process. Evolution of the simulated elements contents showed that only the vanadium concentration in the beta phase changed significantly during the isothermal aging. Thus, the growth of the secondary alpha phase is governed by the vanadium diffusion into the beta phase.