Modelling for the dynamic recrystallization evolution of Ti–6Al–4V alloy in two-phase temperature range and a wide strain rate range

Abstract

In order to evaluate the dynamic recrystallization (DRX) behaviors in α+β-phase temperature range of Ti–6Al–4V alloy, a series of isothermal compression tests with a fixed height reduction of 60% were performed in the temperature range of 1023–1323K and the strain rate range of 0.01–10s−1 on a Gleeble-3500 thermo-mechanical simulator. According to the strain hardening rate curves (dσ/dε versus σ), two characteristic parameters involving the critical strain for DRX initiation (ɛc) and the strain for peak stress (ɛp) were identified. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) type equation XDRX=1-exp-βdε-εcε0.5kd was introduced to characterize the evolution of DRX volume fraction. By further analysis of the true stress–strain curves, the material constants kd and βd were determined to be 0.5994 and 0.9339, respectively; ɛc was described as ɛc=0.1311ɛp, where εp=0.0064ε̇0.0801exp(30579/RT); ɛ0.5 was described as ε0.5=0.022×ε̇0.11146exp(26430/RT). The evolution of DRX volume fraction was described as following: for a fixed strain rate, the deformation strain required for the same amount of DRX volume fraction increases with decreasing deformation temperature. In contrast, for a fixed temperature, it increases with increasing strain rate. As the developed JMAK type equation was applied in the finite element simulation model, a series of simulations for the hot compressions in accordance with experimental conditions were conducted, and the DRX volume fraction distributions in deformed materials were uncovered. Finally, the theoretical predictions and numerical results were validated by the microstructure graphs.