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

In order to evaluate the dynamic recrystallization (DRX) behaviors in alpha + beta-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 1023-1323 K and the strain rate range of 0.01-10 s(-1) on a Gleeble-3500 thermo-mechanical simulator. According to the strain hardening rate curves (d sigma/d epsilon versus sigma), two characteristic parameters involving the critical strain for DRX initiation (epsilon(c)) and the strain for peak stress (epsilon(p)) were identified. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) type equation X-DRX = 1 - exp [-beta(d)(epsilon - epsilon(c)/epsilon(0.5))(kd)] was introduced to characterize the evolution of DRX volume fraction. By further analysis of the true stress-strain curves, the material constants k(d) and beta(d) were determined to be 0.5994 and 0.9339, respectively; epsilon(c) was described as epsilon(c) = 0.1311 epsilon(p), where epsilon(p) = 0.0064(epsilon) over dot(0.0801) exp (30579/RT); epsilon(0.5) was described as epsilon(0.5) = 0.022 x (epsilon) over dot(0.11146) exp(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. (C) 2014 Elsevier B.V. All rights reserved.