Characterization of hot deformation behavior of as-cast TC21 titanium alloy using processing map

The hot deformation behavior of as-cast TC21 titanium alloy has been investigated in the isothermal compression of the alloy using processing maps conducted at the deformation temperature ranging from 1000 °C to 1150 °C, the strain rate ranging from 0.01 to 10 s−1, and the height reduction of 60%. The constitutive equation of as-cast TC21 alloy is developed in the form of the exponential law and the deformation activation energy is calculated to be about 185.51 kJ/mol. Based on the dynamic materials model and Prasadʹs instability criterion, the processing maps of as-cast TC21 titanium alloy are constructed at strains of 0.4 and 0.6. Deformation mechanisms in the stable and unstable regions are verified through the microstructure observation. The maps exhibit a stable domain with the temperature range of 1000–1150 °C and strain rate range of 0.01–0.1 s−1 with two peak efficiencies of power dissipation, one is 48% occurring at 1000 °C/0.01 s−1 that is associated with dynamic recovery, the other is 38% occurring at 1150 °C/0.01 s−1, which displays the feature of continuous recrystallization. Therefore, the optimal processing condition of the alloy is 1150 °C/0.01 s−1. In addition, the material undergoes flow localization at strain rates higher than 1 s−1 which has to be avoided in hot processing for obtaining satisfactory properties. Thus the applicable cogging temperatures and cogging strain rates for as-cast TC21 alloy are 1000–1150 °C and 0.01–0.5 s−1, respectively.