Hot deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with acicular microstructure

The characteristics of hot deformation of an alpha+beta titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si with acicular microstructure were studied using isothermal hot compressive tests in a strain rate range of 0.01-10 s(-1) at 860-1 100 degrees C. The true stress true strain curves of alloy hot-compressed in the alpha+beta region exhibit a peak stress followed by continuous flow softening; whereas in the beta region, the flow stress attains a steady-state regime. At a strain rate of 10 s(-1) and in a wide temperature range, the alloy exhibits plastic flow instability. According to the kinetic rate equation, the apparent activation energies are estimated to be about 633 kJ/mol in the alpha+beta region and 281 kJ/mol in the beta region, respectively. The processing maps show a domain of the globularization process of alpha colony structure and alpha dynamic recrystallization in the temperature range of 860-960 degrees C with a peak efficiency of about 60%, and a domain of beta dynamic recrystallization in the beta region with a peak efficiency of 80%.