High temperature deformation behavior of α + β-type biomedical titanium alloy Ti-6Al-7Nb

Isothermal hot compression tests were carried out in the temperature range 750-900 °C and strain rate range 0.001-10 s^-1 for implant biomedical Ti-6Al-7Nb alloy to obtain the hot deformation behavior. Hot tensile tests were conducted to examine the hot ductility. The stress-strain curves in hot compression tests behave the characteristics of flow softening. According to the kinetic rate equation, the apparent activation energies at 750-850 °C and 900 °C are calculated to be 200 kJ/mol and 130 kJ/mol, respectively. It is concluded that at lower temperature (750-850 °C) and low strain rate (0.001-0.1 s^-1), the deformation is mainly controlled by recrystallization and grain-boundary sliding of the α phase. At higher temperature (900 °C) or large strain rate (1-10 s^-1), dynamic recovery in the β phase is the rate-controlling step. Considering workability and microstructural control, the optimum hot deformation conditions are determined in the temperature range 750-850 °C and strain rate range 0.01-0.1 s^-1.