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.