Identification of the optimal (α + β) forging process parameters of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si based on processing-maps

The deformation behavior of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si at the deformation temperature of 780–990 °C and the strain rate between 0.001 and 70.0 s−1 was systematically investigated for the identification of the optimal process parameters and the control of microstructure in (α + β) forging process. The processing-maps (P-maps) of the Ti-alloy in the above-mentioned deformation conditions were first constructed based on the experimental data of isothermal compression test. The experimental results show that the flow stress of the alloy is affected by the deformation temperature, strain rate and strain in the deformation process. The flow stress curves generated based on the experiments exhibit a steady-state characteristic and the flow softening behavior at the higher temperature and the lower strain rate. The suitable process parameters in (α + β) forging region are identified to be 855–920 °C, 0.001–0.005 s−1 for the strain less than 0.7. Under this process parameter configuration, the optimum deformation condition is 890 °C, 0.001 s−1. When the strain is greater than 0.7, the process parameter configurations for superplasticity deformation identified based on P-maps, microstructure observation and verified by the physical experiment of superplasticity deformation are 785–810 °C, 0.001–0.002 s−1; 875–925 °C, 0.001–0.005 s−1 and 945–990 °C, 0.001–0.016 s−1. The optimum (α + β) forging process parameters are 810 °C, 0.001 s−1; 900 °C, 0.001 s−1 and 960 °C, 0.001 s−1.