Effects of heat treatment and hot deformation on the secondary α phase evolution of TC8 titanium alloy

To investigate the effect of heat treatment and hot deformation on the secondary α phase evolution, the heat treatment and isothermal compression were carried out for the as-received TC8 titanium alloy respectively. An optical microscope (OM) and a scanning electron microscope (SEM) were used to examine the microstructure. In the heat treatment, the secondary α phase can precipitate only as the TC8 titanium alloy is heat treated at a heating temperature of 980 °C followed by air cooling. In the isothermal compression, the secondary α phase precipitates as an irregular morphology due to the high dislocation content in the deformed β phase at a low deformation temperature of 860 °C, while as a regular lamellar colony due to the high supersaturation in the deformed β phase at a high deformation temperature of 940 °C. Meanwhile, the height reduction has a significant effect on the content and morphology of secondary α phase in the isothermally compressed TC8 titanium alloy. Comparing the secondary α phase evolution in the isothermal compression with that in the heat treatment of TC8 titanium alloy, it can be concluded that the hot deformation has a promoting effect on the precipitation of secondary α phase due to the deformation heat, crystal defect and dynamic recrystallization of β phase generated in the isothermal compression of TC8 titanium alloy.