Annealing and vacuum solution treatment of titanium

The purpose of annealing is to homogenize the structure and phase composition, obtain uniform performance, improve plasticity, and eliminate the internal stress formed during pressure processing, welding, machining, etc. Complete annealing is heating above the recrystallization start temperature but below the transformation temperature of the β phase. The annealing temperature is usually selected at 120~200℃ below the transformation temperature of the β phase. Incomplete annealing is performed to eliminate stress, and it is generally selected at 150~250℃ below the recrystallization start temperature. The annealing temperature of the plate is lower than that of the bar and forging. The annealing of titanium alloys is generally carried out in a non-vacuum state, but sometimes vacuum annealing is required to remove hydrogen or prevent pollution from harmful gases such as oxygen and nitrogen. The vacuum annealing temperature is generally 500~750℃. In order to stabilize the structure and performance of heat-resistant titanium alloys, double annealing or isothermal annealing can be used. Double annealing consists of two-stage heating and intermediate air cooling, that is, heating at 20~160℃ below the transformation temperature of phase B, air cooling, and then heating at 300~450℃ below the phase transformation temperature and air cooling. The difference between isothermal annealing and double annealing is that the cooling speed between the two heatings is different. Double annealing uses air cooling. Isothermal annealing is transferred from a high-temperature furnace to a low-temperature furnace for heat preservation and cooling with the furnace.

Solution treatment (quenching) and aging are strengthening heat treatments for titanium alloys, the purpose of which is to obtain a combination of high strength and good plasticity. There are two ways of solution treatment, namely β- phase solution treatment and (α+β)-phase solution treatment. β -phase solution treatment is 30~100℃ above the β-phase transformation temperature, kept warm for 10~30min, air-cooled or water-quenched, and is mainly suitable for metastable β- phase alloys; (α+β)-phase solution treatment is 30~60℃ below the β-phase transformation temperature, kept warm for 30~120min, water-quenched, and aging is to decompose the metastable phase obtained by solution treatment, generally carried out at 450~550℃, and the aging time is 2~8h and then air-cooled .