Structure and Phase-Composition Formation in a Quenched Intermetallic VTI-4 Titanium Alloy with Various Hydrogen Contents during Isothermal Treatment: II. Treatment at 750 and 850°C

The phase composition and the structure formed in a quenched titanium orthorhombic alloy with an initial hydrogen content and with 0.3% hydrogen are studied during isothermal holding at temperatures of 750°C and 850°C for 10–300 min. At these temperatures, the decomposition of metastable B2 phase is found to be accompanied by the precipitation of disperse particles throughout the initial phase volume even after 10 min. The decomposition intensity is shown to be maximal at 850°C; at 750°C, the decomposition of the B2 phase in the hydrogen-containing alloy is not completed even after treatment for 300 min. The largest increase in the microhardness (by 70–80 HV0.05) is observed at 750°C due to the high dispersion of precipitated particles. The diagrams of isothermal decomposition of the metastable B2 phase during holding a quenched VTI-4 alloy with various hydrogen contents in the temperature range 750–1000°C have been constructed.