Microstructure evolution and phase transformation of Ti-6.5Al-2Zr-Mo-V alloy during thermohydrogen treatment

Thermohydrogen treatment (THT) is an effective way to refine microstructure and improve the mechanical properties of the titanium alloys. In the current work, as-cast Ti-6.5Al-2Zr-Mo-V alloy was hydrogenated with different hydrogen contents and processed solution aging. Accordingly, the microstructure evolution and phase transformation were analyzed. Results show that during solution aging, eutectoid decomposition occurs and the product is a mixture of coarse primary α, fine eutectoid product and undecomposed β_H. The size of primary α is closely dependent on the hydrogen content, and large primary α can be obtained at medium hydrogen content. Further, the influence of hydrogen content on the growth of primary α phase was revealed. The primary α is much fine, and the eutectoid product is relatively homogeneous with 0.984 wt% H. After THT, the ultimate strength is beyond 1,100 MPa that has increased by 23.15% compared with that in as-cast state.