Abstract: Effects of solution and aging treatments on microstructure, phase composition and microhardness of BT25y titanium alloy were investigated. The results show that the structure of the forged specimen presents a typical duplex microstructure. Below the β transformation temperature(T_β), with the increase of solution treatment temperature, the content of primary α phase gradually decreases while that of the β transformed structure gradually increases, the thickness of the lamellar secondary α phase and the content of β phase gradually increase. After solution treatment above T_β, the primary α phase disappears completely, and the duplex microstructure completely transforms into the fully lamellar structure. After aging treatment, the shape and size of the primary α phase are not significantly changed, but the β transformed structure is obviously decomposed, and the content of β phase slightly decreases in the solution treated specimens below T_β but increases in the solution treated specimens above T_β. As known, both the increasing content of lamellar β transformed structure and the refinement of microstructure can significantly strengthen the two-phase titanium alloys, but the increase of content of the β phase softens the two-phase titanium alloys. Compared to the solution treated specimen, the microhardness of the aged specimen significantly increases when solution treated below T_β, which is attributed to both the reduction of β phase content and the refinement of microstructure, while the microhardness of the aged specimen slightly increases when solution treated above T_β, which is attributed to both the increase of β phase content and the refinement of microstructure.

Key words: BT25y titanium alloy, heat treatment, microstructure, microhardness