Effect of vacuum annealing on microstructure and mechanical properties of TA15 titanium alloy sheets

The mechanical properties, microstructures, and fractographs of TA15 sheets vacuum-annealed under different patterns were investigated. The results indicate that vacuum annealing significantly improves the mechanical properties of the sheets in comparison with those after ambient annealing. With increasing the annealing temperature, the phase boundaries and secondary α-phase increase, whereas the volume fraction of primary α-phase decreases, resulting in increased strength and decreased elongation. A relatively fine secondary α-phase is obtained after double annealing. The desirable mechanical properties (i.e., ultimate tensile strength, yield strength, and elongation are 1070 MPa, 958 MPa, and 15%, respectively) are obtained through double annealing ((950 °C/2 h, AC)+(600 °C/2 h, AC)). The fractographs obtained after tensile tests show that the deepest and largest dimples are formed in the specimen annealed at 850 °C, which indicates that the best plasticity is obtained at this annealing temperature.