Microstructural control and mechanical properties of a β-solidified γ-TiAl alloy Ti-46Al-2Nb-1.5V-1Mo-Y

In this study, the microstructural control methods and mechanical properties of a β-solidified TiAl alloy Ti-46Al-2Nb-2V-1Mo-Y (at%) were investigated systematically. It was found that a pretreatment of annealing in α + β + γ phase field contributed to decomposition of α/γ lamellar structures via α/γ → α + γ + β. After further nearly isothermal forging at 1240 °C, a fine-grained and fully recrystallized β + γ microstructure was produced. Grain size of the wrought microstructure was totally below 25 µm. We considered that the decomposition transformation of α/γ→γ + β induced by both pretreatment and hot forging, and dynamic recrystallization of β and γ grains directly resulted in the present equiaxed microstructure. By a final annealing treatment of 1360 °C/1 h/FC, fully-lamellar (FL) microstructure with colony size smaller than 100 µm was obtained, while an even finer duplex one was produced by two-step treatment of 1320 °C/2 h/FC + 1250 °C/4 h/FC. This duplex microstructure (DP) displays a superior tensile elongation of 2.2% at room temperature, while the FL one exhibits a yield strength of 700 MPa and a medium elongation 1.5%.