Effects of thermo-mechanical treatment on microstructure and mechanical property of Ti-45Al-5Nb-0.3Y alloy

As-forged Ti-45Al-5Nb-0.3Y alloy is composed of a large number of dynamicly recrystallized (DRX) γ grains with sizes of 1-2 μm, curved or broken lamellae, and a small amount of remnant lamellaes. The deformed regions contained lots of dislocations and a little deformation twinnings. The ultimate tensile strength (σ_b) of as-forged alloy is about 708.1 MPa and the elongation (S) is about 0.95%. The fine duplex (DP), near lamellar (NL) and fully lamellar (FL) microstructures were obtained by further heat treatments. The DP microstructure with lamellar colony size (d_l) of about 20 μm and lamellar volume fraction (φ_l) of about 60% was obtained by heat treatment of 1320°C/30 min/FC, which exhibited the highest δ of about 1.9% and σ_b, of about 658.9 MPa, and showed the transgranular and intergranular cracks. The NL microstructure with d_l of about 60 μm and φ_l of about 95% was obtained by heat treatment of 1340°C/30 min/FC, which exhibited δ of about 1.75% and σ_b, of about 690.2 MPa correspondingly and mainly showed the transgranular cracks. The FL microstructure with d_l of about 40 μm was obtained by heat treatment of 1370°C/15 min/FC, which exhibited δ of about 1.51% and the highest σ_b of about 715.1 MPa and showed the transgranular cracks.