Improving strength and ductility of Ti-4Al-0.005B titanium alloy through tailoring equiaxed and lamellar microstructure during thermal mechanical process

The Ti-4Al-0.005B alloy were rolled at 940 °C or 990 °C followed by annealing at 650 °C. In order to control the final microstructure, rolling at medium temperature of 550 °C was processed in two other plates after rolling at 940 °C or 990 °C. The rolling and tensile behaviors of Ti-4Al-0.005B alloy with equiaxed and lamellar microstructure are comparatively studied using electron backscatter diffraction (EBSD) technique. It is found that the grain refinement mechanism of 940 °C and 940 + 550 °C rolled samples is continuous dynamic recrystallization (CDRX), while the 990 + 550 °C samples combine CDRX and twinning. The strong basal/near basal textures (B/N textures) in 940 °C and 940 + 550 °C rolled samples was mainly related to basal slip and pyramidal slip. Strong transverse textures (T-type texture) formed in 990 °C rolled sample due to variant selection during the β→α phase transformation and 990 + 550 °C rolled sample exhibits a mixed of T-type texture and B/N texture. The 990 + 550 °C rolled sample exhibited a best mechanical properties combined of strength and ductility due to its mixed texture and refined α grains.