Heat treatment and anisotropy of TB6 titanium alloy fabricated by laser deposition manufacturing

The effects of different heat treatment processes on the anisotropy of TB6 titanium alloy fabricated by laser deposition manufacturing were investigated.The evolution of microstructure was analyzed by using optical microscope （OM）， scanning electron microscope （SEM）， and transmission electron microscope （TEM）. The variation trend and influence mechanism of anisotropy with heat treatment were investigated. The present research shows that the original β grains and the morphology of the primary α phase （αp phase） are greatly affected by the thermal gradient. The original β grains in the microstructure of TB6 titanium alloy fabricated by laser deposition manufacturing are elongated along the deposition direction and are ellipsoidal. In addition， the relative slender αp phase parallel to the deposition direction is found. These two factors jointly lead to the anisotropy of room temperature tensile property of the as-deposited samples. The tensile strength in the vertical deposition direction （X-direction ） is 7.3% higher， the yield strength is 5% higher， and the elongation is 32.4% lower than that in the deposition direction （Z-direction）. The low-temperature annealing treatment has little effect on microstructure， only the anisotropy of plasticity is decreased. After high-temperature annealing treatment， the difference in aspect ratio of αp phase is significantly reduced， leading to the anisotropy of the room temperature tensile property decreases. The strength are still higher in the X-direction ， and the elongation is higher in the Z-direction. The strengthening mechanism of the solution-aging treating sample is completely changed due to the precipitation of the secondary α phase （αs phase）. In addition， there is no obvious preferential growth of αs phase after heat treatment， so the anisotropy of the room temperature tensile property tends to be eliminated as the strength increases.