Study on Microstructure and Mechanical Properties of Laser Metal Deposition Near β Titanium Alloy

The microstructure and tensile properties at room temperature of the laser additive manufacturing Ti55511 titanium alloy are studied, the grain morphologies and crystallographic texture of the as-deposited and heat treated Ti55511 titanium alloy are characterized, and the effects of different annealing temperatures on plasticity of the laser additive manufactured Ti55511 titanium alloy are analyzed. The results indicate that the as-deposited Ti55511 titanium alloy consists of coarse β grains, and the β grains grow alternately in the form of columnar and equiaxed grains, presenting a bamboo-like morphology. In the as-deposited Ti55511 titanium alloy, the α lamellae precipitated from the β matrix provides a large number of interfaces, effectively hindering the movement of dislocations, and allows the alloy having high strength and low plasticity. The yield strength and tensile strength of the alloy annealed at 580 ℃ does not show significant changes, and the elongation increases to a certain extent. When the annealing temperature increases to 620 ℃, the yield strength and tensile strength of the alloy reduce, still greater than 1 000 MPa, and the elongation significantly increases. Therefore, the size and volume fraction of the α grains can be regulated through the annealing heat treatment to improve the strength and toughness balance of the alloy. When the stress is parallel to the Z deposition direction, the yield strength and tensile strength of the specimen are slightly lower than those of the specimen whose stress is perpendicular to the Z deposition direction, and the elongation is significantly higher than that of the specimen whose stress is perpendicular to the Z deposition direction.