Solidification Microstructure and Mechanical Properties of Laser Additive Manufactured Near-α Ti-6Al-3Nb-2Zr-1Mo Titanium Alloy

A near-α Ti-6Al-3Nb-2Zr-1Mo (TA31) titanium alloy was deposited via laser additive manufacturing (LAM). The chemical component, solidification microstructure, and mechanical properties of as-deposited LAM TA31 titanium alloy were investigated. Results show that the LAM TA31 titanium alloy has a good metallurgical combination, which meets the chemical component requirements of GB/T 3620. The cross sectional microstructure of the LAM TA31 titanium alloy mainly consists of coarse columnar β-grains with epitaxial growth and a few equiaxed grains at the top. In the columnar zone, the microstructure comprises lamellar α-clusters with same orientation and interleaved lamellar α-networks, in which there is a residual β-phase, showing the characteristics of a basketweave microstructure. The equiaxed zone at the top of the specimens mainly consists of acicular martensite α′ and β phases. From the columnar to the equiaxial zone, the microhardness of LAM TA31 titanium alloy considerably increased from 345.7 to 447.5 HV_0.2; whereas, the change in the microhardness of the columnar grain zone was minor. The mechanical properties of the as-deposited LAM TA31 titanium alloy are anisotropic. The ultimate tensile strength and elongation of the specimens in the L direction are 958.2 MPa and 11.1%, respectively; whereas, those in the T direction are 991.5 MPa and 7.8%, respectively. The impact toughness of the T-direction specimens was 34 J, which is 73.4% of that of the L direction specimens (46.3 J). Additionally, the fracture mechanism of the tensile strength and impact toughness has been analyzed thoroughly for the LAM TA31 titanium alloy.