Effects of double annealing on microstructure and mechanical properties of laser melting deposition TA15 titanium alloy

TA15 titanium alloy bulk specimens were prepared from raw material of spherical powders by laser melting deposition (LMD) technique. The effects of double annealing treatment and deposition direction on the microstructure characteristics and the tensile properties of LMDed TA15 alloy were investigated. The morphology analysis shows that the rod-shaped alpha phase grows obviously with the increase of annealing temperature, and eventually decomposes into lamellar alpha + beta when the annealing temperature is higher than the (alpha + beta)/beta phase transition point. Results of tensile tests indicate that there exists the anisotropy of mechanical property between the horizontal section and vertical section for LMDed TA15 alloy due to the hindrance effect of grain boundary on slip deformation. After double annealing treatment, the plasticity of LMDed TA15 alloy improves remarkably but the tensile strength decreases compared with as-deposited sample. The microhardness of LMDed TA15 alloy firstly increases and then decreases with the annealing temperature increasing, which is closely related to the amount of a phase.