Effect of heat treatment on microstructure and mechanical properties of laser-deposited Ti65 near-alpha titanium alloy

Ti65 samples without obvious defects were successfully prepared by laser deposition manufacturing (LDM), followed by different heat treatments. The microstructures and mechanical properties of the as-deposited and heat-treated samples were investigated. Results showed that the as-deposited microstructure was lamellar structure with precipitations of spherical S2 silicide, tungsten-rich phase and granular Ti3Sn. After annealing, the microstructure turned into a basket-weave microstructure, the volume fraction of silicide was reduced, the tungsten-rich phase was dissolved and more granular Ti3Sn phases with smaller sizes were distributed at the phase boundaries contributing to the improvement of tensile strength and plasticity. After solid-solution plus aging, a duplex microstructure appeared, intragranular a lath was spheroidized, the volume fraction of silicide was minimal and the Ti3Sn phase disappeared, leading to a greater improvement of plasticity and decreasing of tensile strength. Annealing and solid-solution plus aging both enhanced the microhardness of the laser deposited Ti65 sample.