Microstructure and tensile properties of laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe near β titanium alloy

A near β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe is fabricated by laser melting deposition (LMD). The evolution of its macrostructure and microstructure during LMD process are systematically studied. Then the relationship between the microstructure and tensile properties is further investigated. The macrostructure exhibits unique bamboo-like β grain morphology, which forms during the solidification and remelt treatment during the LMD process. The microstructures exhibit fine basketweave microstructure and continuous grain boundary α (αGB), whose formation is associated with the complex thermal cycling treatment. Interestingly, an unique fork-like α is observed but gradually disappears during the evolution process of microstructure. The underlying mechanism is proposed. Besides, tensile tests show that the fine microstructure results in high strength, and the continuous αGB causes the low ductility and intergranular fracture. Meanwhile, the cracks are prone to propagate along the interface between the columnar and equiaxed regions.