Microstructural characterization of laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe near β titanium alloy

Laser melting deposition (LMD) is characterized by high temperature gradients, high cooling rates and reheating treatment effects. These features of LMD generally lead to an unique microstructure. In this study, the macrostructure, microstructure and hardness of laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe near β titanium alloy have been investigated. The macrostructure is characteristic of novel β grain morphology and layer bands. The β grains exhibit successive alternation of large columnar and bamboo-like grain morphology, which is associated with the LMD processing parameters. Layer bands exhibit duplex microstructure and low hardness, while ultra-fine basket-weave microstructure, microsegregation and high hardness are observed between layer bands. Microstructure and hardness of the alloy are non-uniform due to the existence of the layer bands. Thus, special attention is given to the formation mechanism of layer bands. It is found that layer bands are heat-affected zones which resulting from the sub-melting-point reheating treatment when a new layer deposits.