Microstructure evolution and layer bands of laser melting deposition Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

Laser melting deposition (LMD) is a newly developed additive manufacturing technique which offers a potential of time and cost savings for fabricating aerospace titanium alloys components. In this paper, the grain morphology, microstructure and micro-hardness of LMD Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy were investigated. A variety of microstructures and two kinds of distinct layer bands were found in the as-deposited sample. The interlayer bands (ILB) spaced uniformly in the whole sample. However, the dark heat affected bands (HAB) with a special bimodal microstructure were absent in the last three layers. In order to obtain a deep understanding on the microstructure evolution and bands structure, much attention was paid on the microstructures of the last deposited several layers. The microstructure gradient between two HAB was due to the re-heating effect in the α + β region. The formation of interlayer bands was due to the chemical composition homogenization difference within and between ILB, which resulted from the superheating effect.