Microstructure homogenizations of Ti-6Al-4V alloy manufactured by hybrid selective laser melting and laser deposition manufacturing

Recent researches on the addictive manufacturing (AM) of titanium alloys have shown the significant advantages in fabricating complex constructions. Laser deposition manufacturing (LDM) and selective laser melting (SLM) are two representative AM technologies, Ti-6Al-4V alloy samples for the complex structure and functional integration application were fabricated by LDM-SLM hybrid manufacturing process in present research. The microstructure of LDM-SLM hybrid fabrication Ti-6Al-4V components can be divided into three regions: LDM zone mainly composed of the α laths, SLM zone which is fully α' martensitic and a large number of irregular crystals are distributed in the bonding area between the LDM zone and SLM zone, which is named heat affect zone (HAZ). The inhomogeneous microstructure leads to the discrepancy in mechanical behavior, after multiple cyclic thermal treatment at 750 °C/10min↔960 °C/10min, the original α′ martensitic is complete converted to the mixture of α-phase and β-phase and the growth of the thick α laths was restrained. The microstructure and mechanical properties of LDM zone and SLM zone tend to be equivalent at all of cycle-treatement. After cyclic thermal treatment, the strength of LDM samples and hybrid fabricated samples vary slightly, but the plasticity of LDM is improved significantly. The morphology features of α phase and evolutions of crystallographic orientation are the dominant factors of microstructure homogenizations during cyclic thermal treatments, related information was found in the EBSD investigation.