Microstructure evolution and mechanical properties of laser additive manufactured Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy

The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary alpha (alpha(p)) with different morphologies, secondary alpha (alpha(s)) and martensite alpha' can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like alpha phase or acicular alpha phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.