Effects of Heat Treatment on the Microstructure Evolution and Mechanical Properties of Selective Laser Melted TC4 Titanium Alloy

The effects of heat treatments on microstructure and basic mechanical properties of selective laser melted (SLM) TC4 titanium alloy were investigated in detail. The results demonstrated that a lot of acicular α/α′ and β phases exist in the SLM TC4 titanium alloy. With the increase in the aging treatment temperature, the metastable α′ phase of SLM TC4 was decomposed into α + β laths. Moreover, the α/α′ phase and β phase grew coarser, leading to a gradual decrease in strength, that is, plasticity and hardness increased and decreased, respectively. In terms of solid-solution aging treatment, the β phase was transformed into the α′ martensite phase in the solid-solution treatment, and the aging treatment induced the decomposition of the metastable α′ phase into α + β laths. The strength and hardness of SLM TC4 alloy increased as the temperature increased. The optimal mechanical properties could be obtained by water quenching after holding at 960 ℃ for 1 h and then air cooling after holding at 600 °C for 8 h.