Tailoring the mechanical performance of electron beam melting fabricated TC4 alloy via post-heat treatment

In the present study, various post-heat treatment processes were employed to design the different microstructures in the electron beam melting (EBM) manufactured TC4 titanium alloys. After heat treatment, the size and content of alpha and (3 phase increased, and the fabricate interfaces and pores gradually decreased, triggering different tensile properties. As the heat treatment temperature increased, the ultimate tensile strength decreased, while the elongation at break (EL) initially increased and then decreased. After heat treatment at 800 degree celsius, the specimens exhibited the best ductility, where the EL improved by 40.21 % compared to the as-built sample. However, the ultimate tensile strength (UTS) of HT800 specimen decreased from 1024.53 MPa for as-built specimen to 943.41 MPa, which was attributed to the reduction of precipitation strengthening and the growth of alpha and (3 phase. It was noticed that the micro-cracks initiated near the pores due to the stress concentration. Besides, the HT980 specimen exhibited the poorest EL and UTS due to the coarse grain, which resulted in the transformation of fracture mechanism. And the pores caused by EBM process vanished in HT920 and HT980 specimen, making the micro-cracks initiate at alpha/(3 phase boundaries or grain boundaries.