Microstructures and mechanical properties of the forging TC11 titanium alloy repaired by the laser deposition and point-mode forging process

Abstract

Laser deposition and point-mode forging (LD-PF) is a newly developed additive manufacturing repair technology which offers a potential of time and cost saving for repairing the damaged titanium alloy. In this paper, the depth affected by the point forging pin, the grain morphology, the microstructural revolution, micro-hardness distribution and tensile properties for the LD-PF TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) titanium alloy which contains 0 %, 50 % and 100 % repair zone were analyzed. The results show that, the maximum depth affected by the forging pin in the repair zone is 1.8 mm, and the minimum depth is 1.5 mm. There were six different forms of α and β phase shown in a single LD-PF layer. The mean grain size of the equiaxed grains distributed in repairing zone was about 150 μm. The repaired zone micro-hardness is higher than that of both the heat affected zone and rolled substrate zone slightly increased 35 HV owing to the refined equiaxed grains. The deposited layer is strengthened by point-mode forging and further strengthened after depositing a new cladding layer. Compared to the rolled direction substrate, the yield and tensile strength of the repairing zone for LD-PF specimen increased by 12.6 % and 17.0 %, respectively, in contrast to a 48 % decrease in elongation. All of the yield strength, tensile strength and elongation of the longitudinal and transversal combination specimen (LCS and TCS), which contains 50 % substrate, were better than the standard TC11 alloy. The tensile process for the TCS was discussed as some parabolic dimples were observed in the fracture morphology of it. This work provides one of the feasible ways to repair aerospace titanium alloy parts with partial wear defects in the field of laser additive manufacturing.