Microstructure and Fatigue Performance of Ti6Al4V Produced by Laser Powder Bed Fusion after Post-Heat Treatment

Abstract

With the development of additive manufacturing (AM), the Ti-6Al-4V alloy manufactured by laser powder bed fusion (LPBF) is becoming more widely studied. Fatigue fracture is the main failure mode of such components. During LPBF processing, porosity defects are unavoidable, which hinders the exploration of the relationship between fatigue performance and microstructure. In this study, a laser remelting method was used to reduce porosity defects inside the Ti-6Al-4V alloy. Three annealing treatments (AT) and three solution-aging treatments (SAT) were used to study the effect of the two-phase zone (α + β) microstructure on fatigue life and fatigue crack growth behavior. Fatigue life and crack growth rate (CGR) curves were obtained, and fatigue fracture surface and crack growth fracture surface were analyzed. The results show that microstructure influences fatigue life but has little effect on CGR. Compared with the as-built specimen, the fatigue life of the AT and SAT specimens increased significantly at 850℃ by 101 and 63.7 times, respectively. The thickness of the α lath and the location of crack nucleation together affect the fatigue life. In the stable growth stage, the layered microstructure of α colonies is the most resistant to crack growth.

Effects of build direction and microstructure on fatigue crack growth behavior of Ti6Al4V fabricated by laser powder bed fusion

“…Consequently, stresses and equivalent stress-induced strains are produced inside the heataffected zone that greatly influence the microstructure and the direction in which cracks develop. [9][10][11] Yet the complex design aircraft parts are subjected to multiaxial loads. 12,13 When the load direction is different from the angle of the deposition layer as well as the direction of the organization, the mechanical properties of the parts are different, especially in the FCG behavior.…”

“…In particular, throughout the LPBF fabrication of Ti6Al4V components, there is a continuous deposition of layers at high temperature, which creates thermal gradients between the layers. Consequently, stresses and equivalent stress‐induced strains are produced inside the heat‐affected zone that greatly influence the microstructure and the direction in which cracks develop 9–11 . Yet the complex design aircraft parts are subjected to multiaxial loads 12,13 .…”