Fatigue Properties of Laser Powder Bed Fused TA15 Titanium Alloy: Anisotropy, Defect Effects, and Life Prediction

Titanium alloys fabricated via laser powder bed fusion (LPBF) demonstrate significant anisotropy in fatigue properties. In this study, the effects of orientations and hot isostatic pressing (HIP) on the fatigue properties of LPBF TA15 titanium alloy were systematically investigated. Results indicate that HIP treatment can enhance the fatigue performance (170 MPa in horizontal direction, and 450 MPa in vertical direction) due to the defect elimination. The vertical samples exhibit better fatigue strength compared to the horizontal samples in the as‐HIPed state, which is contrary to the result in the as‐built state. In addition, the as‐HIPed vertical samples also demonstrate the superior fatigue efficiency at a stress ratio of −1 compared with other titanium alloys. Considering the effect of defects and microstructure, the fatigue cracking mechanisms were elucidated, and the transformation in the fatigue cracking mechanism from defect‐dominated cracking in the as‐built condition to microstructure‐controlled cracking after HIP treatment has been obtained. The grain boundary α (GB‐α) phase is the dominant factor influencing the fatigue performance, rather than the plastic slip in α clusters. Furthermore, a physically‐based parameter model was established to predict the fatigue life, and the prediction accuracy has been improved through the classification of crack initiation modes.