Investigation of the High-Cycle Notch Fatigue Behavior of L-PBF Inconel 718 Under Two Stress Ratios

Notch and stress ratio play crucial roles on the fatigue behavior of L-PBF Inconel 718. In this study, high-cycle fatigue tests were conducted on smooth and notched specimens of L-PBF Inconel 718 under two stress ratios (R = −1 and 0.5). The multiple-site crack initiation was only detected in notched specimens, and its probability at R = −1 is higher than that at R = 0.5. Secondary cracks were found in the crack propagation region of failed specimens at R = 0.5 but not at R = −1. The secondary cracks tended to propagate in the grains with high Schmid factors, and their maximum length in notched specimens is considerably shorter than that in smooth specimens. A novel method combining the theory of critical distance and a modified Walker model can well predict the notch fatigue life of L-PBF Inconel 718 under both stress ratios.