Very High Cycle Fatigue Behavior of Laser Beam-Powder Bed Fused Inconel 718

In this study, the very high cycle fatigue (VHCF) behavior of Inconel 718 manufactured via a Laser Beam-Powder Bed Fusion (LB-PBF) process is investigated. LB-PBF Inconel 718 specimens are fabricated in vertical direction and subjected to post-processing heat treatment. The experiment is conducted on as built (i.e. non-machined) specimens utilizing an ultrasonic fatigue test system operating at 20 kHz under force-controlled fully-reversed constant amplitude cyclic loading. Fractography analysis is performed using a digital microscope to identify microstructural features that initiate fatigue cracks in the specimens. Experimental results from LB-PBF Inconel 718 specimens are presented and compared to those of wrought Inconel 718. It is determined that the fatigue resistance of as-built LB-PBF Inconel 718 specimens is significantly less than that of the wrought material. This result is attributed to a large presence of LB-PBF process intrinsic defects. In the VHCF regime, subsurface crack initiation is the primary fatigue failure mechanism in as-built LB-PBF Inconel 718 specimens.