High cycle and very high cycle fatigue behavior of additively manufactured Inconel 718: Effects of stress-relieving, surface texture, part orientation, and test frequency

Abstract

This study investigated the tensile and fatigue (in both high and very high cycle fatigue regimes) behaviors of laser powder bed fused Inconel 718 in unmachined surfaces, examining the effects of stress-relieving, part orientation, and fatigue test frequency (i.e., cyclic strain rate). Stress-relieving improved the fatigue performance of the specimens due to the removal of the dendritic microstructure. Diagonal and vertical specimens exhibited comparable fatigue resistance, which was likely due to similarly accelerated fatigue crack initiation from surface micro-notches. No significant effect of test frequency was observed on the fatigue performance of the specimens. The fatigue life of the specimens was estimated based on their surface texture (measured by a hybrid parameter) and the reference fatigue data established from machined/polished specimens. The estimations fell within a scatter band of three from the experimentally obtained fatigue lives.