Fatigue behavior and prediction model assessment of laser powder-bed fusion additively manufactured Nickel-based alloys

Ensuring the reliability and durability of additively manufactured (AM) parts is a critical factor of interest for the adoption of AM parts in large-scale manufacturing. Fatigue is one of the most common modes of failure in mechanical systems and fatigue of AM parts presents new challenges due to inherent defects in as-built AM parts. In this work, statistical assessments were performed on the fatigue behavior of laser powder-bed fusion (LPBF) additively manufactured Nickel alloys (Inconel 625, Inconel 718, Hastelloy X) with different R-ratios, Build orientations and Post-processing conditions. R-ratio and Cycles to failure were identified as the most important parameters for fatigue life. Repeatability of LPBF parts under cyclic loading was also investigated and showed significant deviations under similar conditions. A study of various post-processing conditions was performed to analyze the underlying mechanisms responsible for differences in fatigue life due to post-processing. Machined-Polished samples exhibited the best fatigue life. Finally, the effect of mean stress on LPBF parts was investigated using stress-based fatigue models (Smith-Watson-Topper, Goodman, Morrow). Smith-Watson-Topper showed the best agreement with experimental results for Inconel 615 and Inconel 718.