As-built surface quality and fatigue resistance of Inconel 718 obtained by additive manufacturing

Abstract

It has been recognized that parts produced by additive manufacturing with surfaces in the “as-built” state exhibit reduced fatigue properties. On the other hand, post-process surface finishing is expensive and often unfeasible due to the complexity of parts. Therefore, surface quality parameters must be considered when designing as-built parts for structural applications. This work investigates the as-built surface topography of Inconel 718 samples manufactured via laser powder bed fusion (L-PBF) with three different production systems (SLM 280HL, EOS M290, and RENISHAW AM250) and discusses their respective experimental fatigue behavior. The aim of the investigation is to identify a link between the fatigue response of L-PBF IN718 alloy without post fabrication finishing and the surface morphology; a preliminary comparison among the main surface roughness parameters and the fatigue strength is reported and further investigations are planned to find a univocal correlation. Samples with a mean height (S_a) of approximately 20 μm exhibit lower fatigue strength than those with S_a of approximately 5 μm. Skewness (S_sk) and kurtosis (S_ku) are instead found to be discriminating parameters when comparing surfaces with relatively low surface roughness (S_a 5 μm), with higher values of Ssk and Sku associated with inferior fatigue performance.