A novel test method for the fatigue characterization of metal powder bed fused alloys

This research addresses the conflicting factors of high costs of fatigue testing and large number of influencing factors that need to be investigated for PBF material and process qualification. Metal powders are remarkably expensive, the PBF production process requires expensive systems and fatigue testing requires multiple specimens (depending the required degree of confidence) to characterize a single material/process combination. In this paper a novel fatigue test method aimed at the peculiar needs of PBF technology is initially presented and fatigue data obtained on Direct Metal Laser Sintering Ti6Al4V are validated against standard rotating bending test results. Then, the link between microstructure and directional fatigue behavior is demonstrated using the present methodology and SLM Inconel 718: namely, the stress direction parallel to build direction is the most severe. Finally, the new test method is applied to the investigation of the fatigue notch sensitivity of DMLS Ti6Al4V in relation to the notch fabrication process. Round notches in specimens with opposite fabrication orientations (i.e. up-skin vs down-skin) resulted in two notch fatigue factors and the up-skin notch has a better fatigue strength than the down-skin notch.