Experimental investigation on the fatigue behavior of laser powder bed fused 316L stainless steel

Additive manufacturing of metal powder materials through Laser Powder Bed Fusion (LPBF) allows for a single-step fabrication process of complex geometries. However, the introduction of such an innovative technology opens new questions about the fatigue life of functional components especially intended for applications where the products are subjected to severe time-varying loading conditions. In this context, the present work aims at evaluating the fatigue strength of 316L stainless steel samples fabricated through laser powder bed fusion by controlling the building orientation and the volumetric energy density. The work at first presents the response of the LPBF fabricated samples to a monotonic tensile load for varying building orientations. It follows the presentation of their fatigue response to a reverse bending loading condition. Quasi-static tensile tests show that LPBF specimens have lower elastic modulus but higher ultimate and yield strength than the original bulk material, whereby the results evidence a strong anisotropy related to the building orientation. Porosity and building orientation are found to strongly affect the fatigue behavior, with the fatigue limit which lowers from 50% of the ultimate strength of the bulk material down to 20% for the LPBF-ed specimens. Finally, the observation of the failure surfaces suggests that the early fracture of the samples is due to the concomitant initiations of cracks at different sites that eventually coalesce and promote the failure.