Effect of re-lasing on the fatigue properties of 316L Stainless Steel Produced by laser powder bed fusion

Despite the great success of the metal additive manufacturing process by Laser Fusion on Powder Bed (L-PBF), this technique still lacks maturity in several areas. Among its major challenges, the low fatigue strength of the L-PBF parts is caused, among other features, by two main types of defects. Firstly, the L-PBF process generates a high surface roughness, mainly linked to the phenomenon of partial powder melting on the part surface. Secondly, internal defects are created during the building process and are randomly distributed in the material. The present study investigates the effect of a second lasing on the improvements of the surface roughness, defects population as well as fatigue properties of L-PBF parts. Based on preliminary experiments, two re-lasing strategies were selected. A high cycle fatigue campaign was subsequently carried out with a stress ratio of R= -1 on samples with or without re-lasing, in the as-built state or after polishing. Specimens printed in Net-Shape showed even after re-lasing and polishing, a much lower fatigue strength than those machined in the bulk after additive manufacturing. In addition, results show that the tested re-lasing conditions has a beneficial effect on the quasi-static and fatigue strength of the 316L obtained by L-PBF.