This paper investigates the influence of post treatments on the fatigue properties of 316L stainless steel produced by laser powder bed fusion. Miniaturised fatigue samples are built in vertical orientation with optimised process conditions to result in very low porosities and minimal scatter in results. Fatigue performance is evaluated for two different material conditions: as-built and stress-relieved, at a nominal load ratio of -1. Furthermore, the samples are tested with and without surface machining. A thorough microstructural and fractographic analysis is performed to evaluate the impact of the main fatigue influencing factors. The results show that the fatigue behaviour of machined samples with and without stress relief heat treatment exceeds that of conventionally manufactured 316L.
Over the last decade, additive manufacturing (AM) techniques have been expanding rapidly due to their ability to produce complex geometries with an efficient use of material. In order to design reliable AM parts, the mechanical properties resulting from the manufacturing process need to be understood. The present study investigates the fatigue of AM Ti-6Al-4V and 316L. Miniaturized Ti-6Al-4V and 316L specimens were manufactured using laser powder bed fusion (L-PBF). The geometry, process parameters, and loading conditions were kept constant and the specimens were tested in as-built surface condition. The S-N curves of as-built, stressrelieved and HIP'ed specimens were measured, and an analysis of the microstructure, relative density and surface roughness was performed. The effect of fatigue influencing factors (residual stresses, surface roughness, porosity and microstructure) was systematically investigated. In order to understand the fatigue failure mechanism, identification of crack initiation point, via fracture surfaces analysis, was performed.
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