Combined effect of a spread powder particle size distribution, surface machining and stress-relief heat treatment on microstructure, tensile and fatigue properties of 316L steel manufactured by laser powder bed fusion

International audienceAdditive Manufacturing is a powerful process to build complex geometry. Besides the numerous process parameters influencing the mechanical part performances, others parameters related to the initial powder feedstock or component machining are of most importance. In this study, the combined effect of a wide particle size distribution, surface machining and stress-relief heat treatment on the microstructure and mechanical properties (tension and fatigue) of a stainless steel AISI 316L, produced by laser powder bed fusion, is investigated. In order to correctly investigate those parameters separately, the netshape/machined character of the sample, alongside with the heat treatment is studied for two kinds of powder having different particle size distributions, i.e, narrow and widely spread. Results show that a large spread of particle size is only slightly detrimental to the fatigue life, in particular in high cycle conditions due to a larger porosity related to a weakly more uneven particle spatial distribution in the bed. Nevertheless, this effect is of a second order compared to machining or heat treatments which greatly affect the mechanical behaviour. Surface machining and moderate heat treatment are then the best post-operational steps to increase the fatigue life in high cycle fatigue conditions independently of the particle size distribution. Results are discussed in terms of defects, microstructural modifications, surface roughness, martensitic transformation and mechanical loading