Additive manufacturing (AM) allows for the building up of bulk structures through the fusion of powder particles layer by layer using a high power laser. This novel technique is practical for the fabrication of complex structures without any mold or tool, but this flexibility is accompanied by the delicate balance of AM processing and post-processing parameters which are to be optimized to ensure the desired microstructure in order to obtain the required mechanical properties [1-4]. The current study is aimed at understanding the effect of the AM processing parameters used for the preparation of AM samples on the resulting microstructure, its anisotropy according to growth direction, as well as its implications on the mechanical properties.
Bulk structures of conventional 316L grade stainless steel (with Cr-16.5-18.5%, Ni-10-13%, Mo 2-2.5%, traces of Mn, Si, P, S, C) were produced by AM through selective laser melting (SLM), followed by an annealing heat treatment for material internal stress release. Two sets of processing conditions with variations in parameters such as the incident laser energy, the laser spot size and the direction of growth were varied, and the resulting effect on the microstructures both before and after the heat treatment are studied through diverse microscopy techniques such as SEM, EBSD and TEM. The variation in the phase distributions, grain size and porosity are analyzed as a function of the process parameters. Mechanical properties are measured by tensile tests completed by microhardness. Additionally, XRay Diffraction (XRD) has been used for identifying the phases present in the alloy and also for measuring residual stress and crystallographic texture.
The presence of the pores with unmolten particles has been observed in all samples produced with lower laser energy (Fig. 1). Alongside, the layers formed immediately on top of such pores show different microstructure, with the new phase observed consistently on the same side of the porosity in all samples (Fig. 2). The origin of this phase separation is expected to be from the differential heat dissipation (during fabrication) through the pore as opposed to the bulk material. The mechanical properties of the bulk structures (tensile stress, microhardness) showed that increasing the laser power results to an increase in the yield point. Fracture surface (Fig. 3) shows clearly presence of the pores which influences largely the mechanical properties such as ductility.
Overall, through the variation of the process parameters, the trend in evolution of the microstructural and mechanical properties is elucidated aimed at optimizing the parameters for AM products of 316L stainless steel.
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To cite this abstract:Kaushik Vaideeswaran, Olha Sereda, Youness Zangui, Hervé Saudan, Lionel Kiener, Massoud Dadras; Effect of processing parameters on microstructure and mechanical properties of additively manufactured stainless steel. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/effect-of-processing-parameters-on-microstructure-and-mechanical-properties-of-additively-manufactured-stainless-steel/. Accessed: May 26, 2020
EMC Abstracts - https://emc-proceedings.com/abstract/effect-of-processing-parameters-on-microstructure-and-mechanical-properties-of-additively-manufactured-stainless-steel/