Mechanical behavior of Inconel 718 manufactured by highproductivity rate SLM process

. Inconel 718 is widely employed for elevated temperature applications, where the optimized shapes, internal cooling channels, or lattice structures, allowed by the Selective Laser Melting (SLM) technology, can introduce significant enhancements in terms of component mechanical and thermal properties, machining costs and scrap reduction. The productivity rate of the SLM process is known to be a limiting factor for the industrial spread of the technology. Its enhancement can play a crucial role, as long as it doesn’t significantly affect the fatigue performances of the component. In the present work, it is presented the development of SLM process parameters aimed at enhancing the productivity rate, while preserving the vertical process resolution, and the experimental assessment of the effects introduced on the static and cyclic mechanical properties. Based on a previously developed and validated analytical model of the material SLM feasible region, two sets of process parameters were devised to increase by 50% the process productivity rate. For each process parameters set, tensile and High Cycle Fatigue (HCF) tests were carried out on vertically built round specimens, in the as-built and aged material conditions, both featuring the as-built surface. Metallographic analyses were carried out to investigate the microstructural properties or the presence of internal defects, i.e. porosity, lack of fusion, and hot tearing cracks, produced by each set of process parameters. The surface quality was also investigated in detail through optical microscope analyses and profilometer measurements. Fractographic analyses were used to identify the nucleation region and the crack propagation features, as well as the presence of the defects in proximity to the fracture onset. Despite the increase in the material porosity and surface roughness, in the case of the most promising process parameters set, the fatigue strength was reduced only by 4% both in the as-built and aged conditions, Figure 1. The data were finally investigated in the framework of the √area method developed by Murakami, which resulted in effectively estimating the fatigue behavior of the investigated specimens for all the tested sets of SLM process parameters.