Solution Treatment Study of Inconel 718 Produced by SLM Additive Technique in View of the Oxidation Resistance

The additive manufacturing concept for the production of complex near net shape metal parts is obtaining increasing attention due to the possibility of producing assembled and/or complex parts allowing optimal design and saving time and cost. The possibility to use the free design of Selective Laser Melting (SLM) techniques for the fabrication of complex 3D components using high performing, although difficult to work, materials such as Ni superalloys is really attractive. The particular process conditions that are established during additive manufacturing in SLM leads to microstructures different with respect to those observed in standard cast or wrought analogous material. Therefore, it is usually necessary to apply a post solution treatment, in order to reduce the segregation of heavier elements (in particular Nb) and dissolve the interdendritic precipitates. In this study, the influence of temperature and time of the solution treatment on the microstructure is investigated in order to find the best results in terms of the final oxidation resistance. Oxidation performances of solutioned Inconel 718 fabricated via SLM are reported and discussed. The growth rate of the superficial oxide at the temperature of 850 C was measured and the longterm stability of this passivating layer was tested until 908 h.