Selective Laser Melting Fabrication Of Nickel-based Superalloys And Its Composites:Process, Microstructure And Property

In the present study, bulk-form Inconel 718 parts and the TiC/Inocnel 718 nanocomposite parts were fabricated by using of SLM process. The influence of laser process parameters on evolutions of surface morphologies, densification behaviors, phases and microstructures of fabricated parts were analyzed. The inherent interaction mechanisms regarding the SLM process, mechanical properties and high temperature oxidation behaviors of the shaped parts were also elucidated. The main conclusions were listed as follows:The Inconel 718 powders were shaped into bulk-form parts by SLM under different process parameters in this paper. The results revealed that metallurgical defects including open pores and balling phenomenon were found on the surface of SLM formed parts at a lower laser energy input, which limited the densification of the formed parts. With the development of the applied laser energy, the formed parts became dense while the microstructures possessed homogeneous and refined distribution characteristics within the Inconel 718 matrix. Under the optimized laser process parameters, the SLM shaped Inconel 718 parts exhibited superior mechanical performance in comparison with the traditional casted or forged Inconel 718 components after heat treatment.On basis of the above studies, the process parameters were further optimized, whereafter the Inconel 718 parts in a relatively higher densification level were fabricated by SLM process. The manufactured Inconel 718 parts were then subjected into high temperature oxidation environments in order to analyses its oxidation resistance behaviors. After the high temperature oxidation test, the oxidation film formed on the subjected parts were mainly consisted of the granular Cr2O3 as well as few amounts of spinel phases, while the oxidation microstructure was composed of an external oxidation layer and an internal oxidation zone. The oxidation mechanisms including the chemical adsorption in the initial oxidation stage and the diffusion oxidation process afterwards. The oxidation process was controlled by the outward diffusion of oxide forming elements and inward penetration of oxygen. The above analysis suggested that the improved densification of SLM shaped parts and the grain refinement effects were responsible for the significantly improved high temperature oxidation performance.By incorporating the nanometer sized TiC ceramic reinforcement particles into the Inconel 718 matrix, the TiC/Inconel 718 nanocomposites with homogeneous microstructures and outstanding properties were obtained by SLM. During the SLM shaping process, the relatively lower densification level with large amounts of metallurgical defects inside were revealed within the fabricated parts as the insufficient laser energy was input. With the reasonable development of the applied laser energy, the densification of the fabricated nanocomposites was significantly elevated and the columnar dendrite microstructures as well as the incorporated reinforcements became homogenously distributed within the Inconel 718 matrix. The mechanical properties and the high temperature oxidation behaviors both improved markedly, even compared with the SLM processed Inconel 718 parts.