Effect of heat treatment on the high temperature tensile properties of Inconel 718 alloy manufactured via direct energy deposition

The aim of this study is to investigate the effect of heat treatment on the room temperature and high-temperature mechanical behaviors of Inconel 718, a nickel-based high temperature superalloy, fabricated via direct energy deposition (DED). This additive manufacturing technology decreases production costs and material waste while improving structural integrity through precise microstructure control, which is especially important in aerospace applications. Additionally, the capability of direct energy deposition for fast prototyping speed up the creation of new products, and its involvement in component repair and maintenance increases the lifespan of crucial components while reducing downtime in a variety of industrial sectors. During L-DED, laser-based heating forms a melt pool of the powder which is deposited on the substrate via a nozzle system. Laser based DED systems offer microstructural control and the ability to build components with multiple materials. For maximizing component design envelope, maintaining structural integrity, and improving overall performance in critical industries sectors, it is essential to have a thorough grasp of the mechanical response of the additive-manufactured alloy at varying deformation temperatures and how it can be tailored based on post-AM heat treatment. Regarding the behavior of the additive-manufactured material, it is shown that direct aged heat treatment causes improved tensile strength and yield strength due to the formation of fine precipitates and an increase in the volume fraction of the γ phase. It is also notable that depending on the heat treatment, a decrease in ductility can be observed, principally because the appearance of brittle secondary phases results in less plastic deformation. In addition, this investigation discloses substantial differences in mechanical properties during tensile testing as a function of elevated temperatures over 700 degrees. On the other hand, based on fractography examinations increasing the tensile test temperature leads to the detection of more dimples with larger sizes and the appearance intergranular cracking in the as-built and direct-aged samples, respectively. In summary, this study highlights the effect of heat treatment on the mechanical properties of additive-manufactured Inconel 718. In addition, in this work the potential of L-DED as an additive manufacturing technology is displayed while the effects of post-manufacturing process are mentioned in detail. The results show that direct-aged heat treatment has the potential to increase the strength, albeit on the basis of decreased ductility. Various characterization techniques are utilized to support findings which will offer understanding of how this widely used additive-manufactured superalloy behaves under various operational situations.