Microstructural assessment of additive-manufactured Inconel 718 samples subjected to heat treatments for enhanced mechanical properties

Directed energy deposition-laser beam (DED-LB), a laser additive manufacturing (AM) process, has attracted significant attention as a potential alternative to conventional manufacturing methods, due to its high deposition efficiency, flexibility, and precision. Despite these advantages, components produced by DED-LB often face critical challenges, including residual stresses, micro-segregation, and the formation of non-equilibrium phases due to rapid cooling during the AM process. These issues are particularly critical for Ni-based superalloys such as Inconel 718 (IN718), widely used in the aerospace, energy, and marine industries for their excellent high-temperature strength and corrosion resistance. The mechanical performance of IN718 primarily depends on precipitation hardening via γ' and γ'' phases. In contrast, the formation of deleterious phases, such as δ and Laves, can severely impair performance by depleting key alloying elements and increasing brittleness. Thus, heat treatments (HTs) are vital in addressing these challenges by reducing micro-segregation, homogenizing elemental distribution, and promoting the precipitation of strengthening phases. Therefore, this study investigates the effects of six distinct heat-treatment routes on the microstructural evolution, hardness, tensile properties, and fracture behavior of DED-LB IN718 samples. The relationship between microstructure and mechanical responses is analyzed and compared to a forged IN718 counterpart. The results offer valuable insights for optimizing heat-treatment strategies to improve the structural integrity and mechanical reliability of DED-LB-fabricated IN718 components.