Improving High-Temperature Mechanical Properties of Additively Manufactured Inconel 718 Through Heat Treatment

Post-heat treatments are vital to produce superior nickel-based superalloys with high performance by directed energy deposition (DED) for harsh service conditions. In this work, directed energy deposited Inconel 718 samples underwent varied heat treatment routes including the direct aging heat treatment (DA), standard solution treatment plus aging (STA), and homogenization plus STA (HSTA). Analysis focused on second phase particle evolution, high-temperature tensile properties (at 650 °C), and fracture mechanisms. Results indicate that as-deposited samples exhibit an obvious serrated flow during the yield stage because of dynamic strain aging (DSA). Considering the massive precipitation of nano γ′ and γ′′ phases after heat treatments, high-temperature strengths increase greatly and surpass the strength of standard wrought Inconel 718. HSTA samples demonstrate the topmost high-temperature strength, while STA samples demonstrate an excellent combination of high ductility and high strength at high temperatures. The “Laves + δ” configuration coordinates deformation at high temperatures, benefiting high ductility. Transitioning from as-deposited, DA, STA to HSTA states alters the high-temperature fracture mechanism of Inconel 718 from transgranular ductile fracture to a mixed mechanism involving transgranular and intergranular fracture. This research concerning high-temperature properties helps to expand the application of additively manufactured superalloys in aerospace field.