Effect of heat treatment on microstructures and mechanical properties of Inconel 718 additively manufactured using gradient laser power

To achieve high-performance nickel-based superalloys by laser powder deposition for applications in the aviation industry, post-heat treatments are always indispensable. We prepared two typical as-deposited microstructures by constant laser power deposition (CLP) and gradient laser power deposition (GLP), respectively. A systematic research on the room-temperature microstructural evolution, hardness, tensile property and fracture morphology of Inconel 718 after three kinds of heat treatments is performed. The as-deposited microstructure and segregation ratio (SR) can significantly influence the microstructure evolution. The as-deposited GLP samples with fine discrete Laves phases and a low SR can achieve a relatively uniform element distribution and γ′′ and γ′ phase precipitation after standard solution treatment plus aging (STA), while CLP samples with coarse long-chain Laves phases and high SR require a high-temperature homogenization plus STA (HSTA) heat treatment to achieve the uniform element distribution. Differences in heat treatments have a greater impact on the fracture mechanism. With the transformation of heat treatments from direct aging, STA to HSTA, the fracture mode of both CLP and GLP samples transforms from a ductile transgranular fracture mode to a mixed mode of transgranular and intergranular fractures.