There have been great developments in Ni-based superalloys over the decades as a next-generation structural material for extreme environments due to its outstanding mechanical properties at superhigh temperatures as well as corrosion and oxidation resistance. [1][2][3] This material is mainly composed of a base Ni and a large amount of Cr. The main strengthening mechanisms of Ni-based superalloys are solid-solution reinforcement (by adding elements such as Co, Mo, and W) and precipitation hardening (by carbide formation), which forms γ 0 phases using elements, such as Al and Ti. [4][5][6] Among them, γ 0 phase has an L1 2 structure (Al and Ti) that has misfit of less than 2% with γ matrix, and this significantly increases the mechanical properties. [7,8] Among Ni-based superalloys using solid-solution reinforcement and precipitation hardening, a Ni-Co-based superalloy has high heat resistance at %725 C, allowing it to be used for applications such as turbine discs. However, Ezugwu et al. reported that the Ni-based superalloys have low processability due to the high concentration of heat resistance elements and complex precipitation hardening, and there is a limit in controlling complicated geometricshaped structural parts. [9] Structural parts such as turbine discs can achieve optimal performance through shape control, but there are limitations in fabricating complicated shapes with conventional manufacturing process. Therefore, to efficiently fabricate the high value-added Ni-Co-based superalloy, an additive manufacturing (AM) technology that enables the fabrication of optimized geometric structural parts for high performance and minimizes material waste can be considered. [10,11] The AM technology is a manufacturing technology that makes products with complex 3D structures based on a computer-aided design (CAD) model. [12] Compared with conventional technologies, such as casting, forging, extrusion, and welding, AM requires less postprocessing and has minimal material waste, and it also has the advantage of being able to apply complex shape designs in accordance with consumer needs. [13][14][15][16][17] Among AM technologies, the laser powder bed fusion (L-PBF)-type selective laser melting (SLM) method is capable of controlling complex shapes, achieving uniform microstructures, and obtaining outstanding mechanical properties, making it the method most commonly applied in manufacturing Ni-based superalloys. [18][19][20][21] However, IN625 and IN718 have a maximum operating temperature of 650 C, and there are limitations in using these materials in extreme high-temperature environments. As a result, while interest in Ni-based superalloys with outstanding performance is increasing, studies that explore the material are still not sufficient.Ni-Co-based superalloys were developed as a material for parts used in extreme environments, such as high-temperature turbine discs, because they have much greater heat resistance compared with IN718 and U720Li at %725 C.
