ScholarWorks@성균관대학교

초록

Inconel 718 (IN718) is a precipitation strengthened nickel-based superalloy widely used in high-temperature structural components for aircraft engines and gas turbines owing to its excellent mechanical strength and creep resistance. However, conventional manufacturing routes such as casting require prolonged heat treatment cycles and complex machining processes, limiting design flexibility. To address these limitations, laser powder bed fusion (L-PBF) process has emerged as a promising next-generation manufacturing technology. Nevertheless, L-PBF-fabricated IN718 often exhibits residual stress and porosity due to rapid solidification and non-uniform thermal histories, necessitating optimized post-processing to ensure microstructural homogeneity in terms of precipitate distribution, defect mitigation, and residual stress relaxation, as well as mechanical reliability. In this study, the relationships between microstructural evolution and mechanical properties of L-PBF-fabricated IN718 were systematically investigated for as-built specimens and specimens subjected to either the standard AMS 5662 N heat treatment or a thermodynamically informed direct hot isostatic pressing (Direct-HIP) process. The precipitation behavior of γ′, γ″, and δ phases under each post-processing condition was analyzed, and the corresponding tensile properties were evaluated. The results demonstrate that the Direct-HIP process significantly reduces the overall post-treatment time while achieving superior mechanical performance compared to the conventional heat treatment. High-temperature tensile testing at 650 °C showed tensile strengths of 1117 MPa and 1163 MPa for the AMS 5662 N and Direct-HIP conditions, respectively. Moreover, the elongation at 650 °C increased from 26% to 35% with the application of Direct-HIP. Overall, this study provides an integrated framework for post-processing optimization of L-PBF-fabricated IN718, contributing to the efficient manufacturing and practical deployment of high performance components.

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