Tailoring precipitation evolution through retained residual Laves networks in LPBF-fabricated Inconel 718

초록

Laser powder bed fusion (LPBF)-fabricated Inconel 718 forms non-equilibrium microstructures with residual stress, elemental segregation, and interdendritic Nb-rich Laves networks. Conventional high-temperature stress relief (HTSR) promotes homogenization but accelerates Laves dissolution, leading to localized coarse delta precipitation during aging. A low-temperature stress relief (LTSR) strategy was therefore proposed. The LTSR condition was designed based on differential scanning calorimetry (DSC) analysis to suppress excessive thermal exposure during stress relief and modify the subsequent precipitation pathway. Compared with the conventional HTSR route, the proposed LTSR strategy preserved a larger fraction of the build-induced interdendritic Laves network, resulting in a distinctly different precipitation evolution after the standard heat treatment. Under the HTSR route, rapid Laves dissolution caused localized coarse delta precipitation. In contrast, the LTSR route preserved the interdendritic Laves mvated-temperature tensile properties and engineering orphology, producing finer, more uniformly distributed precipitates. EBSD and TEM analyses revealed lower kernel average misorientation (KAM) and more homogeneous precipitation behavior. The retained network is considered to influence the subsequent precipitation pathway through delayed Nb redistribution, although direct quantification of Nb redistribution was beyond the scope of the present study. Tensile tests demonstrated that the LTSRtreated condition exhibits a modest increase in ultimate tensile strength, while a slight reduction in elevated-temperature yield strength and ductility is observed at 649 degrees C. These findings demonstrate that the LTSR strategy provides an alternative post-processing route for controlling precipitation evolution through modification of the remaining interdendritic microstructure, offering a new approach for tailoring the microstructure of LPBF-fabricated Inconel 718.

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