Synergistic effect of hydrogen and heat treatment on hydrogen embrittlement in LPBF manufactured and wrought 718

Hydrogen embrittlement (HE) remains a critical limitation for the structural application of Ni-based alloys in hydrogen-enriched environments. In this study, the synergistic effects of microstructural defects and heat treatment on hydrogen diffusion/trapping and embrittlement behavior in Laser Powder Bed Fusion (LPBF) Inconel 718 were systematically investigated in comparison with conventionally manufactured (CM) 718. Multi-scale characterization methods: X-ray micro-computed tomography (μCT), electron backscatter diffraction (EBSD), thermal desorption spectroscopy (TDS), glow discharge optical emission spectroscopy (GDOES), and three-dimensional Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) were employed to quantify defect structures and hydrogen distribution. Results show that microstructures of AM 718 exhibit hierarchical defect networks, including lack-of-fusion pores and high densities of geometrically necessary dislocations (GNDs), which act as stress concentration area and hydrogen trapping sites. Heat treatment and hot isostatic pressing (HIP) significantly reduce dislocation density and partially mitigate porosity, leading to decreased hydrogen uptake; however, residual defects and lattice distortions persist. ToF-SIMS and TEM mapping demonstrates notable hydrogen segregation at melt-pool boundaries and interfaces of layer. Mechanical testing coupled with in-situ Digital Image Correlation (DIC) / EBSD show that hydrogen promotes severe strain localization and premature failure in AM samples. Despite post thermal processing, AM alloys retain higher HE susceptibility than CM materials due to persistent defect-assisted hydrogen trapping. This work establishes a direct link between AM-induced hierarchical defects, spatial hydrogen distribution, and localized deformation, providing critical insight for designing hydrogen-resistant AM alloys.