Hydrogen embrittlement in IN718 is governed by hydrogen interactions with defects. Hydrogen segregates to dislocations, grain boundaries, carbides, Laves, and δ precipitates, reducing cohesion and promoting cracking. In wrought IN718, grain boundaries and carbides/δ are dominant traps, causing intergranular fracture, whereas in AM material the dislocation-cell substructure enriched in Laves and Nb/Ti/Mo adds traps that increase hydrogen uptake and drive intragranular cracking at cell boundaries. Optimized heat treatments dissolve Laves, control δ, and reduce anisotropy, giving LPBF IN718 resistance comparable to or better than wrought. Thermal desorption spectroscopy (TDS) with diffusion modeling quantifies trap characteristics and links features to desorption peaks, enabling accurate HE models and overall microstructure-design strategies. This study aims to establish a quantitative link between hydrogen desorption thermodynamic data obtained by TDS and the microstructural features in wrought IN718 and heat-treated additively manufactured IN718 (AM IN718 + HT) that govern hydrogen trapping and release. We hypothesize that desorption models, providing parameters such as diffusivities, trap binding energies, trap densities, and trapping/de-trapping rates, must be coupled with detailed microstructural characterization to fully interpret the observed desorption response. To test this hypothesis, we employ a suite of advanced characterization techniques, including Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) for phase identification and morphology of IN718 secondary phases, and Electron Backscatter Diffraction (EBSD) for crystallographic orientation mapping. A particular focus is placed on EBSD-based analysis of grain boundary character and connectivity to assess their role as hydrogen diffusion pathways and trap networks. In addition, site-specific lamellae were extracted from multiple AM + HT conditions, targeting distinct precipitate populations, and examined via Transmission Electron Microscopy (TEM) to resolve nanoscale trapping sites. Preliminary TDS and isoTDS results indicate that dislocations, grain boundaries, and second-phase particles exert a strong influence on hydrogen trapping and desorption behavior. Comparative analysis of thermographs for wrought IN718, as-built AM IN718, and AM IN718 + HT reveals systematic differences in activation peak temperatures, desorption energies, and effective diffusivities. This work directly links TDS-derived hydrogen trapping parameters to specific microstructural features in wrought and AM IN718, from grain boundaries to nanoscale precipitates. By combining EBSD-based diffusion analysis, SEM phase mapping, and targeted TEM, we identify which defects and phases most critically control hydrogen behavior. These insights provide practical guidance for designing processing and heat-treatment routes that improve hydrogen embrittlement resistance and support more reliable qualification of AM IN718 components.
