Hydrogen embrittlement (HE) is a major issue for the mechanical integrity of high-strength alloys
exposed to hydrogen-rich environments, with diffusion and trapping of hydrogen being critical
phenomena. Here, the role of microstructure on hydrogen diffusion, trapping and embrittlement in
additively manufactured (AM) and wrought Inconel 718 is compared, revealing the key role played by
dislocation cells. Trapping behaviour in hydrogen-saturated alloys is analysed by thermal desorption
spectroscopy and numerical simulations. A high density of hydrogen traps in cell walls, attributed to
dense dislocations and Laves phases, are responsible for the local accumulation of hydrogen, causing
signi
ficant loss in strength, and triggering cracking along dislocation cell walls. The in
fluential role of
dislocation cells alters fracture behaviour from intergranular in the wrought alloy to intragranular for the
AM alloy, due to the large proportion of dislocation cells in AM alloys. In addition, the cellular network of
dislocations accelerates hydrogen diffusion, enabling faster and deeper penetration of hydrogen in the
AM alloy. These results indicate that the higher HE susceptibility of nickel superalloys is intrinsically
associated with the interaction of hydrogen with dislocation walls.