The excellent mechanical, high temperature and corrosion resistant properties of Ni-based superalloys make them attractive for applications where exposure to hydrogen is inevitable such as sour gas environments in oilfields. These materials are, however, susceptible to the adverse impact of hydrogen, which limits the accepted strength levels of their application. It is thus desirable to understand the mechanism behind embrittlement caused by hydrogen. For this purpose, we investigate the interplay of hydrogen with the underlying microstructure as those microstructural features affecting the behavior of hydrogen do not need to be identical with those determining the strength. Ni-based superalloys exhibit a large variety of precipitate phases, e.g., γ', γ" and δ, depending on the experimental annealing and aging conditions. These precipitate phases are identified using atom probe tomography (APT), whereas thermal desorption spectroscopy (TDS), secondary ion mass spectrometry (SIMS) and other techniques are employed to measure the hydrogen incorporation into the multiphase microstructure.
With the aid of density functional theory (DFT), we resolve the impact of different chemical environments and crystal structures of the precipitate phases on the hydrogen solution enthalpies. Furthermore, we investigate the hydrogen solubility at the interface between the precipitates and the matrix. We reveal how the increased solubility in these planar defects depends on their coherency, by considering both coherent and semi-coherent interfaces. The analysis outlines in comparison with the experiments, which interfaces are most likely nucleation points for hydrogen induced fracture in the material and provide strategies how their detrimental impact can be reduced.