One of the current limitations of Ni-based alloys is their sensitivity to hydrogen embrittlement (HE). A promising strategy to mitigate HE is by designing alloys with features that benignly trap hydrogen. Most secondary-phase particles in nickel alloys have been shown to exacerbate embrittlement. However, γ′ precipitates have been shown to trap hydrogen in nickel based alloys. Furthermore, in austenitic steels it is shown that high γ/γ′ lattice misfit reduces hydrogen embrittlement.
To investigate this phenomenon in nickel alloys, model Ni alloys containing only γ′ precipitates were computationally designed using a combination of thermodynamic calculations, physical models, and a multi-objective genetic algorithm. The alloy compositions were tailored to produce significantly different γ/γ′ lattice misfits, while allowing complete dissolution and precipitation of γ′ through thermal treatments.

Two alloys with distinct γ/γ' lattice misfits were fabricated and their microstructure were analyzed using X-ray diffraction and electron microscopy. Hydrogen diffusion and trapping behaviors were examined using electrochemical permeation, thermal desorption spectroscopy (TDS), and glow discharge optical emission spectroscopy (GD-OES) on both annealed and precipitated states, alongside pure Ni as a reference to study the hydrogen diffusion and trapping behavior. Additionaly, in-situ hydrogen charging tensile tests were performed to study the embrittlement behavior of the alloys.

Results show that both γ/γ′ alloys exhibit significant retardation of hydrogen diffusion and a higher hydrogen concentration compared to pure Ni, confirming the presence of effective hydrogen traps. The low-misfit alloy demonstrated stronger trap binding energies but retained less hydrogen overall than the high-misfit alloy. Analysis of TDS peak shapes indicates a large amount of weakly trapped hydrogen in the high-misfit alloy, likely due to elevated elastic stress fields around the γ′ precipitates. In contrast, the low-misfit alloy contains slightly less hydrogen, but it is strongly trapped. These results suggest that while lattice misfit influences the nature and strength of hydrogen trapping, it is not the sole factor governing trap efficiency.
Despite the observed trapping behavior, in-situ hydrogen charging experiments reveal that γ′ precipitates alone are insufficient to mitigate hydrogen embrittlement under service-like conditions. Thus, while γ/γ′ lattice misfit affects trap characteristics, it does not singularly determine the effectiveness of hydrogen embrittlement resistance.