Effects of Alloying-element Addition on Hydrogen Diffusion and Hydrogen Absorption in Ni

The effects and mechanisms of various alloying elements on the characteristics of Ni-based alloys have not yet been systematically investigated, despite the widespread application of such alloys in diverse domains. To address this gap, in this study, we investigated the effects of the substitutional alloying elements, specifically Fe, Cr, Mo, and Mn, on the lattice expansion, mechanical properties, hydrogen diffusivities, and solubilities of Ni. These elements led to both austenite lattice expansion and strengthening. We measured hydrogen diffusivities under high-pressure hydrogen environments (100 MPa) and desorption at constant temperatures. Notably, all the examined alloying elements reduced the hydrogen diffusivity of Ni in the order: Mn < Mo ≈ Fe < Cr. The effects of alloying cannot be simply explained by lattice expansion or strengthening but are attributed to increased activation energy for hydrogen diffusivity. We also assessed the hydrogen solubility through thermal desorption analysis (TDA) after exposure to high-pressure hydrogen (100 MPa). Except for Fe, alloying elements increased hydrogen solubility in the order: Cr < Mo ≈ Mn. These effects are attributed to changes in the activation energy of hydrogen solubility. Additionally, TDA spectra for almost all the alloys, simulated based on the temperature dependence of hydrogen diffusivity, indicated that hydrogen diffusion through the face-centered cubic lattice remained unaffected by hydrogen trapping.