Solution-Strengthened Nb-Based Alloys for Metal Foil Pumps as Implemented for Direct Internal Recycling

General Atomics is investigating novel Nb-based alloys for low-pressure metal foil pumps, as described in the Direct Internal Recycling concept. Nb has excellent H permeability making it an attractive option for H separation, but is subject to H-induced embrittlement with successive H loadings. Here we investigate H permeability through Nb-based alloys which include various concentrations of metals, namely W, Ni, and Fe. H interactions with metal inclusions are modeled using density functional theory (DFT) to assess H solubility and diffusivity. These data are then used to assess the permeability of Nb-based alloys in comparison to pure group 5 metals, and are validated by experimental measurements of H permeation. These DFT calculations are used to parameterize mesoscale models of diffusion using kinetic Monte-Carlo techniques to accurately determine the effect of dilute-limit inclusions and assess the effect of concentrations. Results show the dependence of H permeability on inclusion species and concentrations, indicating that favorable modifications to the solubility can be attained while still obtaining the high permeability required for metal foil pumps.