Effect of alloying elements (Al, Co, Fe, Ni) on the solubility of hydrogen in vanadium: A thermodynamic calculation

CALPHAD type thermodynamic assessments for the V–M–H (M = Al, Co, Fe, Ni) hydrogen membrane systems have been carried out on the basis of a newly assessed Co–H binary description, a partly modified Fe–H description and existing thermodynamic descriptions for the other M–H (V–H, Al–H, Ni–H) and V–M (V–Al, V–Co, V–Fe, V–Ni) binary systems. A special attention was paid to estimate the thermodynamic descriptions for the non-existing bcc Al–H, Co–H and Ni–H alloys. Thermodynamic parameters for those binary alloys were estimated by using a theoretical approach (atomistic computation) and fitting limited amount of experimental data for the hydrogen solubility in V-rich bcc ternary alloys. The proposed thermodynamic descriptions predict phase equilibria, especially the effect of alloying elements on the hydrogen solubility in the V-rich bcc alloys, in good agreement with available experimental data. The present thermodynamic descriptions can be easily extended to higher order alloy systems and can provide useful information for alloy design of metallic hydrogen membranes with well-balanced hydrogen permeability and mechanical properties.