Analysis of W/Mo alloying on hydrogen permeation performance of dual phase Nb-Ti-Ni alloys based on hydrogen chemical potentials

Substitution of Nb by the subgroup VI elements W and Mo was performed for dual phase Nb-Ti-Ni alloys containing a large fraction of primary bcc-(Nb)phase, particularly Nb₄₅Ti_27.5Ni_27.5 and Nb₅₆Ti₂₃Ni₂₁. The alloying effect on the hydrogen permeation performance as a function of the W/Mo concentration was analyzed based on a description considering the chemical potential of hydrogen. The substitution of Nb by W or Mo leads to a reduced hydrogen solubility, which contributes to enhanced resistance to hydrogen embrittlement. Effect of W/Mo alloying on the mobility of H atom and thus the hydrogen permeability is dependent on the W/Mo concentration and the operative temperature. Simultaneous improved hydrogen mobility and mechanical stability of the membrane, especially at lower temperature T ≤ 523 K, was achieved after W/Mo alloying by 5 at%. Specifically, Nb₄₀W₅Ti_27.5Ni_27.5 and Nb₄₆W₅Mo₅Ti₂₃Ni₂₁ membranes exhibit robust properties during hydrogen permeation cycle between 423 and 673 K.