The diffusivity of hydrogen in nickel-based solid solutions

Abstract

An electrochemical permeation technique has been used to measure the diffusivity of hydrogen in Ni-based substitutional solid solutions in the temperature range 296–333 K. The substitutional solutes were Cu, Al, Si, Ti, V, Cr, Fe and Co. The diffusivity of hydrogen is more or less decreased as the concentration of the solutes is increased, except for the Ti additions for which there is initially a slight increase in the diffusivity, as the Ti content increases up to about 4.0 at.%. The diffusivity data obtained for these alloy systems are discussed in terms of the first-order approximate quasi-chemical model for ternary systems proposed by McLellan R.B. and Dunn W.W. [ J. Phys. Chem. Solids 30, 2631 (1969)]; Alex K. and McLellan R.B. [ J. Phys. Chem. Solids 32, 449 (1971)]; and McLellan R.B. and Farraro R. ( Acta metall. 25, 1217 (1977)]. Within the low concentration range of the substitutional solutes, the calculated values of diffusivity agree with the experimental values. The estimated interaction energies Δϵ between the substitutional solute and hydrogen atoms show that all the substitutional atoms, except for Ti, act as a generator of trapping sites, but the Ti atom initially produces antitrapping sites in the Ni-Ti matrix. The initial increase in the diffusivity in the Ni-Ti alloys may be primarily due to the local atomic displacement associated with the lattice dilation.