An electrochemical permeation technique was used to measure the diffusivity of H in Ni-based substitutional solid solutions at temperatures ranging from 296 to 333K. It was found that the diffusivity of H more or less decreased as the solute concentration was increased; except in the case of Ti. Here, there was an initial slight increase in the diffusivity as the Ti content was increased up to about 4at%. The diffusivity data (table 110) for these alloys were considered in terms of an approximate first-order quasi-chemical model for ternary systems. Within the low-concentration range of the substitutional solutes, the calculated values of the diffusivity agreed with experimental values. The estimated interaction energies between substitutional solute and H atoms showed that all of the substitutional atoms (except Ti) acted as generators of trapping sites. However, Ti atoms initially produced anti-trapping sites in the Ni-Ti matrix. The initial increase in diffusivity for Ni-Ti alloys was attributed to local atomic displacements which were associated with lattice dilatation.

Y.Sakamoto, O.Shimizu, K.Hirayama, K.Baba: Journal of the Physics and Chemistry of Solids, 1988, 49[8], 897-903

Table 110

Diffusion Parameters for H in Ni Alloys