Diffusion of hydrogen in nickel-based alloys

Abstract

The recovery process of hydrogen dissolved in excess in Ni-based alloys is studied by means of the hydrogen quenching method and electrical resistance measurement during isochronal and isothermal annealing treatment. A recovery stage in the electrical resistance due to hydrogen in the alloys shows the same characteristics as observed in the resistance decay of pure Ni that there is a size dependence of the recovery rate and shape of the isothermal recovery curves. The diffusion coefficients of hydrogen are obtained for the alloys in the range 240-360 K using a similar method to that for pure Ni. The values for the high temperatures investigated are nearly the same as those for pure Ni but at low temperatures, especially for the Ni-0.10 at.% Cu and Ni-0.10 at.% Fe alloys, the coefficients are clearly larger than those for pure Ni. The diffusivity of hydrogen must be depressed by trapping at alloying elements in alloys. This anomalous behaviour suggests that another process-grain boundary diffusion-other than lattice diffusion becomes more important in the low-temperature range.