GRAIN-BOUNDARY DIFFUSION OF HYDROGEN IN NICKEL

Grain boundary diffusion of hydrogen in nickel was quantified through permeation measurements performed on fine-grained foils produced by electrodeposition. The permeation data were analyzed with a modified version of the Hart equation. The grain boundary diffusion coefficient at 30-degrees-C is at least 3 x 10(-12) m2/s, which is a factor of 40 greater than the lattice diffusion coefficient; however, the analysis indicates that a 1000-fold increase may not be unreasonable. The activation energy for grain boundary diffusion in this system is 30 kJ/mol, which is approximately three-fourths of the activation energy for hydrogen diffusion in single-crystal nickel. These results indicate that grain boundary diffusion should be considered in models of hydrogen transport during hydrogen-induced cracking of nickel and nickel-based alloys.