Hydrogen diffusion and intergranular cracking in nickel

A new diffusion model is developed to analyze the contribution of grain boundary diffusion to total mass transport in metals. The predictions of the model are compared with experimental results concerning the effect of room temperature hydrogen precharging period upon the intergranular fracture depth in pure nickel specimens fractured at 77 K. It is shown that the fracture mode changes from transgranular into intergranular when the hydrogen concentration in grain boundaries reaches a critical value, in the range of 6.5-9.8 at%. The observed increment of intergranular cracking depth with the pre-charging period indicates that hydrogen transport in this material is not enhanced by grain boundaries. (C) 1997 International Association for Hydrogen Energy.