Hydrogen Ingress in Titanium

A potentiostatic pulse technique was used to study the ingress of hydrogen in titanium (pure and grade 2) in an acetate buffer. Hydrogen ingress did not occur with pure titanium, indicating that the surface oxide is an effective barrier to hydrogen entry. In contrast, the data for Ti grade 2 (UNS⁽¹⁾ R50400) were shown to fit a model for hydrogen diffusion and trapping, allowing values to be determined for the irreversible trapping constant (k) and the flux of hydrogen into the metal. Two values of к were obtained, depending on the level of hydrogen present in the metal. The density of irreversible traps calculated from к for low hydrogen levels suggests that the principal irreversible traps may be interstitial nitrogen, but grain boundaries are another possibility. The additional trapping constant obtained for high hydrogen levels is thought to be associated with hydride formation. The irreversible trapping constants for Ti grade 2 are consistent with its susceptibility to hydrogen embrittlement relative to that of other alloys. The results demonstrate that multiple irreversible traps can be distinguished by using the diffusion/trapping model.