Hydrogen trapping by oxygen and dislocations in zirconium alloys

The presence of a hydrogen peak below the surface of zirconium samples, with an initial hydrogen free zone beneath the oxide when they are oxidised, has been known for many years. A recent argument that the hydrogen peak was a result of stresses resulting from oxide growth was based on anodically oxidised specimens, where a large compressive stress in the oxide cannot be assumed. Both segregation of hydrogen to regions with a high dislocation density, and to regions containing a limited range of dissolved oxygen (similar to 4 to 8 at.%) are well established. It appears that high residual dislocation densities from the initial surface preparation are the most probable explanation of sub-oxide hydrogen peaks in anodically oxidised and in unoxidised specimens. since trapping at dislocations appears to be stronger than trapping by interstitial oxygen. (C) 1997 Elsevier Science S.A.