Transition of creep mechanism by solute hydrogen in Zircaloy-4

The effect of solute hydrogen up to 200ppm on the creep mechanism of Zircaloy-4 was discussed to ascertain the safety of nuclear power plants. Creep tests performed at 673K and revealed that the addition of solute hydrogen decreased the creep rate in intermediate stress regions. According to the followed transmission electron microscopy, the phenomenon reflected the change of rate-controlling mechanisms without or with solute hydrogen: cross-slip in a non-hydrogenated sample with H=10ppm; solute-atmosphere dragging process in hydrogenated samples with H=100 and 200ppm. Because cross-slip works as the annihilation process for the glide dislocations in Zircaloy-4, it is considered that the suppression of cross-slip by solute hydrogen leads to a decrease in the creep rate.