Transition of creep mechanism by solute hydrogen in Zircaloy-4

The effect of solute hydrogen up to 200 ppm on the creep mechanism of Zircaloy-4 was discussed to ascertain the safety of nuclear power plants. Creep tests performed at 673 K 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=10 ppm; solute-atmosphere dragging process in hydrogenated samples with H=100 and 200 ppm. 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.