An investigation was made of the effects of Sn and Nb on dislocation properties in a Zr lattice to elucidate the role of these alloying elements in hydride nucleation processes. According to experimental observations, γ-hydride habit planes were close to the prismatic plane in pure Zr and close to the basal plane in Zircaloy. Dislocation loops were observed around hydride precipitates, implying they play a part in hydride formation. The present ab initio generalized stacking-fault energy calculations revealed remarkable effects of Sn upon unstable-stacking energy and stacking-fault energy: these parameters for basal slip were considerably reduced while those for prismatic slip were increased in the presence of Sn. These results suggested selective stabilization and enhancement of dislocation spreading in the basal plane, promoting possible elementary processes of hydride precipitation with basal habit plane, i.e. screw-dislocation spreading and edge-dislocation emission in the basal plane.

Effect of Sn and Nb on Generalized Stacking Fault Energy Surfaces in Zirconium and Gamma Hydride Habit Planes. Y.Udagawa, M.Yamaguchi, T.Tsuru, H.Abe, N.Sekimura: Philosophical Magazine, 2011, 91[12], 1665-78