Accurate prediction of threshold stress for hydride reorientation in Zircaloy-4 with directly measured interface orientation relationship

Abstract

Hydride reorientation is a major degradation mechanism of zirconium-based alloys used for nuclear fuel cladding tubes. A previous commonly used thermodynamic model has limited accuracy in predicting the threshold stress for hydride reorientation owing to assumptions that all basal pole of α-Zr is oriented along the radial direction on cross-section of cladding tube and all hydrides precipitate at the prismatic plane of α-Zr. We analyzed fractions of each zirconium-hydride interface orientation relationship by EBSD (Electron Backscatter Diffraction) and found that the typical macroscopic radial hydrides are primarily formed upon aggregation of {101¯1}α-Zr // {111}δ-ZrH1.66 and {0001}α-Zr // {111}δ-ZrH1.66 orientation relationships in mesoscale. The former is statistically favored due to the large number of available sites, and the latter is energetically favored due to the low strain energy. Using the fraction-weighted average misfit strain and strain energy and the texture information, we demonstrated that the accuracy of the thermodynamic model can significantly improve. This work consummates the present thermodynamic model for hydride reorientation in zirconium-based alloys.