Crystallography of Zirconium Hydrides in Recrystallized Zircaloy-2 Fuel Cladding by Electron Backscatter Diffraction

Abstract

Precipitation morphology and habit planes of the δ-phase Zr hydrides, which were precipitated within the a-phase matrix grains and along the grain boundaries of recrystallized Zircaloy-2 cladding tube, have been examined by electron backscatter diffraction (EBSD). Radially-oriented hydrides, induced by residual tensile stress, precipitated in the outside region of the cladding, and circumferentially-oriented hydrides in the stress-free middle region of the cladding. The most common crystallographic relationship for both types of the hydrides precipitated at the inter- and intra-granular sites was identical at (0001)α // {111}δ, with {10&1macr;7}α // {111}δ, being the occasional exception only for the inter-granular radial hydrides. When tensile stress was loaded, the intra-granular hydrides tended to preferentially precipitate in the grains with circumferential basal pole textures. The inter-granular hydrides tended to preferentially precipitate on the grain faces opposite to tensile axis. The change of prioritization in the precipitation sites for the hydrides due to tensile stress could be explained in terms of the relaxation effect of constrained elastic energy on the terminal solid solubility of hydrogen at hydride precipitation.