Dissolution of Intermetallic Second-Phase Particles in Zircaloy-2 in High-Temperature Steam

The stability of intermetallic second-phase particles (SPPs) in coated Zircaloy-2 was studied in 700 °C steam environments up to 20 hours. Hydrogen generated from high-temperature steam oxidation of uncoated Zr-induced δ-hydrides formation in the Zircaloy matrix. Synchrotron XRD demonstrated that longer exposure times increased hydride peak intensity and decreased intermetallic SPPs’ peak intensity. Cross-sectional SEM analysis verified the intermetallic SPPs’ volume fraction reduction. The size distribution of intermetallic SPPs was characterized and larger particles were dissolved at longer oxidation time. A correlation between the hydrogen concentration and the volume fraction of intermetallic SPPs at 700 °C steam environment was found, with the volume fraction of SPPs decreasing as hydrogen concentration increases.