Crystallographic and Thermodynamic Insights into Preferential Hydride Precipitation Sites in Zr-2.5Nb Alloy

The Zr-2.5Nb alloy, widely used in nuclear applications, exhibits significant susceptibility to hydrogen-induced embrittlement due to hydride precipitation. This study investigates the preferential sites and mechanisms of hydride precipitation in Zr-2.5Nb alloys using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results show a predominance of intergranular hydrides, with grain boundaries (GBs) serving as the primary nucleation sites. Misorientation and GB energy exhibited a weak influence on intergranular hydride precipitation, while the interaction angle between basal planes and GBs (alpha GB_BP) was found to determine hydride precipitation behavior. A modified thermodynamic model was developed to elucidate the interplay between GB energy, alpha GB_BP, and hydride precipitation. Additionally, the lamellar beta-Zr phase at GBs promotes hydride formation, which largely explains the weak correlation observed between misorientation and intergranular hydride precipitation. These findings provide insights into mitigating hydride-induced degradation in Zr alloys for enhanced performance in nuclear environments.