Microstructural Characterization and Growth Kinetics of the Reaction Layer in U-10wt% Zr/Zircaloy-4 Diffusion Couples

To investigate the compatibility and diffusion behavior between U-Zr alloys and Zr-4 alloys, solid-to-solid U-10wt% Zr/Zr-4 diffusion couples were assembled by vacuum hot pressing and then annealed under vacuum at temperatures ranging from 580 °C to 1100 °C for various time. Scanning and transmission electron microscopes were employed to analyze the microstructures and composition profiles at the interfaces of the couples. The compatibility between the two alloys was investigated. δ-UZr₂ and ∼20-nm-thin U-rich layers existed in the vacuum-hot-pressed samples. The interdiffusion coefficient constant and activation energy are found to be (4.23±0.63)×10⁻⁶ m²/s and (160.73±1.67) kJ/mol, respectively. The interdiffusion coefficients of the U-10wt% Zr/Zr-4 alloy couples are higher than those of U—Zr alloys, especially at low temperature.