Microstructural characterization of accident tolerant fuel cladding with Cr–Al alloy coating layer after oxidation at 1200 °C in a steam environment

Zr alloy specimens were coated with Cr–Al alloy to enhance their resistance to oxidation. The coated samples were oxidized at 1200 °C in a steam environment for 300 s and showed extremely low oxidation when compared to uncoated Zr alloy specimens. The microstructure and elemental distribution of the oxides formed on the surface of Cr–Al alloys have been investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A very thin protective layer of Cr2O3 formed on the outer surface of the Cr–Al alloy, and a thin Al2O3 layer was also observed in the Cr–Al alloy matrix, near the surface. Our results suggest that these two oxide layers near the surface confers excellent oxidation resistance to the Cr–Al alloy. Even after exposure to a high temperature of 1200 °C, inter-diffusion between the Cr–Al alloy and the Zr alloy occurred in very few regions near the interface. Analysis of the inter-diffusion layer by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) measurement confirmed its identity as Cr2Zr.