Diffusion and oxidation behavior of Cr/Cr_xC_y multilayer coating on zirconium alloy in high temperature steam environment

Chromium-coated zirconium alloy cladding has emerged as one of the most promising candidates for improving the safety of zirconium-based fuels in light water reactors during loss-of-coolant accident (LOCA) conditions. However, the interdiffusion between Cr and Zr reduces the protective effect of the Cr coating. In this study, Cr/Cr_xC_y multilayer coatings were successfully deposited on Zr-1Nb alloy cladding using an industrial-scale magnetron sputtering system to improve the high-temperature steam oxidation resistance of zirconium alloy. The high-temperature steam oxidation behavior and element diffusion characteristics of the multilayer coating were systematically studied at 1200°C∼1350°C. Experimental results indicated that the Cr/Cr_xC_y multilayer coating exhibits superior oxidation resistance at 1200°C, maintaining a sufficient thickness and structural integrity of the Cr₂O₃ layer for up to 14,400 s. Furthermore, compared to a Cr coating, the oxidation resistance duration is significantly extended from 1 h to nearly 4 h. Notably, an in-situ formed Zr-C layer effectively limited the Cr-Zr interdiffusion and eutectic reaction at temperatures up to 1350°C, which demonstrates that the Zr-C layer served as a diffusion barrier layer, impeding the diffusion of Cr and Zr atoms.