High-temperature steam oxidation resistance of Cr[sbnd]Si substitutional solid solution coating on Zr-4

Abstract

Zirconium alloy has been used as fuel cladding in LWR for a long time. However, during the loss-of-coolant accident, the zirconium alloy cladding will be exposed to steam environment at 1200 °C, and the damage to the cladding is inestimable. Therefore, in this study, Cr and CrSi coating were prepared on the surface of Zr-4 alloy by magnetron sputtering, and their steam oxidation behaviors at 1200 °C were investigated. The Cr-coated Zr-4 revealed an α-Zr(O) layer with ZrO2 particles at the interface after oxidation at 1200 °C. However, the CrSi coated Zr-4 exhibited excellent oxidation resistance due to the introduction of Si atoms. During oxidation, the diffusion barrier of Zr2Si layer with ZrSi ionic bonds was formed in situ because of the inward diffusion of Si atoms, which effectively inhibited the inter-diffusion of Zr and Cr. The aggregation of ZrO2 at the grain boundaries of the coating was prevented, which cut off the short-circuit path of oxygen diffusion inward. Moreover, the first principles calculation was employed to compare the adsorption energies of the external Zr atoms by Zr2Si and ZrCr2 diffusion layers. The adsorption energy of the in situ formed Zr2Si layer for Zr atoms is higher than that of the ZrCr2 layer, which is evidence of the barrier effect of the Zr2Si layer. Thus, the CrSi coated Zr-4 in this work showed a high prospective in the practical applications.