The oxidation behaviors of Cr2N and Cr/Cr2N multilayer coatings on Zircaloy-4 tubes in high temperature environment

Abstract

The aim of Accident-Tolerant Fuels (ATF) is to delay or prevent oxidation of nuclear fuels cladding in the case of loss of coolant accident (LOCA) conditions. And the usage of cladding coatings is an important strategy to improve fault tolerance of nuclear fuels cladding. Meanwhile, the choice of coating types and the design of coating structure are very important. Here, Cr2N coating and Cr/Cr2N multilayer coating were deposited on Zircaloy-4 tubes by magnetron sputtering. Oxidation resistance tests of original and coated Zircaloy-4 tubes were performed in air atmosphere at different high temperatures. It was found that Cr/Cr2N multilayer coating exhibited lower weight gain rate and fewer cracks on surface than Cr2N coating after oxidation. After oxidation at 800 °C, the cross sectional image shows that the cracks on the Cr2N coating surface expand and reach the substrate, while the Cr/Cr2N multilayer coating was intact without cracking. For Cr/Cr2N multilayer coating, a metallic Cr layer metal formed on the ZrO2 layer after oxidation 900 °C due to redox reaction of Cr2O3 and Zr. The obtained results revealed that Zircaloy-4 tubes coated with Cr/Cr2N multilayer exhibited better oxidation performance.