Oxidation properties and microstructure of a chromium coating on zircaloy-4 fuel cladding material applied by atmospheric plasma spraying

Abstract

To achieve a full protective coat on welding joints at both ends of zircaloy cladding tubes, we studied the rapid deposition of a thick chromium coating on zircaloy-4 cladding tubes by atmospheric plasma spraying. Microstructure, mechanical properties and high-temperature oxidation tests of chromium coatings were also studied. The initial screening oxidation test of the specimen was carried out at 1100 °C, 1200 °C and 1300 °C in dry air, and the oxidation properties of the specimen were explained. The nanohardness and modulus of the sprayed chromium coating were higher than those of the zircaloy-4 substrate. The nitride phase of Cr2N was formed after the high-temperature oxidation test. After oxidation at 1300 °C, there were multilayer structures: surface Cr2O3, residual Cr coating, thin (Zr,Cr)O2 layer, Cr-Zr layer and zircaloy substrate. There were bubble folds on the surface of the chromium coating and voids in the Cr2O3 layer. The oxidation test showed that the chromium coating can effectively slow the severe oxidation of zircaloy-4 cladding tubes. In summary, an APS-thick chromium coating has the potential to improve the oxidation resistance of zircaloy-4 cladding tubes in light water reactors.