High Temperature Steam Oxidation Behavior of Cr-coated Zr-4 Alloy Prepared by Multi-arc Ion Plating at 1000 and 1100 °C

Cr-coated zirconium alloy cladding is an important method to improve the high temperature oxidation resistance of light water reactor fuel assembly. The high temperature oxidation behavior of Cr-coated Zr-4 alloys was studied in steam environment. The Cr-coated Zr-4 alloy samples were prepared by multi-arc ion plating process. High temperature oxidation experiments were carried out in 1000 and 1100 degrees C steam environment. The oxidation mass gain of the samples was obtained by a high precision balance, and the surface and cross-section micro-morphologies, element distribution, as well as phase and thickness of the Cr-Zr diffusion layer were analyzed by scanning electron microscope (SEM), energy dispersive spectroscope (EDS) and X-ray diffractometer (XRD). The results show that there are a large number of droplets of different sizes on the surface of the Cr-coated Zr-4 alloy samples prepared by multi-arc ion plating, and the Cr coating grows preferentially along the (110) crystal plane. The oxidation mass gain per unit area and time approximately follows a parabolic law. The oxidation rate at 1100 degrees C is significantly higher than that at 1000 degrees C. At the same temperature, the oxidation rate of the Cr-coated Zr-4 alloy is lower than that of the uncoated Zr-4 alloy. After high temperature steam oxidation, whisker-like oxides are formed on the surface of the samples, and there are a large number of micro-pores between the oxides. After high temperature steam oxidation at 1100 degrees C for 3 and 4 h, the surface of the samples is oxidized to form worm-like agglomerates. The cross section of the samples has a layered structure, consisting of Cr2O3 layer, Cr coating, Cr-Zr diffusion layer, and alpha-Zr(O) layer (ZrO2 layer). However, the thickness of the surface Cr2O3 layer does not increase synchronously with the increase in the oxidation time, while the thickness of the Cr-Zr diffusion layer increases with the increase in the oxidation temperature and oxidation time, which has a linear relationship with the oxidation time. Therefore, the Cr-coated Zr-4 alloy prepared by multi-arc ion plating shows good resistance to high temperature steam oxidation at 1000 and 1100 degrees C.