Isothermal experiments on steam oxidation of magnetron-sputtered chromium-coated zirconium alloy cladding at 1200 ℃

The isothermal steam oxidation behavior of chromium-coated zirconium alloy cladding at 1200 ℃ is studied. The cladding substrate is Zr-1 Nb alloy with outer diameter of 9.5 mm and thickness of 0.57 mm. The Cr coating is prepared by magnetron sputtering method with thickness of about 11 µm. The oxidation durations are 300 s~14,400 s. After oxidation, blisters are formed on the surface due to the compressive stress in coating, and the coating surfaces are porous or exhibit a morphology with ravines and granular crystals. A four-layer structure (Cr 2 O 3 , Cr, Zr(Cr,Fe) 2 and Zr from outside to inside) is formed in the early stage of oxidation. However, Zr 4+ can migrate into Cr coating through grain boundaries and reacts with Cr 2 O 3 . The redox reaction between Zr and Cr 2 O 3 leads to the coating failure, resulting in the oxidation of Zr alloy substrate. Due to selective oxidation, a certain thickness of Cr coating is retained during the thickening of outer ZrO 2 . The emergence of outer ZrO 2 layer is significantly delayed by Cr coating, and Cr coating is able to reduce the growth rate of outer ZrO 2 layer. Therefore, Cr coating has a protective effect in 1,200 ℃ steam environment and can improve the oxidation resistance of Zr alloy cladding. • Isothermal steam oxidation behavior of magnetron-sputtered Cr-coated Zr alloy at 1200 ℃ is studied. • The oxidation and failure mechanism of Cr coating is discussed. • The oxidation kinetics of Cr-coated Zr alloy cladding is analyzed.