Study of the oxidation behavior of CrN coating on Zr alloy in air

With the aim of improving the oxidation resistance of fuel cladding in a light water reactor, CrN coating, which has good uniformity and compactness with an average thickness of about 13 μm, was deposited by multi-arc ion plating on a Zr alloy substrate heated to 400 °C. A series of comparative experiments of the oxidation resistances of the original (i.e., uncoated) and CrN-coated Zr alloys were performed in air atmosphere at high temperatures. The oxidation tests revealed that the CrN coating did not show any sign of cracking or shedding even after oxidation at 1160 °C. The weight gain of the Zr alloy decreased by 97.7% as a result of deposition of the CrN coating. The oxidation activation energy, calculated using Arrhenius plots, was obviously higher for the CrN-coated Zr alloy than for the uncoated Zr alloy. The results of transmission electron microscopy and X-ray diffraction analyses before and after the oxidation tests revealed that the oxidation product of CrN at high temperature was Cr₂O₃ and that the thickness of the oxide layer increased with an increase in oxidation temperature. Nanoindentation test results showed that the CrN coating also enhanced the mechanical properties of the Zr alloy. Even after oxidation at high temperature, the hardness and Young's modulus of the coating were significantly higher than those of the original Zr alloy. The CrN coating deposited by multi-arc ion plating exhibited excellent oxidation resistance and mechanical properties, which demonstrates its potential as a candidate material for accident-tolerant fuel cladding.