Improvement of oxidation resistance of the Ti-modified Cr-based coating on Zry-4 by Cr₂O₃/Cr₂TiO₅ double oxide layer with coherent interface

The loss of coolant accident (LOCA) has brought great threat to the safety of nuclear power plant. The oxidation resistance of Zircaloy-4(Zry-4) cladding must be improved to prevent the leakage of nuclear fuel. The Ti-modified Cr-based coating with excellent oxidation resistance was deposited on the Zry-4 by magnetron sputtering. The oxidation kinetics and microstructure evolution of the coatings were investigated via isothermal oxidation experiments at 900–1200 °C, respectively. The results of oxidation kinetics shows that the oxidation resistance of the Ti-modified Cr-based coated Zry-4 is significantly improved and the activation energy of the coated Zry-4 is increased by about 25 %. After steam oxidation at 1200 °C, the coating formed a three-layer structure, Cr₂TiO₅, Cr₂O₃ and residual Cr layer. The first-principles calculation shows that the diffusion energy of O in Cr₂TiO₅ is higher than that in Cr₂O₃. Furthermore, the formed Cr₂TiO₅ layer is connected to the underlying Cr₂O₃ layer via a coherent interface, which both improves the bonding of the oxide layer and dissipates the stresses generated during the oxidation.