Microstructural effects on the high-temperature steam oxidation resistance of magnetron sputtered Cr-Al-Si-N quaternary coatings on zirconium coupons

It is of great significance to develop accident tolerant fuel claddings for enhancing the safety margin of light water reactors. Cr-Al-Si-N quaternary coatings were proposed to improve the mechanical properties and the high-temperature steam oxidation resistance of Zr-based alloys. (Cr0.6Al0.3Si0.1)xN1−x coatings with three kinds of microstructure, were prepared on Zr coupons, and then were evaluated on their mechanical properties and oxidation resistance in the high-temperature steams. The “dense & column-free” coating exhibits a combination of the best mechanical properties and the highest oxidation resistance. In comparison with the Zr coupon, its hardness H and indentation modulus E* increased by ~4 times and ~twice, respectively. After coated with the “dense & column-free” coating, the oxidation of the Zr coupon was completely suppressed in the 1000 °C steam for 15 min, and the thickness of the α-Zr(O) layer deceased by 40%–92% in the 1200 °C steam for 30 min. By contrast, the “porous & columnar” coating hardly provided any protection for the underneath Zr substrate in the high-temperature steams. The result demonstrates that the densely fine-grained or amorphous microstructure could effectively suppress inner-diffusion of O atoms and favor formation of a dense and coherent scale on surface, which would be highly desirable for the protection coatings of Zr claddings.