Effect of Cr/Al Atomic Ratio on the Oxidation Resistance in 1200°C Steam for the CrAlSiN Coatings Deposited on Zr Alloy Substrates

Cr-based physical vapor deposition coatings have been considered as having the potential to enhance the accident tolerance of Zr alloy fuel claddings. Comparative studies on the high-temperature oxidation behavior were conducted on the Zr alloy coupons that were coated with magnetron-sputtered CrAlSiN quaternary coatings with various Cr/Al atomic ratios. It has been found that the oxidation resistance and the external scale are closely associated with the Cr/Al atomic ratio. A Cr/Al ~ 3.1 coating provided effective protection for its Zr alloy substrate in 1200°C steam for 6 h, where a dense and homogeneous Cr2O3/α-Al2O3 bilayer scale was evidenced in the whole process. However, for Cr/Al ~ 1.3 and the Cr/Al ~ 0.6 coatings, their oxidation resistance was greatly degenerated, because of the forming of brittle α-Al2O3-rich scales. The results demonstrate that the Cr/Al atomic ratio is crucial to the protective capability of CrAlSiN coatings for Zr alloy coupons in high-temperature steam.