Y3+-Stabilized Zirconia (YSZ) Coatings for Protection Against Water Vapor Corrosion

To enhance the protection of zirconium alloys during loss-of-coolant accident conditions, the water vapor corrosion resistance of Y3+-stabilized zirconia coatings fabricated by plasma electrolytic oxidation on zirconium alloy was remarkably improved in this study. The corrosion resistance mechanisms of the coating were disclosed by simulating water vapor reaction processes in cubic zirconia (c-ZrO2) and tetragonal zirconia (t-ZrO2). The results revealed that the mass fraction of c-ZrO2 in the coatings was increased from 9% to 32% by adjusting the Y3+ concentration. The mass gain and corrosion rate of the enhanced coating were approximately 60% and 37% after 3600 s water vapor corrosion at 1000 °C separately compared to those of traditional zirconia coating. This enhancement is attributed to the slower reaction rates of c-ZrO2 with water vapor than t-ZrO2, which suppresses corrosion and reduces the formation of Zr(OH)4. Thus, less cracks appeared in coatings with higher c-ZrO2 fractions, as their corrosion layers contained fewer corrosion products that induced stress concentration, which, in turn, protects the subsurface coatings from further corrosion. This study provides a viable strategy for developing coatings to protect zirconium alloys against water vapor corrosion in nuclear energy applications.