Systematic investigations on the microstructural evolution and degradation mechanism of Cr3Si-coated Zry-4 under DBA and BDBA conditions

Abstract

Cr₃Si and Cr coatings were deposited on Zry-4 substrates via magnetron sputtering to examine their oxidation behavior in steam ranging from 1200 to 1400 °C. At 1200 °C, a dense Cr₂O₃ layer that formed on the surface of the Cr₃Si-coated Zry-4 followed a power-law function, preventing the internal diffusion of O. Additionally, an in-situ Zr₂Si layer, developed between the Cr₃Si coating and Zry-4 substrate, significantly mitigated the outward diffusion of Zr. However, at 1330 °C in steam, the continuity of the Zr₂Si layer was disrupted due to the formation of ZrCr₂, which facilitated the outward diffusion of Zr to the interface between the remaining Cr₃Si layer and the outer Cr₂O₃ layer. Despite the reduction in the Cr₂O₃ layer thickness caused by redox reactions between Cr₂O₃ and Zr, the Cr₃Si coating still managed to delay the steam oxidation of the Zry-4 substrate for over 60 min at 1330 °C. While on the uncoated side, the thickness of the formed ZrO₂ reached 846 ± 5.2 μm. For the Cr coating, after 30 min of oxidation in steam at 1330 °C, a significant liquid eutectic formed between the Cr coating and the Zry-4 substrate, compromising the coating's overall structural stability. The oxidation resistance of the Cr₃Si coating surpasses that of the Cr coating after exposure to steam at 1400 °C for 10 min. These findings suggest that the Cr₃Si coatings hold promise for robustly protecting zirconium alloy cladding in scenarios involving design basis accidents (DBA) and beyond design basis accidents (BDBA).