Enhancing oxygen-blocking properties of HfB2-MoSi2-SiC coating by CeO2 modification

Abstract

To alleviate the destructive alteration of the glass layer surface caused by gas evolution during the oxygen-blocking process of the HfB₂-MoSi₂-SiC coating, CeO₂ was incorporated to modify HfB₂-MoSi₂-SiC coating, and the anti-oxidation mechanism at 1700°C in air was investigated. Compared with the unmodified HfB₂-MoSi₂-SiC coating, the addition of the refractory CeO₂ to the Hf-B-Si-O system leads to the formation of a stable Hf-Ce-B-Si-O complex phase glass, which substantially enhances the viscosity, stability, and self-healing sealing properties of the glass layer. The introduction of 0.75 vol.% CeO₂ significantly lowers the oxidative activity of the HfB₂-MoSi₂-SiC coating, boosting its average protective efficiency to 99.96% and reducing the maximal oxygen permeability by 43.48%, thus exhibiting superior oxygen-blocking performance. However, excessive addition of CeO₂ leads to an overabundance of oxygen release through its distinctive oxygen vacancy mechanism, which accelerates the formation of Hf-oxides, resulting in excessive viscosity on the coating surface and leaving oxidation defects unrepaired.