Oxidation protection of multilayer CVD SiC/B/SiC coatings for 3D C/SiC composite

A CVD boron coating was introduced between two CVD SiC coating layers. EDS and XRD results showed that the CVD B coating was a boron crystal without other impurity elements. SEM results indicated that the CVD B coating was a flake-like or column-like crystal with a compact cross-section. The crack width in the CVD SiC coating deposited on CVD B is smaller than that in a CVD SiC coating deposited on CVD SiC coating. After oxidation at 700 °C and 1000 °C, XRD results indicated that the coating was covered by product B₂O₃ or B₂O₃·xSiO₂ film. The cracks were sealed as observed by SEM. There was a large amount of flake-like material on hybrid coating surface after oxidation at 1300 °C. Oxidation weight loss and residual flexural strength results showed that hybrid SiC/B/SiC multilayer coating provided better oxidation protection for C/SiC composite than a three layer CVD SiC coating at temperatures from 700 °C to 1000 °C for 600 min, but worse oxidation protection above 1000 °C due to the large amount of volatilization of B₂O₃ or B₂O₃·xSiO₂.