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 degrees C and 1000 degrees C, XRD results indicated that the coating was covered by product B2O3 or B2O3 center dot xSiO(2) 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 degrees 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 degrees C to 1000 degrees C for 600 min, but worse oxidation protection above 1000 degrees C due to the large amount of volatilization of B2O3 or B2O3 center dot xSiO(2). (c) 2007 Elsevier B.V. All rights reserved.