Effect of CVD ZrB2 coating thickness on anti-ablation performance of C/SiC composites

In this study, ZrB2 coatings with different thicknesses were prepared using chemical vapor deposition on SiC (similar to 100 mu m in thickness) coated C/SiC (SiC-C/SiC) composites, and the ablation behaviors were investigated using oxyacetylene torch tests for 20 s. SiC-C/SiC composites with ZrB2 coatings exhibited improved anti-ablation properties compared to uncoated composites, but anti-ablation properties first increased and then decreased with an increase in ZrB2 coating thickness. Composites with 10 mu m ZrB2 coating exhibited the best anti ablation properties, and linear and mass ablation rates were reduced by 38% and 61%, respectively, compared to uncoated composites. Anti-ablation properties of composites with thicker ZrB2 coatings decreased because of cracks and defects in coatings caused by residual thermal stress that resulted from differences in thermal expansion coefficients between the coating and substrate. During oxyacetylene torch tests, ZrB2 and SiC were oxidized to ZrO2 and SiO2 and formed four layers as thermal barriers that provided ablation protection for inner part and prevented it from being further ablated.