Ablation behavior of ZrB2–SiC protective coating for carbon/carbon composites

Ablation behavior of ZrB2–SiC protective coating for carbon/carbon composites during oxyacetylene flame test at 2500 °C was investigated by analyzing the microstructure differentiation caused by the increasing intensity of ablation from the border to the center of the surface. After ablation, a continuous SiO2 scale, a porous SiO2 layer inlaid with fine ZrO2 nuclei, and a continuous ZrO2 scale respectively emerged in the border region, the transitional region, and the center region. In order to investigate the ablation microstructure in the initial stage, the sub-layer microstructure was characterized and found to be mainly formed by coral-like structures of ZrO2, which showed huge difference with the continuous structure of ZrO2 on the surface layer. A kinetic model concerning the thickness change induced by volatilization and oxidation during ablation was built to explain the different growth mechanisms of the continuous ZrO2 scale and the coral-like ZrO2 structure.