Preparation and ablation properties of ZrB2-SiC protective laminae for carbon/carbon composites

In order to improve ablation resistance of carbon/carbon composites, ZrB2-SiC protective laminae were prepared on carbon/carbon composites by a novel processing approach combining pressing, pyrolysis and reactive silicon infiltration. The outer layer of the as-prepared lamina was homogeneously distributed by ZrB2 and SiC; the inner layer contained ZrB2 particles adhered by resin-derived carbon. In oxyacetylene flame tests at 2500 °C for 30 s, carbon/carbon composites were fully protected by ZrB2-SiC laminae without being ablated. The ablation resistance could be optimized by adjusting the C/Zr ratio in the lamina. The linear ablation rate and the mass ablation rate of the specimen with the C/Zr ratio of 0.4:1 were respectively −8.0 μm/s and 1.3 mg/s, the latter of which was merely 45% of that of carbon/carbon composite. After ablation, along the cross-section of the specimen, a coherent ZrO2 scale, a porous ZrO2 layer and a ZrB2 (SiC-deplete) layer formed from the outside to the inside above the unreacted structure. The oxygen diffusion was significantly reduced in the ZrB2 layer. The porous ZrO2 layer led to the negative linear ablation rate. The coherent ZrO2 layer seemed to play a vital role in improving the ablation resistance of the lamina.