Microstructure and ablation properties of zirconium carbide doped carbon/carbon composites

Carbon/carbon composites doped with zirconium carbide were prepared by a three-step process. Carbon fiber felts were first immersed in a zirconium oxychloride solution, followed by rapid densification using thermal gradient chemical vapor infiltration. The densified carbon/carbon composites were then graphitized at 2500 °C. The phase composition and morphology of the composites were investigated by X-ray diffraction and scanning electron microscopy. The ablation properties were tested in an oxyacetylene torch. The results show that the linear and mass ablation rates of the composites after doping with 4.14 wt.% zirconium carbide decreased by 83.0% and 77.0%, respectively. The ablated surface of the carbon matrix for pure carbon/carbon composites was very smooth and glossy, while that for doped carbon/carbon composites was honeycombed and dim. The bonding between carbon fibers and matrix decreased because of the formation of more zirconium dioxide, resulting in carbon fibers peeling off the matrix and the ablation resistance of carbon fibers could not be brought into play when the zirconium carbide contents achieved 4.14 wt.%. Although mechanical denudation does not seem to play a dominant role, the ablation was mainly controlled by heterogeneous mass transfer.