CVD-SiC涂层封孔处理后C/C-ZrC-SiC复合材料的烧蚀行为

Ablation behavior of C/C-ZrC-SiC composites after surface sealing by CVD-SiC coating

为提高聚合物浸渍裂解法制备的C/C-ZrC-SiC复合材料的抗烧蚀性能,采用化学气相沉积(CVD)技术对材料进行了SiC涂层表面封孔处理,并考察材料在氧乙炔环境中的烧蚀行为,明确CVD-SiC涂层对材料的抗烧蚀性能的作用。研究结果表明,CVD-SiC涂层封孔处理后材料表现出优异的抗烧蚀性能,烧蚀240 s后,其线烧蚀率仅为0.94×10-3mm/s,较无涂层材料的降低了39.4%。在烧蚀过程中,中心区域涂层及基体材料的演变过程如下:SiO_2膜包覆ZrO_2结构的形成→SiO_2膜失效→基体中Zr C和SiC的氧化→ZrO_2致密保护层的形成。SiC涂层对材料烧蚀性能的贡献主要体现在以下两方面:烧蚀中心区域的SiC涂层被氧化成SiO_2,其蒸发带走大量的热流,降低了材料的烧蚀温度;此外,SiC涂层的存在有效减少了材料内部的氧化及裂纹的形成。

In order to improve ablation resistance of C/C-ZrC-SiC composites prepared by precursor infiltration and pyrolysis process,chemical vapor deposition (CVD)was used to fabricate SiC coating on this composites for surface sealing.The ablation behavior of the sealed composites under an oxyacetylene torch was investigated.The results show that the composites sealed with CVDSiC coating exhibit excellent ablation resistance after ablation for 240 s,with linear ablation rate of 0.94×10^-3mm/s,which is reduced by about 39.4% than that of the composites without surface sealing.During ablation,it starts from the formation of SiO2 layer with ZrO2 particles,and then Si02 layer failure ,followed by oxidation of ZrC and SiC in the substrate and forming dense ZrO2 scale. The contributions of SiC coating to the ablation resistance of the composites can be divided into two parts.First,the SiC coating in ablation center is oxidized to SiO2 which would evaporate heavily during ablation process,and it takes away a large amount of heat, resulting in a lower ablation temperature.Second,the existence of SiC coating can reduce the oxidation of inner materials and the formation of cracks.