C/C复合材料ZrB_2-SiC基陶瓷涂层的微观结构及氧化机理

Microstructure and oxidation mechanism of ZrB_2-SiC ceramic coating on C/C composite material

为提高C/C复合材料在高温富氧环境中的抗氧化性能,采用两步刷涂+化学气相沉积法在C/C复合材料表面制备含Si_3N_4、MoSi_2、TaC等添加剂的ZrB_2-SiC基多层复合陶瓷涂层。利用XRD和SEM等分析测试手段研究涂层的物相组成和微观结构,并分析讨论涂层在900和1500℃的等温抗氧化机理。结果表明:利用两步刷涂+化学气相沉积法制备的ZrB_2-SiC基复合陶瓷涂层整体厚度约为200μm。Si3N4、MoSi_2可很好地促进ZrB_2-SiC基氧阻挡层的高温烧结,使涂层致密化,并提高涂层在900℃的抗氧化性能;与之相比,TaC则不能很好地发挥致密化作用,对涂层在900℃时抗氧化性能的提高有限。在900℃时,ZrB_2-SiC基陶瓷涂层的氧化过程主要受氧在涂层孔隙等缺陷中的扩散所控制,添加剂主要通过改变涂层的致密化程度来影响涂层的抗氧化性能。在1500℃氧化过程中,涂层抗氧化性能恶化,但致密的化学气相沉积SiC封填层的引入可显著改善涂层在1500℃时的抗氧化性能,涂层表面生成了完整的含有ZrO_2和ZrSiO_4等高熔点颗粒的SiO_2玻璃态氧化膜,为基体提供有效的氧化防护。

To improve the anti-oxidation performance of C/C composites under high temperature and oxygen enriched environment,ZrB_2-SiC based ceramic coatings with Si_3N_4,MoSi_2 and TaC addition were prepared by two-step slurry painting+chemical vapor deposition(CVD).Phase composition and microstructure of the as-prepared coating were investigated by using X-ray diffractometry and scan electron microscopy,and the isothermal anti-oxidation mechanism at 900 ℃ and 1500 ℃ were also analyzed and discussed.The conclusions are as follows,the thickness of the as-prepared ZrB_2-SiC based composite ceramic coating is about 200 μm.The densification and the anti-oxidation properties of the coating can be improved by the addition of Si_3N_4 and Mo Si_2,effectively.While the anti-oxidation properties of the coating can not be improved by the addition of Ta C effectively at 900 ℃.At 900 ℃,the oxidation process of ZrB_2-SiC ceramic coating was mainly controlled by the diffusion of oxygen in pore and other defects in the coating.The anti-oxidation property of coating can be improved by the addition by affecting the density of coating.In the oxidation process of 1500 ℃,the oxidation resistance of the coating decreases.The introduction of the compact structure of CVD SiC sealing layer can improve the oxidation resistance significantly.At 1500 ℃,in oxidation process,SiO_2 glassy oxide film with Zr O_2 and ZrSiO_4 on the coating is generated,this can provide effective oxidation protection for the substrate.