碳化硅抗氧化涂层的失效分析

THE FAILURE ANALYSIS OF OXIDATIONRESISTANT SiC COATING

用理论模型计算和实验测定的方法，研究了带有碳化硅涂层的炭纤维和２ＤＣ／Ｃ复合材料的抗氧化性能。结果表明涂层炭纤维的氧化，实验值高于模型计算值，并且纤维越长，差值越大；说明纤维的氧化，不仅发生在暴露的纤维末端，而且因为涂层本身存在着缺陷，不能完全阻挡氧的输运，氧化也在纤维的径向同时发生。ＳＥＭ观察结果也证实了这一结论。对于Ｃ／Ｃ复合材料，实验中观察到了横向、纵向裂纹和孔洞三类不同的缺陷，涂层的失效同样是氧气通过材料表面缺陷的输运而造成的，穿过表面的氧首先使热解炭基体气化，继而引起基体整体的破坏。

The oxidation of PAN based carbon fibers with SiC coating was studied by experimental investigation and modeling computation. It was found that the experimental results diverged by about 20% from those predicted by modeling computation,indicating that the oxidation proceeds not only from the open ends,but also through defects of the SiC coating on the carbon fibers. SEM observation agreed to this implication. The oxidation test of SiC coated 2D C/C composite was also carried out. Three kinds of defects were observed on the surface,that is,voids and cracks parallel and perpendicular to the fiber axis,which may form during heat treatment cycles on preparation and application because of mismatch of thermal expansion coefficents between the coated SiC and carbon substrate. It was through these defects that oxygen transported and penetrated into the inner part of the composite,causing the gasification of pyrocarbon matrix first and then carbon fibers.