氧化铝含量对炭/炭复合材料表面碳化硅涂层结构和抗高温氧化性能的影响

Effect of Content of Alumina in Pack Cementated Material on Microstructure and High-Temperature Oxidation Resistance of Silicon Carbide Coating of Carbon/Carbon Composites

炭/炭(C/C)复合材料的抗高温氧化性能多依赖于其表面的碳化硅(SiC)涂层。为了弄清包埋料中氧化铝(Al2O3)的含量对SiC涂层性能及机理的影响,用包埋法在C/C表面制备了SiC涂层。通过X射线衍射(XRD)、扫描电镜(SEM)及高温抗氧化试验,研究了包埋料中Al2O3含量对SiC涂层的显微结构、缺陷(裂纹和孔洞)及抗氧化性能的影响,并从热力学角度探讨了Al2O3对涂层生长的促进机制。结果表明:随着包埋料中Al2O3含量的增加,SiC涂层厚度逐渐增大,其晶粒得到细化,抗氧化性能逐渐变好;过量的Al2O3使SiC涂层在生成过程中产生的CO气体逐渐增多,导致SiC涂层的裂纹和孔洞增多,涂层变得疏松,抗氧化性能逐渐恶化。

With a view to the strong dependence of high-temperature anti-oxidation performance of carbon/carbon(C/C) composites on surface SiC coating,SiC coating was prepared on the surface of C/C composites by pack cementation method.The microstructure and defects(particularly crack and hole) of resultant C/C composites coated with SiC coating were analyzed by X-ray diffraction and scanning electron microscopy;and their high-temperature anti-oxidation performance was evaluated as well.Furthermore,the effect of the content of Al2O3 in the pack cementated material on the microstructure and high-temperature anti-oxidation performance of the SiC coating was investigated,while the mechanism for Al2O3 to promote the growth of SiC coating was discussed based on thermodynamic theory.Results show that the thickness and anti-oxidation ability of the SiC coating rise with increasing content of Al2O3 in the pack cementated material,accompanied by refining of the grains therewith.However,in the presence of excessive Al2O3,the amount of CO gas generated during the formation of SiC coating tends to rise,which results in more cracks and holes in the SiC coating thereby decreasing its compactness and gradually worsening its high-temperature oxidation resistance.