Improbement of Oxidation Resistance and Its mechanisms in Fiber Reinforced Ceramic Matrix Composites

利用宏观和微观实验技术和分析方法，研究了碳化硅/碳化硅复合材料的蠕变和氧化行为。为了处理和分析实验数据，2000年购买了一台个人电脑。主要研究结果和成果如下：(1)在空气和Ar气氛中进行蠕变试验，研究氧化对蠕变变形和损伤的影响。利用扫描电子显微镜和电子探针对蠕变氧化前和蠕变氧化过程中纤维、基体以及纤维与基体界面的显微组织和元素分布进行了观察和测量。在蠕变试验中，采用了部分卸载技术来测量杨氏模量，这是一种间接检测损伤的方法。(2)对三种提高抗氧化性的方法进行了评价。结果表明，在基体中添加玻璃颗粒和表面玻璃修复是改善高温氧化和蠕变性能的有效方法。发现了添加玻璃颗粒对蠕变裂纹扩展的影响。界面相的改性，如用BN代替碳涂层是一种很好的方法，但BN仍不是很有前途的纤维涂层材料。(4)发现高温下纤维微观结构的稳定性对蠕变性能也有重要影响。在实验和理论分析的基础上，提出了一种蠕变-氧化寿命预测方法，并指出了提高其抗氧化性的途径。(6)本课题的研究成果已发表在学术会议和期刊上。一些论文将在不久的将来发表在期刊上。

Creep and oxidation behavior of SiC/SiC composites were studied using macroscopic and microscopic experimental techniques and analysis methods in the past two years. To treat and analyze experimental data, a personal computer was bought in 2000. The results and achievements are summarized as follows.(1) Creep tests were carried out in both air and argon to study the effects of oxidation on creep deformation and damage. SEM and EPMA were used to observe microstructures and measure element distribution in fiber, matrix and interfaces between fiber and matrix before and during creep-oxidation tests. The partial unloading technique was used to measure Young's modulus during creep tests, which is a indirect detection method for damage.(2) Three methods for improving oxidation resistance were evaluated. It was found that the addition of glassy particulates in the matrix and glass-healing on surfaces are effective for improbement of oxidation and creep properties at high temperatures. The effects of the addition of glassy particulates in the matrix on creep crack growth were found. However, both of them were not effective at intermediate temperatures.(3) The modification of interphase, e. g., using BN to replace carbon coating, is a good method, but BN is still not promising coating materials for fibers.(4) It was found that stability of microstructure in fiber at high temperatures was also important on creep properties. This is why creep resistance of the composite in argon is lower than that in air if there is no severe oxidation on surfaces by glass-sealing.(5) Based on experimental results and theoretical analysis, a method was proposed for life prediction at creep-oxidation and how to improve oxidation resistance was pointed out.(6) The research results of this project were published on conferences and joumals. A few papers will be published in journals in the near future.