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

近两年来，采用宏观和微观实验技术及分析方法，对SiC/SiC复合材料的蠕变和氧化行为进行了研究。为了处理和分析实验数据，2000年购买了一台个人电脑。研究结果和成果总结如下。(1)在空气和氩气中进行蠕变试验，研究氧化对蠕变变形和损伤的影响。在蠕变-氧化试验前和蠕变-氧化试验过程中，采用SEM和EPMA观察了纤维、基体及纤维与基体界面的微观组织，并测量了元素分布。在蠕变试验中，采用部分卸载技术测量杨氏模量，这是一种间接的损伤检测方法。(2)评价了三种提高抗氧化性的方法。结果表明，在基体中加入玻璃态微粒和表面玻璃化愈合对改善合金的高温氧化和蠕变性能是有效的。在基体中加入玻璃颗粒对蠕变裂纹扩展有一定的影响，但在中温区两者都不起作用。(3)界面相的改变，e.例如，在一个实施例中，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)结果表明，高温下纤维内部微观结构的稳定性对蠕变性能也有重要影响。这就是为什么复合材料在氩气中的抗蠕变性低于在空气中，如果没有严重的氧化表面上的玻璃封接。(5)在试验结果和理论分析的基础上，提出了蠕变-氧化寿命预测的方法，并指出了提高抗氧化性能的途径。(6)该项目的研究成果发表在会议和期刊上。不久的将来，一些论文将在期刊上发表。

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.