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

本文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年买了一台个人电脑。结果和成果总结如下：(1)在空气和氩气条件下进行了蠕变试验，研究了氧化对蠕变变形和损伤的影响。在蠕变氧化试验前和试验过程中，利用SEM和EPMA观察了纤维、基体和纤维与基体界面的微观结构，并测量了元素的分布。在蠕变试验中采用部分卸载技术测量杨氏模量，这是一种间接检测损伤的方法。(2)评价了三种提高抗氧化性能的方法。结果表明，在基体中添加玻璃微粒和在表面进行玻璃修复可以有效地改善材料的高温氧化和蠕变性能。发现了在基体中加入玻璃状颗粒对蠕变裂纹扩展的影响。然而，这两种方法在中等温度下都不有效。(3)对界面相进行改性，例如用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)高温下纤维微观结构的稳定性对纤维的蠕变性能也有重要影响。这就是为什么如果玻璃密封表面没有严重氧化，复合材料在氩气中的抗蠕变性能低于空气中的抗蠕变性能。(5)根据实验结果和理论分析，提出了一种蠕变氧化寿命预测方法，并指出了如何提高抗氧化能力。(6)本项目的研究成果在会议、期刊上发表。几篇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.