Microstructural Change in SiCf/SiC Composite in High-Temperature Atmosphere
Mitsutoshi OKADA and Tohru HISAMATSU
Abstract:In order to clarify the microstructural change of ceramic matrix composite (SiCf/SiC) which can influence the strength, chemical composition and crystal structure of ceramic fiber and matrix are examined by means of electric probe micro-analyzer (EPMA) and Raman spectrometer. Oxidation tests are carried out at the temperature of 1473K`1673K for 1000h in air. Little change in chemical composition is observed in ceramic fiber. Excess amount of carbon exists as disordered graphite in ceramic fiber, and it is found that the disorder proceeds as the test time increases according to R value, which is defined as the ratio of two carbon peaks in Raman Spectra. The crystallization of SiC in fiber is rarely observed in extent of the test. As for matrix, besides silicon and carbon, oxygen is contained even before the test in most of the matrix, while there is the other kind of matrix which contains relatively low amount of oxygen and large amount of carbon. It implies that the microstructure of matrix is not uniform. Inside the specimen, the chemical composition of matrix does not change due to the oxidation test. However, after the oxidation test, the content of oxygen increases and that of carbon decreases due to the oxidation at the vicinity of surface. Raman spectra show the crystallization of SiC in matrix after the oxidation test. And even in matrix, disordered graphite exists, and, according to R value, the disorder proceeds as the test temperature and time increase. Key Words:Ceramic matrix composites, Microstructural change, SiC fiber, Raman spectrometer, Crystallization, Graphite