Oxidation-induced microstructural changes of a polymer-derived Nextel™ 610 ceramic composite and impact on the mechanical performance

This study analyses the effects of heat treatments in oxidative atmosphere on the mechanical and microstructural properties of a fiber-reinforced weak interface composite (UMOX™) which is composed of a mullite-SiOC matrix and Nextel™ 610 fibers with fugitive coatings. Composites of different porosity grades, depending on the polymer infiltration and pyrolysis cycle, are exposed to 1000 and 1200 °C for 50 h. The exposure provokes the formation of silica, which leads to matrix densification and the formation of silica bridges at the fiber–matrix interface, resulting in an increased interfacial bonding strength. Consequently, the fracture toughness and the flexural strength are significantly reduced. The study confirms that SiOC-based materials are suitable for an application at high temperatures in oxygen-rich atmospheres up to 1000 °C. It is, however, important to consider the microstructural changes and thereby induced decrease of the overall mechanical performance during a high-temperature use.