Complete recovery of high temperature oxidation resistance in carbon fiber reinforced SiC composites by a recoating repair methodology

The current work reports on the oxidation behavior and residual flexural strength of carbon fiber-reinforced silicon carbide composites (C/SiC) after induction of thermal crack damage by heat treatment (HT) at 1900 °C and the effect, therein, of a repair process involving recoating by SiC. As-prepared, heat-treated and heat-treated/recoated specimens, were subjected to static oxidation tests in air at a temperature range of 500-1500 °C for 10 h and then tested in three-point bending. It was found that composite weight of heat-treated samples decreased dramatically with increasing oxidation temperature with weight loss values of ~30% being systematically observed for oxidation temperatures above 800 °C. On the other hand, as-prepared and heat-treated/SiC-recoated specimens reached almost their original weight after oxidation. The residual flexural strength of C/SiC composites with thermally-induced crack damage decreased significantly compared to as-prepared specimens, while SiC recoating was found to efficiently enable strength enhancement. Microstructural analysis showed that HT was associated with increased population and dimensions of micro-cracks on the C/SiC surface while SiC recoating enabled repair of HT-induced thermal crack damage hence leading to oxidation resistance recovery of the material.