Oxidation Behavior of C/SiC Composite with CVD SiC-B4C Coating in a Wet Oxygen Environment

A two-layered self healing coating with a B4C internal layer and a SiC external layer is prepared on C/SiC composite by chemical vapor deposition (CVD). Microstructure and component of the coating was analyzed by SEM, EDS, and XRD. Oxidation behavior of SiC-B4C coated C/SiC composite was compared with SiC-SiC coated C/SiC in an environment of $${{P_{{\text{H}}_{\text{2}} {\text{O}}} } \mathord{\left/ {\vphantom {{P_{{\text{H}}_{\text{2}} {\text{O}}} } {{{P_{{\text{O}}_{\text{2}} } } \mathord{\left/ {\vphantom {{P_{{\text{O}}_{\text{2}} } } {P_{{\text{Ar}}} }}} \right. \kern-\nulldelimiterspace} {P_{{\text{Ar}}} }}}}} \right. \kern-\nulldelimiterspace} {{{P_{{\text{O}}_{\text{2}} } } \mathord{\left/ {\vphantom {{P_{{\text{O}}_{\text{2}} } } {P_{{\text{Ar}}} }}} \right. \kern-\nulldelimiterspace} {P_{{\text{Ar}}} }}}} = {{14} \mathord{\left/ {\vphantom {{14} {{8 \mathord{\left/ {\vphantom {8 {78}}} \right. \kern-\nulldelimiterspace} {78}}}}} \right. \kern-\nulldelimiterspace} {{8 \mathord{\left/ {\vphantom {8 {78}}} \right. \kern-\nulldelimiterspace} {78}}}}$$ at 700°C, 1,000°C and 1,200°C for 100 h, respectively. It is demonstrated that the SiC-B4C coating is more efficient to protect the composite from oxidation than SiC-SiC coating below 1,000°C due to the self healing behavior. After oxidized at 700°C for 100 h, the residual flexural strength of SiC-B4C coated C/SiC is about 86%, and that of SiC-SiC coated is about 64%. While after oxidized at 1,200°C, the former is about 86% and the later is about 89%. This is due to the enhanced evaporation of B2O3 at higher temperature.