Impact of High Temperature and Water Vapor on the Oxidation Behavior of Chemical Vapor Infiltration-SiCf/SiC Composite

SiCf/SiC composites are replacing superalloy components in hot sections of gas turbines. The high-velocity combustion gases in gas turbine hot sections contain water vapor. The mechanism of oxidative water vapor attack on SiC is vastly different from that of oxidation in static dry air. Therefore, it is of paramount importance to study the oxidation of these composites in high-velocity combustion environments. This study focuses on the high-temperature oxidation behavior of SiCf/SiC composites with a BN interfacial coating in both static air and combustion environments. The composite was prepared by the chemical vapor infiltration process (CVI). To elucidate the impact of water vapor in a combustion environment, an oxyacetylene flame apparatus was used. Oxidation of the SiCf/SiC composite was investigated at 1200, 1300 and 1400 degrees C, for up to 100 h in static dry air, and for up to 24 h in a combustion environment. The microstructure evolution and recession of the composite under combustion environment were investigated by scanning electron microscopy. The oxidation kinetics of the SiCf/SiC composite showed a parabolic nature in static air; however, in the combustion environment the composite showed accelerated mass loss owing to the concurrent effects of oxidation and recession.