The improvement in oxidation resistance of carbon by a graded SiC/SiO2 coating

A dense functionally gradient SiC/SiO₂ coating has been developed to improve the oxidation resistance of carbon at elevated temperatures. SiC was coated on the surface of a graphite substrate by a reaction between thermally evaporated silicon and carbon at 1400 °C. The SiO₂ layer was deposited by exposing the SiC coated specimens next to a bed of Si powder in a flowing H₂–H₂O gas (P_H2O=2.6×10^?2 atm) at 1400 °C. The formed SiC/SiO₂ layers were dense and had gradient compositions with good adhesion to the carbon substrate. However, as the coating thickness increased, the coating layer became cracked and delaminated from the substrate due to thermal stress. The specimens with the continuous SiC/SiO₂ layer showed a remarkably improved oxidation resistance up to 1200 °C.