Deposition Rate, Texture, and Mechanical Properties of SiC Coatings Produced by Chemical Vapor Deposition at Different Temperatures

Silicon carbide (SiC) coatings were produced on carbon/carbon (C/C) composites substrates using chemical vapor deposition (CVD) at different temperatures (1100 degrees C, 1200 degrees C, and 1300 degrees C). The deposition rate was found to increase with deposition temperature from 1100 degrees C to 1200 degrees C. From 1200 degrees C to 1300 degrees C, the deposition rate decreased. SiC coating produced at 1200 degrees C exhibited a strong (111) texture compared with the coatings produced at other temperatures. Both hardness and Young's modulus were also found to be higher in the coating produced at 1200 degrees C. The variation in mechanical properties with the increase in temperature from 1100 degrees C to 1300 degrees C showed a direct correlation with the change in deposition rate and (111) texture. Microstructure analysis shows that the change in CVD temperature leads to the change in grain size, crystallinity, and density of stacking faults of SiC coatings, which appears to have no significant effect on mechanical properties of SiC compared with the texture observed in SiC coating. For the coating deposited at 1200 degrees C, both the hardness and Young's modulus increased gradually from the substrate/coating interface to the top surface. The nonuniformity of mechanical properties along the cross-section of the coating is attributed to the nonuniform microstructure.