Mechanism of defect formation and control of silicon carbide coating for carbon/carbon composites made by the pack cementation method

Silicon carbide (SiC) and modified silicon carbide coatings were produced by a pack cementation technique on surface of carbon/carbon (C/C) composites. The micro-structure of the as-received coating was investigated by a scanning electron microscope. The formation mechanism of coating defects and effect of modifier on microstructure of the SiC coating and the size of SiC particles are discussed as well. The results show that the size of the SiC particles on the modified coating is smaller and the coating is compacted. No micro-cracks appear on the surface of modified SiC coating, there are fewer pores in the cross section and the particles are smaller. Comparing with the no modifier coating, the anti-oxidation resistance of the modified SiC coating is greatly improved at 1773 K.