Effect of Mo/Si Ratio on the Microstructure and Oxidation Resistance of Si-Mo Coating for C/C Composites

Oxidation protective Si-Mo coatings were prepared by pack cementation on the surface of C/SiC coated carbon/carbon composites. The influences of Mo/Si mass ratio in the pack powders on the microstructure and oxidation resistance of the coating were investigated. It showed that with the Mo/Si ratio increasing from 0.1 to 0.4, the MoSi2 proportion and the dimension of cracks in the coating increased, and the oxidation protective ability of the coated specimens firstly increased and then decreased. The coating with the Mo/Si of 0.2 exhibited better oxidation protective ability because of its more suitable MoSi2 proportion and excellent microstructure than those with the Mo/Si of 0.1, 0.3 and 0.4, which could effectively protect C/C composites from oxidation at 1773 K in air for more than 100 h. The mass loss of the coated samples was primarily due to the reaction between C/C matrix and oxygen diffusing through the penetration cracks in the coating.