Effect of Si/Mo ratio on microstructure and high-temperature antioxidation property of SiC-MoSi₂ coating for carbon/carbon composites

The SiC-MoSi₂ antioxidation coating for carbon/carbon composite surface was prepared by two-step embedding method. The effects of Si/Mo ratio in embedded powders on the microstructure and high-temperature antioxidation property of the composite coating were investigated by means of XRD, SEM and isothermal oxidation test. The results show that with the decrease of Si/Mo ratio, the thickness and compactness of the coating first increase, then decrease. The prepared composite coating is of certain thickness, compact structure and higher content of MoSi₂ when the mass ratio of Si to Mo is 6:1. The composite coating has excelletion antioxidation property and thermal-shock resistance. After oxidized for 87.3 h at 1500°C and treated from 1500°C to room temperature for 9 times, C/C samples with the coating has only 3.22% weight loss. The main reason of coating failure is the formation of some penetration cracks after long-time oxidation.