Oxidation and Mechanical Properties of SiC/SiC-MoSi₂-ZrB₂ Coating for Carbon/Carbon Composites

To improve oxidation resistance of carbon/carbon (C/C) composites, a SiC/SiC-MoSi₂-ZrB₂ double-layer ceramic coating was prepared on C/C composites by two-step pack cementation. The phase compositions and microstructures of as-prepared multilayer coating were characterized by X-ray diffraction and scanning electron microscopy. The oxidation resistance at 1773K and the effect of thermal shock between 1773K and room temperature on mechanical performance of coated specimens were investigated. The results show that the SiC/SiC-MoSi₂-ZrB₂ coating exhibits dense structure and is composed of SiC, Si, MoSi₂ and ZrB₂. It can protect C/C composites from oxidation at 1773K for more than 510h with weight loss of 0.5%. The excellent anti-oxidation performance of the coating is due to the formation of SiO₂-ZrSiO₄ complex glassy film. The coating can also endure the thermal shocks between 1773K and room temperature for 20 times with residual flexural strength of 86.1%.