A SiC/Mo(Six, Al1-x)₂ oxidation-resistant coating for carbon/carbon composites

SiC/Mo(Six, Al1-x)₂ multilayer coatings were prepared on carbon/carbon (C/C) composites using a multi-phase reaction technique to improve their high temperature oxidation resistance. The microstructure and phase compositions of the multilayer coatings were investigated by SEM, XRD and EDS. The coating exhibits a binary-layer microstructure, i.e. an outer Mo(Six, Al1-x)₂ layer and an inner SiC layer with a small amount of Mo_4.8Si₃C_0.6. The oxidation behavior of the coated C/C composites was evaluated in a supersonic flow of about 1500m·s^-1 at 1800K in a wind tunnel. No destruction of the coated C/C composites was found after 4s oxidation after 24 exposures and thermal cycling between room temperature and 2550K for 24 times in air. The excellent oxidation resistance and thermal shock resistance are attributed to a high cohesion between the layers and the C/C composite, and the formation of a continuous and stable glassy film consisting of SiO₂ and Al₂O₃ on the coated layers during oxidation.