Abstract: SiC f/SiC composite material with low density , stability at elevated temperature , oxidation resistance , high corrosion resistance and other characteristics , has huge potential in use of the space and structure of aero engine components and nuclear fusion reactor first wall structure .At present , limited by process conditions , the atom ratio of C to Si is more than 1.3, and there are pore and defects in the SiC f/SiC composite .So that it can't meet the service requirements of high temperature oxidation environment . In this paper, a graded coating with a high purity , low defect, high temperature resistant , anti-oxidation, low hypoxia diffusion coefficient and good matching with substrate , had been prepared by chemical vapor deposition ( CVD) on the surface of SiC/SiC composite material .And SEM was used to observe the microstructure of coating and the binding properties on coating and SiC /SiC substrate .XRD was used to characterize the component of the gradient coating and the changes of component when the coating was oxidized.And then the gradient coating anti-oxidant mechanism was discussed .

Key words: SiC f/SiC composite material with low density , stability at elevated temperature , oxidation resistance , high corrosion resistance and other characteristics , has huge potential in use of the space and structure of aero engine components and nuclear fusion reactor first wall structure .At present , limited by process conditions , the atom ratio of C to Si is more than 1.3, and there are pore and defects in the SiC f/SiC composite .So that it can't meet the service requirements of high temperature oxidation environment . In this paper, a graded coating with a high purity , low defect, high temperature resistant , anti-oxidation, low hypoxia diffusion coefficient and good matching with substrate , had been prepared by chemical vapor deposition ( CVD) on the surface of SiC/SiC composite material .And SEM was used to observe the microstructure of coating and the binding properties on coating and SiC /SiC substrate .XRD was used to characterize the component of the gradient coating and the changes of component when the coating was oxidized.And then the gradient coating anti-oxidant mechanism was discussed .