Formation of a functionally gradient (Si3N4+SiC)/C layer for the oxidation protection of carbon–carbon composites Original Research Article

Silicon infiltration has been used to form a functionally gradient layer on two-dimensional carbon–carbon (2D-C/C) composites. 2D-C/C composites were infiltrated with silicon at temperatures above the melting point of silicon in a NH3-containing atmosphere. Some of silicon-infiltrated C/C composites were then coated with a CVD–SiC coating. Electron probe microscopic analysis, X-ray diffraction and secondary ion mass spectroscopy were employed to characterize the surface layer derived by silicon infiltration. Isothermal and cyclic oxidation tests on the C/C composites were carried out at temperatures up to 1550°C in air. A functionally gradient (Si3N4+SiC)/C layer was formed in the surface region of the C/C composites. Combined with an outer CVD–SiC coating, this composition-graded layer could provide excellent oxidation resistance for C/C composites.