In-situ formation of SiC, ZrB2-SiC and ZrB2-SiC-B4C-YAG coatings for high temperature oxidation protection of C/C composites

Si3N4, (ZrO2+ B4C + Si) and (ZrB2 + SiC + B4C + Y2O3 + Al2O3) were used as precursors for in-situ formation of SiC, ZrB2-SiC and ZrB2-SiC-B4C-YAG coatings respectively. The oxidation behavior of coated C/C composites was studied by cyclic oxidation in air at temperatures between 1500 degrees C and 1700 degrees C. The SiC coating exhibited the lowest weight loss at 1500 degrees C and 1600 degrees C. After initial mass loss for two cycles of oxidation at 1500 degrees C, the ZrB2-SiC coating was found to provide the best protection by the precipitated ZrO2 in SiO2 glass at 1700 degrees C. The ZrB2/SiC-B4C-YAG coating performed well at 1700 degrees C with the formation of a complex YAG glass containing ZrB2/ZrO2.