Microstructure and oxidation behavior of SiOC coatings on C/C composites co-deposited with HMDS and TEOS by using CVD process

Silicon oxycarbide (SiOC) coatings were prepared through isothermal chemical vapor co-deposition by using two precursors of hexamethyldisilane (HMDS) and tetraethyl orthosilicate (TEOS). The microstructure, composition and the protectiveness on C/C composite against oxidation of the coatings prepared at temperatures ranging from 1423 K to 1563 K and pressures ranging from 500 Pa to 1200 Pa were investigated, respectively. After oxidation, cracks and defects were formed in the coatings of all conditions due to the volume shrinkage of amorphous SiO2 crystallization and the mismatch of thermal expansion coefficient (CTE) between SiOC coatings and substrate. The most oxidation-resistant SiOC coating was obtained at 1563 K and 500 Pa, which exhibited the lowest weight loss rate of 4.87 % after 12 h of oxidation at 1673 K in air condition.