Improved mechanical strength and oxidation resistance of SiC/SiC-MoSi₂-ZrB₂ coated C/C composites by a novel strategy

To obtain silicon-based ceramic coated C/C composites with excellent mechanical and antioxidative properties, a SiC/SiC-MoSi₂-ZrB₂ composite ceramic coating was designed and prepared on the surface of C/C composites by a three-step process. Firstly, a pyrolytic carbon (PyC) layer was deposited on the C/C substrate to fill its holes and cracks. Secondly, a SiC porous layer was fabricated on the PyC layer to create many holes subsequently used to distribute massive MoSi₂-ZrB₂ ceramics. Finally, a double-layer SiC/SiC-MoSi₂-ZrB₂ composite ceramic coating was formed on C/C composites after a pack cementation (PC) process, which consisted of a dense SiC inner coating (a thickness of ~ 80 µm) and a uniform and rich MoSi₂-ZrB₂ outer coating (~ 200 µm). The bending strength of the SiC/SiC-MoSi₂-ZrB₂ coated C/C sample was 21.5 % higher than that of the raw C/C sample. Moreover, the SiC/SiC-MoSi₂-ZrB₂ coating provided good oxidation protection for C/C composites at high temperature, and its mass loss was only 0.56 % after oxidation for 305 h at 1773 K in air due to the blocking effect of the compound oxide glass (SiO₂, ZrO₂ and ZrSiO₄) layer on oxygen diffusion into the internal coating and C/C substrate. Therefore, this novel strategy for coating preparation can obtain SiC/SiC-MoSi₂-ZrB₂ coated C/C composites with excellent mechanical and oxidation resistance properties.