SiC/HfB₂-based ceramic/SiC multilayer coating to protect C/C composites against oxidation at medium and high temperatures for long-life service

A dense SiC/HfB₂-based ceramic/SiC multilayer coating was designed on C/C composites by a combined technique of pack cementation, slurry brushing-pressureless reaction sintering and chemical vapor deposition. The coating can protect C/C composites against oxidation at 1473 K for 544 h, 1573 K for 597 h and 1773 K for 382 h. Such good performance was ascribed to the synergistic oxidation resistance of three layers. The cracks were healed by the borosilicate glass generated from the oxidation of HfB₂-based ceramic intermediate layer at medium temperatures, and covered by SiO₂ glass produced from the oxidation of SiC outer layer at high temperatures.