HfSi2-HfB2-SiC coating prepared at low temperature to protect SiC-coated C/C composites against oxidation at 1473–1973 K

To improve the oxidation resistance of carbon/carbon (C/C) composites in 1473–1973 K, a HfSi2-HfB2-SiC coating was prepared on the surface of SiC-coated C/C composites by a combined method of slurry dipping and oxidation sintering at low temperature (below 1473 K). The Hf-Si-O multiphase layer generated by the oxidation of the coating acted as oxygen barriers at 1473–1973 K in air. The in-situ formed HfSiO4 particles enhanced the thermal stability of the SiO2 glass, terminated propagation of the crack, and relieved CTE mismatch between the inner and outer coating. Besides, B2O3 filled pores in the early stage of oxidation and then SiO2 took the place of the B2O3 as a new filler with the increase time of oxidation. As a result, the coating can protect C/C composites for 516 h at 1473 K, 744 h at 1773 K, and 64 h at 1973 K with a mass gain of 0.63 wt%, 1.41 wt% and −1.91 wt%, respectively.