Ultrahigh temperature ceramic HfB2-SiC coating by liquid phase sintering method to protect carbon materials from oxidation

To investigate the anti-oxidation modification behaviors and mechanisms of the pure HfB2 phase in dynamic aerobic environment, HfB2-SiC coating was prepared through liquid phase sintering method. The average particle size of the synthetic pure phase HfB2 powders is about 335 nm. The TG curve of pure HfB2 powders exhibits excellent anti-oxidation modification ability for Si-based coating. After the modification of HfB2 phase, the anti-oxidation ability of SiC coating achieved prominent improvement. The initiative mass loss temperature of SiC coating lagged by 41.8%, while the percentage of mass loss and rate in fastest mass-loss zone of the SiC coating lagged by 57.6% and 33.3%, respectively. The generated B2O3 is responsible for the obviously improved oxidation resistance below 1200 °C. It compensates the oxidation protection weaknesses of the Si-based ceramic coating in this temperature region. With the fluid of the SiO2 glass layer, the dispersed Hf-oxides were inlaid in it to form the compound Hf-O-Si glass layer. The Hf-oxides heterogeneous phases with ultra-high melting temperature are able to improve the stability of the SiO2 glass layer at ultra-high temperature. It improves the ability of microcracks restriction and reduces the erosion of oxygen to the carbon matrix.