Microstructure evolution of SiC-ZrB2-ZrC coating on C/C composites at 1773Â K under different oxygen partial pressures

The oxidation behavior of SiC-ZrB2-ZrC coating on C/C composites was investigated, basing on the microstructure evolution of oxide scale under different oxygen partial pressures at 1773 K. Similar experiments were conducted in SiC coatings, ZrB2 and ZrC ceramic sheets for comparison. The multiphase coating showed the better oxidation resistance at a higher oxygen partial pressure, and its mass change was 1.34% after isothermal oxidation for 6 h at an oxygen partial pressure of 80,000 Pa. With the increase of the oxygen partial pressure, ZrO2 particles with fibrous denticles were replaced by the aggregations of ZrO2 particles and more SiO2 glass was formed in a short time. The formed SiO2 glass could effectively heal the microcracks of oxide scale. Moreover, the ZrB2 and ZrC phases played an important role in deflecting cracks and restraining the propagation of cracks during oxidation. As the oxygen partial pressure increased, the oxide scale of SiC-ZrB2-ZrC coating became denser, presenting a two-layered structure composed of a SiO2 layer and a Si-O-Zr layer at the elevated oxygen partial pressure.