Oxidation protection and behavior of in-situ zirconium diboride-silicon carbide coating for carbon/carbon composites

To protect carbon/carbon (C/C) composites against oxidation, zirconium diboride-silicon carbide (ZrB2-SiC) coating was prepared by in-situ reaction using ZrC, B4C and Si as raw materials. The in-situ ZrB2-SiC coated C/C presented good oxidation resistance, whose weight loss was only 0.15% after isothermal oxidation at 1500 °C for 216 h. Microstructure evolution of coating at 1500 °C was studied, revealing a two-layered structure: (1) ZrO2 (ZrSiO4) embedded in SiO2-rich glass, and (2) unaffected ZrB2-SiC. The formation and collapse of bubbles influenced the coating oxidation greatly. A model based on the evolution of oxide scale was proposed to explain the failure mechanism of coating.