Constructing self-healing ZrSi₂-MoSi₂ coating for C/C composites with enhanced oxidation protective ability

Cracks are fatal defects of ceramic coatings for carbon/carbon (C/C) composites, through which oxygen will severely destroy the substrate at ultra-high temperature environments. Therefore, the coating materials with rapid self-repairing ability should greatly improve their service stability. Here ZrSi₂-MoSi₂ coating was designed and fabricated by supersonic plasma spray on SiC coated C/C composites. Results show that it has narrower surface cracks and better self-healing ability at 1450 °C than pure MoSi₂ coating. Moreover, it efficiently protects C/C composites from oxidation for 42 h with a mass gain of 1.89% compared to MoSi₂ coating with a mass loss of 4.6% for 38 h at 1450 °C. The improvement of the self-healing ability and oxidation protective performance primarily owes to three reasons: 1) the preferential oxidation of ZrSi₂ to rapidly form ZrO₂/ZrSiO₄ particles to reduce the formation of cracks. 2) Low viscosity SiO₂ phase to completely heal the cracks. 3) Protective SiO₂ layer pinned by ZrO₂/ZrSiO₄ particles to restrain re-cracking during cooling.