A novel gradient CrSi2-ZrSi2-SiC-Si coating for long-term oxidation protection of C/C composites at 1773 K

A novel gradient CrSi2-ZrSi2-SiC-Si coating for carbon/carbon (C/C) composites was prepared by optimized preoxidation and two-step pack cementation (PC) process. The microstructure and oxidation behavior of the coating were investigated in comparison to SiC-Si coatings. The results showed that the composite coating is mainly composed of CrSi2, ZrSi2, SiC and Si phases with a certain composition gradient, but no sharp interface. The coated specimens had a 4.83 mg/cm2 weight gain at 1773 K oxidation for 604 h, providing better oxidation resistance than the SiC-Si coated specimens (9.3 mg/cm2, 225 h). Its excellent performance was mainly attributed to the formation of glass and crystalline phases such as SiO2, ZrO2, Cr2O3 and ZrSiO4, which provided better oxygen barrier ability and structural stability than the single SiO2 glass. In addition, the maximum weight gain and steady-state linear weight loss rate of the coating during the oxidation process were related to long-term antioxidation performance.