Roles of modified additives in the repair of damaged SiC-ZrB₂/SiC coating of carbon/carbon composites

Damaged SiC-ZrB₂/SiC (SZS) coatings of carbon/carbon (C/C) composites were repaired using polysiloxane (PSO)-based repair agents. SiC-ZrB₂ powder was used as an inert filler, and Al₂O₃ and isopropyl alcohol (IPA) were introduced as modified additives. The effects of each component of the repair agents on the chemical composition, microstructure, and oxidation behavior of the repaired coatings were investigated, and the repair mechanism was clarified. The repaired area was dense and smooth, showed good compatibility with the original coating, and remained intact after oxidation at 1500 ℃ for 360 min. The addition of Al₂O₃ promoted the pyrolysis of PSO and formation of β-SiC, which was beneficial to the densification and oxidation resistance of the repaired coatings. The introduction of IPA improved the fluidity of the repair agents, and the repair agents infiltrated the coated C/C composites through the micropores on the damaged surface under capillary action, thereby enhancing the interfacial bonding strength. The weight loss of the damaged coating after oxidation decreased from 21.16 % to 0.48 % after repair. This work offers an approach for optimizing the repair of Si-based ceramic coatings.