Improving repair performance for damaged C/C composites via heat-treatment temperature optimization and surface pretreatment

A Ni-based solder BNi-5 was adopted as the repair agent to repair the prefabricated defects on the carbon/carbon (C/C) composites. The effects of different heat-treatment (HT) temperatures and pre-oxidation on the chemical composition, microstructure, and mechanical behavior of the repaired C/C composites were investigated, and the repair mechanism was studied by finite element analysis methods. The repair agent and C/C composites were tightly bonded through mechanical interlocking and chemical reactions, and the flexural properties of the damaged C/C composites were significantly improved after repair. The products at the interface formed a gradient distribution structure of the thermal expansion coefficient when the HT temperature was 1300 °C, which is beneficial to relieve the residual thermal stress at the interface. Meanwhile, the porosity of the surface of the C/C composites was higher after pre-oxidation, which led to more diffusion channels for the repair agent and enhanced the interface bonding ability. The flexural strength was the highest with a recovery rate of 85.2% when the C/C composites were pre-oxidized at 600 °C and the HT temperature was 1300 °C. This work provides a strategy for the engineering application of the damage repair of C/C composites.