Exploring the multi-scale evolution mechanism of the ultra-high-temperature mechanical behaviour of carbon/carbon composites

The microstructure and mechanical properties of Carbon/Carbon (C/C) composites were investigated after ultra-high-temperature heat treatment (HTT) in the range of 30 – 2950 °C. The evolutionary mechanisms of the mechanical behaviour were explained at three scales: graphene sheets, carbon fibre (CF) monofilaments and the C/C composites. The results displayed that the tensile strength of CF monofilaments decreases monotonically as the HTT increases, while C/C composites present a tendency to decrease and then increase, demonstrating that CF/matrix interfacial properties play a decisive role in the tensile properties. Obvious microstructure change of C/C composites after HTT at 2700 °C was observed, meanwhile the high temperature tensile strength (measured at 2000 °C and 2500 °C) for the composites treated at temperature beyond 2600 °C was higher than that of room temperature. The high-temperature mechanical properties of C/C composites were regulated by the competing mechanisms of the graphite crystallite structure and the skin-core structure of CF monofilament, the CF/matrix interfacial strength and the porosity of C/C composites.