Microstructural evolutions of three-dimensional carbon–carbon composite materials irradiated by carbon ions at elevated temperatures

Carbon–carbon composites are deemed as candidate materials for applications in very high temperature reactors (VHTRs). In a VHTR, carbon–carbon composite materials would experience severe environmental impacts of both a high radiation fluence (about 3 × 10¹⁶/cm² per year) and high temperatures (～1200 °C), and radiation damage is accordingly expected. In this study, samples prepared from a three-dimensional pitch-based carbon–carbon composite material were irradiated with a 4 MeV C²⁺ ion beam emitted by an accelerator to deliberately induce various levels of radiation damage on the samples at 1000 °C. Transmission electron microscopy analyses were then conducted to examine the evolution of microstructures in the samples, and a scanning electron microscope was used to examine the changes in surface morphology. It was found that an accumulated fluence of 7.0 × 10²¹/m² at 1000 °C resulted in cracks between the matrix and the fiber in the sample. These interfacial cracks were all parallel to the fiber orientation. The fiber/matrix bonding strength might play an important role in the mechanical property of the carbon–carbon composite material. In the meantime, cracks were also found at the fiber side of the sample irradiated under the same condition.