Microstructural characterization of non-equilibrated 4D carbon/carbon composites in ultrahigh temperature environment

A comparative study has been carried out on microstructure, ultrahigh temperature tensile properties, and erosion behavior of non-equilibrated four-directional reinforced carbon/carbon composites, prepared using polyacrylonitrile based carbon fibers as the reinforcement and coal-tar pitch as the matrix, to assess the effect of microstructural changes on the properties of the composites in an ultrahigh temperature environment. X-ray diffraction and scanning electron microscopic analyses suggest that the carbon matrix is highly graphitized, which is composed of mosaic and domain structures. The composites retain superior tensile properties with a visco-plastic behavior at ultrahigh temperature, which is consistent with the observation of mixed microstructural changes, crack propagation, and deflection as well as fiber debonding. The ablation behavior of non-equilibrated four-directional reinforced carbon/carbon composites is mainly dominated by thermo-chemical ablation and mechanical erosion, and different microstructures exhibit distinguished erosion mechanisms.