Influence of a pre-coated pyrocarbon layer on the microstructure and mechanical properties of ZrC-doped C/C composites

A carbon fiber preform was pre-coated with a carbon layer (PyC) with different thicknesses by chemical vapor infiltration (CVI), then impregnated with a ZrOCl₂ ethanol solution, carbonized at 1 800 ℃ to form ZrC, densified by CVI to a density of 1.75 g/cm³ and graphitized at 2 300 ℃ to obtain ZrC-doped C/C composites. The microstructure and composition of the composites were analyzed by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The mechanical properties were studied by three-point bend tests. The influence of the PyC layer on the microstructure, ZrC distribution and mechanical properties was investigated. Results show that the average flexural strength is 256.85 MPa when the thickness of PyC layer is 1.5-1.7 μm, which is a 67.01% increase compared with the sample without the PyC layer. The cross sections of the composites after flexural failure show a brittle-fracture mode. The ablation resistance of the composites was slightly improved as a result of the PyC layer.