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3D3d, 3D4d, 3D5d-braided Cf/SiC composites were fabricated by precursor infiltration and pyrolysis (PIP) with polycarbosilane as the matrix precursor. The coefficient of thermal expansion (CTE) of C/SiC composites was measured in longitudinal and transversal directions in the temperature range from -150°C to 25°C. The longitudinal CTE varies in the range (0.09-0.68) × 10/°C, and the transversal CTE varies in the range (0.21-1.95) × 10/°C. Various CTEs of 3D-braided C/SiC composites were mainly determined by different braided structures of carbon fibers. The longitudinal CTE is lower than transversal CTE for the negative axial expansion of carbon fibers at cryogenic temperature. Microcracks were examined to understand the effect of structure on the thermal expansion of composites. [ABSTRACT FROM AUTHOR]

Highlights: [•] C/ZrC, C/SiC and C/ZrC–SiC with different SiC content are fabricated by PIP process. [•] C/ZrC has the superior anti-ablation property but the poor anti-oxidation property. [•] The introduction of SiC improves oxidation resistance but degrades ablation property. [•] The C/ZrC–SiC with a certain content of SiC shows superiority over other composites. [•] A high temperature self-healing mechanism has been achieved by C/ZrC–SiC composite. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) needle-punched C/ZrC–SiC composites were successfully fabricated by infiltration and pyrolysis of a novel liquid ZrC precursor and polycarbosilane (PCS) separately. The effects of PIP cycles of PCS on the microstructures and mechanical property of the composites were studied. The C/ZrC–SiC composite with more PIP cycles of PCS had a high performance in mechanical property due to its higher density. The C/ZrC–SiC composite with 6 PIP cycles of PCS had a flexural strength of 142.4±17.5MPa and a fracture toughness of 7.6±0.3MPam1/2, which was superior to C/ZrC composites with the same total 20 PIP cycles. The ablation behaviors of the C/ZrC–SiC composite were studied using an oxyacetylene torch. The formation of continuous molten ZrO2 layer contributed mainly the high ablation resistance in the center region, while the SiC matrix accounted for the improved oxidation resistance beyond the center and transition regions. Moreover, the ZrC matrix homogeneously distributed in composite can act as a reservoir of the ZrO2 phase, and then supplemented the ZrO2 loss continuously in the whole testing. [ABSTRACT FROM AUTHOR]

Abstract In situ observations of damage development within 3-dimensional 5-directional braided carbon fiber reinforced carbon and silicon carbide (C/C-SiC) ceramic composites, fabricated by gaseous silicon infiltration (GSI) and precursor infiltration pyrolysis (PIP), have been obtained using laboratory X-ray computed tomography during in situ flexural tests. The GSI composite has a denser structure than that fabricated by PIP, but contains initial defects within the fiber bundles. The GSI composite ultimately failed due to fracture across the fiber bundles, while failure of the higher strength PIP composite propagated along the interface between the fiber bundle and matrix with a greater degree of fiber pullout. These differences arise from the higher process temperature and greater degree of matrix-fiber reaction of GSI compared to PIP. Digital volume correlation (DVC), applied to the tomographs, measured the 3-dimensional deformations and hence the specimen curvature. This demonstrated the significant reduction in elastic modulus caused by the development of internal cracking with tensile strain in both materials. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) C f /ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The effects of PyC interphase of different thicknesses on the mechanical and ablation properties were evaluated. The results indicate that the C f /ZrC–SiC composites without and with a thin PyC interlayer of 0.15 µm possess much poor flexural strength and fracture toughness. The flexural strength grows with the increase of PyC layer thickness from 0.3 to 1.2 µm. However, the strength starts to decrease with the further increase of the PyC coating thickness to 2.2 µm. The highest flexural strength of 272.3±29.0 MPa and fracture toughness of 10.4±0.7 MPa m 1/2 were achieved for the composites with a 1.2 µm thick PyC coating. Moreover, the use of thicker PyC layer deteriorates the ablation properties of the C f /ZrC–SiC composites slightly and the ZrO 2 scale acts as an anti-ablation component during the testing. [ABSTRACT FROM AUTHOR]