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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: Three-dimensional (3D) Cf/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The Cf/ZrC–SiC composite with relatively more PIP cycles of PCS has a higher density and a lower porosity, which account for the improved mechanical property of the composite. The composite with 6 PIP cycles of PCS has a flexural strength of 136.0±13.1MPa, and a fracture toughness of 7.3±0.3MPam1/2, which is superior to the monolithic ultrahigh temperature ceramics. The relatively low flexural strength and elastic modulus of the Cf/ZrC–SiC composites are attributed to the small stiffness of the matrix because of the debonding feature of the ZrC matrix. The high temperature oxidation testing of the S6-Cf/ZrC-SiC composite reveals that the surface molten ZrO2 layer contributes mainly to the improved anti-ablation property. [Copyright &y& Elsevier]

Effects of SiC/HfC ratios on the ablation and mechanical properties of 3D C f /HfC–SiC composites by precursor impregnation and pyrolysis (PIP) process were investigated systematically. Both strength (flexural and compressive strength) and modulus increase as the SiC/HfC ratio are improved. The compact and stiff HfC-SiC matrix in addition to the carbon fiber and PyC interphase with less reaction damage accounts for the improved mechanical properties of C f /HfC-SiC with higher SiC/HfC ratios. Meanwhile, both weight loss and erosion depth of C f /HfC-SiC are improved with the increased SiC/HfC ratios. Therefore, in order to balance the ablation and mechanical properties, an appropriate SiC/HfC ratio should be considered. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) braided C/ZrC–SiC composites with various SiC/ZrC ratios were fabricated by precursor infiltration and pyrolysis (PIP) process. The effects of SiC/ZrC ratios on the ablation and mechanical properties were investigated systematically. The flexural strength of 3D C/ZrC–SiC grows with the increase of SiC/ZrC ratios. The compact and stiff ZrC-SiC matrix, moreover, the carbon fiber and PyC interphase with the less reaction damage account for the improved flexural strength of C/ZrC–SiC with higher SiC/ZrC ratios. As for the ablation properties, both mass and linear ablation rates drop with the decrease of SiC/ZrC ratios at the beginning. However, the ablation rates start to increase with the further decrease of SiC/ZrC ratio, where the high open porosity deteriorates the ablation properties. Herein, in order to obtain a balance between ablation and mechanical properties, an appropriate SiC/ZrC ratio should be considered. [ABSTRACT FROM AUTHOR]