SiC_f/Si₃N₄ composites are thermal structural materials for structural-functional-integrated requirements. In order to fully utilize the advantages of continuous SiC fibers as semiconductors in the regulation of dielectric properties, the whole weaving technology based on the mesoscopic scale of the fiber preform structure was proposed. In this work, three SiC_f/Si₃N₄ composites were prepared by the CVI process using two-dimensional half (2.5D), three-dimensional four-direction (3D4X), or three-dimensional five-direction (3D5X) braided structures as preforms. First, the tensile strength of the composites was tested. By comparing with the theoretical value, it was found that there were large deviations in the three composites, which originated in the thermal mismatch between SiC fiber and Si₃N₄ matrix. By analyzing the microstructure, pore distribution, and interfacial shear strength of the three SiC_f/Si₃N₄ composites, the interphase zone of 3D4X composites is more effectively protected compared to 2.5D and 3D5X composites after the CVI Si₃N₄ process. Surprisingly, the disruption of the interphase to form the SiC_f/Si₃N₄ hetero-interface gives 2.5D and 3D5X composites a boosted interfacial polarization, and thus dielectric loss capability and high-temperature insensitivity of electromagnetic wave (EMW) absorption. The results of the high-temperature absorption tests showed that 3D5X composites achieve good absorbing properties in a wide temperature range of 25–900°C.

中文翻译：

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结构-功能-集成 SiCf/Si3N4 复合材料在不同光纤预制棒中的界面力学和极化行为

SiC_f/Si₃N₄ 复合材料是满足结构-功能-集成要求的热结构材料。为了充分利用连续 SiC 纤维作为半导体在介电性能调控方面的优势，提出了基于纤维预制棒结构介观尺度的全编织技术。在本工作中，使用二维半 （2.5D）、三维四向 （3D4X） 或三维五向 （3D5X） 编织结构作为预制件，通过 CVI 工艺制备了三种 SiC_f/Si₃N₄ 复合材料。首先，测试了复合材料的拉伸强度。通过与理论值进行比较，发现三种复合材料存在较大的偏差，其原因在于 SiC 纤维与 Si₃N₄ 基体之间的热失配。通过分析三种 SiC_f/Si₃N₄ 复合材料的微观结构、孔隙分布和界面剪切强度，与 CVI Si₃N₄ 工艺后的 2.5D 和 3D5X 复合材料相比，3D4X 复合材料的相间区得到了更有效的保护。令人惊讶的是，界面的破坏形成了 SiC_f/Si₃N₄ 异质界面，使 2.5D 和 3D5X 复合材料的界面极化增强，从而具有介电损耗能力和电磁波 （EMW） 吸收的高温不敏感性。高温吸收测试结果表明，3D5X 复合材料在 25–900°C 的宽温度范围内具有良好的吸收性能。