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SiCf/SiC composites have emerged as one of the most promising materials for aero‐engine hot‐end structures. However, their performance is limited by their susceptibility to oxidation and corrosion reactions with oxygen and water vapor. To overcome this challenge, antioxidant‐modified phases are introduced into matrices of SiCf/SiC composites which improve their water and oxygen resistance. In this study, the resistance of SiCf/SiC composites modified by yttrium silicate matrix (SiCf/SiC‐YS composites) to air at 1000–1400°C and water‐oxygen environments at 1200°C was investigated. The diffusion paths of oxygen in SiCf/SiC‐YS composites and the antioxidant behavior of the yttrium silicate matrix were discussed. Additionally, the differences in oxygen and water‐oxygen corrosion resistance of SiCf/SiC‐YS composites at the same temperature were compared. The strength retention of SiCf/SiC‐YS composites after oxidation and water‐oxygen corrosion at 1200°C were 138.6% and 108.8%, respectively. This indicates that the addition of water vapor accelerated the degradation of SiCf/SiC‐YS composites. By comparing with SiCf/SiC composites, it can be concluded that the modification of the yttrium silicate matrix considerably improved the oxidation resistance of SiCf/SiC composites. [ABSTRACT FROM AUTHOR]

C/SiC composites prepared by chemical vapor infiltration technique (CVI) have been regarded as thermal structural materials widely. However, these composites still suffer from poor functional properties like low thermal conductivity, especially in thickness direction of the composites, limiting their large‐scale applications. Herein, mesophase pitch based carbon fiber (MPCF) and continuous wave laser machining were utilized to construct highly effective heat conductive micro‐pipelines within CVI C/SiC composite. The effect of initial density on the final density and thermal conductivity of the as‐obtained MPCF‐C/SiC composites were investigated. The results revealed that higher initial density would directly enhance the thermal conductivity and reduce the negative impact of the bottle‐neck effect. At temperatures between 100°C and 500°C, MPCF‐C/SiC composites preserved more than threefold of the thermal conductivity (340%) when compared to reference C/SiC composites. This work provides a highly effective route for enhancing the thermal conductivity of C/SiC, which would broaden their future applications. [ABSTRACT FROM AUTHOR]

The dielectric response of polymer‐derived amorphous silicon carbonitride (PDC‐SiCN) material was studied over a wide frequency range from 1 mHz to 10 MHz. Aside from presenting a relaxation process over 105 to 0.03 Hz frequency range, the material showed a strong low‐frequency dielectric dispersion (LFDD), which resulted in extremely high permittivities (up to 105) at frequencies lower than 0.03 Hz. It is identified that this LFDD resulted from relaxation process was not induced by conductivity. Therefore, PDC‐SiCN material showed two relaxation processes. Based on its microstructure, two polarization mechanisms were proposed for PDC‐SiCN: a mechanism based on polarons generated by unpaired electrons present in the material and an interfacial polarization mechanism as a result of different properties of SiCxN4−x matrix and free‐carbon clusters. Interfacial polarization process was simulated based on a parallel plate model involving two different materials. The result indicated that the relaxation time of an interfacial polarization can be distributed over a broad time range in the material. [ABSTRACT FROM AUTHOR]