Effects of Preform Structure on Chemical Vapor Infiltration Mechanism and Properties of SiC_f/SiC Composite Cladding

Silicon carbide (SiC) composite cladding is a promising material for nuclear reactor fuel tubes due to its excellent high-temperature stability, irradiation resistance, and corrosion resistance. However, the relationship between preform microstructure and mechanical properties remains poorly understood, and optimizing preform structures to balance densification efficiency and performance is challenging.This study compares the fabrication processes and performance characteristics of SiCf/SiC composite cladding with three preform structures (±45° double-layer winding structure, 45° double-layer braided structure, and 30° triple-layer braided structure) to elucidate the influence of preform structure on material properties, providing a theoretical basis for the structural design and performance optimization of nuclear-grade SiC composite cladding materials.The results show that under the same deposition time, SiC cladding with a smaller braiding angle exhibits the fastest weight gain and the highest deposition rate, whereas the wound-structure cladding, due to its dense surface layer that is prone to pore sealing, shows the slowest weight gain and deposition rate. Influenced by the Chemical Vapor Infiltration (CVI) process, all three types of SiC composite cladding contain a significant number of internal pores. In particular, the braided-structure samples exhibit long interlayer cracks or large pores, which disrupt the continuity between fibers and fibers, as well as between fibers and the matrix, resulting in lower hoop tensile strength and radial compression strength compared to the wound structure.Furthermore, this study confirms that an increase in braiding angle is associated with a higher circumferential fiber volume fraction, a reduction in pore size, and a decrease in pore area per unit volume, thereby enhancing the hoop strength of the SiC cladding.