预制体结构对SiCf/SiC复合包壳化学气相增密机理及性能影响

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

  • 摘要: 碳化硅(SiC)复合包壳具有优异的高温性能、抗辐照性能和耐腐蚀性能,是核反应堆燃料包壳管的理想候选材料。然而,其性能高度依赖于预制体结构的优化设计,而不同预制体结构制备的包壳材料其微观组织与力学性能的关联规律缺乏系统研究;如何通过预制体结构设计来平衡材料的致密化效率与力学性能仍是一个技术难点。本研究通过对比三种预制体结构(±45°双层缠绕结构、45°双层编织结构、30°三层编织结构)SiCf/SiC复合包壳的制备过程与性能特征,研究预制体结构对材料性能的影响规律,为核用SiC复合包壳材料的结构设计与性能优化提供理论依据:在相同沉积时间内,编织角较小的碳化硅包壳增重最快,沉积速率最高;而缠绕结构的包壳因表层致密易封孔,增重和沉积速率均最慢。受CVI工艺影响,三种SiC复合包壳内部均存在大量孔隙,特别是编织结构样品中出现较长的层间裂纹或大孔隙,破坏了纤维与纤维、纤维与基体之间的连续性,导致拉伸强度和径向压溃强度低于缠绕结构;此外,本研究证实,编织角度的增加与周向纤维体积分数的提高、孔径尺寸的减小以及单位孔面积的减少有关,增加编织角度可有效改善SiC包壳环向强度。

     

    Abstract: 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.

     

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