纤维基体高温蠕变匹配性与SiCf/SiC高温蠕变行为关系研究

SiCf/SiC ceramic matrix composites are regarded as key candidate materials for applications associated with aerospace, nuclear power system and other fields due to their excellent properties. To promote its engineering application, the improvement of creep resistance of the materials is currently a research hotspot for SiCf/SiC composites. Accordingly, this project proposes to tailor the composition and microstructure of SiC matrix to achieve the match of creep resistance between SiC fibers and matrix. This will be realized by optimizing the cross-link and pyrolysis parameters of polymer precursors. Based on the characteristics of domestic SiC fibers, electron beam irradiation crosslinking combined with hydrogen contained atmosphere pyrolysis will be utilized. It is aimed to obtain a similar composition and microstructure between SiC matrix and fibers. Consequently, high temperature creep resistance of the composite is expected to be improved. The curing mechanism of precursor under electron beam irradiation crosslinking and effect of hydrogen contained atmosphere pyrolysis on the composition and microstructure of SiC matrix will be studied. The influence of matching degree between matrix and fibers on the creep resistance of SiCf/SiC composites at elevated temperatures will also be investigated, the underlying mechanisms will be revealed. This research may provide a guideline for microstructure design and properties optimization of SiCf/SiC composites in the future.

SiCf/SiC陶瓷基复合材料在航空航天和核能系统等领域中具有广泛的应用前景。提高SiCf/SiC复合材料高温抗蠕变性能，实现其工程化长寿命应用是当前的研究热点。本项目提出通过优化有机前驱体交联固化和高温分解工艺，调控PIP工艺SiC基体组成/结构，实现SiC基体与SiC纤维高温蠕变性能匹配，提高SiCf/SiC复合材料高温抗蠕变性能的研究思路。针对国产SiC纤维组成/结构特点，通过引入电子束辐照交联工艺和高温分解气氛控制，制备具有相近组成/结构的SiC基体。研究电子束辐照前驱体交联机制和SiC基体组成/结构的关联性，加氢脱碳烧结对SiC基体组成/结构的影响规律，以及基体纤维高温抗蠕变性能的匹配度与SiCf/SiC复合材料高温蠕变行为关系，揭示SiCf/SiC复合材料服役环境高温抗蠕变性能内在机理，从而为长寿命SiCf/SiC陶瓷基复合材料的结构设计和性能调控与优化提供借鉴和指导。

本项目在传统有机前驱体浸渍裂解（PIP）工艺制备SiC/SiC复合材料的基础上，通过引入电子束辐照交联工艺进行前驱体交联固化，系统研究了吸收剂量、退火温度、存储时间及存储气氛等对聚碳硅烷（PCS）前驱体自由基产生和演变的影响，推导自由基衰变和转化机理，并制备和研究了PIP-SiC/SiC复合材料力学性能和抗高温蠕变性能。结果表明：在室温及氮气氛下，PCS经辐照后产生大量硅自由基；低剂量辐照时，硅自由基的浓度随着吸收剂量的增加而线性增加，吸收剂量达到200kGy时硅自由基浓度随吸收剂量增加不再增大，自由基浓度趋于饱和。辐射诱导PCS产生的硅自由基室温下储存在氮气中非常稳定，储存在空气中时硅自由基由于发生氧化反应而快速衰减。温度升高硅自由基的衰减加快，当温度升高至PCS的软化点附近时，可以完全清除硅自由基。消除PCS的辐射诱导自由基有利于减少后续的氧化，提高SiC基体的与国产SiC纤维组成与结构的相似度。其次，电子束辐照交联对浸渍过程SiC基体的增重效率存在重要影响。前期PIP循环时纤维预制体内部只有少量SiC基体，电子束辐照交联的致密化效果最为显著，材料的增重率在前两个PIP循环中一般都超过75%以上。当经过8次PIP与电子束辐照交联裂解循环后，普通交联固化的SiC/SiC复合材料总增重率为80%左右；而电子束辐照交联的陶瓷的总增重率普遍超过为120%，远高于普通高温交联材料，有效提高材料制备效率。由于采用电子束辐照交联后大大地降低了复合材料的气孔率，显然会对材料的力学性能和抗蠕变性能有一定的提升，通过电子束辐照后，SiC基体中因裂纹尺度较低且扩展能力有限，复合材料内部的微小开裂等损伤会被固态氧化产物所封闭，阻碍了氧化反应的进一步进行，因此相对有较高的抗蠕变服役寿命。通过本项目的研究，为长寿命抗高温蠕变PIP-SiC/SiC复合材料提供一条可行的制备路线，使该材料具有广泛的应用前景。