超高温复相陶瓷纤维研制与结构性能研究

Ultra-high temperature ceramics (UHTCs), mainly ZrB2-ZrC-SiC and HfB2-HfC-SiC composite systems, exhibit excellent oxidation resistance and thermal mechanical properties due to their extremely high melting points and formation of complex oxide glass layers which cover and protect the ceramic against oxidation (i.e. B2O3-SiO2-ZrO2). UHTCs have been intensively studied recently to meet requirements of new developed aerospace technologies. UHTCs matrix in the continuous fiber reinforced composites (UHT-CMC) have been prepared successfully by polymeric precursor impregnation and pyrolysis technique. In this study, preparation of ZrB2-ZrC-SiC UHTC fibers were proposed for the first time. This novel ceramic fiber will be fabricated via intensive researchs of synthesis of polymeric precursors of ZrC/BNC/SiC, melting spinning and thermal transformation into inorganic fibers in inert/active atmospheres. Major scientific mission of the process is controlled formation of nano-micro sized ceramic multi-phases distribution inside a fiber body with a diameter less than 10 um and with length above hundred meters. Formation of this novel featured composite ceramics during polymer pyrolysis and heat treatment has been confirmed in our previous research on UHTCs matrix, this knowledge will therefore be applied and extended to fiber formation during tensile elongation. Detailed chemical reactions during synthesis and pyrolysis of multi-components polymeric precursors as well as solid reactions among the formed ceramic phases will be studied. Microstructures, thermo-mechanical properties and oxidation resistance during very high temperature up to 1800℃ of the prepared UHTCS fiber will also be investigated in details. This study is planned to span 48 months with a financial budget of 82,0000 RMB, expected outputs of the research includ published papers, patents, scientific reports and so on.

本项目拟通过分子设计与催化合成等关键技术研究，研制具有良好纺丝性能的有机聚合陶瓷前驱体，并采用熔融纺丝、表面不熔化、陶瓷化和高温热处理技术，制备由ZrB2-ZrC-SiC三元陶瓷组成的超高温复相陶瓷纤维；研究合成前驱体分子结构、平均分子量及其分布对纺丝工艺与陶瓷纤维性能的影响，分析在热解过程中发生的气相和固相反应，研究多相反应对陶瓷微观结构形成过程的影响规律；研究牵伸应力条件下高温热处理对复相陶瓷微观结构以及力学性能的影响机制；研究并获取三元纳微结构复相陶瓷纤维的高温氧化动力学与防氧化方法。力争通过上述前沿探索,为发展新型超高温陶瓷纤维积累技术数据，验证创新工艺方案，并建立该类型复相陶瓷纤维多尺度结构-力学/抗氧化性能关系的机理和预测模型。

有机前驱体法制备SiC纤维是金属基、陶瓷基等复合材料常用的高性能增强纤维之一。SiC纤维的热稳定性和抗氧化性可以通过添加Ti、Zr和Al等元素进行改善。然而，由于此类金属元素的前驱体引入量较低，超过3wt%时会影响纺丝性能；同时由于引入形式为含氧金属有机化合物，因此也将氧引入了SiC纤维中，不利于纤维性能的提升。. 本项目通过分子设计和化学反应控制，合成性能优良的ZrB2-ZrC-SiC陶瓷有机前驱体。在此基础上，系统地研究了有机前驱体熔融纺丝、不熔化、高温陶瓷化等制备技术与ZrB2-ZrC-SiC纤维结构、性能之间的变化规律，取得了一些有意义的研究成果。首先，通过分子设计及催化合成制得了集锆、硅于一体的新型聚锆碳硅烷（PZCS），通过理论计算与实验研究验证了前驱体合成的催化-配位聚合机理；PZCS通过与自制的聚硼氮烷共混-热处理工艺制得了纺丝性能优异的ZrB2-ZrC-SiC陶瓷有机前驱体。其次，优化熔融纺丝工艺得到连续纺丝长度大于 200m的原纤维，再经过不熔化、陶瓷化热处理技术，最终制备了直径12-14μm，离散度小于 10%的ZrB2-ZrC-SiC复相陶瓷纤维，其中金属Zr含量为12~15wt%。同时，结合反应热力学和动力学研究了原纤维的交联机理、不熔化纤维的热解行为和复相陶瓷生成机理，揭示了复相陶瓷纤维材料的多尺度结构、相界面显微组织结构、界面元素分布随热解和氧化温度等的变化规律。最后，详细研究了复相陶瓷纤维制备工艺、微结构与力学性能、氧化性能之间的构效关系，为新型超高温陶瓷纤维的研制积累了研究基础和技术数据。. 本项目的系列结果为超高温复相陶瓷纤维的设计与研究提供了新材料料和新思路，在超高温陶瓷复合材料制备领域有着重要的应用前景。