高导热结构/功能一体化C/SiC复合材料及其抗烧蚀行为研究

Aimed at application requirements of thermal protection structure (TPS) of the new generation hypersonic vehicle to structure-function integrated carbon fiber reinforced silicon carbide (C/SiC) composite with enhanced thermal conductivity, this project intends to introduce high thermal conductivity phases, such as carbon nanotubes (CNTs) and diamond particles, into pyrolytic carbon (PyC) interphase and SiC matrix, respectively, for improving thermal conductivity of C/SiC composites.The variations of thermal conductivity and mechanical properties of CNTs-PyC and diamond-SiC with microstructures will be systematically investigated. The modification mechanisms to thermal conductivity and strength-and-toughness of CNTs and diamonds will be revealed respectively. The synergistic optimization mechanism of TC and strength-and-toughness, as well as the optimized microstructure of C/SiC composites, will be clarified by a high thermal conductivity and strength-and-toughness collaborative design. C/SiC composites with optimized microstructure will be manufactured. The evolutions of performance and microstructures of structure-function integrated C/SiC composites with enhanced thermal conductivity under different ablation conditions will also be systematically investigated, and the anti-ablation mechanism of highly thermally conductive structure/functional integrated C/SiC composites will be revealed. The research results of this project, which could be the theoretical foundation and scientific basis of design for enhanced-thermal-conductivity C/SiC composites, are helpful to deeply understand thermal conduction mechanisms and to enrich thermal conduction theory of C/SiC composites. It has very important scientific meanings to improve performance and lifetime and applications of C/SiC composites, and to promote the development of technology of hypersonic vehicles.

针对航空航天飞行器热防护部件对高导热结构/功能一体化C/SiC复合材料的需求，本项目拟在C/SiC复合材料界面和基体中分别引入CNTs和金刚石高导热相来提高其导热性能。通过系统研究CNTs-PyC和金刚石-SiC导热性能与力学性能随微结构的变化规律，揭示CNTs和金刚石的导热改性机理和强韧化机理，并通过开展高导热与强韧性协同设计，揭示协同作用机理，优化复合材料微结构，获得导热性能与强韧性俱佳的高导热C/SiC复合材料，系统研究其在不同烧蚀条件下的性能和微结构演变，揭示高导热结构/功能一体化C/SiC复合材料的抗烧蚀机理。项目研究成果有助于深化认识C/SiC复合材料导热机理，丰富复合材料热传导理论，并可为设计和发展高导热C/SiC复合材料提供理论基础和科学依据，对于提高材料使用效能和寿命、促进材料应用、推动我国超高速飞行器技术发展有着极为重要的科学意义。

本项目通过CNTs和金刚石改性分别提高了C/SiC复合材料的界面导热和基体导热，掌握了CNTs-PyC界面和金刚石-SiC基体对C/SiC复合材料导热行为和强韧性的影响规律，揭示了C/SiC复合材料导热改性机理，阐明了导热改性与复合材料强韧性之间的协同作用机理，优化了改性工艺参数，并揭示了力学性能与高导热协同C/SiC复合材料的抗烧蚀机理。本项目取得的主要研究结果如下：.（1）随碳纳米管沉积时间增加，碳纳米管引入量快速增多，复合材料的力学性能和热导性能出现先提高后降低的趋势。在碳纳米管沉积时间为60min，即碳纳米管引入量约5%时，复合材料的综合性能达到最优，弯曲强度、断裂韧性和热导率分别达到436MPa、20.3 MPa•m1/2和15.89 W/(m•K) (1400℃)，与不含碳纳米管的复合材料相比，分别提升了21.78%、10.32%和114.7%。.（2）粒径为1、3、5μm金刚石的引入提高了基体热导率，从而使复合材料的热导率得以提高。但粒径大小的影响相差不大，主要与粒径大小引起的界面散射、界面结合强度、孔隙率和尺寸等有关。由于致密度偏低，C/SiC-Diamond复合材料的力学性能不及CVI-C/SiC。.（3）采用CNTs-PyC界面结合3μm金刚石改性SiC基体制备出了高导热C/SiC复合材料，其热导率是CVI-C/SiC复合材料的1.6~2.5倍，力学性能与CVI-C/SiC复合材料相当。.（4）C/SiC复合材料热导率的提升，显著降低复合材料烧蚀面温度，导致烧蚀中心的烧蚀机制转变为化学氧化烧蚀和机械冲蚀，使得SiC基体主要发生被动氧化，生成液态SiO2并附着在纤维和基体表面，阻止了复合材料被进一步烧蚀，从而降低了烧蚀率，提升了复合材料的抗烧蚀性能。