基于纳米尺度SiC界面层优化调控下CNT对热解碳强韧化效能研究

Carbon nanotube (CNT) possesses ultra-high strength, good toughness and also excellent compatibility with carbon materials. Thus, it is desirable to use CNT as reinforcing materials to improve the mechanical properties of pyrocarbon (PyC). However, the existing problems such as difficult densification of CNT three-dimensional structure, defects on CNT surface and strong interfacial bonding strength between CNT and PyC, have greatly weakened the reinforcing and toughening efficiency of CNT in the PyC. In order to resolve these problems, this project proposes the idea about applying a nano-scale SiC interface layer (SiCNIL) onto the CNT surface by chemical vapor deposition (CVD). The final aim is to improve and control the mechanical properties of CNT/PyC composites by means of the CNT surface modification, CNT mechanical strengthening and optimization of CNT-PyC interfacial bonding state using SiCNIL. On the basis of the controllable morphology and adjustable structure of SiCNIL, the general law of influence of SiCNIL on the densification process, graphitization process, microstructure and micro-/macro-mechanical properties of CNT/PyC composites will be systematically explored. Afterwards, the related mechanisms will be established, which will be used as the guidance for the optimization of the morphology and microstructure parameters of CVD SiCNIL, aiming to maximize the mechanical performance of CNT/PyC composites. The accomplishment of this project will provide a meaningful way for the development of PyC with high strength and excellent toughness applied in aeronautic and astronautic fields, and also enrich the interface design and reinforcement theory of CNT composites.

碳纳米管（CNT）拥有极高的强度、韧性以及与碳材料极好的相容性，使之成为改善热解碳（PyC）强韧性能的理想材料。然而CNT三维结构的较难充分填实、CNT存在的结构缺陷以及CNT与PyC之间界面结合过强等问题极大削弱了CNT对PyC的增强增韧效能。针对这些问题，本项目提出借助化学气相沉积在CNT表面制备一层纳米尺度SiC界面层（SiCNIL），旨在通过对CNT表面改性、力学强化以及CNT-PyC界面结合特性调节，实现CNT/PyC复合材料力学性能的提升与调控。在SiCNIL形貌可控、结构可调的基础上，系统研究SiCNIL对CNT/PyC复合材料致密化过程、石墨化过程、微观组织结构、内界面精细结构、界面应力传递行为以及微观、宏观强韧特性的影响规律，揭示SiCNIL的强韧作用及其与CNT协同强韧化机制，为制备航空航天用高强高韧PyC奠定基础，同时丰富和发展CNT复合材料的界面设计和强韧化理论。

本项目借助前驱体浸渍热解法在碳纳米管（CNT）表面制备一层纳米尺度SiC界面层（SiCNIL），旨在通过对CNT表面改性、力学强化以及CNT-热解碳（PyC）界面结合特性调节，实现CNT对PyC的有效强韧化。通过控制聚碳硅烷前驱体溶液浓度和裂解温度实现了高纯β-SiCNIL在CNT表面的纳米级包覆以及预制体由内至外的均匀分布。SiCNIL不仅改变了CNT表面特性，而且大幅度减小了CNT三维网络总表面积与体积比值（A/V值）并缩短了碳氢气体分子的滞留时间，降低了PyC的形成速率，提高了碳氢气体分子在预制体内部的传质和均匀扩散，减少了封闭孔的数量和尺寸，提高了CNT/PyC复合材料整体均匀度和致密化度。SiCNIL提高了CNT/PyC复合材料致密化态和石墨化态下的压缩强度、拉伸强度和断裂塑性。一方面得益于SiCNIL减少了CNT/PyC基体内部结构缺陷，提高了碳基体内聚力；另一方面得益于SiCNIL对CNT-PyC界面结合特性和载荷传递行为的优化调控，SiCNIL弱化了CNT-PyC界面结合强度，将裂纹击穿CNT的失效模式转变为裂纹沿SiCNIL-PyC界面和SiCNIL-CNT界面长距离扩展最终引发CNT断裂长拔出的失效模式，CNT自身强韧机制得到有效发挥，实现了CNT/PyC复合材料力学性能的进一步提升。