LPCVD-HfC纳米线改性C/C复合材料的制备工艺规律及其抗烧蚀机理

With the rapid development of aerospace industry, properties of C/C composites in extreme service environments with high-temperature and high-speed gas flow need to be further improved to meet higher requirements. In this project, HfC nanowires with excellent mechanical properties and good high-temperature stability will be introduced into matrix to develop C/C composites modified one-dimensional high-temperature ceramic nanomaterials. The objective of this project is to improve synchronously mechanical properties and the ablation resistance of C/C composites by solving a key issue about the compromising mechanical properties of C/C composites modified by common ceramic particles. Preparation, microstructures and growth mechanism of HfC nanowires via low-pressure chemical vapor deposition (LPCVD) will be investigated to achieve uniform and controllable growth of HfC nanowires on the surface of carbon cloth. The laminated carbon cloth with HfC nanowires will be needled with carbon fibers, which is used as perform for chemical vapor infiltration (CVI) preparation of HfC nanowire modified C/C composites. The effects of HfC nanowires on deposition and microstructures of pyrolytic carbon, and interface structures will be studied, and technology principles of preparing HfC nanowire modified C/C composites will be proposed. Mechanical and ablation behavior of HfC nanowire modified C/C composites will be analyzed and discussed to reveal the toughening and anti-ablation mechanisms, contributing to the building of the ablation model. The accomplishment of this project will provide foundational theory support for fabrication and application of HfC nanowire modified C/C composites with excellent mechanical and anti-ablation properties in the aerospace field .

航空航天的快速发展对C/C复合材料在高温高速燃气冲刷等极端服役环境下的性能提出了更高要求。本项目提出将兼具优良力学性能和高温稳定性的HfC纳米线引入C/C复合材料中，开发一种一维超高温陶瓷纳米材料改性的C/C复合材料，旨在解决普通陶瓷颗粒改性C/C复合材料存在力学性能损伤的难题，实现力学与抗烧蚀性能的同步提高。拟研究HfC纳米线的低压化学气相沉积（LPCVD）工艺、微结构及生长机理，实现其在炭布上均匀可控生长；将预沉积有HfC纳米线的炭布叠层穿刺后利用化学气相渗透工艺制得HfC纳米线改性C/C复合材料，研究HfC纳米线对热解炭沉积过程与结构、界面结构的影响机制，阐明该复合材料的制备工艺规律；探讨HfC纳米线改性C/C复合材料的力学与烧蚀行为，揭示其增韧机制与抗烧蚀机理，建立烧蚀理论模型。此项目有望为兼具优良力学和抗烧蚀性能的HfC纳米线改性C/C复合材料的制备与航空航天应用奠定理论基础。

航空航天的快速发展对C/C复合材料在高温高速燃气冲刷等极端服役环境下的性能提出了更高要求。为解决普通陶瓷颗粒改性C/C复合材料存在力学性能损伤的难题，本项目将兼具优良力学性能和高温稳定性的HfC纳米线引入C/C复合材料中，基于化学气相沉积工艺制备了一种一维超高温陶瓷纳米材料改性的C/C复合材料。 主要研究内容和结果如下：.（1）降低沉积温度至C–Hf–Ni催化剂合金低共熔温度以下，1000℃以上，可制备出面心立方结构的单晶HfC纳米线，在1025℃时，HfC纳米线呈弯曲线状或“Z”字形状；HfC纳米线有三种常见生长轴方向变化导致形成“Z”字形形貌；HfC纳米线的生长过程受VLS机制控制。.（2）反应气体中高浓度的Hf原子有利于伴有纳米线生长的HfC纳米带的混合产物合成。HfC纳米带的生长轴向为[13(_)3]。VLS机制控制着混合产物纳米结构的轴向生长。该混合产物具有良好的场发射性能，在真空微电子领域具有潜在应用。.（3）在负压气氛下，沉积压力越低，HfC纳米线直径越大；过量H2有利于HfC纳米线生长，而且调节H2流量可控制HfC纳米线以直线形或“Z”字形生长，相反，过量CH4会抑制HfC纳米线各向异性生长；低浓度催化剂有利于HfC纳米线在碳纤维预制体内部生长。.（4）HfC纳米线导致了各向同性炭的形成，热解碳以HfC纳米线为核沉积形成核壳结构。.（5）HfC纳米线改性C/C复合材料的层间剪切强度显著提高，比未改性C/C复合材料提高近五分之三，但弯曲强度和弯曲模量提高幅度不大；HfC纳米线使层间基体与炭纤维的界面结合增强，从而使改性C/C复合材料的层间剪切和三点弯曲断裂均呈现脆性破坏特征。.（6）HfC纳米线有效提高了C/C复合材料的抗烧蚀性能，氧乙炔烧蚀20 s后，其线烧蚀率和质量烧蚀率分别降低了约三分之一和五分之二。HfC纳米线在烧蚀过程中消耗氧化性气体和热量，同时纤维网状骨架对热解炭起稳固作用，提高复合材料的抗烧蚀性能；.项目研究为航空航天领域的高性能C/C复合材料的设计、制备与应用奠定了一定理论基础，具有现实意义。