化学气相共沉积SiC纳米线增韧HfC-SiC梯度复相涂层研究

To prevent carbon/carbon (C/C) composites from oxidation and ablation at the elevated temperature, a SiC nanowires-toughened HfC-SiC multi-phase gradient coating will be developed by a feasible three-step method in the present project. Firstly, a SiC gradient buffer layer is prepared on the surface of the C/C composites by reactive melt infiltration. Secondly, a porous SiC nanowire layer is deposited on the SiC gradient buffer layer by in-situ growth. Lastly, HfC-SiC multi-phase gradient ceramic is co-deposited by chemical vapor deposition into the porous SiC nanowire layer to obtain a dense SiC nanowire-toughened HfC-SiC multi-phase gradient coating. The project is aimed at resolving efficiently the deficiency of the SiC nanowire toughening technology, improving the toughness of HfC coating, resolving fundamentally the mismatch of coefficient of thermal expansion between C/C substrate and HfC coating, and avoiding the cracking and debonding of the coating. In the project, the fabricating technologies and formation mechanism of the coating will be studied systematically, the effect of the SiC nanowires and element distribution on the microstructure, physical properties and oxidation and ablation resistance of the coating will be investigated, the reinforcement mechanism of the nanowires in the coating will be revealed, the relationship between the microstructure of the coating and its oxidation and ablation resistance will be established, the oxidation and ablation mechanism of the coating in different service environments will be revealed. The research results of the project can provide the theoretical foundation for broadening the applications of C/C composites exposed to the extraordinarily high temperature and high gas velocity environment.

本项目针对炭/炭（C/C）复合材料高温易氧化烧蚀难题，开发一种SiC纳米线增韧HfC-SiC梯度复相涂层，拟首先采用反应熔渗法在C/C基体表面制备SiC梯度过渡层，再在SiC梯度过渡层表面原位生长SiC纳米线多孔层，最后通过化学气相共沉积方法将具有梯度分布的HfC-SiC复相陶瓷填充于SiC纳米线多孔层的孔隙中，进而获得致密的SiC纳米线增韧HfC-SiC梯度复相涂层。旨在有效解决现有SiC纳米线增韧技术的缺陷，提高HfC涂层韧性，从根本上解决HfC涂层与C/C基体热膨胀不匹配，避免涂层的开裂和剥落。系统研究涂层的制备工艺和形成机理，探讨涂层中SiC纳米线、元素分布对涂层微观结构、物理性能和抗氧化烧蚀性能的影响规律，揭示纳米线在涂层中的增韧机理，建立涂层微观结构与抗氧化烧蚀性能之间的关系，揭示涂层在不同服役环境中的氧化烧蚀机理，为C/C复合材料在高温高速气流冲刷环境中的应用提供理论基础。

本项目针对炭/炭（C/C）复合材料高温易氧化烧蚀难题，开发了HfC-SiC梯度复相涂层和原位生长SiC纳米线增韧HfC-SiC复相涂层。项目主要研究了炭/炭复合材料表面沉积SiC梯度过渡层的形貌、微观结构和表面状态；原位生长SiC纳米线的尺寸，分布、微观结构和生长机理；化学气相共沉积方法制备HfC-SiC梯度复相涂层微观结构、元素分布及其抗烧蚀性能；化学气相共沉积方法制备SiC纳米线增韧HfC-SiC复相涂层的微观结构，生长机理及其抗烧蚀性能。揭示了SiC纳米线的增韧机理。研究发现：通过工艺优化，采用反应熔渗法制备了由大量的具有规则几何形状SiC颗粒以及连续的游离硅组成的SiC梯度过渡层，涂层中的游离硅均匀地分布在SiC颗粒之间孔隙中。采用原位生长法在SiC梯度过渡层表面合成的SiC纳米线均匀地覆盖在过渡层的表面上。纳米线的直径大约为 20~100 nm，长度达几十微米到几百微米不等，纳米线之间取向杂乱、相互交错，形成了一个疏松的多孔网格状结构。这些原位生长的纳米线纯度较高，在其表面并无其他杂质的存在。采用化学气相沉积法在C/C 表面制备了HfC-SiC梯度复相涂层。通过逐步增加热膨胀系数大的HfC组分，使得涂层热膨胀系数逐步增加，有效缓解了涂层中的热应力。HfC-SiC梯度复相涂层具有优异的抗烧蚀性能，烧蚀60 s后质量烧蚀率为0.1×10-3 g/s·cm2，线烧蚀率为-0.97×10-3 mm/s（负数表示增大）。采用化学气相共沉积法在含有SiC纳米线多孔层的C/C 表面制备了SiC纳米线增韧HfC-SiC复相涂层。在沉积过程中，涂层材料在SiC纳米线多孔层沉积生长时，并不是在SiC纳米线多孔层与SiC梯度过渡层界面处紧密堆积逐步填充孔隙，而是涂层材料围绕着SiC纳米线表面堆积生长，形成“加芯”的形貌特征。SiC纳米线的桥连和变形使得SiC纳米线增韧HfC-SiC复相涂层具有优异的抗烧蚀性能，烧蚀60 s后质量烧蚀率为0.14×10-3 g/s·cm2，线烧蚀率为-0.17×10-3 mm/s。本项目的研究明确了SiC纳米线在涂层中的增韧机理，揭示了采用化学气相共沉积方法在SiC纳米线多孔层中沉积涂层材料的生长机理，为在涂层中引入SiC 纳米线提供理论指导；揭示SiC纳米线增韧涂层的氧化烧蚀机理，为C/C复合材料在高质流冲刷环境中的应用提供理论基础。