C/C复合材料表面TaC/PyC核壳结构纳米线增韧HfC涂层的制备及烧蚀机理

HfC is suitable to be used as the ablation resistant coating material for C/C composites. However, the inherent brittleness of HfC coating and the mismatch of coefficient of thermal expansion between HfC coating and C/C substrate will result in the coating cracking or debonding during preparation and service. In order to resolve this problem, this project proposes the idea about preparing TaC/PyC core-shell structure nanowires (TaCnw/PyC) as the toughening materials for HfC coating on C/C composites. The final aim is to improve the toughness of HfC coating, and then improve the ablation resistance of HfC coating. The influence of technical parameters on the microstructure of TaCnw/PyC will be explored, the growth mechanism of TaCnw/PyC will be investigated to realize the controllable growth of TaCnw/PyC. The effect mechanism of TaCnw/PyC with different microstructure on the deposition process, microstructure, interal stress distribution, mechanical properties, thermophysical properties and ablation resistance of HfC coating will be analyzed. The interface bonding states between TaCnw and PyC and between PyC and HfC will be researched. The toughening mechanism of TaCnw/PyC will be investigated, as well as the ablation mechanism of the coated-C/C composites. The accomplishment of this project will provide foundational theory support for the preparation and application of HfC coating with good ablation resistance on C/C composites.

HfC是C/C复合材料表面抗烧蚀涂层的理想材料，然而HfC涂层本身固有的脆性及其与C/C复合材料间的热膨胀失配使其在制备和服役过程中易开裂、剥落。针对这一问题，本项目提出制备TaC/PyC核壳结构纳米线(TaCnw/PyC)作为C/C复合材料表面HfC涂层的增韧相，以提高HfC涂层的韧性，进而提高HfC涂层的抗烧蚀性能。探究工艺参数对TaCnw/PyC微观形貌结构的影响规律，分析其生长机制，实现其可控生长；系统研究不同形貌结构的TaCnw/PyC对HfC涂层的沉积过程、微观结构、内应力分布、力学性能、热物理性能及抗烧蚀性能的影响机制，分析TaCnw和PyC层之间以及PyC层和HfC涂层之间的界面结合状态，揭示TaCnw/PyC的增韧机制，并阐明涂层C/C复合材料的烧蚀机理。此项目有望为具有优异抗烧蚀性能的C/C复合材料表面HfC涂层的制备与航空航天应用奠定理论基础。

HfC和ZrC是C/C复合材料表面抗烧蚀涂层的理想材料，然而HfC-ZrC涂层本身固有的脆性及其与C/C复合材料间的热膨胀失配使其在制备和服役过程中易开裂、剥落。针对这一问题，本研究引入HfC/PyC核壳结构纳米线(HfCnw/PyC)作为C/C复合材料表面HfC-ZrC涂层的增韧相，以提高HfC-ZrC涂层的韧性，进而提高HfC-ZrC涂层的抗烧蚀性能。本研究首先采用催化辅助CVD工艺在C/C复合材料表面制备了HfCnw，对HfCnw的微观结构进行了表征，分析了HfCnw的生长机制；然后采用CVD工艺在HfCnw表面制备了PyC层，获得了HfCnw/PyC，研究了沉积时间对PyC层厚度的影响，表征了HfCnw/PyC的微观结构；最后采用CVD工艺在带有HfCnw/PyC的C/C复合材料表面制备了HfC-ZrC涂层，研究了HfCnw和HfCnw/PyC的引入对涂层沉积过程、微观形貌、力学性能和抗烧蚀性能的影响，揭示了HfCnw和HfCnw/PyC的增韧机理，分析了涂层C/C复合材料的烧蚀机理。主要研究结果如下：.（1）HfCnw/PyC由HfC核和PyC壳组成，层状非晶结构的PyC层均匀附着在HfCnw表面，HfCnw和PyC层之间结合良好；随着PyC层沉积时间的延长，PyC层厚度逐渐增加。.（2）HfCnw和HfCnw/PyC的引入提高了HfC-ZrC涂层的沉积效率、使得涂层结构由柱状晶转变为等轴晶、抑制涂层开裂。.（3）归因于纳米线的拔出、剥落、桥联、裂纹偏转机制，HfCnw提高了HfC-ZrC涂层的硬度、弹性模量、断裂韧性以及涂层/基体间的结合强度。引入HfCnw/PyC后，随着PyC层厚度的增加，HfC-ZrC涂层的硬度、弹性模量、残余应力逐渐降低，HfC-ZrC涂层的断裂韧性以及涂层/基体间的结合强度逐渐增加。.（4）HfCnw和HfCnw/PyC的引入提高了涂层的热导率、降低了涂层试样的表面烧蚀温度，HfCnw和HfCnw/PyC在烧蚀过程中氧化生成的HfO2纳米线在氧化物层中起骨架作用，提高了氧化物层的抗冲刷和抗烧蚀性能。.（5）PyC层可以降低涂层中的残余应力、提高涂层的断裂韧性、降低涂层表面烧蚀温度，但是PyC的氧化速率非常高，因此随着PyC层厚度的增加，HfC-ZrC涂层的抗烧蚀性能先增加后降低。