C/C-ZrC-SiC复合材料的烧蚀性能及烧蚀机理研究

Carbon/carbon (C/C) composites owning unique properties, such as low density, low coefficient of thermal expansion, and excellent ablation resistance, are potential materials for aerospace applications in nose tips, leading edges for reentry vehicles, and nozzles of solid rocket motor (SRM). Now it has been proved that C/C composites are ideal materials for SRM nozzles. However, with the development of new spacecrafts and SRM, and the use of new high-energy propellant in SRM, the mach number of spacecraft, specific thrust and chamber pressure of SRM increase, resulting in much higher ablation rates of C/C composites. Currently used C/C composites can not meet the demand of the components for new spacecrafts. The ablation resistance of C/C composites can be improved by infiltrating them with ultra-refractory materials, such as carbides/borides.. In the present study, ZrC-SiC modified C/C (C/C-ZrC-SiC) composites were fabricated by subsequent steps: carbon felts were immersed into a ZrC-SiC precursor solution, followed by heat treatment, rapid densification via thermal gradient chemical vapor infiltration with methane and graphitization. The effect of ZrC-SiC contents and particle sizes on the ablation properties of C/C composites will be studied. The equilibrium compositions of oxyacetylene, N2-plasma and propellant combustion gases will be calculated by the chemical thermodynamic softwares based on the principle of free energy minimum. The heterogeneous chemical reactions between these species and ZrC-SiC in C/C composites will be also calculated. Combined with ablation morphology analysis, the ablation behavior and mechanism of the C/C-ZrC-SiC composites in different ablation environments will be studied, which will give us a theoretical guide to prepare anti-ablative C/C composites with low ablation rates.

随着新型航天器用固体火箭发动机的发展以及新型高能推进剂的出现，飞行器马赫数、发动机比冲及燃烧室压强升高导致喉衬用C/C复合材料的烧蚀率急剧增大，已不能满足其作为热端部件的使用要求，C/C复合材料的抗烧蚀性能急需提高。把难熔金属化合物引入C/C复合材料中成为解决此问题的关键技术。本项目采用难熔金属盐溶液浸渍、化学气相渗透致密化和高温石墨化工艺获得ZrC-SiC改性的C/C（C/C-ZrC-SiC）复合材料。研究材料在氧乙炔、氮气等离子和小型固体火箭发动机试车环境的烧蚀性能。采用化学热力学软件基于最小自由能原理计算燃气组成，研究ZrC-SiC和燃气间的热化学反应，并深入研究C/C-ZrC-SiC复合材料在不同烧蚀环境的烧蚀机理。为进一步优化材料工艺设计提供思路，对制备高性能耐烧蚀C/C复合材料具有重要的理论指导意义。

随着战略导弹以及大型运载火箭对采用新型高能推进剂、高压强、大推力固体火箭发动机的急切需求，固体火箭发动机喉衬的抗烧蚀能力需要进一步提高，低烧蚀C/C喉衬材料成为目前急需解决的问题。采用ZrOCl2溶液浸渍法把锆化合物引入炭毡预制体中，经热处理、热梯度化学渗透和高温石墨化工艺制备了C/C-ZrC复合材料。采用三点弯曲法测试了材料的弯曲性能，研究了ZrC对C/C复合材料力学性能的影响规律，通过对材料微观结构和弯曲性能的表征分析，揭示了ZrC对材料力学性能的作用机制。采用氮气等离子烧蚀和固体火箭发动机烧蚀测试了材料的烧蚀性能，采用化学热力学软件计算了不同烧蚀环境的燃气成分以及ZrC和燃气的反应产物，并研究C/C-ZrC复合材料在不同烧蚀环境的烧蚀行为及烧蚀机理。 氮气等离子烧蚀结果表明：除碳升华外，碳与氮等离子体反应主要生成CN、C2N和C2N2等，ZrC和氮气等离子体火焰反应过程中除成CN和ZrN外，还伴随着ZrC的熔化和分解。C/C-ZrC复合材料良好的抗烧蚀性能主要归因于ZrC的液化、分解以及ZrN的液化吸热作用。 SRM烧蚀环境下，材料的烧蚀由热化学烧蚀和机械剥蚀共同控制。锥状纤维和壳状基体的形成来源于材料的热化学烧蚀，基体表面和锥状纤维端头部的碳碎片来源于材料的机械剥蚀。ZrC的优先氧化减少了碳消耗，ZrC氧化生成的ZrO2的液化和气化吸收了燃气的热量，减少了燃气对碳的攻击，从而提高了C/C复合材料的抗烧蚀性能。