Microstructure design, processing and oxidation/ablation behavior of advanced C/C composites modified by polymer-derived ultra-high temperature ceramics

该项目旨在制备轻质、抗氧化和烧蚀的先进C/C复合材料，具有高可靠性和自修复能力，适用于航空航天和飞机热防护系统中的超高温（> 2000 °C）应用。碳/碳复合材料基体在保护气氛中表现出优异的热机械性能，但当在高温下在空气和水蒸气中应用时，它们会遭受严重的氧化腐蚀和烧蚀。在这里，我们提出了一种组合策略，通过引入超高温陶瓷（UHTCs）通过聚合物衍生陶瓷（PDC）路线合成的C/C矩阵及其保护涂层的修改。根据第一性原理计算结果，首先合成合适的UHTC前驱体并进行优化。对于C/C复合材料的基体改性，将制备多孔骨架用于UHTC前驱体的渗透。在前驱体渗透和热处理过程之后，将获得由PDC-纳米复合材料（PDC-NC）改性的C/C基底。对于涂层，在PDC工艺之前，将用树脂和陶瓷前体施加梯度结构。Si气相渗透将进一步与残余碳反应，最终获得PDC-NCs-SiC复合涂层。我们提出的C/C复合材料及其抗氧化涂层概念的基础研究工作，都是由PDC-NC改性的，将集中在材料的成分选择，加工，微观结构控制和使用稳定性。（1）在2000 °C以上的服役条件下，采用第一性原理计算和有限元模拟相结合的方法，分析了UHTCs改性C/C复合材料与保护涂层系统的成分筛选、相容性和微观结构调控。(2)基于从上述理论考虑获得的结果，将对所需的和化学修饰的PDC-NC的合成和形成进行系统的研究。特别地，将选择超高温陶瓷如金属碳化物或氮化物或其包含Zr、Hf和Ta的固溶体作为嵌入SiC或SiCN基基质中的纳米相。将PDC-NCs引入C/C复合材料基体及其抗氧化涂层中，以提高C/C复合材料的抗氧化/烧蚀性能。研究了C/C基体与涂层的成分、界面，包括多相异质界面和形貌，以及热应力分布。(3)在热氧耦合环境下建立了成分、显微组织与抗氧化/烧蚀性能之间的关系。

The project aims to prepare light-weight and oxidation and ablation resistant advanced C/C composites with high reliability and self-repairing ability for applications at ultra-high temperature (> 2000 °C) in aerospace and aircraft thermal protection systems. Carbon/carbon composite matrices exhibit excellent thermomechanical properties in protective atmospheres while they suffer severely from oxidative corrosion and ablation when applied under air and water vapor at elevated temperatures. Here, we propose a combined strategy to modify the C/C matrix and its protective coatings by introducing ultra-high temperature ceramics (UHTCs) synthesized via the polymer derived ceramic (PDC) route. Suitable UHTC precursors will be firstly synthesized and optimized in terms of first principle calculation results. For the matrix modification of the C/C composites, a porous skeleton will be prepared for the infiltration of the UHTC precursors. After the precursor infiltration and heat-treatment process, a C/C substrate modified by PDC-nanocomposites (PDC-NCs) will be obtained. For the coating, a gradient structure will be applied with the resin and ceramic precursor prior to the PDC process. Si vapor infiltration will be further carried out to react with the residual carbon to finally obtain a PDC-NCs-SiC composite coating. The basic research work of our proposed concept on C/C composites and their anti-oxidant coatings, both modified by PDC-NCs, will be focused on the composition selection, processing, microstructure control and service stability of the materials. The following fundamental issues will be addressed in this context: (1) For service above 2000 °C, both first-principles calculations and finite element simulations are applied to analyze UHTCs modified C/C composites in combination with a protective coating system with respect to composition screening, compatibility and microstructure regulation. (2) Based on the results obtained from the above-mentioned theoretical considerations, systematical investigations on the synthesis and formation of the desired and chemically modified PDC-NCs will be performed. In particular, ultra-high-temperature ceramics such as metal carbides or nitrides or their solid solutions containing Zr, Hf and Ta will be selected as the nanophase embedded in a SiC- or SiCN-based matrix. A novel strategy of introducing PDC-NCs in the matrix of C/C composites and their anti-oxidant coatings to improve oxidation/ablation resistance of C/Cs will be developed. Composition and interface between C/C-substrate and coating including multi-phase hetero-interfaces and morphologies, as well as the thermal stress distribution will be studied. (3) The relationship between composition, microstructure and oxidation/ablation resistance will be established under a thermal oxygen coupling environment.