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

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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.