Oxidation behavior of nozzle throat carbon/carbon composites featuring variable density
Creators: name:  M. FRADIN 
name:   G. VIGNOLES 
name:   F. REBILLAT 
name:   K. HARAS 
name:   C. GREGIS 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: STRUCTURES
MATERIALS
HIGHE TEMPERATURE MATERIALS

description: Carbon fiber-reinforced pyrocarbon matrix composites (Cf /CPyC ) are constitutive materials of nonmilitary launcher nozzle throats. Thermo-physicochemical conditions are harsh in this engine region and generate surface recession called ablation. These materials are used not only for their thermal insulation and high-temperature mechanical performances, but also mostly for their resistance to ablation. Indeed, the surface recession rate is a key parameter in nozzle throat design: as soon as the nozzle diameter changes due to ablation, the thrust efficiency decreases. Industrial fabrication processes of Cf /CPyC (shaping fibrous architecture, pyrolytic carbon matrix infiltration by CVI, thermal treatments) result in the formation of a multi-scale pore network and of density inhomogeneities across the nozzle part thickness. It has been observed that nozzle throat erosion rate during real rocket launch is impacted by porosity gradients, as well as by the different nano-textures of the infiltrated pyrocarbons. This work aims at providing tangible elements to AGS in the understanding and prediction of Cf /CPyC oxidation behavior in relation to densification rates and pyrocarbon nano-textures. The evolution of morphology (main affected regions and depths) and topology (specific surface, porosity, pores diameters), effective and intrinsic oxidation kinetics, global erosion rates, surface and volume reaction-to-diffusion competition, according to temperature and density, are all key parameters in Cf /CPyC behavior identification. This has led to establish a coupled-technique and multi-scale method. Retrieving effective kinetics and morphologies through oxidation experiments, used as input parameters of multi-scale numerical and analytical modeling, has already been carried out on fibers preforms and fully densified C/C materials, which are two-phased materials [1, 2]. However, this approach is brand new on porous C/C which are three-phased materials (fiber, matrix, pores). Coupling experimental results with modeling techniques at different material scales aims at determining the reaction-to-diffusion prevalence and intrinsic kinetics parameters, which are not obvious at first sight. Reciprocally, this approach allows to predict materials behavior knowing intrinsic and environmental parameters. To cover a sufficiently large domain of ablation temperatures, this study focuses on two complementary experimental devices for low and high oxidation temperatures: a TGA reactor (723-1273K) and an arc lamp furnace (1000-2500K). The use of the latter is completely original for that kind of study, since initially developed for crystalline growth by zone fusion. In order to follow topological evolutions, experimental means (krypton adsorption, helium pycnometry, mercury porosimetry) and 3D-image processing techniques [3] are compared. Finally, 3D-image correlation has turned out to be a particularly well-suited numerical tool to identify affected zones and depths, compared to 2D imaging.