SiC/Si3N4 MATRIX FOR CMC 2700F : OPTIMIZATION OF A HYBRID PIP-CVI PROCESS AS A TECHNOLOGICAL SOLUTION TO WORK AT HIGH TEMPERATURES WITHOUT COLLAPSING – MATRIX_2

To face the energy, environmental and economic challenges of air transportation, significant efforts are devoted to the next generation of aircraft turbojets, particularly in the field of advanced materials and their elaboration processes. The main objective is a decarbonisation of air transportation by 2050. These efforts are expected to drive us towards more performant and environmental friendly engines in a lower cost. However, these actions require the replacement of the key materials - metallic superalloys – as components of turbine parts (turbine rings, combustion chamber, …) which are no longer the material of the future for this application. The substitution of these superalloys by ceramic matrix composites (CMC) sufficiently stable at high temperatures (1450 ° C) would avoid the use of internal cooling while allowing the temperature increase of internal and external parts of turbojets. Moreover, the density of CMC being much lower than that of metallic superalloys, the use of these materials would also allow lightening the structures. The MATRIX_2 project (36 months, topic « Material » of the call for proposals) of the ASTRID2025 program is part of this context. The study focuses on the development of CMC whose composition is based on the ternary silicon-carbon-nitrogen (Si-C-N) system offering thermomechanical characteristics and a lifetime compatible with use at 1450°C (˜ 2700 F) for long periods of time to be used as internal engine components. The main objective of MATRIX_2 is to optimize a hybrid PIP (Polymer Impregnation Pyrolysis)-CVI (Chemical Vapor Deposition) process as a technological solution for continuous operation at high temperatures. It follows a previous ASTRID project (MATRIX, 2021 edition) which demonstrated a porous network of the PIP matrix not adapted to the CVI process. It is still based on a collaboration (but strengthened) between two research laboratories with internationally recognized and complementary expertise: the Institute of research for ceramics (IRCER, University of Limoges-UMR CNRS 7315-coordinator) and the Laboratory of thermostructural composites (LCTS, University of Bordeaux-UMR CNRS 5801) and a partner from the socio-economic world (Safran Ceramics, SCe). To reach the main objective, the work will consist to act on the formulations, additives (solvent and foaming/porogen agents) and the process to modify the fragmentation of the PIP matrix during pyrolysis and develop a multi-scale porosity that is open on the surface and progressively closed at the core while minimizing the presence of oxygen for the subsequent CVI cycle. The MATRIX_2 project - by focusing in particular on the process-structure-properties relationship through a coupling of experimental analyses and numerical modeling - provides clear added value compared to the literature. In this respect, it has a highly exploratory and innovative character in line with the definition of an ASTRID project. It is organized into five interconnected scientific work packages, ranging from the thermochemical behavior of a typical formulation to the measurement of the functional properties of CMCs and ask for one PhD and one postdoc fellow applications. This organization should make it possible to validate our approach and should enable us to tackle the various scientific and technological issues to use CMC in the next generation of turbojets for civil and military aircrafts. MATRIX_2 thus represents the key step to ultimately lead to the technological building blocks essential for the production of robust and certification-ready "2700 F" CMC components, in accordance with the energy, environmental and economic targets of the market and which offer a variety of properties of interest to the civil and defense sectors.