Microcrystalline SiC/Si3N4 matrix composites for high temperature applications thought a PIP-CVI hybrid process – MATRIX

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. One of the actions to do consists of increasing the operating temperatures of turbomachines in order to increase their efficiency and thus reduce both specific fuel consumption and pollutant emissions while significantly reducing cooling air flow. This objective is in line with the transverse axis on energy. However, this action requires 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. Thus, by entering the scope of the topic « Material » of the ASTRID call, the MATRIX project of the ASTRID2021 program - an exploratory and innovative project with a TRL < 4 - is based on a collaboration between two research laboratories with internationally recognized and complementary expertises: the research institute on ceramics (IRCER, University of Limoges-UMR CNRS 7315-coordinator) and the laboratory of thermostructural composites (LCTS, University of Bordeaux-UMR CNRS 5801) and an industrial partner (Safran Ceramics, SCe). 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 technology implemented in MATRIX is based on a liquid phase infiltration process - Polymer Impregnation Pyrolysis (PIP) - from two formulations of preceramic polymers selected for their rheological properties tailored for impregnation of fiber preforms and their capabilities to form oxygen free-SiC/Si3N4 ceramics without the presence of sp2 carbon and free silicon phases. This tailored composition allows the considered ceramic matrices to be very stable both under an inert atmosphere at high temperature (1450°C) and in air at intermediate temperature (700°C). The liquid phase PIP process will be hybridized with a gas phase infiltration process - Chemical Vapor Infiltration (CVI) - in order to optimize the density of the CMC. The MATRIX project - with a particular focus on the process-structure-properties relationship - is organized into five interconnected scientific tasks, ranging from the preparation of formulations to the characterizations of the properties of CMCs. This organization is expected 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. At the end of the project (30 months), they should lead to the technological building blocks required for the production of robust CMC 2700F as components suitable for further development in an industrial context, in accordance with the energy, environmental and economic targets of the market.