Within C3HARME, the UHTCMC materials were produced following four basic processing methods, spanning from Spark Plasma Sintering (SPS) that allows ultrafast consolidation of the new UHTCMCs, to RadioFrequency Chemical Vapor Infiltration (RF-CVI), which allows a much faster infiltration compared to conventional CVI due to quick and uniform heating from inside-out, Reactive Melt Infiltration (RMI), a reliable zero shrinkage technology which enables complete elimination of pores in the matrix and Polymer Infiltration and Pyrolysis (PIP), which is the main method for fabricating current ceramic matrix composites with silicon carbide matrices or carbon. The partners further investigated cross-processing routes that combine multiple technologies to create innovative routes.
During the project lifetime, by means of all these processes, partners have prepared more than 50 compositions of the new materials mixing UHTC matrices with a melting temperature above 3000 °C. Partners have extensively analyzed the resulting materials to investigate the impact of the different types of fibres and the manufacturing approaches. Overall, the consortium has designed and developed about 1000 samples with a large variety of shapes; from simple ones like discs, bars to more elaborated like screws, nozzle inserts, etc. All the samples have been tested at the lab scale (TRL 4) to characterize the thermo-mechanical features. An extensive experimental campaign was carried out in the Aerospace Propulsion Laboratory and in an environment typical of atmospheric re-entry, the SPES (Small Planetary Entry Simulator) arc-jet wind tunnel available at the University of Naples. Numerical models were also employed to predict the flow field around test articles, the thermal behavior of the samples, and in general the oxidation and corrosion effects.
The campaign carried out allowed to screen for the composition and identified the most promising materials. In general, the developed UHTCMCs mostly displayed comparable or better strength and stiffness than a traditional material used as a reference, a C/SiC composite infiltrated with silicon. Furthermore, in order to assess the possibility to scale–up the processing routes, the samples were produced with increasing size, and its costs were monitored to ensure effectiveness. C3HARME recognized as viable processes: SPS for both propulsion (rocket nozzle) and thermal protection systems (tiles) and PIP for tiles. Indeed, in C3HARME the sintering technology (SPS) was easily scaled up to discs with 400 mm diameter and also increased in thickness. Notably, C3HARME reached the record of a piece of 11 kg with a total height of 160 mm, which is the thickest UHTCMC ever produced. The PIP process was also easily scaled up to produce large sheets of 4 mm thick UHTCMCs thus suitable for the production of TPS tiles.
These two methods were used to manufacture the prototypes for ground tests (e.g. solid rocket motor for nozzles and arc jet tests for thermal protection systems) and the resulting materials also demonstrated good machinability to obtain complex geometry from materials blocks. In particular, the UHTCMC tiles, when exposed to a realistic thermochemical re-entry environment, showed repeatability of the thermal response, structural integrity and a near-zero ablation property. The UHTCMC nozzle prototypes tested in solid rocket motors showed excellent erosion resistance, and thus proved the capability of the material to withstand relevant environment pressure and temperature values. Overall C3HARME started with a Technological Readiness Level of 3 and reached TRL 5/6 for TPS tiles and 6/7 for rocket nozzles in propulsion.
During the project lifetime, C3HARME was presented at several conferences and fairs. Furthermore, project results were published in 41 scientific papers (many others are in preparation), and 2 doctoral theses.
