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Reporting period: 2018-12-01 to 2020-09-30

As the aerospace industry advances towards hypersonic flight, the quest for new, ground-breaking aircraft technologies has begun, and, together with it, the design of new advanced materials able to survive extreme conditions. During space flights, materials in the spacecraft are exposed to extremely harsh conditions: temperatures can suddenly rise above 2000 °C while corrosive gases and winds strongly hit the surface. Only ceramics can withstand such high temperatures, and among them, only ceramic matrix composites (CMCs), which consist of fibers embedded in a matrix, can survive thermal shocks and critical mechanical stresses. However, the harsh environment and the high temperature experienced by a spacecraft can still cause the erosion of CMCs, making expensive vehicles unable to resist several launches and re-entries. C3HARME addresses this technological gap, investigating new innovative materials, to supply the aerospace industry.

We have tackled this challenge by combining the best features of CMCs with the high-temperature resistance of another promising material: Ultra-High Temperature Ceramics (UHTCs). C3HARME had the aim to design, develop, manufacture and test a composite material that joins the physical and chemical properties of CMCs and UHTCs, aiming to create a new class of Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs). The proof of concept of C3HARME’s technology has been tested on prototypes for two spacecraft's components:
• Nozzles of rocket motors, which must survive temperatures above 2700 °C and the corrosive environment produced during the combustion of propellants;
• Tiles forming the Thermal Protection System (TPS) of hypersonic vehicles, which should resist the thermal shocks and stresses during the launch and re-entry into Earth’s atmosphere.
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.
C3HARME utilizes both the experience on UHTCs and CMCs to design a new hybrid outperforming class of materials, benefiting from these different classes of brittle and non-brittle, hard and soft, heavy and light materials, with the potential to successfully tailor the nano-, micro- and macro-structure.
The development of new technologies and materials often requires a final application in mind. For TPS tiles, C3HARME has identified a reusable Upper Stage as a potential future application. In the frame of propulsion applications, the introduction of UHTCMC does not require new concepts and these materials could be employed in currently used architectures in substitution of C-C materials. The availability of a new family of materials, capable of providing structural integrity, thermal protection and near-zero erosion rates will foster the implementation of new propellants for boost and thrust applications, while the development of reusable components will reduce cost and waste. This solution will potentially be a ground-breaking innovation also for many other fields with similar severe conditions, such as combustion and nuclear environments (Generation IV fission and fusion reactors) or the concentrating solar power system, thus paving the way for enormous exploitation opportunities. Not only performance but also timing and costs have been taken into consideration for screening the technologies, thus ensuring a smooth transition to the market. In this regard, the project coordinator (CNR) has deposited a new patent and extended its first patent in EU, US and China ; furthermore, a new Spin-off is under construction.
Prototype for lab scale wind tunnel test
C3HARME's goal
Copyright ESA - IXV Vehicle trajectory mission