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Systematic methods for amplification of sintered ultrahigh temperature ceramic matrix composites for aerospace applications -- progress and Prospects


Introduction: ultra high temperature ceramic matrix composites (uhtcmcs) are the next generation of composites developed for aerospace harsh environment. The identification of these materials needs to be tested in the relevant environment and needs to be expanded. In this paper, the scale-up system of carbon fiber reinforced zirconium diboride and silicon carbide from laboratory to industrial scale is described. The amplification process lasted three years and involved a 10-fold increase in diameter (from 40 to 400 mm) and a 30 fold increase in thickness (from 5 to 160 mm). Small scale products are consolidated by hot pressing of ISTEC, while larger samples are consolidated by industrial spark plasma sintering facility (nanokeer research, Spain). The large discs produced allow the production of 170 mm long bars for tensile testing and large ceramic tiles for hypersonic wind tunnel testing. Thick samples can be used to process complex shapes, such as screws and nuts, and vertical bars are used to characterize properties and nozzle demonstrators along the thickness of composite materials.


When traveling at Mach 5 or higher, the strong heat generated by the air in the atmosphere will damage the structural integrity of the hypersonic vehicle. Corrosive gases and particles affect the surface and affect the temperature of the external contour of the vehicle so that it rises above 2000 ° C, resulting in oxidation and ablation of the surface layer. The thermal protection system (TPS) must withstand these extreme temperatures and strong mechanical vibrations in order to enter orbit or re-enter the atmosphere from space. In the worse environment, the rocket engine nozzle must withstand extreme mechanical and thermochemical conditions, and the temperature exceeds 2500 ° C. In addition, the next generation rocket engine needs a new type of propellant with better performance, which can produce more thrust and carry more load. Ceramic matrix composite (CMC) is the only material that can withstand critical mechanical stress and high thermal shock, but the temperature higher than 1600-1700 ° C is still the operating limit of its use.


Ultra high temperature monolithic composite is a special kind of ceramic matrix composite, which is composed of ultra refractory matrix and carbon fiber (CF). These materials have been extensively researched and developed during h2020 EU project C. The researchers of this work proposed an innovative method in which carbon fibers are uniformly distributed and integrated into the super refractory sintered ceramic matrix. Neither on the fibers nor on the external thermal barrier coating (TBC). Sintering these uhtmcs by typical bulk ceramic scientific methods (e.g., hot pressing (HP), spark plasma sintering (SPS)) is a key processing step to distinguish these non oxide / C. f composite materials ultra-high temperature polychloromethane comes from its predecessor. Sintering is a very fast technology, which allows these CMC to be densified by heat treatment once in a few hours. When mechanical pressure is applied, the only disadvantage of planar shape is geometric limitation. For time-consuming technologies, such as chemical vapor permeation (CVI), and even polymer permeation and pyrolysis (PIP), one-time densification represents a huge advantage. The use of water-based slurry instead of volatile organic compounds and / or liquid chemical precursors makes the process more environmentally friendly than other conventional technologies that require repeated and environmentally friendly debonding cycles.


Previous work has identified key factors affecting the development of these composites, such as the design of matrix components, the setting of manual fiber preform impregnation or filament winding, the densification of composites by hot pressing or spark plasma sintering, mechanical characterization at room and high temperatures, oxidation studies at 1500 to 2100 ° C, and arc jet testing in plasma wind tunnel facilities. The results obtained show that HP and SPS can achieve similar microstructure and properties while reducing the temperature and treatment time of the latter.


The identification of these new materials requires the manufacture of demonstrators for testing in the relevant environment, which in turn requires scaling up. So far, there are few reports on the expansion of ultra-high temperature intermediate control products. In the published scientific literature, to our knowledge, the typical size of uhtcmc samples is 50-300 mm in plane, 4-20 mm in thickness, and no more than 45 mm in thickness. Two US companies produce large CMC components containing UHTC phase, such as ultramet and matech, while Airbus Europe (formerly EADS) is studying sicarbon UHTC enrichment.


In order to prove the potential of these materials to be used as external surface components of thermal protection system, the Italian Institute of ceramic science and technology designed TPS panels based on the actual missions in 2005 and 2012. On two vehicles, uhtcmc based on carbon fiber reinforced zirconium diboride and silicon carbide was used to scale up the system from laboratory to industrial scale. The amplification process took three years, and the diameter increased by ~ 10 times (from 40 to 400 mm) and the thickness increased by ~ 30 times (from 5 to 160 mm). Small products are integrated by hot pressing at ISTEC, while large samples are integrated by industrial discharge plasma sintering equipment (nanokeresearch, Spain). The relevant research was published on the top metal journal Composites Part B: Engineering with the title "a systematic approach for horizontal and vertical scale up of single ultra high temperature ceramic matrix composites for aerospace advances and perspectives".



Figure 1. assembly details for large ceramic tile testing, a) assembly without side plates, b) internal settings showing the connection to the base plane through uhtmcc supports, screws and nuts, c) sketch of nozzle inserts. The quotation is in mm. Provided by Avio spa.

Figure 2. A) sketch of uhtcmc manufacturing process and b) reason for uhtcmc material enlargement.

Fig. 3. Camera picture as sintering manufacturer. From left to right, top: hpd50, spd170, spd400; Bottom: hph45, sph45, sph160. The red circle indicates the manufacturer reporting its microstructure in Figure 4.

Fig. 4. microstructure of samples a) hpd50, b) spd170:c) spd400, d) sph160. for each sample, the micrograph from left to right shows the texture, fiber distribution in the matrix, matrix characteristics, and the fracture surface shows fiber pull-out.

Fig. 5. Microstructure analysis of sample spd400 at different positions in a 400 mm large disk. Fiber distribution, ceramic matrix and fiber / matrix interface were analyzed and compared for each point. The magnification of all frames is the same.

Fig. 6. A) hot pressing cycle of hph45, b) shrinkage curve of 45 mm high sample during SPS cycle of sph45. Deconvolution of the shrinkage curve was performed by using Pearson VII and pseudo Voigt functions for hped and spsed samples, respectively, to obtain a fit 2 with R higher than 0.99. c) The matrix / fiber interface shows nascent ZrB2 and ZrC particles anchored in the fibers and SiC particles embedded in the matrix. Inset: corresponding EDS spectra. d) Δ Temperature dependence of G ° on Eqs. (6) (12) calculation using HSC chemical package.

Fig. 7. A) stress-strain curves obtained by 4-point bending test (hpd50) and 3-point bending test (spd170, spd400 and sph160) under RT. b) and stress-strain curves obtained by 3-point bending test at 1800 ° C; Due to the high noise recorded in the strain measurement, a low-pass FFT filter was applied to the spd170 curve. c) Stress displacement curves obtained by tensile tests at room temperature, 1600 ° C and 1800 ° C D) stress strain curves obtained by 4-point bending tests on bars processed along the manufacturing thickness (stacking direction).

Fig. 8. A) pictures of slices vertically extracted from sph160 blocks and texture sketches of bent specimens. b) The fracture surface of sph160 sample is bent in a stacking configuration, indicating that fracture occurs at the interface.

Fig. 9. A) dog bone rod for tensile strength test; UHTC CMC connector: b) a set of screws (thread M10, pitch 1.5 mm, angle 60 °), c) screws and nuts d) assembling UHTC TPS tiles (194 mm × 240 mm × 4 mm) for hypersonic plasma wind tunnel testing, e) details of the support connection to the tile by screws and nuts.

Figure 10. A) a set of nozzle demonstrators with various shapes and sizes, obtained from the manufacture of hph45, sph45 for testing in different rocket engines, and b) the largest throat obtained from the manufacture of sph160 for demonstration purposes. (b) The illustration in is a top view of the nozzle demonstrator.