Microstructural and mechanical properties of different ultra-high temperature CMCs: tensile and flexural strength up to 1800°C
GALIZIA P. 1, SCITI D. 1, BINNER J. 2, VENKATACHALAM V. 2, LAGOS ANGEL M. 3, SERVADEI F. 1, VINCI A. 1, ZOLI L. 1, REIMER T. 4
1 National Research Council of Italy - Institute of Science, Technology and Sustainability for Ceramics (CNR - ISSMC; former ISTEC), , Faenza, Italy; 2 School of Metallurgy and Materials - University of Birmingham, Birmingham, United Kingdom; 3 TECNALIA, Basque Research and Technology Alliance (BRTA), Donostia-San Sebastián, Spain; 4 DLR German Aerospace Center, Institute of Structures and Design, Stuttgart, Germany
In the frame of Horizon 2020 European C3HARME research project, the manufacture of ZrB2-based UHT-CMCs was developed through different processes: slurry infiltration and sintering (SIS), polymer infiltration and pyrolysis (PIP) and radio frequency chemical vapour infiltration (RF-CVI). This work presents a comparison of microstructures and mechanical properties of four different UHT-CMCs produced through the above processes:
Sintered short fibre composites manufactured by mixing ZrB2 plus SiC powder with pitch Cf milled down to a length of 150 µm. The mixture was consolidated by spark plasma sintering (SPS) at 1900°C.
Sintered continuous fibre composites produced by stacking in a 0/90° arrangement unidirectional fabrics infiltrated with ZrB2/SiC slurry. The green assembly, a disc of 400 mm diameter and 10 mm thickness, was sintered by Nanoker Research S.L. (Spain) in their hybrid SPS furnace H-HP D 400.
PIP composites fabricated via the filament winding and PIP process developed by Airbus (former EADS) and currently used to manufacture the SICARBON™ material. Pyrolytic carbon coated continuous carbon fibres were infiltrated with a slurry of a pre-ceramic SiC polymer, SiC, ZrB2 and Ta powders through filament winding technique. The obtained unidirectional fabrics were stacked in a 0/90°, cured in an autoclave and pyrolyzed at 1600°C in nitrogen atmosphere.
CVI composites prepared using 2.5D continuous Cf preforms infiltrated by a manual injection process with an ethanol based slurry containing ZrB2, nano particles of SiC and Y2O3 and polyethylene imine (PEI). The specimens were densified with pyrolytic carbon using a radio frequency (RF) heated chemical vapour infiltration process (RF-CVI).
Tensile testing with a novel optimized shape of the specimens was performed and compared with the results of flexural tests to assess the structural properties. For the first time, tensile tests up to 1600°C were carried out on UHT-CMCs. Despite the different microstructural features, all the ZrB2-based CMCs demonstrated excellent structural properties even at elevated temperature. The characterization shows how the different amount of porosity and fibre properties, such as its stiffness, strength and elongation, affected the mechanical behaviour of the C3HARME’s composites. Finally, the role of the high level of residual thermal stresses is discussed.
