Composite Material Assignment (Ceramic Matrix Composite - CMC)
1st CMC: Single Wall Carbon Nanotube (SWCNT) Reinforced Alumina
CNTs as toughening elements to overcome the intrinsic brittleness of the ceramic or
glass material. Ceramic matrix composites (CMCs) have been developed to overcome the
intrinsic brittleness and mechanical unreliability of monolithic ceramics, which are otherwise
attractive for their high stiffness and strength. In addition to mechanical effects, the
reinforcing phase may benefit other properties such as electrical conductivity, thermal
expansion coefficient, hardness and thermal shock resistance. The combination of these
characteristics with intrinsic advantages of ceramic materials such as high-temperature
stability, high corrosion resistance, light weight and electrical insulation, makes CMCs very
attractive functional and structural materials for a variety of applications. SWCNT/alumina
composites are highly resistant to contact damage. Although this interpretation is in some
senses disappointing, the high resistance to contact damage is, in itself, a very attractive
property considering applications such as bearings, valves and other wear resistant machine
parts. (Cho, Boccaccini, & Shaffer, 2009)
Figure 1: SEM micrograph showing a fracture surface of the Al2O3/SWCNT
composite. (Wang, Padture, & Tanaka, 2004)
2nd CMC: C-fibre reinforced SiC composites (C/C-SiC composites)
C/C–SiC composites show superior tribological properties predestining these
materials for advanced friction systems. In the fabrication process, carbon fibres have to be
coated prior to the infiltration of silicon in order to reduce the degree of fibre degradation.
Also, highly graphitized carbon fibres are assumed to be mandatory for the fibre preform
because they are more stable in contact with silicon than non-graphitized fibres.
Consequently, C/C–SiC composites and adapted processes have to be developed to improve
these CMC materials for their applicability in high-performance brake systems. The main
requirements on new high-performance brake materials are stable dynamic and static
coefficients of friction, high wear stability for lifetime brake systems, low weight to reduce
the unsprung mass of the transportation system, high degree of freedom in the structural
design, low life cycle costs.
They show superior tribological properties in comparison to grey cast iron or
carbon/carbon. In combination of low density, high thermal shock resistance and good
abrasive resistance, they are promising candidates for advanced brake and clutch systems.
High improvements in wear resistance were achieved by functionally graded C/C–SiC
composites or by ceramic coatings. Almosts wear-free brake disks in combination with
acceptable low wear rates of the pads show a high potential for lifetime brake disks. The
future challenges comprise the reduction of the material costs and improvements of the
quality assurance. (Krenkel & Berndt, 2005)
Figure 2: Porsche ceramic composite brake (PCCB) (Krenkel & Berndt, 2005)
3rd CMC: SiC-SiC composites
SiC possesses superior mechanical properties, high thermal conductivity, low thermal
expansion, thermal shock resistance and chemical inertness. While the use of SiC as a nuclear
ceramic is largely driven by its exceptional mechanical and dimensional stability, there are
other properties of this material that are of concern because of their potential modifications in
reactor environments. Specifically, there is evidence that the excellent thermal conductivity
of non-irradiated SiC (up to ∼490 W/m K at RT) can be reduced by orders of magnitude due
to radiation-induced defects. (Katoh, Snead, Szlufarska, & Weber, 2012)
Graphite-moderated, gas-cooled thermal spectrum fission reactor (GCR) is a wellestablished nuclear technology. High temperature versions of GCR’s, called high temperature
and very high temperature reactors (HTGR and VHTR, respectively), are attracting renewed
interest due to their inherent passive safety feature and capability to provide high temperature
heat for versatile uses. However, the design of these reactors had been severely restricted by
the limited high temperature capability of available metallic heat-resistant alloys. With
advanced composite materials becoming industrially available, the newer reactor designs
started to rely on them for the in-vessel components. Among a number of components that
would be greatly benefited from the use of high temperature composites, control rod
structures for reaction control were identified to require SiC/SiC composite in some designs.
(Katoh et al., 2012)
Figure 3: Prototype SiC/SiC control rods with articulating joints (Katoh et al., 2012)
References
1. Cho, J., Boccaccini, A. R., & Shaffer, M. S. P. J. J. o. M. S. (2009). Ceramic matrix
composites containing carbon nanotubes. 44(8), 1934-1951. doi:10.1007/s10853-0093262-9
2. Katoh, Y., Snead, L. L., Szlufarska, I., & Weber, W. J. (2012). Radiation effects in SiC
for nuclear structural applications. Current Opinion in Solid State and Materials Science,
16(3), 143-152. doi:https://doi.org/10.1016/j.cossms.2012.03.005
3. Krenkel, W., & Berndt, F. (2005). C/C–SiC composites for space applications and
advanced friction systems. Materials Science and Engineering: A, 412(1), 177-181.
doi:https://doi.org/10.1016/j.msea.2005.08.204
4. Wang, X., Padture, N. P., & Tanaka, H. (2004). Contact-damage-resistant ceramic/singlewall carbon nanotubes and ceramic/graphite composites. Nature Materials, 3(8), 539-544.
doi:10.1038/nmat1161