Silicon Carbide Reinforced Copper as a Heat Sink Material for Future Fusion Reactors

T. Köck (Sp), A. Brendel, C. Popescu, H. Bolt, Max-Planck-Institut für Plasmaphysik, Garching (Germany); H. Schurmann, DLR Institut für Werkstoff-Forschung, Köln (Germany) 
Novel copper matrix composites reinforced with silicon carbide fibres are being considered as a new generation of heat sink materials for the divertor of future fusion reactors. The divertor is exposed to intense particle bombardment and heat loads of up to 10-15 MWm-2. Currently the divertor consists of the plasma facing material and the heat sink.
Due to its high thermal conductivity of about 400 W/mK copper could be a promising material for the heat sink. To increase the mechanical properties of copper at the working temperature of 550°C, silicon carbide fibres are used to reinforce the interface area between the plasma facing material and the heat sink.
The silicon carbide fibres (SCS-6, Specialty Materials) have a 3 µm thick carbon rich surface layer and a diameter of 140 µm. In a first step the fibres were electroplated with an 80 µm thick copper layer which acts as the matrix material in the composite. After a heat treatment, which is performed to reduce the porosity, the fibres were bundled in a copper capsule and hot isostatically pressed.
Push-out tests show, that the interfacial shear strength for such a compound is only about 6 MPa. To increase the interfacial adhesion of fibre and matrix, a 100-200 nm thin titanium interlayer is deposited between the fibre and copper by magnetron sputtering. Push-out tests show a ten times higher interfacial shear strength in comparison to the fibre without interlayer. Additional investigations by scanning electron microscopy on these specimens revealed that another weak point of this MMC is the SiC fibre itself. Cracks between the silicon carbide and the carbon rich surface layer are responsible for the failure. Due to these results silicon carbide fibres without this surface layer (SCS-0, Specialty Materials) will be used in the following experiments.
First characterization results for this modified metalmatrix composites will be presented.

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