Heat Sink Materials for the Plasma-facing Components of Fusion Devices

H.-H. Bolt (Sp), Max-Planck-Institute for Plasma Physics, Garching (Germany); V. Barabash, ITER - CT, Garching (Germany); A. Brendel, T. Koeck, C. Linsmeier, Max-Planck-Institute for Plasma Physics, Garching (Germany) 
The plasma-facing components and especially the divertor of fusion devices are subjected to stationary heat fluxes of 10...20 MW/m². For the next generation experimental facility ITER precipitation hardened CuCrZr is used as heat sink material to transfer the heat from the plasma-facing protection material to the water coolant having a temperature of 80°C. In future fusion power reactors the use of CuCrZr will not be possible due to the need to increase the water coolant temperature to 300°C or in the case of helium coolant to at least 400°C. Under neutron radiation CuCrZr as well as ODS Cu show radiaton induced creep which prohibits the high temperature application of these materials.
For this high temperature heat sink application SiC fibre reinforced Cu is being proposed as metal-matrix composite material (MMC). This long fibre reinforced material is expected to be creep resistant also at high temperatures. For the initial development of this material SCS6 fibres have been used, because of the extensive experience regarding the use of these fibres in Ti-based MMCs for aeroengine applications.
During initial experiments the fibre-matrix interface and the bonding characteristics between matrix and fibre have been identified as critical. The application of an atomically deposited nm-scale Ti-interface resulted in excellent adhesion between fibre surface and matrix due to the formation of TiC and Cu-Ti phases. The interfacial shear strength with such tailored interfaces was approx. 60 MPa.
In the frame of an Integrated European Project ExtreMat “New Materials for Extreme Environments” the development of Cu-based high temperature heat sink materials will be pursued on a broader base involving several European partners. It is envisaged that ceramic fibre reinforced Cu will also be of use for other applications where large heat fluxes have to be removed at high temperatures.

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