JEC COMPOSITES MAGAZINE - Issue #33 - June 2007 - 67

MAX PLANCK INSTITUTE FOR PLASMA PHYSICS, EURATOM ASSOCIATION, GARCHING, GERMANY 1 2 3 Metal matrix composite for fusion application KNOW-HOW Metal matrix Background 1- DIPL.-ING. A. HERRMANN, PHD STUDENT 2- DR A. BRENDEL, SENIOR SCIENTIST 3- DR M. BALDEN, SENIOR SCIENTIST 4- PROF. DR DR H. BOLT, HEAD OF DIVISION New Cu/SiC and Cu/W composite materials with improved interface properties are being developed to strengthen a highly stressed zone in fusion reactors. heat sink [7]. To strengthen this zone, two metal-matrix composite (MMC) concepts are suggested: SiC fibre [8] or W fibre reinforced copper. The fibres contribute to the strength of the composite and the copper provides the required thermal conductivity of at least 200 W/mK. Fig. 1: The future DEMO demonstration fusion reactor with potential divertor design concepts: flat-tile and monoblock*. *modified from EFDA, "A Conceptual study of commercial Fusion Power Plants" (2004) Fossil fuels or renewable energy alone cannot meet future energy demands. Furthermore, nuclear fission involves significant drawbacks and risks, e.g. the radioactive waste. An alternative power source is nuclear fusion, where light atoms fuse to heavier ones in a fusion reactor by transforming mass into energy. During the fusion of the hydrogen isotopes, deuterium and tritium, to helium and to an energetic neutron, an energy amount of 17.6 MeV is released [1]. In magnetic confinement fusion devices, the highest loaded zone in a fusion reactor vessel is the divertor, where the fusion plasma touches the vessel wall. The divertor is exposed to heat loads of up to 20 MW/m2 [2], [3]. Therefore, the plasma-facing material (PFM) in the divertor region needs an effective heat sink with cooling channels to remove the heat coming from the fusion plasma. In general, the divertor thus far is composed of two parts: the direct plasma-facing material consisting of carbon or tungsten components, and the heat sink consisting of copper-rich CuCrZr alloy materials with cooling channels [4], [5]. Future fusion reactors like DEMO will operate with coolant temperatures of at least 300°C for efficient energy production. Two different design concepts are proposed: flat-tile and monoblock (Figure 1). The heat flux loading will lead to temperatures of up to 550°C at the interface between the PFM (W, C) and the heat-sink material (CuCrZr) [6]. The temperature gradient and the thermal expansion mismatch of both parts of the divertor create high stresses at the interface between the plasma-facing material and Beside the application of MMC in fusion reactors, composite materials are successfully used as heat-sink materials in space applications or microelectronics. Their properties can be tailored in a wide range, mainly via an appropriate design of the interface between the fibres and the matrix, which plays a key role in macroscopic properties [9], [10]. Thus, the main purpose of the work carried out by the IPP MMC research group is the development of Cu/SiC and Cu/W composite materials with improved interface properties. The low interfacial shear strength between SiC fibre and Cu matrix without appropriate interface indicates a very weak bonding between fibres and matrix. For adjusting a suitable bonding strength between the composite partners, we incorporated a titanium interlayer between SiC fibre and matrix as coupling agent in the case of the Cu/SiC composite, followed by an adequate thermal treatment to affect chemical reactions between the titanium and the carbon coating of the fibres. To optimise the fibre/matrix bonding strength of the Cu/W composite, three interfacial concepts were compared: No33 June 2007 / JEC Composites Magazine

JEC COMPOSITES MAGAZINE - Issue #33 - June 2007

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