A. Herrmann (Sp), M. Balden, A. Brendel, H. Bolt, Max Planck Institute for Plasma Physics, Garching (Germany)
In a fusion reactor the fusion plasma leads to a heat flux of up to 20 MW/m² in the divertor region. The heat has
to be removed efficiently from the plasma facing material (PFM) through the copper based heat sink to the cooling
channels. This will lead to temperatures of up to 550°C at the interface between PFM (W, C) and heat sink
material (CuCrZr). Due to the temperature gradient and different coefficients of thermal expansion, high stresses
occur at the interface of W/C and CuCrZr. Metal Matrix Composites like tungsten fibre reinforced copper has the
potential to strengthen this zone without dramatic lost of the thermal conductivity and thereby serve as a material
for the interlayer of the heat sinks in future fusion reactors.
The metal matrix composite is synthesised using the Matrix-Coated-Fibre (MCF) procedure. Pull-out tests of single
coated fibres were performed to determine the interfacial shear strength and the interfacial friction stress. For
tungsten fibre reinforced copper matrix composites the interfacial shear strength is 38 MPa and interfacial friction
stress is 27 MPa. To improve the interface between the tungsten fibre and the copper matrix, a graded transition
from tungsten reinforcement to the copper matrix is deposited by magnetron sputtering. The copper
concentration is thereby gradually increased from the fibre to the matrix. To understand the reactions between W
and Cu at the interface during the synthesis process of the MMC, dedicated interdiffusion experiments are
performed. Utilizing Rutherford Backscattering Spectrometry (RBS), interdiffusion profiles of W and Cu at 500°C,
650°C, 800°C and 900°C are measured. From these profiles the concentration and temperature dependent
interdiffusion coefficient of W and Cu can be extracted. This knowledge then allows to optimize the MMC synthesis
process.