Investigation of tungsten coatings on graphite and CFC

In the frame of JET's ITER-like wall (ILW) project tungsten coatings on carbon fibre reinforced carbon substrates will be used in the divertor and highly loaded areas in the main chamber. Fourteen different types of samples were produced by physical or chemical vapour deposition and vacuum plasma spray (VPS) with coating thickness of 4, 10 and 200 μm. Similarly, three different VPS W coatings (200 μm) on two different graphite substrates, were produced for use at the strike-point regions of ASDEX Upgrade. All coatings were subjected to thermal screening and thermal cycling tests in the ion beam facility GLADIS. Additionally, the coatings intended for the ILW project were exposed to edge localized mode (ELM)-like thermal loads in the electron beam facility JUDITH. A general failure mode with the CFC substrate is crack formation upon cool-down, whereas the coatings on graphite do not show any crack formation. Additionally, metallographic investigations, x-ray diffraction measurements, adhesion testing as well as measurements on the contents of light impurities were performed.