Tungsten coatings for the JET ITER-like wall project

In the frame of JET's ITER-like wall project for most of the divertor surface tungsten coatings are intended to be employed on bidirectionally carbon fibre reinforced carbon substrates. Since this is thermomechanically rather mis-matched, a variety of deposition conditions were considered. Mostly in cooperation with industry, five Euratom associations provided 14 different types of samples with respect to production method and coating thickness. In a step-wise selection procedure, these were subjected to a thermal screening test and a thermal cycling test in the ion beam facility GLADIS as well as to an ELM-like thermal shock test in the electron beam facility JUDITH. A general failure mode is crack formation upon cool-down. Coatings with several microns of thickness show a distinct delamination feature in addition. Further analysis included metallographic investigation, X-ray diffraction for film stress assessment, adhesion testing as well as measurements on the contents of light impurities.