Development of tungsten coatings on Inconel superalloy for COMPASS upgrade plasma-facing components

• Development of tungsten coating on Inconel for plasma-facing components in tokamaks. • Thin tungsten coating performed by physical vapor deposition (magnetron sputtering) • Post-mortem material characterization by SEM, GDOES, adhesion tests, calotests. • Surface morphology observation show dense coatings, good homogeneity and no defects. • Measurements of thickness, composition, residual stress, nanohardness. Thin tungsten coatings on Inconel superalloy were prepared in the frame of the COMPASS Upgrade project, the new high magnetic field tokamak with metallic walls now under construction at the Institute of Plasma Physics in Prague. The coatings will be used to cover the in-vessel Inconel tiles which are not in direct contact with the plasma, representing ∼75 % of the total first wall surface. This paper describes the latest developments in the coating technology by three different suppliers and presents a comprehensive comparative characterization of the different coatings (morphology, thickness, adhesion) produced by physical vapor deposition. Coatings with thicknesses in the range 7–20 µm were successfully produced and analyzed. Overall, they all show no blisters, no delamination nor other defects such as cracks, large pores, inclusions or droplets, and a good adhesion. All the coatings featured sufficient purity and homogeneity in thickness complying with COMPASS Upgrade specifications. The qualification of the coatings under high heat flux tests is presented in a companion paper.