The Structure of the Tungsten Coatings Deposited by Combined Magnetron Sputtering and Ion Implantation for Nuclear Fusion Applications
Combined Magnetron Sputtering and Ion Implantation (CMSII) technology was used for W coating of about 1800 CFC tiles for ITER-like Wall (ILW) at JET and more than 1300 fine grain graphite tiles for ASDEX Upgrade tokamak. Thermal fatigue and carbidization due to the diffusion of the carbon from substrate were found as main phenomena limiting the service lifetime of the W coatings. Detailed investigation of these coatings using SEM and STEM together with the FIB (Focused Ion Beam) cutting technique revealed two fine networks of nano-pores with the size of 10­20nm for zones of 250­350nm at CFC-Mo and Mo-W interfaces. Formation of these nanopores is associated with the energy of the ions striking the coating during the deposition process. By optimizing this energy the nano-pores disappeared. The structure and the performances of the W coatings produced by the new modified technology (CMSII-M) were compared with those deposited by standard benchmark technology. The HHF (High Heat Flux) tests carried out with an electron beam at a temperature of 1450°C indicated an improvement of the thermo-mechanical properties by a factor of about 1.7.