MANUFACTURING AND HIGH HEAT-FLUX LOADING OF TUNGSTEN COATINGS ON FINE-GRAIN GRAPHITE FOR THE ASDEX-UPGRADE DIVERTOR

Fine grain graphite tiles coated with tungsten layers by plasma spray (PS, thickness 100-550 mu m) and physical vapour deposition (PVD, 30-2 00 mu m), respectively, were subjected to thermal loads up to 17 MW/m( 2) and 2 s pulse duration. The damage limit was evaluated by increasin g the heat flux and the pulse length stepwise, The results proved that PS coatings are capable of withstanding heat loads up to 15 MW/m(2) a t 2 s pulse length without any structural changes, and cyclic loading with 1000 cycles at 10 MW/m(2), The highly dense PVD coatings suffered damage by crack formation at slightly lower heat loads, and thin PVD layers failed under cyclic loading with 1000 cycles at 10 MW/m(2) due to thermal fatigue and melting. The good performance of PS coatings is related to their porosity, which provides a crack arresting mechanism , and to their mechanical strength, depending on the density of the PS layer.