High heat flux testing of wire-based laser metal deposition coated plasma-facing components

The severe environment and loads acting on plasma-facing components (PFCs) of future fusion power plants cause inevitable erosion of their armor. In situ regeneration of tungsten (W) armored PFCs by local deposition of material would open up the possibility of damage healing and compensation of eroded material. The wire-based laser metal deposition (LMD-w) process fulfils the necessary requirements for use in the reactor vessel. Process development for the deposition of W on W substrate has already been carried out and it has been proven that thermal induced damage in the PFM can be healed this way. In this study, W armored PFCs were coated using LMD-w and tested under fusion–relevant thermal loads in the electron beam facility JUDITH 2. One respectively two stacked layers, each ∼0.65 mm in height, were applied on the top surfaces of the W double tiles with surface areas of 28 × 12 mm2 respectively, which are the characteristic dimensions for the plasma-facing surface of monoblocks. Some of the coated surfaces were also smoothed by laser remelting. In the electron beam facility JUDITH 2, the test components were exposed to steady state as well as combined steady state and transient thermal loads that are expected in the divertor area of the future DEMOnstration power plant. The coatings were tested with cyclic (200 and 1000 cycles) steady state thermal loading in the form of surface temperatures equivalent to heat fluxes on monoblock components of 10 MW m−2 (∼1000 °C) and 15 MW m−2 (∼1500 °C). To determine the performance of LMD-w layers under thermal loads that are expected during exposure to edged localized modes (ELMs), some layers were subjected to combined steady state and transient loading scenarios (0.13–0.55 GW m−2, 103 to 105 pulses of 0.48 ms, 200–700 °C base-temperature). The temperature data obtained from the HHF experiments was processed and analyzed. Profile measurements on the coated surfaces before and after the high heat flux (HHF) exposure were used to investigate the influence of thermal stress on the deposited layers. Furthermore, cross-sectional micrographs of the test components were prepared and analyzed.