Speaker
Description
For the ITER plasma-facing first wall the original plan of using beryllium as a wall material has been changed to using tungsten. In this configuration the first operational phase, will be performed with an inertially cooled “Temporary First Wall” [1]. The elements of this wall will experience different loading conditions depending on their respective locations. Correspondingly, the design comprises a mixture of bulk tungsten blocks, tungsten heavy alloy tiles, and tungsten-coated steel components. For this application a tungsten-based solution of cold sprayed (CS) coatings on steel is being developed.
In CS powder particles are accelerated to velocities on the order of 1000 m/s by an inert gas through a Laval nozzle and the bonding to a substrate occurs by plastic deformation upon impact. Therefore, the deposition of pure tungsten coatings by CS is currently not possible and W coating trials with admixtures of chromium, iron and steel have been performed as a follow up of the successful production of W/Ta coatings by CS [2]. This was done together with our Industry Partner Impact Innovations GmbH, Germany. With the finally chosen powder composition, Tungsten powder with 3 wt% admixture of AISI 316L steel, we obtained a coating with a tungsten content of 70 vol% and test samples on 80 * 80 mm² sized substrates with coating thicknesses of 100 and 200 µm, respectively, were produced.
The test samples were high heat flux tested in our facility GLADIS in accordance with the requirements given by ITER: In a first step we applied increasingly high power densities from 0.5 to 2.0 MW/m² with a fixed pulse duration of 4 s. At 2 MW/m² we then increased the pulse duration until a peak surface temperature of 800°C was reached. Finally, we performed a cyclic loading to a peak surface temperature of 800°C. To decrease the cool-down time in between pulses, this was done at a power density of 4.0 MW/m², which corresponded to a pulse duration of 2.8 s. After 100 pulses no deterioration of the coating due to the loading was observed by visual examination. A thorough comparison of pre- and post-characterization will be presented.
In a next step, larger test samples (~ 200 * 300 mm²) will be coated in order to demonstrate the scalability of the process.
[1] R. Pitts et al., Nucl. Mater. Energy 42 (2025) 101854
[2] K. Hunger et al., Fus. Eng. Des. 221 (2025) 115400