Laser re-melting of tungsten damaged by transient heat loads

摘要

Highlights ? Laser surface remelting was used to ?repair“ cracked surfaces of tungsten. ? The samples were previously loaded with thermal shocks by electron beam. ? Closed and smooth (±25 μm) surfaces could be achieved. ? Surface repair could increase plasma facing material lifetime in fusion reactors. Abstract In the current study, a solid state disc laser with a wavelength of 1030 nm and maximum power of 5.3 kW was used to melt the surface of pure tungsten samples (manufactured according to ITER specifications by Plansee SE). Several combinations of laser power and traverse velocity were tested, with the aim of eliminating any pre-existing cracks and forming a smooth and contiguous resolidified surface. Some of the samples were previously damaged by the electron beam simulation of 100 THLs of 0.38 GW/m2 intensity (Δt = 1 ms) on a 4 × 4 mm2 area in the JUDITH 1 facility. These conditions were chosen because the resulting damage (crack network) and the crack depth (～200–300 μm) are known from previous identical material tests with subsequent cross sectioning. After laser melting, the samples were analyzed by SEM, laser profilometry and metallographic cross sectioning. A closed surface without cracks, an increased grain size and pronounced grain boundaries in the resolidified area were found. Profilometry proved that the surface height variations are within ±25 μm from the original surface height, meaning a very smooth surface was achieved. These results successfully demonstrate the possibility of repairing a cracked tungsten surface by laser surface re-melting. This “laser repair” could be used to extend the lifetime of future plasma facing components.