Melt-layer formation on PFMs and the consequences for the material performance

Highlights: • Pretests exhibited that with increasing the pulse duration and pulse number the sample surfaces evolved a pronounced hill-valley structure. • Sequential and simultaneous exposure to thermal and particle loads had no effect on the disruption preloaded samples but on ELM preloaded ones. • The surface roughness increased conspicuously accompanied by partially molten parts. • Simultaneous exposure created small holes all over the entire loaded area. - Abstract: One of the numerous challenges of the demonstration power plant DEMO is the selection of appropriate plasma facing materials (PFMs) and this task is ultimately important to the success for DEMO. Low-activation stainless steel (e.g. EUROFER, P92), which is already intended as structural material, could also become a possible plasma facing material, e.g. for the first wall (FW). Therefore, the ferritic martensitic steel P92 was investigated under DEMO relevant loading conditions. An area of the sample surfaces was firstly molten by transient events with varying power densities (A = 245 MW/m², B = 708 MW/m²) and afterwards simultaneously and sequentially exposed to thermal and particle loads. Surface modifications and pronounced microstructure changes were investigated dependent on the pre-exposure, loading sequence and power density. More precisely, it turned out that there was no connection between the loading sequence and the surface modifications for the preloaded A-samples contrary to preloaded B-samples. The preloaded B-samples exhibited surface roughening, melting and the formation of holes dependent on the loading sequence and power density.