Microstructure and nano-hardness of single crystal tungsten exposed to high flux deuterium plasma

The impact of the high flux deuterium plasma (mimicking ITER conditions) exposure on the surface hardness and microstructure of single crystal tungsten is assessed. Transmission electron microscopy revealed that the plasma exposure resulted in the formation of a dense dislocation network with a density of dislocation lines reaching (1–5) × 1013 m−2, depending on the exposure temperature. A combined analysis of the already available data and obtained here results suggest that under the investigated plasma conditions a highly localized plastic deformation occurs irrespective of the initial dislocation density or availability of grains and subgrains. On the one hand, the presence of the plastic deformation explains the high level of subsurface D trapping measured by nuclear reaction analysis (up to 10−2 atomic fraction within the top layer), and on the other hand—it explains the extra hardness measured within the region of the plasma-induced plastic deformation. A dedicated experiment to validate the above hypothesis is proposed.