Erosion and morphology changes of F82H steel under simultaneous hydrogen and helium irradiation

The use of bare Reduced Activation Ferritic Martensitic (RAFM) steels has been proposed for the first wall in a fusion reactor. Thus, it is necessary to understand the erosion and surface morphology changes under direct and simultaneous hydrogen and helium implantation of RAFM steels under fusion-relevant condition. Experiments were performed at ion energies of ∼1 keV over the temperature range of 500–900 K, consistent with the anticipated operating conditions of the blanket region. The irradiation fluence was 1 × 10²⁴ m⁻² and the He% in the ion beam was 0.5%. Mass loss was measured before and after irradiation to determine erosion. Surface morphology changes were observed by SEM/FIB. RBS was used to quantify the near surface W concentration. From SEM images, surface roughening was observed at T > 750 K and complex surface structures formed with peak-to-peak variation in the ∼μm range. Mass loss increased with increasing surface roughening but the loss for simultaneous hydrogen-helium case was systematically higher compared to hydrogen-only case. A corresponding lower surface W concentration was measured for the simultaneous case, indicating Helium has an important role in W surface enrichment process.