Surface modification and deuterium retention in reduced-activation steels under low-energy deuterium plasma exposure. Part Ⅱ: steels pre-damaged with 20 MeV W ions and high heat flux

摘要

The reduced-activation ferritic/martensitic (RAFM) steels including Eurofer (9Cr) and oxide dispersion strengthened (ODS) steels by the addition of Y_2O_3 particles investigated in Part Ⅰ were pre-damaged either with 20 MeV W ions at room temperature at IPP (Garching) or with high heat flux at FZJ (Juelich) and subsequently exposed to low energy (～20-200 eV per D) deuterium (D) plasma up to a fluence of 2.9 × 10~(25) D m~(-2) in the temperature range from 290 K to 700 K. The pre-irradiation with 20 MeV W ions at room temperature up to 1 displacement per atom (dpa) has no noticeable influence on the steel surface morphology before and after the D plasma exposure. The pre-irradiation with W ions leads to the same concentration of deuterium in all kinds of investigated steels, regardless of the presence of nanoparticles and Cr content. It was found that (ⅰ) both kinds of irradiation with W ions and high heat flux increase the D retention in steels compared to undamaged steels and (ⅱ) the D retention in both pre-damaged and undamaged steels decreases with a formation of surface roughness under the irradiation of steels with deuterium ions with incident energy which exceeds the threshold of sputtering. The increase in the D retention in RAFM steels pre-damaged either with W ions (damage up to ～3 μm) or high heat flux (damage up to ～10 μm) diminishes with increasing the temperature. It is important to mention that the near surface modifications caused by either implantation of high energy ions or a high heat flux load, significantly affect the total D retention at low temperatures or low fluences but have a negligible impact on the total D retention at elevated temperatures and high fluences because, in these cases, the D retention is mainly determined by bulk diffusion.