Abstract
Austenitic stainless steels serve as load-bearing structural materials in the divertor and vacuum vessel components of fusion devices, where they are shielded from the plasma by beryllium or tungsten. Local loss of that armour layer during off-normal events exposes the underlying steel to direct plasma contact, a condition for which surface degradation data remain limited. In this work, 08Cr16Ni11Mo3Ti (analog of 316 Ti) austenitic stainless steel was irradiated with helium plasma at 2 keV ion energy and specimen temperatures of 250, 400, and 550 °C for exposures of 500 and 5000 s. Surface degradation depended strongly on the irradiation conditions; temperature appeared to be the dominant factor, although it co-varied with the ion flux: exposure at 250 °C produced no resolvable change in surface relief, whereas grain-boundary etching appeared at 400 °C and gave way at 550 °C to pronounced preferential sputtering that exposed grains, twin boundaries, and subgrain cellular structure. Mass-loss measurements indicate removal of approximately 3.4 µm after 5000 s at 550 °C, corresponding to a mean erosion rate of ~0.7 nm/s. Microhardness increased by 30–40 HV 0.05 after 500 s at all three temperatures and remained at a similar level after 5000 s at 400 and 550 °C, whereas an unexplained decrease below the unirradiated value was found at 250 °C. The results indicate that under sustained low-energy plasma exposure, the structural integrity of the section is retained while degradation is confined to a surface layer whose properties are tailored by the balance between implantation and erosion.