Surface morphological evolution and nanoneedle formation of 18Cr-ODS steel by focused ion beam bombardment

摘要

Morphological evolution upon intense energetic particle-matter interactions is of fundamental importance for materials utilized in extreme radiation environment, and controlling surface morphology by radiation also provides a new pathway for exploring non-equilibrium process at surface. In this work, surface morphology and microstructural evolution upon low energy ion irradiation of 18Cr-0DS, a candidate structural material for cladding and first wall of future fission and fusion reactors, were investigated by in situ focused Ga~+ ion beam/scanning electron microscopy and ex situ transmission electron microscopy. A surface roughening through pore formation, coalescence and eventually nanoneedle formation was induced on 18Cr-ODS steel surface. Cross-section microstructure analysis indicates that the formation of nanoneedle was not a result of grain recrystallization or chemical composition change. Pre-irradiated materials by He~+ and Fe~+ ions displays enhanced kinetics for surface morphological evolution and lower fluences of focused Ga~+ are required for the nanoneedle formation. These results suggest that the surface roughening and morphological evolution of 18Cr-ODS under low energy ion irradiation is an interplay between a curvature-dependent sputtering and defect accumulation near the surface.