Structural phase transformations of gallium ion irradiated SUS304 steel

The plan-view and cross-sectional microstructures of SUS304 steel irradiated by gallium focused-ion beam were investigated using electron backscatter diffraction and energy dispersive X-ray spectroscopy. Structural phase transformation and gallium implantation were confirmed in the region of irradiated austenite grains. The amount of bcc phase and gallium concentration increased with increasing irradiation dose, which suggests that gallium implantation plays an important role as a ferrite stabilizer and also the source of stress effect. Crystallographic orientation relationships between bcc phase and austenite matrix were analyzed by considering the angular deviation between closed-packed planes and closed-packed directions. Differences in transformation behaviors between (001) and (111) austenite grains were discussed from the view-points of fcc-bcc interface structures. (author)