a Location on the Fe foil used for SEM imaging. Orange represents irradiated region. Green represents unirradiated region. b SEM image of the salt-facing side after 6 h at 650 °C under 2.0 μA cm−2 proton irradiation. Scale bar: 1 mm. c Enlarged SEM image for the edge (unirradiated) region of the foil. Scale bar: 20 μm. d Enlarged SEM image for the center (irradiated) region of the foil. Scale bar: 20 μm. e Machine-learning based segmentation of b, showing auto-identified corroded (in red) and uncorroded (in yellow) regions. The white circle delineates the proton beam perimeter. Scale bar: 1 mm.