High-resolution characterization revealing the effect of dissolved oxygen in lead-bismuth eutectic (LBE) on oxide scale and subsurface phase transformation layer in alumina-forming austenitic (AFA) steel

The oxidation behavior of AFA steel was examined after exposure to LBE with 10 ⁻⁸, 10 ⁻⁶, and 10 ⁻³ wt.% oxygen at 600°C for 500 h. At 10 ⁻⁸ wt.% oxygen, a 50–200 nm oxide scale was formed with a discontinuous Cr ₂O ₃ and a compact Al ₂O ₃ layers, accompanied by nano-cavities in the substrate. At 10 ⁻⁶ wt.% oxygen, the Cr ₂O ₃ layer became continuous, nano-cavities disappeared, and the oxide scale thickness reduced to 50–100 nm. At 10 ⁻³ wt.% oxygen, a defective three-layered oxide scale formed, reaching a thickness of 3–5 μm. Additionally, a subsurface phase transformation layer was developed, characterized by associated NiAl/Ni ₃Al and M ₂₃C ₆.