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

Abstract

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 Cr₂O₃ and a compact Al₂O₃ layers, accompanied by nano-cavities in the substrate. At 10⁻⁶ wt.% oxygen, the Cr₂O₃ 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/Ni₃Al and M₂₃C₆.