Phase-specific corrosion responses of FeCrNiAl dual-phase HEA to oxygen variations in lead-bismuth eutectic

This study elucidates the phase-specific corrosion mechanisms of a FeCrNiAl dual-phase high-entropy alloy (DP-HEA) in lead-bismuth eutectic (LBE) at 500 °C under two representative oxygen concentrations (10⁻⁴ wt% and 10⁻⁷ wt%). Through systematic multi-scale characterization, we reveal a sharp mechanistic transition from oxidation to selective dissolution governed by the dissolved oxygen content. In oxygen-saturated LBE, the Al-rich BCC matrix phase preferentially oxidizes to form a porous FeAl₂O₄ spinel network, while the FCC matrix phase exhibits superior oxidation resistance owing to the formation of Cr-rich oxides. Conversely, in oxygen-deficient LBE, the FCC phase undergoes rapid Ni depletion, structural destabilization, and phase transformation into BCC, whereas the BCC phase—stabilized by B2-NiAl and Fe–Cr intermetallics—remains largely intact. These findings demonstrate the opposing roles of FCC and BCC matrix phases in resisting oxidation and dissolution, respectively, and highlight the importance of oxygen activity in dictating corrosion pathways. A unified mechanistic framework is proposed to describe the corrosion evolution under varying oxygen conditions, providing critical insights for the design of LBE-compatible structural materials for lead-cooled fast reactors.