Realizing high corrosion resistance in liquid lead‑bismuth eutectic of 9Cr ODS alloys via forming Cr₂O₃ protective layer driven by Al and Si co-alloying

Low-Cr (9 wt%) ODS alloys usually develop Fe₃O₄-FeCr₂O₄ layers instead of Cr₂O₃ layers in oxygen-saturated liquid lead‑bismuth eutectic (LBE) at 550 °C. This study achieves enhanced corrosion resistance—manifested as superior spallation resistance and low oxide scale thickness (12.8 ± 3.2 μm) after 1555 h corrosion—in 9Cr ODS alloys via Al/Si co-alloying driven Cr₂O₃ layers formation. Multiscale characterization reveals that lattice mismatch-induced micro-voids at FeCr₂O₄/Fe₃O₄ interfaces compromise scale integrity. A dense Cr₂O₃ layer, discovered for the first time beneath the Fe₃O₄-FeCr₂O₄ layers in 9Cr ODS alloys with 1.5 wt% Al and 1 wt% Si, effectively inhibits LBE dissolution corrosion of the substrate. Layered Al₂O₃-SiO₂ and dispersed Al₂O₃ particles formed beneath the Cr₂O₃ layer, confirm preferential oxygen consumption by Al/Si over Cr in oxygen-depleted zones. Combining thermodynamic evidence establishes that the co-introduction of Al and Si avoids the oxidation of Cr during the initial stage, thereby promoting the outward diffusion of Cr ion to form a continuous Cr₂O₃ protective layer. However, as for the alloys with either 2.5 wt% Si or 2.5 wt% Al, Cr₂O₃ layer does not come into being due to the reduced oxygen concentration or partial Cr oxidation in the matrix.