Corrosion behavior in liquid lead of a novel FCC non-equiatomic high-entropy alloy capable of forming an alumina protective oxide scale

This study presents the design, characterization and evaluation of corrosion resistance and mechanical integrity of a novel Co-free face-centered cubic (FCC) non-equiatomic Fe 33.5 Ni 43.5 Cr 11 Mn 6 Al 6 High-Entropy Alloy (HEA) for structural applications in Generation IV Lead-cooled Fast Reactors (LFRs). The alloy was engineered to form a protective Al-rich oxide scale. Liquid Metal Corrosion (LMC) tests were conducted in stagnant liquid Pb at 550 °C and 650 °C for 1150 h, under controlled oxygen concentrations ranging from 7.4·10 -6 to 8.6·10 -6 wt.% at 550 °C, and from 4.5·10 -5 to 3.6·10 -4 wt.% at 650 °C. Liquid Metal Embrittlement (LME) susceptibility was assessed via Slow Strain Rate Testing (SSRT) between 350 °C to 600 °C. LMC test results revealed bilayer oxide scale formation, with an inner amorphous alumina scale acting as an effective diffusion barrier and a complex outer Mn(Al,Fe,Cr) 2 O 4 spinel prone to detachment. The alloy exhibited self-healing behavior, regenerating protective oxides in areas where Pb penetration took place. No signs of LME were observed up to 400 °C, with embrittlement onset occurring at 500 °C. Despite its high Ni content, which is typically detrimental in liquid Pb due to the its high solubility at elevated temperatures, leading to accelerated degradation, combined with low oxygen availability that hinders protective oxide formation and microstructural heterogeneities (oxide inclusions and local grain size variations), the alloy maintained excellent corrosion resistance and mechanical integrity. These results underscore the exceptional corrosion resistance of this non-equiatomic Fe 33.5 Ni 43.5 Cr 11 Mn 6 Al 6 HEA, positioning it as a highly promising candidate for high-temperature nuclear applications in Pb-cooled systems. • Demonstrated the formation of a stable, protective Al-rich oxide scale in stagnant liquid Pb at 550 °C and 650 °C after 1150 h of exposure. • Despite its high Ni content (~46 wt.%), the alloy showed no significant Ni dissolution. • The alloy exhibited self-healing behavior, regenerating protective oxides after localized Pb penetration. • Maintained microstructural stability and developed L1 2 and B2 precipitates that enhanced mechanical strength. • The alloy was resistant to Liquid Metal Embrittlement up to 400 °C, with embrittlement onset only at 500 °C under extreme Pb exposure.