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Microstructural evolution of inner oxide layer of a Si-modified austenitic stainless steel exposed to oxygen-saturated static lead-bismuth eutectic (LBE) at 550 °C up to 3000 h has been investigated. A dual-phase separated structure consisting of Fe-Cr spinel and (Fe, Cr) 1-x Ni x phase is formed in inner oxide layer, attributed to partitioning of Ni and Cr associated with Fe-Cr spinel formation. SiO 2 is preferentially formed preceding the Fe-Cr spinel at internal oxidation frontier, leading to dispersed SiO 2 nanoparticles within Fe-Cr spinel. The mechanism of LBE penetration into inner oxide layer is further developed based on preferable dissolution process of (Fe, Cr) 1-x Ni x phase. • A dual-phase separated structure consisting of Fe-Cr spinel oxide and (Fe, Cr) 1-x Ni x phase is developed in the inner oxide layer. • The formation of Fe-Cr spinel creates a Ni-riched and Cr-depleted micro-zone that is beneficial for forming (Fe, Cr) 1-x Ni x phase. • The dispersion of nano-sized SiO 2 oxide particles within Fe-Cr spinel is formed in the inner oxide layer. • The continuous LBE penetration into inner oxide layer is directly related to the preferable dissolution of (Fe, Cr) 1-x Ni x phase. [ABSTRACT FROM AUTHOR]

The present study discovered the twin boundaries (TBs) of CoCrNi medium-entropy alloy (MEA) exhibited high corrosion resistance to liquid lead-bismuth eutectic (LBE) at 500 °C with 5 × 10−7 mass% dissolved oxygen. The grain boundaries (GBs) were corroded by LBE, forming brittle Bi 3 Ni phases in LBE interior and at the LBE/CoCrNi interface. First-principles calculation indicated that the Bi diffusion energy barriers at GBs and TBs were 0.69 eV and 1.52 eV, respectively. The high diffusion barrier for Bi atom in CoCrNi MEA contributed to the high corrosion resistance of TBs in the liquid LBE. • This is the first report to estimate the corrosion behavior of medium-entropy alloy in liquid lead-bismuth eutectic (LBE). • The twin boundaries (TBs) show excellent resistance to the LBE attack. • The Bi diffusion energy barriers at grain boundaries (GBs) and TBs are 0.69 eV and 1.52 eV, respectively. • The high diffusion barrier for Bi atom in CoCrNi contributes to the high corrosion resistance of TBs in the liquid LBE. [ABSTRACT FROM AUTHOR]