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FeCrAl alloy is one of the potential candidates of structural materials due to its high strength, low radiation swelling and good oxidation resistance for the application of lead-cooled fast reactors (LFRs). Particularly, FeCrAl alloy can form protective Al-containing oxide scales after exposure to liquid oxygen-rich Pb and lead–bismuth eutectic (LBE) at 400–800 ℃, showing better performance than traditional commercial stainless steels such as T91, 316L and 15-15Ti. Given the possibility that oxygen in liquid metal could be consumed and not be supplied timely in some quasi-static regions of the actual coolant circuit, to figure out the corrosion behavior of FeCrAl alloy in oxygen-depleted LBE is necessary. In this work, the commercial FeCrAl alloy was exposed to static liquid LBE containing Ni impurities with 10−9 wt% oxygen concentration at 600 ℃ for up to 5000 h, and the surface and cross-sectional morphology of the samples was characterized and analysed. It is found that FeCrAl alloy underwent severe dissolution corrosion, and the maximum penetration depth of LBE reached 161.4 μm after the test for 5000 h; PbBi infiltrated into alloy matrix along the GBs and selectively leached Al from the affected grains. Besides, an interesting discovery is the Cr-rich thin layer at LBE/matrix interface and Ni3Al precipitates in LBE penetration front which should be attributed to the deposition of impurity elements dissolved in liquid LBE during the cooling process.

Crevice corrosion is a significant form of localized corrosion that can lead to failures in structural components. However, there is a lack of research on this phenomenon in liquid lead-bismuth eutectic (LBE). In this study, the crevice corrosion behavior of 316 L exposed to stagnant LBE with the oxygen concentration of 1 × 10–6 wt.% at 550 °C for 500 h was examined for the first time. Microstructural characterizations indicated 316 L is susceptible to crevice corrosion and reducing the crevices size facilitates a transition from oxidation to dissolution corrosion. Grain boundaries are able to provide more diffusion channels for oxygen, thereby promoting the development of Cr-rich oxides and chemical segregations beneath the surface scale. A simplified model elucidating the transportation of dissolved oxygen within the crevice environment of LBE has been developed. [Display omitted] [ABSTRACT FROM AUTHOR]

Liquid lead (Pb) is a promising coolant for lead-cooled fast reactors, and has advantages over lead–bismuth eutectic (LBE) in many aspects. But it can also cause severe corrosion to structural materials at high temperatures. In this study, the chemical states of 10 alloying elements as well as H and O in liquid Pb were investigated via ab initio molecular dynamics, and the local structure, dissolution and charge transfer were analyzed systematically. In liquid Pb, the coordination numbers (CNs) of Fe and Ni are the smallest, with the value of 7.72 and 7.01, respectively, and Al, Mn, Mo, Nb, Ti, and Si have the biggest CNs with about 12. This is correlated with the effective atomic radii in liquid Pb. Judged by the dissolution energy, the tendency of alloying elements to dissolve in liquid Pb is Al > Si > Ni > Ti > Cu > Fe > Mn > Nb > Cr > Mo. The calculated Bader charges show that the alloying atoms undergo minimal electron transfer in liquid Pb except Ti. H 2 , H 2 O, and O 2 will decompose quickly and cannot exist in liquid Pb. Then, the alloying element will form a strong binding with O atom, especially Al and Si. O atoms can lead to an increase in the coordination of alloying atoms in liquid Pb and obviously reduce their diffusion coefficients in most cases. These findings can provide guidance for predicting material corrosion and designing future high-performance corrosion-resistant materials. [ABSTRACT FROM AUTHOR]

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]

Using density-functional calculations, we studied the interaction between interstitial impurities (N, C) and γ-Fe(111) surfaces doped, or not, with Cr, as well as the effect of Cr doping on the dissolution corrosion resistance of the γ-Fe(111) surface. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the stainless steel surface. The aim of this work was to study, at the atomic scale, the effects of N and C on the segregation behavior of Cr and the synergetic effect between co-doped atoms on the resistance to dissolution corrosion of austenitic stainless steel surfaces. The results showed that interstitial impurities prefer to be trapped at near-surface sites, which can impact the segregation behavior of Cr such that it shifts from the surface to the subsurface. Electrode potential calculations and density of states analysis demonstrated that doping with Cr or inserting interstitial impurities into the solid solution can improve the surface corrosion resistance of an fcc Fe substrate, but detrimental effects on the surface corrosion resistance are induced by interactions between Cr and interstitial impurity atoms in co-doped surfaces. The formation of near-surface Cr carbides and nitrides (speculated to be Cr2N and Cr23C6 due to the results obtained for particular co-doped surfaces) was also noted. The results of our theoretical calculations explain some of the experimental results observed at the atomic scale. [ABSTRACT FROM AUTHOR]

Effects of alloying elements in popular steels on the oxidation and dissolution corrosion of the surface of γ-Fe(111) have been investigated by performing density functional theory calculations within the local density approximation. First, the segregation of alloying atoms as well as preferential adsorption sites for oxygen and water were carefully examined, and it was found that all of the alloying elements considered had a tendency to segregate to the surface, and that the most preferred adsorption sites were the hexagonal closed packed (hcp) site and the top site for oxygen and water, respectively. The adsorption energies that characterized the tendency for oxygen or water to be adsorbed on the alloy surface showed that all ten alloying elements (especially Cr, Si, and Cu) were able to inhibit the adsorption of oxygen, and that all of the alloying elements except for Nb, Mo, and Ti inhibited water adsorption. The electrode potentials, which indicate the electrochemical stabilities of the surfaces of the alloys, suggested that all of these alloying elements (especially Cr, Mo, and Si) were able to suppress the adsorption of oxygen and water on the investigated surfaces, except for Nb and Ti in the case of water adsorption. Density of states analysis further indicated that all ten alloying elements (especially Cr, Si, Mo, and Cu) enhanced the corrosion resistance of the fcc Fe substrate, except for Nb and Ti with respect to dissolution corrosion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The dissolution properties of liquid Pb/Bi on 4H-SiC (0001) surfaces are explored. • Liquid Bi is more corrosive than liquid Pb on 4H-SiC surfaces. • C atoms are dissolved more easily than Si atoms on 4H-SiC surfaces. • Depletion of C atoms may result in the formation of Si amorphization layer. • A theoretical scheme is proposed to improve the corrosion resistance of 4H-SiC. The dissolution corrosion of liquid Pb/Bi on 4H-SiC (0001) surfaces are studied based on first-principles calculations and experimental studies. The calculation models of 4H-SiC (0001) surfaces are proposed according to the experimental results, and the rationality of the models is verified by our repeated experiments. Clean surface stability is mainly determined by the strength of surface states due to the dangling bonds. Pb/Bi adatoms accelerate the dissolution of C atoms more severely than that of Si atoms and liquid Bi is more corrosive than liquid Pb, which are consistent with our experimental results. Energetics, microstructural and electronic properties are analyzed to reveal the corrosion mechanism of liquid Pb/Bi. Moreover, we provide a theoretical scheme to improve the corrosion resistance of 4H-SiC by adjusting the charges of vacancies and changing the relative position of Fermi level. [ABSTRACT FROM AUTHOR]

Liquid Lead-Lithium (PbLi) alloys are promising functional material which can act as both neutron multiplier and tritium breeder in liquid blanket of fusion reactors, however, their corrosion behavior on RAFM steel is still a challenge. In this work, the dissolution, diffusion, bonding and charging behavior of steel alloy elements in liquid PbLi were investigated by using the first principles molecular dynamics simulations. The dissolution order of the main alloy elements of RAFM steel dissolved into the liquid PbLi was Cr>Fe>V>Mn>Ta>W>C. O atom tend to bond with Li atom in liquid PbLi and the O dissolution energy had negative value of -3.84 eV. The binding energies of Y-O, Ti-O, Al-O, Si-O, Zr-O, Ta-C, V-C, Ta-N and V-N pairs within liquid PbLi at temperature 500°C show that related oxides/carbides/nitrides in RAFM steel do not likely to decompose and may not affect their dissolution corrosion behavior. These data can provide indispensable information for understanding the dissolution corrosion behavior of advanced RAFM steel in liquid PbLi. [ABSTRACT FROM AUTHOR]

The effects of low-temperature oxy-nitriding (LTON) treatment on the liquid lead-bismuth eutectic (LBE) corrosion behaviors of 316 L ASS were investigated in the stagnant liquid LBE under vacuum at 823 K. Results show that the untreated samples were severely selective leaching in contact with liquid LBE. LTON treatment produced an outer porous Fe-Cr spinel film and inner S phase layer on the sample surface, which transformed into a thicker spinel film containing γ low-N and a region distributed with CrN precipitates after liquid LBE corrosion. This was mainly attributed to the oxidation and decomposition of S phase and inward diffusion of the interstitials, owing to S phase is a metastable phase and is easier to be oxidized than matrix at elevated temperatures. This inspired us that improving the ability to form protective oxide film for materials was maybe a good method to mitigate the liquid LBE corrosion. [Display omitted] [ABSTRACT FROM AUTHOR]

This work addresses the early stages (≤1000 h) of the dissolution corrosion behavior of 316L and DIN 1.4970 austenitic stainless steels in contact with oxygen-poor (C O < 10−8 mass%), static liquid lead‑bismuth eutectic (LBE) at 500 °C for 600–1000 h. The objective of this study was to determine the relative early-stage resistance of the uncoated steels to dissolution corrosion and to assess the protectiveness of select candidate coatings (Cr 2 AlC, Al 2 O 3 , V 2 Al x C y). The simultaneous exposure of steels with intended differences in microstructure and thermomechanical state showed the effects of steel grain size, density of annealing/deformation twins, and secondary precipitates on the steel dissolution corrosion behavior. The findings of this study provide recommendations on steel manufacturing with the aim of using the steels to construct Gen-IV lead-cooled fast reactors. [Display omitted] • Grain boundaries, annealing and deformation twins promote LBE dissolution attack. • Coarse-grained steels with many annealing twins are prone to dissolution corrosion. • Fine-grained steels with many deformation twins are prone to dissolution corrosion. • Texture typically affects only the local steel dissolution corrosion behavior. • Ceramic coatings protected DIN 1.4970 cladding tubes from LBE dissolution attack. [ABSTRACT FROM AUTHOR]

Uniaxial creep-to-rupture tests at 550 and 600 °C under a constant load of 300 MPa have been performed to study the effect of lead-bismuth eutectic (LBE) on the creep failure behavior of a solution-annealed 15-15Ti steel. The results show that the secondary creep rate of the steel tested in LBE at 550 and 600 °C is 56 and 6 times higher than that tested in air at the same temperatures, respectively. The transition time from the primary creep to the secondary creep is largely shortened by LBE. As a consequence, the creep life of 15-15Ti in contact with LBE is reduced remarkably. The severe degradation of the creep performance is attributed to uniform dissolution corrosion (elemental leaching) and especially localized intergranular cracking. • A novel machine is constructed for in-situ creep testing in LBE. • Creep deformation rate of 15-15Ti is remarkably accelerated by LBE. • Uniform dissolution corrosion is enhanced by tensile stress. • Localized dissolution at crack tips leads to fast intergranular cracking. [ABSTRACT FROM AUTHOR]

Liquid metal embrittlement (LME) susceptibility of a high-entropy alloy (HEA) with a nominal composition of Fe 40 Mn 10 Ni 10 Co 20 Cr 20 (at.%) and a single face-centered cubic (fcc) structure was tested in oxygen-depleted lead-bismuth eutectic (LBE, Pb 44.5 Bi 55.5 , wt%) and argon (Ar) environments at 250 and 350 °C using slow strain rate tensile tests. A nominal strain rate of 5x10−5s−1 was employed for all tests. The results showed that LBE had no evident impact on the tensile mechanical properties including total elongation to rupture. Fractographic examinations revealed that the fracture surfaces were predominately dimpled, regardless of the environment and temperature tested. All the results indicate that this high-entropy alloy is not susceptible to LME under the experimental conditions tested in this study. However, severe dissolution corrosion with a corrosion depth of 50–100 μm occurred at the surface, although the specimens were pre-exposed to the oxygen-depleted LBE at 450 °C only for about 20h. This was due to the high contents of Ni and Mn, which are two elements having a high solubility in LBE at a high temperature. The dissolution corrosion and the subsequent tensile loading resulted in formation of numerous microcracks at the specimen surface, contrary to the cases tested in Ar. In this regard, the high-entropy alloy is poorly resistant to LBE dissolution corrosion at 450 °C. • Tensile behavior of a high-entropy alloy (HEA) was tested in LBE. • The HEA was not susceptible to LME under the testing conditions employed. • The HEA was poorly resistant to LBE dissolution corrosion. [ABSTRACT FROM AUTHOR]