Articles
Corrosion behavior in liquid lead of a novel FCC non-equiatomic high-entropy alloy capable of forming an alumina protective oxide scale
Roger Castellote-Alvarez, David San-Martin, Cesar Fernandez-Jimenez, Jose A. Jimenez, Christopher Petersson, Esteban Urones-Garrote, Peter Szakalos, Isaac Toda-Caraballo
Corrosion Science 262 (2026) 113651
2026-01-23
Abstract
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 Fe33.5Ni43.5Cr11Mn6Al6 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)2O4 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 Fe33.5Ni43.5Cr11Mn6Al6 HEA, positioning it as a highly promising candidate for high-temperature nuclear applications in Pb-cooled systems.
Protective Al-rich oxide scale formation in low-Cr alumina-forming martensitic steels under liquid lead corrosion
Cesar Fernandez-Jimenez, Isaac Toda-Caraballo, Roger Castellote-Alvarez, Peter Szakalos, Christopher Petersson, José A. Jiménez, Carlos Capdevila, David San-Martin
Journal of Nuclear Materials 623 (2026) 156468
2026-01-17
Abstract
Two alumina-forming martensitic (AFM) steels containing less than 8 wt.% Cr were exposed for over 1000 h at 550 °C and 650 °C in static liquid Pb with controlled oxygen concentration to evaluate the formation of an alumina oxide scale and its protective capacity against corrosion. The AFM-1 steel (3.6 wt.% Al, 7.8 wt.% Cr) formed a continuous, protective oxide scale that effectively resisted Pb penetration under all conditions, particularly at 650 °C, where performance improved due to the dissolution of B2-NiAl precipitates during prolonged exposure, releasing Al that migrated to the surface and enabled the formation of an Al-rich oxide layer, ensuring sustained protection and mitigating the localized nodular oxidation observed at 550 °C. In contrast, the AFM-2 steel (2.9 wt.% Al, 7.5 wt.% Cr) failed to develop a complete protective oxide layer, allowing molten Pb to penetrate and react with the substrate even at 650 °C, causing severe oxidation. These results demonstrate that, beyond a high Ni content (12 wt.%), achieving excellent corrosion resistance in liquid Pb requires a synergistic combination of an optimal Al/Cr balance, dissolution of B2-NiAl precipitates as an Al source, and enhanced atomic diffusion facilitated by the high density of subgrain boundaries in the martensitic microstructure.
Impact of zirconium incorporation on the thermophysical properties of uranium mononitride
Elina Charatsidou, Anita Pazzaglia, Kaitlyn Bullock, Maria Giamouridou, Eleanor Lawrence Bright, Mikael Jolkkonen, Christoph Hennig, Pär Olsson
Journal of Nuclear Materials 623 (2026) 156467
2026-01-17
Abstract
Uranium mononitride (UN) is a promising candidate fuel for next-generation fast reactors due to its high fissile density, superior thermal conductivity, and high melting point compared to conventional oxide fuels. However, scarce experimental data on UN and its thermophysical behaviour under fission product incorporation limits its performance assessment. Zirconium nitride (ZrN) is an efficient thermal conductor and a candidate material for inert matrix fuels. Given its high thermal conductivity, ZrN addition at sufficient concentrations should, in principle, induce percolation conduction and increase thermal conductivity in UN. To decouple chemistry from irradiation-induced porosity, known to dominate thermal degradation at high burnup, this study isolates the intrinsic chemical contribution of Zr incorporation under dense, low-porosity conditions. (U,Zr)N pellets with 6.5 and 20 at. % Zr were fabricated by spark plasma sintering (SPS), using powders produced from arc-melted alloy via the hydride-nitride-denitride route. Synchrotron powder X-ray diffraction confirmed the formation of solid solutions and enhanced Zr solubility after sintering, resulting in improved microstructural homogeneity. Thermal diffusivity was measured between 300 and 1500 K using light flash analysis, and thermal conductivity was derived using heat capacity and density correlations with porosity correction. Despite the intrinsically higher thermal conductivity of ZrN, the incorporation of 6.5 at. % Zr reduced the thermal conductivity relative to UN, consistent with impurity scattering. The 20 at. % Zr composition further decreased conductivity, indicating the microstructure does not meet the conditions required for percolation conduction. Differences in the temperature dependence of thermal diffusivity between UN and Zr-bearing samples highlight a compositional influence on heat transport. The results provide benchmark data for (U,Zr)N and insights into chemical and thermophysical interactions in nitride ceramics.
Mechanistic insight into the ferritization of austenite in Pb via a discontinuous reaction governed by a migrating liquid film
Corrosion Science 258 (2026) 113398
Kin Wing Wong, Peter Szakálos, Christopher Petersson, Dmitry Grishchenko, Pavel Kudinov
2025-10-15
Abstract
The dissolution of austenitic steel in liquid lead-based alloys can induce a phase transformation characterized by a sharp dissolution front separating ferrite and austenite grains, a process commonly referred to as ferritization. Although widely reported, the mechanism driving this transformation remains under debate. This study re-examines ferritization as a discontinuous reaction via a migrating liquid film and proposes a thermodynamically consistent model for the initiation and propagation of the dissolution front. The proposed mechanism is supported by experiments at 500–550°C, literature evidence, and diffusion calculations. Under low oxygen conditions, Cr transport through liquid Pb channels is identified as the rate-limiting step, setting the theoretical corrosion rate in stagnant environments. High-speed erosion-corrosion tests show enhanced corrosion rates, driven by erosion-limited channel lengths that locally boost mass transport. In contrast, under moderate oxygen concentrations relevant for lead-cooled fast reactor (LFR) operation, the rate-limiting step shifts to metal transport across a nanometer-scale amorphous oxide layer at the reaction front. Other Ni-containing austenitic steels, including alumina-forming austenitic (AFA) alloys and Ni-based high-entropy alloys (HEAs) can also be susceptible to discontinuous reactions under direct contact with liquid Pb-based alloys, lacking the self-healing oxide protection as observed in alumina-forming ferritic steels. This limitation may present a concern for the long-term use of bare austenitic steel in liquid Pb environments.
Irradiation-induced polymorphism in Fe–Cr alloys
Scientific Reports 15 (2025) 35050
Ebrahim Mansouri, Xiaoqing Li, Pär Olsson
2025-10-08
Abstract
Direct damage evolution simulations based on electronic structure physics show a significant correlation between Cr concentration and polymorphism in the form of localized formation of C15 Laves phase structures in Fe–Cr alloys under irradiation. We elucidate the role of Cr content in the formation and stabilization of the C15 Laves phase structure, which is crucial to understanding the behavior of materials under extreme conditions. This study also reveals a connection between non-linear magnetic behavior and irradiation-induced swelling in Fe–Cr alloys. These results advance the comprehension of radiation-induced changes in magnetization and suggest a novel experimental approach for detecting C15 clusters in irradiated Fe–Cr alloys.
Assessing the near-surface diffusion of Xe and Kr in Zirconia by time-of-flight elastic recoil detection analysis
Nuclear Instruments and Methods in Physics Research B 566 (2025) 1657736
N. Wikström, M. Giamouridou, E. Charatsidou, P. Olsson, J. Oscarsson, D. Primetzhofer, R.J.W. Frost
2025-06-06
Abstract
The diffusion of two volatile fission products, xenon (Xe) and krypton (Kr), in zirconia (ZrO2) is investigated. Samples of Yttria (Y2O3)-stabilised tetragonal ZrO2 were implanted with either Xe or Kr, at 300 keV, with a fluence of 10¹⁷ at./cm2, and subsequently analysed with time-of-flight elastic recoil detection analysis (ToF-ERDA) to obtain elemental composition depth profiles. Samples were then annealed at 1200 ◦C for 9 h, and the effect of the annealing was assessed by ToF-ERDA measurements. From these measurements, first-order approximations of diffusion coefficients for Xe and Kr in ZrO2 were derived, using a model based on Fick’s second law, these being (1.36 ± 0.87) × 10⁻¹⁹ m²/s and (2.94 ± 1.96) × 10⁻¹⁹ m²/s at 1200 ◦C for Kr and Xe respectively. It was shown that ToF-ERDA can provide data to analyse the diffusion of elements in solid sample matrices and that a model based on Fick’s Law can predict the diffusion of the implanted ions.