Articles
Engineering stacking fault energy and hierarchical precipitates in a near-fully recrystallized DED Ni-based multi-principal element alloy
Renhao Wu, Hyojin Park, Jae Heung Lee, Shi Woo Lee, Longfei Xu, Do Won Lee, Stephan Schönecker, Jalal Kangazian, Tianle Li, Xiaoqing Li, Hyoung Seop Kim
International Journal of Plasticity 201 (2026) 104682
2026-03-26
Abstract
Laser additive manufacturing involves intrinsic rapid solidification rate and elemental segregation, which induce thermal residual stress and metastable microstructures, potentially leading to mechanical performance degradation. To address this, we tailored stacking fault energy (SFE) and hierarchical precipitation to enable near-full recrystallization in a Ni-based multi-principal element alloy. Guided by phase diagram calculation and density functional theory, a Ni-Cr-Fe-Co matrix with Al/Ti/V additions was designed and fabricated to stabilize a medium-level intrinsic SFE while forming hierarchical precipitates (primary BCC/B2 and secondary nanoscale acicular phases) via direct energy deposition in-situ alloying. Uniformly distributed precipitates nucleate preferentially within the grains, with limited formation at the boundaries. This microstructural change further promotes dynamic recrystallization under inherent severe plastic deformation. Consequently, the as-deposited alloy developed ∼92% recrystallized grains and exhibited a yield strength of 790 MPa, ultimate tensile strength of 1164 MPa, and uniform elongation of 24.6%, while multiscale characterizations confirmed plastic deformation interaction of precipitation within the recrystallized grains. This study demonstrates that engineering SFE and hierarchical precipitations promote dynamic recrystallization and synergetic mechanical properties, offering a generalizable strategy for additively manufactured Ni-based alloys.
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.
The mechanistic effects of martensitic resultants on dynamic strain aging in medium-Mn steel
Shuren Fu, Changwei Lian, Dengpeng Ji, Renhao Wu, Xiaoqing Li, Haiming Zhang
Materials Science & Engineering A 940 (2025) 148470
September 2025
Abstract
This study explores the dynamic strain aging mechanism in medium-Mn steel, emphasizing its interplay with the kinetics of strain-induced martensite transformation (SIMT). By tracking the migration of each Portevine-Le Châtelier band, we investigated the complex dynamics of SIMT and its impact on the mechanical behavior. Characteristics of stress serrations are closely related to the dynamic propagation behavior of PLC bands. The epsilon martensite, being softer than austenite, contributes negligibly to the work hardening rate, while plays a key role in coordinating plastic deformation. The alfa' martensite with the hardest value of 6.08 GPa, locally pins the mobile dislocations, triggering the stress serrations in the stress-strain curve. However, as alfa' martensite grows, the pinning effect on dislocations diminishes substantially. We delimited a critical size of alfa' martensite, about 350 nm, beyond which it loses the ability to pin dislocations and instead begins to undergo plastic deformation. Therefore, the serrations intensity is closely governed by the nucleation and growth rates of alfa' martensite: a nucleation-dominant regime intensifies serrations, while a growth-dominant regime reduces them. The deep learning of the effect of SIMT kinetics on DSA mechanism is pivotal for understanding the mechanical stability and ductility of medium-Mn steels under strain.
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
Nils Wikström, Maria Giamouridou, Elina Charatsidou, Pär Olsson, Johan Oscarsson, Daniel Primetzhofer, Robert 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.