Fe-Cr Alloys Research Articles

Composite super-capacitor/Na-ion battery with self-healing Fe–Cr alloy electrodes

In this study, we synthesize a novel self-healing supercapacitor (SC) by combining a thermally and alkali-activated carbon interface with a unique chromium–iron alloy. Detailed device electrochemistry is presented, complemented by characterizations through XRD, SEM, and EDS analyses of electrode surfaces. We introduce rapid cyclic voltammetric measurements to illuminate electrical performance and charge storage of fabricated SCs. SEM measurements demonstrate heightened cycling efficiency, indicating reduced electrolyte degradation and dormant sodium metal formation. XRD measurements support SCs’ self-enhancement, evidenced by sodium metal formation and improved crystalline properties on electrode surfaces. SEM micrographs reveal distinct nanostructures—nanoneedles, nanoflowers, carbon nanotubes, and graphene—formed during charge–discharge cycles. EDS confirms reversible Na metal formation, while increased Cr peaks, acting as corrosion inhibitors, highlight self-healing, extending SC lifespan. Attaining a capacitance of around 30 mF and capacity of 55.6 mWh/kg, the material offers at least 1500 μF/g. Initial results showcase a composite SC/Na-ion battery with favorable and scalable SC characteristics.

Exploring the creep and oxidation behaviors of four types of FeCrAl alloys through small punch test at 600 °C: Experiments and simulations

Four types of iron-chromium-aluminum (FeCrAl) alloys, composed of different elements, were used to investigate the creep performance and high-temperature oxidation resistance. The microstructures in the undeformed regions after the small punch creep test (SPCT) remained consistent with the as-received (AR) FeCrAl alloys, while the grain aspect ratio (GAR) decreased and grains elongated in the deformed regions. Amongst the four alloys, Q1 exhibited the worst oxidation resistance, whereas Q4 showed superior oxidation resistance due to the addition of Si. Precipitates were observed in the deformed regions after SPCT but not in undeformed regions, indicating that deformation had a positive effect on element segregation. Creep models including Norton power law, Monkman-Grant relationship, Larson-Miller Parameters, and Fracture-Time law were obtained. Calculation results from these creep models revealed that under low loads Q4 had lower minimum creep rate δm and longer creep fracture time tr compared to other alloys; however, Q3 demonstrated better performance in terms of δm and tr under high loads. This suggests a strong correlation between creep performance and loads. Additionally, finite element method (FEM) was employed to explore the effects of minor variation (±0.005 mm) in specimen thickness on SPT curves and SPCT curves. FEM results indicated that this slight variation alone did not account for discrepancies observed in load-deflection curves; deviations of ±6.1% for δm and ±6.3% for tr were found corresponding to specimens with 0.5 ± 0.005 mm thickness.

Synergistic effect of helium and hydrogen for vacancy-like defects in pure Fe and Fe9Cr alloy

A synergistic effect between the helium and hydrogen elements exists in fusion reactors materials. To explore its microscopic mechanism, this paper meticulously investigates the H and He action for vacancy-like defects in pure Fe and Fe9Cr alloys by using first-principles calculations. The He and H vacancy-like defects were performed within atomistic simulations in body-centered cubic Fe and Fe9Cr alloys. Via analyzing the structures of the clusters, we find that He atoms in the VacHenHm clusters are more energetically favorable to occupy the center of the vacancy and the H atoms will attach to the free surface. Based on the comprehensive analysis of the vacancy trapping energy, vacancy formation energy, formation volumes, and the electron density maps, He elements play a more dominant role within the H/He synergistic effect, while H elements aggravate the bubble growth. There is no evident chemical bonding between He and H atoms. Concerning the Cr atoms, the Cr-He possesses the strongest repulsive energy within the considered diatomic molecules. The Cr element could weaken the aggregation and reduce the diffusion barriers of the vacancies, thus inhibiting the growth of vacancy-like defects to some extent. These results would help to provide insights into the synergistic effect of He and H for vacancy-like defects in Fe9Cr alloy.

Comparison of the Thermal Stability in Equal‐Channel‐Angular‐Pressed and High‐Pressure‐Torsion‐Processed Fe–21Cr–5Al Alloy

Nanostructured steels are expected to have enhanced irradiation tolerance and improved strength. However, they suffer from poor microstructural stability at elevated temperatures. In this study, Fe–21Cr–5Al–0.026C (wt%) Kanthal D (KD) alloy belonging to a class of (FeCrAl) alloys considered for accident‐tolerant fuel cladding in light‐water reactors is nanostructured using two severe plastic deformation techniques of equal‐channel angular pressing (ECAP) and high‐pressure torsion (HPT), and their thermal stability between 500–700 °C is studied and compared. ECAP KD is found to be thermally stable up to 500 °C, whereas HPT KD is unstable at 500 °C. Microstructural characterization reveals that ECAP KD undergoes recovery at 550 °C and recrystallization above 600 °C, while HPT KD shows continuous grain growth after annealing above 500 °C. Enhanced thermal stability of ECAP KD is from significant fraction (>50%) of low‐angle grain boundaries (GBs) (misorientation angle 2–15°) stabilizing the microstructure due to their low mobility. Small grain sizes, a high fraction (>80%) of high‐angle GBs (misorientation angle >15°) and accordingly a large amount of stored GB energy, serve as the driving force for HPT KD to undergo grain growth instead of recrystallization driven by excess stored strain energy.

Effect of aging and α’ segregation on oxidation and electrochemical behavior of FeCrAl alloys

FeCrAl alloys are promising candidates for next generation nuclear fuel cladding applications due to their high resistance to hydrothermal corrosion, high temperature steam oxidation, fretting, and creep properties. However, a potential area of concern for FeCrAl alloys is the precipitation of Cr-enriched α’ phase which could have an implication on the mechanical, oxidative degradation as well as electrochemical behavior. Studies in this area are limited since most of the past applications of FeCrAl alloys have been in high temperatures above the miscibility gap. In this work, we investigate the high temperature oxidation and electrochemical behavior of a modified APMT (Fe21Cr5Al3Mo) alloy in unaged condition in comparison with a thermally aged condition having α’ phase segregation. The α’ is shown to have no major role in steam oxidation resistance of FeCrAl alloys. The electrochemical behavior in chloride environments shows that the presence of α’ slightly reduces the pitting potential but shows an overall increase in polarization resistance indicating that α’ may enhance corrosion resistance in chloride environments by increasing passivation.

Effects of pre-deformation and annealing on the mechanical properties and microstructure of miniaturized FeCrAl-Y-Si alloys

The evolution of mechanical properties and microstructure in FeCrAl alloys with added Y and Si was investigated using miniaturized specimens. The FeCrAl alloys underwent warm rolling, resulting in thicknesses of 1 mm and 2 mm, followed by annealing at temperatures ranging from 600 °C to 1050 °C. Mechanical properties were determined through three distinct methods: conventional uniaxial tensile testing (UTT), micron indentation hardness testing (MIHT), and small punch testing (SPT). Microstructure evolutions were characterized using various techniques, primarily focusing on electron backscatter diffraction (EBSD). Two types of precipitates containing Y, Si, and Al were observed during annealing. Fracture morphologies revealed that as the annealing temperature (AT) exceeded 900 °C, size effect and brittle failures became prominent in SPT specimens. Brittle failures in SPT can be attributed to the segregation of Y, Si, and Al along the grain boundaries, the size effect, and the dispersed distribution of grain sizes. The optimum inter-pass annealing temperature was identified as 700 °C based on grain orientation spread (GOS) maps. SPT and MIHT results were correlated with UTT results when conducted at room temperature (RT, 25 ℃), and a Hall-Petch equation was derived. It was observed that the correlation equations for SPT were significantly influenced by brittle failures, resulting in relatively larger fitting errors. However, these SPT correlation equations proved effective in predicting total elongation compared to MIHT correlation equations and the Hall-Petch equation. The Hall-Petch equation exhibited the lowest average fitting error though limited by deformed grains. MIHT exhibited the strongest correlation with UTT, particularly in terms of yield strength and ultimate tensile strength. The three fitting methods have distinct advantages and shortcomings in characterizing the mechanical properties of Y and Si-added FeCrAl alloys.

Research Progress of ODS FeCrAl Alloys-A Review of Composition Design.

After the Fukushima nuclear accident, the development of new accident-tolerant fuel cladding materials has become a research hotspot around the world. Due to its outstanding corrosion resistance, radiation resistance, and creep properties at elevated temperatures, the oxide dispersion strengthened (ODS) FeCrAl alloy, as one of the most promising candidate materials for accident-tolerant fuel cladding, has been extensively studied during the past decade. Recent research on chemical composition design as well as its effects on the microstructure and mechanical properties has been reviewed in this paper. In particular, the reasonable/optimized content of Cr is explained from the aspects of oxidation resistance, radiation resistance, and thermal stability. The essential role of the Al element in oxidation resistance, high-temperature stability, and workability was reviewed in detail. The roles of oxide-forming elements, i.e., Y (Y2O3), Ti, and Zr, and the solid solution strengthening element, i.e., W, were discussed. Additionally, their reasonable contents were summarized. Typical types of oxide, i.e., Y-Ti-O, Y-Al-O, and Y-Zr-O, and their formation mechanisms were also discussed in this paper. All aspects mentioned above provide an important reference for understanding the effects of composition design parameters on the properties of nuclear-level ODS FeCrAl alloy.

Enhanced Hydrogen Embrittlement Resistance via Cr Segregation in Nanocrystalline Fe–Cr Alloys

Enhanced Hydrogen Embrittlement Resistance via Cr Segregation in Nanocrystalline Fe–Cr Alloys

Towards high-strength, high-ductility ferritic steels: Pathways to overcome the “475 °C embrittlement” in spinodally decomposed Fe-40Cr alloy

Fe–Cr is a model alloy for ferritic steels used in thermal power generation systems and envisaged as primary structural material for future fusion reactors. However, upon heating and, further, under irradiation, Fe–Cr can suffer from phase decomposition leading to the formation of Fe-rich and Cr-rich regions that induce simultaneous hardening and embrittlement. In this study, we examine the origins of the degradation in mechanical properties by performing room-temperature in situ micropillar compression tests on single-crystalline Fe–40wt.%Cr alloys in solid solution, and in the spinodally decomposed state obtained after annealing at 500 °C for 1008 and 2016 h, respectively. The compressed micropillars are subjected to correlative nanoscale structural characterization using transmission electron backscattered diffraction and transmission electron microscopy. Dislocation slip occurs unequivocally on the {110}〈11¯1〉 slip system for all conditions. While the 2016 h annealed state exhibits a more evolved nanoscale phase modulation than the 1008 h annealed condition, both microstructures display approximately double the yield strength of the solid-solution state without any concurrent loss of ductility. Our findings reveal a fundamental change in plasticity mechanism across the three different microstructures. Deformation in the solid-solution state is associated with kink-mediated local plasticity occurring on multiple glide systems, which activate sequentially based upon the largest instantaneous Schmid factor. This gradually transforms into a less localized Lüders-band like plasticity associated with single-slip activation in the 1008 h annealed state, while the deformation in the 2016 h annealed state is marked by uniform strain hardening related to a homogeneous polycrystalline-like dislocation motion occurring simultaneously on multiple slip systems. Correlations between the spatial and compositional fluctuations in Cr and the associated plasticity dynamics are established. It is shown that the spatial fluctuations in Cr strongly influence dislocation strengthening and the relative mobility of the edge and screw components across all microstructural states. It is further concluded that the phase-separation effect, despite promoting strengthening, does not act as the primary cause of embrittlement, but rather plays a contrary role of enhancing ductility.

Cr diffusion at the FeCr/Cr2O3 interface: A first-principles study

Cr diffusion from matrix FeCr alloy (metallic interconnect) results in Cr poisoning of the cathode of Solid Oxide Fuel Cells, which recently became an urgent issue to be solved. Theunderstanding of Cr diffusion at the microscopic scale at the metal/oxide interface can provide a meaningfulbasis for solving this problem. In this work, we systematically study the stability of the metal/oxide interfaces andCr diffusion at the interface by first-principles approach. Slab models of FeCr (010) surfaces with two types of terminations and Cr2O3(010) surfaces with four types of terminations are proposed, respectively. Then eight types of metal/oxide interface models are proposed accordingly.The interface energy is calculated, and the interface distance is adjusted to determine a stable interface model. The electronic structure of the interface is also analyzed to further illustrate the stability of the interface. Finally, the diffusion pathways of Cr atom at the optimized interface are found using climb image nudged elastic band method, and the diffusion barrier and diffusion coefficient are obtained to provide a quantitative guide to the related experiments in the metallic interconnect as well as a useful theoretical support for solving the problem of Cr poisoning cathode in the SOFCs.

Thermal Properties Investigation of FeCr Alloy Using Lammps Simulation: A Preliminary Study

At present, nuclear reactor technology that is widely used because of its proven reliability is the gen-III + nuclear reactor. Even if it is seen from the aspect of safety and reliability of this generation reactor, it has been proven, but because nuclear energy plays a vital role to meet the growing world energy needs, it is necessary to have a type of nuclear reactor that is tailored to those needs.The next generation of nuclear reactors must meet the requirements of fulfilling safety requirements, be flexible, a longer operating life (more than 60 years), more economical. In order for a reactor to produce higher power, a longer operating life and more economical, reactor structure materials which are capable of being operated at high temperatures are needed. The types of materials that are expected to meet these requirements include various types of ferritic / martensite steel, austenite, alloy steel containing nickel, and metal glass materials and ceramic materials. FeCr metal alloys are alloys that form the metals mentioned above, so it is important to conduct research both in simulation and experiment. Molecular Dynamics simulation of FeCr alloys using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) has been done to explore their thermodynamic characteristics such as heat treatment, solubility of Cr, atomic radial distribution function (RDF). The results of the simulation are illustrated using Visual Molecular Dynamics (VMD) code.
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Effect of rolling on crack behavior of FeCrAl alloys in ultra-long life

PurposeThe purpose of this paper is to determine (1) the relationship between microstructure and fatigue cracking behavior and (2) effect of rolling on the process of crack initiation and propagation in FeCrAl alloys.Design/methodology/approachThe qualitative and quantitative fracture studies were performed using scanning electron microscopy and the non-contact optical measurement system (IFMG5).FindingsThe results show that the formation of facets, rough facets and parallel stripes in the crack initiation and early crack propagation zones are closely related to the sensitivity of crack behavior to the microstructure of the material. Besides, the rolling process has a significant influence on the small crack initiation and propagation behavior. Quantitative analysis demonstrates that the size of the stress intensity factor and plastic zone size in the rough zone is associated with the rolling process.Originality/valueThe findings of this study have the potential to enhance the understanding of the microstructural crack formation mechanisms in FeCrAl alloys and shed light on the impact of rolling on the long-term and ultra-long fatigue behavior of these alloys. This new knowledge is vital for improving manufacturing processes and ensuring the safety and reliability of FeCrAl alloys used in nuclear industry applications.

Carburization behavior of FeCrAl alloy APMT and the critical role of pre-oxidation

The carburization behavior of bare and pre-oxidized APMT has been assessed after long-term graphite exposure at 1000 °C. Bare coupons formed a thick scale after graphite exposure due to carbon interaction and chromium-rich carbides were detected, as predicted from thermodynamic calculations. Pre-oxidation of APMT was conducted in air, and oxidation kinetics were measured through thermogravimetry. The oxide layer formed at 800 °C failed to prevent carburization. However, increasing the pre-oxidation temperature to 1200 °C produced an oxide layer with good resistance to carbon diffusion indicating that the alpha-alumina formed at high temperatures is key in preventing carburization of the material.

Precipitation of Cr-rich clusters in Fe-Cr alloys: Effects of irradiation from first principles modeling and experimental observations

Using exchange Monte Carlo (MC) simulations based on an ab initio-parameterized Cluster Expansion (CE) model, we explore the phase stability of low-Cr Fe-Cr alloys as a function of vacancy (Vac), carbon, and nitrogen content. To parameterize the CE model, we perform Density Functional Theory calculations for more than 1600 supercells containing Cr-Vac-C-N clusters of various sizes in pure bcc Fe, Cr, and Fe-Cr alloys. MC simulations performed for T=650 K show that Cr clustering in Fe-3.28 at.%Cr alloys does not occur if there are no defects or if only vacancies are present. But the addition of a small amount of C or N, at the level as low as 0.02 at.% in an alloy with no vacancies, routinely results in the formation of ordered compounds containing a high amount of Cr, C and N. Cr segregates to interstitial atoms and Cr content in such Cr-rich clusters increases as a function of C and/or N concentration. In the presence of vacancies, C/N aggregate to the core regions of vacancy clusters, making segregation of Cr-rich clusters less pronounced. The structure of Cr-rich clusters varies significantly, depending on the concentration of interstitial atoms and on the ratio of N to C. Predictions derived from MC simulations agree with experimental observations of Fe-Cr alloys exposed to ion irradiation. The concentration of Cr found in clusters containing C and N interstitial atoms is in qualitative agreement, and the absolute Cr content found in the clusters simulated at 650 K is in quantitative agreement with experimental Atom Probe Tomography (APT) observations of Fe-3.28 at.%Cr alloys irradiated at 623 K. The measured C and N content of 42±5 and 151±3 atomic ppm likely results from the contamination that occurred during ion beam irradiation.

Atomistic simulation on the nano-scale oxidation of Fe-Cr alloy surfaces and the diffusion behavior of oxygen

The oxidation of Fe-Cr alloy surfaces was performed by reactive molecular dynamics (MD) simulations. The results shown that the addition of Cr caused a slow internal diffusion of oxygen with a thinner oxide layer in the Fe-Cr alloy, indicating improved oxidation resistance. Furthermore, the achievement of the saturation point in the diffusion flux of oxygen in Fe-Cr alloy was closely linked to the oxide structure, the formation of FeO may inhibit further oxidation by preventing more oxygen ions from reaching the unoxidized interior. Therefore, the evolution of oxide structure played a crucial role in improving the oxidation resistance of Fe-Cr alloys.

Microstructure dependent burst behavior of oxide dispersion–strengthened FeCrAl cladding

Oxide dispersion–strengthened (ODS) FeCrAl alloys are an advanced cladding material that combines the high-temperature steam oxidation resistance of conventional wrought FeCrAl with the irradiation resistance and high-temperature strength of nanostructured ferritic alloys. In the present study, the effect of microstructure on the performance of the ODS FeCrAl alloy system in light-water reactor–accident scenarios is evaluated using a combination of experimentation and modeling. ODS FeCrAl alloy with nominal composition Fe-12Cr-6Al-0.3Zr-0.3Y2O3 was produced into a thin-walled tube via high-precision tube rolling. A portion of the as-received (AR) tube was subjected to a full recrystallization heat treatment. Both variants were subjected to burst testing at Oak Ridge National Laboratory’s Severe Accident Test Station. The recrystallized tube exhibited burst temperature margins 200 °C higher than that of C26M, whereas the AR tube only achieved burst properties comparable to the wrought FeCrAl alloy. The burst experiments were simulated in the BISON finite element code through the development of new viscoplastic material databases for each heat treatment condition, informed by high temperature tensile tests of tube specimens and existing literature data on creep mechanisms. Finally, an ODS FeCrAl burst criterion was obtained using simulated burst experiments across the entire range of test conditions.

FeCrAl fuel/clad chemical interaction in light water reactor environments

This article investigates the fuel-cladding chemical interaction (FCCI) behavior of two commercial FeCrAl alloys, APMT composition (Fe-21Cr-5Al-3Mo wt.%) and C35M (Fe-13Cr-5Al-2Mo-0.2Si-0.03Y wt.%), after neutron irradiation. “H-cup” diffusion multiples of FeCrAl alloys and ceramic UO2 fuel were irradiated at a temperature of ∼300 °C to a total estimated burnup of 26 GWd/tHM. Post-irradiation Examination results demonstrate the excellent degradation resistance of FeCrAl alloys as accident tolerant fuel (ATF) cladding materials in light water reactor conditions. The study concludes that there was no irradiation-induced defects observed in either of the two commercial FeCrAl claddings. The formation of amorphous Al/U mixed oxide was observed at the fuel-clad interface, which can serve as a tritium permeation barrier and protect against potential chemical attack from the fuel. The study attributed the formation of amorphous Al/U mixed oxide to the low temperature and limited time of neutron irradiation. APMT forms more distinct Cr and Cr-Fe intermetallic at the FeCrAl-UO2 interface than C35M due to the higher bulk Cr:Al ratio.

Deriving Metastable Pourbaix Diagrams of Stainless Steels Using Density Functional Theory Calculations

This paper presents a novel method for deriving metastable Pourbaix diagrams of Fe-Cr alloys using Density Functional Theory calculations, with the objective of providing a more comprehensive understanding of the thermodynamic equilibria within passive films, considering the metallurgical characteristics of the alloys and the electrochemical polarization conditions. By using advanced numerical tools and optimization algorithms provided by the Materials Project Database, we have developed an approach that incorporates nonequilibrium effects as a corrective factor for the chemical equilibria observed in passive films. Our findings highlight the significant role of nucleation conditions, particularly for the Cr2O3 oxide, in stabilizing the inner layers of the passive films. Lastly, the method was used to investigate the impact of pulsed polarization conditions on AISI 304 stainless steel and proposed a reaction scheme elucidating the enhanced corrosion protective properties of the passive film.

Molecular dynamic simulations of Ti-6Al and Fe-12Cr alloys for their heat transfer and oxygen transport behaviors

The heat transfer and oxygen transport behaviors of Ti-6Al and Fe-12Cr alloys directly affect their aeronautical material application. In order to investigate the flame retardant mechanism in atomic scale, molecular dynamic (MD) simulations were performed to study the heat transfer and oxygen transport performances of Ti-6Al and Fe-12Cr alloys in the linear and uniform heating treatment. Next, the ignition performances of Ti-6Al and Fe-12Cr alloys were further verified by the frictional ignition tests. Therefore, this is a multi-scale research with a novel combination of MD simulations and ignition tests. Those obtained results show that the heat is more concentrated at the heating edge of Ti-6Al alloy while at the same heating rate. This leads to the intensification of atomic motion at the heating edge, and reduces the structural thermal stability of Ti-6Al alloy’s heating edge. Therefore, the heat transfer performance of Fe-12Cr alloy at the same state is better than that of Ti-6Al alloy. When there is an oxide layer on the surface of these two alloys, Fe-12Cr alloy can inhibit the oxygen transfer more effectively than Ti-6Al alloy, and further improve its flame retardant property. In addition, the frictional ignition tests with Ti alloy rotor under the same airflow environment show that the critical airflow velocity of the Fe-12Cr alloy stator is about 114[Formula: see text]m/s higher than that of Ti-6Al-4V alloy stator at 384∘. Generally, according to MD simulations and frictional ignition tests, it could be concluded that the flame retardancy of Fe-12Cr alloy is higher than Ti-6Al alloy.

Reconciliation between simulated and measured microstructures of metastable FeCr alloys: A phase field approach

This work presents a novel phase field method for modeling the microstructure induced by the thermal decomposition of immiscible metastable binary alloys. This approach bypasses the problem associated with the modeling of the nucleation process introducing a random distribution of critical precipitates as an initial condition for the Cahn–Hilliard equation, extensively used to model the microstructure in the spinodal regime. The comparison between simulated and measured microstructures obtained from atom probe tomography measurements performed on ultra pure Fe0.81Cr0.19 samples justifies the validity of our method. In particular, we succeeded modeling the evolution of the chemical composition of α′ clusters produced during annealing. Such an evolution has been many times reported from atom probe tomography measurements but never explained. Moreover, these simulations allowed proposing a physical mechanism to explain the increase of the yield strength, observed in many annealed FeCr samples.