Fe-Cr Alloys Research Articles

Solidification precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys

AlN inclusions are the major inclusions in FeCrAl alloys and precipitate during solidification. The precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys were theoretically calculated based on the Clyne–Kurz model and a diffusion-controlled growth model. The results indicated that AlN inclusions precipitated at a solid fraction of 0.45. Following precipitation, the Al concentration exhibited a slight decrease compared to scenarios where AlN inclusion precipitation was not considered, although it still showed an increasing trend. Conversely, the N concentration exhibited a significant turnaround, gradually dropping below its initial value. In addition, varying the cooling rate to 0.17, 0.83, 1.67, and 16.67 K/s, the final sizes of AlN inclusions were 46.5, 21.1, 14.8, and 4.7 μm, respectively. Fixing other factors, the solid fractions for AlN precipitation at initial Al concentrations of 4.19, 4.69, and 5.19 wt% were 0.535, 0.45, and 0.365, respectively, and the final sizes of AlN inclusions were 16.2, 14.8, and 13.6 μm, respectively. Similarly fixing the other factors and varying the initial N concentrations to 0.0045, 0.0053, and 0.0060 wt%, the solid fractions of AlN were 0.515, 0.45, and 0.40, respectively, and the final sizes of AlN inclusions were 14.6, 14.8, and 15.0 μm, respectively. This indicates that increasing the cooling rate, increasing the initial Al concentration, and decreasing the initial N concentration could effectively reduce the precipitation size of AlN inclusions. This work provides guidance for the investigation of the precipitation and growth kinetics of AlN inclusions in FeCrAl alloys.

High‐Temperature Mechanical Behavior of Single‐Crystal FeCrAl Alloy Under In Situ Micropillar Compression

FeCrAl cladding is one of the candidate materials for the near‐term accident‐tolerant fuel technologies under development. Research on high‐temperature mechanical behaviors of single‐crystal FeCrAl alloy is rather limited. Previous studies have reported the mechanical property of low‐index orientation in single‐crystal FeCrAl alloy at room temperature. However, the critical resolved shear stress to activate slip systems can be orientation and temperature dependent. Here, single‐crystal grains in a coarse‐grained FeCrAl alloy with different crystallographic orientations are selected to preferentially activate {110}<111> slip systems or {112}<111> slip systems. Micropillars are fabricated in the selected single‐crystal grains and tested at elevated temperatures in situ in a scanning electron microscope. The critical resolved shear stresses of {110}<111> slip systems and {112}<111> slip systems are determined at various temperatures. The critical resolved shear stress shows a temperature dependence and orientation independence. This study provides important insight for understanding the deformation mechanisms of FeCrAl alloys at elevated temperatures.

Characterization of Fe-Cr alloys irradiated by neutrons at intermediate temperature

A series of Fe-Cr alloys, with 3 at.% - 18 at.% Cr, was irradiated in the Advanced Test Reactor (ATR) at the Idaho National Labs (INL), USA, up to a dose of ∼6.7 dpa at a temperature of ∼456 °C. Transmission electron microscopy (TEM) samples were extracted using a focused ion beam (FIB) instrument, and the resulting microstructural defects, such as voids, dislocation loops, network dislocations, Cr rich precipitates, etc., were characterized using a TEM. It was found that the size and number density of these defects varied widely over the different alloys with varying Cr content. As expected, there were no Cr rich precipitates in samples with Cr up to 9 %, and they started appearing only in samples with 12 at.% Cr and above. The particle size decreased from about 15 nm at 12 % Cr to 8 nm at 18 % Cr, while the number density increased from ∼7e20 /m3 to 6e22 /m3 for the same Cr contents. Grain boundary segregation of Cr, along with a precipitate free zone, was observed in the cases where a boundary was present in the sample. Large voids (>1–2 nm) were almost invisible in the Fe-3at.%Cr sample, while the average void size remained almost constant between 15 and 18 nm for samples with 6–15 at.% Cr and increased slightly at 18 at.% Cr to ∼22 nm. Fe-3 %Cr showed a high density of small voids(<2 nm), estimated to be about 1e23/m3. The number density of large voids increased from ∼0 at 3 % Cr to a peak of ∼6.4e20 /m3 at 12 % Cr, then decreased to about 1.1e20 /m3 at 18 % Cr. The dislocation loops, which appeared in linear arrays in the Fe-9 %Cr sample, were analysed in detail using both invisibility criteria and image simulations using the Oxford University TEMACI software, and it was found that they are most likely to be ½ 〈111〉 type loops on {100} planes. These loops seem shaped like sections of helices in some places and are most likely formed by loops near screw dislocations climbing into a helix and then collapsing into a loop array. Similar dislocation analysis was performed in the other samples as well wherever feasible, and it was found that there is a mixture of ½ 〈111〉 and [100] dislocation loops.

Growth of α-Al2O3 layer involving abnormal oxides in FeCrAl alloy tube fabricated by WEDM process and electrical insulating performance in fusion reactor blanket

The tubular specimens of FeCrAl alloy APMT (Fe-22Cr-5Al-3Mo) were fabricated by a wire electrical discharge machining (WEDM) process. The oxidation characteristics of the machined surface were investigated by means of the oxidation tests performed in air atmosphere at the temperatures of 1273 K and 1373 K up to 100 h. The abnormal oxides such as CuAl2O4 and ZnAl2O4 were grew on the recast layer which was locally remained on the machined surface even after the mechanical polishing procedure. The α-Al2O3 layer involving the abnormal oxides was formed on the machined surface in the oxidation treatment at 1273 K for 10 h. The apparent electrical conductivity of the layer involving the abnormal oxides was larger than that without the abnormal oxides. Thick Al-rich oxide layer was formed under the abnormal oxides when the oxidation treatment was performed at 1373 K. The apparent electrical conductivity of the oxide layer became lower due to the presence of the thick Al-rich oxide. This oxide layer formed at 1373 K could function as an electrical insulating layer to reduce the magnetohydrodynamic pressure drop in liquid breeder blanket systems of magnetic confinement fusion reactors.

Corrosion evaluation of austenitic stainless steels in Li2CO3-K2CO3 eutectic salt for thermal energy storage

Molten carbonate salt is one of the promising candidates for high-temperature thermal energy storage tailored towards advanced pumped-thermal energy storage and next generation concentrated solar power technologies. However, severe corrosion of structural materials exposed to molten carbonate salts poses one of the most pivotal threats in terms of limiting their large-scale application at ever-escalating temperatures. Here, we elaborate the compatibility of three commercial austenitic stainless steels specifically SS310, SS316L and Incoloy 625 with Li2CO3-K2CO3 (28–72 wt%) eutectic salt. The corrosion behavior and corrosion mechanism of Fe-Cr (SS316L), Fe-Cr-Ni (SS310) and nickel-based (In625) alloys at 600 °C in air were also investigated. It revealed that SS310 exhibited better corrosion resistance compared to SS316 and In625, with weight loss of 23.8 mg/cm2 and corrosion rate of 522 μm/year after 500 h of exposure at 600 °C. This implies that higher Ni content of the alloy may not necessarily improve the corrosion resistance, it is associated with the basicity of the molten and the solubility of Ni salt in the melt. ICP analysis indicated that the salts exposed to SS310 and In625 at the same exposure time both had nearly 11 times more Ni than that exposed to SS316. Precisely, it is related to the behavior of the Cr-enriched zones formed in the corrosion layers of different alloys. The corrosion mechanism of SS310 specimens in molten carbonate can be generally divided into the following steps: (i) selective oxidation of the metal elements and lithiation reactions of the metal oxides to generate a passivation scale, (ii) an ever-growing middle transition scale consisted of mixed metal oxides and lithium-containing compounds, (iii) cracking and peeling off of the corrosion scale.

Wear and Corrosion Resistances of Arc-Sprayed FeCr Alloy and Fe-Based Coatings for Boiler Heat Exchanger Pipelines

Wear and Corrosion Resistances of Arc-Sprayed FeCr Alloy and Fe-Based Coatings for Boiler Heat Exchanger Pipelines

Exploring the Kinetics of Oxygen Reduction Reaction in Relation to Pitting Corrosion Resistance in Fe-Cr Alloys

Pitting corrosion, a major concern in materials science and engineering, threatens critical metallic structures and components. Its implications reach across daily life and industries such as energy, transportation, and infrastructure, potentially causing environmental harm, economic losses, and even loss of life. This complex process is influenced by factors including material composition, local environment, and mechanical stresses.1 Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film.2 In Fe-Cr alloys, the ORR occurs on this film, undergoing a mixed diffusion and kinetic-controlled process. The number of electrons involved and the corrosion rate are determined by the thermodynamically stable state of the passive film.This research studies the ORR kinetics on FeCr alloys fabricated by arc-melting, using both computational and experimental methods. The rotating disc electrode technique was employed across various Fe:Cr alloys in alkaline and neutral electrolytes. The Koutecky-Levich analysis showed a dominant four-electron ORR pathway in all tested Fe-Cr alloys, with the ORR significantly inhibited by higher proportions of Cr2O3 in the film, suggesting a correlation with high chromium content. Experimental ORR overpotentials, when combined with theoretical potential-pH (Pourbaix) diagrams, helped discern the likely characteristics of the passive films on the alloys. It was deduced that the catalytic properties of potential passive films increased in the order Cr2O3 < Fe3O4 < Fe2O3 < FeCr2O4. These findings, excellently aligned with density functional theory (DFT) modelling, underscore the role of increased chromium levels in slowing pitting progression by suppressing the ORR.In summary, this research offers distinctive insights into the correlation between the kinetics of the ORR and the resistance to localized corrosion in Fe-Cr alloys, which enhances our understanding of the underlying mechanisms of pitting corrosion. Keywords FeCr alloy, pitting corrosion, ORR, rotating disc electrode, DFT Reference [1] B. Zhang, J. Wang, B. Wu, X. W. Guo, Y. J. Wang, D. Chen, Y. C. Zhang, K. Du, E. E. Oguzie, and X. L. Ma, Nat. Commun. (2018) 9, 2559.[2] G. T. Burstein, P. C. Pistorius, and S. P. Mattin, Corros. Sci. (1993) 35, 57.

Oxidation Behavior of Additively Manufactured Ti-added FeCrAl Alloys

Oxidation Behavior of Additively Manufactured Ti-added FeCrAl Alloys

Unveiling the dual role of ion irradiation on the corrosion behavior of lean-Cr FeCrAl alloys in a simulated PWR environment

This study focuses on the synergistic effect of ion irradiation and corrosion on FeCrAl alloys with lean-Cr content (7–10 wt%) and with 13 wt% Cr. Upon subjecting unirradiated, 1-dpa, and 5-dpa samples to a simulated PWR environment for 15 days, it is found that irradiation alters the distribution of outer oxide particles and the composition of inner oxide layer. Our results emphasize the dual role of irradiation, depending on the perspective considered: It suppresses overall corrosion while promoting localized corrosion. Cr content effect on the resistance to irradiation-corrosion coupling is also discussed.

The Impact of HCl on Alkali-Induced Corrosion of Stainless Steels/FeCrAl Alloy at 600 °C: The Story After Breakaway

The impact of Cl on alkali-induced high-temperature corrosion of stainless steels/FeCrAl alloys after breakaway oxidation was investigated in a simulated biomass- and waste-fired boiler environment at 600 °C. For this investigation, three alloys were exposed to low Cl load environment (H2O+KCl) and to high Cl load (H2O+KCl+HCl). Post-exposure analysis showed that the stainless steel SVM12 experiences fast oxidation and forms thick double-layered Fe-rich oxide scales. The corrosion attack is further accelerated with addition of HCl for this material with the effect being more pronounced in the inward-growing scale. The FeCrAl and FeCrNi alloys exhibit slower oxidation kinetics after the breakaway corrosion compared to SVM12 in the H2O+KCl exposure. Furthermore, in contrast with SVM12, the addition of HCl did not accelerate the corrosion attack on these alloys. It is argued that the properties of the secondary oxide layer formed after breakaway corrosion are important in the continued corrosion resistance against chlorine-induced corrosion attack. Especially, the Cr content in the inner scales is suggested to be important in corrosion mitigation.

Hydrogen Production with a Protonic Ceramic Membrane Reactor on Porous Fe–Cr Alloy

Hydrogen Production with a Protonic Ceramic Membrane Reactor on Porous Fe–Cr Alloy

Insights into Prismatic Loop Formation in Irradiated Fe–Cr Alloys from Hypothesis-Driven Active Learning and Causal Analysis

Insights into Prismatic Loop Formation in Irradiated Fe–Cr Alloys from Hypothesis-Driven Active Learning and Causal Analysis

The Charpy Impact Properties of Oxide Dispersion-Strengthened FeCrAl Alloys with Different Cr Contents

The Charpy Impact Properties of Oxide Dispersion-Strengthened FeCrAl Alloys with Different Cr Contents

Recovery of low carbon FeCr alloy using sensor-based separation

The recovery of low-carbon FeCr alloy at Ferbasa's metallurgical unit in Pojuca is a crucial process involving the separation of the metallic alloy from the slag generated during smelting. This study investigates the application of sensor-based sorting (SBS) technology to optimize this recovery. Tests conducted at the STEINERT Latin America Testing Center utilized X-ray transmission (XRT) sensors combined with 3D laser sensors, demonstrating efficacy in distinguishing between alloy and slag particles based on density differences. The results indicated that with only 4% of the mass, it is possible to recover more than 11% of the metal, focusing on particles with an average grade above 23% Cr2O3. The implementation of this technology could increase the mass recovery of the alloy by 3.5% compared to the current process, optimizing resources and improving the efficiency of the existing magnetic separation process. It is concluded that SBS technology, particularly the combination of XRT and 3D laser, is a promising solution to enhance the recovery of FeCrBC alloy.

Effect of Sc on the Water Vapor Oxidation Behavior of FeCrAl Alloys at 1000 °C

Effect of Sc on the Water Vapor Oxidation Behavior of FeCrAl Alloys at 1000 °C

Unveiling niobium pentoxide and cerium oxide-dispersed ferritic stainless steel for solid oxide fuel cells interconnects

Herein, the effect of niobium pentoxide (Nb2O5) and nano-sized cerium oxide (CeO2) on oxidation behavior and area specific resistance (ASR) of the ferritic stainless steel has been investigated for the development of robust metallic interconnects. An oxide-dispersed ferritic stainless steel alloy is fabricated using the powder metallurgy (PM) process. The morphologies of the alloy before and after oxidation are observed through Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscopy (STEM) and Secondary Ion Mass Spectrometry (SIMS) analyses. Addition of Nb2O5 in the alloy formed a C14 Laves phase of (Fe, Cr)2(Nb, Si). The Laves phase and CeO2 controlled the oxidation behavior of the ferritic stainless steels, consequently reducing the oxide scale thickness and improving the ASR. An alloy with 1 wt% Nb2O5 and 3 wt% CeO2 showed an ASR value of 27.1 mΩ cm2 at 800 °C for 1000 h, which is similar to the ASR value of the commercial Fe–Cr alloy. The results of this study indicate that Nb2O5 and CeO2-dispersed ferritic stainless steel using the PM process can be more advantageous than the conventional process for manufacturing metallic interconnects with complex shapes and reducing production costs.

Systematic experimental and model-based evaluation of the synergistic effects of alloy composition and damage rate on the formation of Cr-rich precipitates in Fe–Cr–Al alloys under ion irradiation

Fourteen Fe–Cr–Al alloys with systematically varied Cr and Al compositions were irradiated at 350∘C to 0.24 dpa by 10.5 MeV self-ions as model alloys for the Fe–Cr–Al (oxide dispersion strengthened: ODS) alloys being developed as accident tolerant fuel (ATF) cladding for light water reactors. Three dose rates (8×10−6, 8×10−5, and 8×10−4 dpa/s) were selected to predict the formation behavior of Cr-rich precipitates (CrRP) under neutron irradiation conditions. The effects of Cr, Al composition, and dose rate on the CrRP formation behavior were evaluated using a three-dimensional atom probe (3DAP) analysis. The results showed that the CrRP number density, volume fraction, and Cr concentration increase with increasing Cr composition, decreasing Al composition, and decreasing dose rate. Multiple regression analysis showed that in addition to these primary effects, there was an interaction between them on the CrRP volume fraction: (1) the higher the Al composition, the smaller the increase in the CrRP volume fraction with increasing Cr composition, and (2) the lower the Cr composition, the smaller the increase in the CrRP volume fraction with the decreasing Al composition and dose rate. It was also highlighted that to understand the dose rate effect on the CrRP formation behavior under neutron irradiation, it is useful to examine the irradiation time dependence, including the effective use of thermal aging data as a limit to the zero dose rate, in addition to the dose-dependency perspective. In addition to the systematic database of CrRP-related quantities established in this study, these considerations should contribute to further developing and validating numerical prediction models.

Mechanical property and strengthening mechanism of ZrC nanoparticle dispersion-strengthened Mo containing FeCrAl alloys

Poor mechanical strength at high temperature is the key problem to limit the application of FeCrAl alloys as the candidates for the accident tolerant fuel (ATF) cladding in LWRs. Fe-13Cr-5Al (wt %) alloys were strengthened by adding solid solution element Mo and nanosized ZrC particles, and the strengthening mechanism was assessed by microstructure characterizations including TEM and EBSD. Fe-13Cr-5Al-2Mo-1ZrC alloy has the highest ultimate tensile strength (UTS) and an acceptable ductility at each tested temperature (Room temperature, 400 °C or 800 °C). Especially at 800 °C, the UTS of Fe-13Cr-5Al-2Mo-1ZrC alloy is about 124 MPa, which is 125 % and 34.7 % higher than that of raw Fe-13Cr-5Al (55 MPa) and Fe-13Cr-5Al-1ZrC alloys (89 MPa), respectively. Fe-13Cr-5Al-2Mo-1ZrC alloy has the highest hardness of 306.3 HV, which is 12.8 % higher than that of Fe-13Cr-5Al and 3.7 % higher than that of Fe-13Cr-5Al-1ZrC alloys, respectively. Furthermore, Fe-13Cr-5Al-2Mo-1ZrC samples maintain high strength and favorable ductility after annealing at 1000 °C for 20 h indicating their superior thermal stabilities. The excellent mechanical properties and superior thermal stabilities of Fe-13Cr-5Al-2Mo-1ZrC alloy were not only attributed to the dispersion strengthen by nanosized ZrC particles, the solid solution strengthening by Mo elements, but also the grain refinement structure promoted by the synergistic effects of Mo and ZrC additions.

Synergistic Thermal and Electron Wind Force-Assisted Annealing for Extremely High-Density Defect Mitigation.

This study investigates the effectiveness of combined thermal and athermal stimuli in mitigating the extremely high-density nature of dislocation networks in the form of low-angle grain boundaries in FeCrAl alloy. Electron wind force, generated from very low duty cycle and high current density pulses, was used as the athermal stimulus. The electron wind force stimulus alone was unable to remove the residual stress (80% low-angle grain boundaries) due to cold rolling to 25% thickness reduction. When the duty cycle was increased to allow average temperature of 100 °C, the specimen could be effectively annealed in 1 min at a current density of 3300 A/mm2. In comparison, conventional thermal annealing requires at least 750 °C and 1.5 h. For specimens with 50% thickness reduction (85% low-angle grain boundaries), the electron wind force was again unable to anneal the defects even at 3300 A/mm2 current density and average temperature of 100 °C. Intriguingly, allowing average concurrent temperature of 200 °C eliminated almost all the low-angle grain boundaries at a current density of 700 A/mm2, even lower than that required for the 25% thickness reduced specimens. Comprehensive electron and X-ray diffraction evidence show that alloys with extremely high defect density can be effectively annealed in less than a minute at approximately 200 °C, offering a substantial improvement over conventional high-temperature annealing.

Effect of Nb addition on the steam oxidation behavior and kinetic of FeCrAl alloys

The effects of Nb on the steam oxidation kinetic behavior of FeCrAl alloy were studied. Nb addition significantly decreased the weight gain at 1200 °C. Nb addition also promoted the formation of Al2O3 and suppressed the growth of Fe and Cr oxides, resulting in the thinner oxide film in the heating stage. Also, the oxide film is much easier to wrinkle at 1200 °C. In addition, pre-formed Nb2O5 promotes the formation of discontinuous granular Al2O3 in oxide films and substrates.