Fe-Cr Alloys Research Articles

Steady-state and power transient critical heat flux experiments of FeCrAl and Zircaloy claddings under saturated pool boiling

FeCrAl and Zircaloy cladding tubes are vertically placed in the saturated pool boiling chamber to perform steady-state and power-transient critical heat flux (CHF) experiments. Three FeCrAl-variants, including FeCrAl-C26M, FeCrAl-B126Y, and FeCrAl-B136Y, are tested to compare their pool boiling thermal performances with traditional Zircaloy claddings including Zirlo, Zr705, and Zircaloy-4. In the steady-state pool boiling experiments, it was confirmed that FeCrAl alloys have higher pool boiling CHF values than Zircaloys. Among these tested materials, FeCrAl-C26M has the highest pool boiling CHF, but the FeCrAl-C26M nucleate boiling heat transfer coefficient is less than that of FeCrAl-B136Y. It reconfirms that CHF is enhanced on the post-CHF oxidized samples. However, as the cycling number of post-CHF oxidization increases, the CHF enhancement becomes less appreciable due to the limited physics contributions of the oxide layer. It is noteworthy that the finalized CHF enhancement can vary a lot between different cladding materials. For example, in three Zircaloy variants, their saturated pool boiling CHF results converge to 980 kW/m2 on the post-CHF oxidized samples. In three FeCrAl variants, their pool boiling CHF results are finalized to 1400 kW/m2. This CHF enhancement difference could be possibly attributed to the chemical constituents of oxide layers presented on cladding surfaces. The Fuchs-reactivity initiated accident transients are simulated by direct current programmable power supply to characterize thermal responses of different claddings to various pulse-width power transients. It is found that the heat transfer coefficients show monotonically increasing parametric trend with respect to faster power-transient rates, i.e., shorter pulse widths. Different from the steady-state pool boiling, the transition boiling regime is phenomenologically reflected in the power-transient pool boiling curve. This potentially implies that power-transient CHF featured by surface temperature overshoot may indicate transient thermal-safety margins not so accurately as the power-transient maximum heat flux. The difference gap of power-transient maximum heat flux between various cladding materials can be gradually closed by the progressive increasing of power transient rates.

Kinetics of Transformation, Border of Metastable Miscibility Gap in Fe–Cr Alloy and Limit of Cr Solubility in Iron at 858 K

The study was aimed at determination of the position of the Fe-rich border of the metastable miscibility gap (MMG) and of the solubility limit of Cr in iron at 858 K. Towards this end, a Fe73.7Cr26.3 alloy was isothermally annealed at 858 K in vacuum up to 8144 hours and Mössbauer spectra were recorded at room temperature after every step of the annealing. Three spectral parameters viz. the average hyperfine field, 〈B〉, the average isomer shift, 〈IS〉, and the probability of the atomic configuration with no Cr atoms in the two-shell vicinity of the probe Fe atoms, P(0,0), gave evidence that the transformation process took place in two stages. All three parameters could have been well described in terms of the Johnson–Mehl–Avrami–Kolmogorov equation, yielding kinetics parameters. The first stage, associated with the phase decomposition, proceeded much faster than the second stage, associated with the alpha-to-sigma phase transformation. The most reliable estimation of the position of the MMG and that of the value of the Cr solubility limit was obtained from the annealing time dependence of 〈B〉, namely 24.5 at. pct Cr for the former and 20.3 at. pct Cr for the latter. A comparison of these figures with the recent phase diagrams pertinent to Fe–Cr system was done.

Regulating the dissolution of brittle nano-precipitated phase in FeCrAl alloy by pulse current to repair aging properties

Usually, heat treatment is required to elevate the entire material to a higher energy state, thereby eliminating harmful precipitates and repairing the mechanical properties of aged materials. However, the energy utilization rate of this high-temperature treatment method is low, and the regulation of precipitates dissolution is overly dependent on temperature. In this study, an efficient and energy-saving pulse current method was used to control the brittle Cr-rich α′ phase dissolution in aged Fe-25Cr-5Al grade alloy (Fe-24.32Cr-5.67Al-0.043C in wt.%). Compared with conventional heat treatment, pulse current treatment significantly reduces the dissolution temperature and activation energy of the precipitate, and as the current density increases, the non-thermal effect promoting brittle phase dissolution becomes more pronounced. This study is of great significance for the microstructure control and performance design of materials using pulsed current.

Effects of yttrium on the oxidation behavior of Fe13Cr6AlY alloys under 1200 °C steam

FeCrAl alloys are a candidate material for accident-tolerant fuel cladding in nuclear power plants owing to their high-temperature oxidation resistance, which can be further enhanced by the addition of Y. The main objective of this study was to investigate the effects of Y on the oxidation behavior of Fe13Cr6Al alloys in a 1200 °C steam environment with varying Y concentrations. Initially, Y was present as intermetallic particles in the matrix, which were identified as YFe4Al8. Once the oxidation process began, Y-rich intermetallics served as Y reservoirs and caused two conflicting effects: Y segregation at the oxide grain boundaries and Y-rich oxide formation. The Y segregation caused the inward diffusion of oxygen to be dominant, which changed the oxide growth mechanism and led to enhanced oxidation resistance and oxide adherence. On the other hand, Y formed Y2O3 at the grain boundaries near the oxide/metal interface, which eventually became Y3Al5O12. The Y3Al5O12 pegs allowed rapid oxygen penetration into the metal substrate and caused internal oxidation. Therefore, there is an optimal Y content as a result of these conflicting effects of Y addition. The reticular structure was also carefully analyzed to determine any relationship with the Y-rich oxide pegs. The reticular structure observed on the oxidized surface was identified as Y3Al5O12, which was formed at the grain boundaries of the metal or buried in the Al oxide. The size of the reticular structure coincided with the grain size of the metal near the surface. Data AvailabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also form part of an ongoing study.

Integrated effect of aging and heavy ion radiation on FeNiCrAl duplex alloy for accident-tolerant fuel cladding

Alumina-forming duplex FeNiCrAl alloy with superior mechanical properties and high-temperature oxidation resistance has been regarded as an accident-tolerant fuel cladding material. This work investigated the effect of aging and the radiation resistance of FeNiCrAl duplex alloy after up to 2000 hours thermal aging and 3.5 MeV Fe13+ ion radiation. The ferrite phase containing B2 phase shows much fewer radiation defects and lower radiation hardening rate than conventional FeCrAl alloy. The coherent B2 phase precipitate is critical in hindering dislocation and inhibiting the formation of radiation induced defects which is proved via experiment and molecular dynamics simulation. Besides, the Al depletion of B2 phase and nano-sized precipitation are characterized by using Time-of-Flight Secondary Ion Mass Spectrometry and Atom Probe Tomography. These findings effectively illuminate microstructure evolution of FeNiCrAl duplex alloy after long-term aging and radiation and lead to new insight for designing advanced accident-tolerant fuel material.

Electrolytic coating of iron-chromium alloy of sulphate-chloride electrolyte in machine parts recovery process modelling

Introduction. The technological process of restoring a part should provide more than 80% of the resource and no more than 50% of the cost of a new part. The wear resistance of the applied coating determines the resource of the restored part operating under waterjet and boundary friction. The microhardness of an iron-based electrolytic coating is one of the key indicators of wear resistance. The study of the results of statistical processing and the factors most affecting the increase in the microhardness of the iron-based coating will make it possible to recommend and optimize the deposition conditions for obtaining the most wear-resistant coatings.Materials and methods. The studies on equipment that let to obtain the necessary data with the required accuracy were carried out. The mathematical processing using modern statistical data processing tools that excluded possible errors, let to obtain the dependence of factors with the necessary accuracy was carried out.Results. During the study of the developed sulfate-chloride electrolyte for the deposition of an iron–chromium coating, it became necessary to determine the effect of deposition conditions – ‘factors’ (temperature, acidity of the electrolyte, cathode current density) on the microhardness of the coating – ‘response’. It was found that the combination of the factors ‘temperature’ and ‘cathode current density’ in the coded values of 1.5. 2.0 and -2 are the most significant. The deposition conditions in order to obtain a coating with maximum microhardness are optimized.Discussion and conclusions. As a result of the conducted studies for the effect of the deposition conditions of the Fe-Cr alloy from the sulfate-chloride electrolyte on the microhardness of the coating, it was found that in order to obtain high-quality coatings of the iron-chromium alloy with high microhardness, it is necessary to strictly comply with the requirements of the deposition conditions and acidity to a greater extent. As the current density and temperature of the electrolyte, compared with the acidity of the electrolyte, iron baths are installed and regulated by equipment.

Effect of cryogenic laser surface modification on the microstructure evolution and corrosion resistance of accident-tolerant FeCrAl alloys

Accident-tolerant FeCrAl alloys require a thinner cladding wall than zirconium cladding to overcome the extra neutron loss, thus requiring enhanced corrosion resistance. Surface treatment was used in this study to address this issue via cryogenic laser surface modification. A finite element model based on heat-transfer theory was raised to reveal the temperature field change during cryogenic laser treatment. The relationship between the laser processing parameters and surface morphology was studied with various characterizations to better understand the process mechanism and verify the correctness of the model. Hydrothermal corrosion test was proceeded in an autoclave at 290 °C and 7.5 MPa for 150 h to examine the enhancing corrosion resistance. STEM observations were used to study the microstructure evolution by cryogenic laser processing and corrosion. Electrochemical tests were performed to analyze the relationship between processing parameters and corrosion resistance before and after corrosion. The oxide film thickness and corrosion rate of the cryogenic laser-modified sample were 66 % and 80 % smaller than the as-received sample. The enhanced corrosion resistance was attributed to the microcrystalline layer and the thin duplex passive film that formed during the cryogenic laser process.

Dynamic Precipitation of Laves Phase in FeCrAl Alloy with Zr Addition

FeCrAl alloy is one of potential candidates for accident‐tolerant‐fuel (ATF)‐cladding materials due to its excellent oxidation and corrosion resistance at accident temperature, combining good mechanical properties at service temperature. Alloying strategy is an important way for improving comprehensive properties of FeCrAl alloy through the precipitation of fine Laves phase. Zr alloying can stabilize the Laves phase due to its lower diffusion coefficient and solubility in body‐centered‐cubic ferrite matrix. Herein, it is found that Zr addition changes the dynamic precipitation features of Laves phase in FeCrAl alloy during high‐temperature deformation, from only one type of Fe2M (M = Nb, Mo, Ta) Laves phase to Fe2Zr combining Fe2M‐type Laves phase. The Fe2Zr‐type Laves phase precipitates dynamically first, and the interface precipitates between which with ferrite matrix creates more nucleation sites for subsequent precipitation of Fe2M Laves phase. The results can be possibly applied for alloy design and microstructure tailoring in series of FeCrAl alloys used for ATF cladding in the near future.

Chromium and iron recovery from hazardous extracted vanadium tailings via direct reduction magnetic separation

The large accumulation of extracted vanadium tailings not only causes a waste of resources but also leads to environmental pollution. In this work, a technique was proposed that involves direct reduction followed by magnetic separation for recovering Fe and Cr while removing Na from the extracted vanadium tailings. Thermodynamic analysis and process parameters such as the use of additives and the reduction temperature were experimentally determined. Thermodynamic results showed that a reduction temperature higher than 1250 °C is required for the simultaneous removal of sodium, iron, and chromium. The experimental results indicated that when the Ca (OH)2 addition was added at a rate of 30 %, and the reduction temperature was maintained at 1350 °C for 2 h, Fe-Cr alloys were formed by the reduction of iron and chromium and could be separated by magnetic separation. The addition of Ca (OH)2 greatly facilitates the reduction of the Fe-containing phase in the extracted vanadium tailings, resulting in the formation of Fe-Cr alloy with reduced Cr. Sodium metal was volatilized, with removal rates of 65.9 %, 93.3 % and 93.32 % for Cr, Fe and Na, respectively. The recovery efficiencies for Fe and Cr were 85.9 % and 65.4 % respectively. The magnetic concentrate contained 83.84 % total Fe and 7.25 % Cr, and its main phase was Fe-Cr alloy. In contrast, the magnetic tailing consisted mainly of CaTiO3. The simultaneous method has a significant impact on removing valuable metals and reducing the environmental risk of the extracted vanadium tailings.

Positron annihilation investigation of hardening behavior induced by Fe2+ irradiation in low-Cr FeCrAl alloys

Compared with 13Cr–FeCrAl alloy, micro-alloyed low-Cr FeCrAl alloy is expected to provide higher potential for application as accident-tolerant fuel (ATF) cladding material. In this study, low-Cr FeCrAl alloys with 7–10 wt.% Cr contents were irradiated to different doses of 1 and 5 dpa at 400 °C with 3 MeV Fe2+ ion. The 13Cr–FeCrAl alloy C35MN developed by Oak Ridge national laboratory was also studied for comparison. Samples were examined by Doppler Broadening of Annihilation Radiation (DBAR) and nanoindentation before and after irradiation. Nanoindentation hardness tests showed that irradiation hardening occurred in FeCrAl alloy samples with different Cr contents after irradiation. The hardening response of the 13Cr–FeCrAl alloy increased with the increase of irradiation dose, while the hardness of low-Cr micro-alloyed FeCrAl alloy changed little or decreased after higher dose irradiation. DBAR shows that the defect type of all samples before irradiation is the same and there are a large number of vacancy-type defects in all unirradiated samples. High temperature irradiation reduces the density of the internal vacancy defect of FeCrAl alloy, which is probably caused by the annealing-induced recovery effect on atomic displacement. The defect density of 13Cr-alloy increases with the increase of irradiation dose, while that of 10Cr–FeCrAl alloy decreases with the increase of irradiation dose. This is related to the much finer grain/precipitate size and the higher number density of precipitates, and thus the higher fraction of boundaries in the 10Cr–FeCrAl alloy. The results also showed that the vacancy recovery rate of the 10Cr–FeCrAl alloy is higher.

A Study of the Structural and Energy Properties of (210) and (130) Boundaries in Iron and an Fe–Cr Alloy

The structure and energy properties of symmetric tilt boundaries Σ5 (130)[001] and Σ5 (210)[001] in iron and low-concentration Fe–Cr alloys are investigated from first principles and by the molecular statistics method. It is shown that the boundary strongly changes the interplane distances. The sequence of multilayerrelaxation comprises damped oscillations, gradually decreasing into the grains. The energy for the replacement of iron with chromium atoms near the boundaries is lower than in pure iron. Our calculations indicate the tendency to accumulate Cr atoms and vacancies near the grain boundaries.

A Study of the Structural and Energy Properties of (210) and (130) Boundaries in Iron and an Fe–Cr Alloy

A Study of the Structural and Energy Properties of (210) and (130) Boundaries in Iron and an Fe–Cr Alloy

Sound Generation by Metro Trains during Braking and Its Suppression Method

The causes of acoustic noise occurring during braking of electric vehicles, in particular, in the metro, were analyzed. The spectrum of such noise was measured, and it is shown that high-frequency discrete tones are excited by braking resistors, applied for electrodynamic braking of electric vehicles. Three proposed mechanisms of electromechanical interaction in a Fecral plate, which is a braking resistor element, were considered: the Ampère force and linear and nonlinear magnetostriction. It was shown that predominant odd harmonics indicate the presence of a significant piezomagnetic effect and the inverse effect of linear magnetostriction in the Fecral alloy. A phenomenological approach was used to calculate the piezomagnetic tensor elements for Fecral. Calculations by the finite element method showed that asymmetric cuts introduced into the plate may significantly decrease intensity of acoustic vibrations excited by the braking resistor.

Recent Progress on Creep Properties of ODS FeCrAl Alloys for Advanced Reactors.

In order to meet the growing energy demand, more environmentally friendly and efficient GEN-IV reactors have emerged. Additionally, nuclear structural materials need larger more safety margins for accident scenarios as a result of the Fukushima accident. In order to extend the failure time and lessen the effect of accidents, this design method for accident-tolerant fuel materials calls for cladding materials to maintain good corrosion resistance and mechanical properties during a beyond design basis accident (BDBA). Accidents involving nuclear reactors would undoubtedly result in higher temperatures, which would make it much harder for materials to withstand corrosion. Oxide dispersion strengthened (ODS) FeCrAl alloys have shown promise as candidate materials because of their extraordinarily slow reaction rates under high-temperature steam. However, the addition of the Al element renders the alloy's high-temperature mechanical properties insufficient. In particular, studies on the alloy's creep properties are extremely rare, despite the fact that the creep properties are crucial in the real service environment. Therefore, this paper focuses on the creep properties of ODS FeCrAl alloy, summarizes and analyzes the research results of this material, and provides a reference for future research and applications.

Effect of nickel on the oxidation behavior of FeCrAl alloy in simulated PWR and BWR conditions

Effect of nickel on the oxidation behavior of FeCrAl alloy in simulated PWR and BWR conditions

Effects of Nb and Mo on 1200 °C Steam Oxidation and Mechanical Properties of FeCrAl Alloys for Fuel Cladding Materials

Effects of Nb and Mo on 1200 °C Steam Oxidation and Mechanical Properties of FeCrAl Alloys for Fuel Cladding Materials

Interfacial compatibility and thermal cycle stability for glass-sealed oxygen sensors

The oxygen sensors are extensively utilized in vehicles’ exhaust systems to monitor gases composition and control air-to-fuel ratio, thus reducing harmful emission and improving fuel economy. In equilibrium potentiometric sensors, the sealing performance is essential to ensure data accuracy. In this work, the 64SiO2–18TiO2–10Na2O–7K2O–1Al2O3 (wt%) glass was utilized as seals instead of traditional talcum in zirconium dioxide oxygen sensor. The interfacial compatibility with adjacent components (Fe–16Cr, Al2O3 and 8YSZ) and thermal cycle stability of seals were seriously evaluated in various ways. The equilibrium contact angles were lower 60° at high temperature, exhibiting better wettability and tight bonding at the interface. Besides, the leakage rates between glass and Fe–16Cr alloy were less than 0.01 sccm/cm at 650–800 °C and input gas pressures of 6.9–34.5 kPa. The oxygen sensor coupled with glass exhibited better thermal stability that leakage rate maintained around 0.004 sccm/cm under an input gas pressure of 200 kPa during 100 thermal cycles. Additionally, the oxygen sensor with sealed glass can generate continuous response and recovery, which is better than sealed talcum. Owing to these good performance, the glass is a suitable alternative for oxygen sensor sealing.

Mechanistic study of incipient corrosion for nuclear grade lean-Cr FeCrAl alloys in a simulated PWR environment

This study systematically investigated the incipient corrosion behavior of Fe-13Cr-4.5Al (wt%) and lean-Cr (7–10 wt%) with 5Al (wt%) FeCrAl alloy with a timescale of 4 months under simulated PWR conditions (18.6 MPa and 360 °C) in an autoclave system. The corrosion induced two types of structure of oxide scale. FeCrAl alloys corroded for 3 months exhibited a duplex structure containing outer oxide particles and an inner Cr-rich spinel. During the corrosion test lasting 3–4 months, a triplex structure containing outer oxide particles, an inner compact Cr-rich spinel layer, and a porous spinel layer was observed. Moreover, Cr enriched at the periphery of outer oxides, indicating the formation of FeCr2O4 spinel oxide.

Effect of V content on hydrogen storage properties and cyclic durability of V–Ti–Cr–Fe alloys

Vanadium-based body-centered-cubic (BCC) alloys are ideal hydrogen storage media because of their high reversible hydrogen capacities at moderate conditions. However, the rapid capacity decay in hydrogen ab-/desorption cycles prevents their practical application. In this work, V-based BCC alloys with three different V contents (V20Ti38Cr41.4Fe0.6, V40Ti28.5Cr30.1Fe1.4, V60Ti19Cr19Fe2, named as V20, V40, V60) were prepared by arc melting, and their microstructures and hydrogen ab-/desorption properties were investigated systematically. XRD results show that there is a number of C15-Laves phase presence in V20, which does not appear in V40 and V60. Meanwhile, the lattice constant of the BCC phase clearly decreases as the V content rises. These differences result in a hydrogen storage capacity of only 1.82 wt% for V20 alloy, but 2.13 wt% for V40 and 2.14 wt% for V60, and an increment in hydrogen ab-/desorption plateau pressure. The V40 and V60 alloys are chosen in de-/hydrogenation cycle test owing to higher effective storage capacities, and the results show that the V60 alloy has better cycle durability. According to the microstructural analysis of the two alloys during the cycles, the micro-strain accumulates, the cell volume expands, the particles pulverizes and the defects increase during the cycles, which eventually lead to the attenuation of the hydrogen storage capacity. The increment of the V content obviously improves the elastic properties of the alloy, which further diminishes the micro-strain accumulation, cell volume expansion, particle pulverization and defect increase, eventually resulting in a higher capacity retention and better cyclic durability.

Bridging microscale to macroscale mechanical property measurements of FeCrAl alloys by crystal plasticity modeling

FeCrAl alloys are candidates for accident tolerant fuel cladding of light water reactors. In this work, a microstructure- and temperature-dependent crystal plasticity model is employed to bridge microscale to macroscale mechanical property measurements of FeCrAl alloys. With the visco-plastic self-consistent (VPSC) polycrystal plasticity framework, a mechanism-based single crystal plasticity (MSCP) model adopts the Arrhenius type rate equation to describe the dependence of the critical resolved shear stress for dislocation slips on their temperature-dependent intrinsic frictional resistance and the microstructure-dependent irradiation hardening. The intrinsic frictional resistance associated with {110}<111> and {112}<111> slip systems were measured by in-situ micromechanical testing on unirradiated/irradiated samples at 25-500 °C. The irradiation hardening is estimated by the Bacon-Kocks-Scattergood (BKS) model with density and size of radiation-induced defects measured from microstructural characterization. Several features associated with thermo-mechanical behavior of unirradiated/irradiated polycrystalline FeCrAl alloys are captured. High density of deformation-induced dislocations and radiation-induced defects results in obvious hardening at room temperature, which is weakened at high temperature, and facilitates damage evolution during deformation. Moreover, both high temperature and radiation-induced defects, which facilitate dislocation multiplication, trigger large hardening rate. The proposed method together with application of accelerator-based ion irradiation technique is a surrogate approach to simulate neutron damage, improving the efficiency associated with evaluation of mechanical properties of FeCrAl alloys exposed to temperature, stress and radiation conditions.