Fe-based Alloys Research Articles

Effect of Σ5(2 1 0)[0 0 1] symmetric tilt grain boundary on the compatibility between iron and liquid lithium: Atomistic simulations

The compatibility between Fe-based alloys and liquid Li is crucial for the development of liquid Li blanket in the fusion devices. In this work, molecular dynamics (MD) simulations have been used to reveal the effect of Σ5(210)[001] symmetric tilt grain boundary (GB) on the compatibility between Fe and liquid Li. The results show that the corrosion of Fe bicrystal by liquid Li aggravates with increasing temperature, and the critical temperature for the deterioration of compatibility is about 800 K. In the corrosion process, the Fe atoms near the GB are most likely to escape or even dissolve, and Li atoms preferentially penetrate into the intergranular space along the GB. Based on the simulation, the Fe atoms near the GB have high potential energy and poor structural ordering, and their thermal motion at high temperatures generates a large number of Frenkel defects here, which in turn promote the diffusion of Fe and Li atoms along the GB. In terms of energetics, the lower vacancy formation energies and Li atomic substitution energies near the GB are responsible for the GB corrosion.

Corrosion behavior of various conductive materials in Sb3Sn7 alloy at 450 °C

Sb-Sn alloys are attractive positive electrode materials for liquid metal batteries. In this work, the corrosion behavior of three steels (f/m steel T91, austenitic steels SS304 and SS316L), one Fe-Co-Ni alloy (4J29 Kovar), molybdenum, and three MAX-phase coatings (Cr2AlC, Ti2AlC, Ti3AlC2) is investigated in static exposures to liquid Sb3Sn7 alloy at 450 °C for 750 h in oxygen-poor conditions. The results reveal unacceptably high corrosion rates in the range 0.5 to 1.3 µm/h for the Fe-based alloys, while Mo and MAX-phases show promising corrosion resistance with corrosion rates below 0.1 mm/a despite a small arsenic impurity of the liquid metal.

Effect of Laser Irradiation and Tensile Stress on Microstructure and Magnetic Properties of Fe-Based Amorphous Alloys.

The effect of laser irradiation and tensile stress on the microstructure and soft magnetic properties of the FeSiBNbCu nanocrystalline alloy prepared using a continuous laser has been investigated. The experimental results indicate that a decreased laser scanning speed provides more thermal energy to induce nanocrystals and encourage grain growth. When the scanning speed is excessively high, the crystallization process will cease due to a lack of energy to drive diffusion phase transitions. Nevertheless, the introduction of tensile stress could significantly promote crystallization in FeSiBNbCu alloy samples irradiated at these high laser scanning speeds. This phenomenon can be attributed to the augmentation of compressive thermal stress at the interface between the laser-treated track and the untreated region. This heightened compressive stress promotes the diffusivity of atoms, and, as a result, the transformation from amorphous to crystalline states can be enhanced. As the applied tensile stress increases, both grain size and crystalline volume fraction exhibit a proportional augmentation. Consequently, these changes manifest in the soft magnetic properties. The crystalline volume fraction can reach 62%, and the coercivity is 2.9 A/m at the optimized scanning speed; these values correspond to 54% and 3.3 A/m under specific tensile stress loading.

Microstructure and Wear Behavior of Ti-xFe-SiC In Situ Composite Ceramic Coatings on TC4 Substrate from Laser Cladding.

Titanium alloys are widely used in various structural materials due to their lightweight properties. However, the low wear resistance causes significant economic losses every year. Therefore, it is necessary to implement wear-resistant protection on the surface of titanium alloys. In this study, four types of in situ composite ceramic coatings with two-layer gradient structures were prepared on a Ti-6Al-4V (TC4) substrate using laser cladding. In order to reduce the dilution rate, a transition layer (Ti-40SiC (vol.%)) was first prepared on TC4 alloy. Then, a high-volume-fraction in situ composite ceramic working layer (Ti-xFe-80SiC (vol.%)) with different contents of Fe-based alloy powder (x = 0, 5, 10 and 15 vol.%) was prepared. The working surface of Ti-40SiC (TL) exhibited a typical XRD pattern of Ti, TiC, Ti5Si3, and Ti3SiC2. In comparison, both Ti-80SiC (WL-F0) and Ti-5Fe-80SiC (WL-F5) exhibited similar phase compositions to the TL coating, with no new phase identified in the coatings. However, the TiFeSi2 and SiC phases were presented in Ti-10Fe-80SiC (WL-F10) and Ti-15Fe-80SiC (WL-F15). It is proven that the addition of the Fe element could regulate the in situ reaction in the original Ti-Si-C ternary system to form the new phases with high hardness and good wear resistance. The hardness of the WL-F15 (1842.9 HV1) is five times higher than that of the matrix (350 HV1). Due to the existence of self-lubricating phases such as Ti5Si3 and Ti3SiC2, a lubricating film was presented in the WL-F0 and WL-F5 coatings, which could block the further damage of the friction pair and enhance the wear resistance. Furthermore, a wear-transition phenomenon was observed in the WL-F10 and WL-F15 coatings, which was similar to the friction behavior of structural ceramics. Under the load of 10 N and 20 N, the wear volume of WL-F15 coating is 5.2% and 63.7% of that in the substrate, and the depth of friction of WL-15 coating is only 14.4% and 80% of that in the substrate. The transition of wear volume and depth can be attributed to the wear mechanism changing from oxidation wear to adhesive wear.

Effect of ultrasonic high-frequency micro-forging on the wear resistance of a Fe-base alloy coating deposited by high-speed laser cladding process

In this study, Fe-based alloy coatings were prepared on 27SiMn substrates by laser cladding. To eliminate defects such as insufficient coating precision and excessive residual stress, the effects of ultrasonic high-frequency micro-forging (UH-FM) on coating microstructure and wear resistance were investigated. The experimental results show that the coating's surface roughness and residual stress are significantly reduced after UH-FM. The surface microstructure was broken and refined, and a gradient structure appeared. A part of the fcc phase was transformed into the bcc phase, which increased the resistance of dislocation movement, and the hardness of the coating increased. The width and depth of the abrasion marks and the wear weight loss of the treated coatings were reduced, and the compact oxide layer was distributed more uniformly, indicating that the UH-FM-treated coatings obtained better wear resistance.

Anodic Oxidation and Corrosion Resistance of Ta-Containing High Entropy Alloys

Stainless steels are corrosion resistant, but pitting corrosion sometimes occurs in chloride solutions. Anodic oxidation is one of the effective methods to increase the pitting corrosion resistance. However, unlike valve metals, stainless steels are difficult to improve pitting corrosion resistance by anodic oxidation. In this study, Fe-based alloys containing valve metals were fabricated to investigate anodic oxidation and corrosion resistance.Equimolar CrFeNbNiTa and (CrFeTa)30(NbNi)5 alloys were fabricated by arc melting, and pure metals of Cr, Fe, Nb, Ni, and Ta were used as raw materials. After casting, the ingots were heat-treated at 1200 ℃ for 2 h (furnace-cooling) and cut into 2 mm thick sheets. After that, the specimen surfaces were polished up to 1 μm with a diamond paste. The microstructures were observed using an optical microscope and a scanning electron microscope. The chemical compositions and elemental distributions of the specimens were analyzed by energy dispersive X-ray spectroscopy. Potentiodynamic polarization was performed in 1 M H2SO4. As a reference, Type 304 stainless steel was used.The equimolar CrFeNbNiTa alloy was composed of two phases. One was Cr- and Fe-rich and the other was Nb- and Ni-rich. The (CrFeTa)30(NbNi)5 alloy was a single phase. In the potentiodynamic polarization measurements, the current densities of oxygen evolution reaction of equimolar CrFeTaNbNi and (CrFeTa)30(NbNi)5 alloys were lower than that of Type 304 stainless steel. Moreover, the passive current densities of equimolar CrFeTaNbNi and (CrFeTa)30(NbNi)5 alloys were higher than that of Type 304 stainless steel.

Origin of the enhanced pseudo-elasticity of additively manufactured Fe-17Mn-5Si-4Ni-10Cr-(V, C) shape memory alloy fabricated by laser powder bed fusion

This study investigated the origin of the enhanced pseudo-elasticity of additively manufactured vanadium carbide-containing Fe-based shape memory alloys. The aged samples with two different starting microstructures, as-built and solution-treated, showed completely different final microstructures following identical aging treatments. The sample aged directly from the as-built microstructure exhibited typical solidification structures, molten pools, and cellular structures with fine grain sizes inherited from the laser powder bed fusion process with a high cooling rate. In contrast, the sample aged following solution treatment revealed fully recrystallized grain structures with relatively larger grain sizes than the former. Despite having the same type of carbides, the directly aged sample had finer and denser precipitates than the sample aged following solution treatment. Additionally, compared to the sample aged following solution treatment, the directly aged sample exhibited a larger pseudo-elastic recovery strain. The precipitation behavior may have had a negligible impact on the pseudo-elastic behavior because the increase in the pseudo-elastic recovery strain following aging treatment was not significant for either sample. Besides, thermodynamic calculations predicted that the stability of the face-centered cubic (fcc)-γ phase would be increased by local elemental segregation at cell boundaries. Cell boundaries with high fcc-γ phase stability can act as sites that can apply back stress on the deformation-induced hcp-ε phase, thus promoting reverse motion of the Shockley partial dislocations or deformation-induced hcp-ε phase. Furthermore, the smaller grain size enhanced the stability of the fcc-γ phase.

Degradation of Azo Dye Solutions by a Nanocrystalline Fe-Based Alloy and the Adsorption of Their By-Products by Cork.

In this study, the efficiency of mechanically alloyed Fe80Si10B10 in degrading basic red 46 azo dye is investigated. Moreover, the influences of different parameters, such as pH and time, on the elimination of the aromatic derivatives obtained as by-products of the fracture of the azo group are also analyzed. After beginning the reduction to the normal conditions of pH (4.6) and temperature, the experimental findings showed a discoloration of 97.87% after 20 min. The structure and morphology of the nanocrystalline Fe80Si10B10 powder were characterized by SEM and XRD before and after use in the degradation process. The XRD patterns of the Fe-Si-B powder after redox reaction suggest that the valent zero Fe of the alloy is the reducing agent. Powdered cork was then used as a biosorbent for the removal of the by-products generated, resulting in increasing removal percentages from pH 7 (26%) to pH 9 (62%) and a contact time of 120 min. The FTIR spectrum of the cork after adsorption shows a shift of the bands, confirming the interaction with the aromatic amines. The present findings show that metallic powders and natural cork perform well together in removing azo dye solutions and their degradation products.

The Impact of Oxidation-Induced Degradation on Materials Used in Hydrogen-Fired Microturbines

Abstract Hydrogen-fueled microturbines are being considered as part of the future green microgrid. However, the use of hydrogen as a fuel presents new challenges for selection and development of suitable high temperature materials for hydrogen combustion. The burning of hydrogen is expected to result in higher operating temperatures and higher than typically observed water vapor contents in exhaust gases versus burning natural gas. In this work, foil specimens of various Fe- and Ni-based alloys were oxidized in air + 10% H2O and air + 60% H2O for up to 5000 h at 700 °C to simulate the exhaust atmosphere of natural gas and hydrogen-fueled microturbines. The impact of alloy composition and water vapor content on the oxidation/volatilization induced loss of wall thickness was experimentally evaluated. Enhanced external oxidation and volatilization of Cr2O3 and Ti-doped Cr2O3 scales were observed in air + 60% H2O compared to air + 10% H2O. No significant impact of the higher water vapor content was observed on Al2O3 scales formed on Fe-based alumina-forming austenitic alloys. Lifetime modeling was employed to predict the combined effects of water vapor content, gas flow rates, temperature, and alloy composition on the oxidation-induced lifetime of the investigated materials.

Experimental and numerical investigations of sliding wear behaviour of an Fe-based alloy for PWR wear resistance applications

The excellent wear and corrosion resistance of Co-based alloys make them desirable for tribological applications in the nuclear industry. However, neutron activation of the Co-based alloys leads to significant occupational radiation doses. An alternative Fe-based alloy called RR2450 was developed by Rolls-Royce plc to replace these alloys. This paper presents the first comprehensive study evaluating the sliding wear resistance of RR2450 alloy in representative PWR conditions. The sliding counterface of RR2450 balls was a Co-based alloy, Haynes 25 discs. Four tests were performed at temperatures up to 80 °C, and 12 tests were performed up to 200 °C. Results showed wear performance of RR2450 balls degraded at higher loads and temperatures, with temperature having a significant role. Microstructural investigation revealed voids and hard silicide phases, negatively impacting wear resistance. Nonetheless, the wear performance of RR2450 was similar to a Co-based alloy, a=Stellite 20, at nuclear reactor conditions. Two wear tests with uneven wear tracks were selected for 3D finite element analysis. The wear simulation procedure is based on Archard’s wear equation and is implemented in a commercial FE package, ABAQUS. The FEA method was used to capture the wear on both surfaces, and was shown to predict nominal wear profiles. These comparisons with experiments show that the FEA results can provide representative wear profiles when wear depths and widths are asymmetrical and irregular.

Oxide dependent textured crystallization on amorphous alloy surface

Amorphous alloys produced through rapid solidification offer a host of exceptional properties, with the caveat that achieving a fully amorphous structure. In our laboratory, the FeSiBPC alloy has demonstrated substantial industrial potential, but it contends with a persistent challenge in the form of surface crystallization during large-scale manufacturing. This study delves into the phenomenon of surface crystallization, variables influencing surface crystallization and elucidate its distinctive characteristics were studied. A noteworthy breakthrough emerges with the inaugural characterization of a high-quality fiber texture within an Fe-based amorphous alloy, achieved through Electron Backscattered Diffraction. Our findings underscore the remarkable sensitivity of air pressure within the chamber, revealing its significant impact on the intensity of Bragg peaks related to surface crystals. Moreover, the crucial role of an oxide atmosphere in effectively mitigating surface crystallization and offer insights into the mechanisms governing this preventive action. This study provides valuable insights into the intricate interplay of factors governing surface crystallization in amorphous alloys, offering promising avenues for enhanced industrial applications.

Mass Production and Vast Application States of Bulk Metallic Glasses

Since the first synthesis of bulk metallic glasses (BMGs) by copper mold casting in 1990, much effort has been devoted to the searching of new BMG composition, the clarification of fundamental and engineering properties for BMGs and their industrialization. At present, BMGs have been formed in a large number of multicomponent alloy systems where the empirical three component rule is satisfied. Nowadays, commercialized BMGs are classified to Zr-based and Fe-based alloy groups. When we look at the industrialization of Zr-Al-Ni-Cu-based BMGs, the first commercialization was made for golf clubs in Japan in 1998, followed by watch parts etc. Since then, Zr-based BMGs have been used continuously up to 2013, though their application scale was in a limited state. Since 2014, the application scale was significantly extended in collaboration with the rapid developments of smartphones and electric vehicles. At present, the mass production facilities for Zr-based BMGs have been significantly developed and variety of BMG products have been produced. On the other hand, Fe-based soft magnetic BMGs were found in 1995. Their BMGs have also been used on a huge number of pieces in various kinds of electronic-magnetic instruments. These recent application states for Zr- and Fe-based BMGs are introduced together with new nanocrystalline Fe-based soft magnetic alloys developed through the derivation of alloy composition from Fe-based BMGs.

Prediction of magnetocaloric properties of Fe-based amorphous alloys based on interpretable machine learning

This study developed a machine learning model to accurately predict the isothermal magnetic entropy change (-SM) in amorphous alloys, a key parameter for evaluating magnetocaloric performance. Four machine learning algorithms were compared, and the (Extremely Randomized Trees) ETR algorithm demonstrated exceptional performance with an (R-squared) R2 value of 0.90 and a (Mean Absolute Percentage Error) MAPE of 13.31 % on the test set. Feature selection techniques, including Pearson correlation coefficient (PCC) and Recursive feature elimination (RFE), identified a subset of 7 important features: (Applied Field) Mf, δr, ΔH, ΔTm, ΔS, Tm‾, and Ec‾. The Shapley Additive Explanations (SHAP) method provided insights into feature importance and critical values. Design strategies for new alloys, using the FeZrB system as an example, were proposed based on the predictive model. The model's generalization ability was validated on other amorphous alloy systems, showcasing its wide applicability. This research contributes to the field of amorphous alloys and suggests future directions for machine learning applications.

Influence rules of early transition elements on rapid solidified structure and nanocrystallization behaviors of Fe-Si-B-Cu soft magnetic alloys with high Cu content

Unique rapid solidified structure and nanocrystallization mechanism enable the Fe-based nanocrystalline alloys with high Cu content excellent soft magnetic properties and good manufacturability, and also results in unusual phenomena in terms of alloying effects. In the present work, we systematically studied the influence rules of early transition elements on the rapid solidified structure and nanocrystallization behaviors of Fe-Si-B-Cu soft magnetic alloys with high Cu content and explored the related mechanisms. In terms of rapid solidified structure, the additions of early transition elements always inhibit the formation of pre-existing α-Fe crystals even eliminate them, and the additions that could produce larger atomic mismatch parameter (δ) and negative mixing enthalpy (ΔHmix) show stronger effects. In terms of nanocrystallization behaviors, the increases in δ and negative ΔHmix weaken the competitive growth between the pre-existing nanocrystals during annealing and then coarsen the nanostructure of the annealed alloys and deteriorate their magnetic softness, while the excessive increases in δ and negative ΔHmix could significantly suppress the growth of α-Fe crystals by diffusion inhibition during annealing and thus remarkable refine the nanostructure of the annealed alloys and improve their magnetic softness.

Hysteresis and loss characteristics of Fe-based nanocrystalline alloys based on a novel variable-temperature dynamic Jiles–Atherton hysteresis model

The magnetic characteristics of Fe-based nanocrystalline alloys can be influenced by temperature. The conventional dynamic Jiles–Atherton (J-A) hysteresis model does not take into consideration the impact that temperature has on magnetic characteristics. A novel variable-temperature dynamic J-A hysteresis model is proposed in this paper to effectively address the issue. Firstly, the hysteresis loops of Fe-based nanocrystalline are measured at −50 °C–130 °C and DC state. The five parameters of the J-A hysteresis model are identified at various temperatures using the particle swarm optimization algorithm, and five parameters are fitted as functions of temperature. Subsequently, the five parameters as functions of temperature are introduced into the conventional dynamic J-A hysteresis model to construct a novel variable-temperature dynamic J-A hysteresis model, which can not only reflect the impact of temperature but also accurately calculate the losses. Finally, hysteresis loops and losses of Fe-based nanocrystalline alloy are simulated and calculated at different temperatures and frequencies by the variable-temperature dynamic J-A hysteresis model. Meanwhile, this paper also investigates the trends and percentages of hysteresis loss, excess loss as well as eddy current loss with frequency and temperature. Compared to the results of measured data, the maximum average error of the variable-temperature dynamic J-A hysteresis model is 5.83%.

Clean production of Fe-based amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore and apatite

Clean production of Fe-based amorphous soft magnetic alloys via smelting reduction of high-phosphorus iron ore and apatite

Microstructure and Mechanical Properties of Fe-Based Alloy Coatings Fabricated by Laser Cladding

The Fe-based alloy coating was prepared on the surface of 25Cr2Ni4MoV steel substrate by laser cladding. The microstructure, microhardness, shear strength, friction and wear properties of the laser cladding coating were systematically studied. The results show that a good metallurgical bond has been formed between Fe-based alloy coating and substrate. The laser cladding layer is a typical dendritic crystal, which is composed of light gray and dark gray phases. The shear strength displacement curve shows the typical characteristics of brittle fracture, with an average shear strength of 280.83 MPa. The average dry friction coefficient, wear track depth and average wear volume of laser cladding Fe-based alloy coatings are (0.45 ± 0.01), (26 ± 3) μm and 0.066615 m3, respectively. The average dry friction coefficient, wear track depth and average wear volume of 25Cr2Ni4MoV substrate are (0.60 ± 0.01), (39 ± 3) μm and 0.13085 m3, respectively. The laser cladded Fe-based alloy coating exhibits much better wear resistance than the steel substrate, and the shear strength of the coating displays its potential for the application in the service environment of shear stress.

Prediction and customized design of Curie temperature of Fe-based amorphous alloys based on interpretable machine learning

Predicting the Curie temperature (Tc) is a crucial problem in the field of amorphous alloys. In this study, Fe-based amorphous alloys are taken as an example, and the composition and corresponding Tc are collected through a literature review. Three feature construction strategies are employed to establish the relationship between the composition and Tc using machine learning. The research findings demonstrate that the combination of the Meredig rule and the GBT algorithm yields the highest prediction accuracy. The features are constructed using recursive elimination and enumeration methods, ultimately resulting in an optimal 8-dimensional feature subset. Furthermore, the Shapley Additive exPlanations (SHAP) values are introduced to analyze the interpretability of the prediction model, providing a feature importance ranking and their critical values. Finally, by replacing the Fe and P atoms with Mn and Si atoms, respectively, in the Fe80P13C7 alloy, Fe62Mn18P(13-x)C7Six (x = 4,5,6) alloys are successfully designed to exhibit a Tc close to room temperature (335 K), enabling customized Tc design for Fe-based amorphous alloys.

Corrosion Performance of Fe-Based Amorphous Coatings via Laser Cladding Assisted with Ultrasonic in a Simulated Marine Environment

Fe-based amorphous alloys are considered potential coating materials for applications in marine corrosive environments owing to their high resistance to chloride ion corrosion. Fe-based amorphous alloy (Fe41Co7Cr15Mo14C15B6Y2) was deposited on AISI 1020 steel using ultrasonic-assisted laser cladding. The research findings revealed a gradient structure generated at the junction of the coating and substrate. Ultrasonic promoted crystallization and increased the gradient structure’s average thickness, reducing coating surface cracks. However, ultrasonic had little effect on the amorphous content of the prepared coating surface, which still had a high amorphous content. The Fe-based amorphous coating prepared via laser cladding with ultrasonic demonstrated good corrosion resistance. The corrosion resistance of the coating without ultrasonic was reduced significantly due to cracks. EIS results confirmed that corrosion resistance was related to crystallization and crack issues. Cr element segregation due to crystallization hindered passivation film forming, reducing its corrosion resistance. Crack corrosion enlarged the crack gap and hollowed out the coating and the substrate’s binding zone, accelerating coating failure.

MEMS Fluxgate Sensor Based on Liquid Casting.

Compared with electroplating, liquid casting enables the rapid formation of a three-dimensional solenoid coil with a narrower line width and greater thickness, which proves advantageous in enhancing the comprehensive performance of the micro-electromechanical system (MEMS) fluxgate sensor. For this reason, a MEMS fluxgate sensor based on liquid casting with a closed-loop Fe-based amorphous alloy core is proposed. Based on the process parameters of liquid casting, the structure of the MEMS fluxgate sensor was designed. Utilizing MagNet to build the simulation model, the optimal excitation conditions and sensitivity were obtained. According to the simulation model, a highly sensitive MEMS fluxgate sensor based on liquid casting was fabricated. The resulting sensor exhibits a sensitivity of 2847 V/T, a noise of 306 pT/√Hz@1 Hz, a bandwidth of DC-10.5 kHz, and a power consumption of 43.9 mW, which shows high sensitivity and low power consumption compared with other MEMS fluxgates in similar size.