Fe-Si Alloys Research Articles

Effect of temperature and magnetic field induced hysteresis on reversibility of magnetocaloric effect and its minimization by optimizing the geometrical compatibility condition in Mn–Ni–Fe–Si alloy

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (|ΔSMmax|) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (RCeffe) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases.

Production of 2 μm-thick 6.5 % Si-Fe cold rolled sheet

Although 6.5% Si-Fe alloys have excellent magnetic properties, they have not been used in practical application because they are mechanically hard and brittle. In this study, we attempted an extremely thin 6.5% Si-Fe to realize a high-frequency, low-loss magnetic material, which is highly demanded for next-generation power electronic circuits. It was found that 6.5% Si-Fe with a thickness of 20 µm prepared by the liquid quenching method could be rolled down to 2 µm under certain conditions. The conditions under which the rollability was achieved were investigated in detail, such as grain structure, grain size, crystal orientation, etc. Since the eddy current loss of the 6.5% Si-Fe alloy with a thickness of 2 µm is expected to be extremely low, this material is very promising as a next-generation magnetic material for high frequency applications.

Photoelectron velocity map imaging spectroscopy of group 14 elements and iron tetracarbonyl anionic clusters MFe(CO)4- (M = Si, Ge, Sn).

The heteronuclear group 14 M-iron tetracarbonyl clusters MFe(CO)4- (M = Si, Ge, Sn) anions have been generated in the gas phase by laser ablation of M-Fe alloys and detected by mass and photoelectron spectroscopy. With the support of quantum chemical calculations, the geometric and electronic structures of MFe(CO)4- (M = Si, Ge, Sn) are elucidated, which shows that all the MFe(CO)4- clusters have the M-Fe bonded, iron-centered, and carbonyl-terminal M-Fe(CO)4 structure with the C2v symmetry and a 2B2 ground state. The M-Fe bond can be considered a double bond, which includes one σ electron sharing bond and one π dative bond. The C-O bonds in those anionic clusters are calculated to be elongated to different extents, and in particular, the C-O bonds in SiFe(CO)4- are elongated more. The Si-Fe alloy thus turns out to be a better collocation to activate the C-O bonds in the gas phase among group 14. The present findings have important implications for the rational development of high-performance catalysts with isolated metal atoms/clusters dispersed on supports.

Microstructure and magnetic domain structure of additively manufactured Fe–Si soft magnetic alloys with 3 and 9 wt.-% Si

Electrical steels are numerously used in engineering applications. Nowadays, future challenges related to climate change and e-mobility push the boundaries to higher efficiency also in electrical parts. A promising material group to reduce electrical losses are electrical steels with high silicon contents. However, such steels are difficult to process with conventional methods and, thus, additive manufacturing came into focus in recent years. The present study investigates the processability, crack sensitivity, microstructure evolution and magnetic domain structures of laser powder bed fused Fe–Si alloys with 3 and 9 wt.-% Si. It is shown that specimens, which are built using appropriate process parameters, are dense and free of cracks. Still, Fe–9Si is characterized by a higher crack susceptibility at low temperatures of the build platform. A checkerboard like microstructure with elongated grains alongside build direction evolved. Global magnetic properties from ring core measurements showed lower losses for the Fe–9Si ring. Moreover, it was found that the magnetic domain structures are directly influenced by the crystallographic orientations present in the specimen volumes. The findings elaborated will contribute to advanced possibilities in tailoring the magnetic properties of electrical steels for an increase of the efficiency of envisaged applications.

The Microstructure and Magnetic Properties of a Soft Magnetic Fe-12Al Alloy Additively Manufactured via Laser Powder Bed Fusion (L-PBF)

Soft magnetic Fe-Al alloys have been a subject of research in the past. However, they never saw the same reception in technical applications as the Fe-Si or Fe-Ni alloys, which is, to some extent, due to a low ductility level and difficulties in manufacturing. Additive manufacturing (AM) technology could be a way to avoid issues in conventional manufacturing and produce soft magnetic components from these alloys, as has already been shown with similarly brittle Fe-Si alloys. While AM has already been applied to certain Fe-Al alloys, no magnetic properties of AM Fe-Al alloys have been reported in the literature so far. Therefore, in this work, a Fe-12Al alloy was additively manufactured through laser powder bed fusion (L-PBF) and characterized regarding its microstructure and magnetic properties. A comparison was made with the materials produced by casting and rolling, prepared from melts with an identical chemical composition. In order to improve the magnetic properties, a heat treatment at a higher temperature (1300 °C) than typically applied for conventionally manufactured materials (850–1150 °C) is proposed for the AM material. The specially heat-treated AM material reached values (HC: 11.3 A/m; µmax: 13.1 × 103) that were close to the heat-treated cast material (HC: 12.4 A/m; µmax: 20.3 × 103). While the DC magnetic values of hot- and cold-rolled materials (HC: 3.2 to 4.1 A/m; µmax: 36.6 to 40.4 × 103) were not met, the AM material actually showed fewer losses than the rolled material under AC conditions. One explanation for this effect can be domain refinement effects. This study shows that it is possible to additively manufacture Fe-Al alloys with good soft magnetic behavior. With optimized manufacturing and post-processing, further improvements of the magnetic properties of AM L-PBF Fe-12Al may still be possible.

Investigation of local properties of the Fe-Si alloy subjected to mechanical and laser cutting

Investigation of local properties of the Fe-Si alloy subjected to mechanical and laser cutting

Effect of types of calcium-containing alloy on non-metallic inclusions in high-Al steel

The influence of different calcium-containing alloys on inclusions in high-Al steel is investigated in the current study. The effects of SiCa, AlCa20, AlCa75 and FeSi alloys on the modification of solid inclusions in molten steel are compared, and the mechanism of inclusion evolution is revealed based on the non-uniform distribution of elements and the lattice mismatch between the inclusion particles. The results show that the Ca yield of FeSi alloy is 26%, which is significantly higher than that of other alloys (<5%). In addition, the calcium treatment by FeSi alloy causes less aspiration of molten steel, which is conducive to avoiding the increase of AlN in high-Al steel. After calcium treatment, the primary Al2O3 particles in steel are transformed into CaO-Al2O3-CaS and CaO-Al2O3-MgO complex inclusions, while AlN can only be precipitated in the form of a single particle, or precipitated from the transformed CaO · 2Al2O3 oxide. In general, FeSi alloy has the best effect on the modification of Al2O3 inclusions, which can maximize the transformation of solid particles into liquid inclusions in steel liquid without introducing too much impurities.

Transforming detrimental intermetallics by accumulative thermal and strain energies in the Al–Fe–Si alloy

Transforming detrimental intermetallics by accumulative thermal and strain energies in the Al–Fe–Si alloy

Mitigating the volume expansion and enhancing the cycling stability of ferrous fluorosilicate-modified silicon-based composite anodes for lithium-ion batteries

This study introduces an FeSiF6 additive synthesized via the reaction of HF with Si–Fe alloys. It prevents crystalline Li15Si4 formation and promotes stable SEI film, significantly enhancing the cycling stability of silicon-based anodes.

Synthesis of FeSi-FeAl Composites from Separately Prepared FeSi and FeAl Alloys and Their Structure and Properties.

Composites consisting of iron aluminide and iron silicide phases were studied in this work. Powders of iron aluminide and iron silicide were prepared by mechanical alloying separately. Subsequently, they were blended in three different proportions and sintered by the SPS method under various conditions. After sintering, the composites are composed of FeAl and amounts of other silicides (Fe5Si3 and Fe3Si). Ternary Fe-Al-Si phases were not determined, even though their presence was predicted by DFT calculations. This disagreement was explained by steric factors, i.e., by differences in the space lattice of the present phases. Hardness and tribological properties were measured on composites with various weight ratios of iron aluminide and iron silicide. The results show that sintered silicides with the matrix composed of iron aluminide reach comparable hardness to tool steels. The composites with higher mass ratios of iron aluminide than silicide have higher hardness and better tribological properties.

Process Parameter Optimization for Laser Powder Bed Fusion of Fe-Si Alloy Considering Surface Morphology and Track Width of Single Scan Track.

A laser power bed fusion (L-PBF) manufacturing process was optimized by analyzing the surface morphology and track width w of single scan tracks (SSTs) on Fe-3.4wt.%Si. An SST was evaluated under process conditions of laser power P, scan speed V, and energy density E = P/V. The SST surface shape was mainly affected by E; desirable thin and regular tracks were obtained at E = 0.3 and 0.4 J/mm. An L-PBF process window was proposed considering the optimal w of SST, and the appropriate range of E for the alloy was identified to be 0.24 J/mm to 0.49 J/mm. w showed a strong relationship with E and V, and an analytic model was suggested. To verify the process window derived from the appropriate w of SST, cubic samples were manufactured with the estimated optimal process conditions. Most samples produced had a high density with a porosity of <1%, and the process window derived from SST w data had high reliability. This study presents a comprehensive approach to enhancing additive manufacturing for Fe-3.4Si alloy, offering valuable insights for achieving high-quality samples without the need for time-intensive procedures.

Characterization of Fe-6Si Soft Magnetic Alloy Produced by Laser-Directed Energy Deposition Additive Manufacturing

Commercial electrical steels, Fe-Si alloys with < 4 wt.% Si, are inexpensive and efficient materials for electrical power conversion. Further efficiency improvements require increasing the silicon concentration to 6 wt.%, at which point the material becomes brittle and difficult to form by conventional rolling and sheet fabrication methods. Additive manufacturing stands to overcome challenges with commercial manufacturing techniques by leveraging near-net-shape fabrication. The wide array of process conditions provides additive manufacturing with increased flexibility, enabling control over the microstructure and mechanical properties. This work explores the microstructures and magnetic properties of ring-shaped Fe-Si alloys produced using concentric and cross-hatch tool paths on a laser-directed energy deposition additive manufacturing system. Concentric-built samples exhibit elongated grain structures while cross-hatch-built samples comprise lower aspect ratio grain structures. Thermal finite element analysis simulations model the stress conditions produced by the different scan path geometries. Microhardness measurements probe the mechanical properties as a function of anneal temperature, providing a qualitative understanding of the intergranular defect density. Soft magnetic properties measured under quasistatic and AC conditions show frequency- and microstructure-dependent coercivity and permeability. Finally, analysis of the core loss quantifies how the build strategies and thermal treatments influence efficiency in electrical power conversion applications. Understanding the influences of scan path geometry and thermal treatment provides a pathway towards application of additively manufactured soft magnetic materials.

Modifying C/C–SiC brake pads with different Fe–Si alloy phases to improve the wear resistance of full-carbon/ceramic brake pair

The full-carbon/ceramic brake pair is designed to meet the increased demands for reliable braking at high speeds, heavy loads and complex service environments for vehicle and power machinery. In this paper, braking performance of different Fe–Si modified C/C–SiC composites have been studied using laboratory scale dynamometer. The phase composition/microstructure and mechanical properties of the material were studied. By mating with C/C–SiC brake disc, the effect of Fe–Si alloy modification on the friction and wear performance of full carbon/ceramic brake pair was investigated. The results indicated that the Fe–Si modification can effectively improve the wear resistance of both C/C–SiC disc and pads, and the disc/pads will have the least amount of wear only when the appropriate type of Fe–Si alloy and the suitable amount of Fe–Si alloy phase are introduced. When FeSi75 was used as the fusion infiltration material, the wear of disc/pad was 115.4 and 13.3 mm, respectively. Compared to the unmodified C/C–SiC disc/pad, the wear of Fe–Si modification disc/pad was reduced by 72.7 % and 87.2 %, respectively.

Evaluation of microstructure, mechanical and magnetic properties of laser powder bed fused Fe-Si alloy for 3D magnetic flux motor application

Since their high power-to-volume property, electric machines with 3D magnetic flux (3D-flux) structure are of great current interest. In them, the flux path is typically achieved by utilizing a soft magnetic composite (SMC) material to minimize the eddy current losses. Here, laser powder bed fusion (LPBF) technique is employed to manufacture a soft magnetic core (Fe-3.5 wt%Si alloy) with the following advantages: i) the (001) texture of Fe-Si alloy is well aligned with the Z direction of the 3D-flux path, which is the easiest magnetization direction in the cubic system; ii) the strength and ductility of the annealed alloy are far superior to those of SMCs. The alternating-current ring method was employed to measure the magnetic properties and a simulation of the 3D-flux electric machine was conducted. The results illustrated that the rotary torque generated with the additively manufactured alloy is 19.1% higher than that of SMCs in the weak magnetic field excited by ferrite at the 50 Hz frequency. However, it is important to note that the additively manufactured alloy also exhibited higher total iron loss in strong magnetic field and high electric frequency, indicating a need for further research to optimize the microstructure and reduce losses for medium/high frequency applications.

MHz free electron laser x-ray diffraction and modeling of pulsed laser heated diamond anvil cell

A new diamond anvil cell experimental approach has been implemented at the European x-ray Free Electron Laser, combining pulsed laser heating with MHz x-ray diffraction. Here, we use this setup to determine liquidus temperatures under extreme conditions, based on the determination of time-resolved crystallization. The focus is on a Fe-Si-O ternary system, relevant for planetary cores. This time-resolved diagnostic is complemented by a finite-element model, reproducing temporal temperature profiles measured experimentally using streaked optical pyrometry. This model calculates the temperature and strain fields by including (i) pressure and temperature dependencies of material properties, and (ii) the heat-induced thermal stress, including feedback effect on material parameter variations. Making our model more realistic, these improvements are critical as they give 7000 K temperature differences compared to previous models. Laser intensities are determined by seeking minimal deviation between measured and modeled temperatures. Combining models and streak optical pyrometry data extends temperature determination below detection limit. The presented approach can be used to infer the liquidus temperature by the appearance of SiO2 diffraction spots. In addition, temperatures obtained by the model agree with crystallization temperatures reported for Fe–Si alloys. Our model reproduces the planetary relevant experimental conditions, providing temperature, pressure, and volume conditions. Those predictions are then used to determine liquidus temperatures at experimental timescales where chemical migration is limited. This synergy of novel time-resolved experiments and finite-element modeling pushes further the interpretation capabilities in diamond anvil cell experiments.

Magnetic Properties of the Soft Magnetic Composites Prepared Using Mixtures of Carbonyl Iron, FeSiCr, and FeSiAl Alloy Powders.

The effect of carbonyl iron powder, FeSiCr alloy powder, and annealed FeSiAl alloy powder, both individually and in binary combinations, on the density, microstructure, and magnetic properties (including permeability and power loss) of inductors manufactured by molding compaction was investigated in this study. The investigation demonstrates that hysteresis loss dominates power loss in the tested frequency range. Due to higher compacted density and reduced coercivity, adding 50% carbonyl iron powder to annealed powder resulted in the lowest hysteresis loss, allowing for domain wall movement. On the other hand, adding 50% FeSiCr alloy powder to annealed powder resulted in higher hysteresis loss due to impurity components hindering domain wall motion. Due to extreme plastic deformation, the carbonyl iron powder and FeSiCr alloy powder combinations displayed the most significant hysteresis loss. Eddy current loss followed the same trends as hysteresis loss in the mixtures. This study provides important insights for refining the soft magnetic composite design to obtain higher magnetic performance, while minimizing power loss.

Ni–Fe–P/Fe–Si electrocatalysts on iron sheets: Regulating surface structure to amorphous heterojunction for excellent oxygen evolution reaction

Nickel iron bimetallic phosphide alloys are a promising electrocatalyst for oxygen evolution reaction (OER). In this work, a highly active Ni–Fe–P/Fe–Si heterojunction electrocatalyst for OER has been synthesized by one-step electrodeposition on iron plate. The synergism effect of Ni–Fe–P alloy and Fe–Si alloy particles after dealloying treatment promotes the construction of nanoflower-like heterogeneous structure with rich lattice defects and exposes a highly open multi-stage nanostructure surface. Furthermore, Si induced the localized electron redistribution optimizes catalytic performance by accelerating electron transfer. The optimal Ni–Fe–P/Fe–Si OER catalyst requires a much low overpotential of 209 mV at a current density of 10 mA cm−2, and 270 mV at a current density of 200 mA cm−2. The prepared Ni–Fe–P/Fe–Si electrode can maintain a current density of 10 mA cm−2 within 24 h, which shows significant electrochemical stability. This study provides a new prospect for the preparation of cost-effective heterogeneous catalysts.

Improved slag corrosion resistance of MgO–C refractories with calcium magnesium aluminate aggregate and silicon carbide: Corrosion behavior and thermodynamic simulation

The influence of calcium magnesium aluminate (CMA) aggregate and silicon carbide on the slag corrosion resistance of MgO–C refractories was investigated by the induction furnace tests. The corrosion behavior and the formation of protective slag layer were also comprehensively discussed in present work. The results showed that CaAl2O4 in CMA converted into Al-containing liquid phase when facing the slag, while spinel with better slag corrosion resistance diffused into the refractory-slag interface. The Al-containing liquid phase melted from CaAl2O4 mixed with slag and increased the Al content, increasing the proportion of indirect dissolution, forming more spinel and decreasing the corrosion rate. Furthermore, the spinel and liquid slag formed solid-liquid mixture at the interface, increasing the viscosity and promoting the formation of protective slag layer, which avoided direct contact between slag and refractory. The combined use of CMA aggregate and silicon carbide showed better slag corrosion resistance because silicon carbide increased the oxidation resistance and inhibited the decarburized layer, while the FeSi alloy and higher viscosity also enhanced the slag corrosion resistance of such refractories.

MFe2O4 (M=Mn, co, Ni, Zn) ferrite nanosheets coated flaky FeSiAl composite powder and their magnetism and microwave absorption

Magnetite (MFe2O4, M = Mn, Zn, Ni, Co) nanosheet coated flaky FeSiAl alloy composite powder have been successfully synthesized. The morphology, composition, crystal structures, magnetism and electromagnetic performance of composite powder were studied systematically. Spinel ferrite nanosheet were prepared on the surface of flaky FeSiAl by hydroxide deposition decomposition. This structure will benefit the microwave multiple reflection loss. The saturation magnetization of the composite powder decreased with ferrite coating. The ZnFe2O4 coated composite exhibited higher saturation magnetization while the CoFe2O4 coated composite had the highest coercivity. Owing to the oxide coating, the complex permittivity and dielectric loss of the composite powder were evidently increased while the magnetic loss significantly decreased. Magnetic loss was dominant under 13 GHz and dielectric loss contributed equally as magnetic loss at higher frequency. Therefore, the composite powder attenuate the electromagnetic waves much more efficiently at higher frequency. Our results provide a reference to understand the effect of ferrite nanosheet coating on the magnetism and design the microwave absorption of composite powder materials.

Effect of Preheating on the Mechanical Workability Improvement of High-Strength Electrical Steels during Tandem Cold Rolling

Cold-rolled silicon steel strip products are widely used as the main soft magnetic components in cores of electrical motors, generators, and transformers. In the case of rotating electrical machines, the so-called non-oriented electro-technical steels are normally applied. They are characterized by a similar behaviour to the induced magnetic field found in all sheet plane directions. The kind of soft magnetic alloys that defined herein not only possess an isotropy of electromagnetic properties, but also high mechanical strength; such alloys are called high-strength electro-technical (HSET) steels. These commercially produced HSET steels contain a high silicon content in the range of 3–4 wt.%. However, if the silicon content exceeds 3%, the machinability of Fe–Si alloys is dramatically reduced and they become much more brittle as a consequence. According to this, regular hot band brittle damage occurs during cold deformation at a high-speed tandem rolling mill. In accordance with these reasons, the production of thin high-strength silicon steel grades using the traditional methods of cold rolling deformation is extremely problematic and it is characterised by a high degree of steel sheet mechanical damage. In this scientific work, the effect of preheating hot-rolled strips on their mechanical workability improvement during tandem cold rolling was investigated. The results of this study indicate that the cold rolling of hot bands at elevated temperatures increases their resistance to brittle failure and mechanical plasticity. Moreover, the mathematical simulation clearly demonstrates that residual stress is distributed relatively homogeneously across the thickness of samples, which were cold rolled at 100 °C in contrast to the same ones deformed at room temperature.