Fe-based Nanocrystalline Alloys Research Articles

Effect of the structure and volume fraction of nanophase on the mechanical properties of (FeNi)86B14 amorphous nanocrystalline alloys

The influence of precipitated nanophases on the mechanical properties of Fe-based amorphous nanocrystalline alloys is an urgent issue to be explored. Two amorphous nanocrystalline alloys, i.e., (Fe0.9Ni0.1)86B14 and (Fe0.7Ni0.3)86B14 containing nanophase of the body-centered cubic and face-centered cubic structures, respectively, were selected to investigate the effect of the structure and volume fraction of nanophase on their mechanical properties. The results of nanoindentation experiments and the calculation of the volume and size of the shear transition zone reveal that the two alloys show different mechanical properties. When the volume fraction of the nanophase in (Fe0.9Ni0.1)86B14 is larger than 50%, the elastic modulus is increased suddenly and the volume and size of the shear transition zone is decreased dramatically, while no dramatic change occurs in (Fe0.7Ni0.3)86B14. Moreover, it was found by using molecular dynamics simulations that the main reason for these abnormal mechanical properties is the change of cluster type in the system due to the incorporation of nanophases with different structures.

Effect of the volume fraction of nanocrystals on the mechanical properties of (Fe0·9Ni0.1)86B14 amorphous/nanocrystalline alloy

The effect of the volume fraction of nanocrystals on the macroscopic mechanical properties and microscopic atomic structure of Fe-based nanocrystalline alloys, as well as the relationship between the two, is an urgent issue to be explored. Seven nanocrystalline alloys with different volume fractions of nanocrystals were formed by annealing treatment of (Fe0·9Ni0.1)86B14 amorphous precursor. Through hardness, flat plate bending, and nanoindentation experiments, it is found that when the volume fraction of nanocrystals reaches the range of 45–55 %, there is an abrupt change in the macroscopic mechanical properties. Specifically, when the volume fraction is less than this range, the properties inherit the amorphous matrix, however, larger than this range, the properties are dominated by precipitated nanocrystalline phases. Meanwhile, based on the molecular dynamics simulation method, seven Fe90Ni10 amorphous nanocrystalline models with different volume fractions of body-centered cubic nanocrystals are established, and the deformation mechanism of models and the evolution of their microstructures during the nanoindentation process are obtained intuitively. Moreover, it is further revealed that the significant changes in the Voronoi polyhedral index, which represents the microscopic atomic structure in this range of nanocrystal volume fractions, are the main reason for the abrupt changes in the mechanical properties at the macroscopic level.

Microstructure evolution, stress state and electromagnetic performance of Fe-based nanocrystalline alloy induced by stress-annealing

Stress-induced anisotropy has been applied for FeSiBCuNb nanocrystalline alloy ribbons in transformers with large direct current (DC) component. However, the physical mechanism of anisotropy induced by stress annealing during crystallization remains controversial. Here, a systematic study was conducted on the microstructure, residual stress state, dynamic domain structure and properties of the stress-annealed FeSiBCuNb nanocrystalline ribbons. Present results demonstrate that, the increase of the applied stress greatly increases the residual tensile stress and induces lattice distortion, which acts as pinning site during magnetization, resulting in enhanced domain-wall energy and narrower wall width. Meanwhile, stress annealing promotes the flattening of hysteresis loops and decreases the effective permeability, which improves the DC-bias characteristics of the ribbons, thereby promoting the transition from “hard saturation” to “soft saturation” behavior. Also, stress-induced grain refinement is beneficial to obtaining high hardness. Owing to the stress-induced anisotropy, the stress-annealed sample with applied stress of 113 MPa exhibits excellent combined properties, including low constant effective permeability of 438 at wide frequency range (1 kHz–8 MHz), high DC-bias capability of 74% (30 Oe), low power loss of 49 kW/m3 (100 mT, 100 kHz), and high hardness of 644 HV. This discovery provides an insightful understanding of stress-induced anisotropy mechanism on the high-performance Fe-based nanocrystalline alloys.

XGBoost algorithm-assisted prediction of amorphous formability of Fe-based nanocrystalline precursor

The completely amorphous structure in the precursor is a significantly important prerequisite for obtaining the perfect amorphous-nanocrystalline duplex structure and the excellent soft magnetic properties of Fe-based nanocrystalline alloy ribbons (FNR). However, the correlation between the amorphous formability (AFA) and the key parameters of FNR precursors is not clear. Herein, a data-preprocessed dataset was established, consisting of 158 FNR samples with amorphous and crystallized precursors. This dataset includes features such as elements, thermal parameters, and calculated parameters. Pearson correlation analysis was performed to assess the linear correlation between any two features, resulting in the removal of eight features. Then the features importance was ranked by random forest (RF) algorithm, and top five key features (e.g., ΔT, VEC1, VEC, P, and B) were retained. A classification predictive model in that the structure of FNR precursors is amorphous or crystalline was constructed based on XGBoost algorithm. The accuracy of the classification model by confusion matrix analysis is up to 97.9 %. Furthermore, SHAP (SHapley Additive exPlanations) results reveal that crystallization temperature intervals (ΔT), valence electron concentration without Fe, Ni, and Co elements (VEC1), as well as valence electron concentration (VEC) play an important role in affecting AFA of FNR precursors. When ΔT > 142 °C, VEC1 > 0.69, and VEC >7.27, the FNR precursors readily obtain a fully amorphous structure. The outstanding classification accuracy and the elucidated correlation between the key features and AFA could guide the discovery of novel fully amorphous FNR precursors.

Interpretable machine learning-assisted design of Fe-based nanocrystalline alloys with high saturation magnetic induction and low coercivity

Overcoming the trade-off between saturation magnetic induction (Bs) and coercivity (Hc) of Fe-based nanocrystalline alloys (FNAs) remains a great challenge due to the traditional design relying on trial-and-error methods, which are time-consuming and inefficient. Herein, we present an interpretable machine learning (ML) algorithm for the effective design of advanced FNAs with improved Bs and low Hc. Firstly, the FNAs datasets were established, consisting of 20 features including chemical composition, process parameters, and theoretically calculated parameters. Subsequently, a three-step feature selection was used to screen the key features that affect the Bs and Hc of FNAs. Among six different ML algorithms, extreme gradient boosting (XGBoost) performed the best in predicting Bs and Hc. We further revealed the association of key features with Bs and Hc through linear regression and SHAP analysis. The valence electron concentration without Fe, Ni, and Co elements (VEC1) and valence electron concentration (VEC) ranked as the most important features for predicting Bs and Hc, respectively. VEC1 had a positive impact on Bs when VEC1 < 0.78, while VEC had a negative effect on Hc when VEC < 7.12. Optimized designed FNAs were successfully prepared, and the prediction errors for Bs and Hc are lower than 2.3 % and 18 %, respectively, when comparing the predicted and experimental results. These results demonstrate that this ML approach is interpretable and feasible for the design of advanced FNAs with high Bs and low Hc.

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.

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%.

The effect of the volume fraction of nanocrystals on the brittleness of Fe-based amorphous/nanocrystalline alloys simulated by molecular dynamics

The effect of the volume fraction of body-centered cubic (BCC) crystal in Fe-based amorphous nanocrystalline alloys on room temperature brittleness was investigated via molecular dynamics simulations. Seven model samples with embedded BCC nanocrystal contents ranging from 0 to 33.4 vol.% were obtained. The indentation tests were carried out by spherical rigid indenter to investigate the microstructural evolution and the mechanical properties of those Fe-based amorphous/nanocrystalline alloys in terms of the indentation force, hardness, von Mises shear strain, atomic displacement vector as well as surface morphology. It is found virtually that the plasticity shows a gradient decrease tendency for the three types of samples with 0, less than 16, and more than 20 vol.% nanocrystal, respectively, which is caused by the free volume decreases via monitoring the Voronoi polyhedra.

Magnetic Domain Observation of Milled Nanocrystalline Alloy Powder

Fe-based nanocrystalline alloys have high magnetic flux density and low loss. Therefore, in this study, the magnetic domain structure of the ball-milled magnetic powders of these nanocrystalline alloys was observed using a Kerr effect microscope. The effect of strain removal heat treatment on the magnetic properties of the powder was also investigated by observing and comparing the magnetic domain structure of the milled powder before and after heat treatment during the preparation process of the nanocrystalline-milled powder. Our findings showed that the strain removal heat treatment changed the size and shape of the magnetic domains to a simple structure. In addition, the domain wall motion was found to be sensitive to the magnetic field, resulting in soft magnetic properties.

Optimization of electromagnetic properties for soft magnetic powder cores prepared by gas-atomized FeSiBCuNb powders with continuously distributed the phase structures

The FeSiBCuNb gas-atomized powders (GAPs) show high sphericity, which is conducive to the formation of uniform insulating coating layers. However, it is difficult to obtain completely amorphous GAPs with relatively large particle sizes for Fe-based nanocrystalline alloys. In this work, the raw FeSiBCuNb GAPs with continuously distributed the phase structures are used to prepare soft magnetic powder cores (SMPCs). The effects of annealing process parameters on the average grain size, crystalline volume fraction, magnetic anisotropy constant (K), residual internal stress and magnetic properties of the SMPCs were studied in detail. The results showed that the increase of annealing temperature was more helpful for the magnetic properties of the SMPCs than extension of annealing time, which was due to average magnetic anisotropy constant (〈K〉) on coercivity primarily influenced on the SMPCs under the different annealing temperatures. When the annealing temperature is 500 °C, heating time is 50 min and holding time is 10 min, the NSMCs achieve relatively excellent magnetic properties: the effective permeability is 29.38 at 100 kHz, the quality factor is 126, the losses are 786 mW/cm3 (20 mT, 1 MHz), and the DC-bias characteristic is 67.28% (100 Oe or 7960 A/m). These results provided the potential for utilization of the raw FeSiBCuNb GAPs with continuously distributed the phase structures.

Application-Oriented Characterization and Analysis of Core Materials Under Medium-Frequency Condition

In medium-frequency applications, magnetic components generally operate in high-temperature conditions caused by higher power loss and more difficult heat dissipation, which results in changes in their electromagnetic characteristics. In this paper, the application-oriented characterization of the typical core materials, Mn-Zn ferrite and Fe-based nanocrystalline alloy, is comprehensively studied. The magnetic parameters under sinusoidal (5 kHz-50 kHz) and square (10 kHz) excitation from 20°C to 125°C is analyzed detailedly. Combined with the micromagnetic theory, the influence factors of electromagnetic parameters such as permeability and power factor angle are investigated. The loss variation of ferrite with temperature, flux density and frequency is explained by using the energy loss ratio. The proportion of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> and Pdy in total loss with temperature and frequency is compared, and the loss fluctuation of nanocrystalline alloys and ferrite is analyzed. Moreover, the reasonable range of frequency that needs to consider temperature effect in practical applications is suggested. The difference between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B-H</i> loop bias under asymmetrical square excitation and DC bias conditions is compared and illuminated. The effectiveness and limitation of typical Steinmetz Equations considering the temperature and duty cycle effect are analyzed, and the suggestion of loss calculation is given combined with the material characteristics.

Influence of field-induced anisotropy on magnetic properties and domain structure of Fe-based nanocrystalline alloy via a new continuous magnetic field annealing furnace

Influence of field-induced anisotropy on magnetic properties and domain structure of Fe-based nanocrystalline alloy via a new continuous magnetic field annealing furnace

Optimal Design of a Compound Magnetic Shielding Based on Fe-Based Nanocrystalline Alloy

The magnetic field inside the analyzed double-stator high-temperature-superconducting machine (DS-HTSM) has the characteristics of rich harmonics and non-negligible amplitude, which will seriously reduce the critical current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> of HTS-excitation coil. Therefore, a new compound magnetic shielding (CMS) is proposed in this paper, which is composed of a copper shield layer and a combined flux diverters (FDs) including the silicon steel sheet (SSS) FD and the Fe-based nanocrystalline alloy (FNA) FD. The key is that the iron loss of SSS FD located in the inner Dewar can be reduced due to the flux pre-diversion of the FNA FD on the outside. In addition, the FEA model based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> formula for HTS-excitation coil is built, based on which the optimal design of proposed CMS is conducted. The results show that the critical current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> of HTS-excitation coil in the analyzed DS-HTSM can be improved by 36% after using the proposed CMS.

Ultra-fine microstructure and exceptional low coercivity developed in a high-Bs Fe-Si-B-P alloy by co-alloying Ni, Mo, and Cu

Designing soft magnetic alloys with high saturation magnetic induction (Bs) is of great importance for improving the power density of electric and electronic devices. For high-Bs nanocrystalline alloys, the main problem is the grain coarsening effect induced by high Fe content (>80 at.%), which deteriorates the soft magnetic properties. In present work, we designed new Fe-based nanocrystalline alloys by microalloying a Fe-Si-B-P alloy. The co-alloying of Ni, Mo, and Cu effectively refines the microstructure of nanocrystalline alloys from 28.5 nm to 13.1 nm and increased the stability of soft magnetic properties. Even though there are 28-nm-large surface crystallites in the amorphous precursors, an exceptional low coercivity of 1–2 A/m with a high Bs of 1.81 T was developed after nanocrystallization. These excellent magnetic properties could be maintained within a wide annealing temperature window of 50 K and an annealing time window up to 600 s for high heating rate annealing.

Structural aspects of stress-induced magnetic anisotropy in Fe-based nanocrystalline alloy

This work is focused on the quantitative description of structural anisotropy in the Fe73.6Cu1Nb3Si15.5B6.9 alloy induced in the process of nanocrystallization during tensile annealing. Structural changes induced by annealing under uniaxial tensile deformation were investigated using X-ray diffraction. It was shown that Fe3Si nanocrystalline grains growing in the tensile direction have a higher value of the lattice spacing. An opposite behavior is seen in transversal direction. The difference between the value of the lattice strain determined in the longitudinal and transverse directions is proportional to the magnitude of the tensile stress applied and represents a quantitative parameter determining the degree of stress induced anisotropy (SIA). Strain pole figure (SPF) measurements provide evidence that the SIA is uniaxial, and its main axis is aligned along tensile direction. Quantitative comparison of the SPFs shows that the strain partitioning among different Bragg reflections is not even and {400} family of planes exhibits the highest magnitude of the SIA. Furthermore, it was found that the magnitude of the SIA for a given set of Bragg reflections {hkl} is inversely proportional to its Young’s modulus Ehkl.

Measurement and Simulation of Magnetic Properties of Nanocrystalline Alloys under High-Frequency Pulse Excitation

In order to broaden the application of nanocrystalline soft magnetic materials in electrical engineering under extreme conditions, nanocrystalline alloys must also have good characteristics under high-frequency and nonsinusoidal excitation. In this paper, the magnetic properties of Fe-based nanocrystalline alloys excited by high repetition frequency pulses were measured. Excitation frequency and duty cycles are two important factors in the study of magnetic properties under pulse excitation. With the amplitude of the pulse remaining constant, different local hysteresis curves were obtained by changing the frequency and duty cycle. The experimental results proved that the higher the frequency is and the smaller the duty cycle is, the narrower the local hysteresis loop is. Finally, the finite element method (FEM) was used to model the magnetic core coupling with an impulse circuit based on the measured magnetic properties. Compared with the experimental results, the simulation results showed that the field-circuit coupling analysis model can effectively reflect the influence law of the frequency and duty cycle on magnetic properties.

Magnetic properties, anisotropy, and domain structure of Fe-based nanocrystalline alloy induced by continuous stress-annealing treatment

The effect of tensile annealing temperature (Ta) on microstructure, soft magnetic properties, magnetic anisotropy, and domain structure for the Finemet nanocrystalline alloy prepared using a home-made continuous tension annealing equipment has been investigated in detail. Results show that the Ta has a great influence on the magnetic properties of the nanocrystalline alloy by affecting its stress-induced anisotropy constant (Ku), average domain width between the strip-like domain patterns (dw) and domain-wall energy (γw). Hereinto, the average anisotropy constant < K > is absolutely dominated by the Ku under the given Ta range with a constant tension stress of 49.1 MPa. The effective permeability (μe) exhibits a completely opposite variation trend to the physical parameters of Ku, dw and γw. The corresponding total core loss decreases first and then increases, which is mainly due to the variation of hysteresis loss with the increasing Ta. These results are helpful to obtain the stress-annealed nanocrystalline alloy with excellent soft magnetic properties for the preparation of high-precision and low-loss current transformers.

Superior high-frequency performances of Fe-based soft-magnetic nanocrystalline alloys

Soft-magnetic nanocrystalline alloys with ultralow power loss are strongly desired for high-frequency power electronic applications. In this work, an industrial ultrathin FINEMET alloy (Fe73.5Si15.5B7Cu1Nb3) ribbon, with 14 μm in thickness, was fabricated by using a roller thermal conductivity-controlled cooling strategy coupled with a bottom blowing argon technique. A magnetic core made of the ultrathin ribbon exhibits excellent high-frequency soft-magnetic properties, with super high permeability of 48,000 at the condition of 1 A/m and 100 kHz and an ultralow core loss of 94 kW/m3 at the condition of 0.2 T and 100 kHz. It is found that the excess loss accounts for the largest proportion in power loss, and this proportion increases with decreasing thickness. The finest grain of nanocrystals, narrowest magnetic domain width, weakest transverse field-induced anisotropy, and considerably increased electrical resistivity (188 μΩ cm) synergistically contribute to the superior soft-magnetic performances at 100 kHz of the ultrathin alloy. This work demonstrates the attractive high-frequency application prospects of ultrathin nanocrystalline alloys in power electronics and information communication due to their excellent performance and huge energy-saving effects, and provides new and comprehensive insights into the power loss of ultrathin nanocrystalline alloys.

Effect of Ge on soft magnetic properties at elevated temperature for Si-rich Finemet-type alloy

• The effect of Ge doping on the soft magnetic properties is investigated for Si-rich Finement-type alloy. • The Curie temperature is enhanced by doping Ge in Si-rich Finemet-type alloy. • The initial permeability μ i of 540°C-annealed Fe 72 Ge 2.5 Cu 1 Nb 3 Si 17.5 B 5 alloy possesses a relatively large value of 5000 until 600°C. The results obtained by partially substituting Ge for Fe in the Fe-based nanocrystalline alloy for improving the magnetic properties at high temperatures are presented in this work. These studies were performed on the Fe 74.5- x Ge x Cu 1 Nb 2 Si 17.5 B 5 ( x =2.5, 5, 7.5) alloys. The nanocrystallization and the Curie temperature are dependent on the Ge concentration. The onset temperature of primary crystallization decreases with the increase of Ge, indicating that the dual-phase nanocrystalline structure could be formed at a relatively lower temperature compared with the Ge-free alloy . For the alloy with x =2.5at%, the Curie temperature of the amorphous alloy is enhanced to 405°C. The initial permeability μ i of 540°C-annealed alloy possesses a relatively large value of 5000 until 600°C. Such a magnetic softness at elevated temperature is superior to that of Finemet-type Fe-based nanocrystalline alloys ever reported.