Finemet Alloy Research Articles

Effect of magnetoelastic anisotropy on properties of Finemet-type microwires

Magnetic properties and DSC peak near Curie temperature, TC, of amorphous and nanocrystalline microwires with different ratios ρ=d/D were studied. The investigated compositions were close to Finemet-type: Fe70.8Cu1Nb3.1Si14.5B10.6, Fe71.8Cu1Nb3.1Si15B9.1 and Fe73.8Cu1Nb3.1Si13B9.1.The effects of magnetoelastic energy, stored during the Finemet-type microwires fabrication, on hysteresis loops, TC and heat capacity of Finemet-type microwires were investigated. Hysteresis loops of all as-prepared microwires showed rectangular shape, typical for Fe-rich microwires. As expected, coercivity, Hc, increases with the decrease of the ratio ρ. On the other hand, the change of heat capacity at TC, ΔCp, exhibits linear increase with the ratio ρ. This relationship holds for microwires in the initial state as well as after annealing. Glass removal results in considerable change of both Hc and ΔCp, which reveals the effect of internal stresses. Structural relaxation of microwires results in a shift of TC calorimetric peak of amorphous phase to higher temperatures, while crystallization leads to peak disappearance. This effect was attributed to the dependency of TC calorimetric peak on the value of magnetostriction of magnetic phase, which declines to zero with Finemet alloys crystallization.

Crystallization Kinetics of Amorphous Finemet Modified with Co

The aim of this work is to present experimental results of investigation on crystallization process of Co-containing Finemet-type alloys. To different Finemet alloys, there exist different changing trends of the initial crystallization temperature after Co addition. Addition of Co in Fe73.5Cu1Nb3Si13.5B9 alloy reduces the stability of the amorphous phase, and leads to the formation of nanocrystallites at lower temperature. While adding Co increases the stability of Fe76.9Cu0.6Nb2.5Si11B9 amorphous phase, and results in higher nanocrystallites temperature. Using the method of Kissinger, possible reasons were analyzed for the variation of the apparent activation energy of crystallization determined from DSC thermograms.

Structural evolution and the kinetics of Cu clustering in the amorphous phase of Fe-Cu-Nb-Si-B alloy

An attempt has been made to investigate the evolution of the structure of the amorphous phase of Fe73.9 Cu0.9 Nb3.1 Si13.2 B8.9 (finemet) alloy by a combination of wide-angle x-ray scattering, small angle x-ray scattering (SAXS), Mössbauer spectroscopy and X-ray absorption near edge spectroscopy on the supposition that they would provide complementary information. Before the onset of nanocrystallization, the amorphous phase undergoes a structural relaxation resulting in small increase in the hyperfine field and a decrease in the width of the first diffraction maxima. There is an increase in the topological ordering in the system, though chemical inhomogeneity sets-in due to the clustering of Cu atoms in the pure amorphous state of this alloy. Annealing at 400 °C (well below the crystallization temperature) for different time durations results in occurrence of Cu clusters having fcc structure. Kinetics of Cu clustering is studied using SAXS. The incubation time for the clustering at 400 °C is ∼120 min. With further annealing, the average cluster size gradually increases from the initial value of ∼0.4 nm, reaching a value of ∼0.6 nm after annealing for 720 min. Cluster size exhibits a t1/2 dependence, suggesting a diffusion controlled growth.

Recoilless fraction, structural, magnetic and thermal properties of Fe 73.5Cu 1Nb 3Si 13.5B 9 alloy

Differential scanning calorimetry, X-ray diffraction and room temperature Mössbauer spectrum measurements of Fe 73.5Cu 1Nb 3Si 13.5B 9 (Finemet) alloy have been carried out in order to study its structural and magnetic properties as a function of annealing temperature. The DSC profile of as-quenched Finemet showed two exothermic peaks at 530 and 702 °C, corresponding to two crystallization processes. The Finemet alloy remains amorphous at 450 °C with one broad peak in XRD pattern and one broad sextet in Mössbauer spectrum. When the Finemet alloy was annealed at 550 °C, only well indexed body-center-cubic phase was detected. After being annealed at 650 and 750 °C, the XRD patterns showed the coexistence of α-Fe(Si) and Fe–B intermetallic phases with the increase in XRD peak intensities, indicating the growth of crystallites and the decomposition of Fe 73.5Cu 1Nb 3Si 13.5B 9 alloy at elevated temperatures. The Mössbauer spectra of annealed Finemet alloy could be fitted with 4 or 5 sextets and one doublet at higher annealing temperatures, revealing the appearance of different crystalline phases corresponding to the different Fe sites above the crystallization temperature. The appearance of the nanocrystalline phases at different annealing temperatures was further confirmed by the recoilless fraction measurements.

Curie temperature behaviour at relaxation and nanocrystallization of Finemet alloys

Dependence of Curie temperature (Tc) on time and temperature of annealing for Finemet-type amorphous alloys is studied by DSC. Structural relaxation of an amorphous phase at annealing is accompanied by increase of Tc. The σ-shaped time dependencies, however, are not characterized by the definite final value of Tc: long-term annealing of amorphous phase results in continuation of slow increase of Tc for every temperature. Apparent values of activation energy of relaxation were evaluated from the Tc time–temperature dependencies. It is found that the average value of activation energy increases with progress of the relaxation process. Correlation of the Tc data with structural alterations reflects redistribution of components in amorphous phase during annealing. Further increase of the annealing temperature results in precipitation of α-Fe(Si) nanograins in an amorphous matrix, that accompanied by gradual degradation of corresponding to Tc heat capacity peak. DSC measurements of Tc allow to detect the starting moment of amorphous phase crystallization.

First-principles calculations of structure and magnetic properties of -Fe(Si)phase precipitated in the Finemet alloy

The structure and the magnetic properties of -Fe(Si) phase precipitated in the Finemet alloy, and some factors influencing the magnetic properties of -Fe(Si) phase are investigated by first-principles calculation based on the density functional theory. From the angle of electron spin, the magnetic properties of -Fe(Si) phases with different solubilityies of Si located at the different sites of the -Fe superlattice are investigated. The calculation results show that the spin-state density is a critical factor influencing the magnetic properties. It is found that -Fe(Si) phase with Si at the vertex sites shows better magnetic properties than those with Si at the core sites. It is concluded that with the solubility of Si in the -Fe(Si) phase increasing, the probability of Si occurring at the vertex sites increases, which results in better magnetic properties. The calculation results accord with the previous experimental results. The present work is helpful for understanding the magnetism of the Finemet alloy.

Analysis of the magnetoresistance contributions in a nanocrystallized Cr-doped FINEMET alloy

The magnetoresistance (MR) was measured at 200, 250 and 300K in magnetic fields up to B=12T for a nanocrystallized Fe63.5Cr10Nb3Cu1Si13.5B9 alloy. Both the longitudinal (LMR) and transverse (TMR) component of the magnetoresistance decreased from B=0 to about 0.1T. This could be ascribed to a giant MR (GMR) effect due to spin-dependent scattering of conduction electrons along their path between two Fe–Si nanograins via the non-magnetic matrix. Such a scattering may occur if the nanograin moments are not or only weakly coupled in the absence of a strong exchange coupling (due to the high Cr content in the matrix) and/or only weak dipole–dipole coupling is present (due to sufficiently large separations between the nanograins). For larger fields, the GMR saturated and a slightly nonlinear increase in MR with B was observed due to a contribution by the residual amorphous matrix. The anisotropic MR effect (AMR≡LMR−TMR) was negative for all fields and temperatures investigated. By measuring the MR of melt-quenched Fe100−xSix solid solutions with x=15, 18, 20, 25 and 28, the observed AMR could be identified as originating from the Fe–Si nanograins having a D03 structure.

The Migration Behavior of Atomic Clusters in Early Nanocrystalline Process of Soft Magnetic Finemet Alloy

The Finemet alloys are commonly used as cores in transformers and generators, stress and field sensors in technological application for their excellent soft magnetic characteristics. To clarify the nanocrystallization mechanism of Finemet especially about the atomic migration in early stage is very essential for developing their distinctive characteristics. In this study, we investigate the migration behavior of atoms in order to clarify the mechanism of the early-stage nanocrystallization in amorphous Finemet alloys. The Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous ribbons were prepared by single-roller melt-spinning process in argon atmosphere, and then annealed at 350 degrees C-400 degrees C for 10 minutes in vacuum. The atom force microscope (AFM) and the coincidence Doppler broadening spectra (CDB) were used to characterize the migration behavior of different atoms in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloy during the early-stage nanocrystallization. The X-ray diffraction (XRD) patterns show that all annealed samples are in the amorphous state. But the AFM observation shows clearly that there are many small atomic clusters (nuclei) which distribute in the amorphous matrix of the annealed samples. With increasing annealing temperature, there is a significant increase in the amount of atomic clusters and a dramatic drop in the average size of clusters with very limited Cu contention in the samples, which reflect the structural evolution into more homogeneity. The CDB spectrum indicates that the peaks of positron annihilation spectrum are gradually reduced, which means the number of grain boundary and the defects in samples are gradually increased. It can be concluded that more defects are introduced by the formation of atomic clusters through atomic migration during the early-stage nanocrystallization in Fe(73.5)Si(13.5)B9Nb3Cu1 amorphous alloys.

Influence of Plastic Deformation on Nanocrystallization of Finemet Alloy

Influence of Plastic Deformation on Nanocrystallization of Finemet Alloy

High frequency behaviours and Mössbauer study of field annealed FeCuNbSiB alloy ribbons

This paper investigates the high frequency behaviours and magnetic anisotropy of rapidly solidified FINEMET (Fe73.5Si13.5B9Nb3Cu1) alloy ribbons annealed in an applied magnetic field. It finds that the ribbons annealed with the applied magnetic field show much higher resonance frequencies and have even higher permeability at higher frequencies than the samples annealed without the magnetic field and the non-annealed ribbons. Mössbauer spectroscopy had been employed to study the spatial distribution of the magnetic moments of five selected FINEMET alloy ribbons in different heat-treated conditions. The results show that an easy plane has been established after annealling in the magnetic field, while for the other ribbons this effect is not significant. Hence, the relationship between magnetic field annealing and high frequency property has been bridged by the bianisotropic theory.

Influence of Al and Ni on the magnetic properties of Finemet alloys

Crystallization behavior and soft magnetic properties of the FeSiBCuNbM (M=Al or Ni) Finemet alloys are investigated by X-ray diffraction, differential scanning calorimetry, hysteresis loop tracer, and vibrating sample magnetometry. The nanocrystalline alloys are prepared by annealing melt-spun amorphous ribbons at different temperatures. Results indicate that the partial substitution of Ni or Al for Nb results in the increase of saturation magnetic induction density ( B s) of the alloys. The alloys with Al or Ni show favorable combination of soft magnetic properties. The partial substitution of Ni for Nb enhances the B s value, while Al decreases coercivity. The mechanism underlining the magnetic behavior is discussed.

Structural Evolution Mechanism of Early-Stage Nanocrystallization of Finemet Amorphous Ribbons

The Finemet alloy is used to make transformers for its excellent soft magnetic property. In order to study its distinctive character, it is essential to clarify the structural evolution mechanism especially in early nanocrystallization. The Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73.5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> amorphous ribbons were prepared by single-roller melt-spinning process under argon atmosphere, and then annealed at 350°C, 380°C and 400°C for 10 mins respectively. We conduct the X-ray photoelectron spectrum (XPS) and the atom force microscope (AFM) to investigate the structural evolution mechanism in early nanocrystallization of Finemet. The X-ray photoelectron spectrum present the Cu atoms enrich in the surface and the Nb atoms redistribute to the iron-rich layer following with the increasing annealing temperature. The atomic force micrographs for the annealed specimens present a significant increase in the amount of the clusters and a dramatic drop in their average size. The structure evolution as observed is subjected to the atomic redistribution, which is crucial to the formation of the Cu-enriched clusters. In this paper, we discuss the behavior of different elements and elaborate the transformation of microstructure during the process of atomic migration.

Microstructure and soft magnetic properties of Finemet-type ribbons obtained by twin-roller melt-spinning

Abstract Soft magnetic ribbons of Finemet-type (Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ) alloys are synthesized by the twin-roller melt-spinning technique directly from the melt, at tangential wheel speeds of 15, 18, 19 and 20 m/s. The microstructure and the magnetic properties are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and hysteresis loops measurements. Samples cooled at 20 m/s are amorphous, while those quenched at lower wheel speeds are partially crystalline. All samples studied present saturation magnetization values (150–160 A m 2 /kg) higher than the commercial Finemet alloys (∼135 A m 2 /kg), obtained by controlled crystallization of amorphous single-roller melt-spun alloys. Optimal soft magnetic properties – σ S =(154±8) A m 2 /kg and H C =(6.9±0.9) A/m – are found in samples quenched at 19 m/s, consisting of size-distributed bcc Fe–Si nanograins (∼18 nm in average) embedded in an amorphous residual matrix. A minority nanocrystalline magnetic phase (≤10 nm) is also detected.

Effects of substitution of Mo for Nb on less-common properties of Finemet alloys

Particular properties of Fe–Nb/Mo–Cu–B–Si rapidly quenched ribbons were examined. Apart from minor variation, no significant difference due to the Mo for Nb substitution was observed in alloy density and its annealing-induced changes. The same holds for the anisotropic thermal expansion of as-cast ribbon when annealed and for induced anisotropy when annealed under stress. The Mo-substituted ribbons show only slightly higher crystallinity and lower coercivity if annealed in inert gas ambience than in vacuum. Some diversity in surface to interior heterogeneity of the differently annealed ribbons can still be distinguished. Preserving a minor percentage of Nb together with Mo does not seem substantiated to obtain favorable soft magnetic properties of ribbons annealed in inert gas.

Microstructure and magnetic properties of Fe 72.5Cu 1M 2V 2Si 13.5B 9 (M=Nb, Mo, (NbMo), (MoW)) nanocrystalline alloys

The microstructure and magnetic properties of Finemet-type Fe 72.5Cu 1M 2V 2Si 13.5B 9 (M=Nb, Mo, (NbMo), (MoW)) alloys have been systematically studied. Results show that the nanocrystalline alloy with M=NbMo has the smallest grain size of about 8 nm. The order of the effect of Nb, Mo and W additions in decreasing the α-Fe grain size in nanocrystalline alloys is Nb>Mo>W. The best DC soft magnetic properties are obtained in the alloy with M=Nb. In the case of AC soft magnetic properties, the Nb alloy also exhibits a very low core loss comparing with typical Finemet alloy. Therefore, the Nb alloy is suitable for use as a transformer core material. In addition, it is shown that a narrow grain size distribution and a uniform dispersion of α-Fe grains in the amorphous matrix are very crucial for the development of new Finemet-type nanocrystalline alloys with good soft magnetic properties.

Low-Temperature Thermo-Cycling of FINEMET and Metglas Amorphous Alloys: Last Achievements in Theory and Experiments

Abstract The novel phenomena of irreversible changes in structure and main physical properties of FINEMET and Metglas amorphous metallic alloys (AMA) after low-temperature treatment (LTT) (so called ΔT effect) are studied theoretically and experimentally. It is shown theoretically that the cooling process in AMA during LTT is achieved at a rate comparable to the rate of quenching from the melt. Arising thermo-elastic stresses cause changes in the structure of the short-range order due to the drift of metalloid atoms, which is supported by sample oscillations with the eigenfrequencies. Such homogenization of the AMA structure leads to changes in the main physical properties. The proposed physical model of the ΔT effect is verified by structural investigations and magnetic and thermo-magnetic studies of metal-metalloid and FINEMET type AMA.

Nanocrystallization of Finemet alloy after intensive plastic deformation

The Finemet alloy prepared by the crystallizaton of an amorphous precursor is a basic model material for study of magnetic nanoparticle structures. It was shown that intensive plastic deformation localized into adiabatic shear bands causes intensive heating and structural changes in the amorphous alloy. These changes influence the magnetic properties of the amorphous precursor and the Finemet crystallization. Direct creep measurements during the crystallization of Finemet alloys were performed and the creep properties of the residual amorphous phase formed during the nanocrystallization were described. It was shown that due to relatively high temperatures the residual amorphous phase undergoes intensive structural relaxation resulting in the obvious embrittlement of these materials.

Influence of annealing on the electrochemical behavior of finemet amorphous and nanocrystalline alloy

The electrochemical corrosion behavior of finemet alloy at various heat treatment temperatures was investigated. Thermal behavior and structural changes were studied using differential scanning calorimetry and X-ray diffractometry, respectively. The electrochemical corrosion of amorphous and annealed samples was investigated in 0.10 M NaOH solution using electrochemical impedance spectroscopy and linear sweep voltammetery. Changes in morphology of the samples before and after corrosion were characterized using optical microscope. The results showed that structural relaxation and nanocrystallization during the heat treatment improved corrosion behavior of the alloy. The heat-treated alloy at 650 °C showed a corrosion rate of 1.37 × 10−8 A cm−2 and a positive shift of +417 mV in the corrosion potential compared to the amorphous alloy. Also, the heat-treated alloy at 650 °C showed a higher charge transfer resistance up to 50 kΩ due to corrosion resistance, compared with amorphous sample that showed a charge transfer resistance of 0.5 kΩ.

Study of nanocrystallization in FINEMET alloy by active screen plasma nitriding

Abstract The nanocrystallization process of amorphous Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 was investigated by active screen plasma nitriding (ASPN) treatment at temperatures ranging from 410 °C to 560 °C for 3 h in two gas mixtures of 75% N 2 –25% H 2 and 25% N 2 –75% H 2 at 5 mbar atmosphere. The amorphous ribbons were then annealed under vacuum at the same time and temperatures mentioned above. The structure of the samples was analyzed using various techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Microhardness measurements, electrical resistivity and Vibrating Sample Magnetometer (VSM) were used to study mechanical, electrical and magnetic properties of the samples, respectively. It was observed that the ASPN treatment leads to finer grain size and higher crystalline volume fraction and modifies the structural features of Fe(Si) phase. The Fe(Si) lattice parameter for the nitrided samples decreased up to 520 °C, indicating that Si atoms form a solid solution in α-Fe and it was raised at 560 °C, due to Si ex-solution in the Fe(Si) phase and the formation of more nitrided phases. In ASPN treatment, the lowest magnitude of coercivity and the maximum saturated magnetization were obtained at 440 °C in 75% N 2 –25% H 2 and at 560 °C in 25% N 2 –75% H 2 gas mixtures, respectively. Our proposed method (ASPN treatment) increased the microhardness and electrical resistivity of the samples.

Advanced isoconversional kinetics of nanocrystallization in Fe 73.5Si 13.5B 9Nb 3Cu 1 alloy

Nanocrystallization kinetics of amorphous Finemet alloy was studied using Vyazovkin advanced isoconversional method under non-isothermal condition. Well known Kissinger model-fitting method and four isoconversional methods of Kissinger–Akahira–Sunose (KSA), Flynn–Wall–Ozawa (FWO), Tang, and Starink were also used for the determination of activation energy. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) patterns were used for thermal and structural analyses, respectively. According to Vyazovkin and other isoconversional methods, the mean value of variable activation energy, as a function of conversion, was obtained as 350 kJ mol −1. While, according to Kissinger method, the constant value of activation energy was obtained as 270 ± 10 kJ mol −1 for the same experiments, which shows inaccuracy of this method. The mean value of kinetic exponent 〈 n〉 was 1.44 ± 0.05 by considering instantaneous nucleation condition ( n = m), which is consistent with one-dimensional growth mechanism. Kinetics and mechanistic predictions were also performed using numerical reconstruction of the experimental kinetic function. Comparison of the numerically reconstructed model with theoretical ones showed that no single model could perfectly fit the numerical values of kinetic function and the mechanism of transformation changes with conversion progress. Nevertheless it could be seen that nanocrystallization almost follows the one-dimensional diffusion mechanism.