Hot-press sintering of MA Fe-based nanocrystalline/amorphous soft magnetic powder

Microstructures and magnetic properties of Fe84Nb7B9,Fe80Ti8B 12 and Fe32Ni36（Nb/V）7Si8B17 powders and their bulk alloys prepared by mechanical alloying（MA） method and hot-press sintering were studied. The results show that: 1) After MA for 20 h,nanocrystalline bcc singl e phase supersaturated solid solution forms in Fe84-Nb7B9 and Fe8 0Ti8B12 alloys,amorphous structure forms in Fe32Ni36Nb7 Si8B17 alloy,duplex microstructure composed of nanocrystalline γ- （FeNi） supersaturated solid solution and trace content of Fe2B phase forms in Fe32Ni36-V7Si8B17 alloy. 2) The decomposition process of supersaturated solid solution phases in Fe84Nb7B9 and Fe80Ti8B 12 alloys happens at 710780 ℃,crystallization reaction in Fe （32）Ni36Nb7Si8B17 alloy happens at 530 ℃（the temperature of peak value） and residual amorphous crystallized further happens at 760 ℃ （the temperature of peak value）,phase decomposition process of supersaturated solid solution at 780 ℃ （the temperature of peak value） and crystallization reaction at 431 ℃ （the temperature of peak value） happens in Fe32Ni36V7S i8B17 alloy. 3) under 900 ℃,30 MPa,（0.5 h） hot-press sintering conditions,bulk alloys with high relative density（94.7%95.8%） can be ob tained. Except that the grain size of Fe84Nb7B9 bulk alloy is large,s uperfine grains （grain size 50200 nm） are obtained in other alloys. Exc ept that single phase microstructure is obtained in Fe80Ti8B12 bul k alloy,multi-phase microstructures are obtained in other alloys. 4) The magne tic properties of Fe80Ti8B12bulk alloy（Bs=1.74 T,Hc= 4.35 kA/m） are significantly superior to those of other bulk alloys,which is r elated to the different phases of nanocrystalline or amorphous powder formed dur ing hot-press sintering process and grain size.

FRACTAL STRUCTURE OF THE CORE LOSS SPECTURM OF Fe-B-Si AMORPHOUS SOFT MAGNETIC ALLOY

The core loss spectrum P(f) of Fe-B-Si amorphous soft magnetic alloy has been studied.It is found that P(f) has the fractal structure.The effect of heat treatment on the fractal dimension Df is discussed.

Behavior of Medium-frequency Core Loss in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency have been investigated in the ranges of 100 Hz<= f<=25000 Hz and 0.1 T< =Bm <=1.0 T for three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys. The measured and calculated results showed that the total power loss per cycle clearly exhibited a nonlinear behavior in the range below 3 kHz～5 kHz depending on both the magnetic state and the value of Dm, whereas it showed a quasi-linear behavior above this range. The total loss was decomposed into hysteresis loss, classical eddy current loss and excess loss, the obvious nonlinear behavior has been confirmed to be completely determined by the dependence of the excess loss on frequency. It has been indicated that the change rate of the excess loss per cycle with respect to frequency sharp decreases with increasing frequency in the range below about 3 kHz～5 kHz, wherease the rate of change slowly varies above this range, thus leading to the quasilinear behavior of the total loss per cycle. In this paper, some linear expressions of the total loss per cycle has been given in a wider medium-frequency segment, which can be used for roughly estimating the total loss.

General Properties of Low-frequency Power Losses in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency f and amplitude flux density Bm have been investigated for the three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys in the ranges of 10 Hz<=f<=1000 Hz and 0.4 T<= Bm <=1.0 T. The total loss P is decomposed into the sum of the hysteresis loss Physt, the classical eddy current loss Pel and the excess loss Pexc. Physt has been found to be proportional to Bm^2 and f. The behavior of Pexc/f vs f being equivalent to P/f vs f clearly exhibits nonlinearity in the range not more than about 120 Hz, whereas the behavior of P/f vs f roughly shows linearity in the range far above 100 Hz and not more than 1000 Hz. In the range up to 1000 Hz, Physt is dominant in the original high permeability state and the state of low residual flux density, whereas Pexc in the state of high residual flux density is dominant in the wider range above about 100 Hz. The framework of the statistical theory of power loss has been used for representing the behavior of Pexc/f vs f. It has been found that the number n of the simultaneously active 'Magnetic Objects' linearly varies as n = n0 + Hexc/H0 as a function of the dynamic field Hexc in the range below about 120 Hz, whereas n approximately follows a law of the form n = n0 + (Hexc/H0)^m with 1 < m < 2 in the range far above 100 Hz and not more than 1000 Hz. The values of the field HO in principle related to the microstructure and the domain structure have been calculated for the three states.

Fractal Structure of the Core Loss Spectrum of Co-based Amorphous Soft Magnetic Alloy with Constant Permeability

In order to check the traditional core loss formula, the core loss spectrum P(f) of Co-based amorphous soft magnetic alloy with constant permeability has been studied. It is found that within a high frequency range from 10 kHz to 200 kHz and at Bm = 0. 1 T,the P(f) has the fractal structure P (f) = Po, and with the increasing of induced anisotropy energy Ku, the fractal dimension Dfrises, thus the total power loss at high frequency increases and the frequency characteristic of P(f) becomes worse.

Influence of heat treatment on high frequency soft magnetic properties of Finemet amorphous alloy

In order to study high-frequency soft magnetic properties of Finemet amorphous alloy,the microstructural change and nanocrystallization under different heat treatment conditions were investigated by XRD and TEM. The crystallite size of α-Fe was calculated from the XRD pattern using the Scherrer formula,while the high frequency magnetic properties were measured at room temperature by TPS-200SA exchange tester. The results of XRD and TEM indicate that the nanocrystallization occurs at 500 ℃. When the annealing temperature increases to 560 ℃,the amorphous alloy becomes totally nanocrystallized and the crystallites distribute homogeneously,thus an excellent combination of soft magnetic properties is obtained.

Ductile Fe-based amorphous alloys with high iron content

Fe-based amorphous alloys with high iron content of 76at%-80at%were synthesized in the Fe-Mo-Si-P-C-B alloy system by the single roller melt-spinning technique.The amorphous ribbons exhibit high Vickers microhardness and good ductility,which can be indented and bent 180°without breaking.A number of shear bands could be observed around the indents and the bending traces.Studies on the magnetic properties of the amorphous alloys show that they possess high saturation magnetizations of 1.34-1.6 T,which increases with the increase of iron content.The core losses of these Fe-based amorphous alloys at various magnetic inductions were tested and found to be significantly dependent on their components.The Fe-Mo-Si-P-C-B amorphous alloys with excellent mechanical properties and soft magnetic properties have promising potential in functional applications.

Thermal Stability and Magnetic Properties of (Fe,Co)-Zr-Nd-B Amorphous Alloys

A new type of Fe-based amorphous alloy containing rare earth element was prepared by melt spinning technique. The glass-forming ability (GFA),thermal stability and magnetic properties were investigated in the composition range of Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) ( x =0% to 6%,atom fraction). They exhibit the glass transition and supercooled liquid region before crystallization. The width of supercooled liquid region obtained for the series of Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) exceeds (40 K,) among which the maximum width for Fe_(70)Co_8Zr_5Nd_2B_(15) amorphous alloy reaches 61 K. Another main attraction is that the selected Fe-based amorphous alloys have good soft magnetic properties. The saturation magnetization ( J _s) is in the range of 1.10 to 1.37 T,and coercive force ( H _c) in the range of 2.28 to 8.15 A·m (-1) for Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) amorphous alloys. It is found that the saturation magnetization ( J _s) increases with the increment of the relative content of the Nd for the Fe_(70)Co_8Zr_(7- x )Nd_ x B_(15) alloys. The H _c values for the glasses with Nd content of 1%,2% and 3% are below 3 A·m (-1). The research indicates that Fe_(70)Co_8Zr_5Nd_2B_(15) amorphous alloy has good high GFA and good soft magnetic properties,of which the width of supercooled liquid region,J _s,and H _c are 61 K,1.25 T and 2.28 A·m (-1),respectively.

Effect of Y element on atomic structure, glass forming ability,and magnetic properties of FeBC alloy

The atomic structure of amorphous alloys plays a crucial role in determining both their glass-forming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe_(86-x)Y_xB_7C_7(x = 0, 5, 10 at.%) amorphous alloys via both experiments and ab initio molecular dynamics simulations. Furthermore, we explore the correlation between local atomic structures and properties. Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters, which can potentially enhance both glass-forming ability and thermal stability. These findings have been experimentally validated. The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals, resulting in a reduction in ferromagnetic coupling between Fe atoms. This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system, which is consistent with experimental results. The results could help understand the relationship between atomic structure and magnetic property,and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.

Preparation and Study of the Crystallization Behavior of the Fe87Zr7B5-x Nanocristalline Soft-Magnetic Alloys

A series of materials of composition Fe87Zr7B6,Fe87Zr7B5Ag1,Fe87Zr7B5Cu1 have been prepared by the melt spinning method for different cooling speed to get completely or partly amorphous ribbons.It is proved that the crystallization process is composed of 2 steps.The first step is the precipitation of&-Fe only and the second step is the phase separation of&-Fe,Fe2Zr and Fe2B.All our own made materials have been used in the library monitoring system.Most of them showed a capability of triggling the alarm of the system.The triggling sensitivity at different positions and different sample geometry were investigated and the physical mechanisms were analyzed.

Structural origin of magnetic softening in a Fe-based amorphous alloy upon annealing

The underlying structural origin of magnetic properties is still elusive in Fe-based amorphous alloys.In this study,distinctive soft magnetic properties were developed in Fe_(76)Si_(9)B_(10)P_(5)amorphous ribbons through systematic design of annealing process.Combining with synchrotron radiation,high-resolution transmission electron microscopy and first principle ab initio molecular dynamic simulation,it is found that the atomic structural evolution both in short range order and medium range order is responsible for the magnetic softness at proper annealing temperature.In short range,formation of separated and densely coordinated Fe-metalloid clusters is instigated to adapt energy minimization,resulting in strengthening of ferromagnetic exchange interaction locally.In medium range,a homogeneous exchangecoupling from the uniformly strong and weak ferromagnetic regions is generated,which significantly weakens magnetic heterogeneity and leads to the excellent magnetic softness.Our findings may provide an effective/promising pathway to modulate the magnetic properties for Fe-based amorphous alloys,and give a comprehensive and quantitative understanding of the structure-properties relationship in amorphous materials.

Influence of bath composition on the electrodeposition of cobalt-molybdenum amorphous alloy thin films

Cobalt-molybdenum （Co-Mo） amorphous alloy thin films were deposited on copper substrates by the electrochemical method at pH 4.0. Among the experimental electrodeposition parameters,only the concentration ratio of molybdate to cobalt ions （[MoO4^2-]/[Co^2＋]） was varied to analyze its influence on the mechanism of induced cobalt-molybdenum codeposition. Voltammetry was one of the main techniques,which was used to examine the voltammetric response,revealing that cobalt-molybdenum codeposition depended on the nature of the species in solution. To correlate the type of the film to the electrochemical response,various cobalt-molybdenum alloy thin films obtained from different [MoO4^2-]/[Co^2＋] solutions were tested. Crack-free homogeneous films could be easily obtained from the low molybdate concentrations （[MoO4^2-]/[Co^2＋]≈0.05） applying low deposition potentials. Moreover,the content of molybdenum up to 30wt% could be obtained from high molybdate concentration; in this case,the films showed cracks. The formation of these cracked films could be predicted from the observed distortions in the curves of electric current-time （j-t） deposition transients. The films with amorphous structure were obtained. The hysteresis loops suggested that the easily magnetized axis was parallel to the surface of the films. A saturation magnetization of 137 emu·g^-1 and a coercivity of 87 Oe of the film were obtained when the deposition potential was -1025mV,and [ MoO4^2-]/[Co^2＋] was 0.05 in solution,which exhibited a nicer soft-magnetic response.

Formation and crystallization behavior of Fe-based amorphous precursors with pre-existingα-Fe nanoparticles-Structure and magnetic properties of high-Cu-content Fe-Si-B-Cu-Nb nanocrystalline alloys

Structure,crystallization behavior,and magnetic properties of as-quenched and annealed Fe_(81.3)Si_(4)O_(13)Cu_(1.7)(Cu1.7)alloy ribbons and effects of Nb alloying have been studied.Three-dimensional atom probe and transmission electron microscopy analyses reveal that high-number-density Cu-clusters and Pre-existing Nano-sized a-Fe Particles(PN-a-Fe)are coexistence in the melt-spun Cu1.7 amorphous matrix,and the PN-α-Fe form by manners of one-direction adjoining and enveloping the Cu-clusters.Two-step crystallization behavior associated with growth of the PN-a-Fe and subsequent nucleation and growth of newly-formedα-Fe is found in the primary crystallization stage of the Cu1.7 alloy.The number densities of the Cu-clusters and PN-a-Fe in melt-spun Fe8_(1.3-x)Si_(4)B_(13)Cu_(1.7)Nb_(x)alloys are gradually reduced with enriching of Nb,and a fully amorphous structure forms at 4 at.%Nb,although smaller Cu-clusters still exist.After annealing,2 at.%Nb coarsens the average size(D_(α-F)e)of theα-Fe grains from 14.0 nm of the Nb-free alloy to 21.6 nm,and 4 at.%Nb refines the D_(α-Fe)to 8.9 nm.The mechanisms of theα-Fe nucleation and growth during quenching and annealing for the alloys with large quantities of PN-α-Fe as well as after Nb alloying have been discussed,and an annealing-induced oc-Fe growth mechanism in term of the barrier co-contributed by competitive growth among the PN-a-Fe and diffusion-suppression effect of Nb atoms has been proposed.A coercivity(HC)αDα-Fe^(3)correlation has been found for the nanocrystalline alloys,and the permeability is inverse with the H_(C).

Excellent magnetic softness-magnetization synergy and suppressed defect activation in soft magnetic amorphous alloys by magnetic field annealing

Fe-based amorphous alloys with high saturation magnetic flux density(B_(s))are increasingly attractive from both scientific and technological points of view,however,they usually suffer from the trade-off between magnetization and softness.In this work,we explore the soft magnetic properties(SMPs),magnetic and atomic structures,and defect activation during creep deformation of as-quenched and annealed Fe_(82.65-x)Co_(x)Si_(2)B_(14)Cu_(1.35)(x=0-20)amorphous alloys(AAs).Improved magnetic softness-magnetization synergy has been realized in all these alloys by field annealing.Particularly,superb SMPs with superhigh B_(s) of 1.86 T,low coercivity of 1.2 A/m and high effective permeability of 16300 are obtained in the Fe_(66.65)Co_(16)Si_(2)B_(14)Cu_(1.35) AA.The locally regularized arrangement of domains,homogenized structure with less structural/magnetic defects and suppressed crystal-like ordering by field annealing contribute synergistically to the superb SMPs.Besides,the relaxation time spectra obtained from creep deformation indicate less liquid-like and solid-like defects activated in the field-annealed AA,which is correlated with the structural homogenization and superb SMPs.This work provides new and comprehensive insight into the interplay among external field,heterogeneous structure,SMPs and defect activation of Fe-based AAs,and offers a promising pathway for softening amorphous alloys with high Bs.

Fe-based bulk amorphous alloys with high glass formation ability and high saturation magnetization

It was well known that it was very difficult to prepare high performance Fe-based bulk amorphous alloys with both high Fe content and good glass-forming ability, especially for the Fe content （or total magnetic elements content） higher than 80 at%. In this paper, a series of Fe81-xCoxMO1P7.5C5.5B2Si3 （x = 0, 5, 10, 15, 20） bulk amorphous alloys （BAAs） with high saturation magnetization have been developed by copper mold casting method with fluxed ingot. It has been found that using Co replacing Fe in the Fe-Mo-P-C-B-Si alloy could significantly enhance the glass-forming ability and magnetic property. For the BAA with Co content of 0 at%, 5 at%, 10 at%, 15 at% and 20 at%, its saturation magnetization Js（Js=μoMs） was 1.55, 1.60, 1.62, 1.65 and 1.59 T, respectively. Among these alloys, the Fe66Co15- Mo1P7.5C5.5B2Si3 BAA exhibited a critical size of 2 mm in diameter and a high Js of 1.65 T. It suggested that these alloys with high magnetic element content possessed great potential in application due to their high glass-forming ability and high magnetic property.

Design of FeSiBPCu soft magnetic alloys with good amorphous forming ability and ultra-wide crystallization window

The Fe_(81.3)Si_(4)B_(13–x)PxCu_(1.7) soft magnetic alloys with high Cu and proper P elements addition were synthesized with the aim of ensuring the amorphous forming ability(AFA)while expanding the crystallization window(CW).It is found that the atomic ratio of P/Cu of∼3 is advantageous for AFA whereas a small amount of P addition promotes the precipitation ofα-Fe grains and excessive P addition induces surface crystallization behavior of the present alloys.High Cu concentration can expand the annealing temperature(Ta)window whereas proper P addition effectively expands the annealing time(ta)window.The Fe_(81.3)Si_(4)B_(13-x)PxCu_(1.7) soft magnetic alloy was successfully synthesized with a large Ta window of up to 130°C and ta window of 90 min,which is a breakthrough for nanocrystalline alloys with high saturation magnetization.Microstructure analysis reveals that the ultra-wide CW is related to the unique nucleation mechanism,that is,theα-Fe grains are precipitated attaching to the Cu or CuP clusters and enveloping the Cu clusters,resulting in the high number density ofα-Fe nanocrystals.The ultra-wide CW promises the potential material in flexibly choosing the annealing process according to the performance.

Nitrogen-induced optimization of corrosion resistance for nanocrystalline soft magnetic Fe-Zr-B alloys

The poor corrosion resistance restricts the industrial applications of nanocrystalline soft magnetic Fe-Zr-B alloys.We reported a facile plasma-nitriding surface process to enhance the corrosion resistance of a nanocrystalline Fe90 Zr7 B3 alloy without deteriorating its soft magnetic properties.Potentiodynamic po-larization and electrochemical impedance spectroscopy were performed to investigate the corrosion be-havior.The nitrided alloy shows higher corrosion resistance than the untreated alloy,as evidenced by a nobler corrosion potential,lower corrosion current and higher polarization resistance of surface corrosion film,while their magnetic properties are similar.The microstructures of both nanocrystalline alloys were examined by high-resolution transmission electron microscopy(HRTEM)and the compositions of their corrosion films analyzed by X-ray photoelectron spectroscopy(XPS).For the nitrided alloy,a more homo-geneous nanocrystalline structure developed in the surface nitrided layer containing corrosion-resistant nitride phases(Fe3 N and ZrN)provides a higher resistance against chloride corrosion.Moreover,the ni-trided layer facilitates the formation of a more protective corrosion film with the increased ratios of Fe2+/Fe3+and O2−/OH−as well as higher enrichment of Zr-and B-oxides,while the N-species(NH4+and NO3−)formed in the corrosion film behave as good corrosion inhibitors and further enhance the film pro-tection.Our findings provide a simple strategy for the preparation of corrosion-resistant nanocrystalline soft magnetic alloys to satisfy a variety of engineering requirements.

Reduction of High-Frequency Core Loss of a Fe_(77.2)Si_(11)B_(8.5)Cu_(0.8)Nb_(2.5)Soft Magnetic Nanocrystalline Alloy by Minor Alloying

Enhancing saturation magnetic flux density(Bs)while reducing high-frequency core loss in Finemet-type nanocrystalline alloys is of great significance in achieving the miniaturization,high-frequency,and energy-saving of modern power electronic devices.In this work,we first designed a high-Bs Fe_(77.2)Si_(11)B_(8.5)Cu_(0.8)Nb_(2.5)alloy by appropriately reducing the non-magnetic elements in typical Finemet nanocrystalline alloys,and subsequently alloyed 2 at%Co,Al,and Mo,respectively.The effects of alloying elements on structure and static and high-frequency magnetic properties were studied.The results reveal that,alloying Al or Mo reduces the averageα-Fe grain size(Dα-Fe)in the nanocrystalline alloys,while Co exhibits a slight influence.The added Al or Mo results in decreases in both the Bs and coercivity(Hc)of the nanocrystalline alloys,whereas Co increases the Bs without changing Hc,and meanwhile,all alloying elements show minimal effects on effective permeability(μe).Furthermore,the addition of Co,Al,or Mo lowers the core loss(Pcv)at 0.2 T/100 kHz of the based nanocrystalline alloy with reductions of 10.9%,29.6%,and 26.8%,respectively.A Fe_(75.2)Si_(11)B_(8.5)Cu_(0.8)Nb_(2.5)Al_(2)nanocrystalline alloy exhibits outstanding soft magnetic properties with Bs,Hc,μe at 10 kHz and 100 kHz,and Pcv at 0.2 T/100 kHz of 1.34 T,0.8 A/m,27,400,18,000,and 350 kW/m3,respectively.The reduction in Pcv is primarily attributed to the decreased eddy current losses,originating from the increased electrical resistivity by elements alloying.

Magnetic field annealing of FeCo-based amorphous alloys to enhance thermal stability and Curie temperature

Annealing temperatures and applied magnetic fields are two important parameters for the performance modification of magnetic alloys.This article investigated the effect of different annealing temperatures on crystallization condition,magnetic properties and thermal stability of the amorphous magnetic alloy Co_(36)Fe_(36)Si_(4.8)B1_(9.2)Nb_(4)(at%).Results indicate that the annealing temperature can significantly affect the size and content of precipitated nanocrystals in the amorphous alloy,and the precipitation of nanocrystalline phases can result in the distinct change of magnetic properties and Curie temperature.When the annealing was performed at 595 ℃ for 30 min under an applied transverse external magnetic field of 9550.0A·m^(-1),the amorphous alloy shows excellent soft magnetic properties with the saturation magnetization of alloy reaching 110.00 mA·m^(2)·g^(-1),the residual magnetic induction intensity of 4 × 10^(-6) T and the coercivity as low as57.3 A·m^(-1).Furthermore,the Curie temperature of the field-annealed samples can reach up to 440 0C,approximately 58℃ higher than that of the as-quenched species.

Influence of thermal history on the crystallization behavior of high-Bs Fe-based amorphous alloys

A crucial step in creating cutting-edge soft magnetic alloys is the nanocrystallization of Fe-based amorphous alloys.However,it is unclear how the thermal history affects the nanocrystallization.In this work,high-precision nanocalorimetry and in-situ hightemperature transmission electron microscopy are used to systematically examine how the pre-annealing relaxation process affects the nanocrystallization of Fe-based amorphous alloys.We discover that the glass with more thermal energy storage will crystallize into superb nanocrystalline structures with exceptionally advanced soft magnetism.The soft magnetic properties of Fe-B nanocrystalline alloys can be improved by increasing the relaxation temperature.This finding provides solid and clear evidence for the influences of thermal history on crystallization behavior for Fe-based amorphous alloys,which is helpful for designing advanced soft magnetic nanocrystalline alloys.