Fe–B–P–Cu nanocrystalline soft magnetic alloys with high Bs

The effects of the addition of Cu on the crystallization processes, nanostructures and soft magnetic properties for the Fe_80.8–84.8B_8–10P_6–8Cu_1.2 alloys were investigated. The Fe–B–P–Cu alloys show two separated distinct exothermic peaks upon heating due to the addition of Cu. Furthermore, the interval temperature between each one for the Fe_82.8B₉P₇Cu_1.2 alloy is 103 K, and the first and second exothermic peaks result from the phase transition from amorphous to α-Fe and then to Fe₃(B,P), respectively. A uniform nanocrystalline structure composed of α-Fe grains with a 17 nm diameter was realized by annealing just above the first exothermic peak, and this nanocrystalline alloy exhibits high B_s of 1.70 T and low H_c of 4.9 A/m. Therefore, the nanocrystalline Fe–B–P–Cu soft magnetic alloy with high B_s and low H_c has a large industrial advantage due to miniaturization, high efficiency and low material cost of electric devices.     

Three-dimensional atom probe study of Fe–B-based nanocrystalline soft magnetic materials

Solute clustering and partitioning in new Fe–B-based soft magnetic materials with high saturation magnetic flux density (B_s), (Fe_0.85B_0.15)_100?xCu_x (x = 0.0, 1.0, and 1.5) and Fe_82.65Cu_1.35Si_yB_16?y (y = 0.0, 2.0, and 5.0) melt-spun alloys, were investigated by three-dimensional atom probe and transmission electron microscopy. Although Cu clusters form after annealing in all the samples, it was found that only the clusters of 4–6 nm can serve as heterogeneous nucleation sites for α-Fe. While annealing the Si-free alloys at 410 °C led to the precipitation of Fe₃B, only α-Fe nanocrystals were observed in the Si-containing alloys. Lorenz TEM observation indicated the Fe₃B particles pin magnetic domain walls. The Fe_82.65Cu_1.35Si_yB_16?y alloy with y = 2.0 crystallized by annealing at 400 °C exhibited optimal nanocrsytal/amorphous microstructure without the precipitation of Fe₃B, which led to the lowest coercivity while keeping a high B_s ～1.85 T.     

Nanocrystalline Fe–Nb–(B,Ge) alloys from ball milling: Microstructure,thermal stability and magnetic properties

Fe₇₅B₂₀Nb₅, Fe₇₅Ge₁₀B₁₀Nb₅ and Fe₇₅Ge₂₀Nb₅ alloys were prepared by ball milling from pure powders and their microstructure and magnetic properties were studied. A nanocrystalline solid solution of α-Fe type is the main phase formed, although traces of some intermetallics were found in the Fe–B–Nb alloy. The local arrangements of Fe atoms in Ge containing alloys continuously evolve with milling time. The obtained powders are thermally stable even heating up to 773 K. After heating up to 1073 K, intermetallic compounds are detected. The best soft magnetic properties are achieved after heating up to 773 K, due to stress relaxation of the nanocrystalline microstructure (for Fe–Ge–Nb alloy, coercivity ∼ 600 A/m).     

Effect of solute segregation on the strength of nanocrystalline alloys: Inverse Hall–Petch relation

We have used a high-energy ball mill to prepare single-phased nanocrystalline Fe, Fe₉₀Ni₁₀, Fe₈₅Al₄Si₁₁, Ni₉₉Fe₁ and Ni₉₀Fe₁₀ powders. We then increased their grain sizes by annealing. We found that a low-temperature anneal (T < 0.4 T_m) softens the elemental nanocrystalline Fe but hardens both the body-centered cubic iron- and face-centered cubic nickel-based solid solutions, leading in these alloys to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of solute segregation to the grain boundaries of the nanocrystalline alloys. Our analysis can also explain the inverse Hall–Petch relationship found in previous studies during the thermal anneal of ball-milled nanocrystalline Fe (containing ∼1.5 at.% impurities) and electrodeposited nanocrystalline Ni (containing ∼1.0 at.% impurities).     

Microstrucural characterization of gas atomized Fe73.5Si13.5B9Nb3Cu1 and Fe97Si3 alloys

Powder particles of Fe_73.5Si_13.5B₉Nb₃Cu₁ and Fe₉₇Si₃ soft magnetic alloys have been prepared by gas atomization. The gas atomized powder was microstructurally characterized and the dependence of coercivity with the composition and powder particle size investigated. As-atomized powder particles of both compositions were constituted by a bcc α-Fe (Si) solid solution. The Fe_73.5Si_13.5B₉Nb₃Cu₁ powder particles presented a grain microstructure with dendrite structure, which dendrite arms were enriched in Nb. The coercivity increased as the particle size decreased, with a minimum coercivity, of 5 Oe, measured in the Fe₉₇Si₃ alloy in the range of 50–100 μm powder particle size. The coercive fields were quite higher in the Fe_73.5Si_13.5B₉Nb₃Cu₁ than in the Fe₉₇Si₃ powder, due to the Nb addition, which produced a phase segregation that leads to a noticeable magnetic hardening.     

Microstructure and magnetic properties of FeMoBCu alloys: Influence of B content

Fe_91–xMo₈Cu₁B_x (x = 12, 15, 17, 20) amorphous and nanocrystalline alloys were studied to examine the influence of B content on their microstructure and magnetic behaviour. Changes in the magnetic properties provoked by microstructural evolution upon thermal treatments of as-cast samples were also analyzed. Nanocrystallization kinetics can be described by an isokinetic approach except for the 20 at.% B content alloy. The Curie temperature of the amorphous as-cast samples increases with the alloy’s B content. Mössbauer results suggest the presence of Mo atoms in the nanocrystals. Crystalline volume fraction and mean grain size of the nanocrystals at the end of the nanocrystallization process are higher for the lowest B content alloy. The 20 at.% B content alloy develops a boride phase just after the early stages of the nanocrystallization process, which provokes a magnetic hardening in this alloy. The softest magnetic behaviour of the studied compositions corresponds to nanocrystallized 17 at.% B content alloy.     

Cr effects on magnetic and corrosion properties of Fe–Co–Si–B–Nb–Cr bulk glassy alloys with high glass-forming ability

Effects of the Cr addition on glass formation, magnetic and corrosion properties of {[(Fe_0.6Co_0.4)_0.75B_0.2Si_0.05]_0.96Nb_0.04}_100−xCr_x (x = 1, 2, 3, 4 at.%) alloys have been investigated. It was found that the addition of Cr element slightly decreases the glass-forming ability (GFA), but is very effective in increasing corrosion resistance and improving soft magnetic properties for this Fe–Co–B–Si–Nb bulk glassy alloy within the composition range examined. The Fe–Co–B–Si–Nb–Cr alloys exhibit high GFA. Full glassy rods with diameters up to 4 mm can be synthesized by copper mold casting. The Fe-based bulk glassy alloys (BGAs) exhibit a high saturation magnetization of 0.81–0.98 T as well as excellent soft magnetic properties, i.e., extremely low coercive force of 0.6–1.6 A/m and super-high initial permeability of 26,400–34,100. Furthermore, corrosion measurements show that corrosion rate and corrosion current density of these Fe-based BGAs in 0.5 M NaCl solution decrease from 7.0 × 10⁻¹ to 1.6 × 10⁻³ mm/year and 3.9 × 10⁻⁶ to 8.7 × 10⁻⁷ A/cm², respectively, with increasing Cr content from 0 to 4 at.%. The success of synthesizing the new Fe-based BGAs exhibiting simultaneously high GFA as well as excellent good soft magnetic properties combined with high saturation magnetization and enhanced corrosion resistance allows us to expect future progress as a new type of soft magnetic materials.     

Enhancement of glass-forming ability of FeGaPCB bulk glassy alloy with high saturation magnetization

The effect of Mo and Si additions on the glass-forming ability (GFA) of Fe–Mo–Ga–P–C–B–Si alloys was investigated. The addition of 2 at% Mo combined with 2 at% Si was found to be effective for the extension of the supercooled liquid region (ΔT_x) defined by the difference between glass transition temperature (T_g) and crystallization temperature (T_x). The ΔT_x value is 26 K for the Fe₇₈Ga₂P₁₂C₄B₄ alloy, and increases to 52 K for the Fe₇₆Mo₂Ga₂P₁₀C₄B₄Si₂ glassy alloy. In addition, this glassy alloy exhibits a highly reduced glass transition temperature (T_g/T_l) of 0.59. Large ΔT_x and high T_g/T_l enabled us to prepare the Fe₇₆Mo₂Ga₂P₁₀C₄B₄Si₂ bulk glassy alloy successfully with a diameter of 2 mm and with a high saturation magnetization (I_s) of 1.32 T. The Fe₇₆Mo₂Ga₂P₁₀C₄B₄Si₂ glassy alloy also exhibits good soft magnetic properties, i.e., high effective permeability at 1 kHz of 9700 and low coercive force of 3 A/m.     

Glass-forming ability and soft magnetic properties of (Co0.6Fe0.3Ni0.1)67B22+xSi6−xNb5 bulk glassy alloys

The glass-forming ability (GFA) and soft-magnetic properties of (Co_0.6Fe_0.3Ni_0.1)₆₇B_22+xSi_6?xNb₅ (x = 0–1.5) bulk glassy alloys was investigated. The DSC curves show that the (Co_0.6Fe_0.3Ni_0.1)₆₇B_22+xSi_6?xNb₅ bulk glassy alloys have a wide supercooled liquid region (ΔT_x) of about 60 K, and high reduced glass transition temperature (T_g/T_l) lies in the range from 0.628 to 0.649. By copper mold casting method, the bulk glassy alloys with diameters up to 4.5 mm can be formed. In addition to high GFA, the Co-based bulk glassy alloys also exhibit good soft-magnetic properties, i.e., saturation magnetization of 0.58–0.61 T, low coercive force of 0.83–1.46 A/m, and high permeability of (1.79–2.2) × 10⁴ at 1 kHz under a field of 1 A/m. These Co-based bulk glassy alloys are promising for future applications as a new structural and functional material.     

Large-scale first-principles determination of anisotropic mechanical properties of magnetostrictive Fe–Ga alloys

Magnetostrictive Fe_1?xGa_x alloys, as a new class of smart materials, have great potential in sensing and actuator applications. However, the fundamental understanding of the anisotropic elastic responses at high Ga concentration remains one of the most challenging problems for the binary alloys. Here, we apply the density functional theory and large-scale ab initio molecular dynamics simulation to investigate the effect of high Ga concentration on the elastic anisotropy of the Fe–Ga alloys with supercell models obtained by non-linear and non-uniform annealing processes. It is demonstrated that the formation of D0₃-like structures has an important effect on the softness of the tetragonal shear modulus and a negligible influence on the rhombohedral shear modulus. Meanwhile, the Fe dangling bond to its nearest Ga atoms results in a decrease in the Young’s modulus and the negative Poisson’s ratio in the [1 1 0] direction. The improved Young’s modulus in the [1 1 0] direction compared to that in the [1 0 0] direction is attributed to the different arrangement of the pure Fe layer and the Fe–Ga mixed layer along the [1 1 0] and [1 0 0] axes. Furthermore, the ductility of Fe_1?xGa_x alloys is enhanced at high Ga content, playing a key role in the enhanced magnetostriction.     

Novel FePBNbCr glassy alloys “SENNTIX” with good soft-magnetic properties for high efficiency commercial inductor cores

According to a recent study, Fe-based glassy alloys are expected good soft-magnetic properties such as high saturation magnetization and lower coercive force. We focused on Fe-based glassy alloys and have succeeded in developing novel glassy Fe_97?x?yP_xB_yNb₂Cr₁ (x = 5–13, y = 7–15) alloys for an inductor material. The glassy alloy series of Fe_97?x?yP_xB_yNb₂Cr₁ (x = 5–13, y = 7–15) have high glass-forming ability with the large critical thickness of 110–150 μm and high B_s of 1.25–1.35 T. The glassy alloy powder with chemical composition Fe₇₇P_10.5B_9.5Nb₂Cr₁ exhibits an excellent spherical particle shape related to the lower melting point and liquid phase point. In addition, Fe–P–B–Nb–Cr powder/resin composite core has much lower core loss of 653–881 kW/m³, which is approximately 1/3 lower than the conventional amorphous Fe–Si–B–Cr powder/resin composite core and 1/4 lower than the conventional crystalline Fe–Si–Cr powder/resin composite core due to the lower coercive force of 2.5–3.1 A/m. Based on above results, the glassy Fe₇₇P_10.5B_9.5Nb₂Cr₁ alloy powder enable to achieve ultra-high efficient and high quality products in a commercial inductor. In fact, the surface mounted inductor using Fe–P–B–Nb–Cr powder/resin exhibits the high efficiency of approximately 2.0% compared with the conventional inductors made of the crystalline Fe–Si–Cr powder/resin composite core.     

The characterization of structure,thermal stability and magnetic properties of Fe–Co–B–Si–Nb bulk amorphous and nanocrystalline alloys

Recently bulk amorphous alloys have attracted great attention due to their excellent magnetic properties. The glass-forming ability of bulk amorphous alloys depends on the temperature difference (ΔT_x) between glass transition temperature (T_g) and crystallization temperature (T_x). The increase of ΔT_x causes a decrease of the critical cooling rate (V_c) and growth of the maximum casting thickness of bulk amorphous alloys. The aim of the present paper is to characterize the structure, the thermal stability and magnetic properties of Fe₃₆Co₃₆B₁₉Si₅Nb₄ bulk amorphous alloys using XRD, Mössbauer spectroscopy, DSC and VSM methods. Additionally the magnetic permeability μ_i (at force H ≈ 0.5 A/m and frequency f ≈ 1 kHz) and the intensity of disaccommodation of magnetic permeability Δμ/μ(t₁) (Δμ = μ(t₁ = 30 s) ? μ(t₂ = 1800 s)), have been measured, where μ is the initial magnetic permeability measured at time t after demagnetisation, the Curie temperature T_C and coercive force H_c of rods are also determined with the use of a magnetic balance and coercivemeter, respectively.Fe–Co–B–Si–Nb bulk amorphous alloys were produced by pressure die casting with the maximum diameters of 1 mm, 2 mm and 3 mm.The glass transition temperature (T_g) of studied amorphous alloys increases from 807 K for a rod with a diameter of 1 mm to 811 K concerning a sample with a diameter of 3 mm. The crystallization temperature (T_x) has the value of 838 K and 839 K for rods with the diameters of 1 mm and 3 mm, respectively. The supercooled liquid region (ΔT_x = T_x ? T_g) has the value of about 30 K. These values are presumed to be the origin for the achievement of a good glass-forming ability of the Fe–Co–B–Si–Nb bulk amorphous alloy. The investigated amorphous alloys in the form of rods have good soft magnetic properties (e.g. M_s = 1.18–1.24 T). The changes of crystallization temperatures and magnetic properties as a function of the diameter of the rods (time of solidification) have been stated.     

Manufacturing of the bulk amorphous Fe61Co10Zr2+xHf3−xW2Y2B20 alloys (where x = 1, 2, 3) their microstructure,magnetic and mechanical properties

In this paper the microstructure, magnetic properties and mechanical studies results for Fe₆₁Co₁₀Zr_2+xHf_3?xW₂Y₂B₂₀ (for x = 1, 2 or 3) alloys are presented. The samples used in the investigations were obtained by a suction-casting method. The samples were produced in the forms of rods with diameter of 1 mm and length of about 20 mm and plates with thickness of 0.5 mm and surface area of about 100 mm². The results show that the best soft magnetic properties were achieved by Fe₆₁Co₁₀Zr₃Hf₂W₂Y₂B₂₀ amorphous alloy in the form of a plate. This sample has the highest value of saturation magnetization (1.09 T) and the smallest values of coercivity (H_C = 1.5 A/m) and core losses. All investigated samples of amorphous alloys were characterized by substantially greater values of microhardness and, unfortunately, slightly lower values of wear resistance compared with their crystalline counterparts.     

Fe–B–Si–Zr soft magnetic bulk glassy alloys

The present work is devoted to fabrication of Fe–B–Si–Zr multi-component bulk glassy alloys with good mechanical and soft magnetic properties. Glass formation in Fe–B system is first considered with an empirical cluster-plus-glue-atom model. A basic composition formula [B–B₂Fe₈]Fe is proposed as the framework for multi-component alloy design. Considering the structural stability of the model glass, Si and Zr are introduced to the [B–B₂Fe₈] cluster to replace the center B and shell Fe atoms, from which a series of Fe–B–Si–Zr alloys with composition formulas [Si–B₂Fe_8−xZr_x]Fe (x = 0–0.6) are derived. Copper mold casting experiment shows that bulk glassy alloys are formed within the Zr content range of x = 0.2–0.6, and the largest glass-forming ability appears at [Si–B₂Fe_7.6Zr_0.4]Fe with a critical size of 2.5 mm. The bulk glassy alloys exhibit high fracture strength as large as 3850 MPa. Magnetic property measurement indicates that these alloys exhibit good magnetic softness with high saturation magnetization (1.26–1.48 T) and low coercive force (1.6–6.7 A/m). The alloying effects of Si and Zr on bulk glass formation, thermal glass stability and magnetic softness are discussed with the empirical model.     

Ball milling of Fe83Zr6B10Cu1 amorphous alloy containing quenched in crystals

A Fe₈₃B₁₀Zr₆Cu₁ melt-spun amorphous alloy has been ball milled in the presence of partially crystalline ribbon pieces, in order to speed up its mechanical nanocrystallization process. Microstructure and magnetic properties of the resulting powder were studied as a function of the milling time. A continuous increase of the crystalline fraction of α-Fe was observed after pulverization of the sample. A linear increase of Cr contamination with the milling time (up to 1.5 at.% after 24 h) was measured. This element seems to be preferentially in the crystalline phase. Saturation magnetization and coercivity were also measured as a function of temperature. The temperature dependence of coercivity is similar to that found in soft magnetic nanocrystalline alloys.     

Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu

Fe–Pd–Cu thin films are of great interest for applications in magnetic shape memory microsystems due to their increased martensitic transformation temperature. Here we analyse the consequences of Cu addition to Fe–Pd on the binding energy and magnetic properties by a combination of thin film experiments and first-principles calculations. Strained epitaxial growth of Fe₇₀Pd_30-xCu_x with x = 0, 3, 7 is used to freeze intermediate stages during the martensitic transformation. This makes a large range of tetragonal distortion susceptible for analysis, ranging from body-centred cubic to beyond face-centred cubic (1.07 < c/a_bct < 1.57). We find that Cu enhances the quality of epitaxial growth, while spontaneous polarization and Curie temperature are reduced only moderately, in agreement with our calculations. Beyond c/a_bct > 1.41 the samples undergo structural relaxations through adaptive nanotwinning. Cu enhances the magnetocrystalline anisotropy constant K₁ at room temperature, which reaches a maximum of ?2.4 × 10⁵ J m^?3 around c/a_bct = 1.33. This value exceeds those of binary Fe₇₀Pd₃₀ and the prototype Ni–Mn–Ga magnetic shape memory system. Since K₁ represents the maximum driving energy for variant reorientation in magnetic shape memory systems, we conclude that Fe–Pd–Cu alloys offer a promising route towards microactuator applications with significantly improved work output.     

Effect of substitution of refractory elements for Fe on the magnetic properties of melt-spun Pr9.5Fe80.5B10 nanocomposites

Magnetic properties and phase evolution of Pr-deficient and B-excess Pr_9.5Fe_80.5B₁₀ ribbons obtained by refractory elements substitution have been investigated. From thermal magnetic analysis (TMA), it was proved that both Pr₂Fe₂₃B₃ and Fe₃B phases have been completely suppressed for the ribbons with all the selected refractory elements substitution. A slight substitution of the adopted refractory elements (Cr, Nb, V, Ti and Zr) for Fe not only suppresses the formation of metastable Pr₂Fe₂₃B₃ and Fe₃B phases but also leads to the presence of a large amount of the Pr₂Fe₁₄B phase. Accordingly, the coercivity of the ribbons was improved remarkably from 8.3 kOe for ternary Pr_9.5Fe_80.5B₁₀ ribbons to 10.1–13.2 kOe for all chosen refractory element-substituted nanocomposites. The optimal magnetic properties of B_r = 9.0 kG, _iH_c = 13.2 kOe and (BH)_max = 16.9 MGOe can be obtained in Pr_9.5Fe_78.5Nb₂B₁₀. Finally, from minor loop analysis, the coercivity of all studied ribbons is mainly dominated by domain wall pinning.     

Influences of additional alloying elements (V,Ni, Cu,Sn, B) on structure and mechanical properties of high-strength hypereutectic Ti–Fe–Co bulk alloys

High-strength nonequilibrium hypereutectic bulk alloys were obtained recently in the Ti–Fe and Ti–Fe–Co systems by arc-melting. Following these results, the influences of the additional alloying elements (V, Ni, Cu, Sn, B) on high strength hypereutectic Ti–Fe–Co bulk alloys are studied and analyzed in the present work. The structure of the hypereutectic quaternary Ti₆₇Fe₁₄Co₁₄Sn₅, Ti₆₇Fe₁₄Co₁₄V₅, Ti₇₀Fe₁₇Co₇Cu₆, Ti₇₀Fe₁₇Co₇Ni₆, and Ti_69.4Fe_14.8Co_14.8B₁ alloys obtained in the form of arc-melted ingots of about 20–30 mm diameter and 10–15 mm height was studied by X-ray diffractometry and scanning electron microscopy. The mechanical properties were tested by an Instron-type machine. Ti₆₇Fe₁₄Co₁₄Sn₅ alloy exhibits a high ultimate compressive strength of 1830 MPa and a large plastic strain of 24% which exceeds the ductility values obtained for Ti–Fe and Ti–Fe–Co alloys. The addition of Sn causes formation of a relatively rough eutectic structure which is preferable for the high strength hypereutectic alloys. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and cracks propagation while fine eutectic rods of submicron size are quite effortlessly cut by deformation bands and cracks.     

The constitution of the ternary system Fe–Ni–Si

The ternary system Fe–Ni–Si was investigated using X-ray diffraction (XRD), metallography (SEM), energy dispersive spectroscopy (SEM/EDS), magnetic susceptibility measurements, and differential thermal analysis (DTA). The existence of the ternary phase τ is corroborated and its crystal structure is confirmed to be isostructural to Cr₃Ni₅Si₂. At 700 °C the homogeneity of this phase extends from 43 to 55 at.% iron at constant 20 at.% Si. Furthermore, for the binary phases NiSi₂, Ni₂Si and Ni₃₁Si₁₂ extensive solubilities for iron are found, while the solubility of Fe in NiSi, Ni₃Si₂ or Ni₃Si does not exceed 5 at.%. On the other side of the system, the phases FeSi and Fe₃Si have large solubilities for Ni, while this is rather limited in FeSi₂. The (binary high temperature) phase Fe₅Si₃ is stabilized by Ni at least down to 700 °C. Tie lines exist between τ and solid solutions based on Fe₃Si, Ni₃₁Si₁₂ as well as γ (Ni). DTA measurements for the vertical section Fe₂Si–Ni₂Si strongly indicate that Fe₂Si and θNi₂Si form a complete series of solid solutions θ(Fe, Ni)₂Si and are thus isostructural. A critical evaluation of the available crystal structure data for Fe₂Si supports this assumption. Iron rich θ(Fe, Ni)₂Si is a weak ferromagnet. The magnetic moment of ～1 μB per Fe-atom in θ(Fe, Ni)₂Si is only half of the magnetic moment per Fe-atom measured for τ Fe₅Ni₃Si₂. A reaction scheme accounting for all DTA data of the entire system is established and in combination with observations on the first crystallizing phase(s) the liquidus surface of Fe–Ni–Si is revised.     

Magnetic property enhancement of directly quenched Nd–Fe–B bulk magnets with Ti substitution

Magnetic properties, phase evolution, and microstructure of directly quenched Nd_yFe_85?x?yTi_xB₁₅ (x = 0–4; y = 8–10) bulk magnetic rods with a diameter of 0.7 mm were studied. The experimental results show that Ti substitution can not only suppress the formation of the Nd₂Fe₂₃B₃ and one unknown phases, leading to the presence of the large amount of Nd₂Fe₁₄B phase, but also refine the grain size, resulting in the remarkable enhancement of magnetic properties. Besides, proper Ti substitution and Nd concentration can well modify phase constitution and uniformly refine grain size. In this study, the optimal magnetic properties of B_r = 6.5 kG, _iH_c = 10.3 kOe and (BH)_max = 8.7 MGOe are achieved in Nd_9.5Fe_72.5Ti₃B₁₅ magnet.