Temperature changes for the hysteresis loop of an amorphous magnetic microwire in a glass shell

We investigated the hysteresis loop of an Fe_72.Si₁₃B₁₅ microwire in a glass shell characterized by a rectangular hysteresis loop. The gel covering of the outer surface of the microwire transforms it into an hysteresis-free loop.     

Effect of nanocrystallization on giant magnetoimpedance effect of Fe-based microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of Fe_70.8Cu₁Nb_3.1Si_14.5B_10.6 and Fe_71.8Cu₁Nb_3.1Si₁₅B_9.1 Finemet microwires. We observed that GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored either controlling magnetoelastic anisotropy of as-cast FeCuNbSiB microwires, and/or controlling their structure by heat treatment or by changing the fabrication conditions. High GMI effect has been observed in as-prepared Fe-rich and heat treated microwires with nanocrystalline structure.     

The process of crystallization from amorphous state in ribbons of Fe–Si–B–based alloys under the effect of a high DC magnetic field

The effect of a high dc magnetic field (up to 29 T) applied during the crystallizing annealing of amorphous ribbons on the structure of Fe₈₁Si₇B₁₂ and Fe_73.5Cu₁Nb₃Si_13.5B₉ alloys has been studied. In the Fe₈₁Si₇B₁₂ alloy, an increase in the average size of grains that form during magnetic annealing has been revealed; in the Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy, a small decrease is observed in the average grain size. The possible reason for this may be the differences in the specific features of the processes of crystallization of these alloys. No effect of the magnetic field on the crystallographic orientation of the arising grains has been revealed.     

Dynamic magnetoelastic properties of the Fe<Subscript>80</Subscript>Si<Subscript>10</Subscript>B<Subscript>10</Subscript> amorphous alloy subjected to crystallization annealing

Dynamic magnetoelastic properties of the Fe₈₀Si₁₀B₁₀ amorphous alloy have been investigated by the method of double electromagnetoacoustic transformation (EMAT) depending on the temperature of crystallization annealing. The anomalous changes in the differential magnetostriction and damping and velocity of ultrasound revealed in the region of surface crystallization are similar to changes in the parameters of the double EMAT in the Fe_73.7Cu_1.0Nb_3.2Si_12.7B_9.4 finemet, although some distinctions have been observed.     

Structural transformations and wear resistance of abrasive-affected amorphous Fe- and Co-based alloys

The abrasive wear resistance of the Fe₆₄Co₃₀Si₃B₃, Fe_82.6Nb₅Cu₃Si₈B_1.4, Co_86.5Cr₄Si₇B_2.5, and Fe₈₁Si₄B₁₃C₂ amorphous alloys (ribbon 30 μm thick) has been investigated upon sliding over fixed abrasives (corundum and silicon carbide). The character of fracture of the surface and structural transformations initiated in these materials by the abrasive action have been studied by the metallographic, X-ray diffraction, and electron-microscopic methods. It has been shown that the abrasive wear resistance of the amorphous alloys is smaller by a factor of 1.6–2.9 than that of the Kh12M and U8 tool steels possessing approximately the same level of hardness. A pronounced softening of the surface layer of the amorphous alloys in the process of wear, which is characterized by a decrease in their microhardness reaching 12.5%, has been found. It has been shown that in the surface layer of these amorphous alloys upon wear there arises a small amount (on the order of several volume percent) of the nanocrystalline structure, which does not exert a marked effect on the microhardness and wear resistance of the alloys. In the alloys under study, the main factor that is responsible for their comparatively low abrasive wear resistance is their local softening in the process of wear caused by specific features of deformation processes occurring heterogeneously under the action of high shear contact stresses.     

The Effects of Strain-Annealing on Tuning Permeability and Lowering Losses in Fe-Ni-Based Metal Amorphous Nanocomposites

Fe-Ni-based metal amorphous nanocomposites with a range of compositions (Fe_100?x Ni _x )₈₀Nb₄Si₂B₁₄ (30 ≤ x ≤ 70) are investigated for motor and transformer applications, where it is beneficial to have tunable permeability. It is shown that strain annealing offers an effective method for tuning permeability in these alloys. For an Fe-rich alloy, permeability increased from 4000 to 16,000 with a positive magnetostriction. In a Ni-rich alloy, permeability decreased from 290 to 40 with a negative magnetostriction. Significant elongations (above 60%) are observed during strain annealing at high stress. Crystallization products have been determined in all alloys heated to 480°C. γ-FeNi is formed in all alloys, while (Fe₃₀Ni₇₀)₈₀Nb₄Si₂B₁₄ also undergoes secondary crystallization at temperatures of approximately 480°C to form a phase with the Cr₂₃C₆-type structure and a likely composition of Fe₂₁Nb₂B₆. Toroidal losses have been measured for (Fe₇₀Ni₃₀)₈₀Nb₄Si _y B_16?y (0 ≤ y ≤ 3) at various annealing temperatures. At an induction of 1 T and frequency of 400 Hz and 1 kHz, the toroidal losses obtained are W_{1.0T, 400 Hz} = 0.9 W/kg and W_{1.0T, 1 kHz} = 2.3 W/kg, respectively. These losses are lower than losses recently reported for state of the art 3.0% and 6.5% silicon steels, a Metglas Fe-based amorphous alloy, and some Fe-based nanocomposites.     

Interaction of the surface of ribbons of amorphous soft-magnetic iron-based alloys with water and their magnetic properties

The effect of interaction of the surface of ribbons of amorphous soft-magnetic alloys with water on the magnetization distribution and magnetic properties has been investigated on the example of ribbons of amorphous rapidly quenched alloys Fe₈₁B₁₃Si₄C₂ and Fe₇₇Ni₁Si₉B₁₃. It has been shown by these investigations that the interaction of the surface of ribbons of amorphous silicon-containing soft-magnetic iron-based alloys with water leads to a reduction in the maximum magnetic permeability. The decrease in μ_max is caused by a magnetization redistribution in the plane of the ribbon, namely, by an increase in the volume of domains with an in-plane magnetization oriented transversely to its axis. This is connected with the formation in this direction, due to a locally directed ordering, of an enhanced concentration of atoms incorporated into the ribbon surface and inducing a pseudo-uniaxial tension that favors a reorientation of the magnetization. The degree of changes in the magnetic properties depends on the temperature of water.     

Crystallization mechanism of Fe78Si13B9 amorphous alloy induced by ion bombardment

The crystallization behavior of Fe₇₈Si₁₃B₉ amorphous alloys induced by Ar ion bombardment was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. The crystallization process of amorphous alloys can be controlled by adjustment of ion incident angles (θ), beam density and substrate temperature. The compressive stress caused by ion bombardment will result in the decrease of critical nucleation energy and induce the crystallization of amorphous alloy even at very low temperature, and the thermal effect converted from energetic ions will improve the crystallization of amorphous alloys. The crystallization process of amorphous alloy induced by ion bombardment was a stress induced phase transformation process assisted by thermal effect.     

Magnetization distribution in a soft magnetic amorphous alloy ribbon in as-quenched state and efficiency of heat treatment

The effect of heat treatment in air on the formation of magnetic properties has been studied based on the example of soft magnetic Fe₇₇Ni₁Si₉B₁₃ and Fe₈₁B₁₃Si₄C₂ amorphous ribbons characterized by positive magneto-striction. The magnetization distribution in the ribbons in the as-quenched state was shown to affect the efficiency of annealing. Under certain conditions, heat treatment, which results in the formation of mainly amorphous state of ribbon surface, is more efficient for samples characterized by high volume of orthogonally magnetized domains. This can be related to high in-plane tensile stresses, which are induced by hydrogen and oxygen atoms introduced into the ribbon surface upon its interaction with atmospheric water vapor.     

Micromagnetic simulation of the distribution of magnetization in semiinfinite single crystals

The enrichment of the Fe_73.5Si_13.5B₉Cu₁Nb₃ amorphous alloy in iron was found to change the kinetic regime of primary crystallization, which becomes two-stage rather than single-stage. The observed peculiarities of the crystallization behavior of the alloy were explained assuming that niobium plays a key role in the formation of its amorphous structure.     

CRYSTALLIZATION PROCESS AND NON–ISOTHERMAL CRYSTALLIZATION KINETICS OF MELT–SPUN Nd–Fe–B AMORPHOUS THICK RIBBONS

利用熔体快淬法在12 m/s的辊速下制备了Nd₆Fe₇₂B₂₂和Nd₆Fe₆₈Ti₄B₁₇C₅非晶厚带. 通过DSC和XRD, 并借助Kempen模型和 Kissinger方程, 研究了合金的非晶晶化过程及非等温晶化动力学. 结果表明, 两种合金厚带具有不同的晶化过程以及晶化动力学机制. Nd₆Fe₇₂B₂₂合金的晶化过程分为三步完成: 非晶
相 (AP)→ Nd₂Fe₂₃B₃→Nd₂Fe₁₄B+ α--Fe +Fe₃B→Nd₂Fe₁₄B+α--Fe+Fe₃B+NdFe₄B₄, 而Nd₆Fe₆₈Ti₄B₁₇C₅ 合金一步完成晶化: AP→Nd₂(Fe, Ti)₁₄(B, C)+α--Fe + Fe₃B. 与Nd₆Fe₇₂B₂₂合金由界面控制的多晶型晶化不同, Nd₆Fe₆₈Ti₄B₁₇C₅合金以扩散控制的共晶型晶化为主.     

Structural transformations and tribological properties of amorphous alloys upon wear at room and cryogenic temperatures

The abrasive wear resistance of the Fe₆₄Co₃₀Si₃B₃, Co_86.5Cr₄Si₇B_2.5, Fe_73.5Nb₃Cu₁Si_13.5B₉, and Fe_82.6Nb₅Cu₃Si₈B_1.4 commercial amorphous alloys (ribbon 0.03 mm thick and 12 mm wide) has been investigated under the conditions of abrasive and adhesive wear upon sliding friction. The character of fracture of the surface and structural transformations that occur in these materials upon wear have been studied by the metallographic and electron-microscopic methods. It has been shown that at room and cryogenic (−196°C) temperatures of tests the abrasive wear resistance of the amorphous alloys is two-three times lower than that of tool steels Kh12M and U8. A comparatively small abrasive wear resistance of the amorphous alloys is explained by local softening of these materials in the process of wear. Under the conditions of adhesive wear of like friction pairs at room temperature in air and argon, the amorphous alloys are characterized by the rate of wear that is smaller approximately by an order of magnitude than in steels 12Kh13 and 12Kh18N9. It has been established that upon wear the deformed surface layer of the alloys under study retains a predominantly amorphous state but in local sections of this layer nanocrystalline structures that consist of crystals of bcc and fcc phases and borides are formed. The possible effects of this partial crystallization on the microhardness, friction coefficient, and wear resistance of these alloys have been considered.     

Effect of electrolytic oxidation and hydrogenation on the magnetization distribution and magnetic properties of ribbons of amorphous soft magnetic iron-based alloys

The effect of electrolytic oxidation and hydrogenation on the magnetization distribution and magnetic properties of ribbons of amorphous soft magnetic iron-based alloys has been investigated on the example of the Fe₇₇Ni₁Si₉B₁₃ and Fe₈₁B₁₃Si₄C₂ alloys. The results of the investigation showed that hydrogenation and oxidation of the surface of the ribbon lead to changes in the magnetic properties, which agree with changes in its magnetic state. A decrease in the volume of domains with orthogonal magnetization observed upon oxidation is caused by the large effective diameter of oxygen atoms inducing a higher level of planar tensile stresses upon incorporation into the ribbon surface. A reduction (observed in both cases) in the volume fraction of domains with a planar magnetization oriented along the ribbon axis is connected with the appearance of pseudo-uniaxial tension in the plane of the ribbon across its axis, since the concentration of atoms incorporated into the surface is enchanced in this direction. The interaction of the surface of the ribbon at room temperature with vapor leads to identical changes in the magnetic characteristics and redistribution of magnetization in its plane.     

Regularities of the effect of the value of initial bending stresses on their relaxation under the annealing of amorphous magnetically soft alloys of various classes

It has been shown that, in some amorphous alloys, the value of initial bending stresses σ_m can influence the development of the relaxation of these stresses during the annealing of the alloys. These alloys include Co₆₉Fe_3.7Cr_3.8Si_12.5B₁₁, with a nearly zero saturation magnetostriction (λ_s < 10^–7) and the Fe₇₈Ni₁Si₈B₁₃ alloy with λ_s = 25 × 10^–6. In the iron-based Fe₈₁Si₄B₁₃C₂ and Fe₅₇Co₃₁Si_2.9B_9.1 alloys, no effect of the initial bending stresses on their relaxation has been observed. No this effect has also been observed in the metalloid-free alloys Со₈₀Mo₁₀Zr₁₀ and Со₈₀Mo₈Ni₂Zr₁₀ with a nearly zero saturation magnetostriction λ_s. When this effect manifests itself, the activation energy U of the given process becomes a function of two factors; i.e., this energy depends on both the composition of the alloy (that is, interatomic forces) and the value of the initial bending stresses. In this case, the activation energy U cannot be considered to be characteristic of the material.     

Influence of thermally induced structural transformations on hardness in Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

Effect of heat treatment on mechanical behavior of Fe_89.8Ni_1.5Si_5.2B₃C_0.5 amorphous alloy was investigated by measuring microhardness. It was shown that the as-prepared amorphous alloy has an unexpectedly high microhardness. This can be attributed not only to boron dispersed in the alloy, but also to the structure which exhibits aspects of a nanocomposite of nanoparticles dispersed in an amorphous matrix. As the alloy crystallizes at temperatures above 540 °C, microhardness decreases continuously as a function of heating temperature. This is attributed to separation of boron out of the amorphous matrix into nanocrystals of Fe₂B phase. Further decrease in microhardness is attributed to crystallite growth with the accompanying change in the dominant nature of the interfaces from amorphous/crystal to crystal/crystal, and creation of a porous structure. When the crystallization is complete, the alloy exhibits microhardness close to that of a hypothetical mixture of α-Fe and Fe₂B phases of the same composition.     

Effect of ion irradiation on the nanocrystallization and magnetic properties of soft magnetic Fe7<Subscript>2.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>2</Subscript>Mo<Subscript>1.5</Subscript>Si<Subscript>14</Subscript>B<Subscript>9</Subscript> alloy

The effect of accelerated Ar⁺ ions on the crystallization process and magnetic properties of nanocrystalline Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy has been studied using X-ray diffraction analysis, transmission electron microscopy, thermomagnetic analysis, and other magnetic methods. Irradiation by Ar⁺ ions with an energy of 30 keV and a fluence of 3.75 × 10¹⁵ cm^–2 at short-term heating to a temperature of 620 K (which is 150 K below the thermal threshold of crystallization) leads to the complete crystallization of amorphous alloy, which is accompanied by the precipitation of the α-Fe(Si) solid solution crystals (close in composition to Fe₈₀Si₂₀), Fe₃Si stable phase, and metastable hexagonal phases. The crystallization caused by irradiation leads to an increase in the grain size and changes the morphology of grain boundaries and volume fraction of crystalline phases, which is accompanied by changes in the magnetic properties.     

Effect of boron on the thermodynamic stability of amorphous polymer-derived Si(B)CN ceramics

The reason for the higher thermal persistence of amorphous polymer-derived SiBCN ceramics (T ～ 1700–2000 °C) compared to SiCN ones (T ～ 1500 °C) has been a matter of debate for more than a decade. Despite recent experimental results which indicate a major kinetic effect of boron on the thermal persistence of the ceramics, no experimental investigation of the thermodynamic stability of the materials has been reported. In this work, we present measured energetics of a series of the amorphous ceramics with various boron contents (0–8.3 at.%) using high-temperature oxidative drop-solution calorimetry. Through measurement of the drop-solution enthalpies in molten sodium molybdate at 811 °C, the formation enthalpies of the amorphous ceramics from crystalline components (SiC, BN, Si₃N₄, C) at 25 °C were obtained and found to be between ?1.4 and ?26.6 kJ g-atom^?1. The determined enthalpy data plus the estimated positive entropy of formation values point to the thermodynamic stability of the amorphous ceramics relative to the crystalline phases, but such stabilization diminishes with increasing boron content. In contrast, the higher boron content increases the temperature of Si₃N₄ crystallization despite less favorable energetics for the amorphous phase, implying more favorable energetics for crystallization. Thus the so-called “stability” of SiBCN ceramics in terms of persistence against Si₃N₄ crystallization appears to be controlled by kinetics rather than by thermodynamic stability.     

Crystallization behaviours around the glass transition temperature in an amorphous Fe–Nb–B alloy

Crystallization behaviours around the glass transition temperature in an amorphous Fe₇₀Nb₁₀B₂₀ alloy were investigated by means of transmission electron microscopy. Dense bcc-Fe nanocrystals initially appeared as the primary phase, followed by the dense formation of the (Fe,Nb)₂₃B₆ nanocrystalline phase. The bcc-Fe nanocrystals were formed even by annealing at a temperature that is 38 K lower than the glass transition temperature. A difference of the low temperature behaviours between the present conventional amorphous alloy and a bulk metallic glass was discussed.     

Effect of pulsed laser heating on the magnetic properties of the amorphous alloy Fe76Si13B11

The appearance of magnetic anisotropy has been established by magnetometric methods in the amorphous Fe₇₆Si₁₃B₁₁ ribbon after pulsed laser heating in an external magnetic field. Effects of laser heating on the physical properties of the alloy, in particular, on the Curie temperature and the temperature of crystallization, have been investigated. It is shown that the value of the remanence of the alloy samples after such treatments in a longitudinal magnetic field increases by a factor of more than three. There is suggested a mechanism of the appearance of a uniaxial magnetic anisotropy of amorphous ribbons during the pulsed laser heating in a magnetic field under conditions that do not lead to the crystallization of the alloy.     

Mechanical alloyed Ti–Cu–Ni–Si–B amorphous alloys with significant supercooled liquid region

This study examined the glass formation range of Ti_94–x–yCu_xNi_ySi₄B₂ alloy powders synthesized by mechanical alloying technique. According to the results, after 5–7 h of milling, the mechanically alloyed powders were amorphous at compositions with (x+y) equal to 20–40%. For the compositions with (x+y) larger than 45% or smaller than 10%, the structure of ball-milled powders is a partial amorphous single phase or coexistent partial amorphous and crystalline phases, respectively. The thermal stability of the amorphous powders was also investigated by differential thermal analysis. As the results demonstrated, several amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T_g and T_x, i.e. ΔT(=T_x–T_g), are 52 K for Ti₇₄Ni₂₀Si₄B₂, 74 K for Ti₆₄Ni₃₀Si₄B₂, 58 K for Ti₆₄Cu₂₀Ni₁₀Si₄B₂, and 61 K for Ti₇₄Cu₁₀Ni₁₀Si₄B₂.