Diagnosis of the structural state of bulk nano- and submicrocrystalline magnetically soft materials

Different structural states, namely microcrystalline, submicrocrystalline, nanocrystalline (each with a different set of grain sizes) and amorphous ones, in magnetically soft materials intended for fabricating sensitive elements in high-tech equipment are considered. The effects of the structural state of Fe₅Co₇₀Si₁₅B₁₀, Fe₆₀Co₂₀Si₅B₁₅, Co_81.5Mo_9.5Zr₉, and Fe_{73.5 − x} Co _x Cu1Nb₃Si_13.5B ₉ (x = 0, 10, 20, 30 at.%) amorphous alloys on their magnetic characteristics in different nanocrystallization conditions are analyzed. The correlation of the peculiarities of the fine structure and the grain sizes in the alloys under study with their magnetic parameters and informative parameters of the Barkhausen effect is shown.     

An isotropic magnetic-field transducer based on the giant magnetic impedance effect

A comparative analysis of the giant magnetoimpedance effect and the results of a mathe- matic simulation are presented. This simulation was used for optimizing the topology of a wide-angle magnetic transducer equipped with a sensitive element that consists of two crossed Fe₃Co₆₇Cr₃Si₁₅B₁₂ amorphous ribbons that form different angles between them.     

Effect of Plastic Deformation on the Magnetic Properties of Rapid-Quenched Cobalt-Based Metal Wires

The effect of plastic deformation on the magnetic parameters of rapid-quenched nanostructured Co₆₆Fe₄Nb_2.5Si_12.5B₁₅ wires was established for the first time, as well as their sensitivity to tensile stresses. Plastic deformation changes magnetic anisotropy induced by the rapid quenching of cobalt-based metal wires, and, as a consequence, determines their magnetic parameters. Remanence is a characteristic that is most sensitive to plastic deformation. A conclusion is drawn that plastic deformation of wires leads to an increase in magnetostriction constant.     

Pecularities of nanocrystal formation in rapidly quenched (FeCo)MoCuB amorphous alloys

The effect of the substitution of Fe by Co on the enhancement of glass‐forming ability limits and subsequent nanocrystallization was studied in a rapidly quenched amorphous system (Fe_xCo_y)₇₉Mo₈Cu₁B₁₂ for y/x ranging from 0 to 1. The effect of Cu on nanocrystallization was investigated by comparison with Cu‐free amorphous Fe₈₀Mo₈B₁₂. Systems partially crystallized at the surface layer were prepared for y/x = 0 using different quenching conditions. The effect of heat treatment of master alloys used for ribbon casting was also assessed. The microstructure and surface/bulk crystallization effects were analysed using transmission electron microscopy and electron and X‐ray diffraction in relation to the expected enhancement of high‐temperature soft magnetic properties, drastically reduced grain sizes (～5 nm) and Co content. Unusual surface phenomena were observed, indicating the origin of possible nucleation sites for preferential crystallization in samples with low Co content.     

Transmission electron microscopy study of crystallization in Fe-Si–B–Cr–C amorphous alloy

The crystallization behaviour of Fe₇₂Si_9.1B_14.8Cr_2.2C_1.9 alloy was studied. Three forms of the examined alloy were studied: water‐atomized powder, as‐spun ribbon and fully crystallized ribbon. Transmission electron microscopy studies of the examined alloy in the form of powder revealed partial crystallization of Fe₂B. The as‐spun ribbon was found to be fully amorphous, and no evidence of any crystalline phases was detected. Formation of metastable phases in the fully devitrificated ribbon was observed. The examined alloy, heated to above its crystallization temperature, consisted of α‐Fe₃(Si), Fe₂₃(C,B)₆, Fe₃B and Fe₂B crystalline phases.     

Heating effect of electron beam bombardment

The effect of heat in a target bombarded by an electron beam with certain energy was studied. A physical model was proposed according to the pattern of electron scattering, separately for a bulk specimen in electron probe microanalysis and a thin-film specimen in transmission electron microscopy. Then formulas of rising temperature were deduced for these two events. The results of a melting experiment of Bi-coating on glass and crystallizing of amorphous Fe₇₈Si₁₂B₁₀ film under electron beam bombardment confirmed the proposed model.     

Three-Component Portable Magnetometer Equipped with Ferromagnetic Transducers Built around Bistable Amorphous Microwire Cores

The paper is dedicated to designing small portable magnetometers with autonomous power supplies for measuring magnetic fields in the range of 0.2–200 A/m. Ferromagnetic transducers are built around bistable amorphous microscopic wires 10–20 mm in diameter from the alloy (Co₉₂Fe₈)₆₃Ni₁₀B₁₆Si₁₁ in glass insulation. The properties of these cores and characteristics of transducers built around these cores have been studied; regimes of magnetization and dimensions of the cores have been selected. The IGMP-3B three-component magnetometer incorporating a one-chip microcomputer for medical and biological research is described in detail.     

Magnetoimpedance Properties of Amorphous CoFeSiB Wires in a Wide Frequency Range: Focus on Sensor Applications

The magnetic properties and specific features of giant magnetoimpedance in rapidquenched amorphous wires of composition (Co_0.94 Fe_0.06 )_72.5Si_12.5 B₁₅ are investigated. The working interval and sensitivity to changes in an external quasistatic magnetic field have been calculated for the alternating current frequencies from 1 MHz to 1 GHz. Parameters that are optimum for using such wires as sensitive elements in magnetic field sensors have been calculated, and the probe sensitivity to the external magnetic field has been determined. A sensor prototype was designed that, when tested, confirmed the possibility of using the giant magnetoimpedance in sensors based on amorphous CoFeSiB wires for flaw detection.     

Local structure studies of Fe-Nb-B metallic glasses using electron diffraction

Local atomic structures in Fe₈₄Nb₇B₉ and Fe₇₀Nb₁₀B₂₀ amorphous alloys were examined by means of electron diffraction with the help of computer calculation. Electron diffraction patterns were taken by using energy‐filtered transmission electron microscopy (TEM) to eliminate inelastic scattering. We constructed structure models with 5000 atoms fitting to experimental interference functions. Voronoi polyhedral analyses were performed for the obtained final structure models. Local atomic structures of the alloys were closely related to those of the crystalline phases that appeared on annealing. A difference of stability of two amorphous phases was discussed on the basis of structure models.     

Structure and Barkhausen effect parameters of amorphous alloys after various heat treatments

The influence of the structural state of amorphous magnetically soft Fe₆₀Co₂₀Si₅B₁₅ and Co_81.5Mo_9.5Zr₉ alloys on the magnetic properties and informative parameters of the Barkhausen effect is studied. The structure of amorphous ribbons is investigated using transmission electron microscopy. The results obtained allow the conclusion that the study of the Barkhausen effect provides magnetic and structural information about an alloy. The parameters of the Barkhausen effect are shown to correlate with features of the fine structure of the investigated devitrifying amorphous alloys.Translated from Defektoskopiya, Vol. 40, No. 9, 2004, pp. 63–68.Original Russian Text Copyright © 2004 by Noskova, Shulika, Lavrentev, Potapov, Korzunin.     

Dry Sliding Tribological Properties of Fe-Based Bulk Metallic Glass

The dry or unlubricated sliding friction and wear properties of as-cast and annealed BMG (bulk metallic glass) with nominal composition of Fe_66.7C_7.0Si_3.3B_5.5P_8.7Cr_2.3Al_2.0Mo_4.5 against Si₃N₄ ceramic ball was studied, along with a conventional material, using a ball-on-disk tribotester at room temperature. The overall average coefficient of friction value of the as-cast BMG was in the range of 0.26?C0.42, which was better than the conventional material SUJ2 (0.36?C0.46) and comparable with SUS304 (0.31?C0.40). The wear mechanism of the Fe-based BMG changed with wear condition. The wear rate increased with increasing load. The hardness of the BMG increased during annealing, however, the wear resistance did not increase proportionally.     

Magnetic characterization of microscopic particles by MO-SNOM

This paper reports on the development of a magneto‐optical scanning near‐field optical microscope and the experimental near‐field study of the domain structure for a model magnetic particle of 16 × 16 µm² of a Co_70.4Fe_4.6Si₁₅B₁₀ amorphous thin film, deposited on a silicon substrate. We present the topographic, optical and magneto‐optical differential susceptibility (MODS) images of the particle. Imaging by using the local MODS reveals the domain structure. These images are also used for positioning the tip in order to acquire local hysteresis loops, with submicrometre spatial resolution.     

Effect of Flash Temperature on Tribological Properties of Bulk Metallic Glasses

The tribological properties of Cu-based and Zr-based bulk metallic glasses (BMGs) sliding against Si₃N₄ under dry and water lubrication were studied on a pin-on-disc tribometer. The wear mechanisms of bulk metallic glasses were investigated based on the calculated flash temperature. The friction coefficients if fully amorphous alloy are about 0.7, while those of BMGs with nanocrytalline are a little higher. The wear rates of Cu-based BMG (V101) are about one order of magnitude lower than those of Zr-based BMG (Vit1) under dry friction, even two orders of magnitude lower under water lubrication. The wear resistance of bulk metallic glasses was influenced by the flash temperature. The calculated flash temperature (3,337 K) on the friction surface of Zr-based amorphous alloy exceeds its glass transition temperature, even its melting temperature. The high flash temperature leads to glass transition accompanied with viscous flow and material transfer, which is responsible for the poor wear resistance of Zr-based BMGs.     

Dry-sliding Tribological Properties of Nano-Eutectic Fe<Subscript>83</Subscript>B<Subscript>17</Subscript> Alloy

This paper reports the tribological performance of the nano-eutectic Fe₈₃B₁₇ alloy under dry sliding against Si₃N₄ ceramic ball in ambient environment with varying applied loads and sliding speeds. Worn surfaces of the nano-eutectic Fe₈₃B₁₇ alloy were examined with a scanning electron microscope (SEM) and an X-ray energy dispersive spectroscope (EDS). The wear debris of the samples were also analyzed by X-ray diffractometer (XRD). The wear rate of the nano-eutectic Fe₈₃B₁₇ alloy was of the magnitude of 10⁻⁴ mm³/m, which was lower than that of the coarse grained Fe₈₃B₁₇ alloy. The friction coefficient of the nano-eutectic Fe₈₃B₁₇ alloy was almost the same as that of the coarse grained Fe₈₃B₁₇ alloy. The Fe₂SiO₄ oxide layer was formed on the worn surface of the nano-eutectic Fe₈₃B₁₇ alloy. However, on the worn surface of the coarse grained Fe₈₃B₁₇ alloy was found only a little Fe₂SiO₄. These results demonstrated that the nanostructure improved the wear resistance of the Fe₈₃B₁₇ alloy, but did not significantly affect the friction coefficient. The wear mechanism of the nano-eutectic Fe₈₃B₁₇ alloy was delamination abrasion mainly.     

Transmission electron microscopy studies of plasma-etched silicon nitride/silicon carbide composites

Transmission electron microscopy has been used to isolate and examine the intergranular glass phase in hot-pressed silicon nitride/silicon carbide composites. Previously there have been difficulties in locating a suitable region for studies of this nature because the interfering nitride and carbide grains inhibit isolation of the glass for examination. Radiofrequency plasma etching of thinned sections of 6 wt% Y₂O₃, 2 wt% A1₂O₃ in Si₃N₄ containing 30 vol% of SiC proved to be fruitful in isolating the glass phase. A mixture of CF₄ and O₂ quantitatively remove the acicular nitride phase without any evidence of attack on either the glass or carbide. Composites containing ceria and magnesia as substitutes for yttria behave similarly. This indicates that glasses containing minor to major concentrations of elements forming stable fluorides inhibit the attack of fluoride ions on silica glasses containing these elements.     

High resolution transmission electron microscopy of Sm-Co based permanent magnets

Interface microstructures between rhombohedral Sm₂Co₁₇ and hexagonal SmCo₅ phases in a sintered permanent magnet of Sm(Co_0.675Fe_0.175Ni0.05Cu_0.1)₇ have been investigated by edge-on observations with the many-beam imaging technique. In the specimen annealed at 800°C for 4 h which shows a maximum magnetic coercivity, the interface boundaries were coherent accompanying the lattice distortion; the habit planes were parallel to the {101}_2:17 and {111}_1:5 planes with the orientation relationship of (0001)_2:17//(0001)_1:5 and [1010]_2:17//[1120]_1:5. In the specimen annealed for 150 h which shows a lower coercivity, the interface boundaries were characterized with regular alignments of interfacial edge dislocations. The observed interface structures were discussed in connection with the change in magnetic properties.     

Theoretical analysis of novel weak current sensor using FeCuNbSiB single nanocrystalline toroidal core and double-winding

An Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline toroidal core made by isothermal furnace annealing shows good thermal stability of magnetic properties and excellent soft magnetic properties due to the full release of the internal stresses of the core during the annealing process. Based on the feature of the magnetic core, a novel non-contact type weak current sensor adopting single nanocrystalline core and double-winding excited by multivibrator bridge is proposed. The measuring principles for static current are given in theory by an established mathematical model of the sensor. The theory is in good agreement with the experimental results and it indicated clearly the key factors affecting performance parameters for the sensor. The multivibrator bridge output signal was analyzed by Fourier transform. Furthermore, according to the theoretical results, the method to design the signal conditioning circuit was introduced. __________ Translated from Chinese Journal of Scientific Instrument, 2005, 26(12) (in Chinese)     

Electron-beam-induced fabrication of metal-containing nanostructures

An experimental system based on a transmission electron microscope JEM-100CX has been developed for electron beam-induced chemical vapor deposition. Direct electron beam-induced growth of nanometer-wide self-supporting rods has been performed inside the microscope operating in scanning mode by decomposition of carbonyls of chromium Cr(CO)₆, tungsten W(CO)₆, and rhenium Re₂(CO)₁₀. In situ phase and structure transformations under annealing inside the microscope column were studied. Nanoscale rods and strips grown from rhenium carbonyl are of special interest because, after annealing, they consist of a single pure rhenium phase. The described method of metallic nanoelements fabrication enables us to produce highly conductive nanowires and tips for application in nanoelectronics, emission electronics, and scanning tunneling microscopy.     

Nanobeam diffraction fluctuation electron microscopy technique for structural characterization of disordered materials—Application to Al88−xY7Fe5Tix metallic glasses

A fundamental experimental challenge in understanding the physical properties of non-crystalline (i.e., highly disordered) materials is that of fully characterizing the structural order that is present. Medium-range order is particularly difficult to characterize. Fluctuation electron microscopy (FEM) is a relatively new spatially resolved, diffraction technique that measures statistical fluctuations in the scattering of electrons arising from nanometer-scale ordered regions in a sample. The scattering fluctuations can be measured from dark-field (DF) images (the most common approach) or from a series of nanobeam diffraction (NBD) patterns. Here, the effectiveness of the NBD–FEM method for measuring atomic structure in disordered materials is evaluated. In particular, we show that the NBD–FEM statistical measures of fluctuations in diffraction intensity depend strongly on several instrumental parameters; measurement and analysis methodologies that constrain these parameters to minimize associated artifacts are presented. For illustration, the structure of the Al₈₈Y₇Fe₅ metallic glass is examined. It has been shown previously that the substitution of 0.5 at% Ti for the Al in this alloy significantly increases the glass forming ability. We provide NBD–FEM evidence indicating that the atomic structure of the glass is modified upon microalloying, in agreement with earlier extended X-ray absorption fine structure and high-energy X-ray diffraction studies.     

Tribological Performance of Fe<Subscript>67</Subscript>B<Subscript>33</Subscript> Alloy Prepared by a Self-Propagating High-Temperature Synthesis Technique

A bulk Fe₆₇B₃₃ alloy was prepared by a self-propagating high-temperature synthesis technique that is convenient, low in cost, and capable of being scaled up for tailoring the bulk materials. The Fe₆₇B₃₃ alloy is composed of dendrites with the t-Fe₂B phase and eutectic matrix with the α-Fe and t-Fe₂B phases. The content of the dendrite t-Fe₂B is above 80 vol.%. The compressive fractured strength and Vickers microhardness are 3400 MPa and 12.4 GPa, respectively. The tribological performance of the Fe₆₇B₃₃ alloy is investigated under dry sliding and water lubricant against Si₃N₄ ceramic ball. The wear rates of the Fe₆₇B₃₃ alloy are of the magnitude of 10⁻⁵ to 10⁻⁴ mm³/m under water lubricant. It is lower than that of the Fe₆₇B₃₃ alloy under dry sliding (10⁻⁴ mm³/m). But both the friction coefficients are almost identical. Oxide layers form in both environments via different tribochemical mechanisms, which led to significant differences in wear behavior.