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Influence of Cu content on thermodynamic parameters (configurational entropy, Gibbs free energy of mixing, Gibbs free energy of amorphous phase formation), crystallization kinetics, structure and magnetic properties of Fe86-xCuxB14 (x = 0, 0.4, 0.55, 0.7, 1) alloys is investigated. The chemical composition has been optimized using a thermodynamic approach to obtain a minimum of Gibbs free energy of amorphous phase formation (minimum at 0.55 at.% of Cu). By using differential scanning calorimetry method the crystallization kinetics of amorphous melt-spun ribbons was analyzed. It was found that the average activation energy of &alpha, Fe phase crystallization is in the range from 201.8 to 228.74 kJ/mol for studied samples. In order to obtain the lowest power core loss values, the isothermal annealing process was optimized in the temperature range from 260 &deg, C to 400 &deg, C. Materials annealed at optimal temperature had power core losses at 1 T/50 Hz&mdash, 0.13&ndash, 0.25 W/kg, magnetic saturation&mdash, 1.47&ndash, 1.6 T and coercivity&mdash, 9.71&ndash, 13.1 A/m. These samples were characterized by the amorphous structure with small amount of &alpha, Fe nanocrystallites. The studies of complex permeability allowed to determine a minimum of both permeability values at 0.55 at.% of Cu. At the end of this work a correlation between thermodynamic parameters and kinetics, structure and magnetic properties were described.

The effects of Co for Fe substitution on magnetic properties, thermal stability and crystal structure of Fe85.45&minus, xCoxCu0.55B14 (x = 0, 2.5, 5, 7.5, 10) melt spun amorphous alloys were investigated. The Cu content was firstly optimized to minimize the energy of amorphous phase formation by the use of a thermodynamic approach. The formation of crystalline &alpha, Fe type phase has been described using differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. The classical heat treatment process (with heating rate 10 &deg, C/min) in vacuum for wound toroidal cores was optimized in the temperature range from 280 to 430 &deg, C in order to obtain the best magnetic properties (magnetic saturation Bs and coercivity Hc obtained from the B(H) dependencies) at 50 Hz frequency. For optimal heat-treated samples, the complex magnetic permeability in the frequencies 104&ndash, 108 Hz at room temperature was measured. Finally, magnetic core losses were obtained for 1 T/50 Hz and 1.5 T/50 Hz values for samples annealed at T = 310 &deg, C. An analysis of transmission electron microscope images and electron diffraction patterns confirmed that high magnetic parameters are related to the coexistence of the amorphous and nanocrystalline phases.

In the present work, we investigated in detail the thermal/crystallization behavior and magnetic properties of materials with Fe84.5-xCoxNb5B8.5P2 (x = 0, 5, 10, 15 and 20 at.%) composition. The amorphous ribbons were manufactured on a semi-industrial scale by the melt-spinning technique. The subsequent nanocrystallization processes were carried out under different conditions (with/without magnetic field). The comprehensive studies have been carried out using differential scanning calorimetry, X-ray diffractometry, transmission electron microscopy, hysteresis loop analyses, vibrating sample magnetometry and Mössbauer spectroscopy. Moreover, the frequency (up to 300 kHz) dependence of power losses and permeability at a magnetic induction up to 0.9 T was investigated. On the basis of some of the results obtained, we calculated the values of the activation energies and the induced magnetic anisotropies. The X-ray diffraction results confirm the surface crystallization effect previously observed for phosphorous-containing alloys. The in situ microscopic observations of crystallization describe this process in detail in accordance with the calorimetry results. Furthermore, the effect of Co content on the phase composition and the influence of annealing in an external magnetic field on magnetic properties, including the orientation of the magnetic spins, have been studied using various magnetic techniques. Finally, nanocrystalline Fe64.5Co20Nb5B8.5P2 cores were prepared after transverse thermo-magnetic heat treatment and installed in industrially available portable heating equipment.

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe72−xNi8Nb4CuxSi2B14 alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔGamorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔGmix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures Tx1onset and Tx1 of the alpha-iron phase together with the activation energy Ea for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 104 Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).

The magnetic properties correlated with crystal structure of soft magnetic ribbons of the nominal composition Fe81.3−xCoxMo0.2Cu0.5Si4B14 synthesized by a melt spinning technique are reported. The crystallization process was monitored by differential scanning calorimetry (DSC) that allows identification of the primary crystallization temperature. Thereafter crystallization process is being optimized by changing heat treatment parameters in order to get best possible magnetic properties. The resulting crystal structure of the properly annealed cores has been investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) methods. It was found that the structure consists of α-Fe(Co,Si) nanograins with the mean size of 20 nm. Additionally, the magnetic saturation and coercivity from the measured hysteresis loops of studied samples have been determined. The microstructure was further correlated with Co content and nanograins size in order to discuss its impact on magnetic properties.

In this work, a detailed microstructural investigation of as-melt-spun and heat-treated Fe67Co20B13 ribbons was performed. The as-melt-spun ribbon was predominantly amorphous at room temperature. Subsequent heating demonstrated an amorphous to crystalline &alpha, (Fe,Co) phase transition at 403 &deg, C. In situ transmission electron microscopy observations, carried out at the temperature range of 25&ndash, 500 &deg, C and with the heating rate of 200 &deg, C/min, showed that the first crystallized nuclei appeared at a temperature close to 370 &deg, C. With a further increase of temperature, the volume of &alpha, (Fe,Co) crystallites considerably increased. Moreover, the results showed that a heating rate of 200 &deg, C/min provides for a fine and homogenous microstructure with the &alpha, (Fe,Co) crystallites size three times smaller than when the ribbon is heated at 20 &deg, C/min. The next step of this research concerned the influence of both the annealing time and temperature on the microstructure and coercivity of the ribbons. It was shown that annealing at 485 &deg, C for a shorter time (2 s) led to materials with homogenous distribution of &alpha, (Fe,Co) crystallites with a mean size of 30 nm dispersed in the residual amorphous matrix. This was reflected in the coercivity (20.5 A/m), which significantly depended on the volume fraction of crystallites, their size, and distribution.

This paper focuses on the phenomenon of the magnetic flux density dispersion Bd on the gaps of the Fe73.5Cu1Nb3Si13.5B9 multi-gap nanocrystalline block core. Present state-of-the-art shows, that there is no comprehensive knowledge about the value of the magnetic flux density dispersion Bd on the gaps of nanocrystalline block core and the possibilities of its minimisation. The magnetic flux density dispersion Bd is the source of local eddy currents, which are the cause of increase of power loss and temperature in the chokes’ core. To discuss the effect of gap width and the method of its filling on the power losses in the core, the comparison between inserts of Teflon and magnetic mat composed of 70% Fe53.9Co29.1B13Nb1Si2Cu1 powder with a fraction of 20–36 µm and 30% Ultimeg epoxy resin 2004L was performed.

In this paper the influence of copper addition on the formation of the amorphous phase and the nanocrystallization process of Fe79.8−xCo2CuxMo0.2Si4B14 (x = 0, 0.25, 0.5, 0.75, 1, 1.5, 2) ribbons was described. The formation of crystalline phases was described using differential scanning calorimetry, X-ray diffractometry, Mossbauer spectroscopy and transmission electron microscopy. It was confirmed that the addition of copper decreases the glass forming ability, while facilitating the process of nanocrystallization. The analysis of the Avrami exponent allowed to state, that for fully amorphous alloys the crystallization of the α-Fe phase is associated with diffusion-controlled growth with decreasing nucleation rate and the Fe2B phase with interface controlled growth with increasing nucleation rate. Additionally, with increasing copper addition onset temperature of crystallization of α-Fe phase shifts to lower values, whereas for second, Fe2B phase, these changes are not so visible. Optimization of the annealing process of toroidal cores made from amorphous ribbons with different copper content allowed to obtain nanocrystalline, soft magnetic materials characterized by low coercivity ~9 A/m and high saturation induction of about 1.6 T. Analysis of transmission electron microscope images and electron diffraction confirmed that high magnetic parameters are related to the coexistence of the amorphous and nanocrystalline phases, which was confirmed also by Mossbauer spectroscopy.

In this paper, crystallization behavior of BCC iron phase in two Finemet-type ribbons with different cobalt content has been studied. Studied ribbons consist of 58.8 and 65 M percents of cobalt (Fe 14.7 Co 58.8 Cu 1 Nb 3 Si 13.5 B 9 and Fe 13.8 Co 65 Cu 0.6 Nb 2.6 Si 9 B 9 ). Identification of crystallized phase has been performed by means of X-ray diffraction and Neutron Diffraction. Kinetics parameters of this process have been obtained through the Differential Scanning Calorimetry measurements with different heating rates. The main aim of this work was to check the correlation between the kinetic parameters such as activation energy, rate constant and crystallization difficulty and the cobalt content in the studied ribbons. It was shown that the slight increase of cobalt amount leads to the significant change of activation energy from 300 to 250 kJ/mol.

This paper presents results of a research work related to the development of the production technology of the amorphous cores designed for application in permanent magnet brushless direct current (PMBLDC) motors. The cores were made from the Metglas 2605 SA1 amorphous ribbon, from which rings of the specific external and internal diameters were cut using a laser technique. Next, the rings were stacked up so as to form a core of a required height, subjected later to the consolidation by pressing, followed by an appropriate heat treatment. Finally, the cores were coated with an epoxy resin to protect them against delamination and used as stators in a prototype high-speed electric motor, 1 kW in rated power and 70 000 rpm in a rotary speed. The motor incorporating these amorphous cores was subjected to the performance tests, which confirmed their proper operation and satisfactory mechanical characteristics and efficiency. It was found that power losses in the stators from the amorphous material were considerably smaller than those in the conventional stators from the silicon steel, and they did not exceed 7 W. Therefore, an application of the amorphous soft magnetic materials in the high-speed PMBLDC motors may contribute to eliminating the need of using additional cooling systems in these motors.