The effect of various heat treatments on the magnetic properties and microstructure of magnets manufactured using low-oxygen technology from the (Nd,Pr)31.9Febal.(Co,Cu,Al,Ga)1.7B0.8 (wt

Sm(Fe,Co,Ti)12-based alloys with low contents of rare-earth elements are promising materials for manufactoring high-energy permanent magnets. The (Sm,Zr)(Fe,Co)10.3Ti0.7 alloy has been produced by strip casting with low quenching rates. The structure and magnetic properties of the alloy were studied by scanning electron microscopy, as well as X-ray and thermomagnetic analysis. The initial inhomogeneous alloy was subjected to solid-solution treatment at 1150°С. The alloy retained a high-anisotropy state typical of the Sm(Fe,Co,Ti)12 phase.

This paper presents methods and approaches that can be used for production of Sm-Co-Fe-Cu-Zr permanent magnets with working temperatures of up to 550 °C. It is shown that the content of Sm, Cu, and Fe significantly affects the coercivity (Hc) value at high operating temperatures. A decrease in the content of Fe, which replaces Co, and an increase in the content of Sm in Sm-Co-Fe-Cu-Zr alloys lead to a decrease in Hc value at room temperature, but significantly increase Hc at temperatures of about 500 °C. Increasing the Cu concentration enhances the Hc values at all operating temperatures. From analysis of the dependence of temperature coefficients of the coercivity on the concentrations of various constituent elements in this alloy, the optimum chemical composition that qualifies for high-temperature permanent magnet (HTPM) application were determined. 3D atom probe tomography analysis shows that the nanostructure of the HTPM is characterized by the formation of Sm2(Co,Fe)17 (2:17) cells relatively smaller in size along with the slightly thickened Sm(Co,Cu)5 (1:5) boundary phase compared to those of the high-energy permanent magnet compositions. An inhomogeneous distribution of Cu was also noticed in the 1:5 phase. At the boundary between 1:5 and 2:17 phases, an interface with lowered anisotropy constants has developed, which could be the reason for the observed high coercivity values.

The structure and magnetic state of Fe100-xNix alloys (x & LE; 20) quenched from 1100 degrees C have been studied by means of Mo & BULL;ssbauer spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetization measurements. The concentration dependences of the lattice parameter of bcc structure and of spontaneous magnetic moment were measured at room temperature. From the analysis of Mo & BULL;ssbauer spectra, concentration dependences of average hyperfine parameters have been determined. Both isomer shift and hyperfine field increase with increasing Ni content in the alloy. Fitting of the spectra with a set of subspectra gives grounds to conclude that the structure of quenched Fe-Ni samples represents a system of bcc regions of varying content, which is formed as a result of separation of the alloy composition. This conclusion is supported by the data of transmission electron microscopy.

Differential scanning calorimetry (DSC) has been used to study the martensitic transformation in Fe100 – xNix alloys containing 3 to 25 at

—The granulometric composition of Nd–Fe–B powders has been studied in detail after vibratory milling for various times both without and with the addition of siloxane. Sintered magnets were produced by the powder metallurgy method that excluded the pressing of powders. Correlations between the particle size distribution in the initial powders, microstructure of sintered magnets, and their magnetic hysteresis properties have been established. The difference in methods for estimating the size of powder particles by two methods is demonstrated. It is shown that the size distributions of powder particles and magnet grains are bimodal and are described by a superposition of two lognormal distributions.

Sm(Fe,Co,Ti) 12 -based alloys with low contents of rare-earth elements are promising materials for manufactoring high-energy permanent magnets. The (Sm,Zr)(Fe,Co) 10.3 Ti 0.7 alloy has been produced by strip casting with low quenching rates. The structure and magnetic properties of the alloy were studied by scanning electron microscopy, as well as X-ray and thermomagnetic analysis. The initial inhomogeneous alloy was subjected to solid-solution treatment at 1150°С. The alloy retained a high-anisotropy state typical of the Sm(Fe,Co,Ti) 12 phase.

Hard magnetic Nd-(Fe,Co)-B powders prepared by ball milling from melt-spun ribbons are investigated. The effect of doping by 1 wt% Cu on magnetic properties is shown. Furthermore, the thermal stability of the Nd-(Fe,Co)-B powder with Cu doping is studied. The structure and morphology of the powders are observed. The contribution of the Nd2(Fe, Co)14B and α-(Fe,Co) phases to the magnetic properties is determined using the temperature dependences of AC susceptibility in the range of 17 to 847 °C. The reversal magnetization and energy product of the Nd-(Fe,Co)-B powders with and without Cu doping are investigated and discussed.

The phase boundaries of martensitic transformation in Fe-Ni alloys with the composition in the range of 0 - 20 Ni at.% have been determined by X-ray diffraction, differential scanning calorimetry, measurements of magnetic susceptibility and magnetization. It is shown that the alloys quenched from 1100 degrees C at room temperature are in a single-phase state of alpha 2 martensite, except for Fe 80 Ni 20 , which additionally contains a small amount of gamma phase. It is found that in the Fe 97 Ni 3 alloy, the temperature-induced magnetic and structural transformations occur independently of each other. At a nickel concentration from 5 to 20%, the structural alpha -> gamma transformation upon heating is accompanied by the magnetic transition from the ferromagnetic to the paramagnetic phase, which is a first-order phase transition. When cooling the alloys with x <= 10, the paramagnet - ferromagnet transition starts several degrees ahead of the structural gamma -> alpha transformation. The lattice volume changes and thermal effects upon the martensitic transformation are determined. It is shown that the phase diagram including metastable martensitic transformation can be used together with the equilibrium phase diagram to determine the structural states of the Fe-Ni system.

The current research paper analyzed the structure and magnetic properties of bulk Sm2.40Fe17 and Strip-Cast (SC) Sm2.08Fe17 alloys. Strip Cast alloy was found to have low volume fraction of the secondary phases (SmFe3 and ?-Fe phase) with finer grain size (2?3 times lower) in comparison with bulk alloy. Owing to such microstructural features, the Strip Cast alloy has the advantages of low nitrogenation temperature, reduced time duration for nitrogenation and effective nitrogenation of even coarser particles which tend to result in better magnetic properties compared to bulk alloy. The additional ball milling of the SC Sm2.08Fe17N3 powder in toluene, after adding 0.5% Zn stearate, resulted in achieving a coercivity of 9.3 kOe. The angular dependence of coercivity measurements indicates that the dominant coercivity mechanism is the nucleation of reverse domains at defects for coarser particles and non-uniform rotation of magnetic moments for the sub-micron level singledomain particles.

The phase transformation and magnetic hysteresis properties of melt-spun Fe41Pd41B8Si6P4 ribbons subjected to the annealing at temperatures of 500–550 °C were studied after holding for 0.1–60.0 h by transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermomagnetic analysis. The additions of P, B and Si to the FePd alloy allowed us to achieve the coercivity of 124 kA·m−1, which is 2.6 times higher than that of the melt-spun ribbons of the binary equiatomic FePd alloy. The high-coercivity Fe41Pd41B8Si6P4 alloy is nanocrystalline and is composed of the ordered L10-phase grains approximately 40 nm in size and inclusions of the Fe2(P, B) and Pd2(Si, B) phases. The coercivity kinetics is controlled by the phase transformation which can be divided into three stages: transformation from the bcc structure to nanosized regions of the fcc and Fe2P phases; transformation from the fcc to L10 nanosized regions with somewhat different degrees of tetragonality and their ordering; and extensive growth of the weight fraction of L10 phase from the fcc nanosized regions. P and B atoms occupy interstitial sites in the iron plane of L10 lattice, thus decreasing its Curie temperature (TC).

The structure and temperature stability of high-temperature permanent magnets Sm(Co0.796−xFe0.177CuxZr0.027)6.63 (x = 0.117 and 0.130) were studied using x-ray diffraction analysis, thermomagnetic analysis, and scanning and transmission electron microscopy. The magnets have a nanocrystalline cellular structure composed of the R2:17 cell phase, 1:5 boundary phase (27–28% by volume), and Z-phase platelets. The 1:5 phase is formed in the course of isothermal annealing at 850°C and exists in the entire temperature range from 850°C to 400°C. The Curie temperature of the R2:17 and 1:5 phases is approximately 815°C and 580°C, respectively. The magnets have the following hysteresis properties at room temperature: Br = 890–920 mT, JHc = 2.4–2.6 MA/m, BHc = 629–676 kA/m, and (BH)m = 143–159 kJ/m3. In the temperature range of 20–500°C, the temperature coefficients of Br and JHc of the magnets (x = 0.117 and 0.130) do not exceed |− 0.070| and |− 0.172|%/°C, respectively.

Elastomers such as hydrogenated nitrile butadiene rubber (HNBR) are known to have inferior dimensional stability upon temperature changes compared to metallic materials. This can result in thermal contraction mismatches between metal and elastomer sealing components during cooling, possibly leading to seal leakage. It has also been reported that MnCoGe alloys have been developed that undergo a phase change which results in a volumetric expansion during cooling through the phase change temperature region. This article reports the effect of adding MnCoGe-alloy particles into a HNBR elastomer with the purpose using the thermal expansion of the alloy particles to counteract the thermal contraction of this elastomer during cooling. The composite material is produced using a combination of solvent casting and traditional shear mixing in a two-roll mill followed by compression moulding. With the MnCoGe volume fraction of ≈ 17%, a considerable suppression of the thermal expansion coefficient of the base elastomer was achieved, going from 185×10−6 °C−1 to nearly zero in the range of temperatures from -5 °C to +15 °C. The positive effect of the filler on the thermal expansivity was apparent in wider temperature range of -20 to +40 °C.

Sm – Co – Fe – Cu – Zr sintered high-temperature permanent magnets (HTPM) produced by the “POZ-Progress” Company are studied. The microstructure of the magnets is determined by scanning electron microscopy and x-ray diffraction analysis. The Curie temperature and the magnetic properties of the materials are described. The hysteresis loops of the magnets are measured in strong pulsed fields at room and elevated temperatures. The temperature dependence of the magnetic susceptibility is plotted using the method of compensated transformer in a variable magnetic field.

The origin of coercivity of the sintered Sm(Co0.78Fe0.10Cu0.10Zr0.02)(7) magnets has been studied in the course of step annealing by X-ray diffraction and magnetic measurements. The Cu redistribution in the Sm(Co, Cu)(5) boundary phase of the cellular structure modifies the domain-wall energy and increases the coercivity upon step cooling. Interphase stresses are considered to be the main reason for copper redistribution upon slow cooling. It is shown that the coercivity abruptly increases in the course of annealing at a temperature of 500 degrees C, which is close to the Curie temperature of the Sm(Co, Cu)(5) phase. The effect may be caused by an increase in the interphase stresses at the boundary of the coherent 1: 5 and 2: 17 phases in the course of the annealing at the temperature close to the Curie temperature of the 1: 5 phase. The accelerated Cu diffusion into the boundary compensates these stresses. The new scheme of the Cu redistribution over the cell-boundary phase is suggested. Contrary to the known schemes, it assumes that Cu is localized in the 1: 5 phase near the interface between the phases, rather than in the center of the 1: 5 phase.

The non-stoichiometric intermetallic compounds RENi2Mnx (RE = rare earth) with the cubic MgCu2-type structure display a large variety of magnetic properties which is due to a complex interplay between the degrees of freedom of the 3d and 4f electrons and their interactions. We performed a comprehensive study of the electrical resistivity, magnetic properties and the electronic structure of ErNi2Mnx (x =0, 0.25, 0.5, 0.75, 1, 1.25) compounds by employing a suitable set of complementary experimental approaches. We find an increase in electrical resistance compared to ErNi2 upon Mn doping, the residual resistivity ratio decreases with increasing manganese content. The Curie temperature exhibits a sharp increase to around 50 K for Mn concentrations x ≥ 0.5, whereas the saturation magnetization decreases with growing Mn content x ≥ 0.5. Valence band X-ray photoelectron spectroscopy reveals an increasing intensity of Mn 3d states near Fermi energy in dependence of Mn concentration and Curie temperature. Resonant photoelectron spectroscopy of ErNi2Mn0.75 reveals that the photoemission decay channels dominate the valence band spectra across the Er N5 and Mn L3 X-ray absorption maxima, whereas the L3VV Auger dictates the resonant valence band spectra close to and at the Ni L3 X-ray absorption edge.

Crystal structure and magnetic and thermomagnetic properties of the (TmxPr1-x)(2)Fe-17 system have been studied. The alloys with x = 0-0.4 and x = 0.8-1 crystallize into a rhombohedral structure of the Th2Zn17-type and into a hexagonal structure of the Th2Ni17-type, respectively. Both these structures coexist in the concentration range x = 0.5-0.75. The compounds with 0 < x < 0.6 are ferrimagnets, while in the compounds with x = 0.6-1, an additional high-temperature helimagnetic state appears. The lattice parameters, spontaneous magnetization, and the peak entropy change -Delta S-M of the (TmxPr1-x)(2)Fe-17 system decrease with increasing Tm content. The temperatures of helimagnetic ordering and ferrimagnet-to-helimagnet transition decrease non-monotonically as Tm content increases, with the minimum values being for the composition with x = 0.8. Microdeformations in the alloys with x = 0.5-0.9 have been detected by means of neutron diffraction. (C) 2017 Elsevier B.V. All rights reserved.

It is demonstrated how the high degree of powder alignment in PLP magnets can be achieved by loading the powder into a container placed in a magnetic field of moderate strength. The strip-cast alloy with a composition of 30.00 Nd, 1.95 Dy, 66.42 Fe, 0.99 B, 0.54 Co, 0.1 Ga (wt%) was subjected to hydrogen decrepitation and then milled in a vibratory mill in toluene to an average particle size of 2.9µm determined by the FSSS method. The powder was compacted in the magnetic field of 0.2 – 1.2T to the filling density 2.6 – 3.2×103kg/m3. It is shown that loading the powder into a container placed in a magnetic field enhances the degree of powder alignment in sintered Nd-Fe-B magnets produced from non-pressed powder. At the filling density less than 3.2×103kg/m3, the density of magnets is high but insufficient, because of the formation of magnetostatic chains of particles, which impedes the powder compaction. The simulation by the discrete-element method qualitatively proves that the magnetostatic interaction of the chains of particles that are formed in the course of loading in the magnetic field stimulates a decrease in the density of the sintered magnets and its non-uniform distribution over the sample. As a result of the optimization of the parameters of the alignment and compaction of the powder loaded in a magnetic field, PLP magnets with Br ≥1.34T, Нc ≥950kA/m, (BH)max ≥340kJ/m3, and the degree of alignment exceeding 96% were produced.

The influence of the nanocrystalline state of Fe and Fe75Si25 particles and their electrical resistance on the microwave properties of composite materials that contain these particles has been investigated experimentally. The main factors that determine changes in the frequency dispersion of the permeability are the skin effect and the decrease in the internal field of anisotropy of the particles. In the case of Fe particles, the role of skin effect of prevails.

Исследуются магнитные свойства и сверхтонкие взаимодействия в карбиде Fe7C3, полученном путем механосинтеза (МС) -Fe в толуоле. Установлено, что граница температурной устойчивости МС-карбида не превышает 775 К. Температура Кюри синтезированной фазы изменяется от 509 до 525 К. Данные мессбауэровских экспериментов (57Fe) показывают, что элементарная ячейка Fe7C3 содержит 32 атома Fe, локализованные по пяти кристаллографическим позициям с мультиплетностью: 4 : 8 : 8 : 8 : 4. Для каждого неэквивалентного положения рассчитаны параметры сверхтонкого взаимодействия. Особенности распада при T 775 К позволяют предполжить, что наиболее вероятной последовательностью фазовых переходов в МС-карбидах Fe–C является последовательность: ? , где ? – модифицированный карбид Экстрёма–Одкокка Fe7C3.