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

The results of the application of a combination of several surfactants in preparing submicron hard magnetic Sm 2 Fe 17 N 3 powders by milling in a centrifugal mill are reported. Along with methyl caproate, to protect the powder against oxidation, the efficiency of siloxane has been studied. The application of the combined surfactants allowed us to increase both the ( BH ) max of the Sm 2 Fe 17 N 3 powder to 23.6 MG Oe and its corrosion resistance. The effect of milling kinetics on the angular dependence of the coercive force H c has been determined. Information on the primary mechanism of magnetization reversal of the powders has been obtained.

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 results of the application of a combination of several surfactants in preparing submicron hard magnetic Sm2Fe17N3 powders by milling in a centrifugal mill are reported. Along with methyl caproate, to protect the powder against oxidation, the efficiency of siloxane has been studied. The application of the combined surfactants allowed us to increase both the (BH)max of the Sm2Fe17N3 powder to 23.6 MG Oe and its corrosion resistance. The effect of milling kinetics on the angular dependence of the coercive force Hc has been determined. Information on the primary mechanism of magnetization reversal of the powders has beenobtained.

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.

Magnetic properties and microstructure of (Nd,Dy)–Fe–B magnets with Dy in the range from 0 to 10.3 wt % and oxygen less than 0.26 wt % are studied. High-coercivity magnets with Dy 8 wt % have maximum energy density product (BH)max ≥ 35 MG Oe and coercivity МНс ≥ 30 kOe; their operating temperature can be as high as 180°С. Phase composition and structure of (Nd,Dy)–Fe–B magnets were studied by X-ray diffraction and scanning electron microscopy. In addition to the main (Nd,Dy)2Fe14B phase and (Nd,Dy)2O3 oxide, in triple junctions, there are two (Nd, Dy, Fe, М)Ox phases with fcc structure (symmetry group 225, Fm $$\bar {3}$$ m) but with different content of O, Fe, and additional elements M (M = Co, Cu, Ga). It was shown that the total content of (Nd,Dy,Fe,М)Ox oxides grew with the total concentrations of oxygen and dysprosium in magnets.

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.

Our previous Mossbauer studies have shown that the A1 to L1(0) structural transformation in equiatomic FePd is a complex transformation of the cascade type. The FePd ordering involves more phases that one may expect. In addition to the ordered L1(0) phase it can proceed via the cubic ordered L1(2) (Pm-3m) phase and intermediate low-symmetry phases, namely the disordered tetragonal phase A6 (I4/mmm), the modified L1(0)* phase (P4/mmm), the ordered hexagonal Fe2Pd and FePd2 (P-3m1), the ordered tetragonal FePd2 (I4/mmm) and probably, the orthorhombic 5:3 (Cmmm) phases. We theoretically investigate the phase stability of proposed phases using first principle density functional calculations. Structurally, tetragonal L1(0)* modified, cubic FePd3, tetragonal FePd2 and orthorhombic Fe3Pd5 are energetically stable and likely to form in the course of the A1 to L1(0) structural transformation. All these phases show interesting magnetic properties. We report magnetization, Curie temperature and magnetocrystalline anisotropy of these phases.

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 work compares the peculiarities of the high-coercivity state formation in the Sm-Co-Fe-Cu-Zr high-temperature and high-energy permanent magnets (HTPM and HEPM) in the course of the heat treatment with the stepwise decreasing temperature from 830 to 400 degrees C. Two types of magnets with varying Fe concentration, i.e., Sm(Co0.88-xFexCu0.09Zr0.03)(7) with x = 0-0.12 (the HTPM5) and SM(Co0.91-xFexCu0.06Zr0.03)(7.5) with x = 0.24-0.33 (the HEPM5) were studied at different temperatures of heat treatment for phase formation by x-ray diffraction followed by magnetic property measurements. Microstructure characterization was performed using transmission electron microscopy, whereas the three-dimensional elemental distribution at near-atomic scale was obtained using atom probe tomography. In HEPM5, the main increase in coercivity and relaxation of stresses accompanied by intensive enrichment of the 1:5 phase in Cu are observed at high temperatures (T approximate to 700 degrees C). In HTPM5, the coercivity monotonously increases in the entire temperature range of the slow cooling from 700 to 400 degrees C at a rate of 0.5 degrees C/s. At the temperature close to the Curie temperature (similar to 550 degrees C) of the Sm(Co,Cu)(5)-type phase, the anomaly of the coercivity increment has been observed. The interphase stresses grow and the elemental redistribution appears to be accelerated simultaneously. The non-uniform Cu distribution in the 1:5 phase can be described by the formation of Cu-rich interlayers at the interface of the Sm(Co,Cu)(5) and Sm-2(Co,Fe)(17)-type phases. (C) 2019 Elsevier B.V. All rights reserved.

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.

We present the results of ab initio simulations of the series of intermetallic Sm-Co compounds. We show that the "open core" approach allows calculating intrinsic properties of Sm-Co compounds with sufficient accuracy for all structures of the series. The calculated magnetic moments, both total and on the cobalt atom, as well as the elastic constants agree with the available experimental data. Using the data, we recover embedded atom potential for Sm-Co alloys, which is suitable for studying the interface of coherent SmCo5 and Sm2Co17 phases.

Formation of the L1(0) structure in FePd alloys doped with nonmetallic elements is studied on melt-spun and annealed samples. The melt-spun Fe41Pd41P18-x-yBxSiy (x = 0-14; y = 0, 6) ribbons were annealed at the temperatures of 400-650 degrees C for different holdings in the range from 5 min to several hours and studied by X-ray and thermomagnetic analysis and TEM. The saturation magnetization, Curie temperature of the L1(0) phase, and grain size of the melt-spun doped Fe41Pd41P18-x-yBxSiy ribbons decrease in comparison with those of the melt-spun binary FePd alloy. The refined grain structure results in enhancing coercivity. Among all as-annealed samples, the P addition favors the amorphization of the as-spun Fe41Pd41P18 ribbons and refines grains of the formed L1(0) phase, but decreases magnetization. Substitution of B for P gives rise to magnetization of the Fe41Pd41P18-x-yBxSiy alloys, but decreases their coercivity. A partial substitution of Si for B at the same P content refines grains and enhances the coercivity without a decrease in the magnetization of the Fe41Pd41P4B8Si6 alloy. It is suggested that P and B atoms occupy interstitial sites in the L1(0) lattice in the iron plane, weakening the exchange interaction and decreasing the Curie temperature. The additions of P, B, and Si to the FePd alloy allowed us to obtain the Fe41Pd41P4B8Si6 ribbons with the coercivity of 1560 Oe, which is 2.6 times higher than that of the melt-spun ribbons of the FePd alloy.

Behavior of the coercivity of the high-temperature Sm(Co0.88–xFexCu0.09Zr0.03)7 magnets depending on the temperature and time of annealing with the temperature decreasing stepwise from 700 to 400°С was investigated. It is shown that the growth rate of coercivity abruptly increases at the initial stage of annealing in the vicinity of the Curie temperature of the SmCo5 phase. The origin of the effect is the counter diffusion of Cu and Co atoms through dislocation tubes, which form because of enhanced stresses and a partial breakage of coherent coupling at the interface of the Sm2Co17 and SmCo5 phases. Diffusive enrichment of the SmCo5 phase in Cu close to the interface with Sm2Co17 leads to relaxation of stresses and increases in the gradient of the magnetic domain-wall energy and coercivity.

The structure and magnetic hysteresis properties of the cast Sm1-xZrx(Fe0.92Ti0.08)(10) (x = 0-0.3) alloys and melt-spun ribbons prepared from them were studied. In the cast alloy with x > 0.2, a considerable amount of the eutectic phase is found in the SEM micrographs. Analysis of the temperature dependences of the magnetic susceptibility and XRD patterns allows amorphous state in the as-spun ribbons with x > 0.2 to be determined. The specific magnetization measured in a field of 17 kOe and remanence decrease with increasing annealing temperature from 800 to 900 degrees C and weakly depend on Zr concentration. The maximal value of coercivity H-c = 4.7 kOe is obtained on the ribbons with x = 0.2 after annealing at 850 degrees C for 10 min. After additional hydrogenation of the ribbons, both the coercivity and remanence increase by 54% and 7%, respectively. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.