Sm2Fe17 Alloy Research Articles

Magnetic properties of (Sm, Zr)(Fe, Co)10−xTix (x = 0, 0.5, 1) bulk magnets

It would be desirable if the magnetic properties of Sm–Fe alloys could be increased without the need for nitrogenation. In this experiment, Sm–Fe bulk magnets were prepared from the Sm–Fe powders by the spark plasma sintering (SPS) technique without nitrogenation. The structures and magnetic properties of the Sm–Fe bulk magnets prepared by the SPS technique were investigated. By optimization of the composition and production process, it was found that the (Sm0.7Zr0.3)(Fe0.7Co0.3)9Ti magnet with the fine Th2Zn17-type phase showed a high coercivity of 4.35 kOe.

Preparation of Sm–Fe–N Hard Magnetic Nanopowder From Micrometer-Sized Sm–H and Fe Mixed Powder

Fine Sm-Fe-N powder with a mean particle diameter of 58 nm was prepared by a low oxygen-induction thermal plasma process (LO-ITP). Sm-H fine powder prepared by a jet mill process and Fe mixed powder were chosen as starting materials. The obtained Sm-Fe alloy had a TbCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> -type crystal structure at temperatures <700 °C but changed to the stable Th <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sub> -type structure at temperatures >800 °C. Nitrogen sufficiently diffused into the lattice, and a TbCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> -type Sm-Fe-N nanopowder was obtained. TEM observation revealed single crystals of the synthesized powder. The coercivity of nitrided nanopowder was only 0.16 T at 300 K due to the existence of a large amount of Fe.

Low temperature synthesis of Sm-Fe alloy powder by reduction-diffusion process using new reductant of Li-Ca eutectic melt

In this study, the low-temperature reduction-diffusion (LTRD) process using a Li-Ca reductant, which has a low eutectic point of about 230 °C, was demonstrated. The RD reaction was possible at a very low temperature of 400 °C significantly less than 850 °C, which is the lowest practicable temperature of the conventional RD process, by identifying the production of the SmFe2 phase. The LTRD process in this study also made it possible to investigate the Sm-Fe binary phases synthesized at the low temperature and the Sm-Fe phase transitions depending on the temperatures with the compositions of Sm and Fe.

Development of TbCu7-type Sm-Fe-N anisotropic magnet powder and its sintered magnets

Anisotropic TbCu7-type Sm-Fe-N magnet powder and its sintered magnets were developed using TbCu7-type Sm-Fe alloy powder synthesized by a modified low-temperature reduction diffusion process. Using Sm metal powder instead of SmCl3 and Ca and using the eutectic salt LiCl-CaCl2 to lower the synthesis temperature, an almost single-phase TbCu7-type Sm-Fe powder was obtained. By nitriding the powder with an NH3-H2 mixture gas, a TbCu7-type Sm-Fe-N anisotropic magnet powder was demonstrated for the first time. Furthermore, by sintering the anisotropic powder with a high-pressure current sintering process, a TbCu7-type Sm-Fe-N anisotropic sintered magnet with a relative density of 86.8% was produced. The magnetization ratio σr/σ90 kOe was decreased by the formation of the α-Fe phase as a result of the decomposition of the TbCu7-type Sm-Fe-N phase in the sintering process, whereas the coercivity was slightly increased. This result indicates that the TbCu7-type Sm-Fe-N magnet is less affected by the existence of α-Fe compared with a Sm2Fe17N3 magnet.

Diffusion behavior of iron and samarium atoms in Sm2Fe17 alloy compound layer

The Sm2Fe17 alloy compound has been widely studied and used as a precursor for Sm2Fe17Nx rare-earth permanent magnets. However, the growth mechanism of Sm2Fe17 remains unclear. In this study, based on the high temperature diffusion method, a Sm2Fe17 layer was prepared by fabricating a Sm–Fe (sat)/Fe(s) diffusion couple in the temperature range of 1060–1140 °C. Results indicated that the diffusion of Fe and Sm atoms is the rate-determining step in the growth of the Sm2Fe17 layer. The atomic concentrations of Fe and Sm in samples with different holding times at 1060–1140 °C were analyzed using an electron microprobe, which revealed that the growth of the Sm2Fe17 layer primarily depended on the diffusion of Fe atoms. The diffusion coefficients of Fe atoms in the Sm2Fe17 layer were 2.33 × 10−9, 4.29 × 10−9, and 5.37 × 10−9 cm2 s−1 at 1060, 1100, and 1140 °C, respectively. Moreover, the relationship between the diffusion coefficient of Fe atoms (DFe) and temperature (T) was obtained.

Magnetic properties of Sm(Fe,Ti)10 alloys and their nitrides

Sm-Fe alloys with compositions of SmFe10 and SmFe9.5Ti0.5 were prepared by rapid solidification processing. The as-quenched and annealed specimens did not show sufficiently high coercivity for use as permanent magnets, but the coercivity was improved by subsequent nitrogenation of the specimens. The specimens exhibited the maximum coercivity when nitrogenated at 743 K for 20 h in this study. The optimally nitrogenated SmFe10 specimen consisted of the TbCu7-type and α-Fe phases and showed a coercivity of 10.1 kOe, whereas the optimally nitrogenated SmFe9.5Ti0.5 specimen consisted of the Th2Zn17-type phase without the α-Fe phase and exhibited a high coercivity of 17.0 kOe.

Magnetic properties of (Sm,Zr)Fe10 and (Sm,Zr)Fe9.5Ti0.5 melt-spun ribbons

(Sm,Zr)Fe10 and (Sm,Zr)Fe9.5Ti0.5 alloys were obtained by the melt-spinning technique in order to investigate the possibility of producing high-coercivity Sm-Fe alloys without nitrogenation. The (Sm,Zr)Fe10 alloys contained the TbCu7-type and α-Fe phases and exhibited a maximum coercivity of 1.88 kOe in the case of the (Sm0.9Zr0.1)Fe10 ribbon annealed at 1073 K. On the other hand, the (Sm,Zr)Fe9.5Ti0.5 alloys contained the Th2Zn17-type and α-Fe phases and showed a maximum coercivity of 4.5 kOe when the (Sm0.7Zr0.3)Fe9.5Ti0.5 ribbon was annealed at 1173 K.

Preparation of Sm2Fe17 alloy and induced mechanism by calciothermic reduction

SmF3 cannot be directly reduced to metallic samarium by calcium. In this work, we presented the thermodynamic calculation and preperation of Sm2Fe17 alloy by calciothermic reduction. The composition, crystal structure, elements distribution, chemical valence and induced mechanism of Sm2Fe17 alloy were analyzed and characterized by ICP, XRD, SEM, EDS and XPS. The results show that the feasibility of preparing Sm2Fe17 alloy by iron-induced SmF3 calciothermic reduction. The Sm and Fe component of SmFe alloy approximates the nominal composition of Sm2Fe17 alloy with 10% excess of SmF3 over the stoichiometry. The micrograph of the SmFe ingot exhibits fish-bone-like morphology and is composed of α-Fe, Sm2Fe17 and SmFe3 phases. The Sm and Fe elements of the samples demonstrate zero valency. Electrons from metallic Sm are drawn toward to the orbits of Fe and an Sm-Fe bond with ionic bond property is formed and being reduced by calcium to obtain Sm2Fe17 alloy.

Phase transformation mechanism and magnetic properties of Sm-Fe alloys produced by melt-spinning and high-energy ball milling

The phase transformation mechanism and magnetic properties of the Sm-Fe alloy powders produced by melt-spinning and high-energy ball milling are investigated. The amorphous phase is stable between 2 and 5 h, and the SmFe9 phase is precipitated from the amorphous matrix after milled for 5 h. The time of 3–5 h is optimal to obtain the largest number of short-range/medium-range order in the amorphous alloy, which can contribute to the formation of uniform microstructure in the subsequent crystallization annealing process. The magnetic properties of the nitrided powders produced by crystallizing the amorphous precursors are improved compared to the properties of those produced by direct melt-spinning. The coercivity (Hcj) and the remanence (Br) are increased by 1.28 kOe and 23.6 emu/g, respectively. This kind of micro-regulation plays a key role in improving the magnetic properties after nitrogenating and lays the foundation for the production of bulk materials in the future.

Improved efficiency for preparing hard magnetic Sm2Fe17NX powders by plasma assisted ball milling followed by nitriding

The plasma assisted ball milling technology is employed for the preparation of hard magnetic Sm2Fe17NX magnetic powders for the first time. Using conventional high-energy ball milling, Sm2Fe17 alloy powders can only be prepared from Sm2Fe17 alloy precursor but not from Sm and Fe metal precursor. However, by the plasma-assisted ball milling, Sm2Fe17 alloy powders with very fine grains can be directly obtained from the mixture of pure Sm and pure Fe fragments. It is also found that the Sm2Fe17 alloy has been partially nitrided by plasma assisted ball milling under nitrogen atmosphere. The precipitation of soft magnetic α-Fe phase and the oxidation of Sm2Fe17 particles can also be effectively inhibited by the plasma during milling. In addition, the nitriding effect of Nd-Fe alloy powders prepared by plasma-assisted ball milling is better than those prepared by conventional high-energy ball milling during the subsequent nitrding process, since the plasma field can increase the initial free energy of Sm2Fe17 powder and reduce its difference with the energy barrier. The present wok indicates that the nitriding efficiency of Sm2Fe17 alloy can be greatly improved by adding plasma field during the powdering.

不同冷却速率下钐铁合金的组织演变行为研究

不同冷却速率下钐铁合金的组织演变行为研究

Effect of solid solution treatment and nitrogenation on magnetic properties of Sm2+αFe17Nx powders

The effect of solid solution treatment (SST) of Sm-Fe alloys and conditions of the nitrogenation on the structure and magnetic properties of the Sm2+αFe17Nx (α = 0 ÷ 0.6) powders has been investigated. It is observed that the nitrided powders with the best hysteresis properties can be prepared from the Sm2.4Fe17 alloy after the SST at a temperature of 1050°C (5 h) and heat treatment at 525°C in a H2: N2 = 1: 1 gas mixture with a pressure of 2.5 atm. The additional ball milling of the powder enhances the coercivity to 6.4 kOe.

Stoichiometric study of metastable TbCu7 type Sm-Fe phase synthesized by HDDR treatment

• Compositional variety of HDDR-synthesized TbCu 7 type Sm-Fe alloys is examined. • HDDR treatment is carried out for raw Sm-Fe alloys with various Fe-rich compositions. • TbCu 7 type Sm-Fe alloys synthesized by HDDR behaves like stoichiometric SmFe 8.5 alloy. • Transition from Fe-rich compositions to SmFe 8.5 occurs in a stage of HD reaction. Hydrogenation-disproportionation-desorption-recombination (HDDR) treatment of Fe-rich SmFe x alloys with x > 8.5 was conducted in order to investigate the possibility that the HDDR treatment can synthesize metastable TbCu 7 Sm-Fe phases with a Fe-rich composition, which are expected to provide large saturation magnetization . Fe-rich alloys prepared by melt spinning were HDDR-treated at 600 °C. As a result, the constituent phases of all the alloys transformed into non-Fe-rich TbCu 7 type SmFe 8.5 and iron phases in spite of the Fe-rich compositions of the original Sm-Fe phases. Thus, the TbCu 7 type Sm-Fe phase synthesized by HDDR treatment behaved as the stoichiometric compound of SmFe 8.5 . Electron microscope analysis revealed that the exclusion of excess iron from the original Sm-Fe phase occurred in the stage of disproportionation. In addition, the Sm-Fe phase prepared via a combination process of melt spinning and HDDR treatment had a very refined microstructure with grain sizes smaller than 100 nm, resulting in a large coercivity of 14.1 kOe after nitrogenization.

Influence of Boron Addition on Magnetic Properties of Sm2Fe17 Alloy

Influence of Boron Addition on Magnetic Properties of Sm₂Fe₁₇ Alloy

Electrochemical behavior for preparation of Sm2Fe17 in CaCl2-CaF2-SmCl3 system

Sm2Fe17 alloy as a precursor of a potential permanent magnet (Sm2Fe17Nx) has been paid attention to, but the pure one obtained has been still very difficult until now due to having a distinct difference of melting point between Fe and Sm metals as raw materials, it impairs seriously the magnetic performance of Sm2Fe17Nx. In this work, this problem was solved successfully using a method of molten salt electrolysis. A chronopotentiometry was used at 1100 °C to obtain a single phase Sm2Fe17 alloy as product on iron cathode in CaCl2-CaF2-SmCl3, simultaneous a series of electrochemical measurements were carried out to reveal the electrochemical behavior. The preparation of Sm2Fe17 alloy was carried out by the chronopotentiometry to find that the thickness of Sm2Fe17 layer increasing with the increase of the initial concentration of Sm3+ when the initial concentration of Sm3+ was less than 1.74 × 10−5 mol cm−3, while it increased not obvious when the initial concentration of Sm3+ exceeded 1.74 × 10−5 mol⋅cm−3 due to increasing the resistance of Fe diffusion as increasing of Sm2Fe17 layer thickness in the late process.

Changing phase equilibria: A method for microstructure optimization and properties improvement in preparing anisotropic Sm2Fe17N3 powders

Sm2Fe17N3 compound possesses excellent intrinsic permanent magnet properties. Sm2Fe17N3 is usually produced by nitridation of the Sm2Fe17 alloy; however, it is difficult to avoid the formation of α-Fe and SmFe3 phases in the Sm-Fe system, which may have adverse effects on the magnetic properties of the final magnets. In this study, the three-phase region of SmCu + SmCu2+Sm2Fe17 was determined experimentally and a partial isothermal section of the Sm-Fe-Cu phase diagram at 450 °C was established. Based on this newly determined three-phase region, a parent alloy free of α-Fe and SmFe3 phases was obtained and the effects of Sm-Cu assistant phases on the microstructure and magnetic properties of nitrided powder were investigated. Anisotropic Sm2Fe17N3 powders free of α-Fe and having a high (BH)max exceeding 31 MGOe and Hcj of 13.9 kOe were obtained using a parent alloy containing 3 at.% of Sm-Cu assistant phases. The magnetization reversal process of anisotropic Sm2Fe17N3 powders with and without α-Fe was investigated and the underlying mechanisms were analyzed.

Preparation and characterization of Sm2Fe17 alloy in LiF-CaF2-SmF3 molten salt

A suitable temperature range of Sm2Fe17 alloy formed only was chosen to investigate the electroreduction of Sm3+ on molybdenum and iron electrode in LiF-CaF2-SmF3 molten salt, which were studied by CV and SWV at different temperatures and concentrations of Sm3+. The reduction of Sm3+ to Sm0 on the iron electrode included two steps. Firstly, a soluble-soluble reaction appears at −0.33 V vs. Cr/Cr2O3 corresponds to the electroreduction of Sm3+ to Sm2+. The electroreduction of Sm3+ to Sm2+ is a reversible process, which is controlled by the diffusion of Sm3+ in the LiF-CaF2-SmF3 molten salt. Secondly, Sm2+ can be reduced at −0.78 V vs. Cr/Cr2O3 on the iron electrode in LiF-CaF2-SmF3 molten salt due to a lower activity of metallic samarium in the Sm2Fe17 alloy than that of samarium metal, and that makes samarium in Sm-Fe alloy more stable while that of Sm2+ could be not reduced by a molybdenum electrode. By experiment of potentiostatic electrolysis it was confirmed that the cathode product from LiF-CaF2-SmF3 melts at −1 V vs. Cr/Cr2O3 for 4 h is a thin layer metallic plate only composing Sm2Fe17 alloy.

Preparation of TbCu7-type Sm-Fe powders by low-temperature HDDR treatment

Low-temperature hydrogen-disproportionation-desorption-recombination (HDDR) treatment of Sm-Fe alloy powder was conducted to prepare a metastable TbCu7 type Sm-Fe alloy powder with a grain size of more than a few hundreds of nanometers. While a treatment temperature above 700 °C produced the familiar Th2Zn17 type alloy, one below 600 °C resulted in successful synthesis of the TbCu7 type Sm-Fe alloy with submicron-size grains. This TbCu7 type alloy powder, however, showed no significant improvement in magnetic properties compared to the Th2Zn17 type, as its composition was estimated to be near SmFe8.5 and thus did not achieve the expected Fe-rich composition. Therefore, cross-sectional transmission electron microscope observation of the unfinished TbCu7 type alloy powder was conducted in order to explore means of forming the Fe-rich phase.

Effect of Nitrogenation and Hydrogenation on the Magnetic Properties and Structure of the Sm2Fe17 Alloy: Analysis of XMCD Data

Changes in the local magnetic and structural properties of Sm2Fe17 alloys at nitrogenation and hydrogenation of samples have been studied by the X-ray magnetic circular dichroism (XMCD) technique at the Fe K absorption edge and Sm L3 absorption edge using synchrotron radiation. The results have been discussed in comparison with X-ray diffraction data and macroscopic vibration magnetometry measurements. The observed changes in XMCD spectra indicate a noticeable effect of nitrogenation on the local magnetic properties of sublattices of both iron and samarium, whereas hydrogenation of samples makes a small effect. The mentioned effects have been analyzed and discussed in terms of the effect of nitrogen (N) and hydrogen (H) interstitial atoms on Sm 5d and Fe 4p electronic states. The effect of nitrogenation is larger than the effect of hydrogenation because the volume expansion of the crystal lattice of initial Sm2Fe17 in the case of nitrogenation is larger than that in the case of hydrogenation. The studied local magnetization curves for samarium and iron sublattices in magnetic fields up to 17 T also indicate a strong increase in the magnetocrystalline anisotropy at nitrogenation.

Effect of heat treatment on the structure and magnetic properties of Sm-Fe alloys obtained by mechanical alloying

The effect of heat treatment on the structure and magnetic properties of Sm-Fe alloys obtained by mechanical alloying was investigated. The crystallization temperature of Sm2Fe17, an amorphous alloy obtained by mechanical alloying, was determined using differential scanning calorimetry. Based on these results, various samples were annealed at different isothermal holding temperatures, and those with the best magnetic properties were found. Experimental studies show that decreasing the isothermal holding temperature from 750 °C to 630 °C increases magnetic characteristics nearly four times. The saturation magnetization, romance and coercivity of the Sm2Fe17 powder were 121 emu/g, 28.5 emu/g and 800 Oe, respectively.