Permanent Magnet Alloys Research Articles

Prediction of Sm- (Co, Cu, Fe, Zr) binary alloys’ thermodynamic parameters by improved miedema model

Abstract At present, the calculation results of the original Miedema mixing enthalpy model are still somewhat different from the experimental results. Therefore, it is necessary to improve the calculation accuracy of the Miedema model to promote the development of the Miedema model and its application in the design of samarium-cobalt permanent magnet alloys. To solve this problem, the enthalpies of mixing of Sm- (Co, Cu, Fe, Zr) binary alloys were calculated in this paper by using the modified model. The mixing enthalpy (DH), excess entropy (SE), excess Gibbs free energy (GE), component activity (α) and binary Gibbs free energy of Sm-Co, Sm-Fe were calculated. The results show that the improved Miedema model can better match the experimental values. Sm- (Co, Fe, Cu) binary alloys are easy to generate intermetallic compounds. And Sm-Zr is difficult to form intermetallic compounds. The DH, SE and GE of Sm- (Co, Fe) are negative, and there is a large negative deviation from Raoult's law for the activity of each component compared to the ideal solution. The Gibbs free energies for both SmCo5 and Sm2Co17 precipitation reactions are less than zero in the temperature range between 1550 and 1620 K. The Sm2Co17 phase is thermodynamically more stable than the SmCo5 phase.

Computational Exploration of Pd-Based Heusler alloys for permanent Magnets: Density Functional Theory and High-Throughput methods

In this work, we have explored the potential of a relatively new class of Pd-based Heusler alloys as permanent magnets. Our approach began with a high-throughput study using the Automatic Flow (AFLOW) electronic structure database to identify Pd₂YZ-type Heusler systems with tetragonal symmetry and high magnetization. For the alloys that passed our initial selection filters, we performed a detailed investigation of their magnetic properties using density functional theory (DFT) calculations. These calculations included assessments of magnetocrystalline anisotropy energy (EMCA) and exchange interactions. The selected candidates, which met all our criteria, were then subjected to Monte Carlo simulations to analyze the temperature dependence of their magnetization and determine their Curie temperatures (TC). Our results indicate that Pd₂FeNi and Pd₂FePt are promising candidates for permanent magnets. Pd₂FeNi exhibited an EMCA of 2.4 MJ/m3 and a TC of 504 K, while Pd₂FePt showed an EMCA of 4.11 MJ/m3 and a TC of 463 K. Both Curie temperatures are significantly above room temperature by more than 160 K, demonstrating the alloys’ potential for high-temperature applications and their overall suitability as efficient, rare earth-free permanent magnets.

Correlation between hydrogen absorption capacity and microstructure of Fe-rich Sm-Co-Fe-Cu-Zr permanent magnetic alloys

The correlation between hydrogen absorption capacity (HAC) and the microstructure of Sm26.2CobalFexCu4.0Zr2.3 (x = 23 wt%, 25 wt%, 27 wt%, 30 wt%) ingots and cast strips was systematically investigated. As the temperature rises from 373 to 423 K, the activation time, hydrogen absorption time and HAC of the Sm26.2CobalFe23Cu4.0Zr2.3 ingot decrease by 14.4%, 14.1%, and 19.3%, respectively. Dispersed 1:5 phase provides more channels for hydrogen diffusion, which is the main reason that HAC increases with the x increasing. The HAC of the same compound strips increases as the particles size of the pre-crushed decreases. However, no further embrittlement behavior appears in pre-crushed strips, which reaches an equal HAC as ingots. Micro-computerized tomography reveals that ingots contain small spherical-like holes and large flake micro-cracks, whereas strips mainly contain elliptical pores. The effects of grain size and inner defects size on structure stability were invested by Abaqus. Simulation results reveal that the superior embrittlement behavior of the ingots is predominantly influenced by the presence of large flake-like micro-cracks.

Ti‐Doped Nanocomposite Pr2Fe14B/α‐Fe Ribbons with High Coercivity

Nanocomposite permanent magnetic alloys are prepared by the melt‐spinning technique with wheel speed ranging from 21 to 33 ms−1. X‐ray diffraction results show that the as‐spun ribbon is rich of soft α‐Fe, hard Pr2Fe14B magnetic phases, and no other metastable phases are found in our alloy ribbon. Initial magnetization curves reveal that the coercivity mechanism of the ribbons vary with the content of Ti. For x = 2, coercivity is mainly determined by pure pinning; while for x = 1, 3, and 4, it is mainly controlled by the mixture of nucleation of domain and localized pinning at grain boundaries. The coercivity value of 1026 kA m−1, the highest value reported so far, is mainly generated from a pure pinning mechanism in the ribbon with x = 2. The recoil permeability shows a minimum value range from to for x = 2 alloy, suggesting strong exchange coupling between the magnetic grains and then leading to the concurrent reversal of soft and hard phase grains during the demagnetization process. The Henkel plots demonstrate only exchange interaction for x = 1 and exchange interaction with slightly magnetostatic interaction for x = 2, 3, and 4. The exchange interaction exhibits maximum strength for x = 2, which is the reason for high coercivity.

Investigation of rare earth lean Sm-(Fe,Co)-Mo alloys for permanent magnets

Bulk magnets with the composition of Sm1Fe10.5−xCoxMo1.5 (where x = 0, 1, and 2) with the tetragonal ThMn12 structure were prepared and their intrinsic magnetic properties were studied. The cast samples were then subjected to high-energy-ball-milling (HEBM), followed by hot-compaction at 650 °C. The compacted samples were annealed at temperatures ranging from 700 °C to 1000 °C to obtain high coercivity. The effects of Co on the magnetic properties, including the Curie temperature TC, saturation magnetization MS, anisotropy field HA, and energy product (BH)max were investigated. It is observed that Co substitution increases the Curie temperature, the saturation magnetization, and the remanence, but decreases the anisotropy field and the coercivity. Among the investigated samples, the isotropic Sm1Fe9.5Co1Mo1.5 showed the highest energy product (21.5 kJ/m3) after annealing at 750 °C for 48 h, marking a 23 % enhancement relative to our specimen without cobalt substitution.

Fabricating functionally graded Fe–Cr–Co permanent magnetic alloys via laser powder bed fusion

Fabricating functionally graded Fe–Cr–Co permanent magnetic alloys via laser powder bed fusion

Effects of Mo doping on the phase transformation behaviors and the magnetic properties of rare-earth-free MnBi alloy

The high-performance rare-earth-free low-temperature phase Mn–Bi-based permanent magnet alloys (LTP-MnBi) have gained widespread attention, but it still presents a challenge. Here, the LTP-MnBi alloy with Mo element doping was prepared by using arc-melting and subsequent high-vacuum annealing. The crystalline structure, phase transformation behavior, and magnetic properties were systematically investigated. The result showed that Mo element doping significantly improved the stability of the LTP in MnBi alloy. The investigation revealed that the disparity in atomic radius between Mo and Mn, Bi elements played a pivotal role in the formation and stability of the LTP-MnBi. With the increase of Mo content in the LTP-MnBi alloy, the coercivity value remarkably increased from 8.1 kOe to 11.7 kOe with a decrease of saturation magnetization from 71.6 emu/g to 56.5 emu/g, and the maximum energy product gradually reduced from 10.6 MGOe to 7.9 MGOe. The underlying mechanism revealed that magnetic properties were closely related to the fraction and crystal structure of LTP-MnBi. Therefore, magnetic properties of Mo-doped MnBi alloy make them an attractive candidate among the rare-earth-free permanent magnets.

Elastic constants of equiatomic Fe–Ni Invar alloy single crystal

In a disordered fcc structure, the equiatomic Fe–Ni alloy is of great interest as a soft magnetic Invar alloy with a near zero or low thermal expansion coefficient. In the L10 ordered phase, it is of interest as a potential high-performance permanent magnet alloy. In this work, the first detailed measurements of the elastic constants in a [001]-oriented Fe-50 at. % Ni alloy single crystal under a no magnetic field condition were made using the resonant ultrasound spectroscopy technique. The elastic constants measured allow one to understand the nature of atomic bonding in a material and the mechanical response to applied stress. The single crystal sample having a rectangular parallelepiped shape was prepared from a single crystal grown using the vertical Bridgman technique. The elastic constants C11, C12, and C44 were obtained from the resonant frequencies observed over a frequency range of 100–900 kHz. Using these C11, C12, and C44 values, Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio were calculated to be 99.1 GPa, 73.4 GPa, 176.7 GPa, and 0.20, respectively. The large anisotropy factor of 3.29 highlights the strong directional dependence of the material’s mechanical behavior.

Effect of Mg content on the microstructure and magnetic properties of rare-earth-free MnBi alloys

The low-temperature phase MnBi (LTP-MnBi) has become one of the most promising rare-earth-free permanent magnetic alloys owing to its unique positive temperature coefficient of coercivity. However, so far, the maximum energy product of MnBi alloys is still lower than its theoretical value. In this study, Mn55Bi45-xMgx (x = 0, 1, 2, 3, and 4) alloys were prepared by induction melting followed by an annealing process. The effects of Mg content on the microstructure and magnetic properties of MnBi alloys were investigated. The results showed that the partial substitution of Mg for Bi inhibited the formation of LTP-MnBi. With the increase of Mg content, the coercivity increases from 8.1 kOe for x = 0 to 10.0 kOe for x = 4, but the saturation magnetization decreased from 71.7 emu/g for x = 0 to 61.3 emu/g for x = 4. Finally, the calculated maximum energy product of 11.1 MGOe was obtained in the annealed Mn55Bi43Mg2 powder.

Cu adding effect upon the cellular structure and magnetic properties for the (Mn55Al45-xCux)100C2 (x = 0,1,2,3) permanent magnetic alloy

MnAl-C permanent magnetic alloy has a giant anisotropy (Ha) of 57 kOe; however, it is difficult to synthesize high coercivity MnAl-C permanent magnetic material. In this research work, the microstructure, phase composition, magnetic properties and magnetic domain of different content Cu added (Mn55Al45−xCux)100C2 (x = 0, 1, 2, 3) alloys were systematically investigated. The added Cu could stabilize both the ε and ferromagnetic τ phase when the content of the added Cu is x ＜ 2 in the (Mn55Al45−xCux)100C2 (x = 0, 1, 2, 3) alloy system. The added Cu precipitated, formed a cellular structure shell around each Mn-rich τ phase grain and pin the magnetic domain movement. The added Cu promoted the transformation of the domain structure within the Mn-rich τ phase from narrow slender shape to isoaxial grain shape.

Acetic acid leaching of neodymium magnets and iron separation by simple oxidative precipitation

Neodymium-iron-boron (NdFeB) has become the most prominent permanent magnet alloy, with a wide variety of applications and an ever-increasing demand. Their recycling is important for securing the supply of critical raw materials used in their manufacturing. The use of organic acids such as acetic acid has been of recent interest for the recycling of waste NdFeB magnets. Despite achieving good leaching efficiencies, the published literature has not properly investigated the effects of key factors influencing the acetic acid leaching process and their respective interactions, which has led to conflicting findings as to what conditions are optimal. The present work goes to show that no such optimum exists by taking a look at the major factors (concentration, solid-to-liquid ratio, time, and temperature) and their interactions. The results show that leaching efficiencies >95% and even up to 100% can be achieved using a variety of different conditions showing that the leaching reaction is quite flexible, which is helpful for a potential upscaling of the process. The separation of the leached elements presents another problem in NdFeB magnet processing. As a novel application, this work investigated iron separation from the acetic acid leachate by the means of simple and inexpensive aeration. It was found that up to 99% of iron could be precipitated as FeO(OH) (goethite) within 2 h at pH 5 and 80 °C, while only minor neodymium co-precipitation was observed (5%). Separation of iron from the leachate can help obtain purer REE products in further processing. • An environmentally friendly acetic acid leaching process for NdFeB magnets. • Main effects and interactions of key factors illuminated - flexible leaching process. • Iron precipitated as FeO(OH) using a simple and inexpensive aeration method.

NdFeB esaslı kalıcı manyetik alaşımların manyetik özelliklerine uygulanan ısıl işlemdeki sürenin etkisi

In our current study, NdFeB-based permanent magnet ribbon alloys were produced by using melt spinning method, which is one of the rapid solidification methods and very common in the production of ribbon-shaped, amorphous and/or semi-crystalline alloys. During the production of each NdFeB alloy, 15 wt.% of waste magnet was included in the composition of the alloys. The produced permanent magnet alloys were heat treated for 5 and 10 minutes by using a heat treatment temperature of 710 °C and very high heating and cooling rates of 285 K/s. The effect of the heat treatment time applied at the same temperature on the magnetic properties of the strip alloys was investigated. While the increase in heat treatment time resulted in a remarkable change in magnetic coercivity and maximum energy product properties, there was not much change in the properties such as saturation magnetization and magnetic remenance. As clearly seen, increasing heat treatment time resulted in a continuous decrease in magnetic coercivity from 5030.5 Oe to 2279.4 Oe, maximum energy product first showed a dramatic increase from 62.02 kJ/m3 to 103.73 kJ/m3, and then a dramatic decrease to 38.63 kJ/m3, indicating a decrease in the permanent magnetism of the alloy.

Experimental Study on the Grinding of an Fe-Cr-Co Permanent Magnet Alloy under a Small Cutting Depth.

A small cutting depth is the key parameter to realize precision in the machining process. The stability of the machining process will directly affect the quality of machining. In this study, dry grinding experiments using an Fe-Cr-Co permanent magnet alloy with small cutting depths (5 μm) were carried out. The relationship between the number of peaks and valleys and the quality control of the grinding force, wheel speed and feed speed were analyzed. The relationship between the peak and valley values of the grinding force signals and the peak and valley values of the grinding surface obtained using a white light interferometer was revealed. The influence of the grinding parameters on the grinding forces was analyzed by processing the grinding force signals with a low-pass filter based on the rotational speed of the grinding wheel. The experimental results indicated that the difference in grinding force between the peak and valley could be reduced by increasing the grinding wheel speed, which was mainly due to a decrease in average grinding force when the maximum undeformed cutting thickness of the single abrasive decreased. The actual height difference between the grinding surface peak and valley could be realized by increasing the grinding wheel speed. The feed speed of the worktable had no effect on the grinding force signal and the peaks and valleys of the surface morphology. Lower surface roughness could be achieved by reducing the feed speed and increasing the grinding wheel speed.

Effects of Heat Treatment and on Magnetic Properties of NdFeB Based Permanent Magnet Alloys

In this study, the effect of flash annealing heat treatment applied at 680 oC for 5 minutes on the magnetic properties of NdFeB-based permanent magnet alloys produced by melt spinning method, which is one of the fast solidification methods, was investigated by using a very fast heating and cooling rate of 300 K/s. The obtained results showed that there was a remarkable improvement in the magnetic properties of the alloys with the applied heat treatment. Mainly, the hard magnetic properties were optimized by enhancing magnetic remanence from 21.64 emu/g to 55.76 emu/g, magnetic coercivity from 1184.15 Oe to 9146.30 Oe, and maximum energy product from 4.06 kJ/m3 to 62.02 kJ/m3 respectively.

Additive manufacturing of an Fe–Cr–Co permanent magnet alloy with a novel approach of in-situ alloying

Additive manufacturing has become increasingly important in the production of magnetic materials in recent years due to the great demands for miniaturization and complex-shaped magnet parts. In this study, the laser beam-powder bed fusion process (LPBF) has been used to develop an in-situ alloying process for the additive manufacturing of a permanent magnet material of the Fe–Cr–Co system. This novel method allows for the production of complex alloys with a chemical composition suited to each specific case of application, achieved by using elemental powders or simpler commercial alloy powders as base materials. The core focus of this study has been on the development and characterization of the printing process using a Fe-30.5Cr-15Co-1.5Mo alloy. The in-situ alloying process has been developed by performing melt pool tests on the two main component powders Fe and Cr and by conducting parameter studies using two different powder mixtures with different sphericity of their components. The influence of different printing parameters and post-printing treatments on the chemical homogeneity and magnetic properties has been studied for selected samples. In addition, magnetic measurements at different temperatures have been performed to investigate the temperature stability of the magnetic properties of the 3D printed material.Impact StatementAs by today, the current amount of research done on the additive manufacturing of magnetic materials is rather low. Most of research is focused on rare- earth containing magnetic materials. In this work therefore, we are taking another direction in which we will show that LPBF combined with in- situ alloying is an ideal method for the production of a great variety of different rare- earth free magnetic materials. The positive results of our work can both have an influence on the the scientific community, as further research in the field on different promising rare- earth free magnetic materials is to be expected. Furthermore, a positiv economic impact may occur since the production of rare- earth free magnetic materials is dependent on different raw material sources which are both more cost- effectiv and less critical in terms of their supply chain. This effect is also accompanied by a positive environmental impact, since the mining of rare- earth metals usually comes with considerable environmental pollution.

Structural Constituents and Phases in High-Coercivity (Sm,Zr)(Co,Cu,Fe)z Alloys for Permanent Magnets

Structural Constituents and Phases in High-Coercivity (Sm,Zr)(Co,Cu,Fe)z Alloys for Permanent Magnets

Microstructural evolutions, phase transformations and hard magnetic properties in polycrystalline Ce–Co–Fe–Cu alloys

This work focuses on systematic studies of Ce–Co based 1:5 permanent magnet alloys of CeCo4.4-xFexCu0.6 and CeCo3.9-xFexCu1.2 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.8) by varying Co:Fe. The overarching aim of this manuscript is to elucidate the hard-magnetic properties through a better understanding of phase formation by the structural, microstructural, and magnetic properties in these materials. Improved mutual solubility of Fe in the 1:5 phase has been observed with an extended homogeneity range by Cu substitution. For both composition series, Fe contents of x ≤ 0.6 show a homogeneous microstructure with a single 1:5 phase and good magnetic properties. The composition region 0.6 < x ≤ 0.9 appears to be near the boundary of solubility and evolution of other phases. At x = 1.8, it is found that the homogeneous 1:5 phase and magnetic hardness deteriorated due to the evolution of secondary phases such as 2:17, 2:7, and Fe–Co. The addition of Fe improved both the magnetization and Curie temperature via increased effective exchange interactions, while an increase in Cu content enhanced coercivity.

Correlation of mechanical properties and electronic structures for NdFeB permanent magnet under hydrostatic pressure based on first-principle calculation

In the present study, the mechanical properties of Nd2Fe14B phase, h-Nd2O3 phase and c-Nd2O3 phase under hydrostatic pressure are calculated by means of first principle based on density functional theory. The results show that Nd2Fe14B phase belongs to a brittle phase, whereas h-Nd2O3 and c-Nd2O3 phases are ductile, where the plasticity of h-Nd2O3 is better than that of c-Nd2O3 phase. Consequently, h-Nd2O3 and c-Nd2O3 phases play an important role in accommodating plastic deformation of NdFeB permanent magnet alloy. Furthermore, the electronic structures of Nd2Fe14B, h-Nd2O3 and c-Nd2O3 phases are calculated based on first principle in order to reveal the mechanisms for the involved mechanical properties. It can be found that according to the electronic structure of Nd2Fe14B phase, the brittleness of Nd2Fe14B phase is attributed to the covalent bonds existing between the B atoms. Under the action of hydrostatic pressure, the charge density of h-Nd2O3 and c-Nd2O3 phases are shifted to the O atoms and simultaneously Nd atoms shall lose the involved electrons. Furthermore, under the action of hydrostatic pressure, h-Nd2O3 phase exhibits decreasing plasticity, but c-Nd2O3 phase presents increasing plasticity, which is attributed to the stronger localization of the electronic structures.

Effects of tensile loading during annealing of alnico melt spun ribbons

Conventional magnetic annealing (MA) of the permanent magnet alloy alnico involves application of an external magnetic field at temperatures within the spinodal decomposition range. This field biases the growth of the Fe-Co rich, ferromagnetic α1-phase in an energetically favorable 〈001〉 direction in alignment with the applied field within an Al-Ni rich, paramagnetic α2-phase. Utilizing a magnetic field to bias the α1-phase may limit alnico from reaching theoretical coercivity due to (1) the field having maximum biasing ability at temperatures near the Curie temperature where large α1-phase nanorods form and (2) connectivity of the α1-phase occurs unavoidably during MA. Both decrease the effective shape anisotropy of the α1-phase, thereby reducing coercivity. Herein, we explore tensile-loading as a biasing mechanism to control and optimize the final alnico nanostructure beyond that achieved by MA. Two samples of melt-spun alnico were heat-treated at 860 °C for 5 minutes: one sample was subjected to 10 MPa tensile stress for comparison with a stress-free control sample. Structural and magnetic characterization revealed that the stress-annealed ribbon sample possessed expected phase assemblages, but was distinguished by a ∼2× larger grain diameter and an elongated anisotropic α1-phase within grains that were oriented to a shear stress along 〈001〉 directions at an angle of ∼45° relative to the loading direction. Both types of annealing produced a similar increase in the coercivity and remanence, but a decrease in saturation magnetization.

Microstructure and Magnetic Properties of Fe-doped MnBi Permanent Magnet Alloys

The melt-spinning method combined with annealing technology was used to prepare Mn-based permanent alloys in the paper. The influences of Fe-doping on the microstructure and magnetic performances of the MnBi alloys were studied. According to the results of XRD pattern, the fraction of the LTP-MnBi in the as spun MnBi ribbons increases with the doping of Fe element, a significant increase of the LTP-MnBi is due to annealing treatment. The magnetization at the 20 kOe field of MnSUB55/SUBBiSUB40/SUBFeSUB5/SUB melt-spun ribbons increases to 45 emu/g after being annealing. With the addition of Fe, the coercivity HSUBcj/SUB of the annealed ribbons increases first and then decreases. The results of δM plots show that the reduction of HSUBcj/SUB for the MnSUB55/SUBBiSUB40/SUBFeSUB5/SUB melt-spun ribbons can be attributed to enhanced exchange coupling interaction between MnBi LTP particles. The grain refinement contributes directly to an enhanced exchange coupling for the addition of 5 at% Fe from TEM images. The dependence of coercivity on temperature for the annealed MnBi alloy melt-spun ribbons is discussed.