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Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid development of application fields, such as the green energy industry, has resulted in increased demand for magnetic characteristics, especially the coercivity (Hcj). In this paper, two types of (Nd, Dy)-Fe-B magnets with comparable Hcj values were prepared using by grain boundary diffusion (GBD) method and dual alloy (DA) method. The composition, microstructure, domain structure, and magnetization reversal process of GBD and DA magnets were subjected to comparison. Additionally, an analysis of the specific coercivity mechanism was also conducted by fitting the Brown's equation. The results of composition and microstructure analysis revealed the formation of core-shell structural grains were formed in both GBD and DA methods. Specifically, the GBD method exhibited a higher concentration of Dy in the shell, constituting 26.8 % of the total rare earth (RE) content. In contrast the DA magnets had Dy accounting for 15.8 % of the total RE content in the shell. This discrepancy was identified as the primary factor contributing to the superior efficiency in enhancing the coercivity (Hcj) observed in the GBD method. The fitting results showed that GBD magnets were more inclined to nucleate in the core region in grain, whereas DA magnets nucleate at the edge of the grain shell layer. Both the observation of magnetic domains and magnetization reversal processes analysis revealed that the demagnetization process in GBD magnets is more uniform, which leads to better squareness. Our finding can provide theoretical and experimental basis for the preparation of high-performance Nd-Fe-B magnets.

Processes of magnetization in exchange-coupled rapidly quenched nanocrystalline alloys Nd2(Fe1 – xCox)14B, where x = 0, 0.07, 0.2, 0.5, have been studied. Initial magnetization curves and interaction plots δM(H) for various demagnetized states were obtained. Based on comparison of measurement results, influence of the pinning type mechanism on magnetization process in the Nd2(Fe1 – xCox)14B melt-spun ribbons is shown. Using δM(H) plots, a change in intergrain exchange interaction depending on cobalt concentration in rapidly quenched Nd2(Fe1 – xCox)14B nanocrystalline alloys was investigated. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, a bibliometric study was carried out to perform a scientific and technological analysis of exchange-spring magnets, an alternative permanent magnet synthesized by reducing or eliminating the use of critical raw materials, such as rare earths. The bibliometric analysis utilized the Scopus database, Orbit-Intellixir, VOSviewer, Orbit-Intelligence and Loglet Lab 4 software for maturity analysis, keyword network representations, charts and graphs for scientific articles and/or patents. A special analysis was performed on nanocomposite and thin-films systems based on Nd-Fe-B, SmCo5 and Mn–Al–C alloys, either mixed or layered with a soft magnetic phase, where relevant information on their magnetic parameters was compilated in tables, highlighting the nanostructured systems that have been exhibited the best permanent magnet properties. The bibliometric analysis revealed that the primary production of scientific articles is concentrated in industrialized countries, and they are predominantly published in journals dedicated to magnetism. A patents analysis showed that Nissan motors is by far the main applicant, with most of its patents is focused on technological domains related to electrical machinery, apparatus, energy and metallurgy. On the other hand, the S-curve of maturity for scientific articles indicated that the study of exchange-spring magnets is entering a mature state. In contrast, patent production, following a bi-logistic model, is in a saturation stage for the second S-curve. Maturity analyses, employing S-curve, bi-logistic and multi-logistic models, were performed on nanocomposites and thin films based on Nd-Fe-B, SmCo5 and Mn–Al–C alloys, respectively. We found that the investigation in Nd-Fe-B-based alloys is close to enter to a scientific saturation stage, while an average growth stage is observed for the SmCo5 and Mn–Al–C-based alloys. This suggests that research on alternative magnets, capable of fulfilling technological applications where a Nd-Fe-B magnets are commonly used, is a topic of significant interest.

In this paper, the Tesla meter and magnetic force microscope were used to study the open-circuit remanence and magnetic domain structure of Nd-Fe-B permanent magnets (PMs) in high-power density permanent magnet synchronous motors (PMSMs). An experimental platform was built to simulate the internal demagnetization environment of PMSM. Nd-Fe-B PMs were subjected to high temperature, DC demagnetizing field and alternating demagnetizing field. The results show that even when the working point of Nd-Fe-B PM is higher than the knee point, demagnetization still occurs in the simulated motor environment. The relationship between macroscopic magnetic properties and magnetic domain structure is investigated. With the decrease of open-circuit remanence, the average width and the magnetization of the magnetic domain in the magnetization direction decrease. Due to the width of the magnetic domain decreasing, the number of magnetic domains increases, and the area of the domain wall increases. As a transition region with weak magnetism, the increase of the domain wall area will lead to a decrease in magnetic properties. This work is helpful to understand the demagnetization mechanism of Nd-Fe-B magnets in the PMSMs.

Permanent magnets today are used in a wide range of transportation, industrial, residential/commercial, consumer electronics, defense, domestic, data storage, wind energy, and medical markets and applications. There are five classes of commercial permanent magnet materials; however, magnets based on Nd-Fe-B account for over 60% of the global magnet production by value. They typically contain around 31 wt.% of rare earth elements (REEs), principally, Nd and Pr, plus Dy for higher-temperature performance. Nd-Fe-B magnets are forecast to grow throughout this decade, largely driven by the growth in electric vehicles of all types. However, several studies forecast a shortfall of the primary REEs from mined resources. In this paper, the sourcing, processing, and recycling of REEs are discussed. Additionally, presented are the advantages and disadvantages of the major recovery and recycling technologies for REEs. [ABSTRACT FROM AUTHOR]

This research focuses on the surface modification of Nd–Fe–B magnetic powder to enhance its thermal and oxidation resistance without compromising magnetic properties and to improve adhesion to the polymer binder for enhanced mechanical properties. A three-step surface modification process involving phosphatization treatment, tetraethyl orthosilicate (TEOS) application, and 3-aminopropyltriethoxysilane (APTES) grafting, was applied to the powder, which was then compounded with polyamide 12 and injection-moulded into cylinders and dog-bone-shaped tubes. The resulting magnets exhibited remanence (Br) of 487.6 mT, coercivity (Hci) of 727.7 kA/m, and energy product (BHmax) of 39.3 kJ/m3. The modified magnets demonstrated exceptional corrosion resistance and thermal stability, with less than 5% irreversible flux loss after exposure to hot water, temperature shock, and pressurised steam. Furthermore, the modified magnets displayed significantly higher tensile strength, elongation at break, and elastic modulus with improvements of 62%, 16.7%, and 19.9%, respectively, compared to the non-modified batch. Additionally, the modified batch showed a notable 52% increase in flexural stress during flexural testing. These findings underscore the potential of silane surface modifications in producing injection-moulded permanent magnets based on Nd–Fe–B alloy, extending their shelf life and enhancing their overall performance.

To solve the problem of the low coercivity of Nd-Fe-B-based nanowires impeding their application in magnetic storage media, highly ordered Nd-Fe-B/Fe-Co composite nanowires were fabricated in an anodic alumina template by means of the alternating electrochemical deposition method. In this paper, the effect of soft and hard magnetic phase compositing on the magnetic properties of Nd-Fe-B-based nanowires was investigated, and the coercivity improvement mechanism was demonstrated. The results show that after annealing at 600 °C for 2 h, Nd-Fe-B/Fe-Co nanowires crystallize into a multiphase structure containing a hard Nd2(Fe, Co)14B phase and soft NdB4, NdB6, Fe7Nd, and Fe7Co3 phases. It is characterized that the Nd2(Fe, Co)14B phase preferentially nucleates, followed by NdB4 + NdB6 + Fe7Nd, while Fe7Co3 has been formed in as-deposited nanowires. The existence of a Nd2(Fe, Co)14B phase with high anisotropy fields, the remanence enhancement effect produced by exchange coupling between hard–soft magnetic phases, and the pinning effect between different phases make the composite nanowires approximately exhibit single hard magnetic phase characteristics with coercivity and remanence ratio as high as 4203.25 Oe and 0.89. The results indicate that synthesizing Nd-Fe-B/Fe-Co exchange-coupled composite nanowires via alternating electrodeposition is an effective way to optimize the magnetic performance of Nd-Fe-B-based nanowires. [ABSTRACT FROM AUTHOR]

High-performance Nd-Fe-B-based rare-earth permanent magnets play a crucial role in the application of traction motors equipped in new energy automobiles. In particular, the anisotropic hot-deformed (HD) Nd-Fe-B magnets prepared by the hot-press and hot-deformation process show great potential in achieving high coercivity due to their fine grain sizes of 200–400 nm, which are smaller by more than an order of magnitude compared to the traditional sintered Nd-Fe-B magnets. However, the current available coercivity of HD magnets is not as high as expected according to an empirical correlation between coercivity and grain size, only occupying about 25% of its full potential of the anisotropy field of the Nd2Fe14B phase. For the sake of achieving high-coercivity HD magnets, two major routes have been developed, namely the grain boundary diffusion process (GBDP) and the dual alloy diffusion process (DADP). In this review, the fundamentals and development of the HD Nd-Fe-B magnets are comprehensively summarized and discussed based on worldwide scientific research. The advances in the GBDP and DADP are investigated and summarized based on the latest progress and results. Additionally, the mechanisms of coercivity enhancement are discussed based on the numerous results of micromagnetic simulations to understand the structure–property relationships of the HD Nd-Fe-B magnets. Lastly, the magnetization reversal behaviors, based on the observation of magneto-optic Kerr effect microscopy, are analyzed to pinpoint the weak regions in the microstructure of the HD Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Remanence is an important parameter of magnetic property for Nd-Fe-B magnets, and high remanent magnetization is a prerequisite for high-performance magnets. In this paper, the surface morphology perpendicular to the texture orientation direction and parallel to the texture orientation direction is analyzed by Nd-Fe-B permanent magnets with different compositions. For the first time, the relationship between the remanence of a magnet and the degree of texture orientation is explained in depth using the fractal dimension. The fractal dimension of surface morphology combined with the remanence equation yields the degree of texture orientation of the magnet, which is in agreement with the trend of the squareness factor of the demagnetization curves. Among the three samples, the Nd-Fe-B sample has the highest degree of texture orientation, the Pr-Nd-Fe-B sample has the lowest degree of texture orientation, and the Nd-Ce-Fe-B sample is in between the first two. The multiples of uniform (pole) density obtained by EBSD further prove the correctness of the degree of texture orientation calculated by the fractal dimension. The combination of EBSD morphology and fractal dimension to obtain novel insights into the correlation between remanence and the degree of texture orientation will contribute to the development of high-performance Nd-Fe-B with high remanence. [ABSTRACT FROM AUTHOR]

Abstract—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. [ABSTRACT FROM AUTHOR]

In this research, the feasibility of additive manufacturing of permanent bonded magnets using fused deposition modelling (FDM) technology was investigated. The study employed polyamide 12 (PA12) as the polymer matrix and melt-spun and gas-atomized Nd–Fe–B powders as magnetic fillers. The effect of the magnetic particle shape and the filler fraction on the magnetic properties and environmental stability of polymer-bonded magnets (PBMs) was investigated. It was found that filaments for FDM made with gas-atomized magnetic particles were easier to print due to their superior flowability. As a result, the printed samples exhibited higher density and lower porosity when compared to those made with melt-spun powders. Magnets with gas-atomized powders and a filler loading of 93 wt.% showed a remanence (Br) of 426 mT, coercivity (Hci) of 721 kA/m, and energy product (BHmax) of 29 kJ/m3, while melt-spun magnets with the same filler loading had a remanence of 456 mT, coercivity of 713 kA/m, and energy product of 35 kJ/m3. The study further demonstrated the exceptional corrosion resistance and thermal stability of FDM-printed magnets, with less than 5% irreversible flux loss when exposed to hot water or air at 85 °C for over 1000 h. These findings highlight the potential of FDM printing for producing high-performance magnets and the versatility of this manufacturing method for various applications. [ABSTRACT FROM AUTHOR]

Polymer-bonded magnets are a class of composite material that combines the magnetic properties of metal particles and the molding possibility of a polymeric matrix. This class of materials has shown huge potential for various applications in industry and engineering. Traditional research in this field has so far mainly focused on mechanical, electrical or magnetic properties of the composite, or on particle size and distribution. This examination of synthesized Nd-Fe-B-epoxy composite materials includes the mutual comparison of impact toughness, fatigue, and the structural, thermal, dynamic-mechanical, and magnetic behavior of materials with different content of magnetic Nd-Fe-B particles, in a wide range from 5 to 95 wt.%. This paper tests the influence of the Nd-Fe-B content on impacting the toughness of the composite material, as this relationship has not been tested before. The results show that impact toughness decreases, while magnetic properties increase, along with increasing content of Nd-Fe-B. Based on the observed trends, selected samples have been analyzed in terms of crack growth rate behavior. Analysis of the fracture surface morphology reveals the formation of a stable and homogeneous composite material. The synthesis route, the applied methods of characterization and analysis, and the comparison of the obtained results can provide a composite material with optimum properties for a specific purpose. [ABSTRACT FROM AUTHOR]

The Nd-Fe-B hot-deformation magnet with high resistivity was successfully prepared by hot-pressing and hot-deformation of Nd-Fe-B fast-quenched powder with amorphous glass fiber. After the process optimization, the resistivity of the magnet was increased from 0.383 mΩ·cm to 7.2 mΩ·cm. Therefore, the eddy current loss of magnets can be greatly reduced. The microstructure shows that the granular glass fiber forms a continuous isolation layer during hot deformation. At the same time, the boundary of Nd-Fe-B quick-quenched the flake and glass fiber from the transition layer, which improves the binding of the two, and which can effectively prevent the spalling of the isolation layer. In addition, adding glass fiber improves the orientation of the hot deformation magnet to a certain extent. The novel design concept of insulation materials provides new insights into the development and application of rare earth permanent magnet materials. [ABSTRACT FROM AUTHOR]

Effects of low-melting Pr–Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd–Fe–B magnets were investigated. A small amount of Pr–Cu addition enhances the coercivity of the hot-deformation Nd–Fe–B magnets obviously. The coercivity of the hot-deformation Nd–Fe–B magnets with 4.0 wt% Pr85Cu15 addition increases to 1271 kA·m−1, 75.69% higher than that of Pr–Cu-free magnet (723 kA·m−1), and then decreases with 5 wt% Pr85Cu15 addition. It is observed that there a uniform RE-rich phase is formed wrapping the Nd2Fe14B main phase in the sample with 4.0% Pr85Cu15 addition by scanning electron microscopy (SEM), which promotes the coercivity. The angular dependence of coercivity for the hot-deformation Nd–Fe–B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning. The domain wall pinning is weakened, while the nucleation is enhanced after Pr–Cu addition. The remanence, intrinsic coercivity, and maximum magnetic energy product of the original Nd–Fe–B magnet are 1.45 T, 723 kA·m−1, and 419.8 kJ·m−3, respectively, and those of the sample with 4.0% Pr85Cu15 alloy addition are 1.30 T, 1271 kA·m−1, and 330.0 kJ·m−3, respectively. [ABSTRACT FROM AUTHOR]

Permanent magnets based on neodymium‐iron‐boron (Nd‐Fe‐B) alloys provide the highest performance and energy density, finding usage in many high‐tech applications. Their magnetic performance relies on the intrinsic properties of the hard‐magnetic Nd2Fe14B phase combined with control over the microstructure during production. In this study, a novel magnetic hardening mechanism is described in such materials based on a solid‐state phase transformation. Using modified Nd‐Fe‐B alloys of the type Nd16Febal‐x‐y‐zCoxMoyCuzB7 for the first time it is revealed how the microstructural transformation from the metastable Nd2Fe17Bx phase to the hard‐magnetic Nd2Fe14B phase can be thermally controlled, leading to an astonishing increase in coercivity from ≈200 kAm−1 to almost 700 kAm−1. Furthermore, after thermally treating a quenched sample of Nd16Fe56Co20Mo2Cu2B7, the presence of Mo leads to the formation of fine FeMo2B2 precipitates, in the range from micrometers down to a few nanometers. These precipitates are responsible for the refinement of the Nd2Fe14B grains and so for the high coercivity. This mechanism can be incorporated into existing manufacturing processes and can prove to be applicable to novel fabrication routes for Nd‐Fe‐B magnets, such as additive manufacturing. [ABSTRACT FROM AUTHOR]

Grain boundary diffusion is an effective approach to enhance coercivity for Nd-Fe-B magnets with reduced consumption of heavy rare earths (HRE). However, during diffusion treatment, the HRE tends to accumulate at the magnet surface, leading to an insufficient coercivity improvement and a decreased magnetic hysteresis loop squareness. Here, a Pr-Al-Cu/Tb-Al-Cu dual-alloy diffusion source is proposed to improve the diffusion of Tb element. During the GBD process, the low melting point Pr-Al-Cu alloy has higher diffusion rate than the Tb-Al-Cu alloy. The formation of continuous grain boundary phase by Pr-Al-Cu diffusion is beneficial to constructing effective channels for the subsequent diffusion of Tb. As a result, the dual-alloy diffusion enhances the coercivity of an initial magnet from 1040 to 1911 kA/m and a high loop squareness of 91.31% is also obtained. In comparison, the coercivity of the magnet treated by the Pr-Tb-Al-Cu single-alloy source was only enhanced to 1832 kA/m with loop squareness of 87.44%. The microstructure characterizations revealed that, by dual-alloy diffusion, both Pr and Tb can infiltrate deeply from the diffusion surface to the interior of the magnet. The formation of (Nd,Tb)2Fe14B phase with high anisotropy field and continuous grain boundary phase contribute to the coercivity enhancement. Using the dual-alloy diffusion source, the HRE resources can be efficiently utilized for increased infiltration depth by avoiding the formation of over-thick Tb-rich grain shells. This facile and flexible process is also attractive for industrial application.

Although coercivity is one of the fundamental properties of permanent magnets, it has not been well understood. In this paper, micromagnetics and thermal activation magnetization reversal theories are briefly reviewed, and then our recent macroscopic and microscopic experimental approaches for thermally activated magnetization reversal in advanced Nd-Fe-B hot-deformed magnets are explained. Our experimental results are well supported by the recent atomistic spin model calculations. Moreover, the systematic micromagnetics simulation study makes much clearer the physical picture of the thermally activated magnetization reversal process in permanent magnets. [ABSTRACT FROM AUTHOR]

In this study, low-iron Zn–Fe alloy coatings and pure Zn coatings, with or without trivalent chromium passivation treatment, were electrodeposited onto a sintered NdFeB magnet from a weak acid chloride bath. The surface morphology and structure of the coatings were then examined using the X-ray diffraction, a scanning electron microscope and 3D white-light interfering surface analysis. Meanwhile, the electrodeposition behavior and anti-corrosive properties of the coatings were investigated using cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy, and natural salt spray tests. The results indicate that a passivated Zn–Fe alloy coating with a 0.9 wt.% Fe content provided much better corrosion resistance than a pure Zn coating and could provide both anodic protection and physical barrier function in the NdFeB substrates. The Fe element in Zn–Fe alloy coating was predominantly in solid solution in η-phase and small amounts in elemental form, which was beneficial to acquire a compact coating and passivation film. Finally, the passivated Zn–Fe alloy coating withstood 210 h against a neutral 3.5 wt.% NaCl salt spray without any white rust, which was 3–4 times longer than the pure Zn coating. [ABSTRACT FROM AUTHOR]

To understand the influence mechanism of B and Ga content on magnetic properties of NdFeB ribbons, Nd 29.89 Fe bal Ga y Co 5.93 B x (wt%, x = 0.80–0.98, y = 0.24–1.04) alloys were prepared and magnetic properties, phase composition, coercivity mechanism, and microstructure of these alloys were investigated systematically. The melt-spun ribbons exhibited 2:14:1 phase grains with varying grain sizes and amorphous grain boundary phases at a wheel speed of 25 m/s. By reducing the B content within a specific range, grain refinement was achieved, resulting in narrower triangular grain boundaries, more uniform and continuous thin grain boundaries. Meanwhile, further increasing the Ga content, the grain shape changes from elongated to equiaxed, and the grain size is greatly refined. However, for x = 0.89, y = 0.84 strip, the coercivity is still reduced due to the large number of directly contacted grains. Consequently, an alloy composition of Nd 29.89 Fe bal Ga 0.64 Co 5.93 B 0.89 yielded excellent comprehensive magnetic properties, including a remanence of 8.5 kGs and a coercivity of 18.01 kOe. The corresponding magnetic properties enhancement mechanism is further discussed. • By reducing the B content, grain refinement was achieved, resulting in more uniform thin grain boundaries. • The grain shape changes from elongated to equiaxed, and the grain size is greatly refined with increasing Ga content. • Nd 29.89 Fe bal Ga 0.64 Co 5.93 B 0.89 alloy yielded excellent comprehensive magnetic properties: Br = 8.5 kGs and H cj = 18.01 kOe. [ABSTRACT FROM AUTHOR]

The RE 6 Fe 13 Ga phase (RE, Rare Earth) exhibits tremendous promise for achieving high-performance magnets. However, the challenge of controlling its formation and distribution hinders improvements in coercivity and squareness of Ga-doped magnets. In this study, we present a strategy to regulate the chemical composition of the RE-rich phase (0–9 at.% Cu, without Ga) and subsequently modify the phase transformation pathways of the RE 6 Fe 13 Ga phase in Ga-doped magnets by incorporating a Pr-rich Ga-Cu-containing aiding alloy. Remarkable magnetic performance was achieved, with values of B r =13.36 kGs, μ 0 H cj =20.82 kOe, (BH) max =43.75 MGOe, and μ 0 H k90 /μ 0 H cj =0.99. Through quantitative analysis of chemical and structural properties and phase fractions at grain boundary (GB) triple junctions, we elucidate the phase transformation pathways in the magnets. The reaction between amorphous RE-Ga-rich phases and the matrix phases, along with partial consumption of the RE-rich phases with the Mn 2 O 3 -type structure (space group Ia 3 ¯), led to the formation of the RE 6 Fe 13 Ga phase, accompanied by the presence of an amorphous Fe-rich transitional phase sharing a similar chemical composition. The gradual and partial involvement of the RE-rich phase improved the melt's wettability and delayed the formation of the RE 6 Fe 13 Ga phase. Consequently, a uniform microstructure was achieved, establishing the conditions for high magnetic performance. Thin metallic GBs and thick RE-rich, amorphous Fe-rich, and RE 6 Fe 13 Ga GBs were formed in the magnet. The former ensured squareness, while the sufficient coverage of the latter contributed to exceptional coercivity. The Pr-rich aiding alloy induces chemical heterogeneity, reinforcing the magnetic properties. This study advances our understanding of phase transformation pathways in Ga-doped magnets and introduces an effective approach for achieving high-performance magnets. [Display omitted] [ABSTRACT FROM AUTHOR]

• Gd-substituted nanocrystalline Nd-Fe-B alloys show a notable increase in thermal stability. • Gd substitution increases the Curie temperature (T c) of the RE 2 Fe 14 B phase. • Temperature coefficients α and β for Nd-Fe-B alloys are enhanced by Gd substitution. • Gd exhibits a heightened propensity for incorporation into the RE 2 Fe 14 B grains. Thermal demagnetization of Nd-Fe-B permanent magnets at elevated temperature presents a noteworthy challenge. Current research endeavors are concentrated on enhancing the thermal stability of Nd-Fe-B magnets. This study investigates the use of the cost-effective element Gd as a substitute for Nd in nanocrystalline melt-spun [(Nd 0.8 Pr 0.2) 1-x Gd x ] 14.3 Fe 76.9 B 5.9 M 2.9 (M = Co, Cu, Al and Ga) (wt.%; x = 0–0.6) alloys. Although Gd substitution is not conducive to the magnetic properties of the alloys at room temperature, the Gd-substituted alloys exhibit excellent high-temperature performance. The Curie temperature (T c) of the RE 2 Fe 14 B phase increases from 582 K to 643 K, with increasing Gd substitution from 0 to 0.6. The α and β coefficients for Gd-free (x = 0) alloy are −0.120 %/K and −0.468 %/K, respectively. By Gd substitution, they respectively increase to −0.068 %/K and −0.295 %/K for x = 0.6 alloy, which are superior to that of reported nanocrystalline Nd-Fe-B alloys and commercially sintered Nd-Fe-B magnets. Microstructural analysis revealed that Gd substitution promotes grain refinement. Furthermore, it was observed that Gd is uniformly distributed across both the grain boundary and main grains. Overall, this study offers a cost-effective and straightforward approach for enhancing the thermal stability of Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]

Diffusion efficiency and oxidation resistance of Pr-Tb-Cu source were simultaneously improved by introducing Al or Ni. The diffusion efficiency of source is effectively improved by deepening element infiltration and modifying interface of the magnet. The added Al or Ni forms a passivation layer on the source and increases the amorphous phase in the source, thus maintaining a high efficiency of sources after oxidation. Furthermore, the modified sources enhanced the chemical stability of magnet mainly because of the increased Volta potential of intergranular phase. This study provides a potential strategy for exploring high-efficient and durable diffusion sources for Nd-Fe-B magnets. [Display omitted] • Multicomponent grain boundary diffusion sources for Nd-Fe-B magnets are proposed. • Added Al or Ni can boost the diffusion efficiency and chemical stability of Pr-Tb-Cu. • The addition of Al or Ni is beneficial to improving the corrosion resistance of magnets. • Mechanisms in the enhancement of chemical stability and coercivity are clarified. [ABSTRACT FROM AUTHOR]

• Laser powder bed fusion of Nd-Fe-B magnets followed by post-process heat treatment. • Post-process heat treatments allow enhancement of magnetic properties. • As build condition affects response to heat treatment. • Crystallization of amorphous constitute enhances coercivity. The effect of post-process heat treatment on magnetic properties by laser powder bed fusion (LPBF) additively manufactured Nd-Fe-B magnets was studied in dependence of heat treatment temperature and as built condition. The magnets show very different magnetic performance in the as built condition, which depends on the adjusted LPBF process parameters. Heat treatments subsequent to LPBF processing lead to a remarkable change in the magnetic properties, whereby the response characteristics of the magnets depend on the as built condition and magnets with low initial coercivity show a large potential of improvement in case of low temperature heat treatments. Crystallization of amorphous constitutes in the microstructure, whose volume fraction depends on the LPBF manufacturing parameter, is responsible for this improvement. Exceeding the optimal heat treatment temperatures leads to the precipitation of α-Fe and deteriorates coercivity but enhances remanence of the magnets. Magnets with low initial coercivity require higher heat treatment temperatures to obtain optimal magnetic performance and show an increased stability against overaging. [ABSTRACT FROM AUTHOR]

A systematic study of the dependence of the Grain Boundary Diffusion Process (GBDP) on texture using Dy and Dy-Nd-Cu in microcrystalline sintered and nanocrystalline hot deformed Nd-Fe-B magnets was performed. Diffusion parallel or perpendicular to the texture direction, the nominal c-axes orientation in the polycrystals, was investigated. By measuring thin slices from the respective samples, coercivity as a function of (i) magnet thickness and (ii) diffusion depth was obtained showing that GBDP efficiency depends on the diffusion direction, diffusion source as well as the grain morphology originating from the magnet production route. In nanocrystalline hot deformed magnets perpendicular diffusion is superior due to the platelet-like shape of the grains. Microcrystalline sintered magnets consist of equiaxed grains hence the main effects originate in anisotropic lattice diffusion and pole surface hardening. The magnetic properties are correlated with a comprehensive analysis of microstructure, chemistry and magnetization reversal. • Comparing texture's effect on GBDP in Dy, Dy-Nd-Cu in microcrystalline sintered & nanocrystalline hot deformed magnets. • GBDP efficiency relies on diffusion direction, source, and grain morphology from the magnet production route. • Perpendicular diffusion is more effective in hot deformed (nanocrystalline) magnets due to their platelet-like grain shapes. • Comprehensive analysis links magnetic properties with microstructure, chemistry, and magnetization reversal studies. [ABSTRACT FROM AUTHOR]

The grain boundary diffusion process (GBDP) is one of the most efficient treatments for increasing the coercivity (H c) of Nd-Fe-B magnets. However, this enhancement typically occurs at the expense of remanence (M r). In this study, micromagnetic simulations were performed to quantify this tradeoff in hot-deformed Nd-Fe-B magnets subjected to the GBDP using a Nd-based eutectic alloy. The GBDP was imitated in a series of models with a gradually increasing volume fraction of the infiltrated Nd-rich nonmagnetic phase. This infiltration reduced the remanence and grain connectivity via the remaining thin magnetic intergranular phase (IGP), which in turn increased the coercivity. We distinguished between the roles of exchange and magnetostatic interactions in this coercivity enhancement. Furthermore, the simulated M r vs. H c curves defined realistic limits for coercivity that depended on the IGP magnetization, which was estimated to be 0.9 ± 0.1 T by reproducing experimental M r vs. H c data from the literature. [Display omitted] [ABSTRACT FROM AUTHOR]

To solve the problem of the low coercivity of Nd-Fe-B-based nanowires impeding their application in magnetic storage media, highly ordered Nd-Fe-B/Fe-Co composite nanowires were fabricated in an anodic alumina template by means of the alternating electrochemical deposition method. In this paper, the effect of soft and hard magnetic phase compositing on the magnetic properties of Nd-Fe-B-based nanowires was investigated, and the coercivity improvement mechanism was demonstrated. The results show that after annealing at 600 °C for 2 h, Nd-Fe-B/Fe-Co nanowires crystallize into a multiphase structure containing a hard Nd2(Fe, Co)14B phase and soft NdB4, NdB6, Fe7Nd, and Fe7Co3 phases. It is characterized that the Nd2(Fe, Co)14B phase preferentially nucleates, followed by NdB4 + NdB6 + Fe7Nd, while Fe7Co3 has been formed in as-deposited nanowires. The existence of a Nd2(Fe, Co)14B phase with high anisotropy fields, the remanence enhancement effect produced by exchange coupling between hard–soft magnetic phases, and the pinning effect between different phases make the composite nanowires approximately exhibit single hard magnetic phase characteristics with coercivity and remanence ratio as high as 4203.25 Oe and 0.89. The results indicate that synthesizing Nd-Fe-B/Fe-Co exchange-coupled composite nanowires via alternating electrodeposition is an effective way to optimize the magnetic performance of Nd-Fe-B-based nanowires.

High-performance Nd-Fe-B-based rare-earth permanent magnets play a crucial role in the application of traction motors equipped in new energy automobiles. In particular, the anisotropic hot-deformed (HD) Nd-Fe-B magnets prepared by the hot-press and hot-deformation process show great potential in achieving high coercivity due to their fine grain sizes of 200–400 nm, which are smaller by more than an order of magnitude compared to the traditional sintered Nd-Fe-B magnets. However, the current available coercivity of HD magnets is not as high as expected according to an empirical correlation between coercivity and grain size, only occupying about 25% of its full potential of the anisotropy field of the Nd2Fe14B phase. For the sake of achieving high-coercivity HD magnets, two major routes have been developed, namely the grain boundary diffusion process (GBDP) and the dual alloy diffusion process (DADP). In this review, the fundamentals and development of the HD Nd-Fe-B magnets are comprehensively summarized and discussed based on worldwide scientific research. The advances in the GBDP and DADP are investigated and summarized based on the latest progress and results. Additionally, the mechanisms of coercivity enhancement are discussed based on the numerous results of micromagnetic simulations to understand the structure–property relationships of the HD Nd-Fe-B magnets. Lastly, the magnetization reversal behaviors, based on the observation of magneto-optic Kerr effect microscopy, are analyzed to pinpoint the weak regions in the microstructure of the HD Nd-Fe-B magnets.

Although coercivity is one of the fundamental properties of permanent magnets, it has not been well understood. In this paper, micromagnetics and thermal activation magnetization reversal theories are briefly reviewed, and then our recent macroscopic and microscopic experimental approaches for thermally activated magnetization reversal in advanced Nd-Fe-B hot-deformed magnets are explained. Our experimental results are well supported by the recent atomistic spin model calculations. Moreover, the systematic micromagnetics simulation study makes much clearer the physical picture of the thermally activated magnetization reversal process in permanent magnets.

In this work, SEM images analysis and fractal dimension calculations are performed on the fracture surfaces for N50-type with low coercivity, 30 EH-type with high coercivity, and isotropic Nd-Fe-B permanent magnets. It is discovered for the first time that the difference between the fractal dimensions of fracture surface parallel and perpendicular to the c-axis D∥ and D⊥ for N50-type magnet with low coercivity is large, and the difference between the fractal dimensions of D∥ and D⊥ for 30 EH-type magnet with high coercivity is small. However, there is almost no difference in the fractal dimension of D∥ and D⊥ for isotropic magnet. The correlation between anisotropic fractal dimension of the fracture surface and coercivity is revealed. The difference between the fractal dimension of fracture surface D∥ and D⊥ not only reflects the difference in micro morphology, but also serves as an important performance parameter to characterize the coercivity of the magnet, which provides new insights for studying the relationship between the magnetic properties and the microstructure of permanent magnetic materials.

The impact of laser powder bed fusion (LPBF) on coercivity of Nd-lean commercial MQP™-S powder is investigated. It is found that different processing parameters, such as laser power, scan velocity, and hatch spacing, have a remarkable impact on the magnetic performance of LPBF-processed Nd–Fe–B permanent magnets. The increase of energy input during manufacturing will also increase coercivity and a maximum value of 920 kA/m ($\mu _{0}H_{c} =1.15$ T) was achieved without any further post-processing. Among other parameters, hatch spacing was identified as the major contribution to coercivity and its role is discussed on basis of the several re-melting events if hatch spacing becomes increasingly smaller than the laser focus diameter. The maximum coercivity is obtained, for hatch spacing of 35 $\mu \text{m}$ and laser focus diameter of 110 $\mu \text{m}$ , which led to a threefold re-melting of the sample. [ABSTRACT FROM AUTHOR]

We have studied influence of the microstructure of initial hydrogenation-disproportionation-desorption-recombination (HDDR) treated isotropic powders on the magnetic and microstructural properties of Nd–Cu infiltrated Nd-Fe-B hot-deformed magnets. To control the microstructure of the initial HDDR powders, the starting strip-cast alloys were heat-treated prior to the HDDR process (HDDR powder A). Compared to the HDDR powders prepared from the un-treated strip-casts (HDDR powder B), non-uniform and discontinuous Nd-rich intergranular phases were formed in the HDDR powder A. Therefore, most of the Nd-rich phases in the HDDR powder A were agglomerated at the triple junctions after the hot-deformation (Hot-deformed magnet A). In contrast, homogeneous Nd-rich intergranular phases enveloping the laterally elongated grains are observed in the hot-deformed HDDR powder B (Hot-deformed magnet B). As a result, the coercivity of hot-deformed magnet A is lower than that of the hot-deformed magnet B. Interestingly, after the Nd–Cu infiltration, the coercivity of hot-deformed magnet A increases more rapidly than that of the hot-deformed magnet B because the faster diffusion of liquid Nd–Cu via the c-plane intergranular phases occurs in the hot-deformed magnet A, while the agglomeration of Nd–Cu into the triple junctions occurs in the hot-deformed magnet B. High resolution transmission electron microscopy showed that the Nd–Cu infiltration on the hot-deformed magnet A leads to the formation of thicker and non-ferromagnetic intergranular phases on the (001) planes of Nd2Fe14B grains, resulting in the magnetic isolation of individual grains and increase of pinning force against the domain wall motion.

Remanence is an important parameter of magnetic property for Nd-Fe-B magnets, and high remanent magnetization is a prerequisite for high-performance magnets. In this paper, the surface morphology perpendicular to the texture orientation direction and parallel to the texture orientation direction is analyzed by Nd-Fe-B permanent magnets with different compositions. For the first time, the relationship between the remanence of a magnet and the degree of texture orientation is explained in depth using the fractal dimension. The fractal dimension of surface morphology combined with the remanence equation yields the degree of texture orientation of the magnet, which is in agreement with the trend of the squareness factor of the demagnetization curves. Among the three samples, the Nd-Fe-B sample has the highest degree of texture orientation, the Pr-Nd-Fe-B sample has the lowest degree of texture orientation, and the Nd-Ce-Fe-B sample is in between the first two. The multiples of uniform (pole) density obtained by EBSD further prove the correctness of the degree of texture orientation calculated by the fractal dimension. The combination of EBSD morphology and fractal dimension to obtain novel insights into the correlation between remanence and the degree of texture orientation will contribute to the development of high-performance Nd-Fe-B with high remanence.

In this research, the feasibility of additive manufacturing of permanent bonded magnets using fused deposition modelling (FDM) technology was investigated. The study employed polyamide 12 (PA12) as the polymer matrix and melt-spun and gas-atomized Nd–Fe–B powders as magnetic fillers. The effect of the magnetic particle shape and the filler fraction on the magnetic properties and environmental stability of polymer-bonded magnets (PBMs) was investigated. It was found that filaments for FDM made with gas-atomized magnetic particles were easier to print due to their superior flowability. As a result, the printed samples exhibited higher density and lower porosity when compared to those made with melt-spun powders. Magnets with gas-atomized powders and a filler loading of 93 wt.% showed a remanence (Br) of 426 mT, coercivity (Hci) of 721 kA/m, and energy product (BHmax) of 29 kJ/m3, while melt-spun magnets with the same filler loading had a remanence of 456 mT, coercivity of 713 kA/m, and energy product of 35 kJ/m3. The study further demonstrated the exceptional corrosion resistance and thermal stability of FDM-printed magnets, with less than 5% irreversible flux loss when exposed to hot water or air at 85 °C for over 1000 h. These findings highlight the potential of FDM printing for producing high-performance magnets and the versatility of this manufacturing method for various applications.

The Nd-Fe-B hot-deformation magnet with high resistivity was successfully prepared by hot-pressing and hot-deformation of Nd-Fe-B fast-quenched powder with amorphous glass fiber. After the process optimization, the resistivity of the magnet was increased from 0.383 mΩ·cm to 7.2 mΩ·cm. Therefore, the eddy current loss of magnets can be greatly reduced. The microstructure shows that the granular glass fiber forms a continuous isolation layer during hot deformation. At the same time, the boundary of Nd-Fe-B quick-quenched the flake and glass fiber from the transition layer, which improves the binding of the two, and which can effectively prevent the spalling of the isolation layer. In addition, adding glass fiber improves the orientation of the hot deformation magnet to a certain extent. The novel design concept of insulation materials provides new insights into the development and application of rare earth permanent magnet materials.

Polymer-bonded magnets are a class of composite material that combines the magnetic properties of metal particles and the molding possibility of a polymeric matrix. This class of materials has shown huge potential for various applications in industry and engineering. Traditional research in this field has so far mainly focused on mechanical, electrical or magnetic properties of the composite, or on particle size and distribution. This examination of synthesized Nd-Fe-B-epoxy composite materials includes the mutual comparison of impact toughness, fatigue, and the structural, thermal, dynamic-mechanical, and magnetic behavior of materials with different content of magnetic Nd-Fe-B particles, in a wide range from 5 to 95 wt.%. This paper tests the influence of the Nd-Fe-B content on impacting the toughness of the composite material, as this relationship has not been tested before. The results show that impact toughness decreases, while magnetic properties increase, along with increasing content of Nd-Fe-B. Based on the observed trends, selected samples have been analyzed in terms of crack growth rate behavior. Analysis of the fracture surface morphology reveals the formation of a stable and homogeneous composite material. The synthesis route, the applied methods of characterization and analysis, and the comparison of the obtained results can provide a composite material with optimum properties for a specific purpose.

The coercivity of the sintered Nd-Fe-B permanent magnets prepared by the dual-main-phased (DMP) process can be significantly enhanced. This paper provides a comprehensive review of this method. The methodology and process of the DMP method are outlined, along with its mechanisms and advantages in improving magnet performance. Furthermore, this study highlights the outstanding performance of DMP magnets in terms of mechanical properties and corrosion resistance. Lastly, the future development trends and research directions for the DMP method are explored, such as optimizing process parameters, exploring novel alloy designs, and developing higher-performance magnet materials. [ABSTRACT FROM AUTHOR]

We report magnetic and microstructural changes in Nd-Fe-B sintered magnets after the grain boundary diffusion process (GBDP) of low-melting LRE-Al-Cu alloys [LRE (Light Rare-earth) = La and Pr]. A distinctive microstructural feature of the magnets GBD treated with La-Al-Cu (LAC) and Pr-Al-Cu (PAC) were characterized via the electron probe microanalysis and high-angle annular dark-field scanning transmission electron microscopy analysis at a depth of 50 μm from the magnet surface. The formation of a thick high-anisotropy Pr-Al-rich shell was clearly observed in the PAC-GBDP magnets, whereas there was no distinct shell formation in the LAC-GBDP magnets. La, Al, and Cu were dissolved in the Nd-rich grain boundary phase (GBP) rather than in the main phase, thereby thickening the GBP. This resulted in a difference in the coercivity gain between PAC-GBDP (+6.4 kOe) and LAC-GBDP (+3.3 kOe). The point to note here is that the remanence reduction induced by LAC-GBDP (−0.2 kG) is much smaller than that induced by PAC-GBDP (−1.2 kG) because the grain boundary diffused La-Al-Cu, which can dilute the saturation magnetization of the Nd 2 Fe 14 B (2–14-1) crystal, does not dissolve into 2–14-1. Furthermore, the squareness of demagnetization curves of the LAC-GBDP magnets (98%) was much improved than that of the PAC-GBDP magnets (86%). This is because chemically induced liquid film migration (CILFM), an undesirable grain growth phenomenon induced by shell formation, does not occur in LAC-GBDP magnets. In conclusion, the deterioration in remanence and squareness, which are serious problems in the LRE-GBDP, can be minimized by the LAC-GBDP; thus, the utilization of La in the GBDP is a promising method for obtaining a high maximum energy product of the magnets. Based on the results of this analytical work, we propose a guide for developing a cost-effective novel GBDP source that can prevent grain growth by CILFM and increase the magnetocrystalline anisotropy of the shell. • The distinct microstructure of the grain boundary diffused (GBD) magnets with La-Al-Cu and Pr-Al-Cu were characterized. • Pr-Al-Cu causes undesirable grain growth from Pr-Al-rich shell formation by Chemically induced liquid film migration (CILFM). • La-Al-Cu prevents CILFM and concentrated at the grain boundary, thereby maintaining high remanence and squareness. • Novel cost-effective La-based GBD source was proposed for enhanced magnetic performance. [ABSTRACT FROM AUTHOR]

Nd-Fe-B magnets were manufactured by laser powder bed fusion (LPBF) using commercially available spherical powder (MQP-S-11-9). The magnets were manufactured at four different volume energy densities but similar relative densities to investigate the relations between the process, structure, and characteristics. Unlike the nanocomposite microstructure of the initial powder, the microstructure of the LPBF samples had (Nd, Pr) 2 Fe 14 B grains separated by grain boundary phases through the remelting and solidification of the initial powder. The cooling rate of the melt pool increased as the volume energy density decreased, suppressing the crystallization of α-Fe in the grain boundary phase. When the volume energy density was less than 86 J/mm3, the crystallization of α-Fe was fully suppressed, and the grain boundary phases became amorphous, resulting in higher coercivity than that of the initial powder. The magnet with the strongest magnetic properties of H ci = 10.3 kOe, B r = 6.2 kG, and (BH) max = 7.5 MGOe was produced when LPBF was performed under the conditions of P90, V500, H70, and L30 (volume energy density = 85.7 J/mm3). The solidification behavior of Nd-Fe-B magnets during LPBF was analyzed in detail using thermodynamic simulations. In this study, the microstructure of the fusion zone (FZ) and the heat affected zone (HAZ) according to process parameters was analyzed, and the effect of the solidification microstructure on the magnetic properties of Nd-Fe-B magnets was reported. [Display omitted] • Nd-Fe-B magnets were manufactured by laser powder bed fusion (LPBF) using spherical powder of Nd 2 Fe 14 B/α-Fe nanocomposites. • The microstructure had (Nd, Pr) 2 Fe 14 B grains separated by grain boundary phases through the remelting and solidification. • The highest magnetic properties, B r = 6.2 kG and H cj = 10.3 kOe, reached in samples with the fast-cooling rate. • The solidification behavior of Nd-Fe-B magnets during LPBF was analyzed in detail using thermodynamic simulations. [ABSTRACT FROM AUTHOR]

• High-coercivity nanostructured Nd-Fe-B alloy powder synthesized. • The influence of the stoichiometric composition on the magnetic properties is investigated. • The influence of iron content on coercivity is investigated. • Higher Nd and B contents enhance the formation of the high-coercivity Nd 2 Fe 14 B phase. • X-ray diffraction analysis reveals the tetragonal crystal structure of the nanostructured Nd-Fe-B alloy. For the first time, a nanostructured alloy powder with high coercive force was obtained by a chemical method without the addition of Dy, which can compete with physical methods of production. The work carried out a study of the influence of stoichiometric composition on the magnetic properties of nanostructured Nd-Fe-B alloys. Alloys with different contents of Nd, Fe, and B were synthesized: Nd 12 Fe 84 B 6 , Nd 14 Fe 80 B 6 , Nd 16 Fe 76 B 8 , and Nd 16 Fe 72 B 8. With a decrease in the iron content in the first two compositions, a decrease in the iron content in the soft magnetic phase α-Fe was observed, which led to an increase in the coercive force H c and a decrease in the values of M s and M r. Experiments have shown that an increase in the content of Nd and B promotes the formation of the hard magnetic phase Nd 2 Fe 14 B and an increase in the coercive force. For example, the nanostructured Nd 16 Fe 76 B 8 alloy demonstrated a maximum coercive force of H c = 8439 Oe, while compensating for the values of M s (109 emu*g−1) and M r (78 emu*g−1). A comprehensive study of the nanostructured Nd 16 Fe 76 B 8 alloy was carried out, including structural analysis. XRD using FullProff and Vesta software revealed the tetragonal crystal structure of the Nd 2 Fe 14 B phase, providing details of the atomic arrangement. The unit cell contains four layers with Nd and Fe atoms, and boron atoms are embedded in the center of the octahedron of Nd and Fe atoms, playing an important role in the magnetic exchange interaction. The results of Mössbauer spectroscopy confirmed the presence of the Nd 2 Fe 14 B phase and revealed details of the state of Fe atoms in the structure of six sextets. [ABSTRACT FROM AUTHOR]

• The impact of HDDR preparation processes, with or without homogenization heat treatment, on Nd-Fe-B powders/bonded magnets. • The residual α–Fe phase impedes the disproportion of Nd 2 Fe 14 BH x, reducing the remanence of HDDR bonded magnets. • The angular distribution of surface magnetic field intensity for Nd–Fe–B multipole magnetic rings. We investigated the influence of hydrogenation-disproportionation-desorption-recombination (HDDR) preparation processes, with or without long-time homogenization heat treatment, on the microstructure and hard magnetic properties of Nd 12.7 B 6.5 Co 2.1 Cr 0.1 Al 0.5 Nb 0.3 Ga 0.5 Fe 77.3 powders/bonded magnets. Hard magnetic properties such as remanence (B r = 1.01 T), coercivity (H cj = 949.39 kA/m), and maximum magnetic energy product (BH) max = 181.54 kJ/m3 were achieved for HDDR bonded magnets with homogenization heat treatment. In contrast, magnets prepared without homogenization heat treatment exhibited B r = 0.65 T, H cj = 854.69 kA/m, and (BH) max = 66.98 kJ/m3. The notable decrease in remanence for magnets prepared without homogenization treatment is attributed to the presence of α–Fe in the parent alloy, which inhibits the hydrogenation-disproportionation process and consequently affects the orientation of the crystallographic texture. Furthermore, we fabricated bonded quadrupole magnetic rings using HDDR powder prepared with homogenization heat treatment. The study also explored the relationship between disproportionation temperature and surface magnetic field intensity for these quadrupole magnetic rings. [ABSTRACT FROM AUTHOR]

Grain boundary diffusion of the heavy rare-earth element Tb, facilitated by multielement alloys, was investigated in Nd-Fe-B sintered magnets. This study systematically examined magnets treated with various diffusion sources: conventional TbH x powders, a mixture of TbH x and Pr 45.0 Cu 18.3 Al 27.5 Ga 9.2 (at%) alloys, and integrated Tb 10.0 Pr 35.0 Cu 18.3 Al 27.5 Ga 9.2 (at%) alloys. Results indicated that, although the total Tb content was considerably reduced from 2.80 to 0.49 wt%, the coercivities of the magnets employing multielement composite diffusion sources were still enhanced to a high level, comparable to those treated with TbH x alone. Notably, the coercivity of the magnets diffused with Tb 10.0 Pr 35.0 Cu 18.3 Al 27.5 Ga 9.2 substantially increased to 24.14 kOe from the original value of 14.19 kOe, and the Tb utilization rate reached 73.47%. In addition, the coercivity increment per unit mass of Tb was 20.31 kOe/wt%. Microstructural observations and analyses of the diffusion process revealed that the assisted diffusion by the multielement composite effectively prevented superficial Tb accumulation, thereby enhancing diffusion efficiency. This process resulted in the formation of typical continuous grain boundaries and a core-shell structure. Furthermore, it was observed that low-melting-point metal elements, particularly Al, preferentially infiltrated the magnet interior and wetted the grain boundary channels during the early diffusion stages, facilitating efficient Tb diffusion. This study lays the groundwork for developing highly efficient magnets with reduced heavy rare-earth content. • High-performance magnets were prepared by diffusing Tb with assist of multi-elements. • Coercivity increase of 9.95 kOe was achieved when consuming only 0.49 wt% Tb. • Favorable microstructures were formed by collaboratively diffusing multi-elements. • Priority diffusion of low-melting-point elements promoted the diffusion effect of Tb. [ABSTRACT FROM AUTHOR]