A novel two-step grain boundary diffusion approach utilizing PrYCu and DyH was employed on the sintered NdCe-Fe-B magnets (50 wt% Nd substituted by Ce). The coercivity of the two-step diffusion magnet reached 16.14 kOe, much higher than the magnet with only DyH diffusion (12.68 kOe). The coercivity enhancement was more distinct than that in conventional Dy/Tb diffused high-Ce magnets and enhanced thermal stability significantly. Microstructural and compositional analyses suggested that the pre-diffusion of PrYCu could form the Y-rich Ce-lean shell, which inhibited the Dy from diffusing into the interior of the grains during DyH diffusion. Instead, Dy trended to migrate into the deep interior of the magnets, accounting for the improved Dy diffusion efficiency and coercivity in the high Ce content magnet. Magnetic domain observation verified the strengthened demagnetization-resistance over a more extensive depth range. This work laid a foundation for the advancement of high-Ce content magnets with superior performance.

To address the key issue of coercivity degradation associated with the presence of the CeFe2 phase in Cecontaining Nd-Fe-B sintered magnets, this study systematically investigates the regulation mechanism of Ce redistribution and CeFe2 phase evolution under different annealing temperatures. By tailoring the annealing temperature within the range of 360-520 degrees C, 400 degrees C is identified as the critical temperature window for achieving optimal magnetic performance, where the coercivity reaches 13.99 kOe-an increase of 1.09 kOe compared with the as-sintered state. Comprehensive analyses using XRD, EPMA, and TEM reveal that moderate annealing promotes the redistribution of Ce between the grains and grain boundaries, significantly reducing the fraction of the CeFe2 phase while inducing the formation of amorphous Ce-Fe layers and rare-earth oxide grainboundary phases. This composite interfacial structure effectively weakens intergranular magnetic exchange coupling and enhances magnetic isolation, thereby substantially improving coercivity. The results demonstrate that the coercivity of Ce-containing Nd-Fe-B magnets is synergistically governed by Ce diffusion behavior and the equilibrium of the CeFe2 phase. Precise control of thermal treatment enables effective suppression of CeFe2 phase and optimization of grain-boundary structure, providing new theoretical insights and processing routes for the development of low-cost, high-performance Ce-containing Nd-Fe-B magnets.

This work enhances the coercivity of high-Ce-content Nd-Ce-Fe-B sintered magnets by grain boundary diffusion of Pr(90-x)HoxCu5Al5 (x = 0, 20, 40, 60, wt%) alloy powders, and investigates the effect of Ho content in the diffusion source on the magnetic properties and microstructure of the magnets. The coercivity of high-Ce-content sintered magnets increases with the increase of Ho content in the diffusion source. When the Ho content in the diffusion source reaches 60 wt%, the coercivity of the magnets reaches 14.92 kOe, with an increment of 3.13 kOe. Microstructural analysis demonstrates that in Pr-Ho-Cu-Al-diffused magnets, a Ho-rich shell with higher magnetocrystalline anisotropy field is formed on the surface layer of the matrix grains, which suppresses the nucleation of reverse magnetization domains. Meanwhile, a continuous and uniform grain boundary phase is formed, thereby effectively enhancing the coercivity of the magnets.

•Resolving spatially and identifying chemical atoms in layered GeS material.•GeS nanosheets with a thickness of 2, 3 layers exhibit high optical nonlinearity.•Realizing a passively mode-locked fiber laser based on a GeS saturable absorber.•2D GeS is a promising nonlinear material for mid-infrared waveband applications.

Hydrogen–disproportionation–desorption–recombination (HDDR) Nd–Fe–B magnetic powders are promising to prepare bulk anisotropic magnets, but high magnetic performance has not been achieved due to the absence of an Nd-rich phase in the powder and the low degree of orientation of the bulk magnets. In this study, an alternative process of pre-orientation sintering via magnetic alignment followed by spark plasma sintering was proposed to prepare the precursor of hot-deformation (HD) magnets, and a high maximum energy product of 294 kJ m −3 was achieved in the HD magnet with a relatively low height reduction of 35%, then an improved coercivity of 1107 kA m −1 could be obtained followed by a grain boundary diffusion of Pr 40 Tb 30 Al 20 Cu 10 . Microstructure analysis indicates that pre-orientation of HDDR powders facilitates grain rotation and alignment during the HD process, thereby reducing the minimum deformation ratio. It helps to obtain the deformed grains with lower shape anisotropy and smaller grain size, enabling a good compatibility of magnetic and mechanical behaviors. In-situ Lorentzian transmission electron microscopy results show that the magnetic domains have been strongly fixed by the thick intergranular RE-rich phase and the fully Tb-diffused grains, which contributes to the improved coercivity after grain boundary diffusion. This study provides a guiding significance for the preparation of the anisotropic Nd–Fe–B HDDR magnets with optimized performance.

Manipulation of the internal architecture is essential for electromagnetic interference (EMI) shielding performance of metal-based coatings, which can address the electromagnetic pollution in large-size, complex geometries, and harsh environments. In this work, oriented segregated structure with conductive networks embedded in magnetic matrix was achieved in Fe-based amorphous coatings via Ni-Cu-P functionalization of (Fe0.76Si0.09B0.1P0.05)(99)Nb-1 amorphous powder precursors and then thermal spraying them onto aluminum (Al) substrate. Benefiting from the unique magnetic-electric structure, the coating@Al composite delivered prominent EMI shielding performance. The EMI shielding effectiveness (SE) of modified coating@Al composite is similar to 41 dB at 8-12 GHz, doubling the value of Al substrate and is 15 dB greater than that of Ni-Cu-P-free coating@Al composite. Microstructure analysis showed that the introduced Ni-Cu-P insertions forcefully suppress the serious oxidation of the magnetic precursors during thermal spraying and form a dense conductive network in the magnetic matrix. Electron holography observation and electromagnetism simulation clarified that the modified coating can effectively trap and attenuate the incident radiations because of the electric loss from Ni-Cu-P conductive network, magnetic loss from Fe-based amorphous coating, and the electromagnetic interactions in the oriented segregated architectures. Moreover, the optimized thermal isolation and mechanical properties brought by structural improvement enable the coating to shield complex parts in thermal shock and mechanical loading environments. Our work gives an insight on the design strategies for metal-based EMI shielding materials and enriches the fundamental understanding of EMI shielding mechanisms. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Amorphous alloy is a kind of double green soft magnetic material with high saturation magnetic induction, low coerce, low loss, high stability and other excellent properties. Instead of cold rolled silicon steel sheet, it can reduce the loss and improve the efficiency of the motor to a great extent. Combined with the characteristics of amorphous alloy and based on the design theory of permanent magnet motor, this paper uses the MATLAB software to write the electromagnetic design program of amorphous alloy permanent magnet synchronous motor, which has the characteristics of visual parameter input, rapid electromagnetic calculation, and convenient man-machine interaction. An example is given to verify the reliability of the program.

Hot-deformed Nd-Fe-B magnets with and without B-Fe particles are prepared to investigate the effect of B-Fe particles on the magnetic properties. After the addition of 0.5 wt% B-Fe particles, the coercivity of the hot-deformed magnet is increased. It is found that B-Fe particles inhibits the abnormal growth of grains around the melt-spun ribbons' boundaries results in fine grains. Besides, by further annealing, the fine grains have a modification effect on the boundary, which reduces the demagnetization nucleation field, thereby further optimizing the coercivity of the magnet.

Stress-induced alignment of Nd2Fe14B nanograins along (001) planes represents a practical process with which to create uniaxial high-anisotropy NdFeB magnetic materials. The residual non-oriented coarse-grain defect at ribbons’ surfaces not only deteriorates the [001]-oriented structure but also facilitates the low-field nucleation of reversed magnetic domains. Although the local structural defect has proved to be controllable via doping refractory ceramic nanomaterials, the natures of coarse-grain suppression and corresponding magnetic configuration variation remain poorly known. Herein, we comprehensively discuss the correlation between structures and magnetic configurations to address the role of WC dopants in the kinetics of stress-induced deformation system. The statistical data suggest that the reinforced stress caused by WC nanoparticles effectively suppresses the size of Nd2Fe14B grains and induces their anisotropic growth. Simultaneously, the evolved (006) polar figures further confirm that the crystallographic orientation of interfacial Nd2Fe14B grains is also improved by reinforced stress. The analysis for magnetic configurations around dopants confirms that the coarse-grain inhibited structure reduces the low-field nucleation probability of reversed magnetic domains. Relying on their combined effect, the coercivity is increased by about 12%. These observations are further verified by the micromagnetic simulation computations. All these above findings may enrich the knowledge of stress-induced deformation mechanism and deepen the fundamental understanding of the correlation between structure and magnetic features.

Nano-crystalline and micron-crystalline Nd-Fe-B powders were employed to hydrogenation-disproportionation-desorption-recombination (HDDR) process to investigate the structural factors of deformation ability in HDDR powders. It was found that the deformation ability and magnetic properties of the final die-upset magnet were optimized significantly by nano-crystalline powders. Structure investigation shows that the variations in coercivity and deformation ability were attributed to the Nd-rich phase distribution in HDDR powders. Meanwhile, enhancement of remanence and squareness indicated the uniform distribution of Nd-rich phase and the narrow grain size distribution by using nano-sized crystalline powders were in favor of c-axis alignment of 2:14:1 phase.

The effect of the morphology of the melt-spun powders on the compressive and bending strength of hot-deformed Nd-Fe-B magnets has been investigated. The results suggest that the refinement of the melt-spun powders can effectively reduce the mechanical anisotropy of the hot-deformed Nd-Fe-B magnets in two directions parallel and perpendicular to c-axis without sacrificing the magnetic properties. The observation for microstructure shows that the refinement of the melt-spun powders reduced the shape anisotropy of the particles and improved the mechanical properties of the hot-deformed Nd-Fe-B magnets perpendicular to c-axis, thereby improving the mechanical anisotropy of the hot-deformed Nd-Fe-B magnets.

Pre-diffusion grain boundary strategy was proposed to fabricate die-upset Nd-Fe-B magnets with excellent magnetic properties. Microstructure modification of die-upset magnets played a key role in determining the magnetic properties. The effective coercivity enhancement of die-upset magnets through pre-diffusion process was enhanced from 0.076 T/wt%Pr to 0.114 T/wt%Pr with a slight remanence loss. Driven by heat, the Pr-Cu eutectic alloys were diffused into melt-spun ribbons with weakened exchange couple of matrix phase, which led to enhanced coercivity. The uniform distribution of intergranular phase was obtained in die-upset magnet with pre-diffusion process and the remanence reduction was limited with a high squareness factor. Microstructure analysis confirmed that the pre-diffusion process suppressed the longitudinal/lateral ratio of platelet-shaped grains and grain growth in die-upset process. Simultaneously, the pre-diffusion process facilitated the formation of continuous and uniform grain boundaries (GBs). The grain size was distributed over a narrow range of value with similar local critical nucleation field, which resulted in the improved squareness. The thick and continuous intergranular phase strengthened the magnetic isolation between neighboring Nd2Fe14B phases and offered more "pinning" sites for domain wall shift. The modified structure hindered the nucleation and spread of reverse domains in a low magnetic field in favor of the coercivity enhancement. The view-direct time-dependent behavior of reverse magnetic domains indicated that the coercivity mechanism for die-upset magnet was a combination of "pinning" effect and nucleation model. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hot-deformed Nd-Fe-B magnets co-doped with and without Tb-Fe addition are prepared to study the effect of Tb-Fe particles on the magnetic properties and thermal stability. With the addition of 2 wt. % Tb-Fe particles, the coercivity increases by 28.7%, while the remanence decreases by only 3.6%. It is observed that Tb atoms are diffused from the Tb-Fe particles to neighboring Nd-Fe-B melt-spun ribbons, in which Nd atoms in 2:14:1 grains are partially substituted by Tb atoms. The formation of local high-anisotropy (Nd, Tb)(2)Fe14B regions promotes the locally magnetically hardening, suppressing the nucleation of reversed magnetic domains at the low-anisotropy surface magnetic "defects". This can be employed to explain the coercivity enhancement of diffusion-processed hot-deformed magnets. In addition, the thermal stability of the magnet is improved due to the higher Curie temperature of (Nd, Tb)(2)Fe14B grain. (C) 2018 Elsevier B.V. All rights reserved.

The anisotropic hot deformed magnets consisting of Nd-rich and Ce-rich 2:14:1 main phases were prepared using dual alloy process. After heat treatment, crystallographic alignment was improved and compositional heterogeneity reduced. Coercivity and remanence descended with increasing Ce-Fe-B addition, and then were improved after diffusing heat treatment compared with magnets without heat treatment. Moreover, the magnetization behaviors of magnets were discussed and the coercivity mechanism was controlled by inhomogeneity of the domain wall pinning. The interaction domains were observed and the moment of Ce-rich grain was prior to reversal by comparison with Nd-rich grain in an applied field due to the lower magnetocrystalline anisotropy. (C) 2017 Published by Elsevier B.V.

Low-melting eutectic diffusion has emerged as a practical approach to enhance the coercivity of hot-deformed Nd–Fe–B magnets. Herein, we report a high-efficient stress-induced eutectic diffusion method to develop high-coercivity hot-deformed Nd–Fe–B magnets. In this method, fast Pr–Cu eutectic diffusion is accomplished with the hot-pressed and hot-deformed processes simultaneously. The coercivity of diffusion-processed magnets is substantially increased by about 33% with a slight remanence loss. The applied stress effectively controls the distribution of Pr–Cu eutectic and relieves the remanence loss. Microstructure analysis confirms that the Pr–Cu concentration gradient constructed in hot-pressed precursors effectively suppresses the near-surface grain growth during the hot-deformation process and reduces the lateral/longitudinal ratio of platelet-shaped grains. The formation of thick and continuous Pr-rich grain boundaries weakens the exchange coupling between neighboring grains, offering more “pinning” sites for domain wall displacement. Partially Pr-substitution improves the locally magnetically “hardening” of 2:14:1 main phases. The optimized structural and magnetic characterizations hinder the nucleation and propagation of reversed magnetic domains at low magnetic fields, which is beneficial to coercivity enhancement. These findings clarify the characteristics of the stress-induced diffusion method and give a new insight into the structural modulation for Nd–Fe–B materials.

Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets. Firstly,rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process. The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process. The resulting magnets possess many advantages such as near-net-shape, outstanding corrosion resistance, and ultrafine-grain structure. The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report. As a near-net-shape technique, the hot deformation process has notable advantages with regard to the production of irregular shapes, especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls. The difficulties associated with the fabrication of crack-free,homogeneous, and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design,adjustment of deformation parameters, and application of theoretical simulation. Considering the characteristics of hotdeformed magnets which include grain shape and size, anisotropic distribution of intergranular phases, etc., investigation and improvement of the mechanical and electric properties, in addition to thermal stability, with the objective of improving the application of hot-deformed magnets or ring-shaped magnets, is of practical significance.

The microstructure of ribbons interface was optimized by doping the hexagonal boron nitride nanoplatelets (h-BNNP) in hot-deformed magnets. The remanence increased markedly and reached to a maximum value of 14.06 kGs. The coercivity and the energy product exhibited similar variation trends to the remanence, showing maxima of 16.92 kOe and 49 MGOe, respectively. Microscopy observations revealed that surface grains of ribbons tended to align with the interior grains due to the uniform local compressive stress induced by h-BNNP with relatively large flat surface, resulting in hot-deformed magnets with microscopically homogeneous structure and improved texture. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hot-deformed Nd-Fe-B magnets with a larger maximum energy product at higher operating temperature are desirable in a wide range of applications but are very challenging to realize in a common “single phase” structure. Here, we show the macroscopic structural design in hot-deformed magnets by using two kinds of melt-spun powders with/without heavy rare earth. Higher coercivity with a remarkably improved maximum energy product is obtained in the separated multilayer magnet. We find that the multilayer structure can improve the c-axis alignment of platelet-shaped grains in each layer and propose the possible interlayer's long-range magnetic interaction explaining the recoil loop open of designed magnets, coupled with visible field-induced domain evolution. This experimental approach reveals exciting applications of structural design in ultrafine-grained hot-deformed magnets.

Anisotropic ultrafine-grained Nd-Fe-B magnets with WC addition were prepared by hot deformation. With WC nano-particles addition of ~1.0wt.%, the squareness was optimized and the coercivity of the hot-deformed magnets increased substantially by 2.16kOe, from 15.59 to 17.75kOe without expense of the remanent magnetization. The observation for microstructure revealed that the WC nano-particles mainly existed on the interfaces of melt-spun ribbons. Meanwhile, due to the local compressive stress induced by the hard WC nano-particles, the deformability of neighboring grains was remarkably enhanced which leads to the reduction of the coarse grain regions.