Search

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]

Compared to introducing Nd 70 Cu 30 (at%) alloys, the addition of Gd 70 Cu 30 exhibited a better enhancement effect, and both the best coercivity of 9.38 kOe and magnetic energy product of 29.72 MGOe were simultaneously obtained when the Gd 70 Cu 30 addition amount reached 4 wt% in the Nd-Ce-Fe-B magnet with Ce accounting for more than 14.16 wt% of the entire magnet. The further microstructural analyses showed that the higher coercivity when adding Gd 70 Cu 30 alloy was mainly attributed to the continuous thin-walled grain boundary phases and the typical core-shell structure with a Ce-rich core and Gd/Nd-rich shell. Meanwhile, the unfavorable REFe 2 -type phases had been greatly suppressed and the ratio of Ce3+ ions to Ce4+ ions had been promoted, which was generally beneficial for the improvement of magnetic properties. This work provides further insights into preparing sintered magnets with high Ce-content and high-performance. • High Ce-content magnets were prepared by intergranular addition of Gd-Cu alloys. • The microstructure was obviously optimized by introducing appropriate Gd-Cu alloys. • The mixed valence state of Ce shifted to a trivalent that favors magnetic properties. [ABSTRACT FROM AUTHOR]

SmCo permanent magnets are used in some of the strongest permanent magnets, particularly for applications between about 200 and 550 °C. However, their brittleness limits their practical use. Improving their mechanical properties is therefore of great practical significance. Cryogenic treatment is firstly applied in SmCo permanent magnets to enhance the mechanical properties. The flexural strength has been increased by 14.3% along the weakest orientation, and the impact toughness has been increased by 7.0%. After cryogenic treatment, the intrinsic coercivity is slightly increased, and the other magnetic properties are almost unchanged, which is different from other methods to improve mechanical properties at the expense of magnetic properties. The enhancement of flexural strength and impact toughness primarily stems from a decrease in residual stress. This study provides an effective and convenient approach to enhance the mechanical properties in Sm 2 Co 17 permanent magnets without sacrifice of magnetic properties. • Cryogenic treatment is firstly applied in SmCo permanent magnets to enhance the mechanical properties. • Flexural strength increased by 14.3%, impact toughness increased by 7.0%. The magnetic properties are almost unchanged. • A convenient method to enhance the mechanical properties of Sm 2 Co 17 magnet without loss of magnetic properties is provided. [ABSTRACT FROM AUTHOR]

Development of NdY-Fe-B magnets not only reduces the cost of Nd-Fe-B type magnets but also promotes the balanced utilization of rare-earth resources. However, the lower coercivity of NdY-Fe-B magnets hinders their further development. This study investigated the coercivity of NdY-Fe-B magnets via intergranular doping of Ho 76 Al 12 Ga 12 powders. Although this process improved the coercivity, the remanence substantially deteriorated with the increasing content of the Ho 76 Al 12 Ga 12 alloy. A coercivity of 1.37 T was achieved in a NdY-Fe-B magnet with a Ho 76 Al 12 Ga 12 alloy doping of 7 wt%, showing a coercivity increment (Δ H cj) of 0.64 T compared to the original magnet. This can be attributed to the observed microstructural and elemental distributions, as well as the analysis of the magnetic domain wall movement. An abnormal Ho-biased layer is observed between the Y-rich core and the Ho-rich shell in the matrix grains, exhibiting a higher anisotropy field compared than the shell layer. Further analysis revealed that the movement of magnetic domain wall movement was obstructed by the Ho-biased layer, demonstrating a domain-wall pinning effect within the matrix grains. Additionally, the formation of a Ho-rich shell in the outer area of the 2:14:1 matrix grain and the presence of a continuous uniform grain boundary phase were found to be important for improving both coercivity and thermal stability. • The coercivity of NdY-Fe-B magnets have been improved by intergranular doping of Ho 76 Al 12 Ga 12 powders. • An abnormal Ho biased layer is observed between the Y-rich core and Ho-rich shell in the matrix grains. • The magnetic domain wall is obstructed by Ho-biased layer, which is considered to the reason for coercivity improvement. [ABSTRACT FROM AUTHOR]

The development of Rare-earth iron-boron sintered magnets (RE-Fe-B) based on high-abundance cerium (Ce) is crucial in terms of economic efficiency. In this work, a series of high Ce-content sintered magnets were prepared by incorporating Pr 45 Fe bal B (Pr45) into [(PrNd) 0.5 Ce 0.5 ] 29.5 Fe bal B. The further microstructural analysis revealed that the addition of Pr45 alloy resulted in the formation of a thick and widely distributed Pr-rich shell around the Ce-rich grains. Adding Pr45 alloy also significantly suppressed the impurity phase and expanded the diffusion channels of the base magnets. Thus, the coercivity (H cj) of the base magnets was remarkably enhanced from 5.65 kOe to 9.77 kOe ∼ 16.39 kOe. Subsequently, the grain boundary diffusion of dysprosium hydride (DyH x) powders was carried out in the optimized base magnets. Results of microstructural analysis showed that the matrix phase grains formed a dual-shell structure comprising a Dy-rich shell in addition to the original Pr-rich shell, thereby enhancing the anisotropic field of the matrix phase grains. The increment in H cj of the diffused magnets ranged from 3.03 kOe to 5.36 kOe (the original unoptimized diffusion magnet coercivity was only 1.69 kOe). This work provides a novel solution for preparing high-coercivity Nd-Ce-Fe-B sintered magnets. • High H cj Ce-magnets are prepared by adding Pr-rich phase and Dy GBDP. • The diffusion of Ce magnets is promoted due to improved microstructures. • A model of dual-shell grain structure is designed to enhance the H cj of Ce-magnets. [ABSTRACT FROM AUTHOR]

Nd-Ce-Fe-B sintered magnets with Ce-substitution amounts of 30 wt% were treated by one- and two-step grain boundary diffusion processes, in which DyH x and low-melting-point Pr 70 Cu 10 Al 15 Ga 5 (at%) alloys were designed as the diffusion sources and diffused into the magnets according to the different steps and orders. Results showed that the increase of coercivity was only 2.7 kOe when introducing heavy rare-earth Dy by the one-step diffusion of DyH x , reflecting the difficulty of conventional diffusion modification on high Ce content magnets. Note that by the two-step grain boundary diffusion (no matter which diffusion source was diffused preferentially in the first step), the coercivities were significantly enhanced over 18.5 kOe from the original 13.64 kOe, with the obvious improvements of thermal stability. Microstructures and compositions analyses revealed that the grain boundaries were greatly optimized after the diffusion of Pr 70 Cu 10 Al 15 Ga 5 , supporting favorable diffusion channels for the introduction of Dy in the subsequent second step. By contrast when introducing Dy first and then diffusing the Pr 70 Cu 10 Al 15 Ga 5 second, the elements in the low-melting-point alloys could drive the superficial Dy to migrate into the deep interior of the magnets. Thus, both the two types of two-step grain boundary diffusions were conductive to improving the utilization of heavy rare-earth Dy in high Ce content magnets. Besides, dynamic domain evolution analyses demonstrated the positive effect of diffusion on anti-demagnetization. This work provided a foundation for the development of high Ce content magnets with high performances. • High-performance Nd-Ce-Fe-B magnet was prepared by two-step grain boundary diffusion. • Coercivity increase of 5 kOe was achieved by diffusing DyH x and PrCuAlGa successively. • Microstructures were greatly optimized by collaboratively diffusing multiple elements. • Dynamic domain analyses revealed positive effect of diffusion on anti-demagnetization. [ABSTRACT FROM AUTHOR]

Alnico permanent alloys are still irreplaceable and show great potential in high temperature applications considering their excellent thermal stability, while the market for Alnico alloys is limited by their low coercivity. Rare-earth addition has been shown to increase the coercivity of Alnico alloys. In this work, the effects of Dy-addition on the crystal structure, microstructure, spinodal decomposition phases and magnetic characteristics of Alnico alloys were systematically investigated. The results indicate that the Dy element forms Dy-rich precipitates and influences the morphology and composition of spinodal decomposition structure. The 0.3 wt% Dy addition improves the coercivity from 132 kA·m−1 for the Dy-free alloys to 141 kA·m−1 for the Dy-added alloys and slightly optimizes the thermal stability. The enhancement of coercivity is attributed to the refined and uniform spinodal decomposition structure by reducing the mismatch degree and coherency strain. However, the magnetic properties of the 0.6 wt% Dy added alloy decrease due to the damaged structure with excessive Dy-rich phases and more connected α1 phases. A method for improving coercivity and thermal stability is suggested. • Dy forms the Dy 2 Co 17 H-type magnetic Dy-rich phase. • Dy enters the FeCo-rich (α1) phases and their coarsening and decomposition are suppressed. • With 0.3 wt% Dy addition, the coercivity and thermal stability of Alnico alloys are improved due to the refined and uniform SD structure. [ABSTRACT FROM AUTHOR]

The magnetic properties and thermal stability are associated with the grain size and defects around grain boundaries in Sm 2 Co 17 permanent magnets. It is of scientific and practical interest to study the grain growth and the evolution of defects around grain boundaries during heat treatment process. In this study, the grain sizes after sintering, solution, isothermal aging and final aging are quantitatively characterized, and its influence on magnetic properties and flux losses are systematically analyzed. In addition, the Cu-rich and Zr-rich precipitates and Cu-lean regions around grain boundaries are carefully examined from sintering to final aging. The results show that solution treatment is the most effective approach to promote the grain growth, while the grain growth during isothermal aging and final aging is also non-negligible. The grain growth helps to reduce the grain boundaries and reduce the flux loss. This study provides a convenient and cost-effective approach (increasing the heat treatment time) to improve the thermal stability without significant sacrifice of magnetic properties. On the other hand, the Cu-lean regions and incomplete cellular nanostructures form during isothermal aging, while the Cu-rich and Zr-rich precipitates form during sintering. The formation of Cu-rich and Zr-rich precipitates mainly stems from the excess addition of Cu and Zr, which is indispensable to improve the working temperature. • The grain growth is quantitatively analyzed to find an effective approach to tune the grain size and flux loss. • Increasing the heat treatment time can enhance the thermal stability without significant sacrifice of magnetic properties. • The defects evolution around grain boundaries is systematically characterized during heat treatment process. [ABSTRACT FROM AUTHOR]

Various features can benefit the sintered NdFeB material modeling process, as they provide more dimensional information related to the target and make the model more accurate. In this work, by introducing composition and process features as input, we successfully built a sintered NdFeB performance prediction model by comparing different machine learning models with good generalization capability, high accuracy, and sound interpretation compared to previously published work. In addition, using the Shapley additive interpretation (SHAP) method, the unexplainable problem of ML models is solved by evaluating the contribution of the features in the regression model to the results. The intuitive SHAP value plots showed the complex relationship between input variables and magnet performance. Finally, we used the above machine learning model to complete the process framework for evaluating the performance of sintered NdFeB materials. Our work is expected to accelerate performance screening and material development of sintered NdFeB. [Display omitted] • A machine learning model has been developed to predict the remanence and coercivity properties of sintered NdFeB. • The developed models demonstrate high accuracy and generalization on the respective test sets. • Interpretation of machine learning models using SHAP analysis. • The machine learning model is utilized to propose a material design framework for sintered NdFeB. [ABSTRACT FROM AUTHOR]

Bulk LaFe 11.6 Si 1.4 H y /Al composites with the saturated hydrogen content were prepared by hot pressing and subsequent hydrogenation. Al particles were dramatically deformed when pressed at 773 K, and a reaction of La(Fe,Si) 13 and Al phases took place at 873 K. The reinforced skeleton structure consisting of malleable Al phases in the composites allows brittle La(Fe,Si) 13 H y particles to be well bonded after hydrogen absorption. As a result, these LaFe 11.6 Si 1.4 H y /Al hydrides show a good comprehensive performance for magnetic refrigeration, i.e. , large entropy changes of 9.8–12.5 J/kg K under 2 T, large adiabatic temperature changes of 3.36–3.97 K under 1.9 T, high thermal conductivity of 11.4–45.6 W/m K, and high bending strength of 16.8–48.2 MPa. Particularly, the 20 wt% Al composite possesses a compressive strength of 122 MPa and plastic deformation of 4.6 %. • Fully hydrogenated LaFe 11.6 Si 1.4 H y /Al composites were prepared. • These composites exhibit large entropy changes of 9.8–12.5 J/kg K under 2 T. • These composites possess high thermal conductivity of 11.4–45.6 W/m K. • A plastic deformation of 4.6 % can be achieved in the composite with 20 wt% Al. [ABSTRACT FROM AUTHOR]

Four types of bulk hot-deformed Nd-Fe-B composite magnets were designed by mixing Dy-free powders (M) and Dy-containing powders (G) or stacking them: (M-G) mix , MGGM, GMMG and MGMG. The four composite magnets with same Dy content show great differences in their magnetic properties. The remanence (B r) of the MGGM magnet (13.48 kGs) is highest while the coercivity (H c) of the GMMG magnet (22.24 kOe) is highest. The overall magnetic performance ((BH) max + H c) of the MGGM magnet (∼65) is highest. For the (M-G) mix magnet, the ribbon texture throughout the whole magnet is inferior, indicating the poor deformability of the mixed powders. Comparing the overall texture of the MGGM and GMMG magnets, the ribbon texture of M powders located at the top and bottom sections is much better than that of G powders located at the top and bottom sections, which is the main reason for the excellent remanence and overall magnetic performance of the MGGM magnet. Finite element simulations were performed to explain the deformation behaviors of hot-deformed magnets and facilitate discussions of the overall microstructure differences of the composite magnets. [Display omitted] • The overall magnetic performance was enhanced by the design of macrostructure. • The overall texture of power ribbons was optimized by the design of macrostructure. • The overall microstructure difference of composite magnets was analyzed by experiments and simulations. [ABSTRACT FROM AUTHOR]

The effects of the addition of (Pr 0.25 Nd 0.75) 10 Dy 80 Cu 5 Al 5 alloy powders on the magnetic properties and microstructure of the hot-deformed Nd-Fe-B magnets were investigated in this work. Through the addition of (Pr 0.25 Nd 0.75) 10 Dy 80 Cu 5 Al 5 , an ultrahigh coercivity of 3.14 T was obtained in a 6-mm-thick hot-deformed magnet, and the temperature coefficient of coercivity and remanence were improved from −0.475%/℃ and −0.145%/℃ to −0.383%/℃ and −0.110%/℃ at 20 −180 ℃, respectively, showing the excellent thermal stability. Microstructure observations indicated that the formation of thick nonferromagnetic intergranular phase, the reduction of grain size and aspect ratio and the formation of the (Nd,Pr,Dy) 2 Fe 14 B main phase were achieved after the addition of (Pr 0.25 Nd 0.75) 10 Dy 80 Cu 5 Al 5 , which were the main reasons for the enhancement of coercivity and thermal stability. • (PrNd)-Dy-Cu-Al alloy diffusion is proposed for preparing high-performance magnets. • Ultrahigh coercivity is achieved in diffused magnets with lower consumption of HRE. • Excellent thermal stability (β = −0.383%/℃) is also obtained in the diffused magnets. [ABSTRACT FROM AUTHOR]

Magnetic properties and microstructure of Sm(Co 0.647 Fe 0.28 Cu 0.053 Zr 0.02) 7.84 magnets prepared by HD powder with different residual hydrogen content (25, 715, 1512 ppm) have been investigated. The squareness and coercivity increase from 0.56 to 0.63 and 24.03 to 26.37 kOe as the hydrogen content increased from 25 to 1512 ppm. TEM results show that similar cellular structure and lamellar structures are formed in these magnets. Due to superabundant vacancies induced by hydrogen, the average grain size of final magnets increases from 50.22 to 62.29 μm with the increase of hydrogen in HD powder. Larger grain size results in fewer grain boundary areas where no clear cellular structure formed. The kerr observation indicate that the reversal domain formed at the grain boundary areas is easier to grow up, while the reversal of in-grain domain shows much harder. • The sintered 2:17 type Sm-Co magnets are prepared by powders with hydrogen. • The H cj and squareness can be improved with higher H content in HD powder. • Larger grain size in 2:17-type SmCo magnets with higher H content in HD powder. • Larger grain size, less grain boundaries, less weaker pining sites. [ABSTRACT FROM AUTHOR]

Abstract Grain boundary modification induced giant coercivity enhancement from 945 kA/m to 1904 kA/m was achieved in Sm 25 Co 48 Fe 20 Cu 5 Zr 2 magnets by doping 0.4 wt% CuO. Different magnetization reversal behaviors were clearly observed between un-doped and doped magnets. Compared with un-doped magnets, Cu enrichment along grain boundary promoting regular cellular structure was obviously found in doped magnet. The in-situ Kerr observation indicated that complete cellular structure could strengthen the pinning field of grain boundary regions and the propagations of magnetization reversals into interiors of grains were restrained by the modified grain boundaries, which resulted in the remarkable coercivity increment. Highlights • Enhanced coercivity from 945 kA/m to 1904 kA/m is achieved. • Complete cellular structure is formed in modified grain boundary areas. • Magnetization reversal differences occur between un-doped and doped SmCo magnets. [ABSTRACT FROM AUTHOR]

Abstract 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 Fe 14 B 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 Fe 14 B grain. Highlights • The coercivity enhancement is achieved while the remanence loss is small. • Thermal stability is improved in the diffusion of Tb-Fe particles. • Small remanence loss is attained. [ABSTRACT FROM AUTHOR]

It is a major challenge for Nd-Fe-B based permanent magnets to improve the utilization of heavy rare-earth resources. For enhancing the diffusion efficiency of heavy rare-earth elements in the hot-deformed Nd-Fe-B magnets, an intergranular diffusion of DyF 3 aided by a trace of nano-Cu was implemented by dual alloy process. Through the trace addition (0.2 wt%) of nano-Cu, the coercivity increment of the Cu-containing magnet is higher than that of the Cu-free magnet after the diffusion of DyF 3 , and the remanence was maintained at a high level. SEM results revealed that a considerable amount of bulky elongated Dy-rich phase was blocked by (Nd,Pr)-rich phase and hardly infiltrated into powder flakes in the Cu-free magnet. But most of the bulky Dy-rich phase dissolved and infiltrated into adjacent powder flakes with the aid of nano-Cu. TEM results revealed that the Dy concentrations of main phase and grain boundary phase in the Cu-containing magnet are both higher than those in the Cu-free magnet. SEM and TEM results confirmed that the trace addition of nano-Cu contributes to the diffusion of Dy into the main phase and grain boundary phase at the surface of powder flakes, which is the main reason for the further enhancement of coercivity. Further discussions on the enhancement mechanism of coercivity were made by using micromagnetic simulations. [Display omitted] • The effects of nano-Cu on the diffusion behaviors of DyF 3 were investigated. • The diffusion efficiency of Dy was improved with the aid of nano-Cu. • The reasons for the enhancement of coercivity were explained by SEM and TEM. • Micromagnetic simulations were implemented to explain the experimental results. [ABSTRACT FROM AUTHOR]

In this work, the effect of Zr content on magnetic properties and electrical resistivity of Sm(Co bal Fe 0.09 Cu 0.09 Zr x ) 7.68 ( x  = 0.020, 0.025, 0.030, 0.035) high temperature magnets has been investigated. More Zr content results in the decrease of average cell size and the increase of the density of lamellar structure. In addition, a large number of phase boundaries between lamellar phase and cellular structure have also been formed. The intrinsic coercivity of 550 °C enhances from 3.21 kOe to 6.05 kOe with the increase of Zr content. Furthermore, electrical resistivity shows obviously different variation in different directions with increasing Zr content. At room temperature and 127 °C, the electrical resistivity improves from 68.2 μΩ cm to 91.7 μΩ cm and from 87.1 μΩ cm to 103.3 μΩ cm with increasing x from 0.020 to 0.035 in the direction parallel to c -axis, respectively. However, there is only a slight increase in the electrical resistivity in the direction perpendicular to c -axis. The rise of electrical resistivity in different directions has been discussed. Research results indicate that increasing the density of the lamellar phase is an effective way to increase electrical resistivity in the 2:17-type Sm-Co magnets. [ABSTRACT FROM AUTHOR]

In this study, we presented an effective approach for the substantial coercivity enhancement of Dy-free sintered Nd-Fe-B magnets with Ga-doping. The coercivity was substantially enhanced from 10.1 kOe to 19.8 kOe by effective microstructure optimization and phase constitution regulation in antecedent alloys. A good isolation of 2:14:1 grains by Nd-rich intergranular phase is obtained in final magnets accompanying with the formation of intermetallic Nd 6 Fe 13 Ga phase. However, when dehydrogenating above 500 °C, masses of preformed Nd 6 Fe 13 Ga phases are detected in the initial strip casting alloys and the homologous magnet suffers an unanticipated degradation of coercivity. Magnetic domain observation and thermal magnetic analysis imply a pronounced difference in the magnetism of grain boundary (GB) phases, which closely associated with the composition homogeneity of Nd-rich phases in antecedent alloys. The mechanism of the coercivity variation in the sintered magnets with different GBs magnetism is discussed based on magnetic behavior analysis. [ABSTRACT FROM AUTHOR]

Thermal stability of coercivity and domain structure in sintered Nd–Fe–B magnets with various grain sizes has been studied. Microstructure analysis shows that the improved thermal stability arises from the grain morphology beneficial to a small effective demagnetization factor N eff . In-situ magnetic domain evolution during thermal demagnetization indicates that lower surface stray field in fine-grained magnets suppresses the reversion of domain in high temperature condition, which results from temperature-dependent competition between the local demagnetizing field and effective anisotropy field of surface grains. [ABSTRACT FROM AUTHOR]

Anisotropic Nd-Fe-B magnets with WC addition were prepared by hot deformation process. The effect of WC addition on the compressive and bending strength of hot-deformed Nd-Fe-B magnets has been investigated. The results suggest that the mechanical properties of hot-deformed magnets without WC addition show distinct anisotropy. Meanwhile, WC addition lowers the mechanical anisotropy in two directions parallel and perpendicular to c -axis, especially the compressive strength. The optimum mechanical properties are obtained at 1.0 wt % WC addition without sacrificing the magnetic properties. The observation for microstructure reveals that the fracture mechanism of hot-deformed magnets is a typical intergranular fracture and the crack is prior to propagate along the ribbon boundary. The improved mechanical properties might be attributed to both the grain refinement at ribbon boundaries and the reinforced effect of WC addition. [ABSTRACT FROM AUTHOR]

High performance (La, Ce, Pr, Nd)-Fe-B anisotropic nanocrystalline magnets were fabricated through die-upsetting process by incorporating misch-metal in Nd-Fe-B magnets via dual alloy method. Although coercivity decrease with the increase of misch-metal monotonously, there are no significant decrease in remanence. Magnet with remanence of 13.46 kGs and maximum energy product of 43.5 MGOe was obtained with 30 wt% misch-metal substitution, which is quite promising in practical application. High remanence was resulted from good texture and microstructure analysis revealed that Ce tended to diffuse into 2:14:1 phase uniformly, while the excessive La tended to assemble into the interface of melt-spun ribbons. [ABSTRACT FROM AUTHOR]

Commercial N55 sintered Nd-Fe-B magnets were processed by grain boundary diffusion (GBD) with Tb-Cu and Tb-Y-La-Cu alloys. The coercivity increased significantly to 1824 and 1901 kA/m for the Tb 70 Cu 30 and Tb 52.5 Y 7 La 10.5 Cu 30 (at%) GBD-treated magnets. Notably, when further increasing the proportion of Y and reducing that of Tb to the composition of Tb 39.5 Y 20 La 10.5 Cu 30 , the coercivity increment was still large and rather similar to that of Tb 70 Cu 30 , accompanied by an obvious optimization of thermal stability. Microstructure analyses demonstrated that the remarkable performance enhancement of Tb-Y-La-Cu GBD-treated magnet was mainly attributed to the synergistic effect of Y and La on Tb, in which, the competitive diffusion of Y and Tb effectively inhibited the lattice diffusion of Tb in grains while La tends to combine with oxygen to form La 2 O 3 and reduce the consumption of Tb at the grain boundary oxide, improving the effective function depth for magnetic hardening shell structure. • Coordination behaviors of Tb, Y and La in GBD process were studied systematically. • Coercivity and thermal stability enhancement were achieved by grain boundary diffusing Tb-Y-La-Cu alloys. • The diffusion behavior of Tb was modulated by the synergistic effect of Y and La. • The effect of Tb/Y co-substitution on the demagnetization behavior was analyzed. [ABSTRACT FROM AUTHOR]

High-Co-containing RE-(Fe, Co)-B (RE, rare earth) sintered magnets by dual-main-phase route (DMP, sintering the mixture of Co-free and Co-containing RE 2 Fe 14 B powders) were developed in this work, which effectively suppresses the formation of Co-rich intergranular phases and significantly increases the Co-substitution level in Nd-Fe-B magnets. Magnetic properties of B r = 13.74 kGs, H cj = 13.09 kOe, and (BH) max = 44.32 MGOe were obtained even when 35 at. % Co substitutes for Fe in the dual-main-phase magnets. Phase components analysis indicated that the typical RE(Fe, Co) 2 and RE(Fe, Co) 4 B were detected until the relative concentration of Co up to 35 at. %, which are commonly conceived as harmful to magnetic properties. Microstructural analysis revealed the distribution of each intergranular phase at grain boundaries and the inhomogeneous distribution of RE in the core and shell of the grain. Compared to the addition of Co through alloying, introducing Co by mixing RE-(Fe, Co)-B and RE-Fe-B allows a metallurgical reaction between Co-rich intergranular phases and 2:14:1 matrix phase, accompanied by dramatical elemental interdiffusion during the sintering, thus the formation of Co-rich intergranular phases can be suppressed to a certain extent. These efforts provide another possibility to obtain Nd-Fe-B magnets with higher Co content and achieve better thermal stability. • Optimization of magnetic properties and thermal resistance by dual-main-phase method. • The construction of the core-shell structure optimizes the coercivity. • Dual-main-phase method delays the formation of the Co-rich phase. [ABSTRACT FROM AUTHOR]

Conventional hot-deformed Nd-Fe-B magnets exhibit significant mechanical anisotropy in the two directions perpendicular and parallel to c-axis, resulting in a complicated machining process. In this work, hydrogenation-disproportionation-desorption-recombination (HDDR) powders were added to reduce the mechanical anisotropy of hot-deformed magnets. The effects of the addition of HDDR powders on the compressive strength of hot-deformed magnets and their corresponding microstructures have been investigated. The mechanical anisotropy was maximally decreased by 68 % at 20 wt. % addition. Microstructure observation indicated that a heterogeneous structure containing two kinds of grains with different morphology was formed after the addition of HDDR powders. Further analyses revealed that the reduction of mechanical anisotropy was mainly attributed to the change of the shape anisotropy of grains and the disruption of the regular stacking structure of the melt-spun ribbons. This work provides a new insight for the preparation of high performance hot-deformed Nd-Fe-B magnet with outstanding comprehensive service capability. [Display omitted] • A special heterogeneous structure was constructed by the addition of HDDR powders. • The mechanical anisotropy was greatly decreased by 68 % by 20 wt. % HDDR addition. • Regular ribbon stacking structure was disrupted due to the addition of HDDR powders. • Grain shape anisotropy was reduced due to the addition of HDDR powders. [ABSTRACT FROM AUTHOR]

Thermally stable Nd 0.6 Y 0.4 -Fe-B magnet with 0.83 at% Tb alloying was yielded with a coercivity of 1.58 T and a temperature coefficient (β 20–120 ℃) of − 0.531%/°C. Microstructure analyses showed that the aggregation of Y in the core region essentially dominated the heterogeneous distribution of rare earth (RE) elements in the matrix phase grains, leading to the enrichment of Pr, Nd and Tb in the outer layers of matrix grains. The preferred regulation of Y for Tb distribution contributed to the spontaneous Tb-rich shells with strengthened anisotropy field, significantly mitigating the inevitable degradation of coercivity caused by the high Y-substitution. Continuous non-ferromagnetic grain boundary phases were also constructed to isolate the adjacent grains. The synergistic effect of above microstructural modification presents a reliable new strategy to compensate for the magnetic dilution effect of Y and promote the effective utilization of Tb. • Tb doped Nd-Y-Fe-B magnet by regulating the heterogeneous RE distribution was developed. • a coercivity of 1.58 T with a β 20–120 of − 0.531%/°C was yielded in Nd 0.6 Y 0.4 -Fe-B magnet. • Typical Y-rich core and novel Tb-rich shell was spontaneously formed in single main phase magnet. • Compared with Pr and Nd, Y showed a more significant regulatory effect on the distribution of Tb. [ABSTRACT FROM AUTHOR]

Anisotropic CaCu 5 -type SmCo 4.8 Cr 0.12 C 0.08 alloys with a dendritic nanostructure and an out-of-plane <0001> texture were fabricated using the melt-spinning method at a speed of 50 m/s. The microstructure changed from randomly orientated equiaxial grains for the ribbon melt-spun at 30 m/s to dendritic ones for that spun at 50 m/s. High-angle annular dark-field scanning transmission electron microscopy and X-ray energy dispersive spectroscopy analysis reveal that the distribution of carbon in SmCo 5 grains obtained at higher speeds is highly inhomogeneous and leads to the formation of C-depleted and C-rich dendrite structure with a [ 0001 ] C − r i c h S m C o 5 ∥ [ 0001 ] C − d e p l e t e d S m C o 5 orientation relationship. Moreover, the incorporation of C into the SmCo 5 phase helps to increase the Curie temperature to about 845 °C. A high coercivity of 40.3 kOe and a relatively high remanence of 42.0 emu/g were measured in the direction normal to the ribbon plane. [ABSTRACT FROM AUTHOR]

A Dy-Cu eutectic injection process accompanying by hot deformation had the potential to fabricate the high-performance die-upset magnets. The good fluidity of Dy-Cu eutectic liquid accelerated the formation of near-surface texture and suppressed largely the grain growth during subsequent heat treatment. By the high-temperature microstructure evolution, the maximum energy product of injected magnets was substantially increased by 17.8%, from 45 to 53 MGOe. The near-surface microstructure of injected magnets was studied to clarify the effect of inhomogeneous Dy-Cu distribution on the texture and grain size. [ABSTRACT FROM AUTHOR]

Commercial NdFeB sintered magnets were processed by grain boundary diffusion process with serial Tb 10 Pr 90- x (Cu,Al,Ga) x (at%) alloys, in order to study the influence of rare earths and non-rare earth metallic elements proportion change on the diffusion effect for alloy diffusion sources with low Tb content. The coercivity increased significantly from 14.20 kOe to 24.10 kOe, 25.46 kOe and 25.36 kOe respectively for the diffused magnets treated with Tb 10 Pr 80 (Cu,Al,Ga) 10 , Tb 10 Pr 60 (Cu,Al,Ga) 30 and Tb 10 Pr 40 (Cu,Al,Ga) 50. However, the coercivity optimization effect deteriorated drastically when the total amounts of metallic elements (Cu, Al and Ga) in diffusion resources reached 70 at%. Microstructure analyses demonstrated that the remarkable coercivity enhancements achieved by the relatively low metallic content sources were mainly attributed to the excellent diffusion effects, in which the Tb diffusion depths were rather deeper and the core-shell structures were easily distinguishable. Meanwhile, due to certain differences in thermodynamic characteristics and diffusion behaviors for these serial of diffusion sources, the effective introductions of Tb and Pr from the original coated sources to the inner of the magnets were respectively different. Especially, the utilization rate of Tb obtained an optimum value of 94.74% using Tb 10 Pr 60 (Cu,Al,Ga) 30 alloy and the utilization rate of Pr reached the peak value of 81.76% in the use of Tb 10 Pr 40 (Cu,Al,Ga) 50 alloy, providing experiment support for the further design of alloy diffusion sources with low Tb content. In addition, in-situ magnetic domain observation for the typical diffused magnets in this work was carried out to study the demagnetization behavior and coercivity mechanism of the magnet. • Effect of non-rare earth proportion change in alloy source on diffusion was studied. • Coercivity increase of 11 kOe was achieved by diffusing alloy with only 10 at% Tb. • Tb utilization rate reached 94.7% in use of Tb 10 Pr 60 (Cu,Al,Ga) 30 alloy for diffusion. • Dynamic domain analysis revealed the positive effect of Tb content in shell layer. [ABSTRACT FROM AUTHOR]

The grain boundary modification by Pr 64 Fe 12 Al 9 Ga 15 addition was performed in the B-lean Nd-Y-Fe-B multi-main-phase (MMP) magnets. The effects of the additive on the microstructure and magnetic properties were investigated. A pronounced coercivity enhancement was achieved from 4.96 kOe to 8.15 kOe with 2 wt% Pr 64 Fe 12 Al 9 Ga 15 addition, while the coercivity tended to be invariable with further increasing of Pr 64 Fe 12 Al 9 Ga 15 content to 4, 6, and 8 wt%. Detailed microstructure analysis revealed that the significant amounts of RE 6 Fe 13 (Ga, Al) 1 intergranular phase were generated by introducing Pr 64 Fe 12 Al 9 Ga 15 additive in the B-lean Nd-Y-Fe-B MMP magnets. The formation of RE 6 Fe 13 (Ga, Al) 1 contributed to the optimization of the distribution of grain boundary (GB) phase, strengthening the intergrain magnetic isolation. However, the further increases of the additive content led to the agglomeration of RE 6 Fe 13 (Ga, Al) 1 in the triple junction region, which caused a reduction in remanence. Meanwhile, excessive addition for additives revealed that the thicker GB layer was unessential to further increase in coercivity, the intergranular exchange coupling had already been decoupled in magnets with adequate addition. In addition, more Pr atoms were primarily substituting the Nd atoms, but Y atoms were not substituted by Pr in the shell region of matrix grains. It was deemed that the magnetic anisotropy of the grain shell was essentially unchanged even with the formation of Pr-rich shell. These results reported here enlighten the microstructure design of Nd-Y-Fe-B MMP magnets. • A pronounced coercivity enhancement is achieved with 2 wt% Pr 64 Fe 12 Al 9 Ga 15 addition. • The coercivity tends to be invariable with further increase of Pr 64 Fe 12 Al 9 Ga 15. • The formation of RE 6 Fe 13 (Ga, Al) 1 optimizes the distribution of grain boundary phase. • The thicker GB does not to further enhance the coercivity when exchange is decoupled. • More Pr atoms are primarily substituting the Nd atoms over Y atoms in the shell area. [ABSTRACT FROM AUTHOR]

SmFe 12 -based permanent magnet materials with ThMn 12 structure have received extensive attention in the exploration and development of new rare-earth-lean permanent magnets. However, the coercivity influence mechanism has not been clearly defined, hindering the development of high coercivity. In this work, the synergistic effect of Sm content and annealing process on phase formation and microstructure evolution has been investigated. The results demonstrate that the SmFe 12 hard magnetic phase can be obtained massively in ingots with x from 0.95 to 1.2, however, α-Fe can be completely eliminated only when x exceeds 1.0. Simultaneously, continuous grain boundary has been proposed by annealing at 1180 °C for 1 h in the Sm 1.1 (Fe 0.8 Co 0.2) 10.5 Ga 0.5 Ti alloy, accompanied by the purification of ThMn 12 -type phase. Elemental distribution analysis demonstrated that Sm and Ga prefer to enter grain boundary during the annealing process, providing the possibility of obtaining continuous non-ferromagnetic grain boundary. However, the distribution of Sm and Ga in the grain boundary is not uniform, and there are some other regions with more Fe and Co, which is difficult to achieve effective demagnetization coupling between grains, resulting in the easy de-magnetization of the grains. TEM results show that nano-sized weak magnetic 1:9 phases are observed and exist around the 1:12 phase, which may be a region prone to demagnetization in an opposing magnetic field. Overall, this work reveals some new and important factors restricting the development of high performance in ThMn 12 -type magnets. • Sm and Ga tend to enter grain boundary during annealing but their distribution in the grain boundary is heterogeneous. • Nanoscale weak magnetic 1:9 phase in the grain epitaxial region may hinder the development of 1:12 sintered magnets. • 1:12 phase formation is sensitive to annealing temperature and time, with the optimum annealing process is 1180 ℃, 1 h. [ABSTRACT FROM AUTHOR]

Magnetic properties and microstructures of sintered Nd-Fe-B magnets with different Nd-Cu powders addition (0, 2.7, 4.5, 6.2 and 8 wt%) and their corresponding diffused magnets using Tb-Cu alloys were studied systematically. The results showed that the enhancement of coercivity after diffusion was positively correlated with the intergranular phase proportion of the base substrates, and the relatively larger coercivity increments with 8.69 and 9.16 kOe were obtained at the addition of 6.2 and 8 wt% respectively, while the coercivity increments only reached 3.54 kOe and 4.00 kOe for the diffused magnets prepared by the substrates with 0 and 2.7 wt% Nd-Cu powders addition. The further microstructure analyses demonstrated that the higher coercivities were mainly attributed to the rather deeper diffusion depths of Tb elements, and the Nd-rich grain boundary phases in the base substrates were beneficial to construct the effective diffusion channels for subsequent diffusion process. Meanwhile, just due to the lack of efficient diffusion channels in the substrates with lower intergranular phase proportion, a large amount of Tb atoms accumulated on the interface between diffusion source and base magnet, forming a Tb-Fe transition layer and significantly deteriorating the utilization of heavy rare earths. This work supplemented insight and experimental foundation for the base substrate design in the preparation of diffused magnet with high performance. • Diffusion effect for Tb elements in different magnets were studied systematically. • Coercivity enhancement of 9.1 kOe was achieved by constructing diffusion channels. • The element metallurgical behavior in the diffusion couple interface was analyzed. • The in-situ observation for the intergranular phase melting process was performed. [ABSTRACT FROM AUTHOR]

The change of microstructure and magnetic properties after heated to high temperature remains a critical concern for the application of SmCo magnets. In this work, the influence of final aging temperature on thermal stability of microstructure and magnetic properties in Sm(Co 0.777 Fe 0.1 Cu 0.09 Zr 0.033) 7.61 high temperature magnets is studied. Meanwhile, the main structure determining the magnetic loss and underlying mechanism are discussed. The results show that the flux loss mainly stems from the reversed domain structure at grain boundaries, which are defects with incomplete cellular nanostructures. Thus, grain size is the key factor determining the flux loss. When the final aging temperature increases from 400 to 600 °C, the grain size decreases monotonically, leading to higher flux loss. On the other hand, the microstructure and magnetic properties tend to reach the equilibrium state at the operating temperature. Therefore, the thermal stability of microstructure and magnetic properties can be enhanced by reducing the temperature difference between final aging temperature and operating temperature. This work offers in-depth insights into the fundamental understanding of magnetic loss and provides methods to reduce magnetic loss in 2:17-type SmCo magnets. The flux loss can be reduced by increasing the grain size, while irredeemable magnetic properties loss can be reduced by increasing the thermal stability of microstructure. • The flux loss mainly stems from the reversed domain structure at grain boundaries, which are defects with incomplete cellular nanostructures. • The thermal stability of microstructure and magnetic properties can be enhanced by reducing the temperature difference between final aging temperature and operating temperature. • This work offers in-depth insights into the fundamental understanding of magnetic loss and provides methods to reduce magnetic loss in 2:17-type SmCo magnets. The flux loss can be reduced by increasing the grain size, while irredeemable magnetic properties loss can be reduced by increasing the thermal stability of microstructure. [ABSTRACT FROM AUTHOR]

The grain boundary diffusion process of Pr-Al-Cu at various temperatures has been applied in the sintered Nd-Fe-B magnets. Detailed evolution of the grain boundary phases and its influence on the magnetic properties were investigated. Microstructure analysis showed that the shell morphology rich in Pr and Al was significantly formed in the diffusion process at 700 °C, which was determined as (Pr,Nd) 2 (Fe,Al) 14 B phase, while Al is homogeneous in the 900 °C diffused magnets. After the annealing treatment, continuous grain boundary phases were generated in the 700 °C diffused magnet to isolate the neighbouring grains even at the depth of 1000 µm, whereas that in the 900 °C diffused magnet were scarce. Thus a pronounced enhancement of coercivity from 16.21 kOe to 21.36 kOe was yielded in the annealed 700 °C diffused magnet. Transmission electron microscopy showed that the thickness of the Pr and Al rich shell in the matrix phase grains was dramatically decreased during the annealing process. The absent shell layers facilitate the formation of (Pr,Nd) 6 (Fe,Al,Cu) 14 phase in the intergranular regions. Also the residual diffusion source on the surface of the diffused magnets was supposed to promote the development of continuous grain boundary phases during the annealed process. Based on these results, the temperature-dependent microstructure and magnetic properties evolution was detailedly discussed. [Display omitted] • An optimum diffusion temperature of 700 ℃ followed with 500 ℃ annealing could be determined in the Pr-Al-Cu diffused magnet with about 5 kOe coercivity enhancement. • The diffusion and substitution behaviors of Al presented significant differences between 700 °C and 900 °C diffused magnet with Pr-Al-Cu alloys. • The continuous grain boundary phases were formed under the metallurgical reaction of the preformed Pr/Al-rich shell and the infiltrated residual Pr/Nd. [ABSTRACT FROM AUTHOR]

The segregation of Cu is crucial for the magnetic properties of 2:17 type SmCo magnets, which is firstly affected by the ordering process during aging treatment. In this research, the ordering process is successfully regulated by doping nano ZrO 2 , which achieves a prolonged ordering process and an increased duration of twin boundaries in 2:17 type SmCo magnets. The continuous migration of twin boundaries in a longer period drives extra Cu to converge towards the cell boundary center, resulting in about 10.52 kOe coercivity only by isothermal aging treatment. The precipitation sequence of the lamellar phase and the cell boundary phase is exchanged. A new understanding of Cu segregation contributes to the development of high performance 2:17 type SmCo magnets. [Display omitted] • The ordering porcess was significantly prolonged with ~17 h in 2:17 type SmCo magnets. • The coercivity with over 1 T was achieved without slow cooling treatment. • The higher efficient of Cu segregation was achieved. [ABSTRACT FROM AUTHOR]

The magnetic properties, thermal stability and phase evolution of sintered Nd-Fe-B magnets with intergranular addition of Pr–Co were investigated. The thermal stabilities of coercivity and remanence were simultaneously enhanced without heavy rare earth elements, resulting from the partial substitution of Pr for Nd and Co for Fe in matrix phase, respectively. After Pr–Co addition, RE-rich phase reduced and new phases containing Pr and Co, such as (NdPr) (FeCo) 2 (NdPr) 3 (FeCo) and (NdPr) 2 (FeCo) 17 phases, were formed. With the increase of Pr–Co addition amount, intrinsic coercivity firstly decreased sharply which was mainly caused by the formation of soft ferromagnetic (NdPr) (FeCo) 2 phase, and subsequently presented a remarkable recovery induced by the formation of non-magnetic (NdPr) 3 (FeCo) phase and transformation of (NdPr) (FeCo) 2 phase from ferromagnetic to non-magnetic. Due to the reduction of matrix phase proportion, the remanence decreased monotonously after the addition of Pr–Co for more than 10 wt. %. [ABSTRACT FROM AUTHOR]

Effects of magnetic field heat treatment on the structure and magnetic properties of Sm–Co/α-Fe nanocomposite permanent magnetic materials fabricated by high energy ball milling are investigated in the present work. After a magnetic field heat treatment below 700 °C on as-milled amorphous Sm–Co/α-Fe samples, the nanocomposite magnets with strong hard and soft magnetic interaction, showing a hysteresis loop of single phase characteristic, are obtained. The coercivity increases with the increase of annealing temperature. The coercivity, remanence and remanence ratio of the Sm–Co/Fe nanocomposite magnets are all enhanced after a heat treatment at a magnetic field as compared with those of nanocomposite magnets heat treated without a magnetic field. X ray diffraction analysis shows that the diffusion between the Sm–Co hard and α-Fe soft phases is suppressed by the magnetic field applied during the heat treatment process, leading to the inhibition of the grain growth of nanocrystal Sm–Co and α-Fe phases, and a finer nanostructure is obtained. Thus, a higher coercivity, remanence and remanence ratio are realized in Sm–Co/α-Fe nanocomposite magnets after the magnetic field heat treatment. Magnetic field heat treatment also makes the direction of c axis of Sm–Co hard grains along the heat treatment magnetic field direction, leading to an enhancement of magnetic anisotropy of the Sm–Co/Fe nanocomposite magnets. [ABSTRACT FROM AUTHOR]

Effective grain boundary (GB) reconstruction process has been proposed by introducing Pr-Fe-Al-Ga intergranular additive in the B-lean Nd-La-Ce-Fe-B multi main phase (MMP) magnets. A coercivity of ~2.0 T was yielded in the Nd-Fe-B sintered magnet with 24 wt% Nd substituted by La-Ce. Detailed structural analysis revealed that the RE 6 Fe 13 (Ga, Al) 1 phase was apparently formed in the triple junction area, triggered by the conducive intergranular composition environment provided by the B-lean composition and the Pr-Fe-Al-Ga addition. Simultaneously, continuous nonferromagnetic GB phases were generated to decouple the intergranular exchange, accompanied by the suppressed fraction of REFe 2 and REO x phases. Elemental distribution analysis demonstrated that Pr preferred to enter La/Ce-rich grains to form a Pr-rich shell that enhanced the magnetocrystalline anisotropy field of La/Ce-rich grain surface. Overall, the Pr-rich magnetic hardening shells and the reconstruction GB structure jointly gave rise to the restrained reversion of magnetic domains, thus an extraordinary coercivity was achieved in the Nd-La-Ce-Fe-B magnet. These phenomena may provide a new insight for the development of high-figure-of-merit Nd-La-Ce-Fe-B permanent magnets. [Display omitted] • A coercivity of ~2.0 T was yielded in Nd-Fe-B sintered magnet with 24 wt% Nd substituted by La-Ce. • The B-lean matrix and Pr-Fe-Al-Ga addition provide a conducive chemical environment to form the RE 6 Fe 13 (Ga, Al) 1 phase. • The RE 6 Fe 13 (Ga, Al) 1 phase inhibits the REFe 2 and REO x phases and promotes the formation of continuous grain boundaries. • Compositional gradient of Pr accelerates the development of Pr-rich shell and preferentially replaces the La/Ce-rich grains. [ABSTRACT FROM AUTHOR]

A surfactant-assisted high-energy ball milling technique was employed to synthesize Nd 2 Fe 14 B/α-Fe nanoparticles and nanoflakes from melt-spun nanocrystalline powders. The microstructure evolution in ball milling process was investigated. In the beginning stage (0–4 h) of ball milling, raw powders were crushed into micrometre-sized particles. While flakes were mainly formed by reducing thickness of particles via peeling layer by layer along preferential planes in the late stage (8–16 h). The selected area electron diffraction and high-resolution transmission electron microscopy images show that preferential cleavage planes are basal planes. With ball milling proceeding, more and more defects were induced by ball milling. As a result, the coercivity and remanence decreased to 1.6 kOe and 3.2 kGs, respectively. After 16 h ball milling, the exchange decoupling occurred due to severe amorphorization. A weakly-textured nanocomposite magnet was fabricated after 12 h ball milling and the anisotropy in magnetic properties can be further improved by employing settling down process to select particle size and aligning particles in external field. [ABSTRACT FROM AUTHOR]

The microstructure of die-upset nanocomposite magnets with different height reduction was studied to investigate the mechanism of texture development in processes of die upsetting coupled with Nd–Cu grain boundary diffusion. At beginning stage of die upsetting process, inhomogeneous Nd–Cu grain boundary diffusion results in two kinds of different grain boundary microstructures. As for adjacent grains with grain boundary phase, the stress-induced solution-precipitation underlies the formation of the platelet-shaped grains and texture enhancement. Whereas there are two types of texture enhancement for the neighboring grains without grain boundary phase: grain boundary sliding and grain devouring. As die upsetting further proceeds, the stress-induced solution precipitation is the dominant mechanism for texture enhancement due to fuller Nd–Cu grain boundary diffusion. [ABSTRACT FROM AUTHOR]

• The La/Ce elements are trapped in the RE 2 Fe 14 B shell by the inducement of Y. • LaCe-substituted MMP magnets have dual-type shell morphologies. • LaCeY-substituted MMP magnets have one-type shell structure. • The synergistic effect of Y and LaCe in MMP magnets is analysed. [Display omitted] The effects of Y and LaCe substitution in Nd-Fe-B multi-main-phase (MMP) magnets were investigated by co-mixing with the binary or ternary components. The microstructure and magnetic properties showed some differences after Y and LaCe-substitution. The coercivity was increased for the LaCe-substituted MMP magnets with two-types shell structures due to the stronger magnetic isolation between adjacent grains. Y-substituted MMP magnets with one-type shell structure exhibited a relatively lower coercivity due to the deterioration of anisotropy owing to the La/Ce/Y enrichment in the core-shell structure. The La element preferred to migrate to the grain boundary regions in the LaCe-substituted MMP magnets, while it was trapped in the 2:14:1 shell by the inducement of Y in the Y-substituted MMP magnets. This work provides new insights into the fabrication of La/Ce/Y magnets with high performance. [ABSTRACT FROM AUTHOR]

• A self-diffusion process was developed to recover (BH) max and squareness. • The microstructure of the magnets was homogenized by the self-diffusion process. • Micromagnetic simulations were implemented to explain the experimental results. • The improved squareness was due to the homogeneous magnetization reversal process. [Display omitted] To recover the remanence (or maximum energy product ((BH) max)) and squareness with high coercivity in diffusion-processed hot-deformed Nd-Fe-B magnets, new efforts have been made in this work. Annealing at a selected temperature of 800 ℃ under pressure was applied to the hot-deformed magnets diffused by the Nd 70 Cu 30 or Nd 70 Cu 15 Ga 15 alloy. After this process, the thick powder boundary phase dissolved in the matrix and diffused into the intergranular regions. The c-axis misalignment of Nd 2 Fe 14 B grains near the diffusion surface was significantly improved, leading to increased remanence by 0.10–0.18 T and (BH) max by 47–85 kJ/m3 in the two diffusion-processed magnets. The distribution of the powder boundary phase, the proportions of the intergranular Nd-rich phase, the c-axis alignment of grains and the grain sizes from the diffusion surface to the center of the magnets tend to be relatively uniform. The squareness factor of the demagnetization curve increased from 0.89 to 0.95 for the Nd 70 Cu 30 -diffused magnet and from 0.85 to 0.93 for the Nd 70 Cu 15 Ga 15 -diffused magnet after the process, returning to the level of the as-deformed magnet. Microstructure analysis and micromagnetic simulations indicate that the improved squareness factor is due to the homogeneous magnetization reversal process caused by the homogeneous microstructure. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the influence of substitution of Nd with Pr on the magnetic of sintered permanent magnets was investigated. The samples were prepared by traditional powder metallurgical technique. The nominal composition of the alloys is (Nd1−x Pr x )29Dy1.3R3.1Febal (R=Al0.3Cu0.2 Co1.5 B1Zr0.1, wt%) with x varying from 0 to 1 in steps of 0.2. Experimental results show that the overall magnetic properties, especially the intrinsic coercivity and thermal stability of the magnets, could be improved by substituting Nd with Pr in the magnets. When the Pr replaces all Nd in the magnets, excellent performance magnets with Br=13.65KGs, Hcj=22.13KOe, (BH)max =46.1MGsOe are obtained with a low Dy content (1.3wt%). [Copyright &y& Elsevier]

Abstract: Commercial rapidly-quenched Nd–Fe–B ribbons blended with fine Cu powders (10–30μm) were hot pressed to obtain fully dense magnets and then die upset into highly anisotropic, oriented magnets. The effects of Cu addition on the magnetic properties and bending strength of hot deformed Nd–Fe–B magnets were investigated. It was found that the coercivity (H cj) and maximum energy product (BH)max as well as the bending strength were enhanced significantly by Cu addition. Detailed microstructural investigations were carried out by transmission electron microscopy/high-resolution transmission electron microscopy (TEM/HRTEM). It shows that there are two types of grain boundaries in Cu-doped magnet, one is parallel and the other is trigonal. However, energy dispersive X-rays (EDX) analyses indicate that the two type intergranular phases are NdCu2. Analyses indicate that the enhanced texture of Cu-doped magnet is due to the lower melting point of the intergranular phase, leading to the enhancement in magnetic properties. Improvement of bending stress in Cu-doped magnet is related to the trigonal grain boundaries and the rheology of the intergranular phase. [Copyright &y& Elsevier]

• The coercivity was significantly enhanced from 15.18 kOe to 26.30 kOe in the Pr60Tb13Al27 GBD magnet. • The grain boundary structure and Tb-rich shell structure were optimized simultaneously in the Pr60Tb13Al27 GBD magnet. • The effect of Pr on the grain boundary structure and Tb-rich shell in the Pr60Tb13Al27 GBD magnet was analyzed. [Display omitted] Commercial sintered Nd-Fe-B magnet was grain boundary diffusion (GBD) processed by Pr 60 Tb 13 Al 27 and Tb 73 Al 27 alloys. Although the Tb content is only 13 at% in the Pr 60 Tb 13 Al 27 alloy, the coercivity was significantly enhanced from 15.18 kOe to 26.30 kOe in the magnet diffused by Pr 60 Tb 13 Al 27 , higher than 24.08 kOe of the Tb 73 Al 27 GBD magnet. This suggests that the substitution of Tb(60 at%) by Pr in the Tb 73 Al 27 alloy can further enhance coercivity. Detailed microstructure analysis showed that, in the Pr 60 Tb 13 Al 27 GBD magnet, the Tb-rich shell thickness was reduced and the two-layer Tb-rich shell was formed. Furthermore, a large number of continuous grain boundary phases was observed, which significantly enhances the exchange-decoupling effect between adjacent grains. The effect of Pr for the Tb-rich shell and grain boundary structure was discussed based on the experimental results. [ABSTRACT FROM AUTHOR]