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Microstructural analysis during the step-cooling procedure of iron-rich Sm(Co0.65Fe0.26Cu0.07Zr0.02)7.8 anisotropic sintered magnets was investigated systematically. The sintered magnet exhibits the maximum energy product of about 32 MGOe together with a remanence of about 11.5 kGs. It is found that the cellular structure has formed at the stage of isothermal annealing (heat treating at 1103 K for 20 h). Moreover, the average cell size of the 2:17 cell phase in magnets decreases from ~150 to ~105 nm, and the density of the lamella phase increases from ~0.03 to ~0.05 1/nm during the step-cooling procedure. It is also found that the Cu concentration is homogeneous in the specimen quenched at a temperature of 1103 K and then becomes nonuniform, especially enriched in the cell boundaries during the step cooling to 873 K. Interestingly, the typical twining structure along the [010] zone of the main phase exists in the specimen quenched at 873 K. Furthermore, it is inferred that the magnetization mechanism of the specimens transforms from the nucleation-dominated type to the coexisting type of pinning and nucleation effect during the step-cooling procedure. [ABSTRACT FROM AUTHOR]

The (R,Ce)–Fe–B magnets have been successfully industrialized in recent years. The mechanical property of sintered permanent magnets is one important aspect of their comprehensive performances, which directly influences the service reliability and the production cost. In this paper, the bending strength, fracture toughness, Vickers hardness, and brittleness index of commercial (R1–xCex)30.5–31.5Febal.B1M1 magnets with different cerium contents have been investigated. The micro-fractures of the magnets were observed by a scanning electron microscopy equipped with energy dispersive X-ray analysis system. It shows that the bending strength and the fracture toughness of (R,Ce)–Fe–B magnets have a downward tendency with increasing Ce content x, while the Vickers hardness of the magnets varies irregularly with Ce contents in this paper. The optimum mechanical properties have been obtained in the (R1–xCex)30.5–31.5Febal.B1M1 magnet with $x = 0.15$ ; the bending strength, fracture toughness and brittleness index of the magnet with $x =0.15$ are obviously superior to those of the ordinary sintered Nd–Fe–B magnets. Some flocculent oxide phases have been discovered in the (R,Ce)–Fe–B magnet with $x = 0.15$ . The flocculent phases may absorb the crack propagating energy, and reduce the stress concentration at a crack tip, which is beneficial to strengthening and toughening of (R,Ce)–Fe–B magnets. However, the mechanical properties are obviously worse for the magnet with $x = 0.45$ (Ce/ $\sum $ RE = 45%). That is probably because the microstructures of the magnet with $x = 0.45$ become deteriorated, in which abnormally large grains have been observed. [ABSTRACT FROM AUTHOR]

To obtain the excellent magnetic properties for the Ce substitution magnets, we proposed a dual-main-phase method to prepare the high-permanence (CePrNd)–Fe–B magnet with low cost. The main phase in this method means the hard magnetic phase with high anisotropy field. Compared with the traditional sintered method adjusting the composition of the magnet, the dual-main-phase method can also design the distribution of the main phase in the magnet, which makes the structure satisfy the demand of the magnet with outstanding properties. Compared with the magnet prepared by the single-alloy method, the coercivity of the magnet prepared by the dual-main-phase method is dramatically enhanced from 7.7 to 12.1 kOe, which may be due to the distribution of the grain boundary phase between the different kinds of main phases. [ABSTRACT FROM AUTHOR]

The electrical resistance is one of the important properties for Nd2Fe14B magnets with low eddy-current loss. We have coated Nd–Fe–B melt-spun particles with CaF2 by the liquid-phase coating technique and then performed hot-pressing and hot-deformation to make Nd2Fe14B/CaF2 composite magnets. The morphology and distribution of CaF2 in the magnets and its influence on the coercivity mechanism and the electrical properties of the Nd2Fe14B/CaF2 magnets have been investigated by scanning electron microscope, hysteresisgraph, and four-probe resistivity meter. The morphology of CaF2 depended on the liquid-phase synthesis parameters, especially the concentrations of the reactants. On the surface of Nd–Fe–B particles, there formed only a few CaF2 nanoparticles and nanoflakes when 0.5 and 1 mol/l reactant aqueous solutions were used as precursors. With the increase of the concentrations of the reactants, there obtained a flake-shaped thin CaF2 coating on the Nd–Fe–B particles. In addition, the CaF2 coating became thicker, $\sim 150$ –200 nm, with further increasing the concentrations of the reactants to 2 mol/l. After compaction and hot-deformation, the electrical resistances of the Nd2Fe14B/CaF2 magnets fabricated using the concentrations of the reactants of 2 mol/l reached approximately 580 $\mu \Omega $ cm, which increased about 348% comparing with the corresponding pure Nd–Fe–B magnet. It is interesting to find that the coercivity of the Nd2Fe14B/CaF2 composite magnets increased from 12.42 to 13.5 kOe when the concentrations of the reactants increased from 0.5 to 1.5 mol/l and then decreased to 10.2 kOe with further increasing the concentrations of the reactants to 2 mol/l. The reason for the increment of coercivity may be that CaF2 nanoparticles and nanoflakes acted like lubricants that were beneficial to the rotation and the orientation of Nd2Fe14B particles during the hot-deformation process. [ABSTRACT FROM AUTHOR]

Nd-Fe-B/NdF3 composite magnets have been prepared by two different mixing methods: 1) mixing in agate mortar without lubricant and 2) milling in a planetary ball mill with heptane. The comparison of two mixing methods and their influences on the electrical and magnetic properties of the Nd-Fe-B/NdF3 composite magnets have been investigated. The results show that the microstructures of the composite magnets fabricated by mixing in agate mortar without lubricant were not uniform. But method 1 contributed a better magnetic property compared with method 2. The electrical resistivities of the Nd-Fe-B/NdF3 composite magnets fabricated by method 1 in the direction parallel to the pressing direction increased with increasing NdF3 amounts. The remanence and maximum energy products of the Nd-Fe-B/NdF3 composite magnets prepared by method 1 reduced to some extent with increasing NdF3 amount. Method 2 contributed to obtaining a more homogenous microstructure. Method 2 has little influence on the electrical resistivity when the amounts of NdF3 were kept constant. But, it is detrimental to the magnetic properties of the composite magnets. [ABSTRACT FROM AUTHOR]

Fabrication of rare-earth-based permanent magnets with both high electrical resistivity and excellent magnetic properties for the traction motor applications is highly challenging. In this paper, Nd-Fe-B/Dy2O3 composite magnets have been fabricated by hot-pressing and die-upset. The influence of Dy2O3 filler on the microstructures, electrical resistivity and magnetic properties of the Nd-Fe-B magnets have been investigated by scanning electron microscope, four-probe resistivity meter and hysteresis graph. The results showed that the electrical resistivities of the Nd-Fe-B/Dy2O3 composite magnets increased with the increase of Dy2O3 amount and reached 1270 \mu \Omega cm when the Dy2O3 amount increased to 20 wt.%. Whereas the electrical resistivity of the nondoped Nd-Fe-B magnets is 230 \mu \Omega cm. The cross-section SEM images of the composite magnets showed that the Dy2O3 phase formed laminated structure and some agglomerate phenomenon. The agglomerate areas became larger with the increase of Dy2O3 amount. The residual magnetic flux density (Br) and maximum energy product of the Nd-Fe-B/Dy2O3 composite magnets decreased due to the nonmagnetic Dy2O3 filler. It is interesting to find that coercivity of the Nd-Fe-B/Dy2O3 composite magnets increased from 7.8 kOe to 9.64 kOe when the Dy2O3 amount increased from 10 wt.% to 20 wt.%. The reason may be that some of the dysprosium diffused into the Nd-Fe-B matrix and formed (Nd,Dy)2Fe14B compounds. In the mean time, some of neodymium-rich phase diffused to Dy2O3 phase, replaced dysprosium and formed Nd2O3. This probably happened during the die-upset process at 850 ^\circC. [ABSTRACT FROM AUTHOR]

The coercivity of the die-upset Nd–Fe–B magnets was enhanced remarkably by the Nd–Cu eutectic alloy addition. The initial magnetization curves show that the magnetization reversal transforms from the nucleation fields for an Nd–Cu free magnet to the coexistence of the nucleation and domain-wall pinning fields for the magnet with Nd–Cu addition. The transmission electron microscopy images reveal that more triple-junction regions, which are enriched with Nd and Cu elements, distribute in the die-upset magnets with Nd–Cu addition. These regions become the domain-wall pinning center and enhance the coercivity of the magnets. Moreover, the thickness of the grain boundary phase increases with the Nd–Cu addition, which declines the coupling between the Nd–Fe–B grains and then further improves the coercivity. [ABSTRACT FROM AUTHOR]

In this paper, the structure and magnetic properties of the (Ce, Nd)–Fe–B magnets without Dy and Tb substitution have been investigated. The purpose of the investigation is to develop the applicable Ce–Fe–B magnets with Ce content over 50 wt.%. Sintered (Ce, Nd)–Fe–B magnets with the nominal composition of (Nd1−xCex)30(Fe, TM)balB1 ( x=0 –0.75) in wt.% were fabricated by advanced powder metallurgy processes. The effects of Ce substitution on the microstructure and magnetic properties of the (Ce, Nd)–Fe–B magnets were discussed. It was found that the (Ce, Nd)-rich boundary phase with lower melting point is helpful to obtain improved boundary microstructures and refined grain magnets. Good magnetic properties of Br = 13.5 kG, H_{\mathrm {cj}}= 9.5 kOe, and (BH)_{\mathrm {max}} = 42.8$ MGOe were obtained in the Dy-free (Ce, Nd)–Fe–B magnets with 30 wt.% Ce substitution. A higher coercivity (>10 kOe) has been achieved in the Ce–Fe–B type magnets by the modifications of alloy compositions and the optimization of preparation conditions, in which the proportion of Nd and/or Pr is lower than 35 wt.% of the total rare-earth content. [ABSTRACT FROM AUTHOR]

To increase the electrical resistance of Nd–Fe–B magnets, CaF2 were used to fabricate Nd–Fe–B/CaF2 composite permanent magnets by hot-pressing and hot-deformation techniques. The influence of CaF2 on the microstructures, electrical resistances, and magnetic properties of the Nd–Fe–B/CaF2 composite magnets has been investigated. The results show that the cross-sectional microstructure of the composite magnets appeared as layered-structure and wet blending contributed to the formation of smooth CaF2 layers. The electrical resistances of the Nd–Fe–B/CaF2 composite magnets increased with the amounts of CaF2 and reached $1280~\boldsymbol \mu \Omega $ cm in the direction parallel to the pressing direction when the volume of CaF2 was 20 vol.%, which increased 456% higher than that of the Nd–Fe–B magnet ( $230~\boldsymbol \mu \Omega $ cm). But the maximum energy products of the Nd–Fe–B/CaF2 composite magnets decreased with the increase of the amounts of CaF2. [ABSTRACT FROM AUTHOR]