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The effect of Mn on hydrogenation behavior and magnetic properties of 2:17 type SmCo alloys was investigated. The as-cast Sm(Cobal.Fe0.2MnxCu0.08Zr0.025)7.2 alloys with x = 0 , 0.04, 0.08, and 0.12 were all decrepitated under hydrogen pressure of 0.3 MPa at room temperature. The hydrogenation ability of as-cast alloys was obviously improved with the increase of Mn content. The size of particles was decreased with the increase of Mn content due to the network structure diminishing with Mn content increasing. The phase and microstructure changes of as-cast alloys were discussed. Research results show that Mn-doped has a great effect on the grain boundary phase, which lead to the high hydrogen absorption ability and the broken of as-cast alloys. The following magnetic properties were obtained for Sm(Cobal.Fe0.2Cu0.08Mn0.04Zr0.025)7.2 magnet: B_{r} = 10.6 kGs, H_{\text {cj}} = 28.35$ kOe, and (BH)_{\mathrm {\mathbf {max}}} = 26.74 MGOe. [ABSTRACT FROM AUTHOR]

Two methods of pre-crushing power, hydrogen decrepitation (HD) and mechanical crushing (MC), were applied to prepare Sm (CobalFe0.28Cu0.06Zr0.02)7.84 magnets. Their microstructures and magnetic properties were investigated. Compared with a conventional MC method, the Sm2O3 content was decreased and the coercivity was enhanced from 8.67 to 24.03 kOe with an HD method. The larger grain size and less grain boundaries defects were obtained in HD magnets. In addition, the HD technology improved effective Sm content of magnets by decreasing oxidation of Sm. The effective Sm content played a significant role on microstructure and magnetic properties changes of the two kinds of magnets. In combinations with the changes of alloy composition and microstructures, the effect of HD technology on effective Sm content was discussed. [ABSTRACT FROM PUBLISHER]

Ultrafine-grained sintered Nd–Fe–B magnets were produced from jet-milled hydrogenation–disproportionation–desorption–recombination powders in a proper sintering condition. The coercivity of $\sim 15$ kOe was obtained by sintering below 950 °C, and the average grain size was <1~\mu \text{m} . For the newly fine-grained magnets, a higher magnetic field is needed to magnetize them, giving rise to a two-step initial magnetization curve involving domain wall pinning at the grain boundary phase. Microstructure observation indicated that the Nd-rich phases did not encapsulate the 2:14:1 phases effectively, resulting in defects and interactions between adjacent 2:14:1 grains, which are responsible for the relatively low coercivity of the fine-grained magnets. [ABSTRACT FROM AUTHOR]

The intergranular addition process using Y72Co28 eutectic alloy powders has been applied to (Pr, Nd)27Dy4Fe67.65Cu0.15Al0.2B1(wt.%) sintered magnets, resulting in an enhanced thermal stability. It was found that the coercivity of magnets at 100 °C increased while the addition of Y72Co28 is 1 wt.%, whereas the magnetic properties decreased slightly at room temperature due to lower magnetocrystalline anisotropy field ( H\! {A} ) of Y2Fe14B. The temperature coefficient of remanence ( $ \alpha $ ) and coercivity ( $ \beta $ ) for the magnets improved significantly. Microstructure observation indicated that Y atoms prefer to enter into the 2-14-1 phase and form a core-shell structure with an outer layer of (Nd, Dy, Y)2(Fe, Co)14B. Magnetic domain and intrinsic properties analysis suggested that the improved thermal stability resulted from the modified grain boundaries and the introduction of Y in matrix phases. [ABSTRACT FROM AUTHOR]

Positive temperature coefficients of coercivity are first obtained in the series of Sm1-xDyx(Co0.695Fe0.2Cu0.08Zr0.025)7.2 magnets. The temperature range with a positive temperature coefficient of coercivity is gradually moving to higher temperature with the increase of x. Thermal magnetic analysis shows a spin reorientation transition of cell boundary phase in these magnets. It is interesting to find the abnormal coercivity is controlled by the spin-reorientation-transition cell boundary phases, and the spin reorientation temperature of cell boundary phase is consisted with the start point of the temperature range with abnormal behavior. The different temperature coefficients are discussed in terms of a nucleation model. [ABSTRACT FROM AUTHOR]

We present an effort to enhance the magnetic properties of sintered Ce–Fe–B-based magnets by optimizing the microstructure of strip-casting (SC) alloys. The results indicated the microstructure in the Ce30.5Febal.B1 SC alloy was characteristic for peritectic solidification and Ce2Fe14B coexisted with CeFe2 and primary Fe-rich phase. After alloying a little amount of Ho and Nd, the microstructure of Ce–Fe–B strip was optimized toward that of Nd–Fe–B strip. Experimental results indicated that all magnetic properties, especially the energy product, were enhanced after optimizing the microstructure of SC alloy. Fracture surface images of the magnets illustrated the grain boundary structure was also modified due to optimization of the microstructure of SC alloys. [ABSTRACT FROM AUTHOR]

Dysprosium diffusion and microstructure alteration behaviors in sintered Nd-Fe-B magnets via dual-alloy method have been investigated. The sintered magnets were prepared by blending Dy-free and Dy-rich powders with varying proportions. Results indicate that Dy element has already diffused from Dy-rich powders into the 2:14:1 phase of Dy-free powders and tended to homogenize in the bulk magnet, attributed to the coalescence of grains and dysprosium element concentration gradient. In addition, Dy and Pr/Nd elements counterdiffusion process redistributes the grain boundaries homogeneously. The fracture surfaces of magnets prepared via dual-alloy method almost appear intergranular fracture. It demonstrates that both of (Nd/Pr,Dy)2Fe14B phase formation and microstructure alteration have favored to coercivity enhancement and thermal stability improvement of the magnets. [ABSTRACT FROM AUTHOR]

Abstract: The effects of varying Nd-contents on the magnetic properties of Nd12.8+x Fe81.2−x−y−z Co y Ga z B6 ribbons and the resulting die-upset magnets have been investigated. It was found that the Nd content has a significant effect on both magnetic properties and texture of the die-upset magnets. An optimum Nd content exhibits good texture, while both Nd-lean and excessively Nd-rich Nd–Fe–B alloys lead to unsatisfactory textures. The magnetic properties and texture of the die-upset magnets strongly deteriorated with a further increase in the Nd-content. The thermo-mechanical characteristics and the formation mechanism of two kinds of cracks in backward-extruded ring magnets have also been investigated. [Copyright &y& Elsevier]

High-performance Nd–Fe–B magnets with nominal composition of Nd13.25Dy0.2Fe78.87Co1Cu0.1Al0.5B6.08 (at%) have been produced by using strip casting technique. It was found that the temperature gradient of alloy in the solidification stage determines the grain size and the grain alignment of the alloy strips. The growth direction of grains parallels the direction of heat flow during solidification stage. The average solidifying rate of strips is more than \ 10^3^\circC/s, which can effectively depress the formation of \alpha-Fe dendrites. It is observed that the concentration of rare earth has a significant decrease from free side to wheel side of the strip. The results of magnetic properties of final magnets produced with different strips indicate that the nonuniform phase structure can deteriorate the squareness of demagnetization curve and the temperature coefficient of coercivity. Effects of the temperature gradient in the solidification process on the microstructure of alloy strips, magnetic properties, and thermal stability of the final magnets are investigated systematically. [ABSTRACT FROM AUTHOR]

The effects of hydriding degree on the microstructure and magnetic properties of sintered NdFeB magnets have been studied. The degree of crushing depends on the absorption content of hydrogen and affects the magnetic properties of final magnet. Insertion of hydrogen atoms leads to a significant increase of the unit cell volume. And the crush mechanism depends on the internal stress resulting from differences in the expansion rates of the two phases. The remanence of final magnets increases monotonously while the coercivity decreases sharply with the increasing of hydriding degree, attributed to the strip fracture features and the morphology of particles. [ABSTRACT FROM AUTHOR]

Hot-deformed Nd-Fe-B ring magnets have wide potential applications. These ring magnets, however, exhibit axial inhomogeneity of magnetic performance. In this work, the effects of density, pressure, deformation temperature, deformation rate, and texture on axial magnetic performance were investigated over ring magnets prepared by backward extrusion method. It was demonstrated that the texture accounted for the variation of magnetic performance along axial direction. Microstructures of the ring magnets were examined with SEM, which further revealed two different origins of axial inhomogeneity of magnetic performance. The deformation degree of Nd-Fe-B grains plays a critical role in the performance difference between the top and middle part of ring magnet. But that between the middle and bottom part mainly results from different alignment orientations of platelet Nd-Fe-B grains. It was both deformation degree and alignment orientation that determined the axial texture and consequent magnetic performance of hot-deformed ring magnets. [ABSTRACT FROM AUTHOR]

The purpose of this study was to save heavy rare earth Dy in NdFeB production. By ways of optimizing preparation process and replacing Nd with Pr, Dy-free magnet with high coercivity was successfully prepared, the nominal composition is Pr14B6Co2.2Cu0.2Al1Fe76.7 (at %). The effect of Pr on magnetic performance and microstructure of the magnet were investigated systemically, alloy Nd13.65B6Co2.2Cu0.2Al1Fe76.9 (at %) was prepared by the same preparation process as comparison. The results indicated that magnet Pr14B6Co2.2Cu0.2Al1Fe76.7 has much higher coercivity than that of magnet Nd13.65B6Co2.2Cu0.2Al1Fe76.9. Microstructure investigation showed that the presence of small grains, thin and smooth RE-rich film, associated with higher coercivity. [ABSTRACT FROM AUTHOR]

Nanocomposite (Pr8.2Fe86.1-xCoxB5.7)0.99Zr0.01 (x = 0-10) ribbons consisting of Pr2(Fe,Co)14B and α-(Fe,Co) phases were prepared by a melt-spun technique. The microstructure and magnetic properties were studied. The results show that the Curie temperature increases drastically with increasing Co content. The optimal permanent magnetic properties are obtained at x = 2, and the value of Hci, Ms, Mr, and (BH)max are 6.52 kOe, 150.2 emu/g, 120.9 emu/g, and 22.34 MGOe, respectively. Typical magnetization behaviors of nanocomposite magnets are found in these ribbons. The significant remanence enhancement indicates that a strong intergrain exchange coupling exists in all ribbons studied in this work. By Co substitution, the intergrain exchange coupling is enhanced significantly. The study of microstructure shows that the larger grains of Pr2(Fe,Co)14B hard phase are surrounded by the smaller grains of α-(Fe,Co) soft phase with size about 10-20 nm in the ribbon with Co substitution. This kind of microstructure is in favor of exchange coupling between magnetically hard and soft phases and results in excellent magnetic properties. [ABSTRACT FROM AUTHOR]

The influence of the RE-rich phase distribution in the precursor alloys on the anisotropy of the hydrogenation disproportionation desorption recombination (HDDR) processed powders is investigated. The homogenized ingot alloy and the as-cast strip casting (SC) alloy with a uniform RE-rich grain boundary phase lead to high anisotropy of the refined powders, acquiring degrees of alignment (DOA) of 0.62 and 0.54, respectively. The RE-rich phase aggregation results in a deteriorated DOA of the powders due to the drastic disproportionation rate, while a thin and uniform RE-rich phase distribution is beneficial for DOA. A reaction model of the initial particle microstructure is proposed for optimizing the HDDR powder anisotropy. [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]

Highlights • High-coercivity Nd-Fe-B magnets with "core-shell" structure were prepared by the hot-pressed pretreated technology. • The core-shell structures can maintain the high Br, while also effectively enhancing the H cj. • The hot-pressed pretreated technology can be used to prepare large pieces of high performance Nd-Fe-B bulk magnets. Abstract The high-coercivity Nd-Fe-B magnets with "core-shell" structure grains were prepared by doping TbCu powders and hot pressing after pre-sintering in the traditional powder metallurgy process. The coercivity for the hot-pressed pretreated Nd-Fe-B magnet is obviously enhanced to 28.6 kOe from 24.3 kOe by TbCu alloy doping. The Tb contents at the shell structure of grain in the hot-pressed pretreated magnet is 5.7 wt% while that in the dual-alloy magnet is 3.0 wt%. The enrichment of Tb elements in the shell layer further enhances the anisotropy of the grain surface and effectively improves the utilization efficiency of heavy rare earths. The existence of the hard (Tb, Nd) 2 Fe 14 B shell, which can effectively inhibit the reverse nucleation of magnetic domains, contribute to enhance the coercivity with few reduction of the remanence. Compared with the grain boundary diffusion process, this technology can be used to prepare large pieces of high performance Nd-Fe-B bulk magnets without diffusion depth limit. [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]

HDDR processed Nd-Fe-B powders blended with Nd-Cu powders were hot-pressed and then hot-deformed to obtain fully dense, anisotropic magnets. The microstructure evolution in hot-pressed and hot-deformed HDDR magnets was studied to illustrate the impact of Nd-Cu diffusion on coercivity and deformation ability. It was found that the coercivity and the deformation ability were improved significantly by Nd-Cu addition. The coercivity of hot-deformed magnets was increased from 3.81 kOe to 13.01 kOe after 2 wt% Nd-Cu additions and the annealing at 900 °C for 2 h. Scanning electron microscopy and transmission electron microscopy observations revealed that the variation in coercivity was attributed to the diffusion of Nd-Cu along the grain boundaries during hot pressing and hot deformation. [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]

Anisotropic ultrafine-grained Nd-Fe-B magnets with WC addition were prepared by hot deformation. With WC nano-particles addition of ~ 1.0 wt.%, the squareness was optimized and the coercivity of the hot-deformed magnets increased substantially by 2.16 kOe, from 15.59 to 17.75 kOe 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. [ABSTRACT FROM AUTHOR]

A dual-alloy method was applied to tune the distribution of Ce for enhancing the performance of Nd-Ce-Fe-B sintered magnets with a nominal composition of (Nd 0.75 Ce 0.25 ) 30.5 Fe bal Al 0.1 Cu 0.1 B. In comparison to the single alloy of (Nd 0.75 Ce 0.25 ) 30.5 Fe bal Al 0.1 Cu 0.1 B, the coercivity was enhanced from 10.3 kOe to 12.1 kOe and the remanence was increased from 13.1 kG to 13.3 kG for the magnets with a dual-alloy method. In addition, the remanence temperature coefficient α and coercivity temperature coefficient β were also slightly improved for the magnet with the dual alloys. The results of microstructure characterizations show the uniform distribution of Ce for the magnet with a single alloy, and the coexistence of the Ce-rich and Ce-lean regions for the magnet with the dual alloys. In combinations with the nucleation of reversal domains and magnetic recoil curves, the property enhancement of magnets with a dual-alloy method was well explained. [ABSTRACT FROM AUTHOR]

Two kinds of lamella phases were observed in the phase transformations during aging of Sm(Co 0.695 Fe 0.2 Cu 0.08 Zr 0.025 ) 7.2 magnets, which formed before and after the disappearance of microtwins respectively. Microtwins appeared with the precipitation of disordered 2:17R phases and disappeared with 2:17R phase ordering. Dy was introduced to investigate these transformations by stabilizing the 2:17H phases. A simplified atomic model was given to describe the formation of microtwins and a reasonable assumption was proposed as well to clarify the mechanism of these transformations. [ABSTRACT FROM AUTHOR]