Nd-Fe-B metal magnets are produced by different two methods. One is hot deformed method and the other is sintered one. Sintered magnets are made from cast alloy and the crystalline alignment is controlled in external magnetic field. On the other hand, hot deformed magnets are made from melt-spun ribbons with nano structure. Hot deformed magnets have so fine structure that coercivity is higher than that of sintered one. Crystalline alignment with their c-axis parallel to the press axis is promoted by plastic deformation at high temperature. It is apparent that hot deformation conditions play an important role on crystalline alignment. The magnet samples are made by upsetting method and it is studied that the influence of hot deformation conditions (Reduction ratio:R, Upsettng temperature:T and Strain rate:ε) on the crystalline structures in order to obtain a high performance hot deformed magnet. The conditions of R and T influence on the remanence, while that of R and T influence on the coercivity. It is found that the remanence of the hot deformed magnet increased with increasing R, related to a crystalline alignment associates with the predominant c-plane growth in their crystals. By optimizing these conditions, magnet with the composition of 30.4Nd-6.0Co -0.91B-0.56Ga-bal.Fe (wt%) shows high performance, and the remanence B_r, coercivity H_cJ and maximum energy product (BH)_max are 1.37 T, 1138 kA/m and 347.3 kJ/m³, respectively.

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Anisotropic Nd-Fe-B powder made through hot-forming process is a promising material for high performance bonded magnet. It is important to clarify effects of various conditions in hot-deformation process on magnetic properties of anisotropic powder in order to improve them. In this study, we investigated effects of deformation temperature and strain on magnetic properties of anisotropic powder. The results showed that both of hot-deformation temperature and strain greatly influenced magnetic properties of the anisotropic powder. Consequently, the optimum temperature and strain condition to achieve the maximum hard magnetic properties were obtained. Anisotropic compression-molded bonded magnets made from hot-upset powder through the optimum condition were fabricated; the bonded magnet with the composition of Nd_0.137Fe_0.735Co_0.067B_0.055Ga_0.006 showed the highest-class (BH)_max value of 178 kJ/m³, on the other hand the bonded magnet with the composition of Nd_0.130Dy_0.016Fe_0.726Co_0.068B_0.054Ga_0.006 had not only high coercivity of 1.6 MA/m but high (BH)_max of 138 kJ/m³.

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Population of the elderly who need long-term care has reached to 2 million in 1993 in Japan, which is expected to increase to 16 % of all of the elderly in 2025. It is important for aged and disabled persons to keep their quality of life better, that is, going out and joining in social activities. Assistive technologies such as power-assisted wheelchair are helpful for reducing physical load of the attendant. Daido Steel developed a radial gap DC brushless motor with high torque by using radially-oriented ring magnet, NEOQUENCH*2-DR. The motor showed low cogging-torque for an innovative electric-power assistive wheelchair to make the operation by the attendants smoother and friendly. This time, Daido has developed a prototype coreless and axial gap motor to achieve the non-cogging-torque and direct-drive. Typical specifications of the motor equipped with isotropic bonded magnet NEOQUENCH-P are 135 kgf-cm in rated torque and 120 rpm in non-load speed.

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As the number of systems using high frequency electromagnetic waves has increased in recent years, such as IMT-2000 system, electromagnetic compatibility (EMC) problems have become apparent.

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Isotropic Nd-Fe-B bonded magnets, which are widely used in various instruments, have (BH)_max of 5 ~ 12 MGOe. It is required to enhance the (BH)_max of bonded magnet for a development of its new applications. In this study, the hot-upsetting of Nd-Fe-B powder packed into a metal container has been tried in order to simplify the production process of anisotropic powder, and to enhance its hard magnetic properties. Consequently, it was found that the high-performance anisotropic powder was obtained by the relatively simple production process. This hot-formed anisotropic powder material is thought to be the promising candidate for the high-performance bonded magnet. Results obtained in this study are as follows: (1) High (BH)_max powder was obtained by the direct hot-upsetting of Nd-Fe-B quenched powder packed in the iron container. (2) Alignment of the Nd₂Fe₁₄B crystals; enhancement of the (BH)_max , occurred effectively in the hot-upsetting at 750 ~ 850 °C. (3) The (BH)_max of the upset Nd-Fe-B powder increased with increasing the percent reduction of the iron container in the hot-upsetting, and saturated around 85 % of the percent reduction. The saturated (B H)max of the upset Nd_0.137Fe_0.735Co_0.067B_0.055Ga_0.006powder was about 38 MGOe, being enough value to show high performance as an anisotopic bonded-magnet. (4) Compression-molded Nd 0.137 Fe_0.735Co_0.067B_0.055Ga_0.006bonded-magnet showed the following magnetic properties: B_r = 9.51 kG,_iH_c = 14.3 kOe, and (BH)_max = 20.5 MGOe. Compression-molded Nd_0.130Dy_0.016Fe_0.726Co_0.068B_0.054Ga_0.006 bonded-magnet showed the following magnetic properties: B_r = 8.15 kG,_iH_c = 21.2 kOe, and (BH)_max = 15.4 MGOe. (5) Temperature coefficients of B r and i H c of the compression-molded Nd_0.137Fe_0.735Co_0.067B_0.055Ga_0.006 bonded-magnet were -0.096 %/°Cand -0.46 %/°C, respectively.

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Sm-Fe-N hard magnetic materials are good candidates for high performance bonded magnets. Rapid-quenching method should be highly favorable for the fabrication of isotropic magnet powder with high coercivity. We report here the magnetic properties of Sm-Fe-N powders produced by three kinds of rapid-quenching processes. Sm₂Fe₁₇ powders were prepared by gas-atomization (GA), rotating-disk atomization (RDA), and melt-spinning (MS) methods. The Sm₂Fe₁₇ GA powder had dendritic solidification structure, while the RDA powder had microcrystalline structure with size of 3-5μm. Coercivities (H_cJ ) of their nitrides were 56 (for GA) and 217 kA/m (for RDA). The HcJ of nitrided Sm₂Fe₁₇ MS powder with wheel velocity (V_s) of 5-20 m/s, which had also microcrystalline structure, was 53 to 509 kA/m. These coercivity values are not sufficient for practical value (600 kA/m) for bonded magnet applications. From the study of additive effects, it was found that C, C-Si, C-Ga, or C-Al addition decreased the grain size of quenched Sm₂Fe₁₇ powder. Consequently, high coercivity was obtained; the HcJ of nitrided Sm₂Fe₁₅C₁Si₁ MS powder with Vs of 10 m/s was 898 kA/m, and 708 kA/m for the nitrided Sm₂Fe₁₅C₁Si₁ RDA powder. The compression-molded bonded magnet made from Sm₂Fe₁₈Si_0.1N_x MS powder showed a high (BH)_max of 82.7 kJ/m³.

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