• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.1
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• pp.27-31
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• 2017

In this study, the effect of Tb inward diffusion on the magnetic properties of the Nd-Fe-B sintered magnets was studied. After sintering of the magnets, $TbF_3$ slurries were dip-coated on the surface of the samples, then heat-treatment was followed for $TbF_3$ diffusion. The element distribution in the magnets and the diffusion profiles of Tb ions were analyzed by an EPMA (electron probe micro-analyzer). Prolonged heat treatment resulted in a deeper diffusion length of Tb ions. Coercivity of the $1^{st}$ heat-treated sample showed 21.86 kOe, while that of the $1^{st}$, $2^{nd}$ heat-treated and annealed sample revealed 34 kOe.

• Journal of Powder Materials
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• v.30 no.2
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• pp.116-122
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• 2023

Because magnets fabricated using Nd-Fe-B exhibit excellent magnetic properties, this novel material is used in various high-tech industries. However, because of the brittleness and low formability of Nd-Fe-B magnets, the design freedom of shapes for improving the performance is limited based on conventional tooling and postprocessing. Laser-powder bed fusion (L-PBF), the most famous additive manufacturing (AM) technique, has recently emerged as a novel process for producing geometrically complex shapes of Nd-Fe-B parts owing to its high precision and good spatial resolution. However, because of the repeated thermal shock applied to the materials during L-PBF, it is difficult to fabricate a dense Nd-Fe-B magnet. In this study, a high-density (>96%) Nd-Fe-B magnet is successfully fabricated by minimizing the thermal residual stress caused by substrate heating during L-PBF.

• Proceedings of the Korean Magnestics Society Conference
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• 1994.10a
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• pp.50-51
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• 1994

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.34-40
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• 2002

In order to improve the microstructure of the strip cast Nd-Fe-B alloys that are frequently used for production of high energy sintered magnets, influence of various strip casting conditions on the microstructure and phase formation and distribution were investigated. Nd-Fe-B strips consisting of microstructures suitable for preparation of high energy sintered magnets could be obtained when the wheel speed was below 5 m/s. The compositional limit that can avoid the crystallization of free iron in the as-cast state was estimated to be Nd$\_$14/Fe$\_$79/B$\_$7/. Regardless of the compositional variation, <001> preferred orientation of Nd$_2$Fe$\_$14/B normal to the strip surface was always occurred below 5 m/s, which would eventually enhance the grain alignment during pressing the powder under a magnetic field. While the coercivity of the strip cast alloys increased with the increase of the wheel speed, mainly due to the refinement of Nd$_2$Fe$\_$14/B grains, it decreased with the reduction of Nd content in the alloy composition as the formation of free iron increased.

• Journal of Magnetics
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• v.20 no.2
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• pp.97-102
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• 2015

The waste of sintered Nd-Fe-B magnets was recycled using the method of dopingPrNd nanoparticles. The effect of PrNd nanoparticle doping on the magnetic properties of the regenerated magnets has been studied. As the content of the PrNd nanoparticles increases, the coercivity increases monotonically, whereas both the remanence and the maximum energy products reach the maximum values for 4 wt% PrNd doping. Microstructural observation reveals that the appropriate addition of PrNd nanoparticles improves the magnetic properties and refines the grain. Domain investigation shows that the self-pinning effect of the rare earth (Re)-rich phase is enhanced by PrNd nano-particle doping. Compared to the magnet with 4 wt% PrNd alloy prepared using the dual-alloy method, the regenerated magnet doped with the same number of PrNd nanoparticles exhibits better magnetic properties and a more homogeneous microstructure. Therefore, it is concluded that PrNd nanoparticle doping is an efficient method for recycling the leftover scraps of Nd-Fe-B magnets.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.790-791
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• 2006

The fracture behavior and mechanical characteristics of sintered rare-earth magnets were investigated. It shows that the fracture behavior and bending strength of the magnets obviously exhibit anisotropy. Sm-Co magnets tend to cleavage fracture in the close-packed (0001) plane or in the ($10\bar{1}1$) plane. The fracture mechanism of $Nd_2Fe_{14}B$ magnet mainly appears to be intergranular fracture. The anisotropy of fracture behavior and mechanical strength of sintered rare-earth magnets is caused mainly by the strong crystal-structure anisotropy and the grain alignment texture. The effects of Nd content, and Pr, Dy substitution on the impact stability of $Nd_2Fe_{14}B$ magnets were also reported.

• Proceedings of the Korean Magnestics Society Conference
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• 2015.05a
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• pp.136-136
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• 2015

• Proceedings of the Korean Magnestics Society Conference
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• 2015.11a
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• pp.79-79
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• 2015

• Proceedings of the Korean Magnestics Society Conference
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• 2016.05a
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• pp.52-53
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• 2016

• Journal of Powder Materials
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• v.9 no.6
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• pp.381-393
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• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.