Journal of Powder Materials

S. NamKung

4 Articles

Effect of Cu and DyF₃ Powder Additions on the Coercivity of Sintered Nd-Fe-B Magnets: S. NamKung, M.W. Lee, D.R. Dhakal, T.H. Lim, T.H. Kim, S.R. Lee, T.S. Jang; J Korean Powder Metall Inst. 2012;19(4):247-252.; DOI: https://doi.org/10.4150/KPMI.2012.19.4.247

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Abstract PDF: Effect of Cu and DyF_3 powder mixing with Cu-free (Nd, Dy)-Fe-B jet-milled powder on the magnetic properties of sintered magnets was investigated. The coercivity of a magnet prepared from the Cu-free (Nd, Dy)-Fe-B powder was about 10 kOe even though the alloy powder already contained some Dy (3.5 wt%). When small copper powder was blended, however, the coercivity of the magnet increased almost 100%, exhibiting about 20 kOe. On the contrary, the coercivity enhancement was moderate, about 4 kOe, when dysprosium content in the sintered magnet was simply increased to 4.9 wt% by the addition of small DyF_33 powder.

Variation of Magnetic Properties of (Nd, Dy)-Fe-B Sintered Magnets with Compaction Conditions: S. NamKung, M.W. Lee, S.J. Han, T.S. Jang; J Korean Powder Metall Inst. 2012;19(1):1-5.; DOI: https://doi.org/10.4150/KPMI.2012.19.1.001

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In order to improve the remanence of (Nd, Dy)-Fe-B sintered magnets, we investigated the influence of compaction conditions such as packing density, applied field and green density on the magnetic properties. While the remanence decreased with increasing the packing density and green density, it increased with the increase of the applied field. In addition, XRD analysis revealed that the remanence was enhanced as the degree of powder alignment was improved. The green density was more influential on the remanence than the packing density and applied field.

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Effect of Cu and DyF3Powder Additions on the Coercivity of Sintered Nd-Fe-B Magnets
S. NamKung, M.W. Lee, D.R. Dhakal, T.H. Lim, T.H. Kim, S.R. Lee, T.S. Jang
Journal of Korean Powder Metallurgy Institute.2012; 19(4): 247. CrossRef

Magnetic Properties of (Nd, Dy)-Fe-B Sintered Magnets Mixed with Dy Compounds: S. NamKung, M.W. Lee, I.S. Cho, Y.D. Park, T.H. Lim, S.R. Lee, T.S. Jang; J Korean Powder Metall Inst. 2011;18(1):29-34.; DOI: https://doi.org/10.4150/KPMI.2011.18.1.029

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Abstract PDF: In order to increase the coercivity of (Nd, Dy)-Fe-B sintered magnets without much reduction of remanence, small amount of Dy compounds such as Dy_2O_3 and DyF_3 was mixed with (Nd, Dy)-Fe-B powder. After mixing, the coercivity of (Nd, Dy)-Fe-B sintered magnets apparently increased with the increase of Dy compound in the mixture. Addition of DyF_3 was more effective than Dy_2O_3 for the improvement of coercivity. Reduction of the remanence by the addition of Dy compound, however, was larger than expected mostly due to unresolved coarse Dy compound in the magnet. EPMA analysis revealed that Dy was diffused throughout the grains in the magnet mixed with DyF_3 whereas Dy was rather concentrated around grain boundaries in the magnet mixed with Dy_2O_3.

Improvement of the Magnetic Properties of (Nd, Dy)-Fe-B Sintered Magnets by Modification of HD and Annealing Processes: S. NamKung, Y.H. Lee, M.K. Kim, T.S. Jang; J Korean Powder Metall Inst. 2010;17(5):359-364.; DOI: https://doi.org/10.4150/KPMI.2010.17.5.359

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In an attempt to optimize the magnetic properties of (Nd, Dy)-Fe-B sintered magnets, hydrogenation and post-sintering heat treatment processes were investigated at various hydrogenation temperatures and heat treatment temperatures. The coercivity of (Nd, Dy)-Fe-B sintered magnets hydrogenated at 400°C increased to about 1.2 kOe without any detrimental effect on the remanence. Moreover, the coercivity of the magnets was enhanced further by a consecutive 2nd and 3rd step heat treatment. These results eventually leaded to the reduction of the Dy content in a high coercive (> 30 kOe) (Nd, Dy)-Fe-B sintered magnets, as much as 10%.

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Magnetic Properties of (Nd, Dy)-Fe-B Sintered Magnets Mixed with Dy Compounds
S. NamKung, M.W. Lee, I.S. Cho, Y.D. Park, T.H. Lim, S.R. Lee, T.S. Jang
Journal of Korean Powder Metallurgy Institute.2011; 18(1): 29. CrossRef
Effect of Cu Content on Microstructural and Magnetic Properties of a Nd-Fe-B Strip Cast
Song-E Park, Tae-Hoon Kim, Seong-Rae Lee, Dong-Hwan Kim, Seok NamKung, Tae-Suk Jang
Journal of Korean Powder Metallurgy Institute.2011; 18(1): 24. CrossRef

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