Journal of Powder Materials

S.H. Lee

4 Articles

Effect of Magnetic properties and Microstructure of Hydrogenation stage in HDDR process: S.H. Lee, J.H. Yu, Y.D. Kim; J Korean Powder Metall Inst. 2011;18(5):443-448.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.443

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The HDDR(hydrogenation-disproportionation-desorption-recombination) process can be used as an effective way of converting no coercivity Nd-Fe-B material, with a coarse Nd_2Fe_14B grain structure to a highly coercive one with a fine grain. Careful control of the HDDR process can lead to an anisotropic Nd_2Fe_14B without any post aligning process. In this study, the effect of hydrogen gas input at various temperature in range of 200sim500°C of hydrogenation stage (named Modified-solid HDDR, MS-HDDR) on the magnetic properties has been investigated. The powder from the modified-solid HDDR process exhibits Br of 11.7 kG and iHc of 10.7 kOe, which are superior to those of the powder prepared using the normal HDDR process.

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The Influence of Dehydrogenation Speed on the Microstructure and Magnetic Properties of Nd-Fe-B Magnets Prepared by HDDR Process
Hee-Ryoung Cha, Ji-Hun Yu, Youn-Kyoung Baek, Hae-Woong Kwon, Yang-Do Kim, Jung-Goo Lee
Journal of Magnetics.2014; 19(1): 49. CrossRef

Improvement of Microstructural Anisotropy of Nd-Fe-B-Ga-Nb Alloy by the Control of Hydrogen Reaction: S.H. Lee, D.H. Kim, J.H. Yu, D.W. Lee, B.K. Kim; J Korean Powder Metall Inst. 2010;17(1):23-28.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.023

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Abstract PDF: HDDR treated anisotropic Nd-Fe-B powders have been widely used for the sheet motors and the sunroof motors of hybrid or electric vehicles, due to their excellent magnetic properties. Microstructural alignment of HDDR treated powders are mostly depending on the hydrogen reaction in disproportionation step, so the specific method to control hydrogenation reaction is required for improving magnetic properties. In disproportionation step, hydrogenation pressure and reaction time were controlled in the range of 0.15~1.0 atm for 15~180 min in order to control the micorstructural alignment of Nd_2Fe_14B phase and, at the same time, to improve remanence of HDDR treated magnet powders. In this study, we could obtain a well aligned anisotropic Nd-Fe-B-Ga-Nb alloy powder having high remanence of 12 kG by reducing hydrogen pressure down to 0.3 atm in disproportionation step.

Effect of Homogenization Treatment on Magnetic Properties of HDDR Treated Nd-Fe-Ga-Nb-B Alloy: J.H. Yu, S.H. Lee, D.H. Kim, D.W. Lee, B.K. Kim, M.H. Choi, Y.D. Kim; J Korean Powder Metall Inst. 2009;16(4):285-290.; DOI: https://doi.org/10.4150/KPMI.2009.16.4.285

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Abstract PDF: HDDR treated anisotropic Nd-Fe-B powders have been widely used, due to their excellent magnetic properties, especially for sheet motors and sunroof motors of hybrid and electric vehicles. Final microstructure and coercivity of such Nd-Fe-B powders depend on the state of starting mother alloys, so additional homogenization treatment is required for improving magnetic properties of them. In this study, a homogenization treatment was performed at 900sim1140°C in order to control the grain size and Nd-rich phase distribution, and at the same time to improve coercivity of the HDDR treated magnetic powders. FE-SEM was used for observing grain size of the HDDR treated powder and EPMA was employed to observe distribution of Nd-rich phase. Magnetic properties were analyzed with a vibrating sample magnetometer.

An Investigation of Dispersion Behavior of Y₂O₃ Ceramic Particles in Hypo, Eutectic and Hyper Binary Al-Cu Cast Alloys: J.J. Park, G.H. Kim, S.M. Hong, S.H. Lee, M.K. Lee, C.K. Rhee; J Korean Powder Metall Inst. 2007;14(2):123-126.; DOI: https://doi.org/10.4150/KPMI.2007.14.2.123

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Abstract PDF: In this work, the dispersion behavior of Y_2O_3 particles in binary aluminum (Al)-copper (Cu) cast alloy was investigated with respect to Cu contents of 20 (hypoeutertic), 33 (eutectic) and 40 (hypereutectic) wt.%. In cases of hypo and hypereutectic compositions, SEM images revealed that the primary Al and theta phases were grown up at the beginning, respectively, and thereafter the eutectic phase was solidified. In addition, it was found that some of Y_2O_3 particles can be dispersed into the primary Al phase, but none of them are is observed inside the primary 6 phase. This different dispersion behavior of Y_2O_3 particles is probably due to the difference in the val- ues of specific gravity between Y_2O_3 particles and primary phases. At eutectic composition, Y_2O_3 particles were well dispersed in the matrix since there is few primary phases acting as an impediment site for particle dispersion during solidification. Based on the experimental results, it is concluded that Y_2O_3 particles are mostly dispersed into the eutectic phase in binary Al-Cu alloy system.

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