Journal of Powder Materials

D.H. Kim

3 Articles

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

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

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.

Surface Treatment of Mg₉₅Zn_4.3Y_0.7 Alloy Powder Consolidates using Plasma Electrolytic Oxidation: J.H. Kim, H.S. Choi, D.H. Kim, D.Y. Hwang, H.S. Kim, T.S. Kim; J Korean Powder Metall Inst. 2008;15(2):95-100.; DOI: https://doi.org/10.4150/KPMI.2008.15.2.095

Abstract PDF: The investigation is to modify the mechanical and chemical properties of Mg alloys using a combination of rapid solidification and surface treatment. As the first approach, Mg_95Zn_4.3Y_0.7 was gas atomized and pressure sintered by spark plasma sintering process (SPS), showing much finer microstructure and higher strength than the alloys as cast. Further modification was performed by treating the surface of PM Mg specimen using Plasma electrolytic oxidation (PEO) process. During the PEO processing, MgO layer was initiated to form on the surface of Mg powder compacts, and the thickness and the density of MgO layer were varied with the reaction time. The thickening rate became low with the reaction time due to the limited diffusion rate of Mg ions. The surface morphology, corrosion behavior and wear resistance were also discussed.

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