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MS-HDDR 프로세스의 DR 속도 제어를 통한 초미세 결정립 Nd2Fe14B계 자성분말 제조
차희령 ( Hee Ryoung Cha ),이정구 ( Jung Goo Lee ),백연경 ( Youn Kyoung Baek ),유지훈 ( Ji Hun Yu ),권해웅 ( Hae Woong Kwon ),김양도 ( Yang Do Kim ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.5
In the present study, the influence of desorption-recombination (DR) speed during hydrogenation- decomposition-desorption-recombination (HDDR) process on the microstructure and magnetic properties of Nd-Fe-B based magnetic powders has been studied. Nd-Fe-B based alloys were made by mold casting and homogenization heat treatment. They were then subjected to HDDR treatment. During DR reaction, pumping speed and time of hydrogenation were systematically changed to control the speed of DR reaction. It was found that the slower hydrogen desorption during DR reaction can result in a smaller grain size and significantly increases the magnetic properties of the powder. The coercivity and the remanence of the HDDR powders in the size range of 200-300 μm was 12.4 kOe and 11.4 kG, respectively. In addition, the remanence was further increased to 12.0 kG by milling the powders down to 25-90 μm, which resulted in (BH)max of 26.5 MGOe.
희토류 자원문제 해결을 위한 Nd 저감형 Nd-Fe-B계 영구자석 소재 기술 개발 동향
차희령(Hee-Ryoung Cha),백연경(Youn-Kyoung Baek),이정구(Jung-Goo Lee),김동환(Dong-Hwan Kim) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.3
Recently, the demand of high efficient/miniaturized parts is increasing with the development of industry. Especially, the hybrid/electric vehicle market is rapidly growing because of the energy saving and environmental problems. The Nd-Fe-B magnet is one of the most important material in the automobile industry, which determines the efficiency and performance of traction motors. However, the issues on the resource and the price of heavy rare-earth (HRE) metals which are used to improve thermal stability of the magnet are constantly emerging. In addition, as the demand for Nd-Fe-B magnets is rapidly increasing with the growth of the electric vehicle market, Nd is also expected to be in short supply to meet the demand. Thus, there is a growing interest in research to replace Nd/Pr with Ce/La which is more abundant and cheaper than Nd along with the development of HRE lean/free magnets. The present article introduces the trend in research and development of a Nd-reduced rare-earth magnet to solve the problem of rare-earth resources.
차희령(Hee-Ryoung Cha),김태훈(Tae-Hoon Kim),이정구(Jung-Goo Lee) 한국자기학회 2022 韓國磁氣學會誌 Vol.32 No.2
Nd-Fe-B based permanent magnets are widely used for various applications due to their excellent magnetic properties. However, the increasing demand for Nd-Fe-B based permanent magnet with growth of the eco-friendly vehicle market is accelerating the imbalance between the supply and demand of rare-earth elements such as Dy, Tb, and Nd. For heavy rare earth (HRE)-free or Nd-lean magnets, it is necessary to refine the crystal grains to the single domain size of Nd2Fe14B phase (~300 ㎚), and to form the uniform and continuous grain boundaries phase as a non-magnetic phase. The hot-deformed Nd-Fe-B magnet have a very high potential as a HRE-free or Nd-reduced permanent magnet due to its ultra-fine grain size of ~300 ㎚. In this paper, we introduce overall research and development trend for the hot-deformation process of Nd-Fe-B based permanent magnets to develop the high performance HRE-free or Nd-lean permanent magnets.
DyF<sub>3</sub> paste 제조 및 이를 이용한 Nd-Fe-B 입계확산 자석의 특성 연구
전광원,차희령,이정구,Jeon, Kwang-Won,Cha, Hee-Ryoung,Lee, Jung-Goo 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.6
Recently, the grain boundary diffusion process (GBDP), involving heavy rare-earth elements such as Dy and Tb, has been widely used to enhance the coercivity of Nd-Fe-B permanent magnets. For example, a Dy compound is coated onto the surface of Nd-Fe-B sintered magnets, and then the magnets are heat treated. Subsequently, Dy diffuses into the grain boundaries of Nd-Fe-B magnets, forming Dy-Fe-B or Nd-Dy-Fe-B. The dip-coating process is also used widely instead of the GBDP. However, it is quite hard to control the thickness uniformity using dip coating. In this study, first, a $DyF_3$ paste is fabricated using $DyF_3$ powder. Subsequently, the fabricated $DyF_3$ paste is homogeneously coated onto the surface of a Nd-Fe-B sintered magnet. The magnet is then subjected to GBDP to enhance its coercivity. The weight ratio of binder and $DyF_3$ powder is controlled, and we find that the coercivity enhances with decreasing binder content. In addition, the maximum coercivity is obtained with the paste containing 70 wt% of $DyF_3$ powder.
젤라틴 첨가에 의한 구리 박막의 미세구조 변화 및 부식 특성
김민호 ( Min Ho Kim ),차희령 ( Hee Ryoung Cha ),최창순 ( Chang Soon Choi ),김혜성 ( Hae Sung Kim ),이동윤 ( Dong Yun Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.8
We report on the effect of additives on the microstructure and corrosion properties of electrodeposited Cu films. Copper films were fabricated by electrodeposition on various concentrations of gelatin in a copper sulfate electrolyte. The surface morphologies of the Cu films were observed using a scanning electron microscope (SEM), and crystal orientation of the Cu films was analyzed by X-ray diffraction measurement. (220) plane was the dominant orientation when the films were fabricated at ambient temperature, decreasing in dominance with addition of gelatin. On the other hand, (111) plane-Cu films were preferentially grown at 40℃, and were also diminished with adding additives. Corrosion rate measurements using the Tafel extrapolation method based on corrosion potential and current reveal the effect of additives on corrosion behavior. Corrosion behavior was found to be strongly related to the orientation of the films. Consequently, additives like gelatin influence crystal orientation of the films, and if a less dense crystal plane, e.g. (220), is preferentially oriented during electrodeposition, a lower corrosion rate could be produced, since the plane shows a lower current density.
김민호 ( Min Ho Kim ),차희령 ( Hee Ryoung Cha ),최창순 ( Chang Soon Choi ),김종만 ( Jong Man Kim ),이동윤 ( Dong Yun Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.10
To modify the physical properties of Cu thin films, gelatin is generally used as an additive. In this study, we assessed the effect of gelatin on the mechanical properties of electrodeposited Cu films. For this purpose, Cu/gelatin composite films were fabricated by adding 100 ppm of gelatin to an electrolyte, and tension and indentation tests were then performed. Additional tests based on pure Cu films were also performed for comparison. The Cu films containing gelatin presented a smaller grain size compared to that of pure Cu films. This increased the hardness of the Cu films, but addition of gelatin did not significantly affect the elastic modulus of the films. Cu films prepared at room temperature showed no significant change in the yield strength and tensile strength with an addition of gelatin, but we observed a dramatic decrease in the elongation. In contrast, Cu films prepared at 40℃ with gelatin presented a significant increase in the yield strength and tensile strength after the addition of gelatin. Elongation was not affected by adding gelatin. Presumably, the results would be closely related to the preferred orientation of the Cu thin film with the addition of gelatin and at temperatures that lead to a change in the microstructure of the Cu thin films.