• 한국분말재료학회지
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• 제18권5호
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• pp.443-448
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• 2011

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 $Nd_2Fe_{14}B$ grain structure to a highly coercive one with a fine grain. Careful control of the HDDR process can lead to an anisotropic $Nd_2Fe_{14}B$ without any post aligning process. In this study, the effect of hydrogen gas input at various temperature in range of $200{\sim}500^{\circ}C$ 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.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2003년도 춘계학술강연 및 발표대회
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• pp.50-50
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• 2003

• 한국자기학회지
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• 제11권6호
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• pp.250-255
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• 2001

급냉응고법으로 제조된 NdFeB 분말로부터 Current applied(CA)-press 및 Current applied(CA)-deformation 공정에 의해 등방성 및 이방성 NdFeB 영구자석을 제조하고, 이로부터 자기적 특성을 조사하였다. 등방성 NdFeB 영구자석의 보자력은 시료에 가해지는 압력에 따라 크게 다르며, 상대적으로 높은 압력에서 보자력이 크게 나타났다. 반면 잔류자화는 시료에 가해졌던 압력 및 전류의 변화에 관계없이 거의 일정하였다. 등방성 시편인 경우 대체로 최대자기에너지적이 15MGOe이상이며, CA-deformation에 의해 40MGOe이상의 이방성 NdFeB 영구자석이 얻어졌다. 이방성 시편의 가공도가 클수록 B$_{r}$의 증가로 인하여 최대자기에너지적이 증가하였으며, 시편의 가공도가 81%일 때 44.2 MGOe의 고에너지적을 가지는 이방성 NdFeB영구자석이 얻어졌다.

• 한국분말재료학회지
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• 제17권1호
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• pp.23-28
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• 2010

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 $Nd_2Fe_{14}B$ 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.

• 한국자기학회지
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• 제8권4호
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• pp.210-215
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• 1998

Ball Mill을 이요하여 Ar 분위기에서 기계적합금법으로 Nd15Fe77B8과 Nd16Fe76B8 분말을 제조하고, 제조된 분말을 연속 진공열처리 시킨 후 열처리온도에 따른 상변화 및 자기적 성질을 조사하엿다. 450시간 볼밀도처리한 Nd15Fe77B8과 Nd16Fe76B8 합금 분말에서 Nd와 B의 피크는 보이지 않고 전체적으로 $\alpha$-Fe 결정상만 존재하고 있었으며, 이를 $700^{\circ}C$에서 30분간 열처리를 시키면 고상반응에 의하여 Nd2Fe14B와 소량의 NdB6이 흔재된 상을 얻을 수 있었다. $700^{\circ}C$로 열처리 한 Nd16Fe76B8 합금 분말은 iHc9.9kOe, Bs, 12.9 KG, (BH)max 10.1 MGOe의 자기적 성질을 나타내었다.

• 한국자기학회지
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• 제5권5호
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• pp.687-689
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• 1995

Our team works on mixture of hard magnetic materials. As hard magnetic material we used mixture of powders: melt-spun ribbon Nd-Fe-B, ferrite and Alnico. Their different mixtures are basic material for dielectromagnets under our investigation. Main disadvantage of dielectromagnets with Nd-Fe-B alloy powder as a component is a low corrosion resistance. Protection against corrosion is covering dielectromagnets with metallic or organic coating film. The coating film protects dielectromagnets from free particles on the surface and low resistance for mechanical stresses too. The surface of dielectromagnets prepared from mixture of powders if formed by metallic particles - powder of Nd-Fe-B and Alnico, particles of oxide - powder of ferrite and particles of resin - bonding materials. Team work on technology of laying the metallic coating on dielectromagnets prepared from mixture of mentioned powders. Papers show the results of initial investigation on metallic coating technology. It shows influence of type and used technology of the metallic coating film on magnetic properties of dielectromagnets.

• Journal of Magnetics
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• 제7권4호
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• pp.127-131
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• 2002

HDDR characteristics and magnetic properties of $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$(x=0-0.6) alloys were investigated. The effect of applying magnetic field during the recombination step on the anisotropic nature of the HDDR-treated material was also examined. The $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$ phase in the Nd-Fe-B alloys with high Co-substitution alloy had remarkably enhanced phase stability. The $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$(x=0-0.6) alloys with high Co-substitution could be HDDR-treated successfully by only using high pressure hydrogen. However, these alloys had no appreciable coercivity. The poor coercivity of the HDDR-treated $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$(x=0-0.6) alloys with high Co-substitution was attributed to the $Nd{(Fe,Co)}_2$ phase in the alloys. The magnetic filed applied during the recombination step had little effect on the anisotropic nature of the HDDR-treated powder.

• Journal of Magnetics
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• 제20권4호
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2004년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.47-47
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• 2004

• 한국분말재료학회지
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• 제23권6호
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• pp.437-441
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• 2016

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.