• 분석과학
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• 제8권3호
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• pp.351-358
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• 1995

X-선 광전자 분광법을 이용해 산화처리 조건을 달리하여 제조한 $Nd_{14}Fe_{80}B_6$ 조성의 리본합금 표면에서의 산화거동을 조사하였다. 산화 초기 "as-received" 상태의 표면 가장 바깥층은 Nd가 Fe에 비해 더욱 빨리 산화가 일어나 주로 Nd 산화물로 형성되고 Fe는 내부에서 금속상태로 존재하였다. 산화처리 시간이 증가하면 "as-received" 상태에 비해 가장 바깥층에 Fe의 상대적 조성이 증가하기 시작하였으며 산화가 진행됨에 따라 표면에서 먼저 형성된 Nd 산화층을 통해서 점진적으로 Fe 산화층이 형성되는 것으로 나타났다. 산화가 더욱더 진행되면 산화막 바깥층에는 Fe의 상대적 조성이 Nd의 조성 보다 오히려 풍부해지며 Nd는 바깥층보다 산화층 내부에서 풍부해지는 층상구조 형태의 산화막을 형성하였다.

• 한국분말재료학회지
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• 제20권5호
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• pp.359-365
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• 2013

In this study, we fabricated $Nd_2Fe_{14}B$ hard magnetic powders with various sizes via spray drying combined with reduction-diffusion process. Spray drying is widely used to produce nearly spherical particles that are relatively homogeneous. Thus, the precursor particles were prepared by spray drying using the aqueous solution containing Nd salts, Fe salts and boric acid with the target stoichiometric composition of $Nd_2Fe_{14}B$. The mean particle sizes of the spray-dried powders are in the range from one to seven micrometer, which are adjusted by controlling the concentrations of precursor solutions. After debinding the as-prepared precursor particles, ball milling was also conducted to control the particle sizes of Nd-Fe-B oxide powders. The resulting particles with different sizes were subjected to subsequent treatments including hydrogen reduction, Ca reduction and washing for CaO removal. The size effect of Nd-Fe-B oxide particles on the formation of $Nd_2Fe_{14}B$ phase and magnetic properties was investigated.

• 한국재료학회지
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• 제8권9호
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• pp.819-824
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• 1998

합금의 주조시 냉각속도가 $\textrm{Nd}_{16}\textrm{Fe}_{72}\textrm{V}_{4}\textrm{B}_{8}$ 소결자석의 결정립 분포와 착자특성에 미치는 영향에 대하여 조사하였다. 냉각속도가 높은 Cu mold를 사용하여 제작한 시료는 좁은 결정립 분포와 착자특성의 향상을 보였다. B화합물을 생성하는 Cr, Mn, Nb 그리고 w과 같은 첨가원소가 Nd-Fe-B계 소결자석의 착자특성에 미치는 영향에 대해서도 조사하였다. Cr이나 W첨가는 보자력의 향상에 효과적이고 $\textrm{Nd}_{16}\textrm{Fe}_{72}\textrm{Cr}_{4}\textrm{B}_{9}$합금은 $\textrm{Nd}_{16}\textrm{Fe}_{72}\textrm{V}_{4}\textrm{B}_{8}$합금과 비슷한 착자특성을 보였다.

• Journal of Magnetics
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• 제15권1호
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• pp.32-35
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• 2010

The effects of Cu-addition and die-upset temperature on the texture in the die-upset Nd-lean $Nd_xFe_{93.5-(x+y)}-Cu_yGa_{0.5}B_6$ (x = 9-12, y = 0-2) alloys were investigated. The die-upset Cu-containing Nd-lean $Nd_{12}Fe_{81.5-y}-Cu_yGa_{0.5}B_6$ (y = 1, 2) alloys showed a considerable texture. Texture in the Nd-lean alloys developed through basal plane slip deformation. The Cu-addition reduced the melting point of grain boundary phase facilitating grain gliding during the die-upsetting, and providing a greater chance for the $Nd_2Fe_{14}B$ grains to meet the deformation conditions. Die-upsetting at higher temperature facilitated grain gliding and plastic deformation, thus enhancing texture.

• Journal of Magnetics
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• 제10권1호
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• pp.14-22
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• 2005

Precisely refined Mossbauer study and nano structure observation revealed that intergranular phase formed between a-Fe and Nd₂Fe₁₄B phase in NdFeNbB alloys plays a significant role on the magnetic properties. The intergranular interaction was characterized in term of Henkel Plot (δM plot), and hyperfine field, quardrupole splitting and isomer shift were refined to predict the presence and role of the intergranular phase. By the addition of Nb into Nd₈Fe₈₆B₆ composition, coercivity was found to increase by 25% due to the refinement of average grain size of both the soft and hard magnetic phases which was decreased from 50 nm of virgin Nd/sub 8/Fe/sub 86/B/sub 6/ to 25 nm in Nd₈Fe ₈₅Nb₁B₆ alloys. The role of Nb addition was confirmed to stabilize the Nd₂Fe₁₄B lattice preventing from thermal vibration of the corresponding sites substituted Fe by Nb atoms in all sites in the Nd₂Fe₁₄B lattice. The enhanced coercivity was originated from the exchange hardening of soft and amorphous phases surrounding the hard magnetic Nd₂Fe₁₄B crystal.

• Journal of Magnetics
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• 제9권2호
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• pp.27-33
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• 2004

Magnetic properties of $Nd_4Fe_{77.5}B_{18.5}$ compound in term of exchange coupling between $Nd_2Fe_{14}B$ and $Fe_3B$ magnetic nano crystals in melt spun powders were characterized by varying the quenching speed in mass production line. The exchange coupled phenomenon was characterized as functions of nano crystal size and volume fraction of each magnetic phase which was possible by employing Henkel plot (${\delta}M$) and refined Mossbauer spectroscopy. The optimized magnetic properties obtained from the present volume production line were: $B_r= 11.73 kG,{_i}H_c/ = 3.082 kOe$, and $(BH)_{max} = 12.28 MGOe.$ The volume fraction of each magnetic phase for those conditions giving the grain size of 10 nm were ${\alpha}-Fe; 4.2%, Fe_3B; 60.1 %$, and $Nd_2Fe_{14}B; 35.7%$. The superior magnetic properties in the $Nd_2Fe_{14}Fe_3B$ based nanocomposites were confirmed to be dependant on the volume fraction of $Fe_3B$.

• 한국분말재료학회지
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• 제15권6호
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• pp.471-476
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• 2008

Sintered Nd-Fe-B magnets have been widely used due to their excellent magnetic properties, especially for driving motors of hybrid and electric vehicles. The microstructure of Nd-Fe-B magnets strongly affects their magnetic properties, in particular the coercivity. Therefore, a post-sintering process like heat-treatment is required for improving the magnetic properties of Nd-Fe-B sintered magnets. In this study, cyclic heat treatment was performed at temperatures between $350^{\circ}C$ and $450^{\circ}C$ up to 16 cycles in order to control microstructures such as size and shape of the Nd-rich phase without grain growth of the $Nd_{2}Fe_{14}B$ phase. The 2 cycles specimen at this temperature range showed more homogeneous microstructure which leads to higher coercivity of 35 kOe than as-sintered one.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1286-1287
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• 2006

[ $Nd_2Fe_{14}B/{\alpha}-Fe$ ] nanocomposite powders with a nominal composition of $Nd_{12}Fe_{82}B_6$ were prepared by HDDR combined with mechanical milling. The microstructure was studied by Mossbauer spectrometry and TEM. The magnetic properties were investigated by VSM using bonded magnet samples. The results showed that the annealing temperature had significant influence on both the recombination kinetics and the grain size of the $Nd_2Fe_{14}B$ and ${\alpha}-Fe$ phases, and the bonded magnets presented the best magnetic properties when the nanocomposite powders were prepared by annealing at $760^{\circ}C$ for 30 min.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 1995년도 추계연구발표회 논문개요집
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• pp.64-65
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• 1995

• Journal of Magnetics
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• 제14권4호
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• pp.150-154
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• 2009

The effect of Ga and, Nb addition on the kinetics and mechanism of the disproportionation of a Nd-Fe-B alloy were investigated by isothermal thermopiezic analysis (TPA) using $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ (x=0 and 0.3, y= 0 and 0.2) alloys. The addition of Ga and Nb retarded the disproportionation kinetics of the Nd-Fe-B alloy significantly, and increased the activation energy of the disproportionation reaction. The disproportionation kinetics of the $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ alloys measured under an initial hydrogen pressure of 0.02 MPa were fitted to a parabolic rate law. This suggested that during the disproportionation of $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ alloys with an initial hydrogen pressure of 0.02 MPa, a continuous disproportionation product is formed and the overall reaction rate is limited by the diffusion of hydrogen atoms (or ions).