• Journal of Magnetics
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• 제21권2호
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• pp.235-238
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• 2016

Microstructure and magnetization behaviors of $MnBi/Fe_3B/Nd2_Fe_{14}B$ nanocomposite alloy have been investigated. It was found that the coercivity increased firstly and then decreased, and saturation magnetization decreased with the additon of MnBi alloy. The addition of 40 wt.% MnBi powder enhanced the coercivity from 192.8 kA/m to 311.2 kA/m. The ${\delta}M$ and D(H)-H plots suggested the occurrence of a stronger exchange-coupling occurring between the hard and soft magnetic phase for this sample. The dependence of coercivity with temperature was discussed in 40 wt.% $Mn_{55}Bi_{45}$/ 60 wt.% $Nd_{4.5}Fe_{76.5}Nb_{0.5}B_{18.5}$ alloy powder, and a positive temperature coefficient was founded from 298 K to 350 K.

• 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.

• 소성∙가공
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• 제31권2호
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• pp.73-80
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• 2022

In this study, a developed Mg-5Bi-2Al-0.4Mn (BAM520, wt%) alloy was successfully extruded at an extremely high speed of 70 m/min. Microstructural evolution during extrusion and the microstructural characteristics and tensile properties of the very-high-speed extruded BAM520 alloy were then investigated. The homogenized BAM520 billet contained only thermally stable Mg₃Bi₂ phase particles without any Mg₁₇Al₁₂ phase with a low melting temperature. Therefore, the BAM520 alloy exhibited excellent extrudability. The very-high-speed extruded BAM520 alloy had a completely recrystallized grain structure and a typical basal fiber texture. Despite the extremely high extrusion speed of 70 m/min, the extruded BAM520 alloy had a high ultimate tensile strength of 280 MPa due to combined strengthening effects of a small grain size, numerous fine Mg₃Bi₂ particles, and strong basal texture.

• 한국재료학회지
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• 제6권1호
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• pp.90-98
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• 1996

Mn((Cu0.66AI0.34)1-x(Bi0.3Sb0.7)x) 및 Mn((Fe0.66AI0.34)1-x(Bi0.3Sb0.7)x) 합금계의 상의 변화와 자기적 특성을 조사하였다. Mn((Cu, SI)(Bi, Sb)) 합금계는 Bi상, MnSb상, MnBi상, k-상, Heuser상, Mn2Sb 및 $\beta$-Mn상의 혼합상으로 이루어졌으며 x가 증가함에 따라 Bi상과 Mn2Sb상이 증가하고 K-상, Heusler상 및 $\beta$-Mn상이 줄어들거나 사라졌다. 자기적 성질은 자성을 띄는 MnSb상, MnBi상, Mn2Sb상, k-상 및 Hseusler상과 비자성인 Bi상과 $\beta$-Mn상의 상대적 분율에 의해 결정됨을 알 수 있었고, 150K-200K 부근에서 그 이하로 온도가 감소함에 따라 자화값이 급격히 감소하는 현상이 나타났다. Mn((Fe, AI)(Bi, Sb))합금계는 Bi상, MnSb상, MnBi상, MnBi상,$\beta$-Mn상, k-상 및 Mn2Sb상의 혼합상으로 나타났으며, 자기적 성질은 조사한 전 조성에서 강자성을 띄고 있음을 알 수 있었다.

• Journal of Magnetics
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• 제19권3호
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• pp.205-209
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• 2014

$MnBi_{1-x}Ti_x$ (x = 0, 0.4, 0.7, 1) alloys were prepared by arc-melting, followed by heat treatment. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to measure and investigate the phase structure and magnetic properties. The temperature dependent magnetization curves indicate that the phase transitions between LTP and HTP MnBi occur with heating or cooling in $MnBi_{1-x}Ti_x$ ($x{\leq}0.7$) samples. However, MnTi samples are in $Mn_2Ti$ single-phase, with very low magnetic properties. Furthermore, the coercivity exhibits a positive temperature coefficient. The results show that the optimal content of Ti for the coercivity of $MnBi_{1-x}Ti_x$ alloy is x = 0.4. For MnBi sample, the coercivity reaches a maximum value of 1.13 T at 550 K. However, the remanence and energy product show apparent decrease with the addition of Ti in $MnBi_{1-x}Ti_x$ alloys.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.101-104
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• 2003

Influences of transverse compressive stress on the critical current ( $I_{c}$) in AgMg and AgMn alloy sheathed Bi-2223 tapes were investigated at 77 K and 0 T. The $I_{c}$ degradation behavior depending on sample specifications was discussed in viewpoints of n-value and damage morphology. As a result, Bi-2223 tapes showed a significant drop in $I_{c}$ for stresses greater than 50MPa. The AgMg sheathed Bi-2223 tapes representing higher $I_{c}$ showed a lower $\sigma$$_{irr}$ and a significant $I_{c}$ degradation with increase in compressive stress. There existed a voltage tap separation dependency of the $I_{c}$ degradation behavior caused by the transverse compressive stress.sive stress.s.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.79-79
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• 2010

저온용 무연 솔더의 대표 조성으로 고려되고 있는 Sn-58Bi(융점: $138^{\circ}C$) 공정(eutectic) 조성은 우수한 강도에도 불구하고 연성(ductility) 측면에서의 문제점이 지속적으로 보고되고 있다. 따라서 이 합금계의 연성을 최대로 개선시킬 수 있으면서도 실제 상용화가 가능한 합금 조성의 개발 연구가 요청된다. 본 연구에서는 Sn-Bi 2원계 조성에서 최대의 연성을 나타내는 것으로 보고된 Sn-40Bi 조성에 미량의 합금원소를 첨가함으로써 최대의 연성을 확보하는 한편, 그 연성 특성이 변형속도에 어느 정도 민감한지를 인장 실험을 통해 결정하고자 하였다. 합금원소로는 0.1~0.5 wt%의 Ag, Mn, In, Cu를 선택하였으며, 인장 시편을 제조하여 $10^{-2}$, $10^{-3}$, $10^{-4}\;s^{-1}$의 3종류로 변형속도를 변형시켜가며 응력-변형 곡선(stress-strain curve)을 측정하였고, 조성별, 변형속도별로 최대인장강도(ultimate tensile stress, UTS) 및 연신율 결과들을 정리하였다. 합금원소를 첨가한 조성의 경우는 모든 시험 조건에서 Sn-40Bi보다 우수한 연신률을 나타내는 것으로 측정되었으나, $10^{-2}\;s^{-1}$의 빠른 변형속도에서는 그 향상 정도가 상대적으로 감소하는 경향이 관찰되었다. 특히 Sn-40Bi-0.5Ag 조성의 경우 느린 변형속도에서 특히 눈에 띄는 연신률 값을 나타내며, 모든 변형속도 조건에서 가장 우수한 연성을 나타내었다. 한편 Sn-40Bi-0.1Cu 조성의 경우 변형속도에 따른 연신률의 변화 정도, 즉, 변형속도에 따른 연신률의 민감도가 매우 커 $10^{-4}\;s^{-1}$ 속도에서는 Sn-40Bi-0.5Ag에 버금가는 연신률 값이 측정되었으나, $10^{-2}\;s^{-1}$ 속도에서는 가장 나쁜 연신률 특성을 보여주었다. Sn-40Bi-0.2Mn 조성은 최고의 연신률 향상 특성을 나타내지는 않았으나, In을 첨가한 경우보다는 대체적으로 우수한 연성을 나타내었다. 이상의 각 합금별 연성 특성은 인장시험 전의 미세조직 관찰 결과와 인장시험 후 파면부의 조직변화 관찰 결과로부터 해석되었다. 그 결과 석출상의 형성 여부, 인장 시험 중 재결정 조직의 형성 여부, 라멜라(lamellar) 조직의 분율과 라멜라 간격(lamellar spacing)의 정도 또는 $\beta$-Sn과 라멜라 조직 사이의 결정립계와 라멜라 조직 내 결정립계에서의 슬라이딩 모드(sliding mode) 변형 정도, 석출상의 크기와 분포 정도 등이 연신률 및 변형속도 민감도와 같은 연성 특성에 가장 큰 영향을 미치는 인자인 것으로 분석되었다.

• 한국수소및신에너지학회논문집
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• 제28권1호
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• pp.9-16
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• 2017

Hydrogen forms metal hydrides with some metals and alloys leading to solid-state storage under moderate temperature and pressure that gives them the safety advantage over the gas and liquid storage methods. However, it has disadvantages of slow hydrogen adsorption-desorption time and low thermal conductivity. To improve characteristics of metal hydrides, it is important that activation and thermal conductivity of metal hydrides are improved. In this study, we have been investigated hydrogen storage properties of Hydralloy C among Ti-Mn alloys. Also, the characteristics of activation and thermal conductivity of Hydralloy C were enhanced to improve kinetics of hydrogen adsorption-desorption. As physical activation method, PHEM (planetary high energy mill) was performed in Ar or $H_2$ atmosphere. Hydralloy C was also activated by $TiCl_3$ catalyst. To improve thermal conductivity, various types of ENG (expanded natural graphite) were used. The prepared samples were compacted at pressure of 500 bar. As a result, the activation properties of $H_2$ PHEM treated Hydralloy C was better than the other activation methods. Also, the amounts of hydrogen storage showed up to 1.6 wt%. When flake type ENG was added to Hydralloy C, thermal conductivity and hydrogen storage properties were improved.