• Progress in Superconductivity
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• 제12권2호
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• pp.88-92
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• 2011

특수합금 등 금속분말을 이용하는 분말압연 공정을 적용하여 $MgB_2$ 판재를 제조하고 공정변수에 대한 특성을 조사하였다. 압연롤 간격 0.7 mm와 회전속도 0.7 rpm(~120 cm/min) 조건에서 두께 ~1 mm, 폭 ~100 mm, 그리고 길이 수 cm 크기의 $MgB_2$ 판재를 성공적으로 제조하였으며, 측정된 최고 밀도는 2.05 g/$cm^3$이고 이론 값 대비 약 78 %로 계산되었다. 분말압연 공정을 통해 최종 선재의 크기(특히 두께 측면에서)에 가깝게 공정을 시작할 수 있고 높은 충진 밀도를 유지할 수 있으므로 초전도 선재의 특성 향상과 더불어 생산 비용, 생산속도 측면에서도 매우 유리한 방법이 될 것이다. 또한 자기장하 $MgB_2$ 초전도 특성 향상을 위해 자속 고정점 역할을 할 다양한 도핑 물질(분말 형태 또는 액체 형태 등)을 첨가하는 공정에 있어서 도 본 분말압연 공정을 쉽게 적용될 수 있다.

• 한국재료학회지
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• 제4권4호
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• pp.406-415
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• 1994

분말충진법에 의한 Ag/Bi-2223고온초전도선재의 제조방법 및 제조조건에 따른 임계전류밀도를 조사하였다. 전체공정에서 250시간의 열처리 및 2회의 반봅가공 조건에서 임계전류밀도가 가장 높게 측정되었다. 이와 같은 결과는 250시간의 열처리에서 고온상이 크게 성장되었으며, 2회의 반복가공으로 결정입자들이 일방향으로 잘 배열되는 공정조건임을 알 수 있었다. 공정별로는 pressing방법으로 제조한 시편의 임계전류밀도가 $1.05\times 10^4A/\textrm{cm}^2$로 다른 공정에 비해 가장 높았으며, rolling 공정으로는 $0.78\times 10^4A/\textrm{cm}^2$를 갖는 선재를 제조하였다. 7개 및 49개의 세심을 갖는 다심선재를 제조하여 임계전류밀도를 조사하였다. 7개의 다심선재에서 임계전류밀도값은 pressing방법에서 $0.45 \times 10^{4}A/\textrm{cm}^2$ 였으며, 49개 다심은 rolling방법으로 $0.20 \times 10^{4}A/\textrm{cm}^2$를 갖는 선재를 제조하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.668-673
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• 2008

In this paper, we developed a physically-based micromechanical model for inelastic deformation of ceramic powders. The aggregate response of ceramic particles was modeled using the two-surface yield function which considered the shear-induced dilatancy caused by friction, rolling resistance and cohesion between powder particles and consolidation caused by plastic deformation of powder themselves under high compression. The constitutive equations were implemented into the user-subroutine VUMAT of finite element program ABAQUS/Explicit. The material parameters in the constitutive model were identified by calibrating the model to reproduce data from triaxial compression tests and simple compression tests. The density distribution obtained by using the proposed model was in good quantitative agreement with the experimental results of the triaxial compression and cold isostaic compression as well.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.156-157
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• 2006

The preparation of composite powders for plasma spraying by an in-house designed mechanofusion process is investigated. Results show that dry particle coating depends on the chemical and mechanical properties of powders. In metal/oxide and metal/oxide/carbide powder mixtures, fine ceramic particles coat the surface of the metallic coarser particles. A nearly rounded shape of the final composite particles is induced by the mechanical energy input with no formation of new phases. However with the carbide/metal powdered system, only an intimate mixture of components is achieved. It is suggested that the coating mechanism is governed by agglomeration and rolling phenomena.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.393-394
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• 2006

Highly compressible Ni-Mo steels are attractive materials for PM due to high sinter density and ease of processing. Extra-fine Ni admixed PM steels have demonstrated improved mechanical properties and rolling contact fatigue resistance due to a more uniform microstructure and increased Ni diffusion during sintering. Sinter densities of single press single sinter XF Ni-Mo steels can approach $7.5\;g/cm^3$ at moderate compaction pressures. Leaner alloys based on extra-fine Ni powder are possible depending on the performance requirements of the PM steel part. Extra-fine Ni steels are particularly attractive for the growing market of high performance PM gears and sprockets.

• 공업화학
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• 제22권6호
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• pp.642-647
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• 2011

회전형 휘발성 산화장치(voloxidizer)와 200 g $U_3O_8$ 분말을 사용하여 초기 미세 입자층의 운동형태, 열처리 온도 및 시간, voloxidizer의 회전속도에 따른 다공성 그래뉼의 회수율과 특성을 분석하였다. 초기 미세 입자층의 운동형태에 따른 1 mm 이상의 그래뉼의 회수율은 rolling 운동 때보다 slumping 운동일 경우에 보다 높았다. 초기 미세 입자층이 rolling 운동형태인 경우에는 미세입자로부터 그래뉼이 생성됨에 따라서 slumping 운동형태로 변하며 slumping 빈도가 매우 높았다. 열처리 온도의 증가 및 10 h까지는 시간의 증가에 따라서 그래뉼의 회수율이 매우 크게 증가하였다. Slumping 운동형태를 보이는 초기 미세 입자층의 경우에 voloxidizer의 회전속도가 증가함에 따라서 그래뉼의 회수율 은 81.5에서 88.7%로 증가하였으나, 그래뉼 특성 측면에서 보면 회전속도가 2 rpm인 경우에 밀도, 파쇄강도, 구형도가 가장 높았다.

• 한국분말재료학회지
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• 제16권1호
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• pp.33-36
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• 2009

In order to increase the magnetic loss for electromagnetic(EM) wave absorption, the soft magnetic $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was used as the basic material in this study. The melt-spun strip was pulverized using an attrition mill, and the pulverized flake-shaped powder was crystallized at $540^{\circ}C$ for 1h to obtain the optimum grain size. The Fe-based powder was mixed with 2 wt% $BaTiO_3$, $0.3{\sim}0.6$ wt% carbon black, and polymer-based binders for the improvement of electromagnetic wave absorption properties. The mixture powders were tape-cast and dried to form the absorption sheets. After drying at $100^{\circ}C$ for 1h, the sheets of 0.5 mm in thickness were made by rolling at $60^{\circ}C$, and cut into toroidal shape to measure the absorption properties of samples. The characteristics including permittivity, permeability and power loss were measured using a Network Analyzer(N5230A). Consequently, the properties of electromagnetic wave absorber were improved with the addition of both $BaTiO_3$ and carbon black powder, which was caused by the increased dielectric loss of the additive powders.

• 한국분말재료학회지
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• 제10권4호
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• pp.241-248
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• 2003

Biaxially textured Ni tapes were fabricated by a cold working and recrystallization heat treatment processes from powder compact rods. The processing parameters associated with the cube texture formation in Ni tapes were systematically investigated by using X-ray diffraction and pole-figure analysis. The Ni powder used in this study was 5 $\mu$m in size and 99.99% in purity. To find the optimum sintering temperature, tensile tests were performed for Ni rods sintered at various temperatures. The Ni rods sintered at 100$0^{\circ}C$ showed poor elongation and low fracture strength, while the Wi rods sintered above 100$0^{\circ}C$ revealed good mechanical properties. The higher elongation and fracture strength of the Ni rods sintered at higher temperatures than 100$0^{\circ}C$ are attributed to the full densification of the sintered rods. The sintered Ni rods were cold-rolled with 5% reduction to the final thickness of 100 $\mu$m and then annealed for development of rube texture in rolled Ni tapes. The annealed Ni tapes depicted strong cube texture with FWHM(full-width at half-maximum) of in-plane and out-of-plane in the range of 8$^{\circ}$ to 10$^{\circ}$. The NiO deposited on the Ni tapes by MOCVD process showed good epitaxy with FWHM=10$^{\circ}$, which indicates that the Ni tapes can be used as a substrate for YBCO coated conductors.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2002년도 학술대회 논문집
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• pp.138-140
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• 2002

We fabricated textured Ni substrate for YBCO coated film and evaluated the degree of texture in terms of rolling condition and annealing time. The substrate was compacted from pure Ni powder and reduced the thickness to 100 $\mu$m by rolling followed by heat treatment. As decreasing the thickness of substrate, it was observed that the non-uniform deformation such as ‘wave edge’ or ‘wave buckle’ developed locally on it, causing reduced texture. On the other hand, uniformly deformed substrate showed better cube texture indicating the FWHM of in-plane and out-of-plane of about $11^{\circ}$ ~ $14^{\circ}$. In addition, annealing at $1000^{\circ}C$ for 1~ 8 hr did not make a remarkable difference on the texture.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.291-291
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• 1999

Long 19-filamentary Bi-2223 tapes were prepared using the so called "powder-in-tube" method. In the preparation, two types of precursor powders and two different reduction rates during rolling were used. Also two rolling method, which resulted in different filament geometry, were used. The characteristics of the tapes will be presented. Also A coil was prepared using two 56 m-long 19-filament tape. It was consisted of two double pancake coils. Each pancake, which is separated by FRP spacer, was composed of 98 turns. The experimental results will be presented and compared to the simulation result.