• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.378-382
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• 1999

We evaluated the effect of joining process such as contact method, shape of joined area and pressure on the electrical property of Bi-2223 superconducting tape. It was observed that the current capacity was reduced at the transition area of the joined tape and was significantly dependent on the uniaxial pressure. The lap-joined tape, fabricated with a pressure of 1,000-1,600 MPa, show the highest value of current capacity(80-90%) of the tape itself. It is believed the highest value of current capacity results from improvement in core density, contacting area and grain alignment, etc. In addition, the irreversible strain( ${\varepsilon}$ irrev) for the joined tape· was measured to be 0.1%, smaller than that of enjoined tape( ${\varepsilon}$ irrev = 0.3%). The decrease in the strength and irreversible strain for joined tape is believed to be due to the irregular geometry/morphology of the transition area of the tape.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.95-98
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• 1999

The crystalline alignment of Ni substrates textured by RABiTS have a probability distribution in the surface plane. This makes it difficult to obtain a high quality of textures over all the range of a long Ni tape. In order to improve the textures of Ni tape, we have investigated a new method of texturing. We obtained non-cube textured Ni tapes by rolling and annealing a high purity Ni. In these tapes, the [001]-axes were tilted around the rolling direction, and the [100]-axes were parallel to the rolling direction. The average grain size was several cm$^2$. We deposited buffer layer (CeO$^2$/YSZ/CeO$^2$) and YBCO on those tapes. We found out that a YBCO film with grows normal with respect to the surface and this feature is independent of the tilting angles of the Ni [001]-axes.

• 한국초전도ㆍ저온공학회논문지
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• 제1권2호
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• pp.1-7
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• 1999

we evaluated the effects of joining process such as contact method. shape of joined area and pressure on the electrical and mechanical properties of Bi-2223 superconducting tape, Specifically. the current capacity of the jointed tape was measured as a function of uniaxial pressure. and the thermal shock, bonding strength and the thermal of the tape were evaluated and correlated to the microstructural evolution. It was observed that the current capacity was significanrly dependent on the uniaxial pressure The jointed tape, fabricated with a pressure of 1,000-1,600 Mpa. showed the highest value of current capacity results from improvements in core density, contacting area and grain alignment, ect. In addition, the strength of jointed tape was measured to be 86 Mpa, which is about 88% of the unjoined ape's strength. The irreversible strain($\varepsilon$irrev) for the jointed tape was measured to be 0.1%, smaller than that of unjoined tape ($\varepsilon$irrev= 0.3%). The decrease in the strength and irreversible strain for jointed tape is believed to be due to the irregular geometry/morphology of the transition area of the tape.

• 한국재료학회지
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• 제4권5호
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• pp.535-540
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• 1994

Thin film magnet was fabricated by radio frequency magnetron sputtering using $Nd_13/(Fe.Co)_{70}B_{17}$ alloy target and magnetic properties were investigated according to sputtering conditions from the metallurgical point of view. we could obtain the best preferred orientation of $Nd_2Fe_{14}B$ phase at substrate temperatures between $450^{\circ}C$ and $460^{\circ}C$ with the input power 150W, and thin films had the anisotropic magnetic properties. But, as the thickness of thin film increased, the c-axis orientation gradually tended to be disordered and magnetic properties also become isotropic. Just like Nd-Fe-B meltspun ribbon, the microstructure of thin film magnet was consisted of very find cell shaped $Nd_2Fe_{14}B$ phase and the second phase along grain boundary. While, domain structure showed maze patterns whose magnetic easy axis was was perpendicular to film plane of thin film. It was concluded from these results that the perpendicualr anisotropy in magnetization was attributed to the perpendicular alignment of very find $Nd_2Fe_{14}B$ grains in thin film.

• KIEE International Transactions on Electrophysics and Applications
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• 제11C권2호
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• pp.32-36
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• 2001

We investigate the surface order, defects and morphology of hexagonal columnar mesophases, Having a crown ether at one end which forms the center of the column and three fluorinated tails at the other, The orientation of the columns was successfully controlled by surface anchoring: Columns were aligned perpendicularly to an evaporated carbon surface, and the planar alignment do asymmetric compounds was induced by a water surface. TEM images show that there is a high degree of perfection in the packing do the cylinders. The hexagonal columnar mesophase (F(sub)h) was confirmed by direct images and the corresponding electron diffractions, where ordered cylindrical moieties are packed on a hexagonal lattice. The column of 12F8-ABG-15C5 was much straighter, compared with that of 12F8-AG-B15C5, resulting from the degrees of regular stacking. Elementary edge dislocation, grain boundary and +1/2 disclination have been observed, although the defects are generally rare.

• 한국해양공학회지
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• 제27권2호
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• pp.8-12
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• 2013

Four kinds of silicon nitride composites with tri-laminate structure were prepared by stacking tapes with aligned ${\beta}-Si_3N_4$ whisker seeds. The composites were fabricated using a modified tape casting method for enhanced alignment of the whisker seeds. The relative densities of all four samples reached 99% at room temperature. The three-point flexural strengths of the samples according to the stacking sequences were measured at both room temperature and 1723 K. The high temperature strength of sample WWW was $457{\pm}14$ MPa. The fracture of sample WWW occurred mainly along the grain boundary. The room temperature strengths of samples OOO, OWO, WOW, and WWW were $430{\pm}32$ MPa, $470{\pm}19$ MPa, $700{\pm}14$MPa, and $940{\pm}14$ MPa, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.25-29
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• 2003

Pre-treatment of Bi-2223/Ag tapes has been investigated to improve the superconducting property and grain alignment. However, rolling deformability of Bi-2223/Ag wires was degraded by the breakage of Ag alloy sheath after pre-treatment. Various pre-treatment conditions were tried to prevent the problem of sliver sheath and improve the superconducting property of Bi-2223/Ag tapes. Filament precursor of Bi-2223/Ag tapes was modified to be textured easily during main sintering by the optimum pre-treatment with low oxygen pressure and up to $800^{\circ}C$. Critical current was also increased up to 20% than that of no pre-treated tape.

• Journal of Magnetics
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• 제16권3호
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• pp.300-303
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• 2011

The effect of the hot-compaction temperature on the microstructure and magnetic properties of anisotropic nanocrystalline magnets was investigated. The hot-compaction temperature was found to impact both the magnetic properties and the microstructure of die-upset magnets. The remanence of the isotropic precursor increases slightly with the improved hot-compaction temperature, and the grains start to grow on the flake boundary at higher hot-compaction temperatures. After hot deformation, it was found that the change in the magnetic properties was the inverse of that observed with the hot-compaction temperature. Microstructural investigation showed that die-upset magnets inherit the microstructural characteristics of their precursor. For the die-upset magnets, hot pressed at low temperature, scarcely any abnormal grain growth on the flake boundary can be seen. For those hot pressed at higher temperatures, however, layers with large equiaxed grains could be observed, which accounted for the poor alignment during the hot deformation, and thus the poor magnetic properties.

• 대한금속재료학회지
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• 제49권4호
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• pp.291-297
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• 2011

This work investigated the microstructure and mechanical properties of 6063 Al alloy fabricated by shear-drawing (SD) technique where shear and drawing strains were combined together within a predetermined die. To find the optimum condition for sound deformation, three different dies having different inner angle and diameter of the exit channel were prepared. After single deformation of the present sample, the sound deformation took place without an abrupt failure of the sample if the inner angle would be greater than $135^{\circ}$ in this study, when the channel diameter of the SD die was reduced from 10 to 9 mm. Microstructural observation showed that the inner angle of $135^{\circ}$ was found to be more effective than that of $150^{\circ}$ in terms of the alignment of each grain to the shear direction imposed by SD method. In addition, the yield strength of the SD-deformed sample was twice higher than that of the initial counterpart while loosing ductility in tension.

• 한국정보통신학회논문지
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• 제15권8호
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• pp.1771-1776
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• 2011

미세 입자 크기를 갖는 $YBa_2Cu_3Ox$(YBCO) 초전도 분말을 이용하여 $BaPbO_3$ 첨가에 따른 $YBa_2Cu_3Ox$ 초전도 벌크의 임계전류를 향상시키는 요소인 시편의 밀도와 결정들의 정렬 상태를 향상시키고, 기공도를 감소시키기 위한 연구를 수행하였다. 졸겔법으로 미세 크기를 갖는 $YBa_2Cu_3Ox$ 초전도 분말을 합성하여 입자의 크기가 0.2~1 ${\mu}m$의 미세한 분포를 갖는 초전도 분말을 사용하고, $YBa_2Cu_3Ox$ 초전도 시편의 입자 성장을 촉진시키고, 기공과 입계간의 약연접을 감소시키기 위하여 금속 물질 및 구조 화합물인 $BaPbO_3$를 10~30 wt%를 첨가하여 시편을 제작하고 특성을 관찰하였다. 나노 크기를 갖는 YBCO 분말과 $BaPbO_3$ 20 wt%를 첨가하여 제작한 $YBa_2Cu_3Ox$ 초전도 시편은 일반적인 벌크 제작법으로 제작된 시편과 비교하여 임계전류가 20% 향상된 4.74A를 얻었다.