YBCO 박막선재용 Ni 기판의 집합도에 미치는 제조공정 변수효과

지봉기,임준형,이동욱,주진호,나완수,김찬중,홍계원 한국전기전자재료학회 2003 전기전자재료학회논문지 Vol.16 No.10

We fabricated Ni-substrate for YBCO coated conductors and evaluated the effects of pressing and annealing temperature and time on texture. Ni substrate was fabricated by powder metallurgy technique and compacts were prepared by applying uniaxial or isostatic pressure. The texture of substrate made by applying cold isostatic pressure (CIP) was stronger than that by uniaxial pressure which we attribute to the fact that the CIP method provided higher density and more uniform density distribution. It was observed that the substrate annealed at 400 C showed both retained texture and recrystallized texture. On the other hand, the texture of substrate significantly improved at annealing temperature above 500 C, forming strong 4-fold symmetry, [111] II ND texture, and FWHM of 9∼10 . It is to be noted that the degree of texture was almost independent of annealing temperature (500∼1000 C) and annealing time(1∼54 min, at 1000 C). EBSD and AFM analysis indicated that 99% of grain boundaries was low angle grain boundary and RMS was approximately 3 nm, respectively. Development of strong cube texture and high fraction of low angle grain boundary of Ni-substrate made by powder metallurgy technique in our study is considered to be suitable for the application of YBCO coated conductors.

BSCCO 선재에서 극점도를 통한 초전도심의 깊이에 따른 집합조직 연구

지봉기,주진호,나완수,류경우,박노진 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.6

We evaluated the degree of texture through depth of the superconductor core of Bi-Sr-Ca-Cu-O(BSCCO) superconductor tape. The degree of texture was characterized by pole figure analysis indicating that the degree of texture varied significantly with depth of the superconductor core. It was observed that the degree of texture was higher near the interface than inside the superconductor core. Specifically, as getting near to the center from the sheath/core interface, the orientation of BSCCO became dispersed from normal direction(ND) which, in turn, resulted in the degradation of <001>-fiber texture. In addition, the <001> texture was non-uniform an, better texture was developed along rolling direction(RD), compared to transverse direction(TD). Microstructural investigation showed that grain alignment was locally degraded by the existence of second phases. I was observed that larger grain size and better texturing were developed near the relatively straight interface compared to those inside the superconducting core. Based on our study, the region near the interface is thought to carry significant current compared to that inside the core.

BSCCO 초전도 선재의 미세조직 및 임계전류밀도에 미치는 공정변수 효과

지봉기,김태우,주진호,김원주,이희균,홍계원 한국전기전자재료학회 1998 전기전자재료학회논문지 Vol.11 No.11

We evaluated the effect of processing variables on microstructural evolution interface irregularity between Ag sheath and superconductor core and resultant critical current density(J$_{c}$) of (Bi,Pb)$_2$Sr$_2$Ca$_2$Cu$_3$O$_{x}$(2223) superconductor tape. The value of J$_{c}$ was significantly influenced by the interface irregularity, degree of texturing and relative 2223 content. The interface became more irregular(sausage effect), while the degree of texturing gradually improved as the dimension of tape decreased during forming process. As the dimension of wire/tape were changed from diameter of 3.25 mm to thickness of 0.20 mm, J$_{c}$ value was observed to be increased by 10 times. In addition, optimum sintering temperature for improved J$_{c}$ was observed to be 835$^{\circ}C$ in a ambient atmosphere probably due to combined effect of both improved texturing and high 2223 content. Microstructural investigation showed the degree of texturing was degraded by the existence of both second phases and interface irregularity. It was observed that larger grain size and better texturing was developed near relatively flat interface compared to those inside superconducting core.ting core.

분말충진방법과 가공정도에 따른 Ag/BSCCO 초전도선재의 특성

지봉기,김태우,김정호,김중석,주진호 成均館大學校 科學技術硏究所 1998 論文集 Vol.49 No.1

We evaluated the effects of processing variables on interface irregularity. microstructure. and resultant Jc of BSCCC superconductor tape. For the tapes made by PIT technique. the degree of interface irregularity was varied with powder packing methods and forming process variables. It was observed that the degree of interface irregularity of the tape by CIP method was more reduced. compared to that of the tape by ram method. In addition. the degree of interface irregularity was promoted with decreasing the dimension of tape during forming process. As the dimension of wire/tape were changed from diameter of 3.25mm to thickness of 200㎛ during forming process. Jc value was observed to be increased by 10 times. It was likely that the improvenment of Jc was mainly result from the enhanced texturing of 2223 grain. Microstructural investigation showed the degree of texturing was degraded by the existence of both second phases and interface irregularity. If the interface was flat, larger grain size and better texturing near interface were developed compared to those inside superconducting core, The improvements of microstructure near interface may be result of reaction between Ag and superconductor phase.

합금원소 첨가에 따른 Ag 피복 Bi-2223 초전도 선재의 열전도도 측정 및 특성평가

주진호,장석헌,김정호,임준형,김규태,지봉기 한국전기전자재료학회 2003 전기전자재료학회논문지 Vol.16 No.7

The effects of alloying-element additions to Ag sheath on thermal conductivity and mechanical properties of Bi-2223 superconductor tapes have been evaluated. In order to evaluate the effects of sheath alloys and their configuration on the properties of tape, various combinations of Ag and Ag alloys were selected as the inner and outer sheath. Thermal conductivity of the tapes was evaluated by using thermal integral method at 10 ∼120 K. It was observed that the addition of Mg, Sb, and Au to Ag sheath significantly decreased the thermal conductivity at low temperature probably due to the alloying effect. Specifically, the thermal conductivity of AgMg, AgSb, and AgAu at 40 K were 411.4, 142.3, and 109.7 W/(m·K), respectly, which is about 2∼9 times lower than that of Ag (1004.6 W/(m·K)). In addition, the thermal conductivity of alloy-sheathed tape was significantly dependent on their thermal conductivities of constituent sheath materials. The mechanical properties of alloy-sheathed tapes were also evaluated. Yield strength and tensile strength were improved but workability decreased for alloy-sheathed tapes.

니켈 분말 성형체의 냉간압연과 열처리로 제조된 YBCO coated conductor용 양축 정렬된 니켈 테이프

이동욱,지봉기,임준형,정충환,주진호,박순동,전병혁,홍계원,김찬중 한국초전도저온학회 (구 한국초전도저온공학회) 2003 한국초전도저온공학회논문지 Vol.4 No.2

고온초전도 선재용 피복합금의 열전도도 측정 및 특성평가

박형상,지봉기,김중석,임준형,오승진,오승진,주진호,나완수,유재무 한국전기전자재료학회 2000 전기전자재료학회논문지 Vol.13 No.8

Effect of alloying element additions to Ag on thermal conductivity electrical conductivity and mechanical properties of sheath materials for BSCCO tapes has been characterized. The thermal conductivity at low temperature range(10~300K) of Ag alloys were evaluated by both direct and indirect measurement techniques and compared with each other. It was observed that thermal conductivity decreased with increasing the content of alloying elements such as Au, Pd and Mg. Thermal conductivity of pure Ag at 30 K was measured to be 994.0 W/m.K on the other hand the corresponding values of A $g_{0.9995}$/M $g_{0.0005}$, A $g_{0.974}$/A $u_{0.025}$/M $g_{0.001}$, A $g_{0.973}$/Au.0.025//M $g_{0.002}$, and A $g_{0.92}$/P $d_{0.06}$/M $g_{0.02}$ were 342.6, 62.1, 59.2, 28.9 W/m.K respectively indicating 3 to 30 times lower than that of pure Ag. In addition alloying element additions to Ag improved mechanical strength while reduced elongation probably due to the strengthening mechanisms by the presence of additive atoms.s.

Twisting된 Bi-2223 선재의 제조, 미세조직 관찰 및 임계 특성평가

임준형,지봉기,박형상,주진호,장미혜,고태국,이상진,하홍수,오상수 한국전기전자재료학회 2000 전기전자재료학회논문지 Vol.13 No.3

We fabricated Bi-2223 multi-filaments superconductor tape and evaluated the effect of twisting on the microstructural evolution and critical current. Twist pitches of the tapes are in the range of 70- 8mm and uniformly deformed. It was observed that grain size and the degree of texture decreased as decreasing pitch probably due to the formation of the irregular interface between Ag and filaments. In addition critical current of the tapes decreased to 6.5 A with decreasing pitch to 8mm, showing 48% of degradation compared to the untwisted tapes decreased to 6.5 A with decreasing pitch to 8mm, showing 48% of degradation compared to the untwisted tape(12.5 A). These reduction of critical current may be related to the interface irregularity smaller grain size worse texture and the presence of cracks due to the induced strain during twisting processing.

2축 정렬된 Ni 위에 MOCVD법에 의한 NiO의 증착조건

선종원,김형섭,지봉기,박해웅,홍계원,박순동,정충환,전병혁,김찬중 한국초전도저온공학회 2002 한국초전도저온공학회논문지 Vol.4 No.2

Deposition condition of NiO that is one of Possible buffer layers for YBCO coated conductors was studied. NiO was deposited on textured Ni substrates by a MOCVD (metal-organic chemical vapor deposition) method. The degree of texture, and the surface roughness were analyzed by X-ray Pole figure, atomic force microscope and scanning electron microscope. The (111) and (200) textures were competitively developed , depending on an oxygen partial Pressure(PO2) and deposition temperature (Tp). The (200) textured NiO layer was deposited at Tp=450~47$0^{\circ}C$ and PO2= 1.67 Torr Out-of-Plane ($\omega$-scan) and in-plane ($\Phi$-scan) textures of the (200) NiO films were as good as 10.34$^{\circ}$ and 10.00$^{\circ}$ respectively The AFM surface roughness of NiO was in the range of 3~4.5 nm at PO2=0.91~3.34 Torr and at Tp=47$0^{\circ}C$ , and in the range of 3~13 nm at TP=450~53$0^{\circ}C$ and at PO2=1.67 Torr.

{110}<110> 집합조직을 가지는 YBCO 박막 선재용 Ag Substrate 개발

임준형,김정호,지봉기,장석헌,김규태,주진호,김찬중,홍계원 한국전기전자재료학회 2004 전기전자재료학회논문지 Vol.17 No.1

We fabricated textured Ag substrates for YBCO coated conductor and evaluated the effects of annealing temperature on microstructural evolution, texture formation, and surface morphology. Ag ingot, as an initial specimen, was prepared by plasma arc melting(PAM). Subsequently, the ingot was cold rolled to 100 ${\mu}{\textrm}{m}$ thick tape and annealed at temperatures of 600-80$0^{\circ}C$. The texture and surface morphology of the substrate were characterized by pole-figure and atomic force microscopy(AFM) profile, respectively. It was observed that a strong {110}<110> texture was formed after annealing and its symmetry improved as annealing temperature increased. The full-width at half-maximum(FWHM) of {110}<110> pole was as sharp as 10$^{\circ}$ for the substrate annealed at 80$0^{\circ}C$. On the other hand, it was found that the thermal grooving and faceting became remarkable as annealing temperature increased : root-mean-square(RMS) roughness of the substrate annealed at 80$0^{\circ}C$ was 39.2 nm. The substrate of strong texture and smooth surface, fabricated in our study, is considered to be suitable for use as a substrate for the epitaxial deposition of superconductor film.