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Improvement of Critical Current In Bi-2223/Ag HTS Tapes by the Bubbling Control
하홍수,오상수,하동우,이남진,김상철 한국초전도학회 2002 Progress in superconductivity Vol.3 No.2
In general, the bubbling, generated during the fabrication of the tapes, breaks the superconducting filament, and critical current of the tapes will be decreased. Heat-treatment schemes of Bi-2223/Ag HTS tapes were modified, such as pre-annealing of multi-stacked billet, 2-step main sintering and ramp rate etc. The generation of bubbling was drastically decreased from 20 bubbles/m to 0 ~ 1 bubble/m by the modified heat-treatment. Therefore, the value of critical current of the tapes without bubbling was increased almost twice higher than that of already existing tapes. Critical current up to 42 A in 40 m length Bi-22231Ag tapes have been measured at 77K, self-field, 1$mutextrm{V}$/cm criterion. It could be confirmed that elimination of bubbling is effective to maintain the superconducting property along the tape length.
Bi-2223/Ag 고온 초전도 선재 변형에 따른 입계전류 특성
하홍수,오상수,하동우,심기덕,김상철,장현만,권영길,류강식 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.1
In this study, we fabricated Bi-2223/Ag high temperature superconducting tapes using PIT(Powder-In-Tube) process to apply the superconducting magnet, cable and etc. It is inevitable to deform the superconducting taps with axial strain for application. Therefore, for the characterization of the strain sensitivity of the superconducting properties, the degradation of Bi-2223/Ag tapes due to axial strain were investigated by measuring the critical current as a function of applied tension strain and external magnetic field. The critical current of Bi-2223/Ag tapes were decreased slightly up to 0.3∼0.4% applied strain but, drastically decreased more than these strains. Superconducting filament cores consisted of brittle ceramic fibers were broken easily by the large strain and current path were decreased simultaneously.
반용융 성형가공한 SiCp / AZ91HP Mg 복합재료의 피로 및 내마모 특성
하홍수,김명균,안선규,임병수,김영직 ( Hong Soo Ha,Myoung Gyun Kim,Sun Kyu Ahn,Byeong Soo Lim,Young Jig Kim ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.5
N/A The effect of size and mass fraction of SiC particulate on the fatigue and wear have been investigated for semi-liquid formed SiCp/AZ91HP Mg composites. In the study, different particulate sizes of 7, 20, 50 ㎛ were prepared with various mass fraction for sample preparation. By tension-tension fatigue tests, whose procedures are standardized in ASTM standard 647E-93, the da/dN vs. ΔK curves were obtained. Also, the crack propagation paths were observed by optical microscope. As a result of wear test, specific wear loss is decreased with increasing mass fraction and particulate size. Specific wear loss of 30 mass% 50 ㎛ SiC reinforced Mg composite is compared to SKD11. (Received July 21, 1997)
하홍수,김호겸,고락길,김호섭,송규정,박찬,유상임,주진호,문승현,Ha H. S,Kim H. K,Ko R. K,Kim H. S,Song K. J,Park C,Yoo S. I,Joo J. H,Moon S. H 한국초전도학회 2004 Progress in superconductivity Vol.6 No.1
Ni alloy tape is electropolished to be used as a metal substrate for fabrication of IBAD (ion-Beam Assisted Deposition)-MgO texture template fur HTS coated conductor. Electropolishing is needed to obtain a very smooth surface of Ni alloy tape because the in-plane texture of templates is sensitive to the roughness of metal substrate. The critical current of YBCO coated conductor depends on the texture of YBCO that depends on the texture of the IBAD MgO layer. And so the smoothness of the metal substrate is directly related to the superconducting properties of the coated conductor. In this study, we have prepared a reel-to-reel electropolishing apparatus to polish the Ni alloy tapes for IBAD. Various electropolishing conditions were investigated to improve the surface roughness. Hastelloy tape is continuously electropolished with high polishing current density (0.5 ∼ 2 A/$\textrm{cm}^2$) and fast processing time (1 ∼ 3 min). Polished hastelloy tapes have surface roughness(RMS) of below 1 nm on a 5 ${\times}$ 5 $\mu\m^2$ from AFM and SEM.
Bi-2223/Ag 고온초전도 선재의 기계적 특성 평가
하홍수,이동훈,양주생,최정규,윤진국,하동우,오상수,권영길,김상철 한국초전도저온공학회 2002 한국초전도저온공학회논문지 Vol.4 No.1
Evaluation of the mechanical properties of Bi-2223/Ag HTS tapes was carried out by the tension and bending tests. Most of the Bi-2223/Ag tapes retained critical current up to 10 kgf/mm$_2$ axial tension stress, and 0.2% tension strain at room temperature. Applied tension strain exceeding 0.3% in superconducting tapes at 77 K leaded to rapid degradation of the critical current. It was observed that the more filaments, the better axial tension property at 77 K, self-field The influence of bending strain on critical current degradation was revealed to be less sensitive for Bi-2223/Ag HTS tapes with a more number of filaments and higher silver ratio.