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초전도 선재의 전 열처리에 따른 기계적 및 초전도 특성에 미치는 효과
양주생,하동우,이동훈,최정규,황선역,하홍수,오상수,권영길,김명호 한국초전도학회 2004 Progress in superconductivity Vol.5 No.2
Many of research efforts have been focused on the improvement of critical current density (Jc) of silver-sheathed Bi-2223 tapes far practical applications. In this study, the transformation of Bi-2212 phase was investigated, which was transformed to orthorhombic from tetragonal through pre-annealing during powder packing and drawing process. The relationship between hardness of Bi-2212 orthorhombic phase and workability of Bi-2223/Ag tape was investigated. Bi-2223 superconducting wires with 55 filaments were fabricated by stacking and drawing process with different heat-treatment histories. Before rolling process, round wires were pre-annealing at 76$0^{\circ}C$ and in a low oxygen partial pressure. We confirmed that pre-annealing step was to transform to Bi-2212 orthorhombic structure from Bi-2212 tetragonal structure and to reduce the formation of second phases. However the breakages were created at Ag-alloy clad during rolling for pre-annealed Bi-22231Ag tapes. Several pre-annealing scenarios were introduced to reduce the breakages during rolling process. Microstructure and critical current density of pre-annealed Bi-2223 superconducting tapes were investigated. We could achieve proper pre-annealing conditions for Ag-alloy clad Bi-2223 superconducting tapes.
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.
전열처리 조건에 따른 Bi-2223 초전도 선재에서의 특성 변화
하동우,하홍수,오상수,이동훈,윤진국,양주생,최정규,권영길 한국초전도학회 2003 Progress in superconductivity Vol.4 No.2
A lot of efforts have been focused on the optimization of PIT parameters for Bi-2223/Ag wire. Bi-2223 superconducting wires with 55 filaments were fabricated by stacking, drawing process. Before rolling process, round wires were pre -annealed at 760 - 820 $^{\circ}C$ and low oxygen partial pressure. We confirmed that pre-annealing step was to transform Bi-2212 orthorhombic structure from Bi-2212 tetragonal structure and to reduce the formation of second phases. However Bi-2223 phases also were formed at higher than 76$0^{\circ}C$ of pre-annealing temperature. The engineering critical current densities (Je) of Bi-22231Ag tapes were sintered at low oxygen partial pressure were higher than t hat of the wires sintered at air. We could achieve 6500 A/${cm}^2$ of Je for the tape that was initially kept at slightly higher temperature than that of normal heat treatment.
Magnetism in Ni-W textured substrates for coated conductors
송규정,박찬,김석환,김호섭,오상수,주진호,박유미,양주생,고락길,하홍수,김찬중 한국초전도.저온공학회 2005 한국초전도저온공학회논문지 Vol.7 No.2
The magnetic properties of a series of both annealed (biaxially textured) and as-rolled (non-textured) Ni-xW alloy tapes with compositions x = 0, 1, 3, and 5 at.%, were studied. Characterization methods included XRD analyses to investigate the biaxial cube texturing of the annealed Ni-W alloy tapes and studies of the magnetization M for both annealed and as-rolled Ni-W alloy tapes. Both the isothermal mass magnetizations M(H) of a series of samples at different fixed temperatures and M(T) in fixed field, employing a PPMS-9 (Quantum Design), were measured. The Ni-W alloys have shown much reduced ferromagnetism as W-content x increases. Both the saturation magnetization Msat and Curie temperature Tc decrease linearly with W-content x, and both Msat and Tc go to zero at critical concentration of xc ~ 9.50 at.% W.
The Study of Different Buffer Structure on Ni-W Tape for SmBCO Coated Conductor
김태형,김호섭,오상수,하동우,송규정,정예현,염도준,박경채,고락길,이남진,양주생 한국초전도.저온공학회 2006 한국초전도저온공학회논문지 Vol.8 No.4
High temperature superconducting coated conductor has various buffer structures on Ni-W alloy. We comparatively studied the growth conditions of a multi buffer layer (CeO2/YSZ/CeO2) and a single buffer layer(CeO2) on textured Ni-W alloy tapes. XRD data showed that the qualities of in-plane and out-of-plane textures of the two type buffer structures were good. Also, we investigated the properties of SmBCO superconducting layer that was deposited on the two type buffer structure. The SmBCO superconducting properties on the single and multi buffer structure showed different critical current values and surface morphologies. FWHM of In-plane and out-of-plane textures were 7.4o, 5.0o in the top CeO2 layer of the multi-buffer layers of CeO2/YSZ/CeO2, and 7.3o, 5.1o in the CeO2 single buffer layer. 1㎛-thick SmBCO superconducting layers were deposited on two type buffer layer. Ic of SmBCO deposited on single and multi buffer were 90 A/cm, 150 A/cm and corresponding Jc were 0.9 MA/cm2, 1.5 MA/cm2 at 77K in self-field, respectively.