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Fabrication of a large grain YBCO bulk superconductor by homo-seeding melt growth method
Hee-Gyoun Lee 한국초전도저온학회 2022 한국초전도저온공학회논문지 Vol.24 No.3
To fabricate large grain YBCO bulk superconductors by melt process, Sm123 single crystal with a high meltingpoint are mostly used as seeds. However, it also uses Y123 film deposited on MgO single crystal substrate. This studyinvestigated the growth behavior of the Y123 grain during a melt process when single grain YBCO bulk was used asa seed. Single grain Y123 bulk was grown when the seed size was small. When the seed size was relatively large,multiple grains were grown but the grains were still large. Y123 seed crystal was completely decomposed during hightemperature anneal at 1040℃ and new Y123 crystals were nucleated during a slow cooling stage below a peritectictemperature. Thereafter, newly formed Y123 crystals from the seed area are thought to grow into the Y1.8 powdercompact. The crystallographic orientations of newly nucleated Y123 grains are independent of the crystallographicorientation of Y123 seed. It is thought that the crystallographic orientation of newly nucleated Y123 crystal can becontrolled by using Y211-free Y123 single crystal as a seed of homo-seeding melt growth.
Lee, Hee-Gyoun The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.2
This study presents three dimensional (3-D) seeding technique which is a modification of interior seeding. 3-D seeding is beneficial for shortening the processing period and enhancing the magnetic properties of REBCO bulk superconductors fabricated by melt growth. Oxygen channels were provided by using divided powder compacts instead of by using a rubber insert. Microstructure observations revealed that the grains grown from the seeds impinged each other and formed low angle grain boundaries of (001)/(001). It has been shown that the 3-D seeding technique reduces the volume fraction of a-c growth sector and thereby maximizes the area of a-b growth sector which attribute to the high magnetic characteristics of single grain REBCO bulk superconductors.
Effects of seed orientation on the growth behavior of single grain REBCO bulk superconductors
Lee, Hee-Gyoun The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.2
This study presents a simple method to control the seed orientation which leads to the various growth characteristics of a single grain REBCO (RE: rare-earth elements) bulk superconductors. Seed orientation was varied systematically from c-axis to a-axis with every 30 degree rotation around b-axis. Orientations of a REBCO single grain was successfully controlled by placing the seed with various angles on the prismatic indent prepared on the surface of REBCO powder compacts. Growth pattern was changed from cubic to rectangular when the seed orientation normal to compact surface was varied from c-axis to a-axis. Macroscopic shape change has been explained by the variation of the wetting angle of un-reacted melt depending on the interface energy between $YBa_2Cu_3O_{7-y}$ (Y123) grain and melt. Higher magnetic levitation force was obtained for the specimen prepared using tilted seed with an angle of 30 degree rotation around b-axis.
Preparation of Cube-textured Nickel-alloy Tape using Metal Powders
Lee, Hee-Gyoun,Oh, Hyun-Suk,Hong, Gye-Won The Korean Superconductivity Society 2000 Progress in superconductivity Vol.1 No.2
Ni-13%Cr and Ni-70%Cu alloy tapes were prepared by using high purity metal powders as starting materials. The Ni-13%Cr and the Ni-70%Cu mixtures were isostatically pressed, sintered, rolled and texture-annealed. SEM EDS analysis showed that copper and nickel atoms were completely mixed, while the alloying between the chromium powders and the nickel powders was incomplete. In spite of incomplete alloying between nickel and chromium powders, sharp cube-texture was developed for the Ni-13%Cr tape as well as the Ni-70%Cu tape.
Development of Cube Texture in a Silver-Nickel Bi-layer Sheet
Lee, Hee-Gyoun,Jung, Yang-Hong,Hong, Gye-Won The Korean Superconductivity Society 1999 Progress in superconductivity Vol.1 No.1
An Ag/Ni bi-layer sheet was fabricated by the combination of powder metallurgy, diffusion bonding, cold rolling and texture annealing processes. After heat treating the cold rolled thin Ag/Ni bi-layer sheet at $900^{\circ}C$ for 4h, the excellent cube texture was developed on nickel surface. Qualitative chemical analysis using EPMA showed that inter diffusions of Ni and Ag in Ag/Ni bi-layer composite were negligible. It showed that Ag can be used as a chemical barrier for Ni and vice versa.
Lee, Hee-Gyoun,Kim, Jae-Geun,Kim, Woo-Seok,Lee, Seung-Wook,Choi, Kyeong-Dal,Hong, Gye-Won,Ko, Tae-Kuk The Korean Society of Superconductivity and Cryoge 2007 한국초전도저온공학회논문지 Vol.9 No.2
Persistent mode HTS pancake coil has been fabricated using a coated conductor by a "wind-and-flip" method. A coated conductor with the length of 1.2 meters was divided at the center along the length. The sliced coated conductor was wound on a pair of bobbins with a diameter of around 4 cm and two pancake coils connected superconductively without a resistive joint were prepared. By flipping one of the pancake coils, the magnetic field generated by each coil is to be aligned to the same direction and generate meaningful magnetic field while the magnetic fields of two spit coils are canceled without flipping. Permanent current was induced by flowing current to the coil immersed in liquid nitrogen pool using a power supply. A magnetic field of 48.8 Gauss was generated when 20 A of current was flowing in the pancake coils. The "Wind and flip" method can be applied for the fabrication of a long solenoid magnet by winding a sliced coated conductor on a cylindrical bobbin. It is also introduced that the construction of multiple sets of pancake (or solenoid) coils is possible by a "wind-and-flip" method using a wide coated conductor.
Evolution of Cube Texture in the Nickel-Silver-Stainless steel Multi-layer Sheet
Lee, Hee-Gyoun,Jung, Yang-Hong,Hong, Gye-Won The Korean Superconductivity Society 1999 Progress in superconductivity Vol.1 No.1
A Ni/Ag/Stainless steel 310S(SS310S) multi-layer sheet has been fabricated by a combination of vacuum brazing, cold rolling and texture annealing processes. After heat-treating the thin Ni/Ag/SS310S multi-layer sheet at $900^{\circ}C$ for 2h, development of (100)<001>cube texture on Ni surface was revealed by (111) pole figure. Quantitative chemical analysis was made by EPMA for the cross-section of the Ni/Ag/SS310S multi-layer sheet. EPMA results showed that Ag diffusion into the Ni layer, which may suppress the cube texture development, was negligible. A small amount of Cr atoms were detected in the Ni layer. It showed that Ag can be used as a chemical barrier of alloying element atoms in Ni layer for the Ni/Ag/SS310S multi-layer sheet and a strong cube texture was developed for the Ni layer in the Ni/Ag/SS310S multi-layer sheet.
Fabrication of a high magnetization YBCO bulk superconductor by a bottom-seeded melt growth method
Hee-Gyoun Lee,Yi-Seul Hong,Soon-dong Park,Chan-Joong Kim 한국초전도.저온공학회 2019 한국초전도저온공학회논문지 Vol.21 No.4
A large grain YBCO bulk superconductor is fabricated by the top-seeded melt growth (TSMG) method. In the TSMG process, the seed crystal is placed on the top surface of a partially melted compact and therefore the seed crystal is frequently tilted during the melt process due to intrinsic unstable nature of Y211 particle +liquid phase mixture. In this work, we report the successful growth of single-domain YBCO bulk superconductors by a bottom-seeded melt growth (BSMG) method. Investigations on the trapped magnetic field and the microstructures of the synthesized specimens show that a bottom-seeded melt growth method has hardly affected on the crystal growth behavior, the microstructure development and the magnetic properties of the large grain YBCO bulk superconductors. The bottom-seeded melt growth method is clearly beneficial for the stable control of seed orientation through the melt process for the fabrication of a large grain YBCO bulk superconductor.