Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
Volume 68 , Issue 9
Showing 1-37 articles out of 37 articles from the selected issue
  • Kyoji Tachikawa, Kazumasa Togano, Akihiko Nagata
    2004 Volume 68 Issue 9 Pages 615
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
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  • Takao Takeuchi, Yasuo Iijima, Akihiro Kikuchi, Nobuya Banno, Kiyoshi I ...
    2004 Volume 68 Issue 9 Pages 616-623
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    A rapid-heating, quenching and transformation annealing (RHQT) processed Nb3Al conductor has been developed as a promising candidate for a high-resolution NMR superconducting magnet, because of its large critical current densities and n -values. Establishment of a large-billet extrusion, uniform RHQ operation, transformation heat treatment and subsequent Cu-clad stabilizing that are key issues of the long-length processing allows a fabrication of a four hundred meter long RHQT Nb3Al conductor, and thereby its coil application comes in sight with reality. In the present review article, current status of long-length RHQT processed Nb3Al conductors is described.
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  • Kyoji Tachikawa, Yuuya Ikeda, Yasuyuki Koyata, Hiroyuki Izawa, Takao T ...
    2004 Volume 68 Issue 9 Pages 624-628
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Sn-Ta (-Cu) alloys with enough ductility to be fabricated into a thin sheet were synthesized by melting a mixture of Sn+Ta (+Cu) powder. The (Nb, Ta)3Sn wires were prepared by Jelly Roll (JR) process and filamentary process. In the JR process a Sn-Ta (-Cu) sheet was laminated with a Nb sheet and wound into a JR composite. In the filamentary process a Sn-Ta (-Cu) sheet was wrapped around Nb-1 at%Ta rods and bundled into a filamentary composite. Both composites were fabricated into wires without intermediate annealing and then heat treated. The composition and micro-structure of (Nb, Ta)3Sn layers formed in the wires were studied. Ta in the sheet improves the high-field performance, while Cu addition to the sheet decreases the reaction temperature of the wire. The non-Cu Jc of the JR wire without Cu addition to the sheet and reacted at 900°C is about 1.0×108 A/m2 at 23 T and 4.2 K. A nearly the same non-Cu Jc of the wire is obtained at 25 T and 2.1 K, the upper critical field of the wire being about 28.5 T. The JR wire and 13-core filamentary wire with a few mass% Cu addition to the sheet and reacted at 800°C show a non-Cu Jc of about 1.0×108 A/m2 at 22 T and 4.2 K. Both wires exhibit a n value of about 30 at 22-23 T and 4.2 K, which represents a potentiality of the wires for high magnetic field use.
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  • Sakae Saito, Yuichi Nakajo, Hiroharu Sugawara, Jun-ichi Yuki, Nobuyuki ...
    2004 Volume 68 Issue 9 Pages 629-635
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    This paper describes a fabrication process of Nb3Al intermetallic compound wires and measurements of their superconducting properties. Nb3Al superconducting wires are successfully fabricated by the combined process of the clad-chip extrusion (CCE) method and the rapid-heating, quenching and transformation (RHQT) treatment. The CCE method is a processing of Nb/Al composite wire with fine-layered structure, which is characterized by the extrusion of thin chips of clad-rolled Nb/Al sheet. Its chemical composition is controlled by the thickness ratio of the Nb-layer to the Al-layer at clad-rolling. The RHQT treatment is a heat-treatment to convert the Nb/Al composite into Nb3Al, which can produce fine grain structure of Nb3Al intermetallic compound with nearly stoichiometric composition. It is favorable for upgrading the superconducting properties.
    The critical transition temperature and the critical current density are enhanced by optimizing the microstructure of the CCE-processed precursor wire and the transformation condition in the RHQT process. Plastic working of the bcc supersaturated solid solution wire after rapid-heating and quenching is found to be effective for enhancing the critical current density in high magnetic field.
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  • Takaaki Kondo, Petre Badica, Yuko Nakamori, Wei Sun, Sin-ichi Orimo, K ...
    2004 Volume 68 Issue 9 Pages 636-641
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    MgB2 is an intermetallic compound and is a promising superconductor for practical applications due to its high TC value of 39 K. The production cost of MgB2 wires is expected to be low compared to the conventional superconducting wires, since it is composed of cheap and available elements. However, the critical current density JC in applied magnetic fields is not yet at practical level and, hence, the improvement of high field performance remains one of the most important issue to be solved urgently.
    Recent advances are showing that the addition of SiC is effective to improve the high field JC, while the use of MgH2 instead of Mg as raw material is enhancing MgB2 crystal growth. In both situations the mechanisms of these effects are still unclear.
    This paper reports the synthesis of MgB2 superconductor in high-pressure hydrogen-atmosphere, which is an extreme reducing atmosphere. The results are compared with those for inert atmosphere i.e. argon-atmosphere, in order to provide useful information for wire processing.
    Samples were prepared by reacting the mixture of Mg (or MgH2), B and nano-SiC powders in a high-pressure (up to 3.5 MPa) steel vessel, at temperatures below 900°C. Samples that are fabricated in the pressurized hydrogen atmosphere show higher TC, bigger a -axis lattice parameter and larger grain size than for the samples synthesized in Ar-atmosphere, in the same conditions. It turns out that the pressurized hydrogen atmosphere is useful to produce MgB2 with good crystallinity. Nevertheless, the JC in magnetic field is higher for the samples synthesized in argon atmosphere and it is considered that the lattice distortion in a -plane, smaller grain size and fine precipitates, such as MgO, are responsible for the stronger flux pinning. SiC addition is effective regardless the atmosphere and the highest JC was obtained for the sample starting from MgH2+2B+SiC powder mixture heat treated in argon atmosphere.
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  • Kazumune Katagiri, Ryuya Takaya, Kyoji Tachikawa, Yutaka Yamada, Akifu ...
    2004 Volume 68 Issue 9 Pages 642-647
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The stress/strain dependence of critical current and the mechanical properties of nickel sheathed PIT MgB2 mono-core tapes with various kinds of metal powders addition to the core were evaluated at 4.2 K in the magnetic field of 2 T. No marked change in the stress-strain curve was found by the powder addition. The critical current was markedly enhanced by In and Sn powder addition. The critical current was almost constant irrespective of strain up to the irreversible strain where a steep degradation of critical current begins. The irreversible strain for the tape increased from 0.25 to 0.50% by the addition of In and Sn powder. The In addition also suppressed a slight increase in the critical current with strain. The effects of Ag and Cu addition are less as compared with those of the low melting point metal powder such as In and Sn. SEM observations on the longitudinal section of In added tape after the tensile test clarified that the cracks were few and rather large as compared with those in the tapes with no addition or high melting point metal powder addition. The strain characteristics were compared with those of MgB2 with other sheath materials and those of a conventional Nb3Sn wire.
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  • Satoshi Hata, Harini Sosiati, Yoshitsugu Tomokiyo, Noriyuki Kuwano, Ak ...
    2004 Volume 68 Issue 9 Pages 648-655
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Microstructures of MgB2 films on yttria-stabilized-zirconia (YSZ)/Hastelloy substrates were studied by analytical transmission electron microscopy. The MgB2 films with Mg-rich compositions were fabricated by pulsed laser deposition followed by annealing at 600°C or 680°C under Ar atmosphere. Fine grains of MgB2 and MgO crystals 5-30 nm in size that shows a good mutual connectivity are formed in the MgB2 films. The MgB2 films also form voids 5-100 nm in size that may contain amorphous or oxide phases. Two-dimensional elemental analyses revealed that Mg and O atoms are enriched near the MgB2/YSZ interface. From a comparison in microstructures between the 600°C- and 680°C-annealed MgB2 films, it is suggested that the films composed of finer grains of MgB2 exhibit a higher critical current density under high magnetic fields.
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  • Akiyoshi Matsumoto, Hiroaki Kumakura, Hitoshi Kitaguchi, Junnichi Nish ...
    2004 Volume 68 Issue 9 Pages 656-660
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The microstructures and critical current densities of Bi-2212 multi-filamentary round wires were investigated. The microstructures and Jc properties of Bi-2212 composite wires are very sensitive to heat treatment. We studied the dependence of Jc on maximum processing temperature Tmax precisely. The highest Ic values of 450 A (Jc=2.8×109 A/m2) were obtained at very narrow temperature range of Tmax, around 1155 K. The Ic values of wires heat-treated with Tmax below this optimum processing temperature Top were zero. When the wires were heat-treated over Top, however, Ic values were almost half values of the highest Ic values. Scanning electron microscope observation indicated that Bi-2212 filaments were not melted for Tmax below Top. Above Top, on the other hand, many bridges between filaments were observed, which were due to the outgrowth of Bi-2212. The wires heat treated at optimum temperature had fewer bridging of filaments than the wires heat treated above Top. The well-controlled heat-treatment resulted in a few outgrowths from multifilament and high Ic values of wires.
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  • Tsuneo Kuroda, Takayuki Nakane, Hiroaki Kumakura, Yoshifumi Suga, Kuni ...
    2004 Volume 68 Issue 9 Pages 661-667
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The critical current densities of round AgCu alloy-sheathed Bi-2212 wires have been studied for superconducting magnet use. The wires have been fabricated by the powder-in-tube method, using co-precipitated powders with a nominal composition of 2 : 2 : 0.64 : 1.64 (Bi : Sr : Ca : Cu). In these wires each core has been designed to consist of a twofold tube of the oxide layer to increase the interfacial area of the Ag-sheath and the oxide core. The critical current densities per overall cross-sectional area of the wires (Jc) have been increased by increasing the number of cores to 37. Sheathing Ag/Bi-2212 wires with the AgCu-alloy tube as the outermost sheath has enhanced both the mechanical strength and Jc values compared with Ag/Ag/Bi-2212 wires where the sheath is made of pure Ag tubes only. Jc values exceeding 2.6×108 A/m2 at 4.2 K and 10 T have been obtained for AgCu/Ag/Bi-2212 wires heat-treated in air. Heat treatments under oxygen gas flow have caused deleterious effects on Jc values. The micro-structural analyses of the smoothness of the Ag-sheath/oxide-core interface and the packing density of the oxide core have indicated that there is much room for improving weak links within the wires.
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  • Akira Ishii, Kyung Sung Yun, Shunichi Arisawa, Yoshihiko Takano, Takes ...
    2004 Volume 68 Issue 9 Pages 668-673
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We have developed a method for preparing atomically flat high-quality Bi2Sr2CaCu2O8+δ (Bi2212) thin films on MgO (001) substrates by using a combination of pulsed laser deposition (PLD) and a post-annealing process. Before depositing Bi2212 films, annealing of a MgO substrate was performed in a tube furnace. MgO substrates were annealed at 1073-1103 K under 8% of oxygen atmosphere. Thermal annealing of MgO substrates significantly contributed to the morphologies, crystallographic orientations, and superconducting properties of the Bi2212 films. The Bi2212 films were deposited by a PLD system using a KrF excimer laser. Only the Bi2212[100]//MgO[110] epitaxial relationship was observed in the Bi2212 films grown at lower substrate temperatures. Although the as-grown films have an extremely smooth surface, the grain size was limited to ∼100 nm, and the superconducting transition temperature (Tc) of the films were considerably lower than the reported values of Bi2212 bulk materials. In order to improve the superconducting properties of films, post-annealing was subsequently carried out in a tube furnace under various oxygen pressures. The surface morphologies and the in-plane orientation relationships between MgO substrates and Bi2212 films were drastically changed by post-annealing. After post-annealing, we found that the in-plane orientations of the Bi2212 grains thoroughly rotated to the Bi2212[100]//MgO[100]±12.5° epitaxial relationships. According to the AFM images of post-annealed Bi2212 films, periodic step and terrace structures were clearly observed. The step height corresponded to the half unit cell height of Bi2212, and the width of atomically flat terraces was larger than 500 nm. The post-annealing process also affected the superconducting properties of the films as the Tc over 80 K improved with sharp superconducting transitions. We have successfully fabricated high-quality Bi2212 thin films on MgO substrates, whose atomically flat surface morphology and superconducting properties as comparable to those of bulk materials. This technique offers a great technological advantage for high Tc superconducting device fabrications.
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  • Kouhei Yamazaki, Shin-ichi Kobayashi, Takeshi Kato, Kengo Ohkura, Mune ...
    2004 Volume 68 Issue 9 Pages 674-680
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    (Bi, Pb)2Sr2Ca2Cu3OX (Bi2223) superconducting wires (Tc∼110 K) is a promising candidate of high-Tc superconducting wire which can be expected for practical use. We have proceeded with its research of Ag-sheathed wire using Bi2223 superconductor and has developed semi-mass producing long wires (in the kilometer class) with high Jc. And for application, magnet, power transformer and power cable have been developed. At present we improve the performance of Bi2223 wires and have proceeded with cable project in the real scale.
    But it is still necessary for practical use to improve the performance of Bi2223 wires. In this paper, we concentrated on the sintering process and applied controlled over pressure sintering method. The sintering process has a problem which the mass density increased on rolling process decreases during sintering. Since decreased density causes the formation of pores and a decrease of supercurrent between Bi2223 grains which grow during sintering, it is considered to be one of the major causes of the performance of Bi2223 wires. Controlled over pressure sintering is a method which applies gas pressure to Bi2223 wires during sintering because of suppression of decreasing mass density.
    As the results of short samples, controlled over pressure sintering method improved Bi2223 phase homogeneity, misalignment angle, connectivity, critical current density and mechanical property. Furthermore, when cooled in liquid nitrogen and warmed up to room temperature, the wires may often balloon up by vaporization of liquid nitrogen entered in the pores of filaments through the defects of the sheath. However controlled over pressure sintering removes pores in filaments and it is confirmed that wires were not ballooned after cooled in liquid nitrogen under 1 MPa for 24H so far.
    To apply controlled over pressure sintering to long length Bi2223 wires, we developed the large furnace which kilometer-scaled Bi2223 wires can be sintered. The performance of long length wires is almost equal to that of short samples.
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  • Shojiro Ochiai, Noboru Miyazaki, Takashi Nagai, Dan Doko, Hiroshi Okud ...
    2004 Volume 68 Issue 9 Pages 681-687
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The process of damage extension under bending and tensile strains at room temperature and its influence on critical current at 77 K under zero magnetic field were studied for a mutifilamentary Bi2223/Ag/Ag-Mg alloy superconducting composite tape. Under the tensile strain, the damages such as transverse cracking of the Bi2223 filaments, longitudinal cracking along the filament axis and interfacial debonding between Bi2223 and Ag took place. Under the bending strain, in addition to these damages, protrusion of the compressive side due to buckling, accompanied by compressive fracture of the filaments, was observed. From the analysis of the residual stress, tensile stress-strain curve and tensile damage-induced reduction in critical current, the Young's modulus, residual strain and intrinsic tensile fracture strain of the Bi2223 filaments at room temperature were estimated to be 98 GPa, −0.16% and 0.09∼0.13%, respectively. The change of critical current with bending strain was calculated by substituting these estimated values and compressive strength of the filaments as a variable into the proposed model in which the influence of the damages both in tensile and compressive sides on critical current was incorporated. From the comparison of the calculation- and experimental results, the compressive strength of Bi2223 filaments was estimated to be several times higher than the tensile one.
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  • Hiroshi Ikuta, Uichiro Mizutani
    2004 Volume 68 Issue 9 Pages 688-692
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    It was recently reported that the critical current density (Jc) of melt-processed YBa2Cu3Oy based bulk superconductors increases by adding a small amount of Zn because its substitution for Cu depresses locally the superconductivity. Here we report on the effect of adding Zn to melt-processed DyBa2Cu3Oy and SmBa2Cu3Oy, the former is a system that exhibits a similar field dependence of Jc as the Y system and the latter possesses a peak effect in the field dependence of Jc. We observed that the addition of a slight amount of Zn is effective for increasing Jc and the trapped field in both systems. By measuring the local properties of the SmBa2Cu3Oy based bulk superconductor, we found that the increase in Jc is particularly large in the region near the seed crystal, where the amount of pinning centers is deficient before adding Zn due to the segregation of the Sm2BaCuO5 phase. This enhancement in Jc in the region near the seed crystal is probably most important for the increase of the trapped field of bulk samples.
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  • Hironobu Tanaka, Shinya Nariki, Naomichi Sakai, Masato Murakami, Izumi ...
    2004 Volume 68 Issue 9 Pages 693-697
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We have fabricated melt-textured Ho-Ba-Cu-O bulk superconductors with a composition of HoBa2Cu3Oy(Ho123)+0.4Ho2BaCuO5(Ho211) in air. Several kinds of precursor compounds having Ho211 starting powders with different sizes are prepared by calcinining Ho2O3, BaO2 and CuO at 1173∼1273 K. The diameter of Ho211 secondary particles dispersed in the Ho123 phase is reduced with decreasing the particle size of the Ho211 starting powder, resulting in the improvement in Jc properties. The maximum Jc value is 7.2×108 A/m2 at 77 K in self-field. The Ag added large single-domain bulk of 32 mm in diameter is also fabricated. The trapped-field of 1.2 T has been achieved at 77 K for this bulk sample.
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  • Yuichi Nakamura, Tomohiko Misu, Yoshihiro Ooishi, Ryoji Inada, Akio Oo ...
    2004 Volume 68 Issue 9 Pages 698-705
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Directionally solidified REBa2Cu3O7−x (RE=Y, Gd, Sm...: RE123) superconductive oxides are expected for high magnetic field applications such as the superconducting current lead. In this study, the Y123 thin fibers with a diameter of about 0.5 mm were directionally solidified with several pulling rates, and transport current properties were evaluated at 77 K. The continuous growth of Y123 single domain crystal was obtained up to the pulling rate of 2.8×10-6 m/s or less under the temperature gradient of 26 K/mm in the thin fibers while such the structure was obtained only up to the pulling rate of about 5.6×10-7 m/s in usual φ2 mm rods. This increase in the limit of the maximum pulling rate, at which the continuous growth is obtained, could be explained by the suppression of Y123 nucleation since the volume of the undercooled liquid ahead of the growth interface is small in the thin fibers. In addition, the large temperature gradient at the growth interface will be the important factor to supply the necessary solute for the Y123 crystal growth. The high Ic value of 134 A, and corresponding Jc of 1.0×109 A/m2, was achieved in the thin fiber grown at R =1.7×10-6 m/s. This suggests that the directionally solidified thin fiber has the advantage to attain both the high production rate and the high Jc properties.
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  • —Long Length Conductor and Rapid Production Rate for Industrialization—
    Yutaka Yamada, Tomonori Watanabe, Seiki Miyata, Takemi Muroga, Hiroyuk ...
    2004 Volume 68 Issue 9 Pages 706-711
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    For a practical long YBCO coated conductor fabrication, PLD and IBAD methods have been investigated by using reel to reel deposition systems. We discussed critical current density, in-plane texturing, surface roughness, film deposition rate and wire production speed. Consequently, we successfully fabricated a 100 m long IBAD substrate tape. Furthermore, recently we have found the Self-Epitaxial Effect in PLD-CeO2 film on the IBAD layer. This resulted in the better alignment and fast production rate than the conventional IBAD process. This method is very promising for the realization of the mass production of the buffer layer in coated conductors. Using the PLD-CeO2, 50 to 100 m long substrate tapes were successfully fabricated. On this CeO2 layer, YBCO film was deposited by a reel to reel PLD system. Critical current density was increased with increasing the degree of in-plane texturing. At present, we obtained 1 m to 10 m long YBCO with critical current density around 1010 A/m2 at 77 K. Although, by using PLD and IBAD method, the realization of YBCO practical superconducting wire will not be far, we need further improvement, especially, in the production speed.
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  • ∼Self-Epitaxial PLD-CeO2 Cap Layer on IBAD Buffer Substrate∼
    Takemi Muroga, Seiki Miyata, Tomonori Watanabe, Hiroyuki Iwai, Akira I ...
    2004 Volume 68 Issue 9 Pages 712-717
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Processing of a CeO2 layer on an IBAD-Gd2Zr2O7 buffer tape was investigated as a cap layer. In the process of this study, we found that the CeO2 cap layer by the PLD method on the IBAD buffer tape brought about high in-plane grain alignment without Ar ion assistance such as the IBAD process. The Δφ value, degree of the in-plane grain alignment decreased from 25.4 degrees and 11.6 degrees for the IBAD-GZO to 4.9 degrees and 2.4 degrees for the PLD-CeO2, respectively. We call this phenomenon “self-epitaxial PLD-CeO2 cap layer”. Then, we suggested a new process which is a combination of a thin IBAD-GZO by short time deposition and a PLD-CeO2 with high rate deposition in order to enhance the fabrication rate for the buffer layer process. The new self-epitaxial process is very promising as a buffer layer process in terms of both high grain alignment and rapid fabrication.
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  • Hiroyuki Iwai, Takemi Muroga, Tomonori Watanabe, Seiki Miyata, Akira I ...
    2004 Volume 68 Issue 9 Pages 718-722
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In order to fabricate a YBa2Cu3O7−x(YBCO) coated conductor with high critical current density, Jc, we have been investigating the pulsed laser deposition (PLD) processing using the “self-epitaxial ” PLD-CeO2 layer on an ion beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO) buffered Hastelloy tape. For the study using short samples with 10 mm in length and 10 mm in width, the Jc value of YBCO increased exponentially with decreasing the in-plane grain alignment of YBCO and CeO2 layers, and then the Jc value of 4.4×1010 A/m2 was attained at the delta phi value of 2.4 degrees. Furthermore, we also succeeded in deposition of high Jc and thick YBCO film; the thickness of 1.2 μm and the Jc value of 2.3×1010 A/m2. This value corresponds to 276 A/cm-width. Based on these results, 0.9 m to 10 m long YBCO coated conductors were fabricated using the reel-to-reel system. Consequently, Ic and Jc values attained 36.4 A and 7.3×109 A/m2 in the 0.9 m long sample with the thickness of 0.5 μm and 20.5 A and 5.4×109 A/m2 in the 4.5 m long sample with the thickness of 0.38 μm, respectively.
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  • —Fabrication of Biaxially-Textured Long Gd2Zr2O7 Tape by IBAD Method—
    Seiki Miyata, Tomonori Watanabe, Takemi Muroga, Hiroyuki Iwai, Yutaka ...
    2004 Volume 68 Issue 9 Pages 723-729
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We developed biaxially textured Gd2Zr2O7 (GZO) templates by ion-beam assisted deposition (IBAD) for YBa2Cu3O7−δ high temperature superconducting wires. Since “assisting” ions bombard the surface of a film concurrently during deposition, the growth mechanism becomes rather more complicated than the ordinary sputtering method with a single ion beam. Based on the result of investigations about a correlation between the conditions of ion beams and the properties of films, we successfully fabricated a 105 m long IBAD-GZO tape with full width at half maximum of 15 degrees in X-ray φ-scan measurement.
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  • Kaname Matsumoto, Hideyuki Shii, Ataru Ichinose, Hiroki Adachi, Yutaka ...
    2004 Volume 68 Issue 9 Pages 730-736
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We have fabricated biaxially textured Ni and Ni-0.1 mass%Cr (Ni-Cr) tapes, and crystal orientation and microstructure of CeO2 films deposited on the tapes by pulsed laser deposition were investigated. Recrystallized Ni-Cr tapes had a strong cube texture, {100}‹001› orientation, and the surface of the tapes was occupied by the (100) oriented grains. CeO2 films grown on the Ni-Cr surface showed both the (100) preferred orientation and the strong in-plane alignment. Although recrystallized Ni tapes exhibited the {100}‹001› texture and the CeO2 films subsequently deposited on the tapes also have (100) orientation, a large number of (111) oriented grains were included in the films. The difference between the films deposited on the Ni-Cr and the pure Ni tapes depended on the degree of the cube texture and the surface flatness of the tapes. The preferred orientation of CeO2 films was also affected by the oxygen partial pressure during pulsed laser deposition, and the strong (100) orientation was attained under the pressure of 2.7×10-3 Pa. Moreover, the degree of the (100) orientation of CeO2 films was improved with increase of the film thickness. The microstructure of the films and its texture evolution mechanism were discussed.
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  • Yutaka Yoshida, Kaname Mastumoto, Kimihiko Sudoh, Yusuke Ichino, Koji ...
    2004 Volume 68 Issue 9 Pages 737-741
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We have investigated the superconducting properties and the microstructure of the c -axis oriented Sm1+xBa2−xCu3O6+y(Sm-123) and GdBa2Cu3O6+y(Gd-123) thin films deposited on MgO substrates deposited by pulsed laser deposition (PLD). From their Jc-B characteristics, it has been observed that the superconducting properties of Sm-123 (x =0), Sm-123 (x =0.08) and Gd-123 are superior to those of the YBa2Cu3O7−y thin films for B//c, 5 T at 77 K. The Jc values of the Sm-123 (x =0) films measuring 7×108 A/m2 for 5 T at 77 K are comparable to that of NbTi for 5 T at 4.2 K. Furthermore, the superconducting properties in Sm-123 change with the substitution of Sm-Ba. By observing the c -axis oriented high-Jc Sm-123 thin films using the cross-section transmission electron microscopy, we detected the existence of finely dispersed a -axis oriented domains with a size of about 10 nm in the c -axis oriented matrix. Electron microscopic studies with EDX have revealed that the Sm/Ba ratio fluctuates within the range of x =0 to 0.14 with a wavelength of ∼400 nm. It is considered that these domains are formed by a cation combining with the substituted Sm/Ba and a growth temperature difference on the a -axis oriented Sm-123 phase which has a c -axis orientation phase. High-Jc values in high magnetic fields at 77 K demonstrate the potential of REBCO films for high-field applications of oxide superconductor.
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  • Yoshitaka Tokunaga, Junko Matsuda, Ryo Teranishi, Hiroshi Fuji, Tetsuj ...
    2004 Volume 68 Issue 9 Pages 742-747
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In order to shorten the calcination time in the metal-organic deposition (MOD) process using metal trifuluoroacetete (TFA), a new combination of starting materials was developed using F-free salt of Cu and TFA salts of Y and Ba as called “New solution”. Moreover, a new process temperature profile for this solution was developed as an advanced TFA-MOD process where the high heating rate was achieved. Consequently, the overall transport Ic value of 210 A and the Jc value of 1.5 MA/cm2 (77 K, Self field) similar to Ic and Jc values using TFA for all salts were obtained. In order to obtain higher Jc performance, the effects of process parameters such as degree of in-plane alignment Δφ of the buffer layer and PH2O in the annealing process for the Jc characteristics were investigated. As a result, a YBCO film with 1.48 μm in thickness was fabricated on a CeO2/IBAD-Gd2Zr2O7 layer buffered Hastelloy substrate with Δφ=4.7°. The overall Ic value of 292 A (77 K Self-field) corresponding to the Jc value of 2.0 MA/cm2 was achieved. Moreover, the overall Jc value of 2.1 MA/cm2 (77 K Self-field) for the YBCO film with 1.2 μm thickness was achieved by annealing under the PH2O value of 13.5 vol% on a similar metal substrate even with Δφ∼7°.
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  • Shigeru Horii, Masashi Mukaida, Yusuke Ichino, Kaname Matsumoto, Tohru ...
    2004 Volume 68 Issue 9 Pages 748-755
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We report crystallographic and electrical properties of ErBa2Cu3Oy/SrTiO3 (Er123/STO) films which were fabricated by the pulsed-laser-deposition (PLD) method in the temperature range of 720∼780°C, and dramatic enhancement of critical current density (Jc) by an oxygen post-annealing process. The PLD Er123/STO films were found to be crystallographically excellent in the deposition temperature region below 770°C from the intensity of diffraction peaks of 00l, the pole-figure of a reciprocal (102) plane and microstructures of the surface and the cross-section. Interestingly, in this temperature region, Jc values were clearly increased to the order of 1010 Am-2 by oxygen post-annealing in comparison with those of the as-grown films (0.3∼0.6×1010 Am-2). Enhancement of Jc was accomplished in a wide annealing temperature range of 350∼500°C, which is corresponding with an annealing temperature range where the critical temperature shows over 90 K on a polycrystalline sample. On the other hand, Irreversibility fields were almost independent of the annealing temperature. These results indicated that insufficient carrier-doped region was partly existed even in a non-equilibrium process such as the PLD method. Therefore, homogenization of oxygen contents in a whole part of the Er123 film is crucially important for enhancement of critical current properties, which strongly suggests that the oxygen annealing is effective for improvement of functionality of devices in PLD-REBa2Cu3Oy (RE: rare earth elements) thin films.
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  • Masahiko Kai, Atsushi Inoue, Saburo Hoshi, Satoshi Koyama, Teruo Izumi ...
    2004 Volume 68 Issue 9 Pages 756-763
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Many applications for the superconducting magnets using high critical temperature (Tc) oxide superconductors are expected to operate in the persistent current (PC) mode. For the PC mode operation, the PC switch (PCS) is considered to be an essential device. The following properties are required for the PCS material; high critical current, high normal electric resistance in order to cut off the current flow efficiently through thermal switching, and controlled Tc of about several ten degrees higher than the operating temperature in order to attain a quick switching.
    The liquid phase epitaxy (LPE) method could provide REBa2Cu3Oy (RE123) thick films with a high critical current density in the superconducting state, a reasonable electric resistivity in the normal state and could control Tc with doping a third element. We studied how to fabricate Zn-doped RE123 LPE films with a meander shape to realize its Tc value of about 40-60 K and high electric resistance in the normal state as persistent current switch materials for operation of the magnet at about 20 K. We also studied controllability of the Tc and the lateral growth length of Zn-doped RE123 LPE films on the BaZrO3 buffer layer to develop the process for fabrication of persistent current switch materials.
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  • Kiyotaka Matsuura, Takayuki Koyanagi, Tatsuya Ohmi, Masayuki Kudoh
    2004 Volume 68 Issue 9 Pages 764-768
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    A new method for surface modification based on the arc surface alloying has been proposed and its feasibility has been investigated performing niobium aluminide coating on a niobium base metal. When tungsten arc was used to melt an aluminum plate placed on a niobium block, the niobium surface was also melted and a melt pool of an Al-Nb binary alloy was formed on the niobium block. The melt pool solidified into niobium aluminides on the surface of the niobium block, forming a thick NbAl3 layer on the top surface of the coating layer. When an Al-Si alloy plate was used instead of the aluminum plate, a niobium aluminosilicide layer was formed on the niobium block.
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  • Hirokazu Ohno, Tetsumori Shinoda, Yoshihiro Oya-Seimiya
    2004 Volume 68 Issue 9 Pages 769-775
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Formation of A15 type Nb3Al phase at the interface between solid Nb and liquid Al in a bulky Nb/Al composite has been studied at as high temperatures as from 1873 to 2073 K. The A15-phase layer grows keeping the interfaces planar when heated at 2023 K or lower, whereas the interface adjacent to Nb solid solution, Nbs.s, becomes “nonplanar” when heated at 2073 K. It is suggested that the formation process of A15 phase consists of three stages; the rapid dissolution of Nb into liquid Al until nucleation of A15 phase at the Nb/Al interface, and the following two stages (1st and 2nd ones) for growth of A15 phase. The planar growth rate of A15-phase on the 1st stage is considerably faster than that on the 2nd one. A model for the planar growth rate of A15-lphase on the 2nd stage has been presented. The model is based on the unidirectional inter-diffusion fluxes of Nb and Al atoms in the three sequential regions of Nbs.s, A15 and σ-phases. The “nonplanar” growth of A15-phase will be detailed in Part II of the present study.
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  • Mikio Maeda, Jun-ichi Echigoya, Akira Yamaguchi
    2004 Volume 68 Issue 9 Pages 776-780
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Structural change in hydrogenation and dehydrogenation processes of La films was investigated. La/Pd films were produced at substrate temperatures of 300 K-573 K on a SiO2 substrate using magnetron-sputtering equipment. La/Pd films were hydrogenated under a pressure of 1.0×105 Pa in a vacuum chamber. Phase transition from La to LaHx (2<x<3) by hydrogenation resulted in a 6- to 10-fold increase of resistivity. Hydrogenation and dehydrogenation readily occurred near room temperature for La/Pd films. The ratio of the growth direction of [0001] to [1010] changed with substrate temperature in the as sputtered La films. When the growth direction of La film was [1010], the rate of hydrogenation became slow in comparison with that of [0001]. The direction of the La films changed to the [111] direction of LaHx after hydrogenation, though the initial directions of La films were [0001] and [1010]. The processes of hydrogenation and dehydrogenation may affect oxygen which remains inside the La films. In dehydrogenation at room temperature, LaHx (2<x<3) was transformed to LaH2, but not to La.
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  • Takehiko Ishikawa, Paul-Francois Paradis, Yutaka Saita
    2004 Volume 68 Issue 9 Pages 781-786
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Thermophysical properties of liquid and supercooled nickel were measured using electrostatic levitation. Over the 1420-1850 K temperature range, the density can be expressed as ρ(T )=7.89×103−0.65(TTm) (kg · m-3) with melting temperature Tm=1728 K. The isobaric heat capacity was estimated as Cp(T )=36.2+1.9×10-3(TTm) (J · mol-1·K-1) over the 1420-1850 K interval by assuming a constant emissivity. The volume expansion coefficient was also calculated as 8.2×10-5 K-1. In addition, the surface tension can be expressed as γ(T )=1739−2.2×10-1(TTm) (10-3 N · m-1) and the viscosity as η(T )=0.07 exp [6.7×104/(RT )](10-3Pa · s) over the 1553 to 1963 K temperature range.
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  • Masaki Tanaka, Kenji Higashida, Hideharu Nakashima, Hidenari Takagi, M ...
    2004 Volume 68 Issue 9 Pages 787-791
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Fracture toughness of silicon crystals has been investigated using indentation methods and their surface energies have been calculated by molecular dynamics (MD). In order to determine the most preferable fracture plane at room temperature, a conical indenter was forced into a (001) silicon wafer at room temperature. Dominant {110} cracks were introduced from the indent, indicating that fracture occurs most easily along the {110} plane among the crystallographic planes of the ‹001› zone. To confirm this orientation dependence of fracture toughness, surface energies for those planes were computed using molecular dynamics. The surface energy calculated exhibits the minimum value of 1.50 J · m-2 at the {110} plane and it increases up to 2.26 J · m-2 at the {100} plane. Fracture toughness was derived from these computed surface energies, and it was shown that KIC value for the {110} crack plane was the minimum among those for the planes of the ‹001› zone. Fracture toughness of {110} plane and the other planes of ‹001› zone were measured by the indentation fracture (IF) method. The result is qualitatively in a good agreement with those obtained from the MD, although the absolute KIC values estimated by the IF method were larger than those obtained by the calculation.
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  • Jun Kurobe, Manabu Iguchi
    2004 Volume 68 Issue 9 Pages 792-799
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The motions of top and bottom dross with different diameters in hot dip plating baths were investigated using a transparent cold model vessel with a reduced scale of one-tenth. Polystyrene particles of the same density and diameter were used as models both for the top and bottom dross, and NaCl aqueous solutions with different densities were used as models for the plating melts. The typical streak lines of the top and bottom dross model particles were nearly the same as the main stream lines in the model bath regardless of the dross diameter. The top and bottom dross model particles were enriched in the region enclosed with the belt. Some of the model particles were trapped in the clearances between the sink roll and the belt. As the dross diameter became large, the number of top dross model particles floating on the bath surface increased and that of bottom dross model particles staying on the bottom wall increased.
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  • Jun Kurobe, Manabu Iguchi
    2004 Volume 68 Issue 9 Pages 800-806
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The dispersion of melted ingots in a continuous hot dip plating bath was investigated using a transparent cold model vessel with a reduced scale of one-tenth. The used tracers were CaCO3 particles with a mean diameter of 1.0 μm and 5.0 mass%KCl aqueous solution. The dispersion of the CaCO3 particles in the bath was observed by eye inspection. The mixing time and the local concentration of the two kinds of tracers were measured with an electrical conductivity sensor and a Laser beam sensor. The dispersion of the CaCO3 particles was mainly controlled by the main stream of liquid caused by the motion of the belt in the bath. The mixing time and the local concentration of the tracer were dependent on the measurement position. The mixing time was shortest when the tracer was introduced in the exit region, i.e., the belt out-going region. This fact suggests that the mixing time in the real bath is shortest by introducing ingots into the exit region.
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  • Jun Kurobe, Manabu Iguchi
    2004 Volume 68 Issue 9 Pages 807-814
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The melting process of a Zn ingot in the continuous hot dip plating bath was investigated using an ice prism simulated with Nusselt number and a transparent cold model vessel with a reduced scale of one-tenth. The ice prism was used as a model for the Zn ingot. The Nusselt number similitude was selected to determine the size of the ice prism. The melting process of the ice prism fixed in the entry region was observed with a high-speed video camera. The local heat transfer coefficient around the ice prism was calculated from the local melting rate of the prism. The mean flow velocity and the root-mean-square (r.m.s.) value of the turbulence component of water flow approaching the ice prism were measured with a hot-wire anemometer. The mean heat transfer coefficient calculated by averaging the local heat transfer coefficients over the entire surface of the ice prism was hardly dependent on the turbulence intensity under the Reynolds number range considered. The turbulence intensity was defined as the ratio of the r.m.s. value of the turbulence component to the mean flow velocity.
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  • Jun Kurobe, Manabu Iguchi
    2004 Volume 68 Issue 9 Pages 815-824
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The fluid flow phenomena of plating melt, the motions of dross, and the dispersion of melting ingots in a continuous hot dip plating bath were investigated using a transparent cold model vessel with a reduced scale of one-tenth. This model was equipped with a snout and two support rolls. Water was used as a model for the plating melt. The flow pattern in the bath was basically the same as that in the bath without the snout and the support rolls, but re-circulating flows caused by the existence of the snout were observed in the entry region and in the region enclosed with the belt. Water supplied in the snout through the passage above the sink roll was carried by the belt and exhausted into the entry region. Most top dross and bottom dross were carried by the main flow in the entire bath. A part of the top dross floated on the bath surface and a part of the bottom dross accumulated on the bottom of the bath. The dispersion of tracer, being a model for melted ingots, was mainly controlled by the main flow. The local mixing time in the presence of the snout and the support rolls was approximately the same as that measured in the absence of them.
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  • Yasunori Miyata, Manabu Yamamoto, Yasusi Fukuzawa
    2004 Volume 68 Issue 9 Pages 825-830
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Arrayed growth of dendrite is studied analytically in highly supercooled melt. The proposed model takes into account the effect of interfacial shape of dendrite tip, the array of dendrite and the area of dendrite tip. Predictions are compared with experimental results in the solidification of organic alloy. A dendrite is shown to grow almost freely (unconstrained) with other dendrites in lowly supercooled melt, but constrained in highly supercooled melt.
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  • Shintaro Ishiyama, Hans. Peter. Buchkremer, Dovert. Stöver
    2004 Volume 68 Issue 9 Pages 831-837
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    NiAl intermetallics with dispersive Cr particles consolidated by the Hot Isostaic Press (HIP) and Reactive HIP (RHIP) techniques, has been investigated. Mechanical properties of HIPed and RHIPed materials with various Cr concentrations ranging form 0 to 30 mass%Cr, were examined at various temperatures. The consolidation temperature of RHIP materials decreases with Cr addition; when RHIPing NiAl+xCr compounds with 25 mass% has attained, remarkable high ductility over 17% elongation and over 400 MPa tensile strength at 873 K. A very high tensile strength of HIPed NiAl+20 wt.%Cr about 600 MPa with 10% elongation was achieved at 673 K.
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  • Kenichi Nakajima, Yohji Uchiyama, Kohmei Halada
    2004 Volume 68 Issue 9 Pages 838-843
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    New method of environmental load estimation for scraps and by-products production in Life cycle inventory (LCI) based on Input-Output table (I/O table) has been developed. And a new description method of I/O table with scraps and by-products sections for the estimation is developed. In this study, both scraps and by-products are regarded as products, and are dealt with as an independent section in I/O table, respectively. By means of this method, the energy consumption and CO2 emission of process-scrap steel production are estimated as an example study. And a weighted average value of energy consumption and that of CO2 emission with consideration to the monetary amounts of production of industrial-scrap steel were calculated by using the estimated data, respectively.
    Moreover, a reliability of the estimated data is analyzed. And LCI of converter steel and EAF steel are done in order to evaluate an influence by differences of data. As a result, when the value of industrial scrap was assumed to be zero, the energy consumption rates of zero against the maximum is estimated 0.5% for the converter steel, and 20.4% for the EAF steel, respectively. Therefore, in case of converter, it is possible to treat the environmental load of a process scrap for nothing in approximation.
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  • Hideo Abe, Atsushi Kondo, Tohru Watanabe
    2004 Volume 68 Issue 9 Pages 844-850
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In a previous report, the age softening phenomenon of the copper electrodepostits obtained from a copper sulfide plating solution containing a hardener was studied using hardness and SIM measurements. Here results on the continuation of the study of this phenomenon are presented. It was found that for Cu/Ni base plate, the phenomenon called “age softening” at room temperature could be inhibited by adding a polymer containing nitrogen in a concentration of 30 mg/L or above to the plating solution. At 60°C, a concentration of 60 mg/L or above was necessary to inhibit the age softening. It was found that the orientation 100 of the electrodeposits is strengthened in preference to the age softening. On the other hand, adding a concentration of 120 mg/L or above of SPS to a plating solution promotes the age softening at 60°C.
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