All issues
Volume 66, Issue 4
Displaying 1-34 of 34 articles from this issue
- |<
- <
- 1
- >
- >|
-
Kyoji Tachikawa, Akihiko Nagata, Kazumasa Togano2002 Volume 66 Issue 4 Pages 199-200
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDownload PDF (162K) -
Shinji Matsumoto, Tsukasa Kiyoshi, Hitoshi Wada2002 Volume 66 Issue 4 Pages 201-206
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAt the Tsukuba Magnet Laboratory of the National Institute for Materials Science, we have been developing a 1 GHz NMR magnet since 1995. One of the objectives of the magnet is to apply it to determine the stereoscopic structure of protein molecules and to identify the chemical-reacting part between proteins and candidate medicines. The magnet is designed to generate a central field of 23.5 T. An HTS inner coil is expected to generate 2.4 T in the backup field of 21.1 T generated by outer LTS coils. BSCCO superconductors have been considered to be the most promising candidates for fabricating the inner coil from the viewpoints of high-field generation and fabrication wires. The superconducting magnet including two Bi-2212 inner coils made of double pancakes succeeded in generating a central magnetic field of 23.4 T. Bi-2212 long wires have made it possible to wind the inner coil without a joint for a high-resolution NMR spectrometer, the fluctuation of the field (stability of the field) must be less than 0.01 ppm/h. It is too difficult for the present BSCCO superconductors to satisfy this requirement because their n-index values are less than 15. In this paper, we introduce requirements for the inner coil of the 1 GHz NMR magnet and the present status of Bi-2212 inner coil.View full abstractDownload PDF (494K) -
Hiroshi Fuji, Teruo Izumi, Yuh Shiohara2002 Volume 66 Issue 4 Pages 207-213
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA lot of effort has been made to develop superconductive wires/tapes which are beneficial for many industrial applications. Especially, the next generation coated conductors using RE123 (RE=Rare earth element, Y, Nd, Sm etc) materials have high expectations, because of its high critical current density at the liquid nitrogen temperature and under high magnetic fields. Recently, several processes have been tried for obtaining the bi-axially textured buffer layers/metal substrates and depositing superconductors on these substrates, consequently a 10 m long YBCO tape with high Jc was successfully fabricated by several processings. This paper reviews the prospects of the research and development for the coated conductor with comparing the recent progress in Japan and the United States.View full abstractDownload PDF (999K) -
Hiroaki Kumakura, Akiyoshi Matsumoto, Hiroki Fujii, Kazumasa Togano2002 Volume 66 Issue 4 Pages 214-222
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSRecent development of MgB2 tapes and wires fabricated by a powder-in-tube method is reviewed. Two methods are now being applied to fabricate MgB2 tapes and wires for the powder-in-tube method. One is to use MgB2 compound powder and the other is to use Mg+B mixed powders with stoichiometric composition. Commercial MgB2 compound powder is used as a starting material for the first method. Stainless steel, Fe, Cu-Ni alloy and Cu tubes are used as sheath materials. Jc of the as-cold rolled (un-sintered) tape increases with increasing the hardness of the sheath material. Un-sintered MgB2/(stainless steel) tapes showed an extrapolated Jc of ∼4.5×109 A/m2 at 4.2 K and zero field. Annealing after the cold rolling is effective to enhance Jc values. Extrapolated Jc higher than 1010 A/m2 at 4.2 K and zero field was reported for MgB2/Fe tapes annealed at 1223 K after the cold rolling. Multifilamentary (7-core) MgB2 tapes and wires were successfully fabricated by using Cu-Ni tubes. These tapes and wires showed Jc of ∼3×108 A/m2 at 4.2 K and self-field. For the second method, heat treatment after the cold working is essential. Thus, we have to use sheath material that is not reactive with Mg and B. Ta and Fe tubes are used to fabricate MgB2 tapes. MgB2/Ta tapes heat-treated at 1473 K showed Jc of ∼2×109 A/m2 at 4.2 K and self-field. This Jc is much higher than that of the conventionally heat-treated MgB2 bulk. More excellent Jc values were reported for Fe-sheathed tapes. Jc of 3×109 A/m2 at 20 K and self-field was obtained for the MgB2/Fe tape heat-treated at 1173 K. However, the Jc values of MgB2 tapes and wires have not reached the practical level yet. Further research and development are required to improve the current carrying properties.View full abstractDownload PDF (1025K) -
Kyoji Tachikawa, Ryuichi Kato, Makoto Aodai, Takao Takeuchi2002 Volume 66 Issue 4 Pages 223-228
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSNb3Sn superconductors with excellent high-field performance are prepared by the reaction between the Ta-Sn core and the Nb (Nb-Ta) sheath. The mechanism of the formation of thick Nb3Sn layers by the reaction has been studied. No stable compound richer in Sn exists in the Ta-Sn system, and Sn has stronger affinity to Nb than to Ta. Furthermore, Nb in the sheath diffuses into the core at the reaction. These seem to be possible origins for the enhancement of the diffusion of Sn from the core to the sheath synthesizing thick Nb3Sn layers. Ta in the core is incorporated into the Nb3Sn layer at the reaction. Subsequently, the effect of the Cu addition to the Ta-Sn core of the composite has been studied. The Cu addition appreciably decreases the reaction temperature, and reduces the grain size of Nb3Sn. The Cu addition enhances the Jc in lower field, while it reduces the Jc in higher fields. A variety of Jc versus magnetic field performance can be obtained by adjusting the amount of Cu addition to the core. The amount of Cu addition and the Ta:Sn ratio in the core, as well as the reaction temperature of the specimen have been optimized. The development of Nb3Sn conductors capable of generating fields over 20 T at 4.2 K seems to be promising through the present process.View full abstractDownload PDF (768K) -
Yasuo Iijima, Akihiro Kikuchi, Kiyoshi Inoue2002 Volume 66 Issue 4 Pages 229-235
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn 1993, we proposed an RHQT(Rapid-Heating/Quenching and Transformation)-process in order to improve superconducting properties of a Nb3Al multifilamentary wire. The RHQT-processed Nb3Al multifilamentary wire shows not only a superior strain tolerance but also 2-5 times larger Jc (15-23 T, 4.2 K) than those of the bronze-processed (Nb, Ti)3Sn multifilamentary wire. However, its Tc and Bc2 are nearly the same as those of the (Nb, Ti)3Sn wire, and still lower than those of the stoichiometric Nb3Al.
Recently, we found that the Cu-addition caused some significant improvements on the superconducting properties of Nb3Al wire. In the new process, Nb/Al-Cu multifilamentary microcomposite wires were heat treated by using the rapid heating and quenching (RHQ)-apparatus. During the RHQ-treatment, disordered A15 filaments were directly formed instead of the supersaturated bcc filaments in the ordinary RHQT-process without Cu addition. With annealing at 973-1073 K, their superconducting properties improved drastically with the improvement of long-range ordering of A15 crystal structure. The Cu-added Nb3Al wire showed maximum values of Tc=18.3 K and Bc2(4.2 K)=29.2 T, which are nearly the same as those of the stoichiometric Nb3Al, and are much higher than the maximum values of Tc=17.9 K and Bc2(4.2 K)=25.8 T for the RHQT-processed Nb3Al wire without Cu addition.
In addition, Jc(19 T, 4.2 K) of the Cu-added Nb3Al wire is 1000 A/mm2, which is about 10 times larger than that of the commercialized (Nb, Ti)3Sn wire. Therefore the Cu-added Nb3Al wire is a very attractive superconductor for high-field applications. Through TEM observations we found many stacking faults in the Cu-added Nb3Al, while no stacking fault in the diffusion processed Nb3Al. The Cu-addition seems to make the Nb-Al supersaturated bcc phase unstable, and cause the transformation from bcc to A15 during the quenching. Then the transformation occurs at very high temperature with very short duration, resulting in excellent values of Tc, Bc2 and Jc in the Cu-added Nb3Al.View full abstractDownload PDF (975K) -
Satoru Murase, Tomoyuki Tsukii, Tsuyoshi Wakasa, Susumu Shimamoto2002 Volume 66 Issue 4 Pages 236-241
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSNb3Sn compound superconducting wires and Ag sheathed Bi system high Tc wires used for high-field magnet applications are composite superconductors which consist of a superconductor, a stabilizer, a matrix, and a reinforcement. The composite superconductor is subjected to temperature difference in around 1000 K between high temperature where the superconducting layer is formed and cryogenic temperature where the conductor is operated. As each component material which construct the composite superconductor has different thermal expansion coefficient, it is subjected to thermally-induced residual strain. To clarify those strains behavior, we analyzed elastically 3-D strains in the composite superconductors, radial and tangential directions in the cross-sectional plane added to longitudinal direction using a multiple cylindrical model.
Strains in radial and tangential directions varied with combination of component materials having large and small thermal expansion coefficients. If the superconducting layer was placed on the middle or outer cylindrical layer, the strains in the radial tangential directions were to be affected by magnitude of the thermal expansion coefficient of the neighboring component.View full abstractDownload PDF (406K) -
Akiyoshi Matsumoto, Hiroaki Kumakura, Hitoshi Kitaguchi, Kazumasa Toga ...2002 Volume 66 Issue 4 Pages 242-246
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe relationships between a critical current density (JC) and microstructure of Bi-2212/Ag composite tapes prepared by the melt-solidification under a temperature gradient have been investigated. We used a tube furnace with a temperature gradient for the heat treatment. The critical current density (JC) of the order of 4×109 A/m2 at 4.2 K under 10 T were obtained for the tape fabricated under a temperature gradient. We optimized the tape width, temperature gradient and cooling rate in melt-solidification process. The optimum tape width, temperature gradient and cooling rate were 2-4 mm, 200 K/m, and 2 K/h, respectively. JC enhancement of these tapes fabricated by melt-solidification under temperature gradient was attributed the improvement of the c-axis grain alignment, the in-plane texturing near the oxide/silver interface, and large grain size.View full abstractDownload PDF (1034K) -
Takeshi Hatano, Yoshihiko Takano, Akihiro Fukuyo, Masashi Ohmori, Akir ...2002 Volume 66 Issue 4 Pages 247-253
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAn oxygen stream is known to be a crucial condition for the growth of Bi2212 whiskers. However, we have succeeded in the growth of whiskers without oxygen stream. The straightness and surface morphologies of the whiskers have been improved by the growth under the equilibrium Bi-O atmosphere in the nearly airtight crucibles. We studied intrinsic Josephson effects in twist junctions fabricated by overlaying two pieces of whisker in crosswise and S-shaped junctions fabricated by focused ion beam. The former showed a d-wave symmetry in their J′cs as a function of cross angles and the latter showed three excited states in the current-voltage characteristics which might correspond to the relation between the current-driven Josephson vortices and Josephson plasma.View full abstractDownload PDF (983K) -
Xiaoye Lu, Akihiko Nagata, Kazuo Watanabe, Tsutomu Nojima, Kazuhisa Su ...2002 Volume 66 Issue 4 Pages 254-259
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe microstructure and critical current densities of Bi-2223 superconductor with Ag2O and MgO additions after partial-melting and solidification in high magnetic fields were investigated. It has been found that the Bi-2212 grains with their c-axis parallel to the magnetic field are formed after partial-melting and solidification in 8 T magnetic field, and transform into the Bi-2223 grains with c-axis alignment during the further sintering process at 1113 K in zero magnetic field. The optimum partial-melting temperatures Tmax of non-added, 5 mass%Ag2O and 5 mass%MgO added samples are 1147 K, 1143 K and 1153 K, respectively. 5 mass%Ag2O and 5 mass%MgO additions enhance the c-axis alignment of (Bi, Pb)-2223 phase. The largest Jc value appears in the 5 mass%MgO added sample with Tmax=1153 K. MgO particles homogeneously disperse in the oriented (Bi, Pb)-2223 platelets. The MgO added sample has small non-superconducting second phase particles, whereas the Ag2O added sample has large second phase particles.View full abstractDownload PDF (1212K) -
Kazumasa Iida, Junko Yoshioka, Tomokazu Negichi, Naomichi Sakai, Koshi ...2002 Volume 66 Issue 4 Pages 260-266
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTwo blocks of single grain Y-Ba-Cu-O superconductors were welded with various solder materials that have lower decomposition temperature than that of Y-Ba-Cu-O superconductors. Microstructural analyses revealed that no segregation of the secondary phase and/or the residual liquid phase was observed at the joint when the (110) surfaces were directed parallel to the welded region. We also found that Y-Ba-Cu-O joined with a sintered Y-Ba-Cu-O/Ag bar exhibited the strongest coupling.View full abstractDownload PDF (2268K) -
Kosuke Nagashio, Kazuhiko Kuribayashi2002 Volume 66 Issue 4 Pages 267-273
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSContainerless solidification of YBa2Cu3O7−δ(Y123) and NdBa2Cu3O7−δ(Nd123), which are representative of stoichiometric compounds and compounds with solid solution, respectively, was performed in order to investigate the effects of the oxygen pressure on the direct growth behavior of Y123 and Nd123 from the undercooled melt. In the case of Nd123 samples, the dendritic morphology of the Nd123 phase indicates that the Nd123 phase solidified directly from the undercooled melt, which was independent of the oxygen partial pressure. On the other hand, the Y4Ba3O9(Y430) phase, the metastable high temperature phase, solidified as a primary phase at Ar and air gas atmosphere in the Y123 samples. Containerless solidification in oxygen gas flow allowed the direct growth of the Y123 phase, suppressing the primary solidification of the Y430 phase. The mechanism for the direct growth of the Y123 phase is mainly associated with the instability of the Y430 phase at oxygen gas atmosphere. Moreover, the difference in the direct growth behavior in the Y123 and Nd123 systems is understood by the difference in the high temperature phase: the Y430 phase for the Y123 system and the Nd2BaO4 phase for the Nd123 system.View full abstractDownload PDF (1145K) -
Masaru Tomita, Masato Murakami2002 Volume 66 Issue 4 Pages 274-278
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWe have recently succeeded in improving the mechanical properties of bulk Y-Ba-Cu-O superconductors through resin impregnation. In order to clarify the effect of resin impregnation on the mechanical properties, we first measured the adhesive force between resin and bulk superconductors using the tensile test. It was found that the adhesive force is larger than the strength of bulk materials. We also measured the rupture strength of Y-Ba-Cu-O rods having artificial groove filled with and without epoxy resins using a three point bending test. The rupture strength was reduced by introducing the groove. In contrast, the sample with the groove filled with resin exhibited higher rupture strength than that of virgin bulk materials. These results suggest that the improvement of mechanical property through resin impregnation is ascribed to the prevention of crack propagation along the cleavage plane due to the presence of resin.View full abstractDownload PDF (564K) -
Tetsuji Honjo, Hiroshi Fuji, Yuichi Nakamura, Teruo Izumi, Yuh Shiohar ...2002 Volume 66 Issue 4 Pages 279-283
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA MOD-TFA process using the multi-coating method was applied to form thicker Y123 films on LaAlO3 substrates, and the dependence of the low partial pressure of H2O, P(H2O), for Y123 growth was investigated. As a result, it was found that the crystal alignment of thicker Y123 films could be improved by optimizing the P(H2O). In particular, for a thicker film, it was found that low P(H2O) during the Y123 growth is effective in maintaining expitaxial growth. Consequently, the critical current value for 0.01 m wide (Ic*) of the triple-coated film was increased from 11 kA/m-width to 28 kA/m-width in comparison with that of the single-coated film. Further, it was confirmed that the high in-plane aligned buffer layers is necessary to obtain a high critical current density (Jc) film on a metal substrate. Subsequently, the heat treatment under the low P(H2O) was applied to the CeO2/IBAD-YSZ/Hastelloy substrates using the multi-coating method. The triple-coating Y123 film with 1 μm thickness on the metal substrate achieves the Jc value of 16 GA/m2 at 77.3 K in self fields and the Ic* performance of 15.3 kA/m-width.View full abstractDownload PDF (737K) -
Ryota Takahashi, Kyung Sung Yun, Yuji Matsumoto, M. Kawasaki, Toyohiro ...2002 Volume 66 Issue 4 Pages 284-288
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA high-Tc superconducting (HTSC) thin film with single crystal quality and atomically flat surface is a basic requirement for the fabrication of HTSC electronic devices. Despite extensive effort since the discovery of high-Tc superconductivity, this requirement has not been fully satisfied yet. Based on our experience on HTSC thin film growth, we proposed a novel fabricating method of single crystal RBa2Cu3O7−δ(R=Y, Nd) thin films that are free from grain boundaries and have atomic scale surface smoothness. This method was devised in view of the thermodynamic phase diagram of RBa2Cu3O7−δ and the characteristics of vapor phase epitaxy (VPE). Since gas, liquid and solid phases are involved in this film growth, it is denoted Tri-Phase Epitaxy(TPE). Giant single crystal grains, verified by X-ray diffraction and transmission electron microscopy (TEM), should provide a big advantage for the use of these films in such applications as high frequency transmission lines and superconducting tunnel junctions.View full abstractDownload PDF (731K) -
Katsumi Nomura, Saburo Hoshi, Tomoaki Yamada, Atsushi Inoue, Yuichi Na ...2002 Volume 66 Issue 4 Pages 289-296
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGrowth conditions for liquid phase epitaxy (LPE) growth were investigated in order to grow a large REBa2Cu3Oy(REBCO, RE=Y, Yb) film with high quality. Both a thermal stability of the seed film and an appropriate supersaturation to avoid any undesired nucleation should be maintained to grow a high quality film. Especially in the case of growing a large film, it was suggested that the peritectic temperature (Tp) of a grown crystal should be lower than that of the seed film to satisfy the above requirements. We selected a (Y, Yb)BCO mixed crystal system to grow from the YBCO seed film, since the Y1−xYbxBa2Cu3Oy system is a homogeneous solid solution, and the Tp decreases with increasing the x value. A large LPE film of 2-inch in diameter was successfully grown. The composition of the film grown in this work was confirmed to be Y0.86Yb0.14Ba2Cu3Oy. The growth rate distribution along the lateral direction of the film was observed, which was enhanced with increasing the rotation rate during the growth. This phenomenon could be explained by the heat flux from the hot region in the liquid due to the forced convection, which might be stronger for the case of rotating a large substrate. The grown film had both a high crystallinity and its high in-plane uniformity. The films also exhibited excellent superconducting properties with a critical temperature of 92 K and a critical current density of over 109 A/m2 at 77 K in 0 T. These characteristics satisfy the requirements for the substrate of the future superconducting devices.View full abstractDownload PDF (662K) -
Motohide Matsui, Naomichi Sakai, Masato Murakami2002 Volume 66 Issue 4 Pages 297-301
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of Nd422 content on the trapped field was studied for Nd-Ba-Cu-O superconductors. The molar ratio of Nd123 and Nd422 was changed from 10:1.5 to 10:3 in the initial composition. Nd bulk superconductors were fabricated in 1%O2-Ar atmosphere using the TSMG (Top-Seeded Melt-Growth) method. The large segregation of Nd422 particles at the periphery of the bulk was observed with increasing Nd422 content, leading to the less symmetrical trapped-field distribution which was affected by the inhomogeneous microstructures and superconducting properties. Furthermore, the Jc values in low and intermediate field regions were improved with decreasing Nd422 content because of the increase of field induced pinning centers. Therefore, the remanent trapped field value increased with decreasing Nd422 content and also the highest trapped field of 1.4 T was achieved in the sample with a molar ratio of Nd123:Nd422=10:1.5 with 20 mass%Ag2O at 77 K. However, cracking was introduced in large grain samples with small Nd422 content, which could be prevented by increasing Ag2O content from 10 to 20 mass%. Furthermore, the secondary peak effect was observed in the field dependence of a trapped field, showing that the field induced pinning is active in large grain samples.View full abstractDownload PDF (1098K) -
Kei Ogasawara, Naomichi Sakai, Masato Murakami2002 Volume 66 Issue 4 Pages 302-308
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWe have studied the microstructures of subgrains in large-grain RE123 (RE=Y, Sm) bulk superconductors through microscopic observation and x-ray pole figure analyses. For the samples grown by slow-cooling, misorientation of the subgrains increases along with the crystal growth, and also that the misorientation has positive relation to the size and concentration of the second-phase particles. For isothermally grown samples, subgrains are likely to form under large undercooling. We discuss the possible mechanism of subgrain formation. Such subgrains are considered to affect current carrying capabilities in bulk materials, so that we performed magnetic and electric measurements for several samples having different subgrain structures. The results of Jc-B and AC transport measurements indicated that the subgrains act as weak-links, especially under high magnetic fields.View full abstractDownload PDF (1745K) -
Shinya Nariki, Naomichi Sakai, Motohide Matsui, Masato Murakami2002 Volume 66 Issue 4 Pages 309-314
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of Ag addition on the microstructure and the mechanical and field trapping properties of Gd-Ba-Cu-O bulk superconductor has been investigated. The single grain Gd-Ba-Cu-O bulk superconductors 32 mm in diameter were fabricated with 0-30 mass%Ag2O additions by the melt growth method under controlled oxygen partial pressure of 1.0%. From microscopic observations, it was found that the macro-cracks in the a-b plane decreased with Ag addition. The three-point bending test showed that the average strength of Ag-free bulk was 69 MPa at room temperature, while the strength was dramatically improved to 110-115 MPa with 10-30 mass%Ag2O additions. The trapped magnetic field of Ag-free bulk sample was 1.3 T at 77 K. The trapped field of bulk Gd-Ba-Cu-O samples with 10-20 mass%Ag2O exhibited high values of 1.8-2.0 T at 77 K. However, the trapped field of the sample with 30 mass%Ag2O addition was lowered to 1.1 T with decreasing the critical current density. The trapped field of Ag-added sample did not deteriorate with thermal cycles. The trapped fields at lower temperatures were also measured for the Ag-free and 20 mass%Ag2O added bulk samples without reinforcement by the metal ring or resin. The Ag-free bulk exhibited the trapped field of 3.0 T at 65 K, however, the bulk was fractured at lower temperature due to an electromagnetic force. On the other hand, the Ag-added bulk could trap the higher field of 6.7 T at 55 K, thanks to the improvement in mechanical strength.View full abstractDownload PDF (1086K) -
Shinya Nariki, Naomichi Sakai, Masato Murakami2002 Volume 66 Issue 4 Pages 315-319
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of Dy2BaCuO5 (Dy211) contents on the field trapping properties of Ag-added DyBa2Cu3Oy (Dy123) single domain bulk has been investigated. The Dy-Ba-Cu-O/Ag bulks 32 mm in diameter with different Dy211 contents were fabricated in air with the top-seeded melt-growth method using NdBa2Cu3O7 seed crystal. The trapped magnetic fields were measured as a function of external field and compared with the Jc-B properties, in that a similar field dependency was observed. In the case of the Dy123 bulk with excess 5 mol% Dy211, the peak was found at around 0.5-1.5 T of external field in the trapped field measurement at 77 K. The value of trapped field was 1.2 T at the peak field. This result reflects the secondary peak effect in Jc-B properties of the bulk samples. On the other hand, the trapped field of Dy123 bulk with excess 40 mol% of Dy211 exhibited 1.4 T when the applied field was removed. This value monotonously decreased with increasing external field, since this sample showed no secondary peak effect in Jc-B properties.View full abstractDownload PDF (656K) -
Katsuya Hasegawa, Natsuro Hobara, Yuichi Nakamura, Teruo Izumi, Yuh Sh ...2002 Volume 66 Issue 4 Pages 320-328
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSPreparation of SmBa2Cu3Oy(Sm123) and BaZrO3(BZO) films by pulsed laser deposition was investigated using MgO single crystalline substrates. Highly c-axis oriented Sm123 films with a four-fold symmetry were successfully deposited on MgO single crystals, which had a Tc onset of 93 K and a zero resistance at 89 K. The BZO buffer improved in-plane alignment of the Sm123. In addition, highly textured BZO and Sm123 films were realized on in-plane aligned MgO films grown by inclined substrate deposition. The FWHM(full width at half maximum)’s of in-plane and out-of-plane alignment for the textured Sm123 in the combination were reached 10.5° and 4.0°, respectively. The reason that the BZO was effective on the epitaxial growth of Sm123 films can not be explained only by the idea of a simple lattice match, since the lattice constant of BZO is close to that of MgO. The effect of the BZO buffer was discussed in view of the interface energy based on crystallographic consideration. It was found that a chemical bonding at the interface is important for interface energy as well as the lattice match. Further, the conception of the interface energy on hetero-epitaxial growth was applied for the c⁄a-axes orientation behavior of RE123.View full abstractDownload PDF (902K) -
Toru Izumi, Xin Yao, Masahiko Kai, Katsuya Hasegawa, Yoshitaka Tokunag ...2002 Volume 66 Issue 4 Pages 329-333
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSRE123 superconductive oxides are expected to be utilized for electric conductors due to its high superconducting performance at 77 K. The liquid phase epitaxy (LPE) process has an advantage to fabricate a thick superconducting layer at a high growth rate with high superconducting properties for realizing high Jc conductors. We tried two structures to fabricate in-plane aligned Y123 layer on textured Ni substrates with SOE-NiO. One was a double layered LPE structure and the other was a non-reactive buffered structure using a BaZrO3 buffer layer. The in-plane aligned Y123 LPE layer was successfully grown on an NiO/Ni textured substrate for each structure and the Tc value of 90 K was achieved in the non-reactive buffered structure. The in-plane alignment of the seed layer was found to be a crucial factor for the double LPE process since the partial dissolution of worse aligned seed crystals caused formation of non-coverage regions on the surface of the NiO buffer layer, where the NiO buffer layer would react with the solution during the second LPE processing.View full abstractDownload PDF (552K) -
Hiroshi Ikeda, Tamotsu Koyano, Takashi Arima, Kouzo Yoshikawa, Rozo Yo ...2002 Volume 66 Issue 4 Pages 334-338
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWe have investigated the transport and magnetic properties of the recently discovered superconducting MgB2. We obtained irreversibility temperature Tr(H) and irreversibility field Hr(T) from magnetic measurement and irreversibility field Bc2 from resistivity measurement. The irreversibility temperature Tr(H), was determined from the merging temperature of the magnetic moment observed in the zero field cooling (ZFC) process in to the one in field cooling (FC) process. We define the transport irreversibility line from the temperature at zero-resistivity in the presence of magnetic field. We also measured the magnetic relaxation of the remanent. The sample was cooled in zero field and the field above H*, where the flux front penetrated at the center of the sample. The time decay of the remanent moment was measured for about 105 s. The relaxation of the remanent moment showed the linear ln (t) dependence in the whole observed temperature range. Those results of the irreversibility lines are plotted in H-T plane. The magnetic irreversibility lines are consistent with each other, while the transport one locates at the higher temperature side.View full abstractDownload PDF (450K) -
Tohru Watanabe2002 Volume 66 Issue 4 Pages 339-349
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe author has investigated the relationship between the structure of the plated film and plating conditions for 12 pure metals and 28 binary alloys. The structure of the plated film can be discussed based on metallurgical structure, surface morphology, crystal size, crystallographic orientation, adhesion between the plated film and substrate, retained stress, and anomalous structure. The control mechanisms of these features can be independently explained, since there is an independent control theory for each feature. This paper explains the unique control theory for surface morphology of plated films proposed by the author. In discussing surface morphology, two cases must be considered separately: pure metals and alloys. Discussions of pure metal films can be further subdivided into those with low melting points and those with high melting points. Generally, the crystals of plated alloy films are small, and the surface morphology depends on the crystallographic structure of the alloy film. The roughness of the plated film increases with film thickness and is hardly influenced by current density. When the current density is low, the surface roughness dominates. When current density is high, the surface is relatively smooth for both pure metal films and alloy films. It is not due to over voltage. The type of anion in the plating bath influences the nature of the roughness.View full abstractDownload PDF (3371K) -
Tohru Watanabe2002 Volume 66 Issue 4 Pages 350-361
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe structure of a plated film can be classified based on the following seven features: metallurgical structure, surface morphology, crystal size, crystallographic orientation, adhesion between the plated film and the substrate, retained stress, and anomalous structure. The author has found that the control mechanisms of these structures can be independently explained. In other words, there is an independent control theory for each structure. This paper explains a unique theory on the crystal size of plated film proposed by the author. The crystal sizes of the pure metal plated film and alloy plated film must be discussed separately. The crystal size of a pure metal film mainly depends on the melting point of the metal. Crystals of metals with a low melting point are larger, and the crystal size agrees with the roughness of the film surface. However, crystals of metals with a high melting point are smaller, and the crystal size and the size of evenness do not always agree. The crystal size of alloy-plated films depends on the metallurgical structure in a complicated manner.View full abstractDownload PDF (4024K) -
Tohru Watanabe2002 Volume 66 Issue 4 Pages 362-370
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe structure of a plated film can be classified by the following seven characteristics: metallurgical structure, surface morphology, crystal size, crystallographic orientation, adhesion between the plated film and the substrate (epitaxy), retained stress, and anomalous structure. The author has found that the control mechanisms of these structures can be independently explained. In other words, there is an independent control theory for the each structure. This paper will explain the crystallographic relationship between the plated film and the substrate (epitaxy) in the above structures based on much experimental data. Because the plated film is a metallic material, the film and substrate always contact with a crystallographic relationship (epitaxial growth) when the substrate is also a metallic material. The crystallographic relationship ensures the lowest interface energy. The misfit caused by differences in the crystal system or lattice parameters between the plated film and the substrate is accommodated by producing misfit dislocations or misfit twin boundaries.View full abstractDownload PDF (2878K) -
Masayuki Mizumoto, Toshihisa Murano, Akio Kagawa2002 Volume 66 Issue 4 Pages 371-376
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSProcess parameters to control the microstructure of particle reinforced MMC in the low pressure infiltration process (LPI process), have been investigated. The mixed powder of reinforcement particle and pure Al powder in various volume fraction was employed to control volume fraction of particles in PRMMC. The Al-12 mass%Cu alloy melt was forced to infiltrate into the mixed powder bed by applying a certain pressure on the melt surface. The pressure required to infiltrate remarkably increased from 0.05 to 0.5 MPa with a decrease in the particle size from 100 to 20 μm, indicating that the pressure at the advancing melt surface decreased due to capillary force and friction force between melt and particle. In the microstructure of PRMMC obtained, the reinforcement particle was almost homogeneously distributed and a linear relationship was obtained between the volume fraction of reinforcement particle in the mixed powder and the area ratio observed on the microstructure. It was shown that a homogeneous particle distribution and accurate control of the volume fraction of reinforcement particles could be attained in the LPI process.View full abstractDownload PDF (977K) -
Yasuhiro Kawaguchi, Shinsuke Yamanaka2002 Volume 66 Issue 4 Pages 377-383
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCast duplex stainless steel is frequently used in main coolant pipes of PWR (Pressurized water reactor) type nuclear power plants because of its excellent material strength, toughness and superior corrosion resistance. However, it is known that material deterioration referred to as thermal aging occurs when this material is exposed to temperatures over 300°C. As a result, the material toughness decreases. Therefore, in managing the components made of cast duplex stainless steel, it is necessary to evaluate non-destructively such deterioration. In this study, measurement of thermoelectric power, which is sensitive to microstructural change in materials, was used for the evaluation of thermal aging. First, we investigated change in mechanical properties (hardness, tensile stress and notch toughness) due to thermal aging in cast duplex stainless steel. Secondly we measured thermoelectric power (TEP) and investigated change in TEP due to thermal aging and the effect of temperature of a specimen on TEP. Then the TEP was compared with the mechanical properties. As a result, TEP increases with aging time and the tendency becomes more remarkable as ferrite content increases. The increase in TEP of a specimen with 21.3% ferrite due to thermal aging (400°C-10000 h) is 0.61 μV/°C. The TEP slightly decreases with temperature of the specimen at a rate of about −0.009 μV/°C2. Finally we found good correlation between the TEP and ductile-brittle transition temperature, the TEP and notch toughness at 325°C. The correlation coefficients are respectively 0.886∼0.957 and −0.890∼−0.978. Therefore, by using TEP measurement, material deterioration of cast duplex stainless steel due to thermal aging can be evaluated.View full abstractDownload PDF (850K) -
Toshiaki Yoneoka, Toshiharu Sakurai, Toshihiko Sato, Satoru Tanaka2002 Volume 66 Issue 4 Pages 384-392
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAlN ceramics were a candidate for electrically insulating materials and facing materials against molten breeder in a nuclear fusion reactor. In the nuclear fusion reactor, interactions of various structural materials with solid and liquid breeder materials as well as coolant materials are important. Therefore, corrosion tests of AlN ceramics with molten lithium were performed. AlN specimens of six kinds, different in sintering additives and manufacturing method, were used. AlN specimens were immersed into molten lithium at 823 K. Duration for the compatibility tests was about 2.8 Ms (32 days). Specimens with sintering additive of Y2O3 by about 5 mass% formed the network structure of oxide in the crystals of AlN. It was considered that the corrosion proceeded by reduction of the oxide network and the penetration of molten lithium through the reduced pass of this network. For specimens without sintering additive, Al2O3 containing by about 1.3% in raw material was converted to fine oxynitride particles on grain boundary or dissolved in AlN crystals. After immersion into lithium, these specimens were found to be sound in shape but reduced in electrical resistivity. These degradations of the two types specimens were considered to be caused by the reduction of oxygen components. On the other hand, a specimen sintered using CaO as sintering additive was finally became appreciably high purity. This specimen showed good compatibility for molten lithium at least up to 823 K. It was concluded that the reduction of oxygen concentration in AlN materials was essential in order to improve the compatibility for molten lithium.View full abstractDownload PDF (1120K) -
Yubo Wang, Kazuhiro Matsugi, Osamu Yanagisawa2002 Volume 66 Issue 4 Pages 393-399
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFor application of “particle contact theory” proposed by several investigators for compaction using mono-sized spherical powder particles to that for powders of general shape and of general size distribution, metallographical method was carried out to obtain the constitutive equation for isostatic compaction of metallic powders. Comparing the obtained equation with experimental results, the approximated constitutive equation to represent the isostatic pressure, P, to densify powder aggregate from the initial relative density, D0, to the achieved relative density, D, is finally conducted as
(This article is not displayable. Please see full text pdf.)
\ oindentwhere σeq is equivalent stress at the contact surface having the value close to 0.2% proof yield stress of powder material. By mixing a lubricant in powder aggregate, the isostatic pressure to obtain the same relative density is smaller compared with that represented by the above equation.View full abstractDownload PDF (897K) -
Koichiro Inoue, Takeshi Nakata, Yoshiaki Shindo, Tohru Watanabe2002 Volume 66 Issue 4 Pages 400-408
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe crystallographic structure and surface morphology of Au films electrodeposited from two different baths, a cyanide bath and a sulfite bath, were studied by using SEM and XRD. The surface morphology and crystallographic orientation of Au films deposited on a Ni-P amorphous substrate were found to vary according to the electrodeposition bath composition. For Au films deposited in a cyanide bath, the {111} plane appeared to be a preferential orientation, independent of deposition conditions, such as current density, bath temperature and film thickness. However, Au films deposited in a sulfite bath, the preferential orientation varied with deposition conditions.View full abstractDownload PDF (2602K) -
Tsutomu Ito, Satoshi Shibasaki, Masayuki Koma, Masahisa Otsuka2002 Volume 66 Issue 4 Pages 409-417
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh temperature ductility of medium grained and single crystalline Al-6 mol%Mg solid solution alloys has been investigated. It is found that enhanced ductility occurs not only in polycrystalline specimens having grain diameter of 70 μm and 165 μm but also in single crystalline ones in the temperature range above 523 K; maximum elongation for 70 μm grained, 165 μm grained and single crystalline specimens are, respectively, 349%(at 723 K), 322%(at 723 K) and 326%(at 673 K). Experimentally determined strain rate sensitivity index of about 0.3, together with the activation energy for deformation, suggests the solute drag motion of dislocations as a rate controlling process, which in turn is accommodated by the grain boundary sliding. In other words, the high ductility observed here should be referred to as superplastic-like elongation, that is, the phenomenon that has been reported in some solid solution alloys with a large misfit parameter. The fact that the strain rate for largest elongation tends to increase with decreasing grain size may be ascribed to the relative increase in the contribution of grain boundary sliding to the total strain.View full abstractDownload PDF (1045K) -
Yasunori Miyata, Shigeru Nagasawa, Eiji Saito, Yasusi Fukuzawa2002 Volume 66 Issue 4 Pages 418-424
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe cell/dendrite to absolute stable transition of solid/liquid interface is investigated on the dilute copper aluminum alloy. Surface grazing by YAG laser at high scanning rate is used for the alloy. The solidified microstructure is observed by using the scanning election microscope (SEM). The solidification rate and the temperature gradient are estimated by the finite element program, which performs for the thermal conduction analysis. The interface has changed its morphology from cell to planer interface at the transition with increasing in growth rate. Near the absolutely stable growth rate, the primary arm spacing decreases with the increase of solute concentration. The observed primary arm spacing is compared with those predicted by theory for cellular growth.View full abstractDownload PDF (1172K) -
Kyu Seop Park, Kazutaka Matsumura, Hiroshi Fukutomi2002 Volume 66 Issue 4 Pages 425-430
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh temperature uniaxial compression tests in the alpha single-phase region were carried out on the Ti-43 mol%Al intermetallic compound in order to obtain oriented lamellar microstructure. The compression deformation temperatures and strain rates were from 1573 to 1623 K and 1.0×10−4 to 5.0×10−3 s−1, respectively. Fully lamellar microstructures were observed after uniaxial compression deformation in the α single phase region followed by cooling to room temperature. The lamellar colony diameter depended on strain rate and test temperature. The diameter varied between 860 μm and a 300 μm. Stress-strain curves showed work softening and the size of lamellar colony diameter varied depending on peak stresses. This suggests the occurrence of dynamic recrystallization. Texture measurements after uniaxial compression deformation showed the development of fiber texture during dynamic recrystallization. It is seen that the maximum pole density existed in 35 degrees away from the compression plane. The texture sharpens with the decrease in strain rate.View full abstractDownload PDF (756K)
- |<
- <
- 1
- >
- >|