巻号一覧
74 巻, 7 号
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特集「超伝導材料における組織制御技術の高度化 ―実用化を目指して―」
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熊倉 浩明, 松本 要, 太刀川 恭治2010 年 74 巻 7 号 p. 393
発行日: 2010年
公開日: 2010/07/01
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林 和彦2010 年 74 巻 7 号 p. 394-403
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーBismuth based high temperature superconductor has discovered by Dr. Maeda at NIMS (National Institute for Materials Science). Just after the discovery of this material, Sumitomo Electric has carried out the R&D on long length and high performance wire, and many application prototypes for more than 20 years. As a wire manufacturing technology, CT-OP (controlled over pressure sintering) process is very effective to make high performance wire. Power cable and ship propulsion motor applications using bismuth based superconducting wire are highly expected.
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松本 明善, 北口 仁, 熊倉 浩明, 引地 康雄, 仲津 照人, 長谷川 隆代2010 年 74 巻 7 号 p. 404-408
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーBi2212 round wires are one of candidates for application in high magnetic fields and low temperatures because of its high performance of Jc. Furthermore, round wires are suitable to make complicated coils and Rutherford cables. Bi2212 round wires are fabricated by simple heat treatment process of partial melting and slow cooling. However, the Jc values are sensitive to reaction temperatures, especially maximum reaction temperature (Tmax). In this research, we fabricated Bi2212 round wires with different compositions. We prepared four powders with the nominal compositions of between Bi=2.00 and Bi=2.25. Highest Ic value of 260 A (Jc=200 A/cm2) at 4.2 K and 10 T were obtained in Bi2.25 sample with Bi rich composition. From the observations of microstructures, we observed small amount of bridging of filaments in high Ic sample. To understand the growth mechanism of bridging, we report the results of quench experiments during heat processing.
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—不純物ナノロッドの微細構造と成長機構—一瀬 中, 松本 要, 向田 昌志, 吉田 隆, 喜多 隆介, 堀井 滋2010 年 74 巻 7 号 p. 409-415
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーMicrostructures of impurity nanorods as a c-axis correlation pinning centers in REBa2Cu3Oy films (RE: rare earth elements) have been examined by transmission electron microscopy (TEM). On the basis of the microstructure analyses, the possibility of controlling nanorod structures such as diameter and density was discussed. Furthermore, narnorod growth mechanism was discussed in relation with superconducting film growth. As a result, the formation of nanorods was affected by the stress fields generated by differences of crystal length between the superconductors and impurity materials. The various nanorod structures by changing impurity materials or growth conditions could be explained using the segregation coefficient.
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吉田 隆, 舩木 修平, 一野 祐亮, 高井 吉明, 松本 要, 一瀬 中, 向田 昌志2010 年 74 巻 7 号 p. 416-421
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーIn order to improve a critical current density under applied magnetic fields, an addition of BaMO3 (BMO; M=Zr, Sn) nanorods into REBa2Cu3Oy (REBCO) films is actively discussed. Although superconducting properties of the REBCO films are dramatically enhanced by self-assembled BMO nanorods, the growth mechanisms of the BMO nanorods have not been clarified yet. In this study, in order to clarify the growth mechanisms of the BZrO3 (BZO) nanorods and to further improve the superconducting properties, we fabricated a BZO-doped Sm1+xBa2−xCu3Oy (Sm+BZO) film by using modified Vapor-Liquid-Solid (VLS) technique (VLS-Sm+BZO/i). From the surface morphologies, there are BZO particles grown at step in the spiral growth measured by Br-etched VLS films doped with BZO. In general the impurity-related phase was pinning of growth fronts on REBCO films on substrate. Thus, we can conclude the variation of the surface morphology in VLS films is explained, not by the difference the step energy, but impurity phase could be responsible for the pinning and bending of different growth fronts, resulting in the formation of screw dislocations. From the plan-view TEM images, VLS-SmBCO+BZO film is approximately 9 nm in diameter of BZO nanorods, whereas VLS-SmBCO+BZO/i film is 7-8 nm. To create the BZO nano island/dots on the seed layer introduced the increase of the density of BZO nanorods. From the cross-sectional TEM images, columns of BZO nanorods aligned along [001] or the c-axis of SmBCO are clearly seen in the VLS films. Columnar BZO structures growing from the substrate to the surface have been observed. Nano BZO particles grown on the seed layer remained after the VLS growth. Nano BZO rods separated by 5 nm SmBCO spacer layers are shown to exhibit self-organized growth along c-axis of SmBCO.
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尾崎 壽紀, 吉田 隆, 一野 祐亮, 高井 吉明, 一瀬 中, 松本 要, 堀井 滋, 向田 昌志, 高野 義彦2010 年 74 巻 7 号 p. 422-427
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーIn BaZrO3(BZO) doped REBa2Cu3Oy(REBCO) films deposited by pulsed laser deposition, BZO nanorods grow almost parallel to c-axis in REBCO films. In this study, in order to understand the mechanism for the formation of BZO nanorods, we investigated the influence of the substrate temperature of the upper layer (Tsupper) in the low temperature growth (LTG) technique on the growth of BZO nanorods in SmBa2Cu3Oy(SmBCO) films. Furthermore, we discussed the diffusion process on BZO and estimated the activation energy for surface diffusion of constituent atoms in BZO. With decreasing Tsupper, the diameter of BZO nanorods was decreased and the number density was increased. In addition, the angle of inclination of BZO nanords with respect to c-axis in SmBCO became larger with decreasing Tsupper. It is found that the diffusion process could be dominant in the nucleation of BZO. We attributed self-organized growth of BZO nanorods to the diffusion process as well as the strain energy resulting from a lattice mismatch between SmBCO and BZO.
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望月 利彦, 山本 明保, 荻野 拓, 下山 淳一, 岸尾 光二, 堀井 滋, 和田 恭輔, 山田 豊2010 年 74 巻 7 号 p. 428-433
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーSynthesis of c-axis oriented MgB2 bulks was attempted by magnetic orientation technique combined with the electrophoretic deposition (EPD) and the hot pressing (HP) method. Using home-made or commercialized MgB2 powder, EPD was performed under 10 T at room temperature. The EPD-processed films were inserted in SUS316 sheath, uniaxially pressed into a tape shape and sintered at 900°C for 24 h in evacuated quartz ampoules. In addition, HP samples were made by heating at 900°C for 6 h in Ar flow under 30 and 100 MPa. X-ray diffraction analysis revealed that the EPD-processed film in 10 T showed ~15 times higher intensity ratio, I002/I101, than those of randomly grain-oriented ex-situ bulks. This suggests EPD under field is a promising way to synthesize c-axis oriented MgB2 tapes. The c-axis oriented tapes showed much higher critical current density Jc than randomly oriented bulks and excellent high Jc of 6.9×105 A/cm2 was recorded at 20 K. Our study shows a combination of c-axis orientation and an increase in bulk density is a quite effective way to synthesize ex-situ MgB2 tapes and bulks with dramatically enhanced critical current properties.
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山田 豊, 金澤 昌哉, 根本 豊, 太刀川 恭治, 柁川 一弘, 村瀬 暁, 熊倉 浩明2010 年 74 巻 7 号 p. 434-438
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーMgB2 superconducting thin wires sheathed with stainless steel (SS) and pure iron (Fe) have been prepared by in-situ powder-in-tube process. Using Magnesium hydride MgH2 and amorphous B powders with and without SiC nano-sized powder addition, SS/Fe/MgB2 composites have been fabricated through grooved rolling and drawing to form the round wires of 0.53~0.10 mm in diameter. Both SS and Fe sheaths were hardened to be a Vickers hardness of around Hv 650 and Hv 510 through cold-working at room temperature. The transport critical current (Ic) at 4.2 K for the MgB2 wire increases with decreasing the amount of SiC addition in lower magnetic field than 1 T. The Ic at 4.2 K and self-field for the MgB2 wire of 0.10 mm in diameter without SiC addition is 14 A, which corresponds to the critical current density (Jc) of around 1×104 A/mm2. The present MgB2 thin wires are promising as current leads and level sensor for liquid hydrogen.
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熊倉 浩明, 許 子萬, 戸叶 一正, 松本 明善, 和田 仁, 木村 薫2010 年 74 巻 7 号 p. 439-443
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーPowder-In-Tube(PIT) method is the most popular method to fabricate MgB2 wires and tapes. However, PIT processed tapes and wires show relatively low Jc values due to the low density and, hence, low connectivity of MgB2 cores. The internal Mg diffusion (IMD) process is one of the effective methods to obtain high density MgB2. In this paper we report the heat treatment temperature dependence of superconducting properties of IMD processed 7-core MgB2 wires. A pure Mg rod with a diameter of 2 mm was placed at the center of a Ta tube with an outer diameter of 6 mm and inner diameter of 3.5 mm, and space between the Mg rod and the Ta tube was filled with B powder or B-SiC mixed powder. The composite was successfully cold worked into 1.3 mm wire at room temperature without any breakage. Seven pieces of the mono-core wires were bundled and inserted into a Cu-Ni tube and then, cold worked into 1.3 mm wire. The wires were heat treated at 590~800°C for 1 h under an Ar gas atmosphere. At the temperature of 640°C B layer was almost completely reacted with Mg to form MgB2. X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB2. SEM analysis of the heat treated wire clearly indicated that the density of MgB2 layer in the wire was higher than that of a PIT processed wire. Transport Jc values (calculated for the reacted layer) reached 9.9×102 A/mm2 in 10 T at 4.2 K and 1.3×103 A/mm2 in 3 T at 20 K for the SiC added wire heat treated at 640°C. These Jc values are much higher than those of usual PIT processed wires. These high Jc values can be attributed to the high density MgB2 layer obtained by this diffusion method.
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亀谷 文健, 山本 明保, A. A. Polyanskii, D. Abraimov, P. Li, D. C. Larbalestier2010 年 74 巻 7 号 p. 444-452
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーForeseeing practical applications of recently discovered new series of superconductor —Fe-pnictides, one of the most important parameters is current transport across grain boundaries. We combined SQUID measurements, magneto-optical (MO) imaging, scanning and transmission electron microscope (SEM and TEM) and low temperature laser scanning microscope (LTLSM) in order to understand the relationship between the microstructure and intergrain current transport, so called global current, in a random polycrystalline SmFeAsO0.85 (Sm1111) bulk. Our Sm1111 bulk showed significant global critical current density (Jc) which is more than one magnitude higher compared to random polycrystalline pure YBCO bulks at self field and the same temperature. However there was different temperature dependence of intergrain and intragrain Jc, exhibiting granularity at low temperature which was caused by large difference of Jc on two distinct scales. Strikingly most of intergrain current transport at self field relied on SNS Josephson weak links where supercurrent passed across the conductive impurity phase of FeAs, strongly suggesting the need of eliminating such a wetting phase in order to explore internal blocking effects at grain boundaries which are not fully understood yet.
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戸叶 一正, 松本 明善, 熊倉 浩明2010 年 74 巻 7 号 p. 453-459
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーA bulk iron arsenide superconductor of (Ba, K)Fe2As2 was synthesized by a combined process of high temperature heat treatment and deformation using a Ta sheath. Observations by an optical microscope and a scanning electron microscope and the result of x-ray diffraction indicate that the sample has a polycrystalline dense structure with much less impurity phases compared to the samples prepared by conventional sintering process. Magneto-resistance and magnetization measurements have been carried out on the obtained (Ba, K)Fe2As2 sample in order to evaluate superconducting critical properties. The temperature dependence of upper critical field, -dHc2(T)/dT is~6.3 T/K, which corresponds to the value of single crystals. The temperature dependence of irreversibility fields, -dHirr(T)/dT, has also a steep slope at about 10 K below Hc2(T), suggesting that (Ba, K)Fe2As2 superconductors has good potential for magnetic applications at medium temperatures like MgB2. However, the global Jc at 5 K estimated from the magnetization hysteresis results of bulk and powder samples and the transport Jc at 20 K measured by a standard four probe method are as low as ~2×107 A/m2 and ~105 A/m2, respectively, in applied magnetic fields. We also estimated the local Jc from the magnetization hysteresis of powdered sample, which are the order of 109 A/m2 at 5 K and 108 A/m2 at 20 K. Those results indicate that current path is still largely limited in the bulk sample despite its high density and weak link at the grain boundary is most plausible origin of current limitation in the bulk sample.
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太刀川 恭治, 山口 真弘, 佐々木 弘樹, 安藤 智紘, 竹内 孝夫2010 年 74 巻 7 号 p. 460-466
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーSn-Ta, Sn-B and Sn-Nb based alloy buttons have been prepared by the reaction among constituent metal powders at 650~775°C. The buttons were pressed to plates and then rolled to thin sheets. These sheets exhibit similar microstructures, in which a small amount of Ti addition improves the bonding of Ta, B and Nb particles against Sn matrix. The sheet was laminated with a Nb sheet and wound into a Jelly Roll composite. The composite was fabricated into a wire and then heat treated. Thick Nb3Sn layers with nearly stoichiometric A15 composition were synthesized by the mutual diffusion of Nb and Sn between Nb and Sn-based alloy. In the resulting wires, an offset Tc of ~18.1 K and an offset Bc2 (4.2 K) of ~26.5 T have been obtained. A non-Cu Jc of ~125 A/mm2 has been achieved at 22 T and 4.2 K. In this article microstructure and high-field performance of Nb3Sn wires using Sn-Ta, Sn-B and Sn-Nb sheets are evaluated and compared. Swift wire fabrication is possible with no intermediate annealing, which is one of the advantages of the present process. The present wires have enough potential to be used above 20 T at 4.2 K.
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論文
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佐々木 孔英, 釜谷 昌幸, 三浦 照光, 福谷 耕司2010 年 74 巻 7 号 p. 467-474
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーThe correlation between local misorientation and plastic strain induced in polycrystalline copper was investigated. A specimen was subjected to a tensile test in order to introduce plastic strain. From changes in surface images of the specimen during the test, distribution of plastic strain was identified by using the image correlation technique, which derives the strain distribution by image processing. Local misorientations of the strained specimen were measured using electron backscattering diffraction and their spatial distribution was compared with that of plastic strain. The plastic strain was inhomogeneous on a microstructural scale, although uniform macroscopic tensile strain was induced. The maximum local strain was almost twice the average strain and the distribution depended on the microstructure. The grain orientation spread (GOS), which was calculated as the average misorientation among all crystal orientations within a grain, was found to correlate well with grain-averaged plastic strain, although the local misorientation between neighboring points showed poor correlation. The misorientations between neighboring points correlated well with dislocation density introduced by deformation rather than with local plastic strain. It was concluded that, in order to represent the microstructural scale deformation, the strain should be defined not only by deformation per unit length, but also by the dislocation density.
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長谷川 誠, 廣崎 ゆりか, 福富 洋志2010 年 74 巻 7 号 p. 475-480
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーIn order to understand the effect of fine grains on creep property of lamellar orientation controlled Ti-43 mol%Al alloy, compressive creep tests were performed. Uniaxial compression process at α single-phase region and related compression process at (α+γ) two-phase region made the lamellar interface almost parallel to the compression process plane. Fine grains were observed around the orientation controlled lamellar colonies after the process at (α+γ) two-phase region. Volume fraction of fine grains increased with the decrease in true strain rate during the process. Further, in the same true strain rate, volume fraction of fine grains increased with the increase in true strain. These characteristics were almost the same in the case of dynamic recrystallization at the single-phase alloy. Thus, the formation of fine grains at (α+γ) two phase region may indicate the occurrence of dynamic recystallization. Minimum creep rate of the processed material increased with the increase in volume fraction of fine grains. The increase of creep rate of the entire material may be due to the preferential creep deformation of formed fine grains by a diffusional creep mechanism.
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寄書
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長谷川 誠, 野村 拓也, 福富 洋志2010 年 74 巻 7 号 p. 481-483
発行日: 2010年
公開日: 2010/07/01
ジャーナル フリーIndentation tests were performed in order to understand the effect of β phase precipitation on crack formation and propagation of the microstructure controlled Ti-45Al-10V (mol%) alloy. The processes to control β precipitates were composed of cooling from (α+γ) two-phase region followed by heat treatment at α single-phase and (α+γ) two-phase region (process A) and holding at (β+γ) two-phase region followed by heat treatment at α single-phase region (process B). Preferential precipitation of γ phase and subsequent growth of γ phase and formation of fine β phase occur at lamellar colony boundaries. Then, β phase precipitate along lamellar interfaces. Vickers indentation results in the formation of cracks in the materials formed by the process A with the cooling rate of 1 K/s at (α+γ) two-phase region and the process B with the holding time of 36 ks at (β+γ) two-phase region. However, cracks were not observed when the material was fabricated by the process A with the cooling rate of 8×10−2 K/s at (α+γ) two-phase region. This change may be due to the difference of size and distribution of β phase and the growth of γ phase precipitate in different processes.
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