Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
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Volume 75, Issue 3
Displaying 1-8 of 8 articles from this issue
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Regular Articles
  • Structural and Magnetic Properties of Co2FeAl0.5Si0.5 Full-Heusler Alloy Thin Films Deposited on Si Substrates by Molecular Beam Epitaxy
    Tatsuya Saito, Ken Kano, Nobuki Tezuka, Satoshi Sugimoto
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 141-145
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.141
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      We investigated the structural and magnetic properties of Co2FeAl0.5Si0.5 (CFAS) full-Heusler alloy thin films deposited on Si/SiO2/(001)-oriented MgO strucutre by molecular beam epitaxy. The MgO layer deposited at 300°C grew with an enough (001)-orientation to obtain high spin polarization on Si/SiO2 substrate. The CFAS thin films on Si/SiO2/(001)-oriented MgO structure showed only (220) peaks in XRD measurements. However, those films also showed high magnetization, same as the magnetization of L21-ordered CFAS on MgO substrates. Therefore, it is considered that the CFAS thin films on Si/SiO2/(001)-oriented MgO structure have the high ordered structure.
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  • Effects of Preform Densification on Microstructure and Mechanical Properties of SiC/SiC Composites
    Naofumi Nakazato, Hirotatsu Kishimoto, Joon-Soo Park, Hun-Chea Jung, Y ...
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 146-151
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.146
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      As an advanced liquid phase sintering method of SiC/SiC composites production, Nano-Infiltration and Transient Eutectic-phase (NITE) process has been intensively studied, where large volumetric shrinkage during sintering process is an issue to be solved. The objective of this work is to investigate the effects of preform densification on microstructure and mechanical properties of SiC/SiC composites fabricated by hot-press of preforms.
       The significant improvement seen in preform is the suppression of macro-pores at inter-/intra- fiber-bundles. Finally, this is contributing the reduction of volumetric shrinkage to suppress fiber damage and micro pore formation and eliminate macro pore formation after sintering. And, the composites fabricated presents microstructure homogeneity. The improvement in structure is reflected in high flexural strength. However, pseudo-ductility was worth than anticipated. The brittle behavior of the composites is interpreted to be caused by the damage of PyC interphase.
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  • New Method for Production of Solar-Grade Silicon by Subhalide Reduction
    Kouji Yasuda, Kunio Saegusa, Toru H. Okabe
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 152-158
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.152
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      In this study, a new method for producing Si, called “halidothermic reduction,” was investigated with the purpose of producing solar-grade silicon (SOG-Si); by this method, SiCl4 was reduced by gaseous subhalide used as the reductant. Silicon was produced by reacting SiCl4 with Al subhalides, which were produced by reacting AlCl3 with metallic Al. Fibrous Si with diameters ranging from submicrons to several tens of micrometers was deposited as a result of halidothermic reduction of SiCl4 by an Al subchloride (AlClx) reductant at 1273 K. The size of Si deposits and the reaction rate were increased by simultaneously supplying AlCl3 and SiCl4 vapors to a reaction tube holding Al metal. The impurity level of the obtained Si was found to be lower than the detection limit of X-ray fluorescence. Halidothermic reduction is suitable for producing high-purity Si since all reactants and byproducts exist in the vapor phase. Further, this process has high productivity since the overall reaction is a highly scalable metallothermic reduction reaction.
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  • Development of Cu-Zr Alloy Wire with Tensile Strength of 2.2 GPa in Maximum and Its Microstructure
    Naokuni Muramatsu, Hisamichi Kimura, Akihisa Inoue
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 159-165
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.159
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      Round bar ingots of hypoeutectic Cu-4 and -5 at% Zr alloys cast into copper mold were wire-drawn (WD) with drawing ratio η=5.9 and more, and the relationship between the mechanical and electrical properties and microstructures of those wires was investigated. As a result, it became obvious that the WD Cu-5 at% Zr alloy with η=8.6, which was 40 μm in diameter, reached 2234 MPa of ultimate tensile strength (UTS), 1873 MPa of 0.2% proof stress, 4.2% of total strain to failure, 126 GPa of Young's modulus and 16%IACS of electrical conductivity (EC). As for the WD Cu-4 at% Zr alloy, it was able to be wire-drawn down to 27 μm in diameter with η=9.4.
       Both UTS and Young's modulus increase linearly with the drawing ratio η. One of the reasons to indicate the high strength will be the development of nano-sized lamellar structure of α-Cu and Cu9Zr2 inter-metallic compound phase. Furthermore it was observed that nano-sized amorphous phase was formed within the nano-sized layer of Cu9Zr2 inter-metallic compound phase. Increase of the strength for heavily WD of Cu-4 and -5 at% Zr alloy wires will be due to the synergistic effect of deformation twins developed in the α-Cu phase and the formation of the nano-sized lamellar structure consisting of α-Cu and Cu9Zr2 inter-metallic compound phases.
       The highly EC of 16%IACS obtained for the WD Cu-5 at% Zr alloy wire can be explained by few dislocations in the high conductive α-Cu phase.
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  • Formation of Intermetallic Phases on the Bond Interface of Aluminum-Clad Copper
    Wei Xie, Tomiko Yamaguchi, Kazumasa Nishio
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 166-172
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.166
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      It is difficult to bond dissimilar metals such as aluminium and copper using diffusion bonding of dissimilar materials because intermetallic compounds are easily produced at the bond interface and they cause the decline of bonding strength. However, as the aluminium clad copper were produced by vacuum roll bonding, hundreds nm of intermetallic phases are formed on the bond interface. On the tensile testing, it is broken from the base metal of aluminium and high bond tensile strength is available.
       In this study, heat-treatment has been taken to aluminium-clad copper produced by vacuum roll bonding. Observation of microstructure, EPMA, and XRD have been carried to the investigation of the formation of inter-metallic phases. As a result, it is clarified that 3 types of intermetallic phases such as CuAl2, CuAl and Cu9Al4 are formed at the bond interface of Al/Cu clad materials after heat-treatment. And the apparent activation energy of the intermetallic phases for growth behavior has been calculated. It was clarified that the apparent activation energy of CuAl and Cu9Al4 is lower than CuAl2.
       The affect of intermetallic phases on bond strength has also been carried to investigate with the growth of intermetallic phases. The decrease of tensile strength has been clarified. The broken position is in the CuAl2 or between CuAl2 and CuAl. Furthermore, the bond strength of Al/Cu clad material is seriously affected by the thickness of CuAl2.
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  • In Situ Observation of the Effect of Stress on A533B Model Alloy Fe-1.4Mn under Electron Irradiation
    Hitoshi Seki, Syunzi Masubuchi, Hideo Watanabe, Naoaki Yoshida
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 173-178
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.173
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      PWR type nuclear reactor pressure vessels are neutron irradiated with stress during reactor operation. Therefore, it is important to know the effect of irradiation embrittlement of the material with and without stress conditions. It is already known that radiation hardening of the materials controlled by dislocation density in many materials. In the pressure vessel steels and model alloys, dislocation loop density is very sensitive to solutes (namely, Mn, Ni, Si etc.) levels containing in the alloy. Formation of small dislocation loops is prominent without applied stress in the matrix and also in the vicinity of dislocation in Mn containing alloys. These dislocation loops were identified as interstitial type dislocation loops. In this study, Microstructure evolution of Fe-1.4 mass% Mn alloy was studied in high voltage electron microscope (HVEM) by using a tensile sample holder. With stress condition, I-loop density was suppressed. But growth of I-loop becomes prominent.
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  • HRTEM Observation of Intermediate Precipitates in Al-Mg-Si Alloys Containing Ag
    Junya Nakamura, Kenji Matsuda, Tokimasa Kawabata, Tatsuo Sato, Yoshio ...
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 179-187
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.179
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      This study uses high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy to identify the crystal structure of a metastable phase in a Ag-added Al-Mg-Si alloy, which we compared with the crystal structure of the β′-phase in Al-Mg-Si alloys without Ag. SAED patterns and HRTEM images of the β′-phase in the Ag-added Al-Mg-Si alloy were similar to those of the β′-phase in the Al-Mg-Si alloy without Ag. However, the lattice spacings were modified by the substitution of Ag into the β′-phase. Analyses of the obtained HRTEM images and SAED patterns revealed that the β′-phase has a more complex crystal lattice that consists of large (0.69 nm) and small (0.24 nm) hexagons. Discrete variational (DV-Xα) calculations were applied to the small cluster of the β′-phase. The results indicate that it should be possible to substitute silver in the β′-phase.
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  • Influence of Morphological Transition on Crystallization Process in Si
    Kazuki Watanabe, Katsuhisa Nagayama, Kazuhiko Kuribayashi
    Article type: Regular Article
    2011 Volume 75 Issue 3 Pages 188-192
    Published: 2011
    Released on J-STAGE: April 22, 2011
    DOIhttps://doi.org/10.2320/jinstmet.75.188
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      Using CO2 laser equipped electro-magnetic levitator, we carried out the crystallization of Si at undercoolings from 0 K to 200 K. From the point of the interface morphologies, the relationship between growth velocities and undercoolings was classified into two regions, Iand II, respectively. In regionIwhere the undercooling is approximately less than 100 K, thin plate crystals whose interface consists of faceted plane were observed. In region II, the morphology of growing crystals changed to massive dendrites. Although the interface morphologies in region II look quite different from that in regionI, the growth velocities are expressed by two dimensional (2D) nucleation-controlled growth model, and at undercoolings larger than 150 K, the growth velocities asymptotically close to the analysis of the mono-parametric linear kinetics growth model. In this stage, the kinetic coefficient of 0.1 m/sK is equivalent with that derived by the diffusion-controlled growth model. This result means that with increase of undercooling, the rate-determining factor changes from 2D nucleation on the faceted interface to random incorporation of atoms on the rough interface.
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