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 74, Issue 9
Displaying 1-12 of 12 articles from this issue
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  • Preparation of Fine-Grained Single Phase ZnSb Thermoelectric Materials Using a Mechanical Grinding Process
    Chinatsu Okamura, Takashi Ueda, Kazuhiro Hasezaki
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 547-550
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.547
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      Fine grained ZnSb with an orthorhombic structure was prepared using fine grains ground mechanically below 150 μm (several tens micrometers in an average grain size). Source materials were the alloy of 50 atomic percent zinc and antimony (stoichiometric composition), which was quenched from melt at rates high enough to prevent the nucleation and growth of equilibrium phases. The alloy was ground using a mechanical grinding (MG) technique, and the grains were sintered by hot-pressing with 147 MPa at 673 K. The results of the X-ray diffraction (XRD) experiments and differential thermal analysis (DTA) showed that the ZnSb alloys were single phase and crack free.
       The thermal conductivity of the ZnSb alloy was 1.41 Wm−1 K−1 at room temperature, that was about half in comparison with the data for ZnSb single crystal or polycrystals prepared by conventional metallurgy. This could be ascribed to the effect of the grain boundary scattering of phonons.
       As a result, the ZnSb sintered alloy with single phase was found to have a reasonably high ZT (dimensionless figure of merit) value of about 0.8 at 573 K.
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  • Volume Fraction of β-Sn Formed in Sn-X (X=Cu, Ag and Ni) Eutectic and Hyper-Eutectic Alloys
    Yoshiko Takamatsu, Hisao Esaka, Kei Shinozuka
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 551-558
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.551
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      As a result of extensive studies, binary-eutectic Sn-Ag or Sn-Cu alloys have been identified as the leading candidates for lead-free solder. In these alloys the large β-Sn dendrites, such as pseudo-primary dendrite, are often observed. This study has been performed to estimate the volume fraction of β-Sn in hyper-eutectic and eutectic alloys under the presence of intermetallic compound as a primary phase.
       In this study, Sn-X, where X=Cu, Ag and Ni, binary alloys were used. To reveal the volume fraction of β-Sn more clearly, various compositions were used, and these alloys were solidified at two cooling rates (0.05°C/s and 0.70°C/s).
       The volume fraction of β-Sn increased with increaing of the undercooling for β-Sn formation. The estimation model for volume fraction of β-Sn was developed. It was found that the estimated value agreed with the measured value even though the alloy system was different.
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  • Acoustic Emission Properties of Corrosion Pitting in SUS304 Stainless Steel during MgCl2 Droplet Corrosion Testing
    Mitsuharu Shiwa, Kaita Ito, Hiroyuki Masuda, Hisashi Yamawaki, Yoshita ...
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 559-564
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.559
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      Acoustic emission (AE) monitoring for corrosion of small chloride droplet was proposed to investigate its mechanism. The corrosion testing in thin plate specimens of SUS304 stainless steel was conducted on an AE waveform measurement system with a high sensitivity AE sensor. Three types of corrosion were observed in the corrosion testing, which were the open pitting, covered pitting and snake-like corrosion, respectively. There were many AE events in the covered pitting and the snake-like corrosion. On the contrary, there was no AE event in the open pitting. Besides, the cross section of the snake-like corrosion was analyzed by EBSD. It shows that there were some cracks at the {111} interface of Σ3 coincidence boundary and annealing twins under the corrosion surface. Therefore, it can be concluded that the detected AE signals of corrosion testing were mainly attributed to the cracking in the covered pitting and the snake-like corrosion.
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  • Influence of Organic Acids on Corrosion Behavior of Boiler Tube Steels in Simulated AVT Waters Coexisted with Chloride Ions
    Takahiro Nakane, Li-Bin Niu, Shuji Oishi, Hiroshi Takaku
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 565-571
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.565
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      The influence of formic and acetic acids on the corrosion behavior in the simulated all volatile treatment (AVT) waters at pH9.5 is investigated by electrochemical and immersion corrosion tests for boiler tube steels of STB410 carbon steel, STBA24 low- alloy steel and SUS304 stainless steel used in thermal power plants. For STB410 and STBA24 steels, the pitting corrosion susceptibilities are lowered by adding formic acid (HCOOH) and acetic acid (CH3COOH) into the simulated AVT waters added also with chloride ions (Cl−). It is suggested that both these organic acids, coexisted with Cl− ions in the water, will act as inhibitors for corrosion protection of the carbon and low-alloy steels. On the other hand, almost no inhibiting effect of both these organic acids on the corrosion behavior of SUS304 steel is observed, due to the formation of thin and tight passive films containing chromium.
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  • Interaction between Sn Atoms and Vacancies in Neutron-Irradiated Ni-Sn Alloys by Positron Annihilation Spectroscopy
    Koichi Sato, Toshimasa Yoshiie, Qiu Xu
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 572-577
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.572
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      Solute atoms greatly influence irradiation damage structures. For example, voids are formed in pure Ni at 573 K, but they are not formed in Ni-Sn alloys irradiated by fission neutrons at 573 K to 0.2 dpa. In this study, the interaction between solute atoms and vacancies and correlation between void growth and solute atoms in neutron-irradiated Ni-Sn alloys were investigated by positron annihilation spectroscopy. Positron annihilation lifetime measurements showed that void density was lower in Ni-0.05 at%Sn than pure Ni. In Ni-0.3 at%Sn, single vacancies, di-vacancies and small stacking fault tetrahedra (SFTs) were formed and the size did not change below 0.1 dpa. In Ni-2 at%Sn, single vacancies and SFTs were formed and the size also did not change below 0.1 dpa. In Ni-Sn alloys, the total intensities of lifetime related to vacancy type defects were more than 60%. Vacancy concentration was higher than in pure Ni and a large number of positrons annihilated at them. From positron annihilation coincidence Doppler broadening (CDB) measurements, the ratio of annihilation of positrons and low-momentum electrons increased in Ni-Sn alloys compared with pure Ni. The ratio increased with increasing the solute atom concentration. As positron affinity of Sn is lower than that of Ni, positrons are attracted to Sn atoms more strongly than Ni. Complexes of vacancy clusters and Sn atoms are formed and the number of Sn atoms adjacent to vacancy clusters increases with the solute atom concentration. It is expected that Sn atoms change the electron state of vacancy clusters, which leads to the increase of annihilation ratio between positrons and low-momentum electrons.
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  • Adhesive Mechanism between Pt Thin Film and SiO2 Substrate after Annealing Pt/Ti/SiO2 in Air
    Mitsuhiro Wada, Yasunori Tabira
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 578-583
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.578
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      A transmission electron microscopic study equipped with a field-emission gun together with an electron energy loss spectroscopic study were carried out to investigate the adhesive mechanism between SiO2 substrate and platinum layer prepared by magnetron sputtering technique, particularly focused on its deterioration after annealing at 1000°C for 4h in ambient condition. This study describes the details of contact mechanism of Pt (450 nm)/Ti (50 nm)/SiO2 substrate. It is revealed, after annealing, that well-crystallized rutile-type TiO2 particles were segregated from the original Ti metal thin film introduced as a contact layer between Pt and the substrate, spread across the Pt layer or diffused along its grain boundaries, and some of them even reached the surface. This brought about depletion of the contact layer and eventually made most of the Pt film facing the substrate directly, resulting in the weakening of the adhesion of the film.
       Movement of a sub-nanometer sized beam from inside of a TiO2 particle formed between Pt and SiO2 substrate to the Pt side, as well as disappearance of shoulders were observed as oxygen content decreased, somewhat shift of Ti L2,3 peaks to lower energy side. This suggests that Ti4+ in TiO2 reduces towards the TiO2/Pt boundary and may imply metallic state to form a Pt-Ti alloy in the vicinity of the boundary, which plays a crucial role to sustain adhesion of the film.
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  • Formation of Ni Aluminide Containing Zr by Synchronous Electrodeposition of Al and Zr and Cyclic-Oxidation Resistance
    Michihisa Fukumoto, Tsuyosi Yokota, Motoi Hara, Toshio Narita
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 584-591
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.584
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      A Ni aluminide layer containing Zr was formed on a Ni specimen by a synchronous electrodeposition of Al and Zr using molten-salt bath. Al and Zr were hardly electrodeposited and an electrodeposited layer was not formed when the simultaneous electrodeposition of Al and Zr was tried using molten NaCl-KCl containing 3.5 mol%AlF3 and 3.5 mol%ZrF4. On the other hand, the electrodeposited layer consisting of Ni2Al3 layer as an inner layer and NiAl3 layer as an outer layer, in which ZrAl3 particles were formed at the surface region, was formed when the simultaneous electrodeposition of Al and Zr was carried out using the molten NaCl-KCl containing 3.5 mol%AlF3 and 0.05 mol%ZrF4. The cyclic oxidation resistance of the Ni covered by the Ni aluminide containing Zr was evaluated in air at 1423 K. The specimen covered with the Ni aluminide containing the ZrAl3 particles, which was formed using the melt containing 3.5 mol%AlF3 and 0.05 mol%ZrF4, showed a high cyclic-oxidation resistance. On this specimen after the oxidation test, an adhesive scale having a spiked shape, which consisted of Al2O3, was formed.
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  • Fabrication of Various Types of ADC12 Aluminum Alloy Die Castings Containing Different Amount of Gases and Porous Aluminum Fabricated by Friction Stir Processing
    Yoshihiko Hangai, Hiroki Kato, Takao Utsunomiya, Soichiro Kitahara, Os ...
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 592-597
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.592
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      Various types of ADC12 aluminum alloy die casting plates containing different amounts and types of gases were fabricated by varying the die casting conditions. Porous aluminum without the use of a blowing agent was fabricated by friction stir processing using the gases contained in the fabricated ADC12 aluminum alloy die casting plates. The effect of the amount of gases contained in the die castings on the foaming efficiency and the pore structures of obtained porous aluminum observed by X-ray CT inspection were investigated. It was shown that, although the expansion efficiency of each type of gas was not clear, the total amount of gases and porosity of obtained porous aluminum has good correlation. A porosity of approximately 60% was obtained with small area of pores and highly spherical.
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  • Microstructural Observation of Base Metal and Corroded Layer of a Copper Bowl Excavated from Mukaiyama Ruins, Nara
    Takekazu Nagae, Atsushi Hadano
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 598-604
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.598
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      The microstructure of a copper bowl excavated from an Edo-period grave in Mukaiyama Ruins in Nara prefecture has been investigated. The sample was subjected to optical microscopy, scanning electron microscopy, electron probe microanalysis and X-ray diffraction analysis to obtain information about the microstructure of both the base metal and the corroded layers. The bowl was made of copper containing 0.9% lead. Annealing twins were observed in the α-Cu phase, which establishes that the bowl was forged and annealed. The corroded layers were composed mainly of cuprite, malachite and copper phosphate. It is thought that the copper phosphate acted as an inhibitor to corrosion.
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  • Electronic Structure and Thermoelectric Properties of Si2Ti-Type Al-(Mn, X)-Si (X=Cr, Fe) Alloys
    Yasuhiro Toyama, Hirofumi Hazama, Ryoji Asahi, Tsunehiro Takeuchi
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 605-609
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.605
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      In order to make variation in thermoelectric properties of Si2Ti-type Al32Mn34Si34, which possesses a large magnitude of Seebeck coefficient exceeding 300 μV/K, we partially substituted Fe and Cr for Mn, and succeeded in decreasing the number of valence electrons by the latter. The large, positive Seebeck coefficient up to 330 μV/K was observed for Al32CrxMn34−xSi34 (1≤x≤2.5), which consists almost solely of the phase of Si2Ti-type structure. The increase of hole concentration with increasing Cr concentration was confirmed by the fact that the electrical resistivity was decreased with Cr concentration. The positive sign and the decrease of Seebeck coefficient with increasing Cr concentration also lend a support on this scenario. The largest ZT-value with the positive sign of Seebeck coefficient (p-type behavior) was obtained at Al32Cr2.5Mn31.5Si34, and the resulting ZT-value was twice as large as the largest ZT-value of the ternary compound Al33Mn34Si33 that possesses a p-type behavior.
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  • Ion Bombardment Effects on Internal Stress of Magnetic Thin Films
    Yoshiaki Shinohara, Koji Makita, Yoshihito Matsumura
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 610-613
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.610
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      This study examined the effect of argon ion bombardment on the internal stress of a nickel film. As a means of expressing the effect of ion bombardment, we propose an ion bombardment parameter based on the momentum of the ions. The magnitude of the ion momentum determined from the plasma potential was not dependent on the sputter power. With the increase in sputter power, the increase in the impingement frequency of nickel atoms onto the substrate was greater than the increase in the impingement frequency of Ar+ ions. It has become evident that the ratio of impingement argon ions to nickel particles onto the substrate mainly affects the variation in the ion bombardment parameter in relation to the sputter power. Thus, it has been demonstrated that the internal stress of a nickel film can be predicted using the ion bombardment parameter.
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  • Creep Deformation Behavior at Temperature Less than Glass Transition Temperature in Zr-Based Bulk Metallic Glass
    Kazutaka Fujita, Yuuhei Kawamura, Shinji Kimura, Hitoo Tokunaga, Yoshi ...
    Article type: Regular Article
    2010 Volume 74 Issue 9 Pages 614-621
    Published: 2010
    Released on J-STAGE: September 01, 2010
    DOIhttps://doi.org/10.2320/jinstmet.74.614
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      Bulk Metallic Glasses (BMGs) have high strength, high fatigue limit and high fracture toughness. However, the creep property at temperatures enough less than the glass transition temperature (Tg) has not been examined yet, although it is needed for practical uses. Therefore, in this report, the creep test under a constant load in the atmosphere at comparatively low temperature less than the Tg {573 K(T/Tg=0.84) and 473 K (T/Tg=0.69)} was carried out using the Zr55Cu30Al10Ni5 at% BMG. As the result, typical creep curves just like as ones in the crystalline alloys were shown, that is, there were transient, steady state and accelerated creeps, and creep strain rate increased with increasing the test temperature and load. The creep deformation occurred uniformly along the parallel part. Just before the break, a necking occurred and several shear bands came at the region due to induced high stress, and finally fractured along those shear bands in the direction of about 50 degrees for the loading axis like as the tensile fracture in the BMG. The specimen surface was oxidized and got into hard ZrO2. In the ZrO2 layer, many cracks were observed. However, in the inner region eliminating the oxide layer, no cracks, no shear bands and on the fracture surface typical vein patterns were observed. Therefore, it was presumed that the uniform creep deformation along the parallel part occurred through a viscous flow under the equilibrium state maintained glass structure.
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