MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 48 , Issue 10
Showing 1-45 articles out of 45 articles from the selected issue
  • Yoon-Uk Heo, Hu-Chul Lee
    2007 Volume 48 Issue 10 Pages 2546-2550
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    This study examined the twinning mechanism and operating twin system of a face centered tetragonal (FCT) L10 θ-MnNi phase in an equiatomic Mn-Ni alloy using detailed TEM analysis (electron diffraction, high resolution imaging, and HAADF (Z-contrast) imaging techniques) of the structure of the twins formed during the β (B2, bcc) to θ (L10, fct) phase transformation. In addition to the well-documented {111}1⁄6⟨112] deformation twinning system in L10 crystals, {111}1⁄6⟨211]* type pseudo-twin systems were also observed. The Z-contrast image of the twins showed that no atomic shuffling occurred during twinning in the θ-MnNi phase and atomic order was maintained in the {111}1⁄6⟨112] type true-twins.
    *in ⟨ijk], i and j are interchangeable in the tetragonal system but k is not.
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  • Minghui Song, Kazutaka Mitsuishi, Kazuo Furuya
    2007 Volume 48 Issue 10 Pages 2551-2555
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 22, 2007
    JOURNALS FREE ACCESS
    Free-standing tungsten-nanowhiskers about 3 nm in thickness were fabricated on SiO2 substrates with electron-beam induced deposition in a transmission electron microscope operated at 400 kV at room temperature. The growth process of the nanowhisker was observed in-situ and analyzed. The nanowhisker was characterized with high-resolution transmission electron microscopy. Nucleus-deposits smaller than 1 nm formed on the surface of the substrate, grew to 2∼3 nm and then grew out of the surface to form nanowhiskers under the electron irradiation. The nanowhisker grew long at its tip. The density and growth rate of the nanowhiskers were different at different places of the same substrate. A part of the nanowhiskers grew long to about 20 nm at the electron dose of 1.16×1025 e m−2 for an irradiation time of 223 s. The nanowhisker contained nanometer-sized grains of body-centred cubic structural tungsten and an amorphous part. It was found that there exists a critical size about 2–3 nm for a nucleus to grow to a nanowhisker. It is suggested that the nucleation site of the nanowhisker may be controlled by putting appropriate conductive particles in the critical size on the surface of an insulator substrate.
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  • Sang Ho Oh, Ju Hyung Suh, Chan Gyung Park
    2007 Volume 48 Issue 10 Pages 2556-2562
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 19, 2007
    JOURNALS FREE ACCESS
    Transmission electron microscopy (TEM) analyses of the defects formed in epitaxial SrRuO3 films on SrTiO3 (001) substrates are reported. With preparing three different forms of TEM specimens, i.e. plan-view, cross-sectional and free-standing specimens, various TEM techniques were implemented with placing emphasis on the effect of misfit strain on the defect formation. With in-situ TEM heating observations, the present TEM results provide insights into the formation mechanism of misfit dislocations, the occurrence of anti-phase boundary ribbons near the misfit dislocations, and the structural phase transitions of epitaxial perovskite films.
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  • K. Oka, S. Ohnuki, S. Yamashita, N. Akasaka, S. Ohtsuka, H. Tanigawa
    2007 Volume 48 Issue 10 Pages 2563-2566
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 22, 2007
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    For understanding the microstructual details of nano-size oxide particles, three types of ODS ferritic and austenitic steels were examined by high voltage electron microscopy, EDS and AP-FIM. The oxide included Y, Ti and O and showed a shell-like structure with different composition. The shell-like structure depends on crystal structure of the matrix during fabrication process. To evaluate the irradiation stability of the oxide particles, the electron irradiation was carried out to 47 dpa in the temperature range between room temperature and 923 K. During the irradiation, the oxide particles did not show obvious change in size. The irradiation behavior is discussed comparing with the results recently reported.
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  • Hongye Gao, Shoichi Toh, Syo Matsumura, Seishi Abe, Shigehiro Ohnuma
    2007 Volume 48 Issue 10 Pages 2567-2571
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 19, 2007
    JOURNALS FREE ACCESS
    Microstructure of Ge: Ta2O5 granular thin films were observed by Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy with Energy Dispersive Spectrometer (STEM–EDS), and TEM with electron tomography. Three dimensional images Ge: Ta2O5 granular thin films were obtained from a tilt series of images, which were taken at regular tilt intervals. Some convex parts of irregular Ge granules, which overlapped by themselves or Ta2O5 in this thin film, have been well characterized to explain why there are many Moiré patterns in this Ge: Ta2O5 granular thin films. The result acquired by TEM with electron tomography shows Ge crystals have been grown up in a preferred orientation due to the confinement from the surrounding matrix. TEM with electron tomography can be used successfully to show the shapes of Ge particles distributed in the Ta2O5 network of this thin film, also the more detailed aspects of grown direction of this granular thin film.
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  • Masatoshi Nakanishi, Gen-ichi Furusawa, Kokichi Waki, Yasushi Hattori, ...
    2007 Volume 48 Issue 10 Pages 2572-2579
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 10, 2007
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    Effects of substitution of Pt by Cu on the structural and morphological changes of Fe-Pt nanoparticles with chemical homogeneity and mono-dispersion, which were synthesized by the reverse micelle method, have been investigated by in-situ electron diffraction and HREM observation. In the Fe-Pt particles, initially with a chemically disordered face-centered cubic phase (A1), the phase transformation from A1 to a chemically ordered face-centered tetragonal phase (L10) took place between 650 and 680°C. Polycrystalline Fe-Pt particles were reconstructed into A1 single crystals between 550 and 650°C, followed by phase transformation from A1 to L10. The coalescence began almost concurrently with the phase transformation, i.e., between 650 and 680°C. Then, they turned to round-shaped single crystalline particles between 680 and 720°C. In the Fe(Pt,Cu) particles, the phase transformation from A1 to L10 occurred between 550 and 600°C. Same processes, that is, the reconstruction to single crystals, the phase transformation from A1 to L10, the coalescence and the round-shaped particle formation were also observed in the Fe(Pt,Cu) nanoparticles. The temperatures, at which these processes took place, were substantially lower than those for the Fe-Pt nanoparticles.
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  • Tomoko Yoshida, Shunsuke Muto, Jun Wakabayashi
    2007 Volume 48 Issue 10 Pages 2580-2584
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 01, 2007
    JOURNALS FREE ACCESS
    We propose novel methods of depth-resolved EELS (DREELS) and chemical state mapping, and the techniques were applied to the cross-sectional TEM (XTEM) sample of N+ implanted TiO2 catalyst. DREELS is realized by applying the Pixon deconvolution to a conventional energy-filtering TEM (EFTEM)-based spatially resolved EELS (EFTEM-SREELS), demonstrated by Kimoto et al. [J. Electron Microsc. 46 (1997) 369–374.]. And a self-modeling curve resolution (SMCR) technique in multivariate analysis enabled chemical state mapping from EFTEM-based spectrum imaging (EFTEM-SI) data sets. The methods successfully extracted the depth dependence of the N-K ELNES and separately displayed the spatial distributions of the constituent chemical states, whose spectral features were overlapped.
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  • Norihito Sakaguchi, Hideki Ichinose, Seiichi Watanabe
    2007 Volume 48 Issue 10 Pages 2585-2589
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 19, 2007
    JOURNALS FREE ACCESS
    {112} Σ3 CSL grain boundary in silicon was investigated by high-resolution transmission electron microscopy (HRTEM) and ab-initio calculation. A {112} Σ3 CSL boundary consisted of two segments which differed in atomic structure. The segment near the connected corner to {111} Σ3 CSL boundary showed symmetric structure and the other long segment, being distant region from the corner, showed asymmetric structure. It was shown that the asymmetric structure is more stable than the symmetric one. In the symmetric segment a 5-fold coordinated atom presented, which elevated the structure energy of the boundary and produced a new state in the band gap.
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  • Yu Yamamoto, Kazuyoshi Tatsumi, Shunsuke Muto
    2007 Volume 48 Issue 10 Pages 2590-2594
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 10, 2007
    JOURNALS FREE ACCESS
    We established a method for site-selective electronic structure analysis, using TEM-EELS under electron channeling (standing-wave) conditions and first-principles band calculations. In particular, we applied a self-modeling curve resolution (SMCR) technique to separate a set of experimental spectra into individual spectra of individual atomic sites. A case study is presented for Al-K ELNES in oxide ceramics, which shows spinel and garnet structures containing two types of Al sites.
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  • Ming-Che Chen, Che-Wei Kuo, Chia-Ming Chang, Chih-Chun Hsieh, Yin-Yu C ...
    2007 Volume 48 Issue 10 Pages 2595-2598
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    In this study, the accumulative roll-bonding (ARB) process is used to reduplicate Al (1100)/Mg (AZ31) alloy and then made thinner and longer by multi-rolling. Stacks with 24 layers were created and annealed at 300°C for 1 h. The microstructures were observed by using optical microscopy. The diffusion couples between Al and Mg were investigated to study the composition of the Al-Mg system. The layers of the intermetallic compounds Al3Mg2 and Al12Mg17 were observed by a field emission scanning electron microscope. The composition-depth curves of the diffusion zone were obtained by employing electron microprobe analysis after annealing at 300°C for 1 h.
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  • Masatoshi Nakanishi, Gen-ichi Furusawa, Kokichi Waki, Yasushi Hattori, ...
    2007 Volume 48 Issue 10 Pages 2599-2605
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 19, 2007
    JOURNALS FREE ACCESS
    We have developed a method to observe the magnetic field around L10 FePt nanoparticles by in-situ electron holography at elevated temperatures. FePt Nanoparticles with sharp size distribution and chemical homogeneity were synthesized by the reverse micelle method. The as-prepared FePt nanoparticles, which had a disordered fcc structure (A1) with the diameter centered at 6 nm, were coated with a surfactant, dispersed onto a glass plate, and heated in order to undergo a transformation from A1 to an ordered fct structure (L10). The particles were kept separated by the surfactant with their original diameter during annealing. A submicron-size island comprising isolated particles was removed and dispersed on an electron transparent carbon film and then magnetized along one direction. We observed a magnetic field distribution of the submicron-size island of nanoparticles by means of electron holography during heating. Although magnetization decreased between 212°C and 412°C to 25% of the initial strength at 25°C, it increased again during cooling and recovered 67% of its initial strength. However, when an island was heated to 512°C, the magnetization diminished and did not recover again during cooling. The Curie temperature (Tc) of the FePt nanoparticles was determined to be 350°C and was in good agreement with the Tc determined by bulk measurements using a VSM, which was approximately 100°C lower than the reported Tc for bulk Fe55Pt45.
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  • J. J. Kim, H. S. Park, D. Shindo, T. Iseki, N. Oshimura, T. Ishikawa, ...
    2007 Volume 48 Issue 10 Pages 2606-2611
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 11, 2007
    JOURNALS FREE ACCESS
    The magnetic domain structure and magnetization process in Sm2(Fe0.95,Mn0.05)17N5.0 powders are investigated by Lorentz microscopy and electron holography. The magnetic domain walls are aligned along the magnetization easy axis (c axis) and are connected with one another along amorphous layers that are distributed along the direction parallel to the c axis. On the other hand, it is found that the domain walls are always located in the amorphous layer after domain wall motion. These results reveal that the amorphous layers are the pinning centers of the domain walls. Thus, it is reasonable to consider that the coercivity of a Sm2(Fe0.95,Mn0.05)17N5.0 powder is strongly affected by the distribution of the amorphous layers in the powder.
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  • Weixing Xia, Joong Jung Kim, Daisuke Shindo, Akihiro Makino
    2007 Volume 48 Issue 10 Pages 2612-2615
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 19, 2007
    JOURNALS FREE ACCESS
    L10 nanocrystalline FePt alloy is directly formed by rapid quenching the melt with simultaneous addition of Zr and B and high coercivity can be obtained in the composition range of (Fe0.55Pt0.45)78Zr2–4B18–20. Single domain characteristic of the nanocrytalline FePt grains is clarified by Lorentz micorosocpy. Through the measurement of original magnetization curve and hysteresis loop, it is proposed that the mechanism of coercivity belongs to nucleation type. Distributions of lines of magnetic flux at demagnetized state and remanent state for two samples of (Fe0.55Pt0.45)78Zr4B18 and (Fe0.55Pt0.45)78Zr2B20 are observed by electron holography through ex situ experiment by applying a magnetic field. Obvious differences in the reconstructed phase images indicate the difference of the coercivities of the two samples.
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  • Ki Hyun Kim, Joong Jung Kim, Weixing Xia, Daisuke Shindo
    2007 Volume 48 Issue 10 Pages 2616-2620
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 11, 2007
    JOURNALS FREE ACCESS
    The effects of charging on a ZrO2 sintered body due to electron irradiation were investigated by means of electron holography. The charging effects were quantitatively evaluated as a function of the incident electron density. The ZrO2 sintered body was positively charged within a transmission electron microscope. By means of simulations taking into account reference wave modulation due to a long-range electric field, we were able to obtain the amount of charge on the ZrO2 sintered body. Further, fluctuation in the amount of charge on ZrO2 during electron irradiation was found through the presence of an irregular contrast in the reconstructed phase image.
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  • Toshiharu Aiso, Daisuke Shindo, Takafumi Sato
    2007 Volume 48 Issue 10 Pages 2621-2625
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: July 11, 2007
    JOURNALS FREE ACCESS
    The magnetic domain structures and magnetization processes of anisotropic Ba and Sr ferrite magnets are investigated by Lorentz microscopy and electron holography. By utilizing a sharp magnetic needle made of a sintered Nd-Fe-B magnet in a transmission electron microscope, the magnetization process in ferrite magnets is visualized for the first time by in situ Lorentz microscopy. In the anisotropic Ba ferrite specimen, magnetization reversal occurs suddenly along the grain boundaries over a large volume, which includes the volumes of some grains located around the specimen edges. On the other hand, in the anisotropic Sr ferrite specimen, magnetization reversal is not observed due to the large coercivity of the specimen. During the magnetization process from the demagnetized state in the Sr ferrite specimen, the domain wall inside a grain moves gradually along the grain boundary and then stops at the grain boundary.
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  • Zentaro Akase, Daisuke Shindo, Masao Inoue, Akira Taniyama
    2007 Volume 48 Issue 10 Pages 2626-2630
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    By utilizing an alternating current (AC) magnetic system recently installed on our transmission electron microscope (TEM), in-situ Lorentz microscope observations of electrical steel sheets were carried out under an AC magnetic field. The domain walls moved smoothly under a low frequency AC magnetic field. By using diffraction contrast, interactions between precipitates and the motion of the magnetic domain walls were visualized and clarified. Eventually, the magnetic domain walls were found to be pinned at strain fields around precipitates. Observations under higher frequency AC magnetic fields were also carried out. It was demonstrated that in-situ Lorentz microscopic observations under an AC magnetic field are very useful for the investigation of interactions between the microstructure and the motion of magnetic domain walls in electrical steel sheets.
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  • J. J. Kim, W. X. Xia, D. Shindo, T. Oikawa, T. Tomita
    2007 Volume 48 Issue 10 Pages 2631-2635
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    By means of electron holography, the electric potential distributions around a cold-type FEG-emitter (field emission gun emitter) are visualized with a change in the applied voltages. In a biased FEG-emitter, the experimental method for obtaining an unperturbed reference wave is applied in order to carry out quantitative electron holographic analyses. Further, through comparing the experimental results obtained by electron holography with those of the simulations taking into account the three dimensional configurations of the FEG-emitter and the anode, it is found that the experimental technique presented in this study is quite useful in obtaining the quantitative information regarding the electric field distribution around a biased FEG-emitter.
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  • T. Yano, Y. Murakami, R. Kainuma, D. Shindo
    2007 Volume 48 Issue 10 Pages 2636-2641
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    The magnetization distribution in the L21 phase of a Ni2Mn(Al,Ga) alloy, which is a type of ferromagnetic shape memory alloy, has been studied by electron holography and Lorentz microscopy. This alloy contains many antiphase boundaries (APBs), which are introduced by the chemical ordering from the B2 state to the L21 state. In situ Lorentz microscopy observations have revealed that APBs behave as strong pinning sites for domain wall motion. The width of a 180° wall, which was formed at the position of an APB, was estimated to be approximately 10 nm. This narrow domain wall was rationalized by the depression of ferromagnetism within APBs.
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  • Shunsuke Sasaki, Masanori Kajihara
    2007 Volume 48 Issue 10 Pages 2642-2649
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    The kinetics of the reactive diffusion between a binary Ag–5 at% Pt alloy and Sn was experimentally studied at solid-state temperatures using sandwich Sn/Ag0.95Pt0.05/Sn diffusion couples. The diffusion couple was prepared by a diffusion bonding technique and then isothermally annealed at temperatures of T=433, 453 and 473 K for various times up to 408 h in an oil bath with silicone oil. During annealing, an intermetallic layer of Ag3Sn dispersed with fine particles of PtSn4 is formed at each interface in the diffusion couple. The mean thickness of the intermetallic layer is expressed as a power function of the annealing time. The exponent of the power function takes values around 0.35 at T=433–473 K. Thus, the growth of the intermetallic layer is controlled by grain boundary diffusion as well as volume diffusion. The growth rate of the intermetallic layer is greater for the Sn/Ag0.95Pt0.05/Sn diffusion couple than for the Sn/Ag/Sn diffusion couple at T=433–473 K. However, the temperature dependence of the growth rate shows that the growth rate may be smaller for the Sn/Ag0.95Pt0.05/Sn diffusion couple than for the Sn/Ag/Sn diffusion couple at T=393 K. Thus, addition of 5 at% Pt into Ag accelerates the kinetics of the reactive diffusion between Ag and Sn at T>400 K but decelerates the kinetics at T<400 K.
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  • Woei-Shyan Lee, Fang-Jui Fong
    2007 Volume 48 Issue 10 Pages 2650-2658
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    Nanoindentation tests are performed on as-deposited Au/Cr/Si thin films to depths of 300 nm and 1000 nm, respectively. The indentations in as-deposited and annealed specimens are examined using transmission electron microscopy (TEM). The unloading curve of the specimen indented to 300 nm has a smooth profile, while that of the specimen indented to 1000 nm has a pop-out feature at a critical load of 100 mN. The hardness and Young’s modulus of the Au/Cr/Si thin films are determined to be 1.7 GPa and 88 GPa, respectively. A strong correlation is found between the indentation depth, the annealing temperature and the microstructural changes induced in the thin films. A chain-like island structure is observed in the as-deposited specimen indented to 1000 nm and a pile-up of the thin-film material is observed around the indentation site. However, no microstructural change is evident in the as-deposited specimen indented to 300 nm. The greater deformation associated with an indentation depth of 1000 nm followed by annealing at 523 K or 623 K results in the formation of amorphous phase within the indentation zone. At the highest annealing temperature of 723 K, a mixed microstructure comprising amorphous and rod-like eutectic phase is observed.
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  • Kunio Hayakawa, Yukio Sanomura, Mamoru Mizuno, Yukio Kasuga, Tamotsu N ...
    2007 Volume 48 Issue 10 Pages 2659-2664
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    In the present paper, V-bending of polypropylene (PP) is analyzed by the finite element method using a plastic constitutive equation for hydrostatic-pressure-dependent polymers proposed by one of the present authors. The yield surface is expressed by the first and second invariants of stress to describe the hydrostatic-pressure dependence. A plastic potential that is different from the yield surface is employed to describe the incompressibility of polymeric materials. Isotropic hardening is assumed. The proposed constitutive equations are implemented in the finite element code MSC.Marc with user subroutines. The calculated load-stroke curves appropriately describe the effect of introducing the hydrostatic-pressure dependence of PP. Moreover, the calculated results agree with the experimental ones for various thicknesses of specimens. Finally, the calculated distributions of bending stress and bending strain in the specimen also show the effects of hydrostatic-pressure dependence.
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  • Satoshi Hotta, Keigo Matsumoto, Taichi Murakami, Takayuki Narushima, C ...
    2007 Volume 48 Issue 10 Pages 2665-2673
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    Dynamic and static restoration behaviors of pure lead and tin were investigated by compression tests, and the deformation temperature and strain rate were varied in the range from 223 to 348 K and from 2×10−3 to 1 s−1, respectively. Lead and tin used had two purity levels of 99.999% (5N) and 99.9% (3N), and 5N and 4N, respectively. The hot working simulator was reformed so as to enable compression tests at low temperatures ranged from 223 to 273 K. S-S curves observed in lead and tin were those in dynamic recrystallization and dynamic recovery types of metals, respectively, of which activation energies were 92 to 119 kJ/mol in lead and 49 to 52 kJ/mol in tin. Steady state flow stress in lead with 5N purity was lower than that of tin with 5N purity. A reduction of purity level from 5N to 3N in lead significantly increased flow stress, but difference in purity level of 5N and 4N in tin exerted tiny influence on flow stress at strain rate below 1×10−1 s−1. Static recrystallization in lead with 5N purity completed in the holding time of less than 600 s even at 273 K, while tin with the same purity showed a slightly retarded recrystallization progress. A reduction of purity level in both metals extended the time period for completion of recrystallization by more than 2 orders.
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  • Hisamichi Kimura, Hiroaki Matsumoto, Akihisa Inoue
    2007 Volume 48 Issue 10 Pages 2674-2678
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 29, 2007
    JOURNALS FREE ACCESS
    The effects of cold drawing on electrical- and mechanical properties of Cu-5 at% Zr alloy were examined as a function of a drawing ratio (η), and were discussed in relation to the microstructural evolution under drawing process. Microstructure was changed by drawing into the fine fibrous elongated structure with alternating phases of Cu solid solution (Cuss) and Cu9Zr2 intermetallic (Cu9Zr2). Electrical conductivity increases by cold drawing up to η=5.9 as compared with that for the as-cast state, whose relative electrical conductivity is 24 %IACS (IACS: international annealed copper standard). The %IACS shows a maximum value of 36% IACS at η=2.2. It was suggested that the microstructural formation of net-like Cuss phase parallel to the drawing direction enhanced the electrical conductivity by drawing process. Moreover, the strength increased with the increase in the drawing ratio. The increase in the strength can be reasonably explained by the effect of work hardening and the refinement of microstructure. Thus, it was found that the combination of high electrical conductivity of 31∼36% IACS and high tensile strength of 1113∼1798 MPa was achieved in Cu-5 at% Zr alloy by cold drawing.
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  • Elzbieta A. Pieczyska, Hisaaki Tobushi, Wojciech K. Nowacki, Stefan P. ...
    2007 Volume 48 Issue 10 Pages 2679-2686
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    The main characteristics which appear in shape memory alloys (SMAs) are the shape memory effect and superelasticity. In applications of SMAs, the thermomechanical properties of SMAs are most important. The return-point memory does not appear under the stress-controlled conditions. Creep and stress relaxation can be induced due to the phase transformation in the subloop loading under the stress-controlled conditions. In order to design the SMA elements properly, it is important to understand the influence of the thermomechanical loading conditions on the nucleation and progress of the phase transformation and the corresponding deformation behaviors. In the present paper, the conditions for the nucleation and progress of the phase transformation are investigated for SMAs subjected to the subloop loadings under the stress-controlled conditions. The uniaxial tension tests for the TiNi SMAs were carried out in the superelastic region under the various thermomechanical loading conditions. The thermomechanical conditions for the progress of the phase transformation are discussed in the subloop loading under the stress-controlled conditions. Strain increases during unloading and decreases during reloading under the stress-controlled subloop loading. These pseudoviscoelastic behaviors are important for the precise control of SMA elements.
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  • Boyan Yuan, Toru H. Okabe
    2007 Volume 48 Issue 10 Pages 2687-2694
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    A fundamental study on producing fine tantalum powder by reducing electrochemically dissolved tantalum ions (Tan+) by dysprosium divalent ions (Dy2+) in molten salt was investigated in order to develop a new process for pulverizing a tantalum ingot to fine powder for electronic devices. A tantalum rod (anode) was immersed in the NaCl–KCl–MgCl2–DyCl2 molten salt at 1000 K, and it was anodically dissolved in this salt. The electrochemically dissolved Tan+ ions were subsequently reduced in situ by Dy2+ ions in the molten salt to produce tantalum powder. The reaction product, Dy3+ ions, generated during the production of tantalum powder, were reduced by either electrochemical or magnesiothermic reduction at the cathode (liquid Mg–Ag alloy) and regenerated to reductant Dy2+ ions. Fine and uniform tantalum powder with an average particle size of around 0.1 μm was directly and successfully obtained from the bulk tantalum under a specific condition. A possible reaction pathway for the reduction of Tan+ ions by Dy2+ ions in the molten salt was discussed with the aid of an isothermal chemical potential diagram of the Ta–Dy–Cl system at 1000 K.
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  • Zhaoxiang Chen, Fuhe Yuan, Zhongguang Wang, Shijie Zhu
    2007 Volume 48 Issue 10 Pages 2695-2702
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    NiCrAlY coatings were prepared by the newly-developed detonation gun spray process. The oxide scale formation and evolution on these coatings during isothermal oxidation in air at 1100°C were investigated. It was found that semi-molten particles, particle debris and pores, are present in the surface layer of the as-sprayed coating. During 100 h oxidation, the particle debris and some semi-molten particles gradually change into oxide mixture consisting of spinel, chromia and nickel oxides. However, after removal of the surface layer of the coating by a grinding treatment, a dense and single-layer α-Al2O3 scale forms on the surface of the coating during the oxidation. The mechanisms governing the oxide scale formation and evolution are discussed in terms of atomic diffusion and thermodynamic stability. In addition, thermogravimetric analysis showed that the oxidation rate of the ground NiCrAlY coating at 1100°C is much lower than that of the as-sprayed one. The residual stress in thermally grown oxide scales was investigated using photo-stimulated luminescence spectroscopy.
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  • Khyoupin Khoo, Jin Onuki, Takahiro Nagano, Suguru Tashiro, Yasunori Ch ...
    2007 Volume 48 Issue 10 Pages 2703-2707
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 29, 2007
    JOURNALS FREE ACCESS
    Grain size distributions and average grain sizes in the longitudinal direction of the Cu interconnect in 50-, 70- and 80-nm-wide Cu interconnects were evaluated and compared with the resistivities of each interconnect. After annealing, the standard deviation of grain sizes for 50-nm Cu interconnect increased to 27.5, and the average grain size microstructure grew to larger than that of as-deposited 50-nm Cu interconnects. The value of standard deviation of grain sizes in the normal distribution histogram for a 50-nm wire was found to be much smaller than those for 70- and 80-nm Cu wires after annealing. This implies that adequate grain growth should not be expected in the very narrow Cu interconnects (less than 50-nm) of the future if they are made with the conventional annealing process.
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  • Nobuyuki Takahira, Takeshi Yoshikawa, Toshihiro Tanaka, Lauri Holappa
    2007 Volume 48 Issue 10 Pages 2708-2711
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    Wettability of liquid indium and liquid bismuth on a solid iron was investigated to elucidate their different behaviors relating to the unusual wetting phenomena. Sessile drop method was performed to measure the contact angle of each liquid metal on the flat solid iron in H2 from 700 to 1100 K. In addition, we observed wetting behaviors of liquid indium and liquid bismuth on the surface-porous iron substrate. It was found from these experiments that liquid indium wetted and penetrated into the porous layer at 773 K. On the other hand, liquid bismuth did not infiltrate the porous substrate at temperatures lower than about 950 K. The wetting behavior of these liquid metals on the porous substrates is supposed to be related to the wettability of each metal on the flat solid iron.
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  • Seksak Asavavisithchai, Victor H. Lopez, Andrew R. Kennedy
    2007 Volume 48 Issue 10 Pages 2712-2714
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
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    As-received and oxidised TiH2 powders have been characterised using differential scanning calorimetry, thermogravimetry and mass spectrometry. The activation energy for hydride decomposition was determined and was found to increase slightly (from 119 kJ/mol to 134 kJ/mol) after oxidation. These values are much higher than those for hydrogen diffusion (typically 50 kJ/mol) indicating that the rate of hydrogen release, before and after oxidation, is controlled by detrapping.
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  • Yoshitake Nishi, Takashi Ogasawara, Haru-Hisa Uchida
    2007 Volume 48 Issue 10 Pages 2715-2717
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
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    In order to generate the soft bending motion driven by pressure change in hydrogen gas, a soft device was made up and tested. In former research, a unimorph structure was proposed, in which a silicone rubber with LaNi5 alloy powder distributed was piled up on a pure silicone rubber sheet. Using this structure we succeeded a bending motion of the soft device by applying hydrogen gas pressure. However the mechanical response was slow. To improve the active motion, a catalyst of Pd-Al2O3 powder was mixed into the hydrogen storage alloy powder in the rubber. By simple addition of catalyst powder before dispersion into the rubber, we obtained drastically modified responses and displacement in the movement of the device. The catalyst probably accelerated dissociation of hydrogen molecule on the surface of hydrogen storage material particle.
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  • Efendi Mabruri, Shingo Sakurai, Yoshinori Murata, Toshiyuki Koyama, Ma ...
    2007 Volume 48 Issue 10 Pages 2718-2723
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
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    The diffusion in Ni-Co-Re and Ni-Co-Ru systems have been investigated in the temperature range 1323–1523 K through the determination of the interdiffusion coefficients. The main interdiffusion coefficients of these systems were larger than the cross interdiffusion coefficients, indicating that the influences of the own concentration gradients of the elements were generally still dominant. From the ratio of the cross interdiffusion coefficient to the main one, |\\ ildeDijk⁄\\ ildeDiik|, it was found that the effect of Co on the diffusion of Re was more appreciable than that of Ru. Moreover, by the comparison between the diffusion in the binary Ni-Re and in the ternary Ni-Co-Re, it was clear that the presence of Co reduced the Re diffusivity in Ni. The results of this work reflect two folds; the attractive force exists between Co and Re, and the interatomic bonding of Co-Re seems to be stronger than that of Ni-Re.
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  • Takahiro Hayashi, Masayoshi Sekine, Junya Suzuki, Yuma Horio, Hirotsug ...
    2007 Volume 48 Issue 10 Pages 2724-2728
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    P-type Bi0.4Sb1.6Te3 thermoelectric materials were prepared by an angular extrusion technique with rapidly solidified and stacked foils in a temperature range from 643 K to 838 K. Textures of the angular-extruded specimens were observed by Orientation Imaging Microscopy (OIM). The average grain size was monotonously enlarged from 4.7 to 16.1 μm while increasing the extrusion temperature. The texture of the angular-extruded specimens shows that the basal planes are preferably aligned along the extrusion direction. Strong textures were observed in specimens extruded at a temperature range from 683 K to 803 K. The carrier mobility of the extruded specimens depends strongly on both the texture strength and grain size. As the extrusion temperature rises, the bending strength decreases. This change in bending strength is in good agreement with the Hall-Petch relationship. A maximum Z value of 3.33×10−3 K−1 and bending strength of 80.3 MPa were achieved in a specimen angular-extruded at 773 K. The Z value and the bending strength were sufficiently high compared with conventional hot-extruded or hot-pressed specimens. These results indicate that the angular extrusion technique is effective in improving the thermoelectric and mechanical properties of bismuth-telluride based thermoelectric materials.
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  • Motomichi Koyama, Masato Murakami, Kazuyuki Ogawa, Takehiko Kikuchi, T ...
    2007 Volume 48 Issue 10 Pages 2729-2734
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
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    We have investigated the shape memory effect and ductility of Fe-30Mn-(6-x)Si-xAl (x=0, 1, 2 and 3; in mass-%) alloys. The alloy with x=0 shows a good shape memory effect but suffers from poor ductility, while the alloys with x=2 and 3 are well-known TWIP (twinning induced plasticity) steels that show high ductility. In the present study, it was found that the shape memory effect is observed in the samples with x=0 and 1, but disappears when x exceeds 2. On the other hand, the ductility almost linearly increases with increasing the amount of Al. A good combination of the shape memory effect and ductility was achieved in the alloy with x=1.
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  • Yoshitake Nishi, Mitsuru Hirano
    2007 Volume 48 Issue 10 Pages 2735-2738
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    Influences of compressive and tensile stresses on an electrical resistivity of carbon fiber in polyvinyl acetate polymer on bending test are studied as a basic research to develop high sensitive stress sensors. It is confirmed that a compressive stress of less than 0.3 GPa on bending test reversibly decreases the electrical resistivity of carbon fiber due to enhancement of the density of state of π bonding electron. A tensile stress of less than 0.3 GPa on bending test also decreases the electrical resistivity of carbon fiber, reversibly, because of decreasing the density of electron scattering sites.
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  • Kenji Yamauchi, Norihiro Murayama, Junji Shibata
    2007 Volume 48 Issue 10 Pages 2739-2742
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 29, 2007
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    Lithium silicate (Li4SiO4) and lithium zirconate (Li2ZrO3) absorb CO2 in a lower temperature range and the absorbed CO2 is released reversibly in a higher temperature region. In this study, various metal oxides and hydroxides and their complex oxides containing Li were investigated for their CO2 absorption properties at different temperatures in order to get better understanding of the related mechanism.
    The inflection points in the TG curves, at which predominant reaction changes from CO2 absorption to CO2 release, are observed at around 973 K for Li4SiO4 and Li2ZrO3. The CO2 absorption is based on the formation of Li2CO3 through the decomposition of Li-containing complex oxides. From the experimental results and thermodynamical calculations, it is noticed that CO2 absorption takes place very slowly in spite of large equilibrium constant in the lower temperature region below 873 K, while the absorption at 973 K happens quickly. When the absorption at 973 K and the release at 1273 K are repeated 5 times for Li4SiO4, the material maintains its crystal structure to give CO2 absorption and release. On the other hand, CaO shows an inflection point at 1173 K in the TG curve. Magnesium oxide and hydroxide do not react with CO2 below 1273 K.
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  • Jui-wen Liu, Shih-chin Lee, Chih-hao Yang
    2007 Volume 48 Issue 10 Pages 2743-2746
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    Transparent conductive strontium copper oxide (SCO) films were grown on glass substrates by radio frequency magnetron sputtering technique at room temperature with different oxygen partial pressures. Structural, electrical and optical properties of these films were studied. Grazing incidence angle x-ray diffraction (GIAXRD) analysis showed that SrCu2O2 structure was achieved when oxygen partial pressure was raised above 2.0×10−1 Pa. Both carrier density and resistivity of the film varied with oxygen partial pressure. The carrier density and resistivity of the film prepared with 4.0×10−1 Pa of oxygen pressure were 2.89×1021 cm−3 and 6.64×10−2 Ω·cm, respectively. The carrier mobility was 0.092 cm2 V−1 s−1 and the Hall coefficient measured at room temperature indicated that the conduction is p-type. The optical transmittance in the visible range at 550 nm was 29%∼41%.
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  • Jae Sin Park, Young Won Chang
    2007 Volume 48 Issue 10 Pages 2747-2752
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    A new interpretation for the creep behavior of pure magnesium single crystals as well as poly crystals with 99.94 mass% purity has been made by using an internal variable approach. A series of load relaxation tests and creep tests for magnesium single and poly crystals were performed at elevated temperature. The single crystals used in this study were grown from the melt using a modified Bridgman technique. The creep behavior has been well described by the internal variable theory based on dislocation dynamics, consisting of two deformation modes; dislocation glide and dislocation creep deformation modes. The flow curves obtained from the load relaxation tests at elevated temperature could be resolved into a dislocation glide and a creep component effectively by the internal variable theory. The dislocation creep component above 523 K for single crystal magnesium shifted toward the faster strain rate regime with increasing temperature. This could be due to activation of the cross-slip of dislocations from basal to prismatic planes above 523 K.
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  • Kojiro Akiba, Mitsutoshi Ueda, Kenichi Kawamura, Toshio Maruyama
    2007 Volume 48 Issue 10 Pages 2753-2761
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
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    Voids which form in oxide scales strongly influence the mechanical properties of the scale and the adherence between the metal substrate and the scale. The purpose of this study is to demonstrate a method for quantitative estimation of voids formation in NiO scale, and compare the microstructure of the scale formed on nickel at 1373 K with the estimation.
    Calculations of ion fluxes and their divergence in NiO scales can predict the annihilation of the oxides which mostly occurs in the vicinity of the metal/oxide interface and the volume fraction of the voids. These predictions are in good agreement with the observed morphology of NiO scale obtained in high temperature oxidation of nickel at 1373 K.
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  • Kenjiro Sugio, Yasutaka Momota, Di Zhang, Hiroshi Fukushima, Osamu Yan ...
    2007 Volume 48 Issue 10 Pages 2762-2767
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    Three-dimensional local number, LN3D, and two-dimensional local number, LN2D, were defined as the number of gravity centers (GCs) of second phase particles in the measuring sphere and circle with specially determined radiuses, respectively, whose centers were put on GCs of noticed particles. LN3D and LN2D represent local number density including a noticed and its neighboring particles and each particle has a specific value. We suggested the quantitative method to evaluate the particle spatial distribution using the relative frequency distributions of LN3D and LN2D, and this method was examined by computer experiments using overlap permissive spheres. It was shown that randomness of second phase particles was correctly evaluated in 3- and 2-dimensions by this method, and the average and variance of LN3D and LN2D are proper descriptors to evaluate the spatial distribution randomness of second phase particles. It was also shown that spatial distribution randomness of 2-dimensional particles appeared on cut planes of 3-dimensional particles having uniform random arrangement can be evaluated by this method regardless of both the particle volume fraction and the particle size distribution.
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  • Kenjiro Sugio, Yasutaka Momota, Di Zhang, Hiroshi Fukushima, Osamu Yan ...
    2007 Volume 48 Issue 10 Pages 2768-2777
    Published: October 01, 2007
    Released: September 25, 2007
    JOURNALS FREE ACCESS
    We defined 3-dimensional local number, LN3D, 2-dimensional local number, LN2D, and their probability distribution to describe the spatial distribution of second phase particles, and then suggested the statistical relationship of probability distributions between LN2D and LN3D concerning uniform random and clustering spatial distributions. The relationship was validated by computer experiments using particles of overlap permissive spheres, and was applied to the real microstructures of Al-10 vol%SiC composites. Using the relationship, probability distributions of either LN3D or LN2D could be predicted from the measured relative frequency distributions of another dimension in computer experiments with satisfactory accuracy. Using the relationship, the probability distributions of LN3D was approximately predicted from the relative frequency distributions of LN2D that were obtained by measurements of spatial distributions of SiC particles in Al-SiC composites.
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  • Chang Dong Yim, Guohua Wu, Bong Sun You
    2007 Volume 48 Issue 10 Pages 2778-2781
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: August 29, 2007
    JOURNALS FREE ACCESS
    The effect of Ar gas bubbling on the tensile elongation of gravity mold castings of AZ91D magnesium alloy was evaluated qualitatively. The beneficial effect of gas bubbling on the tensile elongation of castings was resulted from the removal of inclusions in melt. The removal efficiency of inclusion by bubble floatation is dependent on processing variables including flow rate of gas, gas blowing time and melt temperature. Considering only the interaction between bubble and inclusion, the removal efficiency of inclusion will increase with increase in flow rate of gas, gas blowing time and melt temperature. But dissolution of gas into melt and entrance of new non-metallic particles formed on the melt surface deteriorated the tensile elongation of castings.
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  • Hiroyuki Shibata, Yoshio Waseda, Hiromichi Ohta, Kazumasa Kiyomi, Kenj ...
    2007 Volume 48 Issue 10 Pages 2782-2786
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 05, 2007
    JOURNALS FREE ACCESS
    A relatively large sample of gallium nitride (GaN) was grown as a single crystal using the hydride vapor phase epitaxy (HVPE) process. The thermal diffusivity of the single crystal has been measured using a vertical-type laser flash method. The thermal expansion was measured using a dilatometer in order to estimate the thermal diffusivity with sufficient reliability. The effect of sample thickness and temperature on thermal diffusivity was evaluated. The specific heat capacity of GaN was also measured by using a differential scanning calorimeter. The thermal properties of single-crystal GaN have been compared with the measured thermal properties of single-crystal silicon carbide (SiC). The thermal conductivity of single-crystal GaN at room temperature is found to be 253±8.8% W/mK, which is approximately 60% of the value obtained for SiC. The excellent thermal property that is obtained in this study clearly indicates that GaN crystals are one of the promising materials for use in high-power-switching devices.
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  • Asahi Kawashima, Takahiro Okuno, Hiroaki Kurishita, Wei Zhang, Hisamic ...
    2007 Volume 48 Issue 10 Pages 2787-2790
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    Compressive tests were made for the as-cast Cu45Zr45Al5Ag5 bulk glassy alloy rods with a diameter of 3 mm at 298 and 77 K, at an initial strain rate of 5×10−4 s−1. It was found that at 77 K, the compressive yield strength, maximum strength and plastic strain to fracture of the glassy alloy rod are higher than those at 298 K. The maximum strength measured at 77 K is about 13% larger than that measured at 298 K. In particular, its plasticity at 77 K is significantly enhanced. SEM observations reveal that more shear bands appear near the fracture plane at 77 K. The higher strength and ductility at a cryogenic temperature (77 K) are probably due to the lower mobility of the squeezed free volume.
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  • Héctor J. Dorantes-Rosales, Victor M. López-Hirata, Joel ...
    2007 Volume 48 Issue 10 Pages 2791-2794
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    The phase decomposition of the β′ phase in the Zn-22 mass%Al and Zn-22 mass%Al-2 mass%Cu at room temperature was followed by means of the X-ray diffraction (XRD), transmission electron microscopy (TEM) and Vickers hardness (VH) measurements. Alloys were homogenized at 623 K for 432 ks and then quenched at 275 K. Immediately, they were characterized by XRD and simultaneously other samples were analyzed by hardness Vickers measurements. The XRD results showed that the β′ phase is unstable at room temperature and its decomposition finished after 1.8 and 18 ks by the following reaction, β′→α+η, for the Zn-22 mass%Al and Zn-22 mass%Al-2 mass%Cu alloys, respectively. The TEM analysis was carried out in the Zn-22 mass%Al-2 mass%Cu alloy, which showed a slower kinetics than the Zn-22 mass%Al alloy. The TEM results showed in situ that the β′ phase is in coexistence with the ε phase and its decomposition occurs by the formation of colonies composed of nanometric grains of the α and η phases. Such colonies extend to cover completely all the surface of the alloy, followed by the coarsening of grains to the micrometer scale. The Vickers hardness results showed an increase in hardness up to a maximum of 108 and 148 VH, followed by a decreasing in hardness of 50 and 80 VH, for the natural aging of the Zn-22 mass%Al and Zn-22 mass%Al-2 mass%Cu alloys, respectively. These results can be attributed to the presence of the nanometric and micrometric grains, respectively.
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  • Jianguo Huang, Xishu Wang, Xiangkang Meng
    2007 Volume 48 Issue 10 Pages 2795-2798
    Published: October 01, 2007
    Released: September 25, 2007
    [Advance publication] Released: September 12, 2007
    JOURNALS FREE ACCESS
    The deformation and failure of Cu and Cu/Ni film/substrate structure were studied by the scanning electron microscope (SEM) in situ observation under three-point bending. It was found that the rapid deformation occurred at sites near to the interface of film/substrate in Cu and Cu/Ni films. The transferring of deformation finally caused the surface wrinkle. The wrinkle stress can be expressed as σwf=k(EfEs2)1⁄3. Based on the results in mesoscale, a simple failure mechanism of films/substrate structure is suggested to understand the transferring process of deformation and failure characteristics.
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