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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 47 (2006), No. 8

  • Lattice Defect Behavior of LaNi4.97Sn0.27 during Hydrogenation Cycles

    pp. 1875-1877

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    DOI:10.2320/matertrans.47.1875

    Lattice defect behavior of LaNi4.97Sn0.27 during the hydrogenation cycles has been investigated by in-situ positron lifetime measurement. Mean positron lifetime increased and decreased by each hydrogenation and dehydrogenation, respectively, independently of the hydrogenation cycles. It suggests that lattice defects are introduced by the hydrogenation and removed from the lattice by the dehydrogenation even at below the migration temperature of vacancy in LaNi5. Furthermore, dislocation density and vacancy concentration kept almost constant at the value of around 6×109 cm−2 and 10 ppm through at least eight hydrogenation/dehydrogenation cycles.
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  • Preparation of White Heart Malleable Cast Iron in Na2O-K2O-SiO2 Oxide Molten Salt

    pp. 1878-1881

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    DOI:10.2320/matertrans.47.1878

    The preparation process of white heart malleable cast iron by heat treatment of white cast iron in Na2O-K2O-SiO2 oxide molten salts at lower temperature than usual production method was studied. The liquidus temperature of the K2O added Na2O-SiO2 (64–36 mol%) system was measured by the hot-thermocouple method and the effect of the treatment temperature on the degree of decarburization of white cast iron was investigated. The result of measuring liquidus temperature indicated that the Na2O-K2O-SiO2 (38.4–40–21.6 mol%) ternary oxide melted at about 893 K. After heat treatments of white cast iron (φ8mm×8mm) containing 3.34 mass% carbon in this oxide molten salt at 1123–1223 K for 72 h, the white heart malleable cast iron could be obtained. Although, the thickness of the surface decarburized layer decreased with the decrease of the treatment temperature, the white heart malleable cast iron having about 30 μm surface layer was obtained even at low temperature of 1123 K. The basicity of this molten salt was 2.53, which was too high to be suitable for the decarburization of white cast iron at 1323 K. It is found that white heart malleable cast iron can be prepared by the heat treatment in high basisity oxide molten salt at lower temperature than 1323 K.
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  • Development of an Internet System for Composite Design and Thermophysical Property Prediction

    pp. 1882-1885

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    DOI:10.2320/matertrans.47.1882

    A thermophysical property prediction system for composite materials was developed and is available via Internet access. This system offers users a platform to design new composite materials and to predict properties such as density, specific heat, thermal conductivity, and thermal diffusivity based on the properties of the component materials and the composite structure. The system is composed of a knowledge base, a materials database, and a simulation system. Two simulation methods, an analytical method and a finite element method, are available to calculate the thermal conductivities of the composites. This system has been successfully used to predict the thermal conductivities of SiC whisker-reinforced aluminum alloy matrix composites, thermal-sprayed ZrO2 thermal barrier coatings, and some other composites. The reliability and effectiveness of this system have proven to be good.
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  • Possible Slip Systems in Body Centered Cubic Iron

    pp. 1886-1889

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    DOI:10.2320/matertrans.47.1886

    The slip systems along the ⟨111⟩ direction in bcc iron are investigated by the energy of the generalized stacking fault, or of the stacking fault between two adjacent crystallographic planes of perfect crystals, in order to obtain the knowledge of the slip phenomena in bcc single crystals. For systematic study, the 15 kinds of slip systems along the ⟨111⟩ direction from {110}⟨111⟩ up to {954}⟨111⟩, {972}⟨111⟩ and {981}⟨111⟩ slip systems are taken into account. The energy of the stacking fault is evaluated by the molecular mechanics method with the embedded atom potential of Finnis-Sinclair type as a function of relative displacement of one side of the two half-crystals across the fault plane in the ⟨111⟩ direction. The maximum values of the fault energies for the slip systems whose slip planes have angles of less than approximately 15 degrees to the {110} plane are nearly same as that for the most preferable {110}⟨111⟩ slip system. The maximum value for the {321}⟨111⟩ slip system is the greatest among the currently analyzed 15 slip systems. The maximum value for the {211}⟨111⟩ slip system is in the middle of those for the {110}⟨111⟩ and {321}⟨111⟩ slip systems, and those for the slip systems whose slip planes have angles between approximately 20 degrees and 30 degrees to the {110} plane are close to that for the {211}⟨111⟩ slip system. In general, there is not inverse correlation between the maximum value of the fault energies for the slip system and the interplanar spacing of the considered slip system, although there is inverse correlation between them within the three slip systems which have three lowest index planes, namely, the {110}⟨111⟩, {211}⟨111⟩ and {321}⟨111⟩ slip systems.
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  • Hydriding Properties of (Mg1−xMx)Ni2 C15-Type Laves Phase Alloys

    pp. 1890-1893

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    DOI:10.2320/matertrans.47.1890

    Mg-based Laves phase alloys (Mg0.7M0.3)Ni2, where M elements were Ca, La, Ce, Pr, Nd and Gd were successfully developed. The alloys can be synthesized by a conventional induction melting and annealing method from intermetallic compounds MgNi2 and MNi2 as a source of Mg, Ni and M elements. The crystal structures of the major phases of annealed (Mg0.7M0.3)Ni2 alloys were C15-type for M=Ca and C15b-type for M=La, Ce, Pr, Nd and Gd Laves structures, respectively. In the alloys except M=Ce, hydrogenation and dehydrogenation reversibly occurred. The maximum hydrogen contents of the alloys are 1.2–1.6 mass% (H/M:0.6–0.8) under hydrogen pressure of 5 MPa at 243–273 K. As the results of measurements of p-c isotherms, in the case of the M=Pr and Nd, two step plateaus were clearly observed. After a few hydrogenation/dehydrogenation cycles, the alloys kept C15-type or C15b-type Laves structures without hydrogen-induced amorphization, disproportionation and decomposition.
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  • Thermal Conductivity Measurement of Tungsten Oxide Nanoscale Thin Films

    pp. 1894-1897

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    DOI:10.2320/matertrans.47.1894

    The out-of-plane thermal conductivity of sputtered tungsten oxide thin films with thickness of 100 to 300 nm was measured by two omega method based on a new analytical model with consideration of the interfacial thermal resistance between the films and the substrate. The influence of the tungsten oxide structure on the thermal conductivity was studied. The result reveals that the tungsten oxide thin films made with 10% reactive gas of oxygen had a mixed phase of WO2 and WO3, while those made with 100% oxygen were WO3 only. The thermal conductivity of WO3 thin films is 1.63 Wm−1 K−1, and that of WO2/WO3 films is 1.28 Wm−1 K−1. The difference is explained by a higher thermal resistance at the interface of WO2 and WO3 crystals caused by the mismatch of phonon state.
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  • Syntheses and Hydrogen Desorption Properties of Metal-Borohydrides M(BH4)n (M=Mg, Sc, Zr, Ti, and Zn; n=2–4) as Advanced Hydrogen Storage Materials

    pp. 1898-1901

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    DOI:10.2320/matertrans.47.1898

    Metal-borohydrides M(BH4)n (M=Mg, Sc, Zr, Ti, and Zn; n=2–4) were synthesized by mechanical milling process according to the following reaction; MCln+nLiBH4/nNaBH4→M(BH4)n+nLiCl/nNaCl. Then the thermal desorption properties of M(BH4)n were investigated by gas-chromatography and mass-spectroscopy combined with thermogravimetry. The results indicate that the hydrogen desorption temperature Td of M(BH4)n correlates with the Pauling electronegativity χP of M; that is, Td decreases with increasing value of χP. The components of desorbed gas for M=Mg, Sc, Zr and Ti (χP≤1.5) are hydrogen only, while that for M=Zn (χP=1.6) contains borane besides hydrogen. The Pauling electronegativity χP of M is an indicator to estimate Td of M(BH4)n as candidates for advanced hydrogen storage materials with high gravimetric hydrogen densities and low desorption temperatures.
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  • Changes in the Surface Characteristics of Gas-Atomized Pure Aluminum Powder during Vacuum Degassing

    pp. 1902-1905

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    DOI:10.2320/matertrans.47.1902

    Vacuum degassing is essential in the preparation of RS P/M aluminum alloys to remove adsorbates and for the decomposition of hydrated-Al2O3 on the powder surface. Changes in the surface characteristics during vacuum degassing were investigated by X-ray photoelectron spectroscopy and temperature-programmed desorption measurement. Hydrated-Al2O3 decomposition to crystalline-Al2O3 and hydrogen desorption on the surface of argon gas-atomized aluminum powder occurred at 623 K and 725 K, respectively. This temperature difference suggests that the reaction converting hydrated-Al2O3 to crystalline-Al2O3 during vacuum degassing should be divided into the two reactions “2Al+Al2O3·3H2O→2Al2O3+6Hsurf” and “6Hsurf→3H2”.
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  • Molecular-Dynamics Study of Self-Interstitial Diffusion in bcc-Iron

    pp. 1906-1909

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    DOI:10.2320/matertrans.47.1906

    Self-interstitial diffusion in α-iron is investigated using an embedded-atom-method potential and molecular-dynamics simulations. Curved Arrhenius plot is obtained for the temperature dependence of diffusion coefficients, which is well explained by the superposition of two transition processes among the two allotropic states of self-interstitial defects, the reformation of ⟨110⟩ dumbbell into another ⟨110⟩ configuration and one-dimensional solitonic propagation of a crowdion on ⟨111⟩ axis.
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  • Synthesis of Ti3SiC2 through Pulse Discharge Sintering Powder Mixture Containing Coarse Ti

    pp. 1910-1913

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    DOI:10.2320/matertrans.47.1910

    Ternary compound Ti3SiC2 was successfully synthesized by pulse discharge sintering (PDS) for Ti/Si/TiC powder mixtures with different molar ratios, where coarse Ti powder (−0.15 mm) was used. When the molar ratio of Ti:Si:TiC was selected to be 2:2:3, the content of Ti3SiC2 reached 97.8% and density reached 99.0% after sintering at 1450°C for 20 min under 50 MPa load. The Ti-Si liquid reaction occurred above the Ti-Ti5Si3 eutectic temperature at 1330°C is thought to assist the synthesis reaction of Ti3SiC2 as well as densification.
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  • Substitution Effect of Rare Earth on Hydrogenation for AB5-Type Alloys

    pp. 1914-1917

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    DOI:10.2320/matertrans.47.1914

    Substitution effects of rare earth elements for hydrogenation of MmNi3.55Co0.75Al0.30Mn0.40 AB5-type alloys were investigated, where Mm consisted of La-Pr-Nd-M (M : Ce, Y, Gd, Tm and Lu), and the amount of La and M was adjusted to keep the lattice volume identical which leads to a similar equilibrium hydrogen pressure. The above alloys showed two-phase reaction during hydrogenation, and both the phases had the orthorhombic lattice with a space group of Cmmm after activation. The Ce containing alloy showed a higher equilibrium hydrogen pressure (0.12 MPa) than the others (0.07–0.10 MPa) at 298 K. In addition, this alloy showed the largest lattice volume expansion among the alloys investigated. However, lattice strain of the hydride phases calculated from line broadening in X-ray diffraction peaks showed to be less than 0.9% for all the alloys investigated.
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  • Role of Iridium in Hot Corrosion Resistance of Pt-Ir Modified Aluminide Coatings with Na2SO4-NaCl Salt at 1173 K

    pp. 1918-1921

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    DOI:10.2320/matertrans.47.1918

    Platinum-iridium films (Ir=0,32,46,83,100 at%) were deposited on the nickel-base single crystal superalloy TMS-82+ through magnetron sputtering. After annealing and aluminizing, the Pt-Ir modified aluminide coatings mainly consisted of PtAl2 and β-(Ni,Pt,Ir)Al phases. Hot corrosion resistance of the different Pt-Ir modified aluminide coatings was evaluated through exposure at 1173 K with the Na2SO4+10 mass%NaCl salt coatings. The lowest mass gain (2.99×10−3 kg/m2, after 100 h) was observed for the Pt-46Ir aluminide coating, which formed the dense and continuous protective Al2O3 scale on the surface. The effect of Ir on the corrosion resistance of Pt-Ir modified aluminide coatings was discussed from three aspects—phase transformation, protective scale formation and the role of a Pt-Ir enriched layer.
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  • Effects of Additional Hf on the Thermal Stability and Mechanical Properties of Cu-Zr-Ag Bulk Glassy Alloys

    pp. 1922-1925

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    DOI:10.2320/matertrans.47.1922

    The thermal stability, crystallization behavior and mechanical properties of the Cu45Zr45−xHfxAg10 (x=0 to 45 at%) glassy alloys have been investigated. The glass transition temperature (Tg), crystallization temperature (Tx), liquidus temperature (Tl) and the supercooled liquid region ΔTx (=TxTg) increase with increasing Hf content. The reduced glass transition temperature (TgTl) values are in the range from 0.54 to 0.59. The Vicker’s hardness (HV), Young’s modulus (E) and compressive fracture strength (σc,f) of the Cu45Zr45−xHfxAg10 (x=0 to 25 at%) bulk glassy alloys increase linearly with increasing Hf content and reach the maximum values of 554, 123 GPa and 2020 MPa, respectively, for Cu45Zr20Hf25Ag10 alloy. A different crystallization behavior is observed for Cu45Zr45Ag10 and Cu45Hf45Ag10 glassy alloys.
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  • Preparation of a Wide Zr55Al10Ni5Cu30 Metallic Glass Sheet by a Twin-Roller Type Casting Method and Its Mechanical Properties

    pp. 1926-1929

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    DOI:10.2320/matertrans.47.1926

    Wide Zr55Al10Ni5Cu30 metallic glassy alloy sheets were successfully produced by a twin-roller casting method. The glassy alloy sheet of 12 mm in width, 0.19 mm in thickness and 650 mm in length has flat surfaces with highly white luster. The exothermic heat of the sample keeps almost constant up to 108 ks at 663 K, decreases gradually with increasing time and becomes almost zero at 1210 ks, in agreement with distinct precipitation of crystallites identified as CuZr2 and Al5Ni3Zr2.
    Mechanical properties, which are tensile stress, fracture strain and hardness, were measured for the samples annealed at various temperatures for different times. At high annealing temperatures slightly above and below Tg, the glassy alloy suffers embrittlement by the beginning of crystallization. The glassy alloys annealed at the temperatures much lower than Tg and Tx become brittle after prolonged annealing, in spite of the fact that they show the glassy structure by XRD and DSC.
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  • Nanocrystallization of Cu50Zr45Ti5 Metallic Glass Induced by Electron Irradiation

    pp. 1930-1933

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    DOI:10.2320/matertrans.47.1930

    The effect of electron irradiation on the structure of melt-spun Cu50Zr45Ti5 metallic glass was investigated. Microstructural evolution during electron irradiation was examined by means of conventional and high-resolution transmission electron microscopy (CTEM and HRTEM) equipped with X-ray energy dispersive spectroscopy (EDS). The glassy phase was not stable under electron irradiation and crystalline nanoparticles with the monoclinic CuZr structure were formed. The volume fraction of the nanocrystalline phase increased with the electron dose while the average grain size remained at about 7 nm. This result indicates that electron irradiation is effective in producing nanocrystalline structures from the metallic glass.
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  • Corrosion Behavior of Ti-Based Metallic Glasses

    pp. 1934-1937

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    DOI:10.2320/matertrans.47.1934

    The corrosion behavior of the Ti47.5Cu42.5Ni7.5Zr2.5 metallic glass as well as its modified glasses by the addition of 5 at% Co, Nb or Ta was investigated by electrochemical measurements. Potentiodynamic polarization was carried out in 0.14 kmol/m3 NaCl solution and 0.2 kmol/m3 phosphate buffer solution with 0.14 kmol/m3 Cl ion. All the metallic glasses examined were spontaneously passivated with significantly low passive current density in sodium chloride solution and phosphate buffer solution. The additional elements improve the corrosion resistance and the effect of Nb or Ta is particular. The results of XPS revealed that the passive films were rich in titanium and deficient in copper and nickel. The higher corrosion resistance for the modified glasses is attributed to stable and protective passive films enriched with titanium cation contained certain amount of additional elements. In phosphate buffer solution, the pitting potentials for all glasses are higher than those in NaCl solution possibly due to inhibiting ability of phosphate ion absorbing on the glassy surface.
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  • Compositional Difference of Thermoelectric Properties in Ag9TlTe5

    pp. 1938-1940

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    DOI:10.2320/matertrans.47.1938

    The ternary silver thallium telluride, Ag9TlTe5, was reported to exhibit an excellent thermoelectric performance because of its extremely low thermal conductivity. We have studied the effect of the compositional difference on thermoelectric properties of Ag9TlTe5 by measuring the thermoelectric data on polycrystalline samples with three compositions. A minimal compositional deviation from the stoichiometric Ag9TlTe5 improved the power factor while the thermal conductivity remained extremely low, leading to an enhancement of the thermoelectric figure of merit.
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  • Thermoelectric Properties of Texture-Controlled Bi1.9Sb0.1Te2.7Se0.3 Compounds Prepared by Angular Extrusion Technique

    pp. 1941-1944

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    DOI:10.2320/matertrans.47.1941

    N-type Bi1.9Sb0.1Te2.7Se0.3 compounds were prepared by an angular extrusion technique with rapidly solidified and stacked foils. The extrusion temperature was varied from 653 to 838 K. Thermoelectric properties and the crystal orientation of the compounds were evaluated. The textures of the angular-extruded specimens were observed by Orientation Imaging Microscopy (OIM). The sizes of grains ranged from 4.6 to 16.2 μm in the specimens. The texture in the angular-extruded specimen showed that the basal plane where preferably aligned along the extrusion direction. Strong texture was observed in the specimens extruded at the temperature of 813 K. Electrical resistivity was shown to decrease with an increase in the angular-extrusion temperature. However the dependence of the carrier concentration on the extrusion temperature was small. Our study has shown that the decrease in electrical resistivity is mainly due to the increase of carrier mobility and that the carrier mobility strongly depends on the strength of the texture formed by angular extrusion. The highest Z value of 3.09×10−3 K−1 was derived from the specimen angular-extruded at 813 K. The present result indicates that the angular extrusion technique is effective in improving thermoelectric properties of bismuth-telluride based compounds.
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  • Atomistic Simulation of the Aerosol Deposition Method with Zirconia Nanoparticles

    pp. 1945-1948

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    DOI:10.2320/matertrans.47.1945

    Impacts of nanometer sized ceramic particles to the substrate with different incident angles were simulated by molecular dynamics to investigate the mechanism of aerosol deposition method. Comparing with the normal incident case, obliquely incident particles to the substrate show different characteristics of fragmentation including particle rolling on the substrate and a tail structure of depositing atoms. Structural modification and its incident angle dependence were also observed in the substrate. Elevations of temperatures in nanoparticle and substrate show different dependencies on the incident angle.
    x

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  • Structure of Iron/Nickel Composite Cluster Assemblies Prepared by Double Glow-Discharge-Sources

    pp. 1949-1952

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    DOI:10.2320/matertrans.47.1949

    Using a double-grow discharge cluster source system Fe and Ni clusters have been produced and deposited simultaneously on a substrate. A mixture of Fe and Ni clusters have been obtained with inserting separation plates between two grow discharge rooms and in the center of a growth tube, where partially alloyed cluster assemblies are formed. Fe-Ni alloy cluster assemblies have been obtained without inserting the separation plate. This alloying behavior is different from core-shell cluster formation in simultaneous deposition of Co and Si clusters, and Fe and Si clusters without inserting the separate plate. The present results suggest that structure and morphology of composite clusters strongly depends on the surface energy and degree of oxidation of elemental clusters.
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  • Morphology and Composition-Controls of CuxS Nanocrystals Using Alkyl-Amine Ligands

    pp. 1953-1956

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    DOI:10.2320/matertrans.47.1953

    Nearly monodispersed-size CuxS nanocrystals(NCs) were obtained by sulfuration of Cu(II)-alkyl-amine complexes using dodecanethiol-solvated sulfur at 363 K. The morphology and chemical composition of CuxS NCs can be controlled by using appropriate alkyl-amine ligands. NCs of Cu-deficient sulfides, Cu1.8S (digenite) or a Cu1.8S-Cu2S mixture, were obtained using octylamine or di-octylamine, while stoichiometric Cu2S NCs using tri-octylamine and oleylamine ligands.
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  • High-Pressure Synthesis of Novel Hydride in Mg-Ni (-H) System

    pp. 1957-1960

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    DOI:10.2320/matertrans.47.1957

    A novel hydride was synthesized in Mg-Ni-H system by high pressure technique using a cubic-anvil-type apparatus. Crystal structure, thermal stability and hydrogen content of the hydride were studied. The novel hydride with a composition of MgNi2Hy was synthesized at 973 K for 2 h under the pressure of more than 2 GPa, and was found to exhibit the body-centered tetragonal structure (space group I4⁄mmm, No.139) with lattice parameters of a=0.327(3) nm, c=0.878(9) nm. Moreover, this hydride could be synthesized from each starting material, such as MgNi2 high pressure phase, MgNi2 (C36) and mixture of MgH2-x mol% Ni (x=65–70). Its hydrogen content was estimated to be 2.23 mass% from fusion analysis and corresponding chemical formula was found to be MgNi2H3.2. This hydride was decomposed into MgNi2 (C36) over 460 K, and has solubility of Ni content and thermal stability of the novel hydride was decreased with increasing Ni content.
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  • Effect of Sigma Phase in Co-29Cr-6Mo Alloy on Corrosion Behavior in Saline Solution

    pp. 1961-1964

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    DOI:10.2320/matertrans.47.1961

    Effect of the sigma (σ) phase in Co-29Cr-6Mo alloy on corrosion behavior in saline solution has been investigated. The area fraction of the σ phase contained in Co-29Cr-6Mo alloy varies depending on the aging time at 1023 K. The σ phase is mainly observed at grain boundaries. The area fraction of the σ phase increases with increasing aging time and reaches 0.6% after aging at 1023 K for 21.6 ks.
    The Co-29Cr-6Mo alloys aged at 1023 K for various aging times were immersed in saline solution at 310 K for 1 week and metal ions released from the alloys were examined by inductively coupled plasma atomic emission spectrometer (ICP-AES). The quantity of a released Co ion does not depend on the aging time and shows almost the same value regardless of the different area fraction of the σ phase, while that of released Cr, Mo and Ni ions increases with increasing area fraction of the σ phase. Results of polarization test in saline solution at 310 K revealed that passive current density and breakdown potential of Co-29Cr-6Mo alloys aged at 1023 K for various aging times exhibit almost the same values, although the alloys have different area fraction of the σ phase. These results suggest that a small amount of the σ phase (<0.6%) hardly affect the formation and breakdown of passive film in the Co-29Cr-6Mo alloy aged at 1023 K.
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  • Fatigue Behavior of Ceramic Matrix Composite Oxidized at Intermediate Temperatures

    pp. 1965-1967

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    DOI:10.2320/matertrans.47.1965

    The effect of intermediate temperature oxidation on fatigue behavior of SiC/SiC is investigated to understand fatigue damage mechanisms. It has been found that fatigue life is decreased by 13% after oxidation at 600°C for 100 hours due to disappearance of carbon interphase by oxidation. The strong bonding between the fibers and matrix caused by SiO2 formation at 800°C for 100 hours leads to the shortest fatigue life.
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  • Liquid Solubility of Manganese and Its Influence on Grain Size of Mg-Al Alloys

    pp. 1968-1974

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    DOI:10.2320/matertrans.47.1968

    We conducted this study to clarify the relationship between manganese solubility and grain sizes of Mg-Al alloys. Mg-5%Al, Mg-9%Al, and Mg-11%Al alloys were prepared using high-purity magnesium (>99.99%) and aluminum (99.99%). These alloys were melted at 1123 K by adding electrolytic manganese (99.99%) and solidified as alloy ingots after continuous stirring for 21.6 ks. The alloy ingots were then remelted at 933, 998, and 1073 K, and held statically at each of these temperatures for 21.6 ks. By this process, the excess Mn that existed over its liquid solubility precipitated and sedimented to the bottom of the melt. Thus, the solubility of Mn in liquid Mg-Al alloys was determined by analyzing the upper surface of the ingots quenched from each holding temperature. Consequently, the following equations were derived as experimental formulae for determining solubility of Mn in liquid Mg-Al alloys at different temperatures: & Y=1.79-6.22×10^-2X (1073 K),
    & Y=1.28-4.41×10^-2X (998 K),
    & and Y=0.90-3.35×10^-2X (933 K), where X is the concentration of Al (mass%) and Y is solubility of Mn (mass%).
    Mg-9% Al alloys containing 0 to 3% Mn were prepared in order to investigate the influence of Mn on grain sizes, and microscopic observations of these alloys were carried out with and without superheating of the specimens. The grain diameter of high-purity Mg-9% Al alloys (0% Mn) is approximately 40 μm, which is finer than that of the commercial AZ91E magnesium alloy with superheating. Therefore, high-purity Mg-9% Al alloys have an essentially fine-grained structure. An increase in the Mn content tended to coarsen the grain structure of Mg-9% Al alloys that contain 0.02 to 2.27% Mn; however, the coarse-grained structure can be refined by superheating. Superheating plays a role in resetting the coarse-grained structure to a high-purity structure (initially fine-grained) when Mn is added. Further, it is clarified that the solubility of Mn in liquid Mg-Al alloys exhibits no relationship with either the grain size or the superheating effect.
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  • Effects of Hot Rolling and Subsequent Tempering on Particle Erosion Behavior of SUS403 Martensitic Stainless Steel

    pp. 1975-1980

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    DOI:10.2320/matertrans.47.1975

    The effects of hot rolling and subsequent tempering on particle erosion behavior of SUS403 MSS were investigated as a function of impact angle, reduction and grain size. The results indicated that, cutting is the dominant wear mode for material removal at oblique impact angle. At the higher impact angle, the mode is based on extrusion and cracking. However, at the medium impact angle, the wear is dominated by mode mixed with cutting and extrusion. The characteristics of the cracking are more obvious with increasing impact angle. The erosion rates of all reduction samples increase first and then decrease with increasing impact angle. The maximum erosion rate occurs at the angle of 45°. After hot rolling, grain refining has an effect on decreasing erosion rates in comparison to the direct quenched and tempered samples. Fine grain associated with high density of grain boundary and with strengthening effect in mechanical properties retards the cracking and then decreases the erosion rate. The effect of grain refining on decreasing erosion rate is more obvious with increasing both the impact angle and the reduction. At the normal impact angle, the percentage of decrement of erosion rate is approximately 45% when the material was rolled with 50% reduction. Increasing in the mechanical properties including hardness, ductility, tensile strength and toughness are contributed to decreasing the erosion rate.
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  • Measuring Elastic Energy Density of Bulk Metallic Glasses by Nanoindentation

    pp. 1981-1984

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    DOI:10.2320/matertrans.47.1981

    The elastic energy storing capability of bulk metallic glasses was evaluated by employing depth-sensing nanoindentation. The elastic energy densities of four glassy alloys, determined by nanoindentation measurements, are fairly close to their theoretical values estimated from elastic modulus and theoretical strength. This study provides an accurate and quick method to measure the elastic properties of bulk metallic glasses.
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  • Strengthening and Toughness of AZ61 Mg with Nano SiO2 Particles

    pp. 1985-1993

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    DOI:10.2320/matertrans.47.1985

    The strengthening mechanisms and bending toughness of the AZ61 Mg based composites reinforced by nano SiO2 particles are examined. The composites were prepared either by spray forming, ingot metallurgy, or powder metallurgy, followed by severe hot extrusion. The spray formed composites exhibit the best nano particle distribution and toughness, but the volume fraction of the nano particles that can be inserted is limited. The nano composites fabricated through the powder metallurgy method possess the highest strength due to the extra strengthening effect from the MgO phase. Strengthening analysis based on the Orowan strengthening mechanism can predict well the composite strength provided that the nano particles are in reasonably uniform dispersion. For composites containing higher nano particle volume fractions greater than 3%, the experimental strength data fall well below the theoretical predictions, suggesting poor dispersion of the reinforcement.
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  • Evaluation of Susceptibility to Hydrogen Embrittlement of 7075 Aluminum Alloy by Hydrogen Addition Using Flax-Treatment Method

    pp. 1994-1998

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    DOI:10.2320/matertrans.47.1994

    It is more difficult with aluminum alloys to investigate the effect of hydrogen on their mechanical properties than with steels because of their stable and protective oxide films, which act as a strong barrier for hydrogen penetration. In this study, after the flux-treatment, 7075-T6 alloy was subjected to thermal desorption spectroscopic (TDS) analysis and tensile test using the slow strain rate technique (SSRT) to establish a procedure for adding hydrogen to aluminum alloys and clarify the influence of hydrogen on their environmental embrittlement. The flux-treatment consisted of applying a flux-solution for soldering on specimen surfaces and vaporizing water of the solution. These flux-treated specimens were exposed in a desiccator for various periods of time and then the solidified-flux and corrosion products were removed from the specimen surfaces before the TDS analysis and the tensile test. The experimental results revealed that hydrogen was absorbed into the alloy by the flux-treatment and the hydrogen content had a tendency to increase with increasing exposure time. Additionally, the fracture strain of tensile specimen decreased with exposure time, resulting in more severe embrittlement. Consequently, this flux-treatment method was considered to be an appropriate procedure for adding hydrogen to aluminum alloys and for evaluating their susceptibility to hydrogen embrittlement when combined with SSRT.
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  • Improved Wear Resistance through Surface Modification of Zr50Cu30Ni10Al10 Bulk Glassy Alloys

    pp. 1999-2005

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    DOI:10.2320/matertrans.47.1999

    We examined the surface modifications of Zr50Cu30Ni10Al10 bulk glassy alloys, including oxidization, nitriding, and diamond-like carbon (DLC) coating to improve wear resistance. Wear abrasion in bulk glassy alloys begins with the formation of shear bands, as in cold-rolled structures. Ultimately, lamellar tearing occurs in the lamellar structure of the shear band in the wear region. Surface modification effectively reduces the wear abrasion corresponding to the easy formation of the shear band. Bulk glassy alloy coated with DLC has outstanding wear resistance due to its low surface-friction coefficient.
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  • Creep Characterization of Aluminum-Magnesium Solid-Solution Alloy through Self-Similar Microindentation

    pp. 2006-2014

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    DOI:10.2320/matertrans.47.2006

    Indentation creep tests were performed on an Al-5.3 mol% Mg solid-solution alloy to examine whether mechanical properties can be extracted accurately from a testpiece, as small as a rice grain. A conical diamond indenter was pressed into a test surface with a constant load F at temperatures ranging from 0.60 to 0.65 Tm (Tm: the absolute liquidus temperature). When the representative flow stress \\barσm and the indentation strain rate \\dotεin in the underlying material decreases to each critical value, \\barσc and \\dotεc, as indentation creep proceeds, the stress exponent n for creep varies distinctively from 4.9 to 3.0. The measured \\barσc decreases with increasing temperature, while the corresponding indentation strain rate \\dotεc increases under the same condition. This temperature dependence is in close agreement with the results derived from the dislocation theory. The activation energy Q for creep in range M (n≅5, \\barσm>\\barσc or \\dotεin>\\dotεc) is approximately equivalent to that for the lattice diffusion of pure aluminum, and the Q value in range A (n≅3, \\barσm<\\barσc or \\dotεin<\\dotεc) is close to that for the mutual diffusion of this alloy. With load-jump tests, F was abruptly increased in the indentation creep test. In range M, instantaneous plastic deformation (IPD) takes place evidently even with a slight abrupt increase in load. On the other hand, the IPD does not occur in range A when load increment is within a certain value. However, the occurrence of IPD is observed under the condition of \\barσm>\\barσc or \\dotεin>\\dotεc. The findings suggest that the creep rate-controlling process changes from the recovery control (n≅5) to the glide control (n≅3) below \\barσc. It is thus demonstrated that the indentation testing technique can be effectively used to extract material parameters equivalent to those obtained from conventional uniaxial creep tests in the dislocation creep regime.
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  • Kinetic Study on the Leaching of Pt, Pd and Rh from Automotive Catalyst Residue by Using Chloride Solutions

    pp. 2015-2024

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    DOI:10.2320/matertrans.47.2015

    Recycling platinum group metals (PGMs) from waste and/or secondary resources is becoming quite important due to the limitation of the natural resource deposits of PGMs. Among the processes of PGMs’ recycling from secondary resources, the hydrometallurgical method draws extensive concerns, particularly for the selection of leaching solution. The present work evaluated the ability of chloride leaching solutions, i.e. HCl–H2O2 and NaClO–HCl–H2O2 to extract Pt, Pd and Rh from a kinetic point of view. The effect of temperature in the range of 277–307 K and time were also examined under the conditions of −500 μm of particle size and 100 g L−1 of pulp density. The kinetic model (I): ((1-α)^-1/3-1)+\\frac13ln(1-α)=k_1t was found to be the most suitable to describe the leaching process of Pt, Pd and Rh in the NaClO contained solution. In this model the interface transfer and diffusion across the leached support layer both affect the rate of leaching reaction. Model (II): (1-(1-α)^1/3)^2=k_2ln(t) fits the kinetic data very well for the dissolution of Pd in the HCl–H2O2 solution, showing that the diffusion across the leached support layer mainly affect the kinetic behaviors and the diffusion coefficient is inversely proportional to leaching time t.
    The NaClO contained solution and HCl–H2O2 solution leaching of Pt, Pd and Rh are strongly dependent on the leaching temperature. In the case of the NaClO contained solution, the activation energy based on model (I) for Pd, Pt and Rh was 63.5, 59.1 and 77.9 kJ mol−1, respectively. It is probably because of that the diffusion of NaClO contained solution across the leached support layer was very slow due to the micro-porous structure of the catalyst; and a high activation energy was needed in effect. Regarding to the leaching in the HCl–H2O2 solution, the activation energy for Pd was 13.4 kJ mol−1 on the basis of model (II).
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  • Calorimetric Investigations of Liquid Cu-In-Sn Alloys

    pp. 2025-2032

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    DOI:10.2320/matertrans.47.2025

    The partial and integral enthalpies of mixing of liquid Cu-In-Sn alloys were determined at 1073 K by a drop calorimetric technique using a Calvet-type microcalorimeter. The three binary interaction parameters and the ternary interaction parameters were optimized based on the Redlich-Kister-Muggiano model. The iso enthalpy curves of the ternary Cu-In-Sn system at 1073 K were constructed. The temperature effect on the ternary system was investigated. Our measurements were compared to the calculations based on several extrapolation models and CALPHAD results.
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  • Evaluation of Cell Toxicity and Surface Properties of Surface Modified Ti and Ti Alloys

    pp. 2033-2037

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    DOI:10.2320/matertrans.47.2033

    This study was performed to investigate the surface properties and cell toxicity of the anodized and hydrothermally treated Ti, Ti-6Al-4V alloy and Ti-6Al-7Nb alloy. Bioactivity was evaluated from the surface activation layers formed on the surface of specimens in simulated body fluid (SBF) for a period of 30 days. Cell toxicity was evaluated based on the optical density of the survival cell. The porous oxide films were formed on all of the specimens by anodic oxidation. The oxide films of Ti were composed of strong anatase peaks without rutile peaks, Ti-6Al-4V alloy was composed of weak anatase peaks and weak rutile peaks and Ti-6Al-7Nb alloy was composed of strong anatase peaks and weak rutile peaks. The oxide films of all of the specimens exhibited an increase in the intensity of anatase peaks after hydrothermal treatment. The surface activation layers were formed only on the oxide films of Ti-6Al-7Nb alloy, also this alloy presented a significantly higher optical density than Ti and Ti-6Al-4V alloy on the MTT assay for cell toxicity evaluation.
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  • Effect of ZrO2 Addition to the CaO-SiO2-MgO-CaF2 Slags on the Sulfur Removal from the 16Cr-14Ni Stainless Steel Melts

    pp. 2038-2043

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    DOI:10.2320/matertrans.47.2038

    The equilibrium distribution ratio of sulfur between the 16 mass%Cr-14 mass%Ni stainless steel melts and the CaO-SiO2-MgO-ZrO2-7 mass%CaF2 (B(= (mass%CaO)/(mass%SiO2) = 2.0) slags was measured at 1873 K to clarify the role of ZrO2 in the desulfurization reaction based on the sulfide capacity concept. The sulfur distribution ratio linearly decreases on increasing the oxygen partial pressure with the slope close to −1⁄2 in the logarithmic scale at a fixed sulfur potential and temperature. The sulfide capacity of the slags is constant up to about (mass%ZrO2)⁄{(mass%ZrO2)+(mass%MgO)}=0.3, followed by a linear decrease on increasing the Z⁄(Z+M) ratio. The effect of ZrO2 substitution for MgO on the decrease in the (apparent) sulfide capacity at Z⁄(Z+M)>0.3 could be explained by the decrease in the basicity of the liquid slag phase due to the formation of CaZrO3 from the computational estimations for the phase equilibria and the thermodynamic activities of slag components. Based on the X-ray diffraction patterns of the slags, it was confirmed that the peak intensity for the Ca2SiO4 is strong through the entire composition range, while the intensity of the peaks corresponding to the CaZrO3 is relatively strong in the composition of Z⁄(Z+M)=0.42 and 0.64. The sulfide capacity can be expressed as a linear function of the mass fraction of CaZrO3 in the slags investigated in the present study, while that exhibits a wide distribution at a relatively narrow optical basicity region, resulting from the effect of ZrO2 on the basicity of the liquid slag phase due to the formation of CaZrO3.
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  • Determination of Standard Gibbs Energy of Formation of Al2Nd by Solution Calorimetry and Heat Capacity Measurement from Near Absolute Zero Kelvin

    pp. 2044-2048

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    DOI:10.2320/matertrans.47.2044

    The thermodynamic properties of Al2Nd were investigated by calorimetry. The standard entropy of formation of Al2Nd at 298 K, ΔfS298o(Al2Nd), was determined from measuring the heat capacities, Cp, from near absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpy of formation of Al2Nd at 298 K, ΔfH298o(Al2Nd), was determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energy of formation of Al2Nd at 298 K, ΔfG298o(Al2Nd), was determined from these data. The results were obtained as follows: ΔfS298o(Al2Nd)/J·K−1·mol−1 = −10.7±1.2, ΔfH298o(Al2Nd)/kJ·mol−1 = −105.03±27, and ΔfG298o(Al2Nd)/kJ·mol−1 = −101.85±27.
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  • Explosive Welding of Titanium/Stainless Steel by Controlling Energetic Conditions

    pp. 2049-2055

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    DOI:10.2320/matertrans.47.2049

    Commercially pure titanium and 304 stainless steel were welded using explosive welding technique. The joints were evaluated using optical microscope, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The study indicates the formation of characteristic interfacial oscillations with vortices at high energetic conditions. The reacted products of the vortices have been identified as FeTi and Fe2Ti intermetallics by X-ray diffraction. Increase in the kinetic energy spent at the interface cause the volume of vortices to increase. Smooth wavy and flat topography has been obtained for thin flyer plates due to less kinetic energy loss. The results demonstrate a good welding interface for multi-layered welding using a thin stainless steel interlayer, as the kinetic energy dissipation at the interface was less.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Synthesis of Ni Nanopowders Using an EHA System

    pp. 2056-2059

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    DOI:10.2320/matertrans.47.2056

    Nickel nanopowders were synthesized using an ethylene glycol-hydrazine-ammonia (EHA) system. Based on X-ray diffraction data, the resulting powders were identified as pure crystalline nickel with an average crystal size of ∼20 nm. The mean diameter of the Ni powders decreased as the amount of hydrazine used was increased. A small amount of an AgNO3 solution, a nucleating agent, was found to facilitate the formation of the nanopowders. Ethylene glycol was found to be effective in preventing the nanopowders from becoming agglomerated.
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  • Effect of Cooling Rate on Mg17Al12 Volume Fraction and Compositional Inhomogeneity in a Sand-Cast AZ91D Magnesium Plate

    pp. 2060-2067

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    DOI:10.2320/matertrans.47.2060

    Mg17Al12 compound is a hardening phase in AZ91D alloy. Moreover, the concentration of Al and Zn has been found to be closely related to the corrosion performance of the magnesium alloy. The aim of this work was to study the effect of cooling rate on distribution of Mg17Al12 compound and compositional inhomogeneity in an AZ91D magnesium sand-cast plate (200×140×20 mm3). A copper chill block, which was placed at the end of mold cavity, was used to increase the cooling rate during solidification. A sand-cast plate was also produced, where no chill block being mounted at the end of mold cavity. The “with chill block” plate showed a rapid increasing in cooling rate with respect to distance from riser, as compared to the “without chill block” plate where almost no cooling rate fluctuation occurred. The volume fraction of Mg17Al12 (β phase) in the “without chill block” plate was higher than that in “with chill block” plate. In the “without chill block” plate, volume fraction of Mg17Al12 was about 13.9 vol% (near the riser) to about 19.3 vol% (close to the end of the plate). However, the “with chill block” plate was solidified in a higher cooling rate, leading to low volume fraction of the β phase (13.4 vol%). Higher cooling rate also resulted in more severe compositional inhomogeneity in the sand-cast plate. The Al and Zn concentration in the “with chill block” plate showed a concave downward dependence against the distance to riser. Moreover, in the “with chill block” plate, concentrations of Al and Zn did not enrich at the position near chill face. Instead, the Al and Zn contents near the chill surface were well below the average value. This finding is in disagreement with previous studies.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Numerical Analysis of Thermoelectric Properties of Bi88Sb12 by the Multi-Carrier Model

    pp. 2068-2071

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    DOI:10.2320/matertrans.47.2068

    The large thermopower maximum observed for the bismuth antimony (Bi88Sb12) alloy as a function of temperature, is studied based on the multi-carrier model using the Boltzmann transport theory and Fermi integration. The chemical potential of this system has been initially calculated at each temperature from the observed Hall coefficient data. It was observed that the calculated chemical potential remains close to the bottom of the conduction band at low temperatures, and then increases at T=70 K, where the thermopower maximum is observed. The calculation also showed a similar maximum at this temperature. From the calculated results, the temperature dependence of the thermopower is associated with the extrinsic-to-intrinsic transition, and thus the Bi88Sb12 alloy is recognized as a strongly degenerate semiconductor.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Production of Bulk Glassy Alloy Parts by a Levitation Melting-Forging Method

    pp. 2072-2075

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    DOI:10.2320/matertrans.47.2072

    A levitation melting-forging (LMF) method was developed to prepare glassy Zr55Cu30Ni5Al10, Ni53Nb20Ti10Zr8Co6Cu3, Ti45Cu25Ni15Zr5Sn5Al5 and Cu55Zr25Ti15Ni5 alloy parts with various shapes of coin, ring and dumbbell of 1 mm in thickness. The glassy alloy samples of 1 mm in thickness for tensile test were also produced by the LMF method. These samples were shaped directly from liquid without any intermediate process. The glassy structure in the samples examined by XRD and DSC is independent of sites. The results show the absence of partial crystallization in the glassy alloy coin prepared by LMF, however, a small quantity of crystallization is found in the glassy alloy coin prepared by copper mold casting. This may be due to the suppression of heterogeneous nucleation resulting from non-contact with container. The density of defects in the glassy alloys prepared by the LMF was decreased significantly because of the absence of spurt.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Electrolytic Copper Deposition from Ammoniacal Alkaline Solution Containing Cu(I)

    pp. 2076-2080

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    DOI:10.2320/matertrans.47.2076

    In order to verify the feasibility of copper electrodeposition from ammoniacal alkaline solutions containing Cu(I), the cathodic polarization characteristics of Cu(I) and the galvanostatic electrodeposition from a Cu(I) solution were investigated. The cathodic polarization curve for the 0.5 kmol m−3 Cu(I)-5 kmol m−3 NH3-1 kmol m−3 (NH4)2SO4 solution showed an increase in the electric current corresponding to the deposition of copper at around −0.22 V vs. SHE which is much higher than the potential for hydrogen evolution. The current efficiencies for the copper electrodeposition from the Cu(I) solution nominally without Cu(II) were greater than 95% in the current density range of 200 to 1000 A m−2. A further increase in the current density resulted in a decreased current efficiency due to the hydrogen evolution. The current efficiency decreased with the increasing Cu(II) concentration and temperature. These results indicate that the present copper electrodeposition method is applicable for the new energy-saving hydrometallurgical recycling process.
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  • Preparation of Highly Active Methanol Steam Reforming Catalysts from Glassy Cu-Zr Alloys with Small Amount of Noble Metals

    pp. 2081-2085

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    DOI:10.2320/matertrans.47.2081

    Methanol steam reforming was carried out over catalysts prepared from glassy Cu-Zr alloys containing a small amount of noble metals. The reforming activity increased when the alloys were treated at a temperature above the crystallization point, whereas the as-cast alloy did not have the same activity. The reforming activity of the heat treated alloys increased with the decreasing content of noble metals down to 1 at%. The DSC (differential scanning calorimetry) of the original alloys revealed that the activity was related to the range of the temperature interval between glass transition and crystallization as well as the heat of glass transition. The glassy Cu-Zr alloys with small amount of noble metals changed to fine copper particles supported on zirconium oxide by the heat treatment. The copper particle size of the treated alloys was related to the endothermic heat. These results indicated that the noble atoms were uniformly dispersed into the glassy Cu-Zr alloys at the glass transition temperature. Highly active reforming catalyst can be prepared from an glassy Cu-Zr alloys containing a small amount of noble metals.
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  • Abnormal Enhancement of Ordered Phase in Sputter-Deposited (Fe1−xCox)59Pt41 Thin Films

    pp. 2086-2091

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    DOI:10.2320/matertrans.47.2086

    Magnetic (Fe1−xCox)59Pt41 alloy thin films have been sputter-deposited on Ti coated Si substrates. The surface morphologies of (Fe1−xCox)59Pt41 (x=0,0.2,0.4,0.8) films changed with increasing Co content. The morphology variation was also correlated with phase transformation. An abnormal enhancement of ordered phase (L10) has been identified at x=0.2, as characterized by X-ray diffraction. Further increase of the Co content suppressed the disorder/order transformation. The abnormal enhancement of ordered phase also correlated to the morphologies of these alloy films. The formation of the order phase (at x=0.2) increased the coercivity of the (Fe0.8Co0.2)59Pt41 thin films. The degree of ordering was also slightly enhanced.
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  • Investigations on the Solidification Behavior of Al-Fe-Si Alloy in an Alternating Magnetic Field

    pp. 2092-2098

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    DOI:10.2320/matertrans.47.2092

    Effects of a low frequency alternating magnetic field on the solidification behavior of the Al-Fe-Si alloy were investigated. Solidification characteristics of the alloy were predicted by software Thermo-Calc and compared to the experimental observations. The solidification sequences of the alloy solidified with and without the application of the AC magnetic field were confirmed by DSC and structural measurements. Al3Fe was the dominant phase in the alloy. A small amount of α-AlFeSi phase with its characteristic dendritic or Chinese script-like morphology was observed to grow in close association with Al3Fe. Distribution of Al3Fe phase was almost homogeneous in the volume of the sample when the alloy was solidified in the conventional condition. When the AC magnetic field was imposed, the Al3Fe phase was accumulated towards the center of the sample. Macrohardness profiles were in good agreement with the structural observations.
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  • A New Co-Base Superalloy Strengthened by γ′ Phase

    pp. 2099-2102

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    DOI:10.2320/matertrans.47.2099

    A γ′ strengthened Co-base superalloy with enhanced high temperature properties has been newly developed and the microstructure is mainly composed of a γ⁄γ′ (fcc/L12) structure. The cuboidal γ′ phase is formed with a bimodal distribution and is suggested to play the role of precipitation hardening.
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  • Syntheses and Characterization of Bulky Mesoporous Silica MCM-41 by Hydrothermal Hot-Pressing Method

    pp. 2103-2105

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    DOI:10.2320/matertrans.47.2103

    Dense MCM-41 bulks were successfully synthesized by a hydrothermal hot-pressing (HHP) method. Adsorption/desorption behaviors were evaluated by nitrogen adsorption/desorption technique. Their microstructural features for dense MCM-41 bulks were observed by SEM. As a result, it was found that these dense MCM-41 bulks possessed a high surface area of over 1300 m2/g and significantly uniform mesopores.
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  • Effect of Rhenium Addition on Tungsten Diffusivity in Iron-Chromium Alloys

    pp. 2106-2108

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    DOI:10.2320/matertrans.47.2106

    The Alloying effect of Re on the diffusivity of W in Fe-15 mol%Cr based alloys was investigated experimentally using the Fe-15Cr/Fe-15Cr-5W and Fe-15Cr-1Re/Fe-15Cr-5W diffusion systems. In these systems, a single ferrite phase existed stably at 1473 K, and Fe and W atoms interdiffused at 1473 K without any attendant changes in the Cr concentration of 15 mol% in them. The measured diffusion length of W atoms was shorter in the Re-containing diffusion system than the Re-free one. Following the binary Boltzmann-Matano method, an apparent interdiffusion coefficient at 1473 K was estimated to be 7.1×10−15 m2/s in the Re-free diffusion system and 1.5×10−15 m2/s in the Re-containing diffusion system. Thus, the presence of Re in the alloy worked to suppress the atomic diffusion of W in a ferrite phase.
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  • Characterization of β′ Phase Precipitates in an Mg-5 at%Gd Alloy Aged in a Peak Hardness Condition, Studied by High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy

    pp. 2109-2112

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    DOI:10.2320/matertrans.47.2109

    The β′ phase precipitated in a 95 at%Mg-5 at%Gd (Mg95Gd5) alloy aged in a peak hardness condition (at 200°C for 100 hrs) is studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Atomic-scaled HAADF-STEM observations of the β′ phase can propose a new structure model with an orthorhombic unit cell of a=0.64 nm, b=2.28 nm and c=0.52 nm and a composition of Mg7Gd. The β′ precipitates have a plate-shape with an about 40 nm width along the [001]m of the Mg-matrix and an about 100 nm length along [210]m-typed directions, and joining of the plate-shaped precipitates establishes a two-dimensional cell structure parallel to the (001)m plane of the Mg-matrix.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Atomic Size Effect in Impurity Induced Grain Boundary Embrittlement

    pp. 2113-2114

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    DOI:10.2320/matertrans.47.2113

    Bismuth segregated to the grain boundary in Cu is known to promote brittle fracture of this material. Schweinfest et al. [Nature 432 (2004) 1008–1011] reported first-principles quantum mechanical calculations on the electronic and structural properties of a Cu grain boundary with and without segregated Bi and argue that the grain boundary weakening induced by Bi is a simple atomic size effect. But their conclusion is incomplete for both Bi and Pb because it fails to distinguish the chemical and mechanical (atomic size) contributions, as obtained with our recently developed first-principles based phenomenological theory. [Phys. Rev. B 63 (2001) 165415.]
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