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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 8

  • Through-Thickness Characterization of Microstructure and Texture in High Purity Aluminum Processed to High Strain by Accumulative Roll-Bonding

    pp. 1978-1985

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    DOI:10.2320/matertrans.MA200702

    The deformation microstructure and texture have been characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) through the thickness of high purity (99.99% purity) aluminum sheets processed by accumulative roll-bonding (ARB) up to a total strain of 4.8. This processing route creates a complex strain path, resulting in a characteristic texture changes through the thickness of the sample, very different from that obtained by conventional rolling, and also in a randomization of the overall deformation texture. The microstructure is composed of an equiaxed structure with a high concentration of high-angle boundaries and a small fraction of a lamellar structure with a high concentration of low-angle boundaries. The observations showed a coupling between the local texture and microstructure; the equiaxed regions are composed of deformation texture components and random texture components while the lamellar regions are composed of the deformation texture components, i.e. rolling or shear texture components.
  • Rolling Textures in Aluminum Single Crystal Deviated by 5 Degrees about Rolling Direction from (001) [100] Orientation

    pp. 1986-1991

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    DOI:10.2320/matertrans.L-MRA2007868

    The development of rolling texture was studied by an X-ray diffraction method using pure aluminum single crystals with an initial crystal orientation deviated by 5° about the rolling direction from the ideal (001) [100] orientation. The crystal was cold-rolled with constraint provided by a polycrystalline aluminum frame. The rolling texture was compared with the texture measured for a different crystal rolled without constraint. The texture rolled without constraint was also compared with the texture of (001) [100] single crystals rolled without constraint reported in our previous study. At 50% reduction in thickness, the texture of the crystal deviated by 5° from the ideal orientation rolled without the constraint was composed of two main orientations, which were characterized by resultant rotations about the transverse, rolling and normal direction axes with respect to the initial orientation. The two main orientations reached {123} ⟨634⟩ at 95% reduction in thickness without passing through {110} ⟨001⟩ and {110} ⟨112⟩. In order to realize crystal rotation from {100} ⟨001⟩ to {123} ⟨634⟩ in rolling, the {100} ⟨001⟩ single crystal should have the initial orientation deviated by 5° from the ideal orientation, and in addition be rolled without constraint. At 95% reduction in thickness, different character of textures was observed in the crystals deviated by 5° from the ideal orientation rolled with and without constraint. In both cases, however, no cube orientation was recognized in the textures.
  • Crystallographic Orientation Distribution Control by Means of Continuous Cyclic Bending in a Pure Aluminum Sheet

    pp. 1992-1997

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    DOI:10.2320/matertrans.L-MRA2007870

    Continuous cyclic bending (CCB) has been proposed as a useful straining technique to produce the high strain on the surface layers and the lower strain in the central layer of the sheet. A pure aluminum sheet is worked by the CCB using the “Roll traveling device” and “Roll driven machine”. It is found that a sharp Cube orientation is formed by the CCB and subsequent annealing in the pure aluminum sheet. Influences of the CCB/annealing process parameters such as partial or final annealing temperature, strain inside grains and repeating effect, on the Cube sharpening are investigated. The sharper Cube orientation is obtained for the higher temperature of the final annealing after the roll traveling device CCB. While a considerably strong Cube texture appears after one routine of the roll driven machine CCB/773 K-3.6 ks, the texture is weakened after two routines repeated to change into a random texture. The 10 Pass and 20 Pass CCBs with a comparatively low degree of working before partial annealing lead to a high Cube fraction more than 60%.
  • Determination of the Phase-Field Parameters for Computer Simulation of Heat Treatment Process of Ultra Thin Al Film

    pp. 1998-2001

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    DOI:10.2320/matertrans.MA200710

    We have simulated grain growth process of an Al ultra thin film by the phase field method. As the model of the calculation, we used the poly crystal model of Kobayashi-Warren in which the phase field and the orientation field are considered. The section of the thin film was divided into 2-dimensional meshes and the time developing equations of the phase field and the orientation field were solved numerically. The parameters for the present calculation have been determined to fit to the results of the grain growth experiment of Al thin film. The relaxation time of grain rotation, only the phase field parameter assumed to be temperature dependent, was determined from the time evolution of averaged grain size in the annealed Al thin film. Isothermal annealing process at various temperatures has been examined using the tuned phase field parameters and the temperature dependence of grain growth was clearly observed.
  • Influence of Grain Boundary Migration on {001} Texture Formation in Al-3 mass%Mg Based Alloys during High Temperature Compression Deformation

    pp. 2002-2007

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    DOI:10.2320/matertrans.L-MRA2007869

    Uniaxial compression tests were conducted on Al-3 mass%Mg alloy and Al-3 mass%Mg-0.2 mass%Sc alloy under various amounts of strain and strain rate at 723 K. High temperature yielding phenomena were observed at 723 K and strain rates ranging from 1.0×10−4 s−1 to 5.0×10−3 s−1. Texture examination elucidated that fiber textures were constructed in all the deformation conditions. Texture measurement revealed that the main component of the fiber texture changed from {011}+{001} to {001} with an increase in strain when the viscous motion of dislocation is the dominant deformation mechanism in the binary alloy. Texture changes are also seen at strength of the {001} component in the binary alloy that increased with increase in strain rates between 5.0×10−4 s−1 and 5.0×10−3 s−1 up to a strain of −1.0, while in the ternary alloy, neither variation of the pole density at (011) nor (001) in inverse pole figure is observed in the same deformation conditions. It is considered that Al3Sc precipitates contribute to the suppression of grain boundary migration. This means that the grain boundary migration contribute to the development of {001} fiber texture.
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    1. Mechanical Properties of 5083 Aluminum Alloy Sheets Produced by Isothermal Rolling MATERIALS TRANSACTIONS Vol.48(2007), No.8
  • Mechanical Properties of 5083 Aluminum Alloy Sheets Produced by Isothermal Rolling

    pp. 2008-2013

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    DOI:10.2320/matertrans.L-MRA2007872

    The microstructure and mechanical properties of AA5083 aluminum alloy sheets consisting of well developed β-fiber texture were investigated. In order to maintain rolling textures after final annealing, the materials were rolled isothermally at 623 K by making use of heated rolls and reheating process every pass up to final thickness of 1 mm. The isothermal rolled sheets consisted of fine subgrain structures through the thickness with a high proportion of low angle boundary less than 15°. Tensile properties showed anisotropy clearly regarding elongation and Lankford value. In the isothermal rolled sheets, the elongation of 0° to rolling direction was below 20% and Lankford value of 45° to rolling direction was over 1.5. Therefore, the average Lankford value showed 1.0. The yield strength of the isothermal rolled sheets was about 40% higher than that of the cold rolled sheets because of subgrain structures. The low ductility of 0° to rolling direction on the isothermal rolled sheets seemed to reduce drawability at room temperature. The warm drawability of the isothermal rolled sheets improved and was superior to the cold rolled sheets because of increasing ductility and keeping higher strength than the cold rolled sheets.
  • Texture Control for Improving Deep Drawability in Rolled and Annealed Aluminum Alloy Sheets

    pp. 2014-2022

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    DOI:10.2320/matertrans.L-MRA2007871

    In order to find a possibility of texture control for improving deep drawability in rolled and annealed aluminum alloys, the relation among recrystallization texture, r-value and limiting drawing ratio was examined for sheet materials with various textures. By using specimens with {111} texture prepared artificially, limiting drawing ratio could be measured in a wide range of average r-value from 0.4 to 1.6. Experimental results demonstrated that there was a positive correlation between average r-value and limiting drawing ratio even in aluminum alloys. This means that an increase in average r-value leads to improvement of deep drawability. Warm rolling that forms shear texture including {111} components, therefore, was conducted to enhance average r-value for Al-Mg and Al-Mg-Si alloys. Recrystallization texture of an annealed Al-Mg alloy consisted of retained shear texture components in the surface layer and cube plus R orientations in the center layer. The average r-value was considerably improved compared with that of a cold rolled sheet. On the other hand, a T4-treated Al-Mg-Si alloy had a relatively weak cube texture on the whole, though the surface layer showed a different texture from the center. In this case, warm rolling was ineffective in improving average r-value, in spite of the existence of surface texture with higher r-value. However, the relation between recrystallization texture and experimental r-value was successfully explained for the Al-Mg-Si alloy as well as for the Al-Mg alloy, based on r-value calculations from overall texture through sheet thickness.
  • Deformation and Texture Evolution during High-Speed Rolling of AZ31 Magnesium Sheets

    pp. 2023-2027

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    DOI:10.2320/matertrans.L-MRA2007875

    Deformation of AZ31 sheets during high-speed rolling at various temperatures was investigated. The thickness of 2.5 mm was reduced 60% by single-pass operation at a speed of 2000 m/min. Textures, microstructures, mechanical properties and bendability of the sheets processed were examined. In the sheets rolled at elevated temperature, equiaxed fine grains (<5 μm) having a basal texture with double peaks were formed around the center of the thickness. The surface layer was sheared very severely by friction to form coarse grains having a well-developed basal texture with a single peak. With increasing the rolling temperature, the grain size increases and the texture weakens slightly at the center. The bendability of the sheet improves with increasing the rolling temperature. The cold-rolled sheet having a deformation microstructure with shear bands and twins shows limited ductility.
  • Crystallographic Texture of Warm Caliber-rolled Low Carbon Steel

    pp. 2028-2035

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    DOI:10.2320/matertrans.MA200703

    The evolution of crystallographic texture with effective strain up to 5.9 is studied in low carbon steel bars fabricated using multi-pass warm caliber rolling. Three-dimensional finite element analysis was carried out to evaluate distributions of effective strain accumulated and strain components introduced with each pass through the rolled bars. The texture at characteristic deformation sites on the cross section in the bars was analyzed using the electron back-scattered diffraction method. Although the texture in the area around the center is dominated by a strong α-fiber (RD||⟨101⟩), in the other two areas, an α-fiber texture is not produced. It is clarified that this difference depends on three deformation modes during rolling. Consequently, the areas around the corners, where effective strain of over 5.7 is introduced, are filled with ultrafine ferrite grains of below 680 nm, and the texture in the areas is random regardless of the increase of the effective strain under a bi-directional simple compressive condition.
  • Factors Affecting Texture Memory Appearing through α→γ→α Transformation in IF Steels

    pp. 2036-2042

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    DOI:10.2320/matertrans.MA200704

    In case where IF steel is heat treated in γ region, α→γ and γ→α transformation during heating and cooling, i.e. α→γ→α transformation, take place during heating and cooling, respectively. The initial texture of α is potentially weakened due to two times transformation in general. On the contrary, the α→γ→α transformed texture resembles the initial texture clearly under specific circumstances. Authors call this phenomenon “texture memory”. A very distinct texture memory effect was found in IF steels. Lowering the γ→α transformation temperature pronounces texture memory significantly. The variant selection at grain boundary of γ seems to play an important role. Moreover, it is considered that the initial α texture has to be sharp to in order to realize texture memory.
  • Change in Microstructure and Texture during Annealing of Pure Copper Heavily Deformed by Accumulative Roll Bonding

    pp. 2043-2048

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    DOI:10.2320/matertrans.MA200701

    Pure copper sheets were heavily deformed up to equivalent strain of 4.8 by the accumulative roll-bonding (ARB) processed and then annealed. The ARB processed copper showed the ultra-fine grained microstructure which consisted of relatively equiaxed grains having grain thickness of about 0.2 μm. The DSC measurement of the ARB processed specimens revealed that the recrystallization temperature significantly decreased with increasing the number of the ARB cycles. The stored energy did not increase so much at later stage of ARB, which corresponded with the change in microstructure. The recystallization behavior of the ARB processed copper was governed by discontinuous recrystallization characterized by nucleation and growth process. Remarkable development of cube texture ({100}⟨001⟩) was found in the specimen deformed to the equivalent strain of 3.2 or larger and then annealed. The concentration of the cube recrystallization texture depended on the number of ARB cycles.
  • EBSD Characterization of the Twinning Microstructure in a High-Damping Mn–Cu Alloy

    pp. 2049-2055

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    DOI:10.2320/matertrans.MA200707

    The {101} transformation twinning bands in Mn–Cu alloys are considered to be the dominant microstructural feature contributing to the high damping capacity of the alloys. Because the face-centered-tetragonal (fct) phase of Mn–Cu alloys has an axis ratio (ca) of nearly 1, an angular resolution for Kikuchi diffraction bands of better than 0.5° is necessary to identify the twin boundaries by the electron backscattering diffraction (EBSD) method. At some angular resolutions, [100] and [001] orientations of the fct phase may be randomly recorded within the single twinning band. In contrast, the image-quality signal of EBSD shows a reflection that is sensitive to the twinning bands. The image-quality contrast is produced by the average orientation difference between the twinning bands. Therefore, the twinning bands of Mn–Cu alloys can be identified by partitioning the orientation distribution of the normal direction for the observed sample section in a range of about 1°. With the aid of {101} stereographic projection, the width of the twinning bands and the intersection morphology were analyzed for a Mn–Cu alloy. The observed intersection morphology was related to a 60° or 90° spatial intersection configuration of different groups of twinning bands. In addition, sharpened ends of twinning bands at the junction regions and secondary twinning phenomena were also characterized.
  • Consolidation and Microstructure Control of Bismuth Antimony Telluride by Compressive Torsion Forming

    pp. 2056-2061

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    DOI:10.2320/matertrans.MA200705

    Bismuth antimony telluride has the best performance among the p-type thermoelectric materials used in the range of temperature between 300 K and 500 K. This material has a trigonal-hexagonal scalenohedral crystal structure and the cleavage parallel to the basal plane of the crystal can readily occur. Suppression of the electrical resistivity and the thermal conductivity will be effective for further improvement of the performance of the thermoelectric elements made from this material. The compressive torsion forming is the severe plastic deformation technique, in which the loads of compression and distortion are simultaneously subjected to the materials without change in its shape. In this work, we have applied this technique to the powder of bismuth antimony telluride for consolidation and improvement of the thermoelectric performance by refining the grain structure and by controlling the crystal orientation. The samples consolidated under various forming conditions were investigated with respect to density, microstructure, XRD, texture, and thermoelectric properties. It was found out that the compressive torsion forming is effective for the microstructure control, the grain structure less than 10 μm can be obtained, and the thermoelectric performance is obviously improved by the compressive torsion forming.
  • Texture Control in Hydroxyapatite by Hot Forging

    pp. 2062-2066

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    DOI:10.2320/matertrans.MA200706

    Crystallographic textures of hydroxyapatite (HAp) and calcium-deficient hydroxyapatite (DAp) were controlled by hot forging. HAp, HAp-40 mass%DAp and DAp green bodies prepared by a colloidal process were hot-forged at 1273 or 1473 K, after which the c-axes of HAp and DAp with a hexagonal-based structure tended to be aligned perpendicular to the forging direction. Crystal rotation of the rod-shaped HAp and DAp during hot forging led to the texture formation, and the tendency of the texture formation enhanced with increasing forging pressure. Hot-forged HAp samples exhibited stronger texture at 1273 K than 1473 K while the texture of HAp-40 mass%DAp and DAp samples was more strongly concentrated at 1473 K. Aspect ratios of HAp and DAp, which might depend on forging temperature, was thought to strongly affect the formation of the crystallographic texture.
  • Molecular Dynamics Simulation on the Modification of Crystallographic Orientation in Fragmented Particles in the Aerosol-Deposition Process

    pp. 2067-2071

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    DOI:10.2320/matertrans.MA200712

    Particle fragmentation and modification of crystallographic orientation in the aerosol-deposition process were investigated by molecular dynamics simulation. Atomistic models of bcc Fe and fcc Ni particles of 10 nm in diameter were subjected to collision to at substrates, and analyzed for their structural modification due to the impact. It was found that particle fragmentation takes place depending on both crystal structure and initial orientation of incident particles. Modification of crystallographic orientation were observed in both bcc and fcc particles and in bcc substrates. Microscopic mechanisms of particle fragmentation and orientation modification were found to be classified into three types, sliding, compression, and third phase generation, which are related to slip systems and relaxation of interface structures.
  • Synthesis of Ca3Co4O9 Ceramics by Citric Acid Complex and Hydrothermal Hot-Pressing Processes and Investigation of Its Thermoelectric Properties

    pp. 2073-2078

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    DOI:10.2320/matertrans.E-MRA2007805

    Ca3Co4O9 ceramics powders were synthesized by the citric acid complex (CAC) method and consolidated by the hydrothermal hot-pressing (HHP) technique. The observation by the scanning electron microscope indicated that the powders obtained by the CAC process showed plate-like grains. The density and the Lotgering factor, which was estimated from the X-ray diffraction data, of the sintered body increased with an increase of the operating pressure during the HHP process. The electrical resistivity was much reduced with an increase of the operating pressure, but the Seebeck coefficient was hardly affected by the HHP conditions. As a result, the sample treated with the HHP under the condition of 573 K, 200 MPa and 3 h showed a maximum power factor.
  • Thermoelectric Properties of Half-Heusler Type LaPdBi and GdPdBi

    pp. 2079-2082

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    DOI:10.2320/matertrans.E-MRA2007807

    The authors studied the thermoelectric properties of LaPdBi and GdPdBi half-Heusler compounds. Polycrystalline samples were prepared by a spark plasma sintering (SPS) technique, and their thermoelectric properties were measured above room temperature. The electrical resistivities of both samples show a semiconductor like behavior and are on the order of 10−6 Ω m. The estimated band gap energies of LaPdBi and GdPdBi are 0.05 and 0.07 eV, respectively. The values of the thermoelectric power are positive and decrease with increasing temperature. The thermal conductivities increase with increasing temperature because of the increase of the carrier contribution to the thermal conductivity. The maximum values of the dimensionless figure of merit ZT are 0.085 at 615 K for LaPdBi and 0.084 at 469 K for GdPdBi, respectively.
  • Fabrication and Thermoelectric Properties of Ag9TlTeX (X=5.0∼6.0)

    pp. 2083-2087

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    DOI:10.2320/matertrans.E-MRA2007837

    Polycrystalline samples of Ag9TlTe5 with different nominal compositions: Ag9TlTeX (X=5.0, 5.05, 5.1, 5.2, 5.3, 5.5, 5.7, 6.0) were prepared and the phase relations were studied by X-ray diffraction (XRD) analysis. The electrical resistivity, Seebeck coefficient and thermal conductivity of Ag9TlTeX (X=5.0∼5.5) were measured from room temperature to around 630 K. The dimensionless figure of merit (ZT) of Ag9TlTe5.0 was quit low (∼0.08), while those of other samples were very high (∼1.0). It was confirmed that the thermoelectric properties of Ag9TlTe5 are significantly influenced by a minimal compositional deviation and the high ZT was obtained when the tellurium content was slightly larger than the stoichiometric composition.
  • Thermoelectric Properties of Combustion Synthesized and Spark Plasma Sintered Sr1−xRxTiO3 (R = Y, La, Sm, Gd, Dy, 0<x≤0.1)

    pp. 2088-2093

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    DOI:10.2320/matertrans.E-MRA2007836

    Thermoelectric properties of combustion synthesized and spark plasma sintered rare-earth-doped (Y, La, Sm, Gd and Dy) SrTiO3 was investigated from room temperature to 870 K toward the viewpoint of energy and time saving without deterioration in thermoelectric properties. All the rare-earth-doped SrTiO3 were successfully synthesized and sintered with high purities and high densities. With temperature increasing, the absolute value of Seebeck coefficient increased and the electric conductivity decreased; the power factor of all the samples decreased except Y-doped sample in the experimental temperature range. In all the samples, the La-doped SrTiO3 and the Y-doped SrTiO3 had the highest and the lowest power factor, respectively. The dimensionless figure of merit ZT of La-doped samples with different doping amount was evaluated and the maximum ZT was 0.22, which was obtained at 800 K from Sr0.92La0.08TiO3 sample. Comparing Y and La-doped samples prepared by our method with that of conventional solid-state reaction method, the thermoelectric properties of our samples were relatively higher. Thus the combination of combustion synthesis and spark plasma sintering has a potential to prepare perovskite-oxide materials with relatively higher thermoelectric properties for high-temperature application.
  • Thermoelectric Properties and Phase Transition of (ZnxCu2−x)V2O7

    pp. 2094-2099

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    DOI:10.2320/matertrans.E-MRA2007856

    The phase stability and thermoelectric properties of the layered structure of (ZnxCu2−x)V2O7 solid solutions were studied for x≥0.2. X-ray diffraction measurements, compositional studies, and thermal analysis verified that the low-temperature form of the (ZnxCu2−x)V2O7 solid solution (monoclinic structure, C2/c) was stable for 0.2≤x≤2 when heated below 863 K in air. On heating, phase transformation occurred at least at 0.2≤x≤2 at a nearly constant temperature of approximately 873 K; above this temperature, a high-temperature form of the (ZnxCu2−x)V2O7 solid solution was formed.
    The Seebeck coefficients of the low-temperature (ZnxCu2−x)V2O7 solid solution exhibited large negative values in the range of approximately −520 to −700 μV/K, and the electrical resistivity increased with Zn addition. The maximum power factor of 1.99×10−7 W/m K2 was obtained at 823 K for the low-temperature form of the (Zn0.2Cu1.8)V2O7 solid solution.
  • Improvement of Thermoelectric Properties of β-FeSi2 by the Addition of Ta2O5

    pp. 2100-2103

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    DOI:10.2320/matertrans.E-MRA2007860

    Our goal is the improvement of the thermoelectric properties for FeSi2. We investigated the improvement of thermoelectric properties, that is, the increase of the power factor and the decrease in the thermal conductivity to add Ta2O5. The thermal conductivity of specimens with 1 mass% and 3 mass% of additive decreased to half in comparison with the sample without additive, because phonon scattering was enhanced as a result of an increase in the number of pores in the samples by the influence of Ta2O5. The figure of merit for sample with 1 mass% and 3 mass% of additive were higher than that for the sample without additive. The highest performance of the sample with 1 mass% of additive was 2.5×10−4K−1∼2.8×10−4 K−1 around 700 K and its dimensionless figure of merit was 0.2 at 700 K.
  • Thermoelectric Properties of the Layered Cobaltite Ca3Co4O9 Epitaxial Films Fabricated by Topotactic Ion-Exchange Method

    pp. 2104-2107

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    DOI:10.2320/matertrans.E-MRA2007864

    To clarify the thermoelectric properties of the layered cobalt oxide Ca3Co4O9 epitaxial film fabricated by the topotactic ion-exchange method [K. Sugiura et al., Appl. Phys. Lett. 89, 032111 (2006)], the electrical resistivity (ρ), Hall coefficient (RH), and Seebeck coefficient (S) of high quality Ca3Co4O9 epitaxial film were examined over the temperature range 10–1000 K. The film exhibited a low ρ of 4.0×10−3 Ω cm and a large S of ∼+200 μV K−1, which leads to the thermoelectric power factor of 1.0×10−3 W m−1 K−2, at 1000 K. Furthermore, the film exhibited good thermal stability at 1000 K in air.
  • First-Principles Study of Electronic Structure and Thermoelectric Properties for Guest Substituted Clathrate Compounds Ba6R2Au6Ge40 (R=Eu or Yb)

    pp. 2108-2113

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    DOI:10.2320/matertrans.E-MRA2007865

    The electronic structure and thermoelectric properties of guest substituted clathrate compounds Ba6R2Au6Ge40 (R=Eu, Yb) are calculated using the full-potential linearized augmented plane wave method based on the density functional theory. The bottom of conduction band for Ba8Au6Ge40 is formed by one relativity dispersive band close to the M point. When the Ba 2a site is replaced by Eu and Yb, the lowest conduction bands at X point shift to lower energy side. The coupling between gusest atom at 2a sites and the host framework becomes weaker with decreasing ionic radii. This multivalley effect in M and X points yields the increase in the density of states near the conduction band edge, resulting in the increase in the Seebeck coefficient for n-type doping. On the other hand, the valence band edge is almost independent of the guests; the f-bands of Eu and Yb are narrow and distant from the band edge. The effect of Eu and Yb substitution on the Seebeck coefficient is small for p-type doping at higher temperature.
  • Modeling the Self-Preservation Effect in Gas Hydrate/Ice Systems

    pp. 2114-2118

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    DOI:10.2320/matertrans.N-MRA2007866

    Molecular dynamics simulations were performed to investigate the possible role of ice shielding in the anomalous preservation of gas hydrates. Two cases of ice shielding were considered: immersion of hydrate particles into bulk ice Ih and wrapping of similar particles in a thin ice shell. For a microscopic-level model of methane hydrate clusters immersed in bulk ice the excess pressure in the hydrate phase at 250 K was found to be sufficient to shift the gas hydrate into the region of thermodynamic stability on the phase diagram. For the second model the temperature dependence of various properties of the hydrate/ice nanocluster was studied. The surface tension estimates based on the Laplace equation show non-monotonic dependence on temperature, which might indicate the possible involvement of hydrate/ice interfacial phenomena in the self-preservation of gas hydrates.
  • High Temperature Ferromagnetism in Fe-Doped ZnO: a Density Functional Investigation

    pp. 2119-2122

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    DOI:10.2320/matertrans.N-MRA2007867

    The electronic structure and related magnetic properties of Fe-doped ZnO system is analyzed in presence of both O- and Zn-vacancy in the framework of TB-LMTO-ASA method within LSDA. Although for the Fe-doped ZnO system, the ground state is antiferromagnetic, in presence of O-and Zn-vacancy the magnetic mechanism is drastically altered. Utilizing the two-centered tight binding model of Anderson and Hasegawa, we have investigated the nature of the two competing interactions : antiferromagnetic super-exchange versus ferromagnetic double-exchange interactions, as a function of the Fe-Fe separation by supercell calculations. The results reveal that for obtaining long-range half-metallic ferromagnetism, Zn-vacancy is more crucial than O-vacancy.
  • Electron Diffraction study of Layer Structures in La-Mg-Ni Hydrogen Absorption Alloys

    pp. 2123-2127

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    DOI:10.2320/matertrans.MBW200631

    In order to improve the hydrogen absorption properties of the layer structure appearing at the nickel rich side of La-Mg-Ni alloy, appropriate amounts of Ni were replaced by some elemental atoms, Mn, Co and Al. The La0.8Mg0.2Ni3.4−xCo0.3(MnAl)x (0<x<0.4) alloy system was synthesized and crystal structures were investigated by electron microscopy. The atomic concentration ratio of (LaMg) to the other atoms was 3.7 in this system. The Pr5Co19-type structure (5:19H-structure) and the Ce5Co19-type structure (5:19R-structure) were found in this alloy system. Electron micrographs of these structures are presented in this paper. Structure analysis of the complex layer structure is demonstrated by careful observation of the electron diffraction pattern.
  • Influence of Al and Ag on the Devitrification Behavior of a Cu-Zr Glassy Alloy

    pp. 2128-2132

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    DOI:10.2320/matertrans.MF200633

    This paper presents an influence of Al and Ag additions on the thermal stability and devitrification behavior of Cu-Zr glassy alloy on heating. The crystallization kinetics and structure changes in Cu50Zr45Al5 and Cu45Zr45Al5Ag5 glassy alloys on heating were studied by X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The addition of Al and Ag to Cu50Zr50 alloy drastically changes its crystallization behavior. It is found that Cu50Zr45Al5 and Cu45Zr45Al5Ag5 glassy alloys show rather eutectic crystallization forming mostly stable phases while Cu50Zr50 glassy alloy exhibits a primary crystallization behavior forming a metastable monoclinic CuZr phase at the initial crystallization stage.
  • Effect of Thermal Treatment on the Intermetallic Compounds Formed at Sn-9Zn-1.5Ag-xBi (x = 0 and 1) Lead-Free Solder/Cu Interface

    pp. 2133-2138

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    DOI:10.2320/matertrans.MRA2007075

    The formation of Intermetallic compounds (IMCs) at the interface between an Sn-9Zn-1.5Ag-xBi solder alloy and a Cu substrate dipped at 250°C and heat-treated at 150°C for various times has been investigated by an optical microscope (OM), an X-ray diffractometer (XRD) and a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). The OM result shows the flat and smooth surface for the Sn-9Zn-1.5Ag-1Bi solder alloy and Cu substrate after dipping at 250°C. The phases of IMCs formed are Cu6Sn5 and Cu5Zn8 for both lead-free solder alloys. After thermal treatment at 250°C for 200 h, the phases of IMCs are Cu6Sn5, Cu5Zn8 and Ag3Sn. The Cu6Sn5 has a scallop morphology, and is located at the interface between the solder and Cu substrate. The adhesion strength for the Sn-9Zn-1.5Ag-1Bi lead-free solder alloy is higher than the Sn-9Zn-1.5Ag solder alloy. After being heat-treated at 150°C, the adhesion strength of the Sn-9Zn-1.5Ag-1Bi solder alloy decreases from 12.67±0.45 to 6.92±0.38 MPa after thermal treatment for 200 h.
  • TEM Characterization of Twinning in Co39Ni33Al28 Alloy

    pp. 2139-2142

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    DOI:10.2320/matertrans.MRA2007602

    A body-centered tetragonal (bct) twin martensite has been found in Co39Ni33Al28 ferromagnetic shape memory alloy by transmission electron microscope (TEM) observation. The twin lamellae have Σ=25 (01\\bar1) twin boundaries and slip system [011]||(01\\bar1). Periodic appearance of the twin lamellae resulted in a modulated structure with a repeat periodicity of 56d01\\bar1 perpendicular to the twin interface. The twinning mechanism during martensite transformation is discussed briefly.
  • Inherent Internal Friction of Ti51Ni39Cu10 Shape Memory Alloy

    pp. 2143-2147

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    DOI:10.2320/matertrans.MRA2007068

    Ti51Ni39Cu10 SMA is more suitable than Ti50Ni50 SMA for use as a high damping alloy at room temperature because it has higher inherent internal friction and wider martensitic transformation temperature range. Experimental results show that tanδ values of both (IFPT+IFI)B2→B19 and (IFPT+IFI)B19→B19′ of Ti51Ni39Cu10 SMA are linearly proportional to σ0⁄ν1⁄2 when the applied ν and σ0 are within 10 Hz and 15 μm, respectively. Since defects and dislocations pin the martensite twin boundaries and obstruct their mobility, it is important to prevent the introduction of defects or dislocations into the solution-treated Ti51Ni39Cu10 SMA to maintain its high inherent internal friction.
  • Quantum-Chemical Design of Covalent Linkages for Interconnecting Carbon Nanotubes

    pp. 2148-2151

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    DOI:10.2320/matertrans.N-MRA2007861

    The possibility of interconnecting carbon nanotubes (CNTs) through their ends using covalent linkages has been computationally explored. By employing density functional theory (DFT) calculations with Gaussian-type orbitals (GTOs) we have optimized the geometry of four CNT-based model junctions each containing five covalent linkages. The linkages investigated here are the disulfide (–S–S–) and peptide (–CONH–) linkages, which are commonly found in proteins, and the ethylenedioxy (–O–CH2–CH2–O–) and ethynyl (–C≡C–) linkages which can be synthesized in the chemistry laboratory. The geometric and electronic structures computed for these four models are thoroughly discussed.
  • Application of the Reactivity Index to Propose Intra and Intermolecular Reactivity in Metal Cluster Interaction over Oxide Surface

    pp. 2152-2158

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    DOI:10.2320/matertrans.N-MRA2007862

    The hard soft acid-base (HSAB) principles classify the interaction between acids and bases in terms of global softness. In last few years the reactivity index methodology is well established and had found its application in a wide variety of systems. This study aims to propose the viability of the reactivity index to monitor metal cluster interaction with oxide surface with a description of the theory developed. We have chosen pure gold cluster from a size between 2 to 12 to be interacted with clean alumina (100) surface. The study aims to postulate a simple a priori scale in terms of intra and inter molecular interaction of gold cluster with alumina surface to rationalize the role of reactivity index in material designing.
  • Standard Gibbs Energy of Formation of Mg3La Determined by Solution Calorimetry and Heat Capacity Measurement from Near Absolute Zero Kelvin

    pp. 2159-2164

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    DOI:10.2320/matertrans.MRA2007603

    The standard Gibbs energy of formation, ΔfGoT, of Mg3La in the temperature range from near absolute zero Kelvin to 525 K were determined by calorimetry. The heat capacities, Cp, from 2 K to 525 K were measured by the relaxation method and DSC. The ΔfGoT(Mg3La) values were determined by combining the Cp data with the standard enthalpy of formation at 298 K which was measured by the Calvet-type calorimeter using hydrochloric acid solution. From 2 to 350 K, the ΔfGoT increases gradually, and it can be evaluated as a linear function of temperature above 350 K as follows:
    ΔfGoT(Mg3La)/kJ mol−1
     =−76.204−2.5304×10−2T+1.2160×10−2T log T
       +1.1814×10−5T2−0.80332 T−1±17.0 (2–350 K)
    ΔfGoT(Mg3La)/kJ mol−1=−79.652+1.9567×10−2T±17.0 (350–525 K).
    This result is expected to be useful as basic thermodynamic data of Mg-based alloys.
  • Growth Process and Characterization of Chromate Film Prepared on Various Metal Plates

    pp. 2165-2169

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    DOI:10.2320/matertrans.MRA2007066

    In a previous study, the properties and mechanism of peeling in terms of nickel electroforming were investigated by changing the activation treatment and the surface roughness of the plate and varying the treatment conditions (concentration, time, and temperature) of potassium dichromate solution. In this study, the chromate treatment was carried out on noble metals, base metals, and Cu-Zn alloy. It was found that chromate films can be formed on noble metal plates. The thickness of chromate film was different on noble metal and base metal plates, and was less than about 15 nm on the noble metal plates, but was in the order of the standard electrode potentials (SEP) on base metal plates. It was found that the chromate films formed on all metal plates contained metal elements of that plate.
  • Agglomeration Simulation of Chain-like Inclusions in Molten Steel Based on Fractal Cluster-Cluster Agglomeration Model

    pp. 2170-2173

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    DOI:10.2320/matertrans.MRA2007037

    Based on the fractal cluster-cluster agglomeration (CCA) model, two-dimensional simulations of cluster aggregation process have been carried out by varying initial particle number, particle size and sticking probability between clusters. Particle size and amount of seed particles have small effects on the shape of clusters. Actual alumina clusters observed in tundish show the chain-like appearance and are very similar to the simulated agglomerated clusters with high sticking probability. The agglomeration process of alumina chain-like clusters around immersion nozzle in the tundish and RH process are plausibly controlled by the random collision process with high sticking probability values.
  • Synthesis of Bismuth Sodium Titanate Fine Particles with Different Shapes by the Gel-Sol Method

    pp. 2174-2178

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    DOI:10.2320/matertrans.MRA2007043

    Polycrystalline spherical Bi0.5Na0.5TiO3 (BNT) particles with narrow size distributions were obtained by the gel-sol method, where the precursory gel was composed of BiX3 (X=OH, NO3), NaOH, and stable Ti4+ complex which was prepared by mixing Ti(i-C3H7O)4 with triethanolamine to inhibit the uncontrolled hydrolysis in aqueous solution. The resulting morphology was readily controlled as single-crystalline rod-like and tubular shapes with the simple tuning of the Bi/Ti molar ratios in the presence of NaClO4.
  • Effect of Iron Substrates on Reduced Porous Morphologies Adequate for Unusual Wetting

    pp. 2179-2185

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    DOI:10.2320/matertrans.MRA2007008

    The authors have found that liquid metal droplets wetted and spread very widely on solid iron substrates in a reducing atmosphere after the surface oxidation of the specimens. This unusual wetting is caused by capillary penetration into the porous layer formed on the iron sample that is reduced after first being oxidized in air. In order to find adequate conditions for the unusual wetting behavior, the effect of the underlying iron substrate on the reduced porous morphology of the oxidized Fe layer has been investigated. Pores in the porous iron layers of all samples formed on iron substrates are 3-dimensionally inter-connected, while those of the porous iron films of some samples without underlying iron substrates were partially isolated and not entirely connected within the films. Adequate porous iron layers that show this unusual wetting behavior were obtained mainly from reduction of the oxidized iron layer formed on the surface of iron substrates rather than from reduction of the oxidized iron films formed without underlying iron substrates.
  • Quantitative Prediction Method for Shrinkage Porosity Considering Molten Metal Supply by Pressure in Squeeze Casting

    pp. 2186-2193

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    DOI:10.2320/matertrans.F-MRA2007863

    It is important to predict shrinkage porosity quantitatively in squeeze casting process by CAE. A new calculation method has been developed considering molten metal supply by pressure in squeeze casting. Using this method, the size of shrinkage porosity in an aluminum suspension part can be simulated quantitatively. The predicted results were compared with the X-ray inspected results of actual castings, and the size of shrinkage porosity has been investigated by changing squeezed pressure. As the results, the predicted size of shrinkage porosities was found to agree well with the sizes of shrinkage porosities of the actual castings.
  • Improvement of Casting Speed and Billet Quality of Direct Chill Cast Aluminum Wrought Alloy with Combination of Slit Mold and Electromagnetic Coil

    pp. 2194-2201

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    DOI:10.2320/matertrans.MRA2007030

    A mold with slits and external cooling water channels was designed for the direct chill casting processing. By imposing a high frequency magnetic field, the surface quality and microstructure of the direct chill cast billets are improved. The casting speed could be improved by the simultaneous use of mold and electromagnetic coil. In the case of one kind of Al-Cu-Mg alloy with a wide freezing range, the critical casting speed to break-out can be improved 60%. The microstructure of the billet cast with electromagnetic field is more fine and uniform than that of the conventionally cast billet, and the subsurface segregation usually observed in the conventional billets is eliminated.
    x

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  • Formation of Silicon Nanowires by CVD Using Gold Catalysts at Low Temperatures

    pp. 2202-2206

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    DOI:10.2320/matertrans.MRA2007059

    Silicon nanowires (SiNWs) on a {100} silicon wafer coated with a gold film were formed by thermal cracking of disilane at 473–573 K. The SiNWs were single-crystalline with 10–100 nm in diameter and a ⟨111⟩ crystal orientation. The optimum conditions for obtaining long SiNWs that are several hundred μm long include a disilane flow rate of 0.017 cm3/s, an argon gas flow rate of 0.33 cm3/s, and a total pressure of 0.67 kPa. The low-temperature formation of SiNWs was explained by lowering the melting point of Au–Si eutectic particles. Self-wiring of SiNWs between gold square dots placed 15 μm from each other was successfully conducted.
  • Effect of Fe Addition on Microstructures and Mechanical Properties of Ni- and C-Free Co-Cr-Mo Alloys

    pp. 2207-2211

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    DOI:10.2320/matertrans.MRA2007004

    A series of Co-Cr-Mo alloys with Fe contents ranging from 5 to 20 mass% were prepared in order to study the effect of Fe addition on the microstructures and mechanical properties (tensile strength, yield strength, elongation, and Rockwell C scale hardness) of Ni- and C-free Co-Cr-Mo alloys. Fe was added with the composition of Co-29Cr-6Mo-xFe (where x=0, 5, 10, and 20). Alloys were heat-treated at 1230°C for 3 h and 1250°C for 5 h. These heat treatment conditions were decided as considering pre-heat treatment followed by hot-forging process. An optical microscope and an XRD were used to determine the microstructure and identify the crystal structure. The volume ratio of γ phase to ε phase increases not only with heat treatment temperature and time but also with Fe content. The tensile strength, yield strength, and elongation are significantly improved by Fe addition. However, the tendency toward σ phase formation becomes higher as the Fe content increases, causing a deterioration of mechanical properties. From the viewpoint of mechanical properties, the amount of Fe addition should be less than 10 mass% in pre-heated condition of Co-29Cr-6Mo alloys.
  • Screening Life Cycle Assessment of Silver-Based Conductive Adhesive vs. Lead-Based Solder and Plating Materials

    pp. 2212-2218

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    DOI:10.2320/matertrans.MRA2006340

    Conductive adhesives are getting growing attention in the electronics industry as they constitute an alternative to lead-free solders and conventional solders. The purpose of the present research is to compare the 10Sn90Pb solder paste to an epoxy based isotropically conductive adhesive (ICA) containing pure silver. The study is done from a life cycle perspective in Japan using input data from literature and the inventory results are evaluated using the Life cycle Impact assessment Method based on Endpoint modeling (LIME) methodology. The findings are that the silver containing adhesive, excluding platings, are superior to the 10Sn90Pb, and that trade-offs exist between 10Sn90Pb and silver-epoxy ICA. For surface platings palladium dominates the results. Overall, the results are dominated by various lead emissions, the silver resource consumption, and the sulfur oxide emissions from palladium production. The most important research limitations are the representativity of the metal production data and end-of-life scenario. The value of the present study is that so far no LIME-based life cycle impact assessment case study comparing 10Sn90Pb solder paste and silver-epoxy ICA including platings has been reported.
  • Material Flow Analysis of Aluminum Dross and Environmental Assessment for Its Recycling Process

    pp. 2219-2224

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    DOI:10.2320/matertrans.MRA2007070

    Approximately 400,000 tons per year of aluminum dross are generated during a melting process of aluminum metal in Japan. The Al dross and the residue, which have high concentration of metallic Al, are mostly used as an Al resource for Al production or as a deoxidizer in the steel industry. On the other hand, the lower grade residue with the Al content less than 20%, is difficult to be recycled and is therefore landfilled.
    This paper deals with (1) a material flow analysis (MFA) of the domestic aluminum dross in order to achieve clear targets for recycling of aluminum dross and residue, and (2) an environmental assessment of newly developed technologies for its recycling, such as the process of hydrogen production from residue.
    The result of material flow analysis on the domestic aluminum dross in 2003 shows that 234.4×103 t of aluminum is recovered and 215.0×103 t of residue is generated from the dross. The residue is mostly used in the steelmaking process, whereas 50.0×103 t of residue is landfilled in the final disposal site. As the result of the environmental assessment through the material flow, there is a possibility of reduction of CO2 emission and waste emissions by using residue (Al content: 10%) as a hydrogen resource, which is presently landfilled.
  • Uptake of Bisphenol A from Aqueous Solution by Mg–Al-Layered Double Hydroxides Intercalated with 2-Naphthalene Sulfonate and 2,6-Naphthalene Disulfonate

    pp. 2225-2229

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    DOI:10.2320/matertrans.M-MER2007873

    Mg–Al-layered double hydroxides (Mg–Al LDHs) modified with aromatic anions were suspended in solutions of bisphenol A to investigate their properties as scavengers. The Mg–Al LDHs were intercalated with 2-naphthalene sulfonate (2-NS) and 2,6-naphthalene disulfonate (2,6-NDS2−) ions, which contain a naphthalene ring with one and two sulfonate (–SO3) groups in their respective structures. The changes in the concentrations of the hazardous aromatic compounds in the suspensions with time were followed. The organic-modified Mg–Al LDHs decreased the bisphenol A concentrations very rapidly, which was attributable to the association between the aromatic ring of bisphenol A and the aromatic anions intercalated in the interlayer. Mg–Al LDH with lower content of aromatic anion in the interlayer was superior to that with the higher content for the uptake of bisphenol A. This was attributed to the larger spaces to accommodate more bisphenol A in the interlayer.
  • Durability of Indium Tin Oxide-Silver-Indium Tin Oxide Films against Moisture Investigated Through The Wettability of The Top Oxide Layer

    pp. 2230-2234

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    DOI:10.2320/matertrans.MER2007038

    With good wettability, the top oxide layer of oxide-Ag-oxide depositions can resist the moisture penetration, and consequently is able to prevent the degradation and enhance the durability of oxide-Ag-oxide depositions. The wettability of the top oxide on the Ag layer is determined according to the contact angle evaluated from the Young’s equation. Before the evaluation, the vOCG’s approach with the three-liquids-method is used to estimate the surface or interface energy of the films.
  • Mechanical Property and Corrosion Resistance Evaluations of Ti-6Al-7Nb Alloy Brazed with Bulk Metallic Glasses

    pp. 2235-2243

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    DOI:10.2320/matertrans.MER2007612

    Exploitation of metallic glass as new brazing filler for Ti-based biomedical alloy was attempted. Ti-6Al-7Nb was used as a brazed material, and candidates of bulk metallic glass brazing filler were Cu60Hf25Ti15, Mg65Cu25Gd10, Zr55Cu30Al10Ni5 and Pd40Cu30P20Ni10. Convergence infrared-ray brazing was conducted for brazing Ti-6Al-7Nb/metallic glass in Ar atmosphere. After brazing, hardness measurement, X-ray tomography, cross-sectional observation, artificial saliva immersion test and tensile test were performed to evaluate brazability, mechanical property and corrosion resistance of the obtained brazing joints.
    The results of brazing using these metallic glass fillers show that all the metallic glasses were brazable to Ti-6Al-7Nb except for Mg65Cu25Gd10. Mg65Cu25Gd10, Cu60Hf25Ti15 and their joints collapsed rapidly during immersion test. Zr55Cu30Al10Ni5 joint was the best in terms of degradation resistance; however, tensile strength was inferior to the conventional one. Pd40Cu30Ni10P20 filler and Zr55Cu30Al10Ni5 filler and their joints did not show any collapse or tarnish during the immersion test. Pd40Cu30Ni10P20 joint showed the excellent properties in terms of both corrosion resistance and tensile strength, which were superior to a joint brazed using Ti-15Cu-25Ni conventional filler. X-ray tomograph indicates that fracture tends to occur in the vicinity of the brazing interface after tensile test.
    The brazed metallic glass fillers were fully crystallized, excluding Pd40Cu30Ni10P20 filler. Pd40Cu30Ni10P20 brazed filler contained maple-leaf like primary dendrite, peritectoid and a few microns interfacial reaction layer in glassy matrix. The results indicated that Pd40Cu30Ni10P20 is promising brazing filler for dental or biomaterial devices.
  • Production of Titanium Powder by the Calciothermic Reduction of Titanium Concentrates or Ore Using the Preform Reduction Process

    pp. 2244-2251

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    DOI:10.2320/matertrans.MER2007115

    With a view to developing a new process for the production of metallic titanium (Ti) powder, the preform reduction process (PRP) based on the calciothermic reduction of Ti concentrates or ore (TiO2) was investigated in this study. A Ti feed preform was fabricated at room temperature by casting and drying a prepared slurry that constituted a mixture of Ti concentrates (upgraded ilmenite (UGI), 97.1% TiO2) or Ti ore (rutile, 96.4% TiO2 with iron (Fe) as the major impurity), flux (CaCl2), and binder. In some experiments, carbon (C) powder was added into the slurry for an efficient Fe removal. The fabricated feed preform was calcined at 1273 K for removing the water and binder present in the preform. During the calcination of the feed preform, some metal impurities such as Fe were removed by selective chlorination. Multiple pieces of the sintered preform were then reacted with metallic calcium (Ca) vapor at 1273 K in a stainless steel reaction vessel, and Ti oxide (TiO2) in the preform was reduced to metal. After reduction, the reduced preform was subjected to a leaching process using an acetic acid solution and a hydrochloric acid solution in order to remove the by-product calcium oxide (CaO), excess reductant Ca, and other impurities in the sample. After leaching, the obtained powder was then rinsed and dried; this powder was shown to be metallic Ti with a purity of 99% up. It was experimentally demonstrated that PRP is a feasible technique to produce metallic Ti powder directly from Ti concentrates or ore.
  • Synthesis of Sodium Gluconate by Bi Promoted Pd/C Catalyst

    pp. 2252-2254

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    DOI:10.2320/matertrans.MRP2006634

    Bi promoted Pd/C catalyst (Bi-Pd/C) was prepared and evaluated for glucose oxidation in this paper. Reaction rate depends on Bi and Pd ratio on activated carbon. Best promotion effect was got when PdCl2 to Bi (NO)3·5H2O weight ratio was 1 to 3 during catalyst preparation. Compared with other noble metal catalyst, the reaction time was reduced and Bi prevented the Pd/C deactivation during this reaction. The reaction cycle for this catalyst was increased a lot compared with other Pd/C catalyst. Through XPS analysis, Bi, Pd was formed on the surface of activated carbon particles. The catalyst reaction cycles for Bi-Pd/C catalyst was exceeded to 20 cycles in spite of the catalyst loss during each cycle. This catalyst can be used for industrial process to oxidize glucose to sodium gluconate.
  • In Situ Observation of Magnetic Domain Structure in Co50Ni20FeGa29 Alloy under the Applied Magnetic Field

    pp. 2255-2257

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    DOI:10.2320/matertrans.MRP2007609

    The magnetic microstructure of Co50Ni20FeGa29 alloy under a magnetic field applied parallel to the [111] direction has been studied via in situ observation by transmission electron microscopy (TEM). The domain walls formed a sawtooth-like configuration with an initial size of ∼10 micron, which shrank as increase of the applied field strength and finally vanished at the field strength about ∼0.46 T. Number of the walls increased during domain boundary motion driven by the applied magnetic field. A geometrical characteristic feature of the domain walls was unchanged until vanishing under the applied field. Based on in situ observation on reorientation of magnetization, the genetic aspect of these domain walls motion was discussed briefly.

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