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

MATERIALS TRANSACTIONS Vol. 49 (2008), No. 8

  • Synthesis of Thermoelectric Fe0.98Co0.02Si2 with Fine Ag Dispersion by Mechanical Milling with AgO Powder

    Mikio Ito, Koji Takemoto

    pp. 1714-1719

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    DOI:10.2320/matertrans.E-MRA2008808

    Abstract

    Synthesis of n-type Fe0.98Co0.02Si2 thermoelectric materials with dispersion of fine Ag particles was tried by mechanical milling of Fe-Si powder with AgO powder and subsequent hot pressing. The AgO phase was reduced by Si, resulting in precipitation of Ag particles, SiO2 phase and ε-FeSi phase. Most of the Ag particles were quite small; less than 100 nm in size. The precipitation of Ag and ε phase significantly decreased both the Seebeck coefficient and the electrical resistivity of Fe0.98Co0.02Si2, in spite of the SiO2 formation. On the other hand, the dispersion of fine Ag particles effectively enhanced phonon scattering, resulting in the reduction in the thermal conductivity in spite of the precipitation of metallic phases. However, the dimensionless figure of merit could not be improved by AgO addition because of the significant deterioration of the Seebeck coefficient. The Si powder addition with AgO powder was found to be effective on recovering the reduction in the Seebeck coefficient.

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  • Electrodeposition of Sb-Te Alloy in AlCl3-NaCl-KCl Molten Salt

    Mikito Ueda, Yusuke Mito, Toshiaki Ohtsuka

    pp. 1720-1722

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    DOI:10.2320/matertrans.E-MRA2008811

    Abstract

    The Electrodeposition of Sb-Te alloy was carried out in AlCl3-NaCl-KCl molten salt containing SbCl3 and TeCl4 at 423 K by constant potential electrolysis. The voltammogram on a glassy carbon (GC) electrode in a melt containing 1.0×10−2 kmol m−3 SbCl3 and 1.0×10−2 kmol/m3 TeCl4 revealed the cathodic current waves at 1.5, 1.1, and 0.9 V vs. Al/Al(III). A stable Sb-Te alloy deposit was obtained at 0.85 V in the melt containing SbCl3 and TeCl4. At the higher concentration ratio of the Sb(III) to (Sb(III) + Te(IV)), a good linear relation was found between the atomic ratio of Sb in the deposit and the concentration ratio of Sb (III) in the melt. The Sb-Te alloy deposit of atomic ratio of 38:62% which was assume to be suitable for a thermoelectric device was obtained with the molten salt containing 7.0×10−3 kmol/m3 SbCl3 and 1.0×10−2 kmol/m3 TeCl4. The XRD pattern of the deposit corresponds to that of Sb2Te3 intermetallic compound. The deposit had homogeneous disk-like granule with the disk size of about 10 μm.

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  • Investigation of Thermoelectric Properties of Si/Ge Multilayer with Ultra-Heavily B Doping

    Akinari Matoba, Hiroyuki Watase, Masahiro Kitai, Kimihiro Sasaki

    pp. 1723-1727

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    DOI:10.2320/matertrans.E-MRA2008813

    Abstract

    Si/Ge and Si/GeB multilayer structured thin films were prepared by using the ion-beam sputtering (IBS) method with changing the growth temperatures from room temperature to 873 K. Then their thermoelectric properties were estimated and the effects of boron on Si/Ge superlattice structure were investigated. It was shown from XRD spectra that samples prepared below 673 K kept the periodic structure, however at exceeding 773 K the structure was broken. Si/Ge multilayer thin films showed larger thermoelectric power than that of bulk-SiGe materials and also Si/GeB multilayer showed decreases of thermoelectric power with increasing growth temperature, which is related to the increase of carrier concentration by boron activation. As for the resistivity, since the Si/GeB multilayers had lower values of the resistivity than that of Si/Ge multilayers, a boron doping effect was identified. In both Si/Ge and Si/GeB, the resistivity had a minimum at 673 K. Since the multilayer structure holds up to this temperature, the decrease in the resistivity can be attributed to the increase in the carrier mobility of the layer with a lower band gap. As a result, Si/GeB showed the larger power factor than that of Si/Ge multilayer at 673 K.

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  • Thermoelectric Properties of Tl8GeTe5 with Low Thermal Conductivity

    Ken Kurosaki, Atsuko Kosuga, Anek Charoenphakdee, Hideaki Matsumoto, Hiroaki Muta, Shinsuke Yamanaka

    pp. 1728-1730

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    DOI:10.2320/matertrans.E-MRA2008815

    Abstract

    We examined the thermoelectric performance of Tl8GeTe5 at temperatures ranging from room temperature to 700 K. We prepared sintered samples and evaluated their thermoelectric properties. Although the electrical properties were not exceptionally high, Tl8GeTe5 exhibited the relatively high dimensionless figure of merit ZT, i.e., 0.19 at room temperature and 0.60 at 700 K, due to the low lattice thermal conductivity.

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  • Thermoelectric Properties of CeFe3CoSb12-MoO2 Composite

    Shigeru Katsuyama, Hiroshi Okada, Katsuhito Miyajima

    pp. 1731-1736

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    DOI:10.2320/matertrans.E-MRA2008819

    Abstract

    We have prepared the CeFe3CoSb12-MoO2 composite by mechanical milling and spark plasma sintering techniques. The Seebeck coefficient of CeFe3CoSb12 is somewhat reduced by the addition of MoO2. The electrical resistivity of the CeFe3CoSb12-MoO2 composite is smaller than that of CeFe3CoSb12 regardless of being mechanically milled. The thermal conductivity of the CeFe3CoSb12-MoO2 composite is generally smaller than that of CeFe3CoSb12. The addition of MoO2 to CeFe3CoSb12 is effective for the reduction of both the electrical resistivity and thermal conductivity. The composite whose molar ratio of CeFe3CoSb12 to MoO2 is 0.95:0.05 and milling time is 5 h shows a maximum dimensionless figure of merit ZT of 1.22 at 773 K, which is larger than ZT of CeFe3CoSb12.

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  • Thermoelectric Properties of La-Doped BaSi2

    Kohsuke Hashimoto, Ken Kurosaki, Hiroaki Muta, Shinsuke Yamanaka

    pp. 1737-1740

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    DOI:10.2320/matertrans.E-MRA2008818

    Abstract

    The authors tried to enhance the thermoelectric figure of merit of BaSi2 by doping La. Polycrystalline samples of La-doped BaSi2: Ba1−xLaxSi2 (0≤x≤0.08) were prepared and characterized. The effect of La-doping was investigated by measuring the thermoelectric properties above room temperature to 973 K. La could dissolve in BaSi2 up to around x=0.03, while LaSi2 appeared as the second phase in the higher x range. Both the electrical resistivity and thermal conductivity of the La-doped samples were lower than those of the non-doped BaSi2. Ba1−xLaxSi2 (x=0.02) indicated the largest power factor and dimensionless figure of merit (ZT). The ZT value was 0.07 at 970 K, which was approximately 7 times larger than that of non-doped BaSi2.

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  • Composite Dispersion of Nanosized AlOOH in Liquid Phase

    Haida Liao, Bolin Wu, Lianmeng Zhang

    pp. 1741-1747

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    DOI:10.2320/matertrans.MRA2008004

    Abstract

    TEM, SEM and laser particle size analysis were used to study hydrothermal crystallization and a charging composite dispersion of nanosized AlOOH, using a self-dispersed nanosized AlOOH crystal powder prepared by sol-hydrothermal method. The results show that the composite method can improve particle dispersion and stability in liquid. The improvement in the dispersion effect is attained by weakening the van der Waals force, reducing the particle surface energy through hydrothermal crystallization, and increasing the charge by partly dissolving the anions or cations at the crystal lattice surface. Based on these results, a mechanism for hydrothermal crystallization and a charging composite dispersion of nanosized AlOOH is proposed. The preparation of nanometer TiO2 and nanometer Al2O3 have been preliminarily studied using the composite dispersion method.

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  • Superconducting Transition in Electron-Doped 12CaO·7Al2O3

    Sung Wng Kim, Masashi Miyakawa, Masahiro Hirano, Yoshimitsu Kohama, Hitoshi Kawaji, Tooru Atake, Hiroki Ikegami, Kimitoshi Kono, Hideo Hosono

    pp. 1748-1752

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    DOI:10.2320/matertrans.MBW200717

    Abstract

    It was reported that a mixed light metal oxide compound, 12CaO·7Al2O3 (C12A7), which is known as a constituent of aluminous cement, became a superconductor at an ambient pressure by the exclusive replacement of extra-framework oxygen ions in subnanometer-sized crystallographic cages with electrons. Temperature dependences of resistivity, magnetic susceptibility, and magnetic field dependent resistivity of single-crystals and thin films revealed superconducting transition at temperature (Tc) of ∼0.4 K and a critical magnetic field of ∼30 mT. Tc varies 0.2–0.4 K with the electron concentration. The interaction of the anionic electrons in the free space (cages) with the cationic framework may be responsible for the emergence of the superconducting state.

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  • Magnetocaloric Effect of Fe(Rh1−xPdx) Alloys

    Katsuhiko Nishimura, Yoshiyuki Nakazawa, Lingwei Li, Katsunori Mori

    pp. 1753-1756

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    DOI:10.2320/matertrans.MRA2008080

    Abstract

    Magnetocaloric effects of Fe49(Rh1−xPdx)51 alloys with x=0.0, 0.01, 0.03, 0.06, 0.07, 0.08, and 0.09, were investigated using resistivity, magnetization, specific heat, and direct measurement of the adiabatic temperature change ΔT. Magnetization measurements yielded experimental values of the isothermal magnetic-entropy change ΔS for all the samples. The critical temperature of the anitiferromagnetic-ferromagnetic transition was found to depend largely on the substitution concentrations of Pd. A broad peak in ΔS, up to 1.7 J·mol−1 K−1 and some 90 K broad around room temperature, was observed with a field change of ΔB=0 to 7 T for Fe49(Rh0.97Pd0.03)51. The specific heat data of Fe49(Rh0.97Pd0.03)51 made it possible to estimate the ΔT values for various external fields. This estimated value of ΔT compares well with the value measured directly using a thermocouple.

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  • Magnetic Properties of Fe74.5−xCuxTa3Si13.5B9 As-Quenched Ribbons

    Bo Li, Jifan Hu, Hongwei Qin, Lun Li

    pp. 1757-1759

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    DOI:10.2320/matertrans.MRA2008058

    Abstract

    Fe74.5−xCuxTa3Si13.5B9 nanocrystalline ribbons with appropriate Cu contents can be prepared without annealing processes. The Fe74.5−xCuxTa3Si13.5B9 as-quenched ribbons with lower Cu contents (x≤1.5) consist of amorphous structure. The nucleation of α-Fe(Si) enhances with the increase of Cu content. An optimal Cu addition for obtaining the largest permeability, smallest saturation magnetostriction and largest magnetoimpedance occurs at x≈3. For as-quenched ribbons with high Cu contents (x≥3.5), soft magnetic properties deteriorate due to the drop of nucleation of α-Fe(Si) and the precipitation of Fe-B phases. For as melt-spun Fe71.5Cu3Ta3Si13.5B9 (x=3) nanocrystalline ribbon prepared with wheel speed of 40 ms−1, the average grain-size of α-Fe(Si) is about 10.5 nm, the initial permeability μ′ is about 35000, the saturation magnetostriction λs is less than 1×10−6, and the maximum value of magnetoimpedance ΔZ⁄Z0 under a field of 7162 A/m is −12.88% at 2 MHz.

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  • Full-Potential Screened KKR Calculations for Magnetism of Co2MnSi, Ni2MnAl and Ru2MnSi, Based on the Generalized Gradient Approximation

    M. Asato, M. Ohkubo, T. Hoshino, F. Nakamura, N. Fujima, H. Tatsuoka

    pp. 1760-1767

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    DOI:10.2320/matertrans.MRA2008100

    Abstract

    We present systematic ab-initio calculations for nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) states of full-Heusler alloys (X2YZ) such as Co2MnSi (X = Co, Y = Mn, Z = Si), Ni2MnAl (X = Ni, Y = Mn, Z = Al), and Ru2MnSi (X = Ru, Y = Mn, Z = Si). The calculations are based on the all-electron full-potential (FP) screened Korringa-Kohn-Rostoker (KKR) Green’s-function method combined with the generalized-gradient approximation in the density-functional formalism. We show that the present calculations reproduce very well the experimental ground states of these alloys (FM of Co2MnSi and Ni2MnAl, AFM of Ru2MnSi) and the available measured values for lattice parameters and magnetic moments. It is also shown that the fundamental features of the magnetism of Co2MnSi (strong FM) and Ni2MnAl (weak FM) are understood by using the Mn spin-flip energies and the Mn-Mn exchange interaction energies in X (= Co, Ni), both of which are obtained by the present FP-KKR calculations for the impurity systems. We can show that the magnetism of Ni2MnAl may be changed from FM to AFM by atomic disorder (B2-structure) occurring at elevated temperatures.

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  • Morphologies of Microstructure in Mg97Zn1Y2 Ribbon upon Ageing at Different Temperatures

    Baishu Wang, Yongbing Liu, Jian An, Rongguang Li, Zhenguo Su, Guihua Su, You Lu, Zhanyi Cao

    pp. 1768-1774

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    DOI:10.2320/matertrans.MRA2008033

    Abstract

    In order to clarify the morphology of the rapidly-solidified (RS)/melt-spun Mg97Zn1Y2 (at%) alloy, which has the secondary phases of long-period stacking (LPS) structure, the ribbon was processed with the thickness of 60 μm and the width of 7 mm, and aged (T5 heat-treated) at different temperatures. The as-spun and aged ribbons were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and laser optical microscopy, and micro-hardness measurement were conducted. It is found that there was a cellular/dendritic transition during melt-spinning process of Mg97Zn1Y2 alloy, and a mild age strengthening with the hardness of 113HV/0.05 at 573 K; more importantly, there was a different evolution of morphologies of the matrix and inter-metallic compounds from general secondary phase strengthened alloys when age temperatures up to the 773 K had been introduced to the as-spun alloy.

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  • Microstructures of Pd47.5Ag47.5La5 Alloy Studied by Transmission Electron Microscopy

    Kunio Yubuta, Wei Zhang, Hisamichi Kimura, Akihisa Inoue

    pp. 1775-1779

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    DOI:10.2320/matertrans.MRA2008045

    Abstract

    Microstructures of Pd47.5Ag47.5La5 alloy produced by three types of procedure methods, i.e., casting, rapid quenching and rolling, were examined by transmission electron microscopy (TEM). The Pd-Ag-La alloy in as-quenched and subsequent cold-rolled states has a finely mixed non-equilibrium structure consisting of a face-centered cubic (fcc) and LaNi3-type phases and the structural feature is independent of the two procedure methods. The grain size and the volume fraction of the fcc phase are measured to be about 100 nm and 72%, respectively. The two phases dispersed homogeneously over the whole specimen. The Pd-Ag-La alloy with such a finely mixed structure is attractive for a hydrogen permeative material.

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  • Relationship between Microstructures and Soft Magnetic Properties of Simultaneously P and Cu-Added Fe-Nb-B Ribbon Alloys

    Kunio Yubuta, Enrico Mund, Akihiro Makino, Akihisa Inoue

    pp. 1780-1784

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    DOI:10.2320/matertrans.MRA2008134

    Abstract

    The additional effect of P and Cu on the magnetic properties of Fe-Nb-B nanocrystalline soft magnetic alloys was investigated from the viewpoint of microstructures. Mean size of α-Fe grain for both Fe83.8Nb6.6B9.6 and Fe83.7Nb6.6B8.6P1Cu0.1 ribbon alloys are measured to be about 8.5 nm, and size distribution of those are measured to be 0.391 and 0.236, respectively, using an oval approximation for shape of α-Fe grains. Values of coercivity for Fe83.8Nb6.6B9.6 and Fe83.7Nb6.6B8.6P1Cu0.1 alloys calculated using a two-phase random anisotropy model are 6.73 and 4.93 A·m−1, and measured ones are 8.64 and 3.74 A·m−1, respectively. The improvement probably originates from the decrease in the distribution of the α-Fe grain size in the crystallized structure by the simultaneous addition.

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  • Size-Dependence of Martensite Transformation Temperature of Yttria-Doped Zirconia and the Distribution of Nucleation Sites

    Motozo Hayakawa, Masanori Tamaki

    pp. 1785-1790

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    DOI:10.2320/matertrans.MRA2008046

    Abstract

    Specimen-size dependence of Mb temperatures (burst-type martensite transformation temperatures) was measured on many small spherical specimens of 1.5 mol%Y2O3-ZrO2 ranging from 100 to 1000 μm diameter. With decreasing size, both reductions of the average Mb temperature and a significant increase in the scatter in Mb temperatures were observed. These data were used to deduce the density and distribution of the potential nucleation sites (embryos) by comparing with simulated Mb temperatures assuming randomly distributed embryos with various densities and potentials. Adjusting the parameters specifying the density and potentials so that the simulated result fit the observed data, the following characteristics were deduced for the embryos: 1) effective embryos are more likely to reside on the surface of a specimen rather than through the volume; 2) even the most unstable embryo requires under-cooling of more than 650 K from the equilibrium phase temperature; 3) the density of embryos increased nearly linearly with decreasing nucleation temperature; 4) the density of effective embryos with nucleation temperature above 77 K is approximately 32/mm2.

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  • Change in Microstructures and Mechanical Properties of Biomedical Ti-Nb-Ta-Zr System Alloy through Cross-Rolling

    Liqiang Wang, Weijie Lu, Jining Qin, Fan Zhang, Di Zhang

    pp. 1791-1795

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    DOI:10.2320/matertrans.MRA2008040

    Abstract

    The microstructures and mechanical properties of Ti-35Nb-2Ta-3Zr alloy, which was fabricated by vacuum consumable arc melting furnace followed by hot pressing, subjected to cross-rolling were investigated in this study. Shear slip and stress-induced α″ martensite phase transformation play an important role in the plastic deformation. Hundred nanometers-sized grains are obtained, when the alloy is cross-rolled at a reduction ratio of 99%. The cross-rolled alloy exhibits considerable low Young’s modulus (around 48 GPa) and high ultimate tensile strength (around 880 MPa) accompanying with ductile fracture. For Ti-35Nb-2Ta-3Zr alloy cross-rolled at a reduction ratio of 60%, excellent isotropy of mechanical properties along different directions of specimens are obtained.

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  • Synthesis of Ni-Based Bulk Metallic Glasses for Penetrating Materials

    Jaehyuck Shin, Jinwook Kwon, Joon Sik Park, Donghyun Bae

    pp. 1796-1799

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    DOI:10.2320/matertrans.MRA2008095

    Abstract

    The Ni-based bulk metallic glasses (BMGs(Ni59Zr16Ti13Nb7Si3Sn2)) modified by Al, Hf and W have been synthesized for a specific application of penetrating materials. When Al was replaced with Zr of the Ni59Zr16Ti13Nb7Si3Sn2 BMG, a large glass forming ability was observed, enabling to fabricate 7 mm cylindrical amorphous specimen. Also, when Hf or W was replaced with Ni of the Ni59Zr16Ti13Nb7Si3Sn2 BMG, the 7 mm amorphous BMG specimen was obtained. For the Al modified BMG (Ni59Zr15Ti13Nb7Si3Sn2Al1), a high strength of ∼2.6 GPa with ∼10% plastic strain was observed. It appears that the Hf modified BMG showed an excellent candidate for the application of penetrating materials among the examined BMGs.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Recovery Behaviour of Pure Magnesium in Cyclic Compression–Quick Unloading-Recovery Process at Room Temperature Investigated by AE

    Yunping Li, Manabu Enoki

    pp. 1800-1805

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    DOI:10.2320/matertrans.MC200705

    Abstract

    Anelastic recovery of pure magnesium at room temperature was investigated in cyclic compression-quick unloading-recovery process where acoustic emission (AE) measurement was applied to analyze the dynamic behaviour and mechanism of anelastic recovery process. By analyzing the RMS voltage of AE signals from both the background and the recovery process, it was observed that the recovery process was accompanied with a gradual decrease in the strength of AE signals. The AE signals in recovery processes of different strain levels seem to be due to the same source of detwinning process because the same slope between amplitude and logarithmic AE count of AE signals in different strain levels was found in the strong elastic waves related to detwinning process. The AE behaviors in recovery process were described in details by AE count rate and AE incubation time. The relations between twinning or detwinning and AE counts in both deformation and anelastic recovery process could be expressed by a general equation.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Influence of Ultrasound on Corrosion Behavior of SUS304 Stainless Steel with Crevice

    Rongguang Wang, Mitsuo Kido

    pp. 1806-1811

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    DOI:10.2320/matertrans.MRA2008091

    Abstract

    Anodic polarization on SUS304 stainless steel with crevice was carried out in 3.5 mass% NaCl aqueous solution. After the anodic current density reached i=10, 12 or 50 A/m2, the potential at that moment was held constantly for a prescribed period. When an ultrasound (US) was applied to the specimen through the solution during the holding period of the potential, the current density on the specimen surface was measured and compared to that without the application of US. As a result, both the pitting corrosion and the crevice corrosion were largely suppressed by the application of US in the solution, and the corrosion current density changed almost synchronistically with the cyclic application and the stop of US. The above effect of US on the suppression of corrosion of SUS304 steel is attributed to the decrease or suppression of the enrichment of hydrogen ions and chloride ions in the crevice or the pits by the stirring effect of US.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Effects of Reinforcing Rib on Draw Bending of Pipes Examined by Finite Element Method

    Noah Utsumi, Eitaro Usuda, Shuji Sakaki

    pp. 1812-1817

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    DOI:10.2320/matertrans.P-MRA2008815

    Abstract

    In recent years, thin aluminum alloy extruded pipes have been applied to structural parts, such as automobile space frames, to save energy. If the aluminum pipes could be processed in a greater variety of ways, such as bending, their range of applications would expand. In our previous study, we evaluated the bending of thin extruded square pipes. In the current study, we examined the bending formability of aluminum alloy pipes with reinforcing ribs using the finite element method (FEM). The influence of the reinforcing ribs on the form accuracy of the aluminum pipes in draw bending was investigated. The effective arrangement and thickness of a reinforcing rib was also investigated. As a result, it was clarified that two types of buckling arise for the reinforcing rib. Furthermore, a critical ratio T=t2⁄t1 (t1: the circular portion thickness of pipe; t2: the thickness of rib) for controlling buckling and flattening was proposed.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Effect of T5 and T6 Tempers on a Hot-Rolled WE43 Magnesium Alloy

    Kun Yu, Wenxian Li, Richu Wang, Bo Wang, Chao Li

    pp. 1818-1821

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    DOI:10.2320/matertrans.MRA2008602

    Abstract

    The influence of T5 and T6 tempers at 523 K on the mechanical properties and microstructure of hot-rolled WE43 alloy has been studied. The microstructure of the alloy under various conditions was studied using an optical microscope, a transmission electron microscope, and a x-ray diffractometer. The mechanical properties were measured on a tensile testing system. The results show that the hot-rolled WE43 alloy has a substantially higher hardness and strength improvement than the cast WE43 alloy. The hot-rolled WE43 alloy with a T5 temper showed better properties than the alloy with a T6 temper because both strain hardening and age hardening increased the strength of the alloy. In addition, the size of the precipitates after a T5 temper was smaller than that after a T6 temper. The yield strength of the alloy parallel to the rolling direction was higher than that perpendicular to the rolling direction.

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  • Effect of Ba Substitution on the Microstructure and Electrical Conductivity of BaxCa1−xRuO3 Thin Films Prepared by Laser Ablation

    Akihiko Ito, Hiroshi Masumoto, Takashi Goto

    pp. 1822-1825

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    DOI:10.2320/matertrans.MRA2008124

    Abstract

    BaxCa1−xRuO3 (BCRO) thin films were prepared by laser ablation on quartz substrates at a substrate temperature (Tsub) of 973 K and an oxygen pressure (PO2) of 13 Pa. The effect of Ba substitution on the microstructure and electrical conductivity (σ) was investigated. Rectangular-shaped CaRuO3 (CRO) island grains grew in BCRO thin films at a Ba fraction (x) below 0.1. BCRO thin films prepared at x>0.2 consisted of fine grains. BCRO thin films at x>0.2 showed metallic conduction, whereas those with an island structure at x<0.1 showed semi-conducting behavior. The σ increased from 2.5×103 S·m−1 to 3.8×104 S·m−1 with increasing x from 0.1 to 1.0.

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  • Effect of Ar/Ar-H2 Plasma Arc Melting on Cu Purification

    Jae-Won Lim, Min-Seuk Kim, N. R. Munirathnam, Minh-Tung Le, Masahito Uchikoshi, Kouji Mimura, Minoru Isshiki, Hyuk-Chon Kwon, Good-Sun Choi

    pp. 1826-1829

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    DOI:10.2320/matertrans.MRA2008054

    Abstract

    Removal of impurities from Cu metal by Ar and Ar-20%H2 plasma arc melting (PAM) has been carried out. Several impurities such as Li, Na, Mg, P, S, Cl, K, Ca, Zn, Pd, Pb and Bi in Cu were efficiently removed when only Ar plasma gas was used. Moreover, removal degrees for the above mentioned impurities were significantly increased after Ar-20%H2-PAM, especially for K, Zn and Pd. It was found that Ar-H2 PAM showed an excellent effect to eliminate impurities with higher vapor pressures than that of Cu metal.

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  • Morphology and Magnetic Properties of Fe and Al Nanocomposites Prepared with Single and Double-Glow-Discharge Sources

    Ryoji Katoh, Kohei Nonaka, Kenji Sumiyama, Dong-Liang Peng, Takehiko Hihara

    pp. 1830-1835

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    DOI:10.2320/matertrans.MRA2007280

    Abstract

    Fe and Al nanocomposites have been prepared using the plasma-gas-condensation cluster deposition system and investigated by transmission electron microscope and magnetization measurements. In Fe-Al alloy clusters assemblies prepared with the single glow discharge source there are bcc Fe-Al and B2-type ordered FeAl phases. In Fe/Al cluster composites prepared with double glow discharge sources, core-shell clusters are obtained: Fe cores are covered by Al and/or Al-oxide crystallites. In magnetization curves of the Fe-Al alloy cluster assembly and Fe/Al cluster composite, magnetic coercivity values are much smaller than that of an Fe cluster assembly. These results indicate that Fe-rich ferromagnetic Fe-Al phases exist in the Fe-Al alloy cluster assembly and Fe cores are covered and their magnetic coupling are weakened by Al and/or Al-oxide layers in the Fe/Al cluster composite.

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    3. Change in Mechanical Properties and Microstructure of ARB Processed Ti during Annealing MATERIALS TRANSACTIONS Vol.49(2008), No.1

  • Stress Corrosion Cracking Behaviour of Excimer Laser Treated Aluminium Alloy 6013

    W. L. Xu, T. M. Yue, H. C. Man

    pp. 1836-1843

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    DOI:10.2320/matertrans.MRA2008105

    Abstract

    The effect of excimer laser surface melting on the stress corrosion cracking behaviour of aluminium alloy 6013 has been investigated by means of a slow strain rate test at the open circuit potential, and at a constant anodic potential. After the laser treatment, a relatively thin non-dentritic re-solidified layer, of the order of a few micrometres, and largely free of coarse constituent particles, has been produced. At the top surface of the re-solidified layer, an oxide-nitride bearing film, having a thickness of a couple of hundred nanometres, is present. The results of the slow strain rate test in a 3.5%NaCl solution showed that, in terms of total displacement to failure and corrosion current density, the stress corrosion resistance of the alloy was greatly increased by excimer laser melting. The superior stress corrosion resistance of the laser-treated material is attributed to the laser-formed oxide-nitride top film acting as a barrier and retarding the initiation of cracks.

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  • Synthesis of Y-Doped n-Type SrTiO3 Thermoelectric Oxides by Polymerized Complex Process

    Mikio Ito, Naoto Ohira

    pp. 1844-1847

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    DOI:10.2320/matertrans.MRA2007322

    Abstract

    Synthesis of the Y-doped n-type SrTiO3 thermoelectric oxides was tried by the polymerized complex (PC) process and the subsequent hot pressing. The X-ray diffraction patterns of the Sr1−xYxTiO3 powder precursors (0≤x≤0.1) synthesized by the PC process showed that the perovskite SrTiO3 structure without any second phases was obtained, indicating that the Y-doped SrTiO3 powder can be fabricated by the PC process, which is a lower temperature process as compared to the conventional solid state reaction (SSR) process. It was found that the perovskite SrTiO3 structure mostly remained after the sintering by hot pressing. The Sr0.9Y0.1TiO3 sample showed the Seebeck coefficient and the electrical resistivity lower than those of the non-doped SrTiO3, supporting an increase in carrier concentration due to Y doping. The power factor of the Sr0.9Y0.1TiO3 sintered compact was almost the same as that of the Sr0.9Y0.1TiO3 prepared by the conventional SSR method.

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  • Hydroxyapatite Formation on Ca-P-O Coating Prepared by MOCVD

    Mitsutaka Sato, Rong Tu, Takashi Goto, Kyosuke Ueda, Takayuki Narushima

    pp. 1848-1852

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    DOI:10.2320/matertrans.MRA2008097

    Abstract

    Ca-P-O coatings of α-tricalcium phosphate (α-TCP) and hydroxyapatite (HAp) films were prepared on commercially pure Ti (CP-Ti) by MOCVD using Ca(dpm)2 and (C6H5O)3PO precursors. The behavior of apatite formation on the Ca-P-O coatings was investigated by immersing specimens in a Hanks’ solution. An apatite phase has regenerated on the α-TCP coating after 1 day, and has covered the whole specimen surface after 14 d. On the HAp coating, an apatite phase has regenerated after 1 h and has covered the whole surface after 6 h. The microstructure of the regenerated apatite phase on the HAp coating has changed from a needle-like to a network texture after 12 h.

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  • Effects of Carbon Content and Thermo-Mechanical Treatment on Fe59Mn30Si6Cr5CX (X=0.015–0.1 mass%) Shape Memory Alloys

    C. H. Yang, H. C. Lin, K. M. Lin, W. H. Ho

    pp. 1853-1857

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    DOI:10.2320/matertrans.MRA2008122

    Abstract

    Slight amounts of carbon (0.015–0.1 mass%) were added into the Fe-30Mn-6Si-5Cr shape memory alloy. The microstructure, precipitation behaviour and shape memory performance of these Fe59Mn30Si6Cr5CX alloys with various thermo-mechanical treatments were investigated. Experimental results show that two particles, the χ-phase and M23C6 carbide, are observed within the grain-boundary phases. M23C6 carbide only appears in an alloy with high carbon content, but the χ-phase can form in all alloys with low and high carbon contents. The deformation-induced defects in the 10% pre-deformed specimens are preferential sites for nucleation of precipitates (the χ-phase and M23C6 carbide) in the following aging treatment. After 550–800°C aging, the rearranged uniform defects and homogeneous precipitates within the grain interior will strengthen the matrix and increase the shape recovery ability. After 850–900°C aging, both the uniform defects and homogeneous precipitates disappear due to recrystallization, and hence the specimen’s shape recovery ratios are significantly reduced.

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  • Thermoelectric Properties of P-Type Heusler Compounds (Fe2−xCox)(V1−yTiy)Al

    Hiroyuki Nakayama, Naoki Ide, Yoichi Nishino

    pp. 1858-1862

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    DOI:10.2320/matertrans.MRA2008078

    Abstract

    We report on the effect of Co and Ti co-doping on the thermoelectric behavior of Fe2VAl based alloys. The doped alloys, (Fe2−xCox)(V1−yTiy)Al, with compositions x=0.01–0.07 and y=0.04–0.20 exhibit a p-type thermoelectric property when the total valence electron number is below 24. The co-doping of cobalt and titanium is believed to cause a substantial shift of the Fermi level from the center of the pseuodgap to a lower energy position. In particular, the alloy with x=0.03 and y=0.10 exhibits a p-type thermoelectric behavior with a large Seebeck coefficient of S=85 μV/K as well as a low electrical resistivity of ρ=2.3 μΩ m at 400 K, so that the power factor, P=S2⁄ρ, reaches 3.2×10−3 W/m K2. The power factor is larger than that of the Ti doped Fe2VAl alloy so far reported. The high power factor caused by the co-doping of Co and Ti might be due to a modification in the band structure on the valence band side around the Fermi level. The co-doping of Co and Ti is also effective in reducing the thermal conductivity, mainly due to phonon scattering.

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  • Effect of Self-Dispersion Nanosized AlOOH on Microstructure and Wear Resistance of Alumina Ceramic Balls

    Liao Haida, Wu Bolin, Zhang Lianmeng, Zhong Lianyun, Wang Huixian

    pp. 1863-1867

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    DOI:10.2320/matertrans.MRA2008061

    Abstract

    The self-dispersed AlOOH nanopowders were prepared by the sol-hydrothermal crystallization and charging composite dispersion method. The nanosized AlOOH were dispersed evenly into the mixed slurry of alumina and fluxing agent by the new batching technology of sol homogeneous dispersion and ball-milling-free for preparation of the ceramic body containing 98.1% alumina. The ceramic ball blank formed by cold isostatic pressing was sintered into ceramic ball at ordinary pressure and the temperature lower than 1500°C for 3 h. Using this method, uniform and fine grains of ceramic ball with better wear resistance were obtained by adding 3.5 mass% nanosized AlOOH to ceramic slurry. The wear rate of the self-made ceramic ball and the compared ceramic ball (which is the most wear resistance ceramic ball at present) under the same testing conditions were 0.004 and 0.056%/h, respectively.

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  • Properties of Ceramic Layer Formed by Centrifugal Thermit Reaction with Silicon Sludge Replacement

    M. T. Le, D. J. Kim, J. R. Lee, C. G. Kim, H. S. Chung

    pp. 1868-1873

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    DOI:10.2320/matertrans.MRA2008109

    Abstract

    A ceramic-lined steel pipe has been prepared by the thermit reaction of aluminum-ferric oxide under centrifugal force with the partial replacement of aluminum by the silicon sludge obtained from a semiconductor wafer cutting processing. The ceramic layer on the pipe inner surface consists of the crystalline structures of mainly corundum (α-Al2O3) and hercynite (FeAl2O4). The sludge replacement increases the layer density from 2.9 g/cm3 to 3.5 g/cm3 and the hardness from 1450 Hv to 1780 Hv. The amorphous phases of mullite (Al6Si2O13) formed between the crystalline structures are found to be responsible for a significant improvement of the ceramic layer density.

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  • Self-Induced Rotary Sloshing Caused by an Upward Off-Centered Jet in a Cylindrical Container

    Daisuke Iguchi, Yoshiaki Ueda, Tatsuya Ohmi, Manabu Iguchi

    pp. 1874-1879

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    DOI:10.2320/matertrans.MRA2008038

    Abstract

    Self-induced rotary sloshing caused by an upward off-centered jet in a cylindrical container is numerically and experimentally investigated. Unlike the regular jet-induced rotary sloshing, the present off-centered case could contain components of higher fluctuation in the surface wave and the amplitude exhibits different values in various view angles. A simple geometrical model for the amplitude is established, by assuming the conservation of the angular momentum of the sloshing wave, and the predicted amplitude is tested against the experimental and computational results. Some results for the flow pattern, sloshing period, possible occurrence regime and trajectory of the peak point of the free surface swell due to the inlet jet are given.

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  • Wave Interference Effect in Thin Film Structures under Pulsed Laser Irradiation

    Kwangu Kang, Seong Hyuk Lee, Hong Sun Ryou, Young Ki Choi, Seungho Park, Joon Sik Lee

    pp. 1880-1888

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    DOI:10.2320/matertrans.MER2008035

    Abstract

    The present article conducts extensive numerical simulations to investigate conduction and radiation heat transfer characteristics in thin silicon layers irradiated by pulsed lasers. The two temperature model is used for estimating carrier and lattice temperatures during laser irradiation. The energy absorption in thin films is predicted by the electromagnetic theory, including wave interference effects through thin film optics. The present study predicts the carrier and lattice temperatures during laser irradiation and examines the influence of film thickness and laser pulse duration on characteristics of energy transport. It is observed that, unlike bulk materials, the variation of the film thickness causes significant changes in the reflectivity of silicon film due to wave interference effects in thin film structures. The maximum value of the reflectivity is estimated to be about seven times larger than the minimum value. For the spatial distributions of carrier and lattice temperatures,
    it is found that a periodic tendency appears for picosecond pulse because of the difference between the pulse duration and the time for energy diffusion. It indicates that the traditional usage of Beer’s law is not appropriate for prediction of radiation heat transfer in thin film structures.

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  • Oxidative Sulfur Removal from Complex Copper Concentrate

    Byung-Su Kim, Hoo-In Lee, Jin-Tae Park, Jeong-Soo Sohn, Jae-Chun Lee

    pp. 1889-1892

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    DOI:10.2320/matertrans.MER2008081

    Abstract

    It is very important to remove sulfur from complex copper concentrates for smelting them by a carbon reduction process since copper concentrates are progressively becoming complex and low grade. The carbon reduction process largely consists of the oxidation process of complex copper concentrate and smelting process of the oxidized concentrate. In the present work, the kinetics study has been performed on a complex copper concentrate to understand the oxidation process over a temperature range of 998 to 1073 K and an oxygen partial pressure range of 15.20 to 50.66 kPa using a thermogravimetric method. It was found that the oxidation rate was very fast under the whole temperature range and almost 95% of sulfur contained in the concentrate was removed after 15 min at 1073 K under an oxygen partial pressure of 21.28 kPa. Sulfur removal ratio as a function of time has been analyzed by using a shrinking-core model and the effect of oxygen partial pressure has been elucidated.

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  • Consideration of the Effect of the Nonspherical Distribution of Electrons in Atomic Structures

    Mitiyasu Miyasita, Katsuhiko Higuchi, Akira Narita, Masahiko Higuchi

    pp. 1893-1899

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    DOI:10.2320/matertrans.MER2008121

    Abstract

    We review the atomic structures by taking into account the effect of the nonspherical distribution of electrons explicitly. Actual calculations are performed for the neutral first-row atoms by means of the variational method. Compared to the conventional atomic structures, degenerate energy levels are split partially due to the lack of the spherical symmetry. The magnitudes of these splittings are not negligibly small. This means that the nonspherical part of electron distribution seems to be essential not only conceptually but also quantitatively in the study on the single-particle picture of atomic systems.

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  • Optimization of Zr-Doped ZnO Thin Films Prepared by Sol-Gel Method

    Chien-Yie Tsay, Kai-Shiung Fan

    pp. 1900-1904

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    DOI:10.2320/matertrans.MER2008111

    Abstract

    Semiconductor thin films of Zr-doped ZnO, with Zr concentrations varying from 0 to 5 at%, have been prepared using a sol-gel method. Crystallinity, microstructure, and optical properties affected by Zr concentration were investigated. In this study, Zr-doped ZnO thin films were deposited onto alkali-free glass substrates by spin-coating. The as-deposited films were preheated at 300°C and then annealed at 500°C in air. The experimental results showed that doping ZnO thin films with Zr not only refined the grain size but also increased transmittance and resistivity. Among all the thin films investigated in the present study, the 3 at% Zr-doped ZnO thin film exhibited the best properties with a transmittance of 86.3% and a RMS roughness value of 5.86 nm. In addition, thin-film transistors were fabricated by spin-coating a 3 at% Zr-doped ZnO active channel layer onto a transistor subassembly. These transistors exhibited n-type depletion mode in which threshold voltage and drain current on-to-off ratio were −18.0 V and 9.6×105, respectively.

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  • An Enhanced Calibration Scheme for the EDM Hole-Drilling Strain Gage Method for the Measurement of Residual Stress in Ferrous Materials

    H. T. Lee, C. Liu, F. C. Hsu, J. M. Hsu

    pp. 1905-1910

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    DOI:10.2320/matertrans.MER2008098

    Abstract

    Recent studies revealed that EDM hole-drilling strain gage method is applicable for the measurement of residual stress in materials with higher hardness and toughness. However, the metallurgical transformation layer formed on the wall of the hole induces an additional stress and therefore generates a measurement error. Usually this error can be calibrated by estimating and reducing the hole-drilling induced extra stress, σIS. However, the value of σIS is highly sensitive to the EDM parameters. Accordingly, the current study aimed at lowering σIS by optimizing the working parameters of pulse current, pulse-on duration and pulse-off duration with experiments. An inverse power law relationship was constructed to predict the magnitude of the hole-drilling induced stress where was referred. A convenient calibration method was proposed where calibration factor can be easily determined. The calibrated results revealed good accuracy where deviation is no more than 10 MPa. The accuracy of the proposed calibration scheme was confirmed in study.

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  • Optimum Processing and Tool Controls for Three-Dimensional Friction Stir Welding

    Hironori Takahara, Masato Tsujikawa, Sung-Wook Chung, Yuzo Okawa, Sachio Oki, Kenji Higashi

    pp. 1911-1914

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    DOI:10.2320/matertrans.L-MRP2008816

    Abstract

    The influence of three-dimensional friction stir welding tool-control on joints’ mechanical properties was investigated. Although FSW is widely applied to linear joints, it is impossible for five-axes FSW machines to maintain all FSW parameters in optimum conditions during three-dimensional (3D) welding. Such 3D FSW joints should be produced according to an order of priority for FSW parameters. Butt joints with rectangular change in the welding direction on a curved plane (curved L butt joints) were welded using different three tool-control methods, which change various welding parameters. Results show that the A and C axes shortcut method is effective for 3D welding.

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  • Martensitic Transformation in NiCoMnSn Metamagnetic Shape Memory Alloy Powders

    Kouhei Ito, Wataru Ito, Rie Y. Umetsu, Makoto Nagasako, Ryosuke Kainuma, Asaya Fujita, Katsunari Oikawa, Kiyohito Ishida

    pp. 1915-1918

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    DOI:10.2320/matertrans.MRP2008126

    Abstract

    Martensitic and magnetic properties of NiCoMnSn metamagnetic shape memory alloy powders obtained by a gas atomization method were investigated. The as-atomized powders showed a dendritic structure which changed to a single-phase one by annealing at 1173 K for 2 h. Although the martensitic transformation behavior was almost the same as that in bulk samples, the transformation thermal interval, namely, Ms−Mf, of the as-annealed powders decreased with increasing annealing time. In the powders annealed at 1173 K for 144 h, a reversible metamagnetic phase transition was confirmed by the application of a magnetic field of 7 T.

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  • Polytetrafluoroethylene (PTFE) Top-Covered Mg-Ni Switchable Mirror Thin Films

    Shanhu Bao, Kazuki Tajima, Yasusei Yamada, Masahisa Okada, Kazuki Yoshimura

    pp. 1919-1921

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    DOI:10.2320/matertrans.MRP2008117

    Abstract

    Pd capped Mg-Ni thin films were prepared on glass substrates by DC magnetron sputtering for a switchable mirror. In order to improve the switching durability, polytetrafluoroethylene (PTFE) thin film was deposited on it as a protection layer by rf magnetron sputtering. Sputtering of PFTE film was carried out at power of 30 W in the Ar and CF4 mixed gas discharge plasma. The characterizations of PFTE thin films were performed with Fourier transformation infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). PTFE films with 900 nm thick deposited on glass substrates have transmittance of 90%. PFTE thin film shows the excellent protection role against the oxidization of Mg and gives the 1000 switching cycles by 4 vol% hydrogen.

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  • Experimental Evaluation of the Rolling Reduction and Heat-Treatment Effects on the Texture and Creep Behavior of a Zricaloy-4 Sheet

    Yoon-Soo Lim, Hyun-Gil Kim, Yong-Hwan Jeong

    pp. 1922-1925

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    DOI:10.2320/matertrans.MRP2008021

    Abstract

    The effect of manufacturing conditions such as a rolling reduction and the final heat-treatment condition on the texture and creep behavior was investigated for the Zircaloy-4 sheet. Various microstructural characteristics could be obtained in this study by controlling of the rolling reduction from 30 to 70% and the final heat-treatment conditions up to 600°C. The crystallographic texture of the prepared Zircaloy-4 sheet was evaluated by using the XRD for the rolling plane. The creep test of the sheet was performed under a constant applied stress at a temperature at 380°C with an axial stress of 120 MPa for the three directions of 0°, 90°, and 45° in the rolling direction. From a comparison of the Kearns number for the normal direction of the sheet, the texture was developed with an increasing rolling reduction, and was somewhat affected by the final annealing conditions. The creep strain was decreased by adding a final annealing, and it was considerably affected by the test direction, because it was observed that the 45° direction in the rolling direction revealed the highest creep strain among the three types of test directions.

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  • Microstructural Evolution and Pressure-Assisted Master Sintering Surface of Silicon Nitride

    Kyong Jun An, Hyun Jong Kim, Myung Keun Han

    pp. 1926-1928

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    DOI:10.2320/matertrans.MRP2008026

    Abstract

    The pressure-assisted master sintering surface (PMSS) of silicon nitride has been constructed, in which the sintered density during hot pressing can be predicted as a function of the integral of a temperature function over time at a given pressure, irrespective of the heating path. High-purity α-Si3N4 powder with the additives of 6.25% Y2O3 and 1% Al2O3 was used for this research. Densifications of silicon nitride were continuously recorded during heating at two different ramping rates of 0.083°C/s and 0.167°C/s up to 1800°C at fixed pressures from 7 to 34 MPa. The activation energy was estimated as 698 kJ/mol. During the hot pressing, the microstructural evolution of α-Si3N4 to β-phase known as a solid/liquid/solid mechanism was also observed. Using the PMSS of silicon nitride, the final density can be predicted to about 1% accuracy for a fixed pressure and an arbitrary temperature-time path.

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  • © 2008 The Japan Institute of Metals and Materials

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