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

MATERIALS TRANSACTIONS Vol. 50 (2009), No. 7

  • Thermoelectric Properties of the Thallium-Tellurium Binary Compounds

    pp. 1582-1585

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    DOI:10.2320/matertrans.E-M2009803

    We are paying attention to extremely low thermal conductivity (κ) materials which have a potential to be next generation thermoelectric materials. Most of the extremely low κ materials that have been reported so far are ternary thallium tellurides such as Ag-Tl-Te ternary system. However, as for Tl-Te binary system, the thermoelectric properties have been scarcely reported. In the present study, the Tl-Te binary compounds, Tl2Te, Tl5Te3, TlTe, and Tl2Te3, were prepared and their thermoelectric properties were investigated. The κ of TlTe was relatively high (approximately 4 Wm−1K−1 at 300 K), while those of Tl2Te and Tl2Te3 were extremely low (∼0.5 Wm−1K−1 at 300 K). These compounds indicated relatively high thermoelectric figure of merit ZT, e.g., Tl2Te showed the highest value of 0.2 at 586 K.
  • Effect of Aluminum and Copper Addition to the Thermoelectric Properties of FeSi2 Sintered in the Atmosphere

    pp. 1586-1591

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    DOI:10.2320/matertrans.E-M2009808

    Thermoelectric materials with composition of Fe0.92Mn0.08Si2.1 + X mass% Cu + Y mass% Al (0≤X, Y≤5) were produced by sintering in air, and their thermoelectric properties and structures were examined. The samples showed fairly good thermoelectric properties. Moreover they were covered with an oxidation resistance layer. The samples without addition of Cu and/or Al did not show any effective thermoelectric properties. In the case of copper addition, the thermoelectric power of the copper added sample was approximately 75% of the sample prepared in a vacuum, while the resistivity was drastically increased. The oxidation of the copper added samples was much less than that without copper. In the case of 2 mass% or more aluminum addition, a silicon oxide layer was formed on the surface of the samples. The oxide layer had much more dense and smooth surface, which was confirmed by an optical microscope and a scanning electron microscope (SEM). The samples, which were added both copper and more than 2 mass% aluminum, showed about 80% of thermoelectric power of the samples prepared in a vacuum.
  • Thermoelectric Properties of Bi2Te3-Related Materials Finely Grained by Mechanical Alloying and High Pressure Torsion

    pp. 1592-1595

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    DOI:10.2320/matertrans.E-M2009807

    Bi2Te3-related thermoelectric semiconductors were prepared by the mechanical alloying (MA) and the vertical Bridgman (VBM)-High Pressure Torsion (HPT) methods. Structures and electric properties of these alloys were then investigated. These samples had a nominal composition of Bi0.5Sb1.5Te3.0 with 0.07 mass% excess Te. The MA sample was sintered into a compact after mechanical alloying while the VBM–HPT sample was deformed by HPT after being cut into a disk from a melt-grown ingot by the vertical Bridgman method (VBM). The orientation factors of the MA and VBM–HPT samples were 0.054 and 0.525, respectively, indicating that the preferred orientation was formed by VBM–HPT. Average grain sizes of both samples were approximately 2 μm. The VBM–HPT sample was shown low electrical conductivity than the MA one in spite of the high orientation factor.
    By estimating the slope of carrier mobility versus temperature the carrier scattering factor of the MA and VBM–HPT samples were estimated to be −1.3 and +0.1. These values are indicative of carrier scatterings by acoustic phonons and by the interaction between acoustic and optical phonons, respectively. The maximum power factor obtained for the isotropic MA sample was 4.1×10−3 W m−1K−2 at 310 K and this was about twice the 2.1×10−3 W m−1K−2 at 440 K obtained for the anisotropic VBM–HPT sample.
  • High-Temperature Thermoelectric Measurement of B-Doped SiGe and Si Thin Films

    pp. 1596-1602

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    DOI:10.2320/matertrans.E-M2009811

    Recent progress of thin-film type thermoelectric, TE, materials accelerates new microdevices working at room temperature to high temperature, and also requires the measurement techniques for the films. Modified four point pressure contact electrodes have been developed in this study, applied for the high temperature measurement of the resistivity and Seebeck coefficient of the boron-doped Si0.8Ge0.2 and Si thin films. The films were prepared by chemical vapor deposition method and then annealed at high temperature of 1050°C, and their Seebeck coefficients were investigated with two different measurement systems, block heating or air cooling electrodes, from 80 to 780°C. For this temperature range, the Seebeck coefficients of the boron-doped Si0.8Ge0.2 film and boron-doped Si film were 150∼350 μV/K and 100∼250 μV/K, respectively. The deviation of Seebeck coefficient was investigated with various measurement parameter, and the optimized temperature difference for the reliable measurement was found to be 2.2°C.
  • Thermal Conductivity of the Ternary Compounds: AgMTe2 and AgM5Te8 (M = Ga or In)

    pp. 1603-1606

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    DOI:10.2320/matertrans.E-M2009810

    We synthesized AgGaTe2, AgGa5Te8, AgInTe2, and AgIn5Te8 by solid-state reactions of Ag2Te, Ga2Te3 or In2Te3, and Te, and prepared their high-density polycrystalline pellets. The thermal conductivity κ was evaluated by the laser flash method from room temperature to around 870 K. These compounds exhibited low κ, e.g. the room temperature values were 1.94, 0.54, 2.05, and 1.08 Wm−1K−1 for AgGaTe2, AgGa5Te8, AgInTe2, and AgIn5Te8, respectively. We discussed the magnitude relations of κ from the viewpoints of the crystal structure and the Debye temperature.
  • Thermoelectric Properties and Electrical Transport of Graphite Intercalation Compounds

    pp. 1607-1611

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    DOI:10.2320/matertrans.E-M2009813

    Graphite intercalation compounds (GICs) have high electrical conductivities, large Seebeck coefficients, and low thermal conductivities as compared with their host graphite materials. Due to these properties, GICs are expected to act as effective thermoelectric materials. The thermoelectric figure of merit of the GICs is not as high as that of other thermoelectric materials; this is because of the small Seebeck coefficient and high thermal conductivity of GICs. However, the thermoelectric power factor of GICs is sufficiently high at present. In previous works, it was suggested that an increase in concentration of the intercalated species improves the thermoelectric performance of GICs. To better understand the thermoelectric properties of GICs, the dependence of thermoelectric properties with the electrical carrier density and mobility were investigated through the measurements of galvanomagnetic properties. As a result, the electrical conductivity of GICs slightly increases with the carrier density and the thermal conductivity increases with the carrier mobility. Furthermore, the carrier mobility decreases with an increase in the carrier density. In conclusion, the thermoelectric performance of GICs is suggested to be improved by an increase in the carrier density, that is, by an increase in the intercalate concentration.
  • Using Severe Plastic Deformation for the Processing of Advanced Engineering Materials

    pp. 1613-1619

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    DOI:10.2320/matertrans.MF200913

    The processing of metals through the application of severe plastic deformation leads to significant grain refinement and provides an opportunity for achieving superior properties. The two procedures of equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) are examined with emphasis on the mechanical properties at low and high temperatures and the nature of the grain refinement. It is demonstrated that grain refinement occurs relatively homogeneously in f.c.c metals through the formation of dislocation cells or subgrains and the evolution of these cells into an array of ultrafine grains separated by high angle boundaries. By contrast, grain refinement in h.c.p. metals such as magnesium is inhomogeneous and occurs through the nucleation of new grains along the initial grain boundaries due to the high stresses generated to activate multiple slip systems. Ultrafine-grained metals generally exhibit high strength but they may exhibit weakening if the processing conditions adversely affect the precipitate morphology. If the ultrafine grains are stable at high temperatures there is a possibility of achieving excellent superplastic properties.
  • Numerical Analysis for the Prediction of Microstructure after Hot Forming of Structural Metals

    pp. 1620-1625

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    DOI:10.2320/matertrans.MF200906

    The importance of structural metals for industrial applications is based on their superior combination of mechanical properties—strength, elongation, toughness and corrosion resistance—achieved at the end of forming processes. A numerical analysis for the prediction of microstructure is strongly required for the optimization of hot forming process parameters, because the microstructure of structural metals, which has the significant effects on mechanical properties, is strongly dependent to forming process conditions as well as the chemical composition. The incremental dislocation density and microstructural evolution analysis method enables the prediction of the change in microstructure after forming. The outline of the analytical scheme is explained briefly, and the results of its application to strip rolling, bar rolling and shape rolling are presented. Finally, the remaining research topics in this field are discussed.
  • Oxide Ceramics with High Density Dislocations and Their Properties

    pp. 1626-1632

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    DOI:10.2320/matertrans.MF200928

    Dislocations are of scientific and technological interest due to their unusual physical properties, which are quite different from those in the bulk. It is, therefore, expected to use dislocations as nanowires which provide functional properties in a crystal. In this study, high densities of dislocations were introduced in oxide single crystals by high-temperature plastic deformation. Insulating sapphire and YSZ single crystal were used as model systems. The electron and ion conductivities were measured for the dislocation introduced crystals respectively. It was found that the dislocations with Ti segregation in sapphire crystal showed excellent electrical conductivity and dislocations themselves in YSZ crystal improved the ionic conductivity. This technique has a potential to be applied for any crystals because of its simplicity, and will be expected to give special and unprecedented properties to common materials.
  • Softening and Microstructural Coarsening without Twin Formation in FCC Metals with Low Stacking Fault Energy after Processing by High-Pressure Torsion

    pp. 1633-1637

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    DOI:10.2320/matertrans.MF200921

    Gold (Au), silver (Ag) and copper (Cu) were severely deformed through the process of high pressure torsion (HPT). The grain sizes were reduced to the submicrometer range and the hardness increased significantly by the HPT process. However, after holding at room temperature, Au and Ag exhibited grain growth and thus softening without heating. The softening and microstrcutural coarsening occurred rather quickly in Ag and moderately in Au but nothing changed in Cu even after keeping for prolonged time. No twins were formed along with the grain growth in the HPT-processed Au and Ag. High density lattice defects and enhanced diffusivity in the metals are responsible for such an unusual softening behavior.
  • Influence of Phosphorus Microalloying on the Microstructure and Mechanical Properties of DA761 Superalloy

    pp. 1638-1643

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    DOI:10.2320/matertrans.MF200908

    Effects of phosphorus microalloying on the microstructure and mechanical properties of direct-aging DA761 alloy have been studied. The aim of this work is to find a new way to develop a higher performance of wrought superalloy. The optimum addition of phosphorus in DA761 alloy is determined by investigating effects of phosphorus and boron on the microstructure and properties of DA761 alloy, that are compared to GH761 alloy treated by standard heat treatment. The stability of microstructure and properties of fine-grain DA761 alloy with optimum content of phosphorus is proved by studying the evolution of microstructure and properties of the alloy after long-term high temperature ageing. The practicability of phosphorus microalloying in improving the mechanical properties of DA761 alloy is verified by smelting a 500 kg ingot and detecting the microstructure and properties of billet near the size of engine disk. The results verify the phosphorus microalloying and fine-grain direct aging treatment in improving commercial GH761 alloy. Mechanism of phosphorus microalloying is also discussed.
  • Effects of Electric Field Treatment on Corrosion Behavior of a Ni-Cr-W-Mo Superalloy

    pp. 1644-1648

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    DOI:10.2320/matertrans.MF200905

    Electric field treatment was performed on a Ni-Cr-W-Mo superalloy to investigate the effects of electric field treatment on its corrosion behavior. The microstructure evolution and the elements distribution at grain boundaries of both annealing twins and high angle grains were examined. The results show that the corrosion resistance can be improved by the electric field treatment and both of the corrosion weight loss and corrosion rate are decreased with the increasing treating time. When the alloy is electric field treated at 1093 K for 600 min with 4 kV·cm−1, the intergranular corrosion rate is 65.3 mm·y−1 with the decreasing ratio of 25.1% compared with the untreated one, and the immersion corrosion rate is 3.9 mm·y−1 with the decreasing ratio of 57.9% compared with the untreated one. The redistribution of elements between the original high angle grain boundaries and the annealing twins occurred by the formation and growth of the annealing twins during the electric field treatment, as well as the improvement of exhaustion of Cr and Mo elements at the grain boundaries. With the increasing treating time, a large amount of original high angle grain boundaries are replaced and the continuously distributed original grain boundaries are separated, which leads to the retardation the growth rate of the corrosion ditches. The corrosion resistance of the alloy is improved due to the changes of corrosion behavior of the grain boundary. Moreover, the promotion effect of electric field treatment on the atom diffusion rate decrease the exhaustion tendency of Cr and Mo elements on both sides of normal high angle grain boundary. Those can be considered as the reasons of improving the corrosion resistance after electric field treatment.
  • Formation and Disappearance of Pores in Plasma Arc Weld Bonding Process of Magnesium Alloy

    pp. 1649-1654

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    DOI:10.2320/matertrans.MF200919

    A new welding technology called “plasma arc weld bonding” was designed by combining the plasma arc welding and adhesive bonding process in the lap welding of magnesium alloy. During the “plasma arc weld bonding” process, the major difficulty was the presence of porosity in the welding joint. This paper analyzed the formation mechanism of pores and the effect of welding parameters on pores behaviors during plasma arc weld bonding process of magnesium alloy by optical microscopy and electron probe microanalysis. The results showed that it easily formed a lot of pores in joint because of the existence of adhesive layer. The decomposition of adhesive in both the sides of welding seam was the main cause for the formation of pores. The regular-shape pores were formed by CO and CO2, and the anomalous-shape pores were formed by the low molecular weight hydrocarbons. The pores behaviors were affected evidently by the heat input, and the favorable joint could be obtained when the heat input was about 396 kJ/m.
  • Time Evolution in 3D Metal Microstructures — Recrystallization

    pp. 1655-1659

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    DOI:10.2320/matertrans.MF200923

    The three dimensional x-ray diffraction (3DXRD) concept is shortly described and new experimental updates are highlighted. The potentials and limitation of the 3DXRD method are compared to those of other 3D methods. 3DXRD has been used for in-situ studies of recrystallization and new migration rate results are presented. Migration mechanism for boundary segments surrounding a recrystallizing grain are described and discussed.
  • In Situ Lorentz Microscopy Observation of Displaced Chain Walls in Permalloy

    pp. 1660-1663

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    DOI:10.2320/matertrans.MF200927

    In situ investigation of displaced chain walls in 80 at% Ni Permalloy under applied in-plane magnetic field has been carried out by out-of-focus methods of Lorentz electron microscopy. The magnetic flux in the plane of the film is schematically illustrated. The in-plane magnetic field applied to the foil is produced by a homemade magnetizing stage. By adjusting magnitude and direction of the electric current through the coils of the magnetizing stage, the magnetization reversal process of the magnetic domain wall has been in situ observed.
  • A Universal Damping Function for Empirical Dispersion Correction on Density Functional Theory

    pp. 1664-1670

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    DOI:10.2320/matertrans.MF200911

    A damped London dispersion interaction is generally adopted in empirical dispersion corrections on density functional theory (DFT), where dispersion parameters are determined empirically to reproduce correct dispersive interactions after assuming a damping function. The key to a successful dispersion correction is choosing an appropriate damping function. In this work we propose a single universal damping function that can represent several damping functions used in literatures with a few adjustable parameters. This universal damping function provides a unified formula that allows convenient comparison and flexible optimization in dispersion corrected DFT methods. Using the optimized universal damping functions and dispersion parameters, we develop dispersion correction methods for HF, B3LYP and PBE theories. We calculate the dispersive energies accurately for rare gas diatomic molecules and benzene dimers with an averaged error <4.1%.
  • Deformation Analysis of Shearing Process Using Results of Notched Round Bar Tension Test

    pp. 1671-1677

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    DOI:10.2320/matertrans.MF200903

    Deformation analysis of shearing process is carried out by using finite element method (FEM). Gurson-Tvergaard-Needlman (GTN) model is applied as a fracture criterion because ductile fracture behavior is a dominant factor in shearing process. Ductile fracture involves micro void nucleation, growth and coalescence of voids. To predict void nucleation in FEM analysis, a void nucleation critical strain model is proposed. Furthermore a notched round bar tension test using image analysis is proposed for deciding material properties relating ductile fracture. Gradual changes in the necking shape and tensile load are measured by using the test. From the results, strain and stress history at the necking section of tensile specimen and relationship between stress triaxiality and microvoid nucleation are obtained. Additionally, obtained damage parameters are introduced to the deformation analysis of shearing process and the results are compared with the experimental result.
  • Numerical Analysis of Coalescence Characteristics of Low Melting Point Alloy Fillers Using a Non-Equilibrium Phase Field Model

    pp. 1678-1683

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    DOI:10.2320/matertrans.MF200915

    A non-equilibrium phase field model (NPFM) is proposed to examine the three-dimensional coalescence characteristics of low melting point alloy (LMPA) fillers, widely used for self-organized interconnection applications. This model sufficiently considers the non-equilibrium process during phase transitions, resulting in accurate prediction of interfaces between two different phases with a high density ratio. The preliminary simulation is carried out for validation of the present model and numerical predictions are in good agreement with analytical solutions for a one-dimensional solidification problem. The proposed NPFM successfully predicts the phase transition, the heat transfer from solid to liquid, and the coalescence behaviors of LMPA fillers, whereas the conventional enthalpy method fails to describe the non-equilibrium phase transition. Moreover, the results show that there exists grid dependency in the mush zone, suggesting that special care should be taken of the mush zone for better prediction of interfaces between different phases.
  • Self-Organized Interconnection Process Using Solderable ACA (Anisotropic Conductive Adhesive)

    pp. 1684-1689

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    DOI:10.2320/matertrans.MF200918

    In this paper, we discuss our design of a new class of low-melting-point alloy (LMPA)-filled anisotropically conductive adhesives (ACA) and a self-organized interconnection process for using these adhesives, and we demonstrate a good electrical conduction for the process. Flow, melting, coalescence, and wetting characteristics of LMPA fillers in the ACA facilitate this process. In order to exploit good coalescence and wetting characteristics of LMPA fillers, the polymer matrix has a sufficient fluxing capability against oxide films of both LMPA fillers and electrode materials. Furthermore, it is essential that the polymer have a low viscosity level around the melting point of the incorporated LMPA to achieve a good electrical conduction path.
    In order to study coalescence and wetting characteristics, we formulated two types of ACA with different volume fractions of LMPA filler (10 vol% and 40 vol%). Our test board had an 18-μm thick Cu line-type pattern (10mm×0.1mm) and an area array-type pattern (square type: 0.1mm×0.1mm, circle type: \\varphi, 0.1 mm) with five different pitches (50 μm to 250 μm). We measured thermal properties of the ACA by differential scanning calorimetry (DSC), and we determined a temperature profile for the interconnection process. We then monitored coalescence and wetting characteristics of LMPA fillers and morphology of conduction path in ACA by using a microfocusing X-ray inspection system and an optical microscope.
    We determined that the developed LMPA-filled ACA have good coalescence and wetting characteristics regardless of pattern types. In addition, we were able to achieve a good electrical conduction path because of the coalescence and wetting characteristics of the LMPA fillers in the ACA.
  • The Elevated-Temperature Creep Behavior of Boron-Modified Ti-6Al-4V Alloys

    pp. 1690-1703

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    DOI:10.2320/matertrans.MF200914

    This work investigated the effect of nominal boron (B) additions of 0.1 mass% and 1 mass% on the elevated-temperature (673–728 K) tensile-creep deformation behavior of a Ti-6Al-4V(mass%) alloy for applied stresses between 400–600 MPa. The alloys were evaluated in the as-cast and cast-then-extruded conditions. Boron additions resulted in a dramatic refinement of the as-cast grain size and TiB whisker volume percents of approximately 0.6 and 6.0 for the Ti-6Al-4V-0.1B and Ti-6Al-4V-1B alloys, respectively. The extrusions were performed in the β-phase field and resulted in the TiB-phase whiskers aligning in the extrusion direction. The creep resistance of the as-cast alloys significantly improved with increased B concentration, where around an order of magnitude decrease in the secondary creep rate was observed between the Ti-6Al-4V-1B and Ti-6Al-4V as-cast alloys. Grain refinement due to the B addition did not deleteriously affect the creep resistance in the temperature and stress ranges considered, where dislocation creep was suggested to be the dominant secondary-creep mechanism. The enhanced creep resistance was attributed to load sharing by the TiB whiskers. For the same nominal B contents, the cast-then-extruded alloys exhibited significantly greater creep resistance and tensile strength than the as-cast alloys. This was explained to be an effect of the α-phase texture and the decreased lath spacing in the cast-then-extruded alloys compared with the as-cast alloys. The cast-then-extruded alloys exhibited four times lower lath widths than the as-cast alloys, and the α-phase was strongly textured such that the basal plane was predominately oriented perpendicular to the extrusion axis. Comparing the cast-then-extruded alloys, the Ti-6Al-4V alloy exhibited the greatest creep resistance. Overall the α-phase consisted of approximately 80% of the microstructure, and the α-phase texture appeared to be more dominant to the creep resistance and tensile strength than the small volume percent of TiB-phase in the microstructure. Although B is not necessary to optimize the elevated-temperature creep performance of the Ti-6Al-4V alloy, when boron was present, greater boron additions increased the creep resistance. In-situ creep observations of the surface indicated that the TiB whisker cracking occurred prior to slip and void formation in the α+β phases. This was followed by α⁄β interface cracking and ductile failure of the α+β microstructure.
  • Effects of Thermomechanical Treatments on Pseudoelastic Strain Characteristics of Ti-29Nb-13Ta-4.6Zr for Biomedical Applications

    pp. 1704-1712

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    DOI:10.2320/matertrans.MF200922

    There is a possibility for β-type Ti-29Nb-13Ta-4.6Zr (TNTZ) to exhibit super-elastic characteristics, which is advantageous for biomedical applications such as orthodontic wires. Thermomechanical treatments are expected to induce super-elastic characteristics in β-type titanium alloys. Therefore, TNTZ specimens were subjected to various thermomechanical treatments, including solution treatments and severe cold rolling, wherein the second solution treatment temperature, second solution treatment time, and reduction ratio of cold rolling were varied in order to investigate the elastic deformation characteristics.
    One of the thermomechanical treatments induces super-elastic characteristics in a TNTZ specimen. In particular, a highest total pseudoelastic strain of 2.8% is measured in the TNTZ specimen subjected to the thermomechanical treatment at a cold rolling reduction ratio of 95%, second solution treatment temperature of 1073 K, and second solution treatment time of 0.3 ks. Tensile loading and unloading stress-strain curves of the TNTZ specimens subjected to various thermomechanical treatments indicate a high total pseudoelastic strain and exhibit three step deformation process. An α″ martensite phase is formed in the TNTZ specimen subjected to the thermomechanical treatment carried out under the above mentioned conditions.
  • Fatigue Behaviors of Ultra Fine Wires of β-Type and α-Type Titanium Alloys

    pp. 1713-1719

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    DOI:10.2320/matertrans.MF200920

    Fatigue behaviors of ultra fine wires of β-type Ti-14Mo-3Nb-1.5Zr alloy and α-type Ti-10Zr alloy and α-type CP (commercially pure) titanium with diameters in the range of 35–100 μm were investigated by rotating-bending fatigue testing in 1 mass% lactic acid solution maintained at 310 K. The maximum number of cycles during fatigue testing was 107. The β-type Ti-14Mo-3Nb-1.5Zr alloy wires showed a clear fatigue limit. On the other hand, the α-type Ti-10Zr alloy wire and α-type CP titanium wire did not show a clear fatigue limit, and their fatigue strengths gradually decreased with decreasing maximum bending stress. The fatigue limit of a β-type Ti-14Mo-3Nb-1.5Zr alloy wire with a polished surface was greater than 50% of its tensile strength, while the fatigue limits of titanium wires with as-drawn surfaces were less than 50% of their tensile strengths. Surface defects that were introduced during the cold drawing process of the wires might act as crack origins of the fatigue fracture. Therefore, surface polishing is an effective technique for improving fatigue properties of titanium wires. The elution of metallic ions from the wires into the 1 mass% lactic acid solution was suppressed at a very low level during fatigue testing of all the investigated titanium wires.
  • Microstructure and Mechanical Properties of SPSed (Spark Plasma Sintered) Ti66Nb13Cu8Ni6.8Al6.2 Bulk Alloys with and without WC Addition

    pp. 1720-1724

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    DOI:10.2320/matertrans.MF200924

    Ti66Nb13Cu8Ni6.8Al6.2 bulk alloys with and without WC addition were fabricated by spark plasma sintering and crystallization of amorphous phase. Microstructure analysis indicates that Ti66Nb13Cu8Ni6.8Al6.2 bulk alloy without WC addition has a ultrafine-grained microstructure with in situ precipitated ductile β-Ti(Nb) phase, composed of soft (Cu, Ni)-Ti2 regions surrounded by hard β-Ti regions. The alloy exhibits high fracture strength of above 2000 MPa and remarkable plasticity of ∼21%. In contrast, Ti66Nb13Cu8Ni6.8Al6.2 bulk alloys with WC addition consist of a microstructure of in situ precipitated ductile β-Ti regions surrounded by a mixed phase regions of (Cu, Ni)-Ti2, TiC, WC and residual glassy phase. The alloys with WC addition display brittle facture behavior. The different plastic deformability for the fabricated bulk alloys with and without WC addition can be explained based on their distinctive microstructures.
  • Thermoelectric Properties of Ca-Mg-Si Alloys

    pp. 1725-1729

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    DOI:10.2320/matertrans.MF200929

    To improve thermoelectric performance of p-type, Ca-Mg-Si alloys were synthesized by mechanical alloying (MA) and/or solid-liquid reaction (SLR). The Ca16.7Mg50.0Si33.3 − MA + SLR (synthesized by SLR with milling powder) and the Ca16.7Mg45.5Si33.3Ag0.5 − MA +SLR were composed of the phases of Mg2Si, CaMgSi and Ca7Mg7.25Si14. Their seebeck coefficient α showed positive, and their power factor P values were 0.02×10−3 W·m−1·K−2 (670 K) and 0.4×10−3 W·m−1·K−2 (730 K) respectively. The Ca25.0Mg25.0Si50.0 − SLR (synthesized by SLR) was composed of the single Ca7Mg7.25Si14 phase, and its α was metallic trend (α\\simeq0) with low electrical resistivity ρ. It is well-known that Mg2Si is n-type semiconductor. These results indicate that the CaMgSi is p-type. Its α was estimated at 750∼900 μV·K−1 (p-type) at 600 K and its ρ was lower than that of Mg2Si above 600 K. The P of CaMgSi single phase is expected more than 1.4×10−3 W·m−1·K−2 (600 K). Thus, CaMgSi is attractive material with high thermoelectric performance of p-type.
  • Novel Miscible Blends Composed of Poly(Methyl Methacrylate) and 2,2-Bis(3,4-Carboxyphenyl)Hexafluoropropane Dianhydride-Based Polyimides with Optical Grade Clarity

    pp. 1730-1736

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    DOI:10.2320/matertrans.MF200916

    Several blends of polymers that varied concentrations of poly(methyl methacrylate) (PMMA) and polyimides based on 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) were prepared in film form by solution casting and using various solvents. The miscibility of the blended films was correlated through a differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and an image analyzer. DSC thermograms revealed two glass-transition temperatures (Tg) for specimens using tetrahydrofuran (THF) as a casting solvent, indicating immiscibility; on the other hand, samples using methyl chloride (MC) and cyclohexanone showed a single Tg, indicating miscibility between the two polymers. The phase separation temperature for the miscible samples showed lower critical solution temperature type (LCST-type) behavior and reached its minimum when the content was about 70 mass% PMMA. Both the transmittance and haze of the miscible blended films were measured according to the American Standards Testing Method (ASTM) specification D1003. The transmittance for 6FDA-6FpDA/PMMA had a value of about 85% in the visual light range. However, 6FDA-6FpDA:DABA 2:1/PMMA showed a low transmittance below wavelengths of 550 nm. For haze, all of the films were clear with values of less than 1%. The mechanical scratch resistance was measured by pencil test (ASTM 3363). Increasing the 6FDA-6FpDA polyimide content was found to increase the scratch resistance of the films.
  • New Fabrication Process of Layered Membranes Based on Poly(Lactic Acid) Fibers for Guided Bone Regeneration

    pp. 1737-1741

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    DOI:10.2320/matertrans.MF200912

    A siloxane-containing poly(L-lactic acid) (PLLA)/calcium carbonate (vaterite) hybrid (Si-PVH) shows excellent proliferation of osteoblast-like cells, which may be enhanced by continuously released silicon-species. In the present work a novel membrane for guided bone regeneration (GBR) was developed using Si-PVH. The membrane was composed of bi-layered nonwoven fabrics; the first layer consists of an Si-PVH fabric with large-sized pores for enhancing bone formation, and the second layer consists of a PLLA fabric with small-sized pores for controlling the intrusion of soft tissues and for reinforcing the mechanical strength of the brittle Si-PVH layer. These nonwoven fabrics with high porosities were prepared by an electrospinning method. The PLLA fabric was placed on the Si-PVH one, and then pressed with a stainless steel mesh heated at 150°C, resulting in the preparation of a bi-layered porous membrane with excellent flexibility. The bi-layered membrane was implanted; the Si-PVH fabric was placed in contact with 8 mm in diameter hole drilled in calvaria of 14-week old rabbits and the PLLA fabric was placed in contact with the skin; new bone formation was observed in the Si-PVH layer. The result showed that the PLLA fibers layer interrupted the intrusion of soft tissues and the Si-PVH one induced the bone formation. The bi-layered membrane is expected to be effective in GBR treatment.
  • Strength and Thermal Shock Properties of Scandia-Doped Zirconia for Thin Electrolyte Sheet of Solid Oxide Fuel Cell

    pp. 1742-1746

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    DOI:10.2320/matertrans.MF200901

    The high temperature strength and the thermal shock resistance of scandia-stabilized zirconia (ScSZ) electrolyte sheet and planar cell specimen of Solid Oxide Fuel Cell (SOFC) with the actual thickness could be evaluated successfully using by piston on ring (POR) and infrared radiation heating (IRH) methods respectively. The fracture strength of ScSZ electrolyte was decreased with increase of experimental temperature and scandia content. The fracture load of cell specimen that was tried to fabricate with anode and cathode-electrodes decreased as compared with electrolyte. The thermal shock strength of electrolyte specimen was changed with fracture strength and thermal expansion coefficient.
  • Characterization of Precipitates in Mg-Sm Alloy Aged at 200°C, Studied by High-Resolution Transmission Electron Microscopy and High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy

    pp. 1747-1752

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    DOI:10.2320/matertrans.M2009046

    Precipitates in an Mg-0.99 at%Sm (Mg99.01Sm0.99) alloy aged at 200°C were studied by the combination of high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Fine precipitates of a meta-stable phase, which is called γ here, in the alloy aged at 200°C for 4 h have a thin lens-shape with a thickness of 2–5 nm and a diameter of 20–60 nm. The γ precipitate has an incommensurate structure with an orthorhombic unit cell of a=2a0=0.64 nm, b\\fallingdotseq6a0\\sqrt3=3.334 nm and c=c0=0.52 nm, where a0 and c0 are lattice constants of a hexagonal unit of the Mg-matrix. In the early stage of aging at 200°C for 0.5 h, isolated structure units forming the γ structure are dispersed in an Mg hexagonal lattice. By annealing at 200°C for 100 h, coarse precipitates of a stable Mg3Sm phase are formed along grain boundaries and inside grains of the Mg-matrix, and wide γ precipitate-free zones appear around them.
  • Spinodal Decomposition in an Fe-32 at%Cr Alloy during Isothermal Aging

    pp. 1753-1757

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    DOI:10.2320/matertrans.M2009029

    Phase decomposition was studied during aging of an Fe-32 at%Cr alloy by means of TEM, hardness and the numerical solution of the linear Cahn-Hilliard differential partial equation using the explicit finite difference method. Results of the numerical simulation permitted to describe appropriately the mechanism, morphology and kinetics of phase decomposition during the isothermal aging of this alloy. The growth kinetics of phase decomposition was observed to be very slow during the early stages of aging and it increased considerably as the aging progressed. The morphology of decomposed phases consisted of an interconnected irregular shape with no preferential alignment for short aging times and a further aging caused the change to a plate shape of the decomposed Cr-rich phase aligned in the ⟨110⟩ directions of the Fe-rich matrix. The increase in hardness seems to be associated with the coherency and nanometer size of the spinodally-decomposed phases in the aged alloy.
  • Multiscale Wavelet-Based Analysis and Characterization of Fretting Fatigue Damage in Titanium Alloys

    pp. 1758-1767

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    DOI:10.2320/matertrans.MRA2008378

    Wavelet analysis is used to rationalize information at various scales in several branches of science, including particle physics, biology, electrical engineering, fluid mechanics, and medicine. However, this powerful technique has not been applied extensively to characterize structures of materials, fretting damage for the present case, even though many critical questions could be addressed. In particular, the following unsolved problems are considered in this paper: (a) The first problem deals with the quantitative characterization of fretted surfaces in a Ti-6Al-4V alloy. This is investigated by analyzing profilometric digital images of fretted surfaces obtained in a range of magnifications. Wavelet analysis of the data is able to identify, by examining the wavelet coefficients, dominant length scales as those regions in scale-space where the energy of the wavelet transform and/or peaks of local concentration dominate. For the range of magnifications examined, i.e. from 1.25× to 100×, the ∼20× magnification is identified as the one with the most useful information. (b) An alternative procedure is employed for the second use of wavelets which deals with the non-uniformity of the contact regions. Wavelet analysis is employed to identify partially slipping regions, which result in the “pattern” of the fretted surface morphology.
  • Nanoindentation Behaviour and Microstructural Evolution of Au/Cr/Si Thin Films

    pp. 1768-1777

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    DOI:10.2320/matertrans.MRA2008385

    The nano-mechanical properties of an as-deposited composite Au/Cr/Si film comprising a Au layer with a thickness of 800 nm and a Cr adhesive layer with a thickness of 10 nm deposited on a Si (100) substrate are investigated by performing nanoindentation tests to a maximum depth of 1500 nm. The microstructural evolutions of as-deposited indented specimens and specimens annealed at temperatures of 523 K, 623 K or 723 K for 2 min are then examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The loading curve for the as-deposited Au/Cr/Si thin film is found to be continuous and smooth. However, the unloading curve has a prominent pop-out feature. The hardness and Young’s modulus of the Au/Cr/Si thin film indented to a maximum depth of 1500 nm are determined to be 2.7 GPa and 110 GPa, respectively. In the as-deposited sample, the microstructure of the indentation zone is characterised by a mixed structure comprising amorphous phase and nanocrystalline phase. Furthermore, well-defined Au, Cr and Si layers are observed in the interfacial region of the thin film. However, at the highest annealing temperature of 723 K, the microstructure of the indentation zone is recovered to a perfect diamond cubic single crystalline state. Finally, silicidation of the Cr layer takes place in all the annealed samples, resulting in the formation of isolated nano-islands of Cr.
  • Effect of Nano-Size Oxide Particle Dispersion and δ-Ferrite Proportion on Creep Strength of 9Cr-ODS Steel

    pp. 1778-1784

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    DOI:10.2320/matertrans.M2009096

    The effects of chemical compositions on the microstructure and high-temperature creep strength of 9Cr-ODS steel was discussed in the light of quantitative data of δ-ferrite proportion and nano-size oxide particle dispersion, which were evaluated by dilatometric analysis and small angle neutron/X-ray scattering analysis, respectively. These quantitative data are well consistent with the conventional data obtained by transmission electron microscope. Both data indicate that the important microstructural feature for creep strength improvement of the 9Cr-ODS steel is the number density of nano-size oxide particles, and ferrite/martensite (F/M) duplex structure is favorable for high population nano-size oxide particle dispersion. Both optimization of excess oxygen concentration and control of the F/M duplex structure are promising technique for nano-structure control of 9Cr-ODS steel. Tungsten solid solution strengthening appears to be small compared with oxide dispersion strengthening enhanced by duplex microstructure formation.
  • Notched Tensile Strength and Fatigue Crack Growth Behavior of Ti-6Al-6V-2Sn Laser Welds

    pp. 1785-1791

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    DOI:10.2320/matertrans.M2009001

    Notched tensile and fatigue crack growth tests were performed on Ti-6Al-6V-2Sn laser welds which were subjected to post-weld heat treatments (PWHTs) at various temperatures. In comparison with the mill-annealed base metal (BM), Ti-6Al-6V-2Sn laser welds showed notch brittleness at different degrees. Generally, the weld metal (WM) had a lower fatigue crack growth rates (FCGRs) than the BM. Fine acicular α distributed uniformly in the β matrix could account for the high hardness of the as-welded WM relative to the BM. With the PWHTs at higher temperatures, the coarsened microstructures of the welds reduced not only the hardness but also the sensitivity to notch brittleness. The fatigue fracture morphology of the WM was much rougher and irregular than that of the BM. A tortuous crack path in the WM as compared to the relatively straight path in the BM resulted in reduced FCGRs in the WM, particularly for the welds subjected to PWHTs at 704°C or higher.
  • Effect of Continuous Rotation Evolutional Control on the Surface Color of Anodized Al–Mg Alloys

    pp. 1792-1797

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    DOI:10.2320/matertrans.MRA2008469

    Al–Mg alloys treated by continuous rotation evolutional control (CREO) were anodized and colored by alternating current electrolysis at 10 V in sulfate solutions containing Cu, Sn, Ni, or Co at 303 K. Electrolysis turned the anodized Al–Mg alloys to rufous (Cu), yellow to gold (Sn), or reddish brown (Ni and Co). Their lightness was enhanced significantly by CREO, regardless of the metal deposited. The gloss of the Al–Mg alloys decreased probably due to increase in surface waviness resulting from CREO, and the enhancement in lightness with CREO is attributed to this decrease in the glossiness. SEM images showed that the micropore density in anodic oxide films on Al–Mg alloys decreased as a result of CREO. The decrease in the micropore density is assumed to enhance the lightness of colored Al–Mg alloys treated by CREO.
  • Adhesion of Atmospheric Micro-Contaminants on SUS304 Steel and Removal by UV Illumination

    pp. 1798-1804

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    DOI:10.2320/matertrans.M2009026

    Micro-contaminants on SUS304 stainless steel were observed and confirmed by atomic force microscope, and the micro-contaminant removal was carried out by ultraviolet (UV) illumination. With an increase in the holding time in air, particle- and film-like micro-contaminants appeared and their amount increased on the specimen surface. Then, the amount of particle-like contaminants decreased and finally almost all the surface was covered by film-like contaminants. The amount of micro-contaminants on the specimen surface decreased with an increase in the UV illumination time, with extensive removal of the organic substance in the contaminants but leaving part of the contained water in the contaminants. The micro-contaminants slowly re-adhered on the treated surface when the surface was re-exposed to air, with a longer period than 172 ks for the recovery to the state before the UV illumination. The surface for macro-droplets after the UV illumination became hydrophilic, while no large change of the wettability for micro-droplets on the same surface can be observed.
  • Preparation of N-Doped TiOx Films as Photocatalyst Using Reactive Sputtering with Dry Air

    pp. 1805-1811

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    DOI:10.2320/matertrans.M2009063

    Pale yellow N-doped TiOx films on the glass substrate were prepared by RF magnetron reactive sputtering of Ti target in a mixed gas of argon and dry air. The characteristics of the N-doped TiOx films were studied by SEM, XRD, UV–Vis spectrophotometer and XPS. The photocatalytic ability was evaluated by degradation of NO gas. The air flow ratio has a significant effect on the produced phase and the bonding states of Ti, O and N, resulting in the variation of the optical property and photocatalytic ability. The large amount of N atoms doped and oxygen deficiency are detrimental for photocatalysis, and N bonding states may not be the major contributing factor for the photocatalysis. It is suggested that the coexistence of N2 gas with O2 gas shifts the TiO2 formation boundary towards the low oxygen concentration, which leads to various N (N oxide) doping states on N-doped TiOx film.
  • Frequency of Bubble Formation from a Multi-Hole Nozzle Attached to a Top Lance

    pp. 1812-1819

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    DOI:10.2320/matertrans.M2009091

    Water model experiments have been carried out to understand the bubble formation from a multi-hole nozzle attached to an immersion top lance in the pretreatment process for sulfur. The number of holes is varied from one to four. Although desulfurization agents such as CaO particles are injected into the reactor together with carrier gas in the real process, only gas is injected, in this study, into a water bath through the holes in the horizontal direction. Three types of bubble formation patterns are observed depending on the gas flow rate: synchronized, partly-synchronized, and non-synchronized bubble formation patterns. The frequency of bubble formation at each nozzle is measured with a high-speed camera. An empirical equation is proposed for the frequency of bubble formation as a function of the number of holes, inner diameter of hole, and the physical properties of fluids.
  • Distributions of Sn, Sb, and Bi between Ag-Pb Alloy and PbO Based Melt at 1273 K

    pp. 1820-1823

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    DOI:10.2320/matertrans.M2009117

    Distributions of Sn, Sb, and Bi between Ag-Pb alloy and PbO based melt were investigated at 1273 K. A chemical equilibrium technique was used in order to measure the distributions. The oxygen partial pressure equilibrated with the melts was measured by an EMF method. The distribution ratios were defined as the weight ratios of Sn, Sb, and Bi in PbO divided by those in the Ag-Pb phase. The obtained distribution ratios were plotted against the logarithm of the oxygen partial pressure. The plots showed that the distribution ratios of Sn, Sb, and Bi increased with an increase in the oxygen partial pressure. Taking the slope of these plots, the oxide forms of the minor elements dissolved in the PbO based melt could be estimated. Sn dissolves in PbO based melts as SnO2 in the oxygen partial pressure range, PO2=10−7.5–10−4. Depend on the concentration of Sn in PbO and that in Ag, the activity coefficient of SnO2 in the PbO based melt at 1273 K was determined to be 62,000. The activity coefficient of BiO1.5 decreases with increasing oxygen partial pressure and that of SbO1.5 increases with increasing oxygen partial pressure. The distribution behavior of such minor elements was compared with that of Ag, and the efficiency of oxidation in the removal of such impurities from Ag was investigated.
  • Fabrication of Surface-Hybrid-MMCs Layer on Aluminum Plate by Friction Stir Processing and Its Wear Characteristics

    pp. 1824-1831

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    DOI:10.2320/matertrans.M2009092

    Aluminum-base hybrid composites reinforced with mixtures of SiC and Al2O3 particles 1.25 μm in average size have been fabricated on an A 1050-H24 aluminum plate by friction stir processing (FSP) and their wear resistance has been investigated as a function of the relative weight ratios of the particles. A mixture of SiC and Al2O3 powders of different weight ratios was packed into a groove of 3 mm width and 1.5 mm depth cut on the aluminum plate, and covered with an aluminum sheet 2 mm thick. A FSP tool of square probe shape, rotated at a speed of 1500 rpm, was plunged into the plate through the cover sheet and the groove, and moved along the groove at a travelling speed of 1.66 mm/s. After the hybrid composite was fabricated on the Al plate, the homogeneity of the particles distribution inside the Al matrix has been evaluated from the macro/microstructure and hardness distribution. Moreover, the wear characteristics of the resulted hybrid composites were evaluated using a ball-on-disc wear tester at room temperatures at normal loads of 2 and 5 N. As a result, it was found that the reinforcement particles were distributed homogenously inside the nugget zone without any defects except some voids that appeared around the Al2O3 particles. The average hardness decreased with increasing the relative content of Al2O3 particles. Regarding the wear characteristics, the wear volume losses of the hybrid composites depended on the applied load and the relative ratio of SiC and Al2O3 particles. The hybrid composite of 80% SiC+20% Al2O3 showed superior wear resistance to 100% SiC and Al2O3 or any other hybrid ratios at a normal load of 5 N.
  • Development of Microstructure and Mechanical Properties in Laser-FSW Hybrid Welded Inconel 600

    pp. 1832-1837

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    DOI:10.2320/matertrans.M2009058

    The present study was carried out to evaluate the microstructure and mechanical properties of Inconel 600 subjected to laser-assisted hybrid friction-stir welding (HFSW). In this process, friction-stir welding (FSW) was performed at a constant speed (400 rpm) while a 2-kW YAG laser preheated the material just in front of the rotating tool. We found that HFSW was 1.5 times faster than conventional FSW. In addition, analysis of the grain boundary character distribution by electron back scattered diffraction (EBSD) showed that the increased welding speed and dynamic grain recrystallization caused the average grain size to decrease from 5.5 μm (in the base material) to 3.2 μm (in the stir zone of the welded specimen). This grain refinement led to 30% and 10% improvements in microhardness and tensile strength, respectively.
  • Precipitation of Icosahedral Phase in Zr-Ni-Nb-Cu-Al Metallic Glasses

    pp. 1838-1842

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    DOI:10.2320/matertrans.M2009072

    The crystallization behaviors of Zr-Ni-Nb-Cu-Al metallic glasses are greatly influenced by the substitution of Ni for Zr. For the glassy Zr71−xNixNb3Cu16Al10 (x=7, 9, 11 at%) alloys, the onset temperature of crystallization Tx increases from 717 to 748 K with increasing Ni content from 7 at% to 11 at%. The primary crystallization reaction of the studied glassy alloys corresponds to the formation of icosahedral phase from amorphous matrix. The precipitation of quasicrystalline phase with a large volume fraction in the Zr64Ni7Nb3Cu16Al10 alloy indicates that the decrease of Ni content promotes the formation of icosahedral phase. Johnson-Mehl-Avrami analysis of isothermal transformation data suggests that the icosahedral phase precipitation proceeds by a diffusion-controlled growth mode with nearly constant nucleation rate. Furthermore, the Zr71−xNixNb3Cu16Al10 (x=7, 9, 11 at%) alloys possess high glass-forming ability, and the critical diameter for glass formation reaching 6 mm, 9 mm and 9 mm by copper-mould casting method, respectively.
  • Hydrogen Absorption and Thermal Desorption Behavior of Ni-Ti Superelastic Alloy Immersed in Neutral NaCl and NaF Solutions under Applied Potential

    pp. 1843-1849

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    DOI:10.2320/matertrans.M2009078

    The hydrogen absorption and thermal desorption behavior of Ni-Ti superelastic alloy immersed in neutral NaCl and NaF aqueous solutions at 25°C under an applied cathodic potential for 2 h have been systematically investigated by hydrogen thermal desorption analysis. The critical potential for hydrogen absorption is independent of the type and concentration of solution. The amount of absorbed hydrogen increases with decreasing applied potential, although it is only slightly changed by the type of solution. The amount of hydrogen desorbed at low temperatures, for the alloy immersed in NaF solutions, is larger than those in NaCl solutions, suggesting that the type of solution affects the hydrogen states in the alloy. The present results indicate that for Ni-Ti superelastic alloy, compared with titanium and its alloys, the critical potential for hydrogen absorption is located in a more noble direction, and the amount of absorbed hydrogen is large in NaCl and NaF solutions. Thus, the hydrogen embrittlement of Ni-Ti superelastic alloy probably occurs more readily than those of titanium and its alloys in NaCl and NaF solutions.
  • Structural and Optical Characteristics of BaTiO3:Yb3+ Powders

    pp. 1850-1854

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    DOI:10.2320/matertrans.MRA2008407

    Yb3+ doped Barium Titanate powders were prepared by the sol-gel method in order to study their structural and luminescent properties. These powders have potential to be used to prepare films for luminescent screens. The synthesized powders were obtained at 2, 4 and 8% mol Yb3+ doped BaTiO3. In order to determine organic compound decomposition, weight loss, and establish the crystallization process, we performed TGA and DTA analyses. The powders were also thermally treated at temperatures ranging from 700 to 1200°C in order to study the structure evolution. Pure doped BaTiO3 powders were carefully studied by X-ray diffraction (XRD). Observations of the powders using scanning electron microscopy (SEM) were done in order to correlate the grain size with the luminescent properties. A comparative study of the spectroscopy properties constituted by emission, absorption spectra, and fluorescence decay measurements using NIR excitation were done. The Yb3+ ions pairs emission was measured in the green region at about 500 nm when pumping at 940 nm.
  • Optimum Hydrogen Desorption Properties in LiH-LiOH Composites

    pp. 1855-1858

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    DOI:10.2320/matertrans.M2009055

    The effect of variation of LiOH content on hydrogen desorption properties in LiH-(30–60) mol%LiOH composites was investigated. The addition of LiOH destabilized LiH in desorbing hydrogen below 300°C for all composites while pure LiH desorbs hydrogen above 650°C. The hydrogen desorption temperature of these composites decreased with decreasing the content of LiOH. The onset temperature of hydrogen desorption lowered to 262°C for the sample of LiH-30 mol%LiOH.
    In the TDS measurement, the generation of water was observed around 420°C for the samples of LiH-(40–60) mol%LiOH due to decomposition of unreacted LiOH. The intensity of the water peak from these composites in TDS decreases with decreasing the content of LiOH. The water generation was unobserved from LiH-30 mol%LiOH composite. These results indicate that LiH-(30 and 40) mol%LiOH is a suitable composition for hydrogen desorption in this study.
  • Effects of Homogeneous Low Voltage Electron Beam Irradiation on Adhesive Strength of Polycarbonate (PC) Sheet Covered with Nylon6 Film

    pp. 1859-1863

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    DOI:10.2320/matertrans.MRA2008489

    The effects of homogeneous low voltage electron beam irradiation (HLEBI) on the adhesive strength of different polymers without glue but with sterilization were investigated. HLEBI at more than 0.043 MGy generated adhesive force and enhanced fracture strain at the interface in polycarbonate (PC) composites covered with nylon6 film. HLEBI at less than 0.130 MGy increased the elasticity (dσ⁄dε) and fracture stress of the composites. Although it was far below that of commercial pure metal, the elasticity (2 GPa) of composites irradiated from 0.130 to 0.216 MGy was very close to that of nylon6. HLEBI from 0.216 to 0.432 MGy increased the fracture strain of the composites, whereas it decreased elasticity (dσ⁄dε). Based on the results, HLEBI from 0.130 to 0.432 MGy apparently maintained the high fracture strength of the composites. To investigate the influence of EB irradiation on adhesive strength, electron spin resonance (ESR) signals related to dangling bonds were observed. Since HLEBI generated dangling bonds in both PC and nylon6, the dangling bonds probably served as reactive and bonding sites for each polymer at the interface. Results indicated that HLEBI enhanced the adhesive strength of the composites, therefore, it was concluded that HLEBI was probably a useful tool for quickly joining the different polymers.
  • Recovery of Platinum Catalyst and Polymer Electrolyte from Used Small Fuel Cells by Particle Separation Technology

    pp. 1864-1870

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    DOI:10.2320/matertrans.M-M2009812

    There are several conventional methods for recycling the membrane electrode assemblies (MEA) found in fuel cells. There are chemical techniques that deal with MEAs in bulk, including a method that dissolves the electrolyte film and a method that recovers the catalyst as a residue after incinerating it harmlessly. There are also physical techniques where the electrodes are detached from the MEA one by one. The former approach has a tendency to ignore the recovery of electrolyte film. Moreover, consideration should be given to the fact that the environmental load increases because it is a high-temperature and high-pressure technique that uses a large quantity of chemicals. The target of the latter approach is mainly on-vehicle fuel cells, and in many cases it is unsuitable for the mass processing of the MEAs on fuel cells used in mobile equipment, which are smaller than the above cells. A physical method that detaches the electrodes in organic solvents, which was an early development, offers a promising way to recover both electrodes and electrolyte films, and it can be used to deal with many small MEAs simultaneously. However, it has been pointed out that it is difficult to reuse the recovered electrolyte films, which are deformed and degraded when this method is used. In this study, the individual recovery of electrodes, which include a platinum group metal (PGM) catalyst, and the electrolyte films from MEAs on fuel cells used in mobile equipment, has been studied by using a milder organic solvent so that the deformation and deterioration of the electrolyte film are minimized.
  • In-Use Stock of Copper Analysis Using Satellite Nighttime Light Observation Data

    pp. 1871-1874

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    DOI:10.2320/matertrans.M2009030

    We have developed a novel methodology for analyzing the worldwide copper stock-in-use by using nighttime light images. Radiance calibrated nighttime light imaged data (RCD) for the entire world has been assembled from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) by the National Geophysical Data Center. It has been recognized that the intensity of nighttime light is strongly associated with such aspects of human settlement as population density and energy consumption. We assumed that the presence of light implies the use of electrical conducting material, namely copper. The stock-in-use data for copper in Japan, North America, Australia and China were obtained from previous material flow analysis studies. We analyzed the relationship between light accumulation and the size of the copper stock in those countries. A significant correlation was found and the feasibility of this method was confirmed. We employed this method to analyze the stock-in-use in other Asian countries. The in-use stock of copper was correlated with the gross domestic product (GDP).
  • Crack-Free Joint in a Ni-Al2O3 FGM System Using Three-Dimensional Modeling

    pp. 1875-1880

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    DOI:10.2320/matertrans.M2009041

    With the recent emphasis on the importance of successfully joining materials, researchers have tried to join metals and ceramics with different coefficients of thermal expansion (CTEs) by using the functionally graded material (FGM) method. This involves inserting interlayers with composition gradients that range from one material to the other, thereby minimizing the stress caused by differences in CTE values. In this study, the FGM that included 10 layers of Ni-Al2O3 with eight inter-layers was studied. Previous studies have focused on controlling the composition of inter-layers and optimizing the dispersion process to prevent cracks. Thermal stress was reduced by varying the weights of the inter-layers and increasing the green-body density by using several powder sizes. The powders were well-dispersed during fabrication by using simultaneous dispersion and dry processes followed by a cold isostatic press (CIP) and pressure-less sintering in an inert atmosphere. As a result, a crack-free Ni-Al2O3 FGM joint was obtained. The residual stress in each layer was calculated to predict cracks using ANSYS simulation and maximum principal stress criterion; experimental values matched simulation results. In addition, an oriented Vickers indentation test was used to assess the quality of the joint. Crack-paths were not deflected across the interface, indicating good bond strength between interfaces. Sample density was measured using the Archimedes method; the sintered joint was less dense than its theoretical density but was denser than the results obtained by using previous methods.
  • Thermoelectric Properties of Ternary Rare-Earth Copper Antimonides LaCuxSb2 (0.9≤x≤1.3)

    pp. 1881-1884

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    DOI:10.2320/matertrans.M2009047

    Ternary rare-earth antimonides LaCuxSb2 with 0.9≤x≤1.3 were prepared by arc melting the constituents and annealing the obtained products at 973 K for 144 h. The annealed products were then consolidated by pressure-assisted sintering at 1043 K for 3 h. X-ray powder diffractometry showed that all the sintered samples crystallized in the tetragonal HfCuSi2-type structure. While the lattice constant c increased with Cu content, the lattice constant a came to minimum at x=1.0. In the temperature range 300–800 K, the Seebeck coefficients of all the samples were positive. The Seebeck coefficient and electrical resistivity were observed to increase with the temperature. The decrease in the Cu content resulted in the increase in the Seebeck coefficient and electrical resistivity, and hence improving slightly the thermoelectric power factor. However, the thermoelectric power factor was substantially smaller than that of state-of-the art thermoelectric materials.
  • Thermal Decomposition of NH4SCN for Preparation of Ln2S3 (Ln=La and Gd) by Sulfurization

    pp. 1885-1889

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    DOI:10.2320/matertrans.M2009060

    The thermal decomposition of ammonium thiocyanate (NH4SCN) was studied by thermogravimetry, differential thermal analysis, and mass spectrometry. It occurred in the temperature range from 400 to 530 K. The decomposition products contained NH3, CS2, H2S, and HNCS gases. Rare-earth oxides were reacted with these gases at 1273 K for 8 h in order to prepare rare-earth sulfides. The single tetragonal β-La2S3 phase was formed after the sulfurization of La2O3. In contrast, the single orthorhombic α-Gd2S3 phase was formed after the sulfurization of Gd2O3. These powders were consolidated by pressure-assisted sintering to fabricate the thermoelectric elements.
  • Plastic Deformation-Assisted Synthesis of Metallic Glass Nanostructures

    pp. 1890-1893

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    DOI:10.2320/matertrans.M2009027

    In this paper, we report synthesis of various metallic glass nanostructures such as rods, wires and spheres via plastically deforming bulk metallic glasses in quasi-static compression at room temperature, and the formation mechanism and factors controlling their dimensions are discussed. The nanostructures are formed via viscous flow of softened layers within the shear band. The length of these nanostructures is dominated by the fracture toughness of metallic glass, which determines the temperature rise during plastic deformation and thus the viscosity of the softened layers.
  • A Combinatorial Screening Method for Corrosion Research Using Ion-Beam- Deposited Thin-Film Alloys and Microelectrochemical Measurements

    pp. 1894-1897

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    DOI:10.2320/matertrans.M2009130

    A combinatorial screening method for corrosion research using an ion beam co-sputtering system and a microelectrochemical probe was proposed. Small chips of pure Cr and Mo were placed on a large Fe-11%Cr plate, and those were used as a complex target for co-sputtering. The composition gradients of the sputter-deposited films were found to be controllable by the arrangement and the number of pure Cr and Mo chips. The optimum condition for fabricating Fe-Cr-Mo combinatorial libraries was investigated, and Fe-19%Cr-x%Mo (5<x<48) and Fe-7%Cr-x%Mo (3<x<46) films were prepared. A microelectrochemical technique was applied to measure the corrosion behavior of the restricted small area on the combinatorial libraries. The small diameter of microelectrochemical probes was appropriate for suppressing the measurement error arising from the compositional gradient within an measured area. The influence of Mo content on the polarization behavior of Fe-Cr-Mo alloys in 1 kmol·m−3 H2SO4 and 1 kmol·m−3 NaCl were investigated. The results obtained were similar to those previously reported for bulk Fe-Cr-Ni alloys, which indicated that the combinatorial screening method proposed in this study would be used for high-throughput tests for corrosion research.
  • Tension/Compression Anisotropy in Hot Forged Mg-Al-Ca-RE Alloy

    pp. 1898-1901

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    DOI:10.2320/matertrans.M2009083

    Die-cast Mg-Al-Ca-RE (RE = rare earth) alloy was upset forged by compression at 573 K with the true strain rate of 0.1 s−1 for grain refinement, and the tension/compression anisotropy at room temperature was examined. Before the hot forging, the die-cast alloy had random texture and yield stresses in tension and compression were similar. However, the forged and fine-grained specimens had (0001) texture inclined by 0–20° to the forging plane, which caused tension/compression yield stress ratio of 1.4 when the specimens were deformed perpendicular to hot forging direction. Grain coarsening by annealing of the forged specimen enhanced the ratio to 1.9 because more c-axis expansion twins formed at the early stage of the compression. Thus, grain refinement is necessary for reducing tension/compression anisotropy in hot-forged Mg alloy parts.
  • Faceting Behavior of Primary Ag in Bi-Ag Alloys for High Temperature Soldering Applications

    pp. 1902-1904

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    DOI:10.2320/matertrans.M2009089

    The solidification behavior and structure of Bi-Ag alloys with low Ag content (0 mass%∼11 mass%) which are now being applied as high temperature Pb-free solders were investigated. The results show that Bi-Ag alloys exhibited a nonequilibrium eutectic solidification feature and a considerably large undercooling. A longer cooling period to reach eutectic temperature enhanced the faceting of primary Ag crystals. The large value of the entropy of solution for Ag near the eutectic point should account for this.
  • Protections Against Surface Discoloration of Nickel Silver Plates

    pp. 1905-1907

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    DOI:10.2320/matertrans.M2009114

    In present study, a quantitative analytical approach has been taken to evaluate means to protect copper alloys (nickel silvers) against surface discoloration under the exposure of high temperatures. The aim is to propose future direction to further improve the surface protection against oxidation for nickel silver plates. Two approaches have been taken: one is to apply surface coating, another is to refine the subsurface grain structure in the bare substrate. Samples of nickel silver (C7521 and C7701) with and without surface coatings were exposed to 300°C and 350°C, respectively, for 10 min. Tested samples were then subjected to spectral colorimeter studies; phase identifications were carried out by XRD. In addition, the coating procedures were carefully studied in order to determine the optimal processing parameters for yielding the maximum protection. In conclusions, coating thickness does not affect the resistance against discoloration, pre-treatment of the substrate surfaces as well as the concentration and soak time of the anti-discoloration solutions can greatly influence the performances of the entire system against the occurrence of surface discoloration.
  • Concentration Dependence of Pressure Effect in La(FexSi1−x)13 Compounds

    pp. 1908-1908

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    DOI:10.2320/matertrans.ERM200901

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