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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 4

  • Short-Range Electron Correlations of CO2 Molecule by First Principles T-Matrix Calculations

    pp. 638-640

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    DOI:10.2320/matertrans.48.638

    In this paper, we obtain the double ionization energy spectra and the two-electron distribution functions from the first principles evaluating the ladder diagrams up to the infinite order (T-matrix) and discuss the short-range electron correlations. The T-matrix, which describes the multiple scattering between electrons (or holes), can accurately represent the short-range repulsive Coulomb interaction. The double ionization energy spectra calculated for the CO2 molecule agree with the corresponding experiments very well. And the two-electron distribution function obtained from the T-matrix clearly shows “Coulomb hole” due to the avoidance of the antiparallel spin electrons confined in a small region.
  • High Magnetization and High Electrical Resistivity in Dense Fe and Fe-Co Cluster Assemblies Prepared by Energetic Cluster Deposition

    pp. 641-645

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    DOI:10.2320/matertrans.48.641

    Using a plasma-gas-condensation-type cluster deposition apparatus, positively charged Fe and Fe-Co alloy clusters have been deposited on a negatively biased substrate together with their neutral clusters. In these cluster assemblies the packing density and saturation magnetization per volume, Ms, monotonically increase, while the magnetic coercivity, Hc, rapidly decreases with increasing the bias voltage, Va. For the dense Fe and Fe70Co30 cluster assemblies prepared at Va=−20 kV, Ms=1.78 and 2.01 T, respectively and Hc<80 A/m, whereas the electrical resistivity, ρ≈1 and 3 μΩ m, respectively. These results indicate that the cluster assembling is a fascinating method to obtain excellent soft magnetic materials with high electrical resistivity because the magnetic exchange coupling between ferromagnetic clusters is so strong as to overcome the magnetic anisotropy of individual clusters and the conduction electrons are scattered by the cluster interfaces.
  • Lifetime Measurement of 7Be in Beryllium Metal Crystal

    pp. 646-648

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    DOI:10.2320/matertrans.48.646

    The decay rate of an electron-capture nucleus is proportional to the electron density in the nucleus. In order to see how the decay rate can be changed artificially, we have measured the half-life of 7Be in a beryllium (Be) metal crystal. We found that it is 53.25±0.04 days, which is slightly longer than that in hosts such as graphite, lithium fluoride, and others that have previously been tested.
  • Time-Dependent Schrödinger Equation Approach and Bethe-Salpeter Equation Approach

    pp. 649-652

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    DOI:10.2320/matertrans.48.649

    In this article, I will compare two different first-principles methods useful in the research of clusters and nanoscale materials. The first one is the time-dependent Schrödinger equation approach for chemical reactions or light harvesting functions in excited states, and the second one is the Bethe-Salpeter equation approach for photoabsorption spectra, exciton wavefunctions, double-ionization energy spectra, and two-electron distribution functions. I will newly derive some exact theorems related to these approaches. While the first approach is convenient and useful, the second approach, which satisfies Friedel sum rule, is more reliable and accurate.
  • A Monte Carlo Simulation of the Formation of Micelles in a Ternary System of Water, Oil and Amphiphilic Polymers

    pp. 653-657

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    DOI:10.2320/matertrans.48.653

    We performed a Monte Carlo simulation for the formation of micelles in a ternary system composed of water solvent, oil solute (1%) and amphiphilic diblock copolymers (around 1%) on a simple cubic (3-D) lattice (51×51×51), using Metropolis algorithm. The diblock copolymers (50 chains) were expressed by the bond fluctuation model where each chain is composed of one hydrophobic end cube and four hydrophilic cubes connected by virtual fluctuating bonds.
    We assumed that the configurational energy depends only on the attractive interaction energy (Epo) between a hydrophobic part of a copolymer and a neighboring oil cell, and the attractive interaction energy (Eoo) between neighboring oil cells. In this simulation, we drew a phase diagram and estimated the magnitudes of Epo and Eoo realizing the stable formation of micelles, which are composed of oil aggregates, hydrophobic part of copolymers, and hydrophilic part of copolymers, from inner to outer sides.
    As a result, it was found that Epo≥1.9 kBT and Eoo≥2.3 kBT are needed to form micelles. Here Eoo should be the lowest value 2.3 kBT on the lower boundary (Epo=1.9 kBT), and Epo should be less than 2.6 kBT on the lower boundary (Eoo=2.3 kBT).
  • Understanding the Structural Stability of Compound Mo-S Clusters at Sub-Nanometer Level

    pp. 658-661

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    DOI:10.2320/matertrans.48.658

    Using first principles calculations within the generalized gradient approximation, the structural stability of compound Mo-S clusters at subnanometer level is discussed based on results obtained for various Mo5Sn isomers with n=5–15. The symmetrical Mo-S bonds generally lead to higher stability, while the formation of S-S bond and the observation of magnetism in these clusters lower the structural stability. Mo5Sn isomers with n=6, 8, and 11 are found to be most stable. The addition of sulfur atoms is quite favorable in the edge capped square pyramid and face capped trigonal bipyramid isomers.
  • Correct Interpretation of Hund’s Rule and Chemical Bonding Based on the Virial Theorem

    pp. 662-665

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    DOI:10.2320/matertrans.48.662

    We have investigated Hund’s spin-multiplicity rule for the second and third row atoms (C, N, O, Si, P, and S) and the methylene molecule (CH2) by means of diffusion Monte Carlo method and complete active space self-consistent field method, respectively. It is found that Hund’s rule is interpreted to be ascribed to a lowering in the electron-nucleus attractive Coulomb interaction energy which is realized at the cost of increasing the electron-electron repulsive Coulomb interaction energy as well as the kinetic energy. We have also studied correlation in the hydrogen molecule H2. Correlation in H2 gives an increase of the electron density distribution n(r) in the left and right anti-binding regions, a reduction of n(r) in the binding region, and an increase in the equilibrium internuclear separation. The importance of the virial theorem is stressed in the evaluation of correlation effects on both Hund’s rule and chemical bonding in H2.
  • Interstitial Oxygen and Dopant Atoms Arrangement in Tin-Doped Indium Oxide

    pp. 666-669

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    DOI:10.2320/matertrans.48.666

    In the present study an attempt to clarify discrepancy between experimental and theoretical results for preference substitution of d or b indium cation sites by tin is performed. For this purpose, the density functional calculations for a number of oxidized and reduced states of ITO with different configurations for tin substituted cation sites are carried out. For reduced states the probability for tin substituents to occupy the b positions is significantly larger than the same value for the d sites. These results indicate that the more favorable occupancy of either b or d cation positions by tin substituent depends on the way of the defect formation.
  • Structures and Stabilities of Rings Composed of C20 Cages

    pp. 670-674

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    DOI:10.2320/matertrans.48.670

    The ring structures with Dnh, Dn, Cnv and Cnh symmetries composed of C20 cages have been investigated using the self-consistent field molecular orbital method. It is found that the formation of the C20-rings is favorable to stability of the C20 systems. The influence of structure symmetries and distortion on the stabilities of the C20-rings is explored. The strain change due to the structure distortion greatly affects the stabilities of the C20-rings. Furthermore, the bonding and electronic properties of the C20-ring are also discussed and compared with those of other fullerene-rings such as C60-rings and C36-rings.
  • Theoretical Studies of the Atomic and Electronic Structure of Nano-Hetero Metal/Inorganic Material Interfaces in Collaboration with Electron Microscopy Observations

    pp. 675-683

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    DOI:10.2320/matertrans.48.675

    First-principles calculations based on density-functional theory have been applied to the energies and atomic and electronic structures of various metal/inorganic material interfaces such as metal/Al2O3, Au/TiO2 and metal/SiC interfaces used in thermal barrier coatings, gold catalysts, and high-power electronic devices, respectively, in collaboration with electron microscopy observations. In each system, it has been shown that the interface stoichiometry, namely the features of interfacial termination species of inorganic materials, as well as the metal species, is one of the most important factors to design the interfacial structure and the adhesive, mechanical, chemical and electronic properties. Recent electron microscopy observations of peculiar dynamical structural changes in Au/CeO2 systems are discussed from this view point.
  • Electronic Structure and Thermoelectric Properties of Noble Metal Clathrates: Ba8M6Ge40(M = Cu, Ag, Au)

    pp. 684-688

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    DOI:10.2320/matertrans.48.684

    Electronic structure and thermoelectric properties of noble metal clathrates Ba8M6Ge40(M = Cu, Ag, Au) were calculated by using a first principle based method to discuss prospect of high performance thermoelectric materials. The calculated band structures show that these clathrate compounds are degenerate semiconductors with p type carrier. The band gaps become narrow by noble metal doping. The band gap narrowing is caused by the valence band lifting due to anti-bonding nature between Ge and M, and conduction band widening due to framework-guest atom coupling via Ba orbitals at 6d sites. The thermoelectric power of Ba8M6Ge40 increases with temperatures monotonically and the magnitude is smaller than 100 μV/K under 1000 K. The carrier concentration of Ba8M6Ge40 is a little larger for the high performance thermoelectric materials. The carrier concentration is controlled by varying the composition of Ba8AuxGe46−x. The optimized carrier concentration in Ba8AuxGe46−x was obtained as 4.4×1026 m−3 (p type) and 6.4×1026 m−3 (n type), respectively.
  • Structure and Stability of Small Bimetallic Al-Based Clusters: An ab initio DFT Study

    pp. 689-692

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    DOI:10.2320/matertrans.48.689

    Dimers and trimers of bimetallic Aluminium-Transition-Metal (Cu, Ni, and Au) atomic clusters have been studied using first principles, plane wave, pseudopotential and projected-augumented-wave potential methods. The structural properties and energy ordering of the clusters are discussed based on the calculated ground state, stable and meta-stable geometries, as well as binding and fragmentation energies.
  • Metal Sandwich Molecules: Planar Metal Atom Arrays between Aromatic Hydrocarbons

    pp. 693-699

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    DOI:10.2320/matertrans.48.693

    Sandwich molecules MnS2 consisting of a layer of transition metal atoms M (palladium) between planar polyacene aromatic hydrocarbon molecules (S) are studied using ab initio density functional theory. The polyacenes range from tetracene C18H12 (four rings) to circumcoronene C54H18 (nineteen rings). Geometry optimization shows that in simple arrangements, where one metal is assigned to each ring, there is a preference for metal atoms to coordinate to carbon atoms on the circumference of the sandwich. This can result in metal-metal distances greater than in bulk metal and so the establishment of planar metal clusters with metal-metal bonds in small systems is frustrated. This effect is studied by changing the number of metal atoms and relaxing symmetry constraints. A neutral molecule Pd5(C18H12)2 with C2v symmetry and a lopsided arrangement of metal atoms is shown to be consistent with experimental work on dications by Murahashi et al. [Science 313 (2006) 1104–1107]. In tetracene sandwiches with n=5 and 9 the palladium atoms adopt η2- and η3-coordination to the edge carbon atoms. In addition to edge bonding, motifs for interior metal atoms are identified from a series of sandwiches with increasing size containing: coronene (C24H12), ovalene (C32H14), circumanthracene (C40H16) and circumcoronene (C54H18).
  • Preparation of Fullerene Polycrystalline Films on Different Substrates by Physical Vapor Deposition

    pp. 700-703

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    DOI:10.2320/matertrans.48.700

    Fullerene (C60) films were prepared on Si, ITO, and Cu substrates by the physical vapor deposition (PVD) method. It was observed that the morphology and structure of fullerene films strongly depend on the substrates. Along with the interactions between fullerenes and substrates increasing from ITO, Si to Cu substrate, C60 forms small polycrystalline grains, large polycrystalline grains and fullerene oligomers under the same experimental conditions. The irreversible C60 polymerization on Cu substrate is suggested to be catalyzed by the copper metal.
  • Physical and Chemical Properties of Gas Hydrates: Theoretical Aspects of Energy Storage Application

    pp. 704-710

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    DOI:10.2320/matertrans.48.704

    A model has been developed permitting to accurately predict on molecular level phase diagram of the clathrate hydrates. This model allows to take into account the influence of guest molecules on the host lattice and to extend the interval of temperatures and pressures of computed thermodynamic potentials and significantly improves known van der Waals and Platteeu theory. The theoretical study of phase equilibrium in gas–gas hydrate–ice Ih system for methane and xenon hydrates has been performed. The obtained results are in a good agreement with experimental data. A new interpretation of so-called self-preservation effect has been proposed. The self-preservation of gas hydrates can be connected with differences in thermal expansions of ice Ih and gas hydrates. This is confirmed by calculations performed for methane and mixed methane–ethane hydrates.
  • The Topological Structures of the Debundled Single-Walled Carbon Nanotubes on a Grid

    pp. 711-717

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    DOI:10.2320/matertrans.48.711

    The scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements of individual single-walled single carbon nanotube (SWNT) have revealed the nature of trigonal warping of SWNTs in the solid-state. The SWNTs are prepared as isolated SWNTs both oxidized followed by amidation in N,N-dimethylformaide (DMF) and in amine surfactant in tetrahydrofuran(THF). The possibility of debundling SWNTs through their interaction with the amide functional group and amine molecules using steric hindrance has been experimentally explored. The measured topological structures of SWNTs in the solid-state differ from simple theoretical predictions and some possible mechanisms of bundling and debundling of SWNTs are discussed. We show that solid-state based characteristics are different from the solution-based characteristics.
  • Exchange-Correlation Effects on Low-Dimensional Plasmons in an Array of Metallic Quantum Wires

    pp. 718-721

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    DOI:10.2320/matertrans.48.718

    We investigate low-dimensional plasmons (PL’s) in an array of metallic quantum wires. By developing a self-consistent local-field-correction (LFC) theory for treatment of the PL’s in the wire array, we take account of both the intrawire exchange-correlation (XC) effect and the interwire correlation effect. By comparing the results involving the LFC with those in the random-phase approximation, we examine the XC effect on the energy distribution and the energy-loss intensity of all the PL modes in an array of a finite number of wires. Our theoretical scheme is applied to an array of Au-atom wires on the Si(557) surface. The XC effect is found to play a significant role because of strong one-dimensional confinement, though a high effective density of the electron system is suggestive of the free-electron-gas character. With an increase in wave number q, the XC effect operates to lower the mode energy increasingly, and to start the decline of the energy-loss intensity at smaller q values. In a smaller q range of qd\\lesssim1, where d denotes the interwire separation, the interwire interaction has the mode energies separated from one another to form an energy distribution of considerable width. Our results of the XC effect and the effect of the interwire interaction yield general insights into the PL’s in a variety of wire arrays.
  • Formation and Atomic Structures of Boron Nitride Nanotubes with Cup-Stacked and Fe Nanowire Encapsulated Structures

    pp. 722-729

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    DOI:10.2320/matertrans.48.722

    Boron nitride (BN) nanotubes, nanohorns, nanocoils were synthesized by annealing Fe4N and B powders at 1000°C in nitrogen gas atmosphere. Especially, Fe-filled BN nanotubes, bamboo-type and cup-stacked type BN nanotubes were produced. Formation mechanism and nanostructures were investigated by high-resolution electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy and molecular mechanics calculations.
  • A DFT Study of the Heme Role in the N-Demethylation of Theophylline Mediated by Compound I of Cytochrome P450

    pp. 730-734

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    DOI:10.2320/matertrans.48.730

    Using accurate DFT calculations we have examined the role that Compound I of cytochrome P450 plays as a catalyst in the conversion of theophylline to 1-methylxanthine. This reaction proceeds in two steps according to the characteristics of the oxygen rebound mechanism. In this study we found that the activation energy for the transition state corresponding to the abstraction of the H atom at the C13 in theophylline is 9.3 kcal/mol. This H atom abstraction is the rate-determining step in this reaction which takes place via a single electron transfer (SET) mechanism and leads to an intermediate containing theophylline cationic and iron-hydroxo species. The rebounding step between the reaction intermediate and the product alcohol complex is a barrierless step. The alcohol complex is then separated from the heme moiety and yields 1-methylxanthine by intramolecular rearrangement.
  • Theoretical Study on the ATP Hydrolysis Mechanism of HisP Protein, the ATP-Binding Subunit of ABC Transporter

    pp. 735-739

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    DOI:10.2320/matertrans.48.735

    ATP binding subunit is known as a subunit of ABC transporter, providing energy through the binding of ATP with the subunit and the subsequent hydrolysis reaction of the bound ATP. In this study, density functional theory (DFT) method was used to study the ATP hydrolysis reaction in HisP protein, an ATP binding subunit of Histidine permease HisQMP2, by considering the ATP binding site, especially the γ-phosphate group, surrounding residues and water molecules. Based on DFT calculations, we proposed that ATP hydrolysis is initiated by the formation of Mg2+ mediated coordinate complex followed by the nucleophilic attack of a single water molecule (Water437) on the γ-phosphate; the hydrolysis product ADP acts as a leaving group. The transition state structure was determined by an approximate saddle-point search.
  • Does Metabolism of (S)-N-[1-(3-Morpholin-4-ylphenyl)ethyl]-3-phenylacrylamide Occur at the Morpholine Ring? Quantum Mechanical and Molecular Dynamics Studies

    pp. 740-744

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    DOI:10.2320/matertrans.48.740

    The mechanism of Cytochrome P450 3A4 mediated metabolism of (S)-N-[1-(3-morpholin-4ylphenyl)ethyl]-3-phenylacrylamide and its difluoro analogue have been investigated by density functional QM calculations aided with molecular mechanics/molecular dynamics simulations. In this article, we mainly focus on the metabolism of the morpholine ring of substrates 1 and 2. The reaction proceeds via a hydrogen atom abstraction from the morpholine ring by Compound I on a doublet potential energy surface. A transition state was observed at an O-H distance of 1.46 Å for 1 while 1.38 Å for 2. Transition state for the rebound mechanism was not observed. The energy barrier for the hydrogen atom abstraction from 1 was found to be 7.01 kcal/mol in gas phase while 19.53 kcal/mol when the protein environment was emulated by COSMO. Similarly the energy barrier for substrate 2 was found to be 11.07 kcal/mol in gas phase while it was reduced to 12.99 kcal/mol in protein environment. Our previous study reported energy barriers for phenyl hydroxylation of 7.4 kcal/mol. Large energy barriers for morpholine hydroxylation indicates that hydroxylation at the phenyl ring may be preferred over morpholine. MD simulations in protein environment indicated that hydrogen atom at C4 position of phenyl ring remains in closer proximity to oxyferryl oxygen of the heme moiety as compared to morpholine hydrogen and hence greater chance to metabolize at phenyl ring.
  • Structure and Stability of the Frank-Kasper W@Si12, and Ti@Si15 and Ti@Si16 Clusters

    pp. 745-747

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    DOI:10.2320/matertrans.48.745

    Ab initio density functional theory plane wave and linear combination of atomic orbitals pseudopotential methods are used to study the stabilities of W@Si12, Ti@Si15 and Ti@Si16 encapsulated clusters. It is shown that three stable W@Si12 isomers and four stable isomers for Ti@Si15 and Ti@Si16 belong to the Frank-Kasper configuration space. Good agreement of the calculated electron affinities with the experimental data provides a clue on the structures of Ti@Si15 which is shown to resemble that for the dimerised Si(001)2×1 surface.
  • Half-Metallicity and Stability of Ferromagnetism in (Fe1−xCox)2CrZ (Z=s, p Elements)

    pp. 748-753

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    DOI:10.2320/matertrans.48.748

    The half-metallicity and the stability of the ferromagnetic state have been investigated in the Heusler type alloys (Fe1−xCox)2CrZ (Z=s, p elements). If only the ferromagnetic state is assumed as the magnetic state of Fe2CrZ, the half-metallicity tends to appear easily as the total number of the valence electrons and the lattice constant decrease. Taking the paramagnetic and the antiferromagnetic state into account, it is predicted that Fe2CrSi and Fe2CrP may be half-metals among Fe2CrZ. However, if the Co atoms are partially substituted for the Fe atoms in Fe2CrZ (Z=Al, Si, P, Ge, Sn), the ferromagnetic state tends to become more stable as the Co composition increases, without losing the half-metallicity. These results suggest that partial substitution of the Co atoms for the Fe atoms is effective in improving the properties as spintronic materials in Fe2CrZ.
  • Magnetic and Magnetotransport Properties in Nanogranular Co/C60-Co Film with High Magnetoresistance

    pp. 754-758

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    DOI:10.2320/matertrans.48.754

    Magnetic properties were investigated for the alternately deposited film of C60 and Co which has found to exhibit tunnel magnetoresistance (MR) of 10–80%. Magnetic field and temperature dependences of magnetization showed typical superparamagnetic behaviors with the blocking temperature of 40 K. The magnetization curve at 300 K was well fitted by the Langevin function with the size distribution of Co particles, and the mean diameter and size distribution were evaluated to be 3.1 nm and ∼1 nm, respectively. Based on the magnetic properties, the structure and magnetotransport properties are discussed in details.
  • Kink Band Formation and Its Effect on Recrystallization in Ordered and Disordered Ni3Fe Single Crystals

    pp. 759-763

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    DOI:10.2320/matertrans.48.759

    In order to study the influence of ordering on deformation and recrystallization, Ni3Fe single crystals, ordered and disordered by appropriate heat treatments, were deformed in tension at room temperature and subsequently annealed at temperatures above the order-disorder transformation temperature. Both ordered and disordered single crystals exhibited a large elongation, while deformation microstructures were totally different. Kink bands formed only in the disordered single crystals. Recrystallization occurred along the kink bands. Many recrystallized grains had ⟨111⟩-rotation relationships with the kink band and were twin related to each other. In contrast, no recrystallized grain formed in the single crystal deformed in the ordered state.
  • Effect of Texture of AZ31 Magnesium Alloy Sheet on Mechanical Properties and Formability at High Strain Rate

    pp. 764-768

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    DOI:10.2320/matertrans.48.764

    The mechanical properties and formability of AZ31 magnesium alloy strips having different textures were investigated at a high strain rate based on that occuring in mass production by press forming. Forming at a high strain rate on the order of 100 s−1 requires a high temperature of over 473 K. To obtain accurate stress-strain curves, a high-speed testing machine that can maintain a constant true strain rate was used, and the change in gauge length on a test piece in a furnace was measured during the testing time of about 0.5 s. For the specimens, rolled strips consisting of fine grains (about 10 μm) and an extruded strip consisting of coarse grains (about 40 μm) were used. The {0001} textures of the extruded strip and one of the rolled strips were strongly oriented parallel to the rolled surface, but the texture of another rolling strip had two peaks that were inclined at 5∼15 deg in front of and behind the rolling direction. At the high strain rate of 100 s−1, elongation decreased for every specimen. Nevertheless, a limiting drawing ratio (LDR) of 2.1∼2.2 was obtained under uniform heating above 503 K in all the specimens except for the extruded strip. The high LDR of the rolled strip having a two-peak texture was maintained in forming at temperatures down to 473 K, in contrast to the LDR of the strongly oriented rolled strip, which reduced rapidly when formed at temperatures less than 503 K.
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  • Surface Strain Measurement of Thermally Sprayed Ceramics Coatings under Static and Cyclic Loadings and Its Application to Detection of Delamination

    pp. 769-774

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    DOI:10.2320/matertrans.48.769

    Thermally sprayed ceramic coatings are commonly used as thermal barriers at high temperature. However, delamination of the coating from substrate (base metal) under various operation conditions, including high temperature and mechanical loads, always leads to serious degradation of the heat shielding effect. It is important to detect the delamination in situ and nondestructively for the maintenance and management of mechanical structures. However, until now, neither a clear definition of the delamination of the coating from the substrate nor an effective method to detect and evaluate the delamination process has been proposed. In this work, the surface strains of a substrate and a thermally sprayed coating were measured using an electronic speckle interferometry (ESPI) method. As a result, generation of delamination of the coating corresponded well to the critical strain εc on the ε−σs curve under a static load, where a large drop in the strain occurred for the coated specimen compared to the substrate only specimen. Furthermore, generation of the delamination under a cyclic load also corresponded well to a large drop in strain for the coated specimen compared to the substrate only specimen.
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    Readers Who Read This Article Also Read

    1. Using Multiple FSP Passes to Cure Onion Splitting of Mg Alloys Deformed at Elevated Temperatures MATERIALS TRANSACTIONS Vol.48(2007), No.4
    2. Localized Deformation Behavior of W-80 vol%Cu Composite at Room Temperature MATERIALS TRANSACTIONS Vol.48(2007), No.4
    3. Computation of Equilibrium-State in Gas/Solid Materials Systems MATERIALS TRANSACTIONS Vol.48(2007), No.4
  • Localized Deformation Behavior of W-80 vol%Cu Composite at Room Temperature

    pp. 775-779

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    DOI:10.2320/matertrans.48.775

    Plastic strain of about 10% was added to the W-80 vol%Cu composite at room-temperature using a three-point bend testing machine. Positions of the specific W-particles were measured before and after deformation using high-magnification SEM photographs. Then the localized deformation behavior of the composite was investigated by comparing the measured and the calculated positions of these specific W-particles after deformation. Results are summarized as follow. (1) In the region without pore, heterogeneous deformation did not occur. (2) In the region near the large pore, heterogeneous deformation occurred as expected.
  • Using Multiple FSP Passes to Cure Onion Splitting of Mg Alloys Deformed at Elevated Temperatures

    pp. 780-786

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    DOI:10.2320/matertrans.48.780

    The investigation of high temperature mechanical properties of the friction stir processed AZ61 alloy with different passes shows that the one-pass processed AZ61 Mg alloy exhibits inferior superplastic deformation ability along the FSP forward traveling direction due to the onion-ring pre-mature splitting. The homogenous microstructure in the multi-pass friction stir processed Mg alloy can avoid the onion-ring splitting and eliminate the anisotropy behavior of high temperature mechanical properties.
  • Computation of Equilibrium-State in Gas/Solid Materials Systems

    pp. 787-792

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    DOI:10.2320/matertrans.48.787

    The determination of equilibrium-state in gas-solid materials systems is of practical interest; this consists of finding the values of intensive variables such as mole-fractions, partial pressures, activities or chemical potentials of constituents that occur in the gaseous and solid phases for stipulated temperature, pressure and initial reactant-gas composition. The mass-action iterative equilibrium constant method, shown to be a direct derivative of the minimization of Gibbs free energy, was used to compute the equilibrium-state in the carburizing and decarburizing iron-carbon heat treatment systems. By suitably combining the equilibrium partial pressure data with the extent of reaction formalism, the optimum feed-gas mixtures that ensured neutral atmospheres were determined.
  • Evaluation of Adhesive Strength of Thermal-Sprayed Hydroxyapatite Coatings Using the LAser Shock Adhesion Test (LASAT)

    pp. 793-798

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    DOI:10.2320/matertrans.48.793

    The adhesive strength between a coating and a substrate is an important factor that characterizes the quality of thermally sprayed Hydroxyapatite (HA) coatings such as those for biomedical applications. In this study adhesive strength was evaluated by the LAser Shock Adhesion Test (LASAT) technique. LASAT was developed to be suitable for determining the coating-substrate adhesion. This study deals with hydroxyapatite coatings on Ti-based alloy substrate produced by atmospheric plasma spraying. In order to discuss the influence of the spray condition on adhesive strength, different types of specimens, i.e. from various powder feed rate spraying and different surface roughness, were LASATested. The results showed that the adhesive strength decreases with increasing number of impinging particles on a given area of surface in unit time. Furthermore, the adhesive strength tendency of low-roughness substrate specimens showed scatter. This tendency depends on the surface profile i.e. skewness value. Consequently, not only the height direction roughness parameter but also the wavelength of roughness, roughness morphological parameter and powder feed rate are important factors for the adhesion of the thermally sprayed HA coatings.
  • Effects of Ca Addition on Solidification Structure of Cu-Sn-Zn Bronze Castings

    pp. 799-806

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    DOI:10.2320/matertrans.48.799

    The substitution of Ca for a part or all of Pb in Cu-Sn-Zn alloys of 88-8-4 type was carried out in order to decrease solidification defects. The relation between cooling rate and segregation of alloying elements or solidification defects was investigated using steps shaped ingots. Finer dendrite structure was obtained due to decrease in the diffusion coefficient and mass transfer of Sn or Zn in the Cu-liquid for Ca addition alloys. The concentration of Ca and the amount of the micro shrinkage cavity in each step was almost constant in Ca added alloys. The same segregation course in the solidification path showed in both 88-8-4-Pb (CAC402) and 88-8-4-Pb-Ca alloys. In Ca added alloys, the enrichment of Sn in the residual liquid and decrease in final solidification temperature were suppressed by expenditure of Sn due to formation of the compounds consisting of Sn and Ca at higher temperatures compared with the melting point of Pb, which resulted in the decrease of the micro shrinkage cavity. Hardness of Ca containing alloys was higher than that of Ca free alloys. The tensile properties were improved by addition of 0.25 mass% Ca, because of the decrease in micro shrinkage.
  • Semisolid Extrusion of Low-Carbon Steel

    pp. 807-812

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    DOI:10.2320/matertrans.48.807

    The semisolid state behavior and semisolid extrusion properties of low-carbon steel were investigated, focusing on the possibility of clarifying a semisolid-forming process. First, the cooling curve of low-carbon steel is assessed by thermal analysis, so as to clarify the semisolid temperature range. The microstructure of the hot-rolled bar obtained at the semisolid temperature is the globular structure similar to those of aluminum and magnesium alloys. Then, to obtain a better understanding of the semisolid deformation behavior of the material, extrusion tests are carried out at various billet temperatures and cooling conditions at the die exit. To prevent the temperature decrease of the billet, a graphite case and block surrounding the billet acted as an insulator in the extrusion tests. The mechanical properties and the microstructure of the extruded products are evaluated and discussed, i.e., the extrusion force in the semisolid state is less than half that of the hot extrusion. The distribution of chemical components, such as carbon, is measured in the radial direction of the cross section of the products. The room-temperature hardness of the as-extruded products shows a specific distribution from the surface to the center. The hardness at the center is approximately two times greater than that at the surface.
  • Resistance Microwelding of SUS304 Stainless Steel Fine Wire

    pp. 813-820

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    DOI:10.2320/matertrans.48.813

    Resistance microwelding of fine crossed stainless steel wires is of increasing industrial importance for medical devices. Therefore, a study has been performed to clarify the basic joining mechanisms. The effect of main process parameters such as welding current, force and weld time were investigated by detailed mechanical testing and metallurgical examinations. Especially, joint strength and microstructures were sensitive for welding current and force. It should be noted that no fusion nugget was formed at the weld interface. Since the joint breaking force was determined by bond area and interfacial strength in the case of interfacial fracture, both of them are needed to be optimized to obtain sound joint. Moreover, heat affected zone should be minimized. A bonding mechanism with several main process stages, wire collapse, surface melting, liquid phase squeeze out and solid-state bonding, was proposed.
  • Crystallization and Embrittlement Behavior of a Zr55Al10Ni5Cu30 Metallic Glass Having Different Si and O Contents

    pp. 821-825

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    DOI:10.2320/matertrans.48.821

    Metallic glasses as non-equilibrium materials crystallize at a critical temperature, accompanying their embrittlement. The size of glassy alloys is dependent on their glass-forming ability. The development of an appropriate joining technique is important for the extension of industrial applications. In the present study, we examine crystallization behavior of Zr55Al10Ni5Cu30 glassy alloy upon annealing. In the beginning of the crystallization process, a clustering, a crystal nucleation and the crystal growth processes take place sequentially.
    The phase transition behavior was examined by differential scanning calorimetry (DSC). The kinetics of the crystallization process can be analyzed by the changes in the volume fraction of the crystalline phase which scales with the exothermic heat release and density measurement. The crystallization process in the Zr55Al10Ni5Cu30 alloy is found to be diffusion-controlled. The values of the Avrami exponent are between 2.3 and 2.8. Therefore, the velocity of nucleation and crystallization processes should scale with the diffusion velocity of the constituent elements in the metallic glass. The diffusion rate can be estimated using the diffusion coefficients of the constituent elements, as a function of time and temperature. The slope of the calculated iso-precipitation line of CuZr2 phase on the fixed TTT diagram is well fitted with the lines representing ductile and brittle behavior of the sample. The results indicate that the most harmful crystalline phase, which causes embrittlement is CuZr2. The influence of Si contamination on the crystallization behavior is also studied in the present work.
  • Hot-Tensile Properties of In Situ Synthesized Multiple-Reinforced (TiB+TiC+Nd2O3)/Ti-Alloy Composites

    pp. 826-831

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    DOI:10.2320/matertrans.48.826

    Novel (TiB+TiC+Nd2O3)/Ti-alloy composites were in situ synthesized utilizing the reaction between Ti, B4C, Nd and B2O3 through homogeneously melting in a non-consumable vacuum arc remelting furnace. There were three kinds of reinforcements in the matrix: near-equiaxed TiC particles, TiB whiskers and plates and Nd2O3 particles. The reinforcements were homogeneously distributed in the matrix. Tensile properties of the (TiB+TiC+Nd2O3)/Ti-alloy composites were tested with strain rate 10−2 S−1 at 873, 923 and 973 K. The results showed that the incorporation of in situ synthesized reinforcements significantly increased the strength of the composites at elevated temperature. With the temperature increasing, the improvement on tensile strength decreases. The improvement on strength mainly attributes to load undertaking of reinforcements and dispersion strengthening of nano-sized Nd2O3 particles.
  • Effect of Bias Sputtering Condition on Structure of LaNi5 Films

    pp. 832-835

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    DOI:10.2320/matertrans.48.832

    Purification of hydrogen using a hydrogen storage alloy film has various advantages such as low operation energy and low costs of the equipment. However, because of the surface roughness of a substrate, the surface of the sputtered film was not smooth and had some pinholes. It was considered that use of a bias sputtering method might solve these problems. Hence, in this study, the influence of the bias power on the composition, microstructure and crystal structure of the LaNi5 sputtered film were investigated. When the film was deposited with a direct current sputter power WS=50 W and a radio frequency bias power WB=20 W, the diffraction peak of LaNi5 was not observed on the film. With WS=200 W and WB=20 W, the film had crystal structures. However, when the WB was increased more than 40 W with WS=200 W, the film became the amorphous structure. It is considered that, to make the amorphous structure and the dense film with higher WS, the WB has to be increased.
  • Fabrication Method for a TiO2 Nanofluid with High Roundness and Superior Dispersion Properties

    pp. 836-841

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    DOI:10.2320/matertrans.48.836

    This study describes the use of a new submerged arc nanofluid synthesis system to fabricate TiO2 nanofluids. Under vacuum conditions, this system uses the energy produced by an arc discharge to vaporize the desired metal. Then, the vaporized metal is cooled rapidly in a low-temperature dielectric liquid, forming nanoparticles that are evenly distributed inside the dielectic liquid. Experiments show that the fabricated TiO2 nanoparticles are much better than those fabricated by aerosol methods. In addition, the fabricated nanofluid has high suspension stability. We use X-ray diffraction to analyze the structure of TiO2 nanofluid. By measuring the Zeta potential of the TiO2 nanofluid with different pH values, the suspension stability of the TiO2 nanofluid is demonstrated. To verify the applicability of the TiO2 nanofluid, this study also analyzes and compares the rheological properties and reaction to light absorption of nanofluids with different average particle sizes.
  • Improvement of Hydrogen Absorption Performances of Mechanically Alloyed Mg2Ni Powders by Water Cooling

    pp. 842-846

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    DOI:10.2320/matertrans.48.842

    In the present study, Mg2Ni intermetallic powders were prepared by mechanical alloying from elemental magnesium and nickel under an Ar atmosphere with or without water cooling treatments. Two different cooling temperature ranges were used to modify the hydrogen absorption properties of the intermetallic Mg2Ni. The powders milled with or without water cooling were examined as a function of milling time by X-ray diffractometry. Then the hydrogen absorption performance of the 15 h as-milled powders were evaluated. The experimental results show that all the as-milled Mg2Ni powders exhibited a mixture of Mg2Ni, magnesium and nickel solid solutions. The maximum hydrogen absorption content of 15 h as-milled Mg2Ni powders was increased from 3.14 mass% to 3.83 mass% by cooling treatment in a temperature range of 264–267 K. The reversible hydrogenation content was also increased from 2.40 mass% to 3.03 mass% in the same cooling temperature range. More than 20% improvement of hydrogen absorption for Mg2Ni intermetallic powders was achieved by water cooling treatment.
  • Properties of GeSbSn Layer Used as Phase-Change Recording Medium

    pp. 847-853

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    DOI:10.2320/matertrans.48.847

    This paper is to study the properties of phase-change material of GeSbSn used in blue-ray disks and high-speed DVDs, especially on different ratio between Sb and Sn, as well as their crystallization rate, through a series of optical, thermal, and dynamic testings. For GeSbSn material system, there are two exothmal peaks under a condition of high Sn content in the material. For our four samples of GSS01-GSS04, the smaller the ratio of Sb/Sn, the lower the temperature of first exothermal peak. It means that the write-in power of high-speed DVD disk can be decrease. However, the thermal stability due to the activation energy of crystallization increases with the Sb/Sn ratio. By optical measurements for these samples, the optical contrast is greater than 0.6 at a wavelength of 650 nm and that than 0.5 at a length of 405 nm. All of them are meet the requirements of 4X speed DVD. In dynamic test, the modulation of readout signal for GSS01-GSS02 decresses below 0.5 as the ratio of Sb/Sn becomes lower, while the jitter at 14T for GSS04 is over 12% as the ratio of Sb/Sn is too high be used. Consequently, only GSS03 (Ge14Sb64Sn22(at%)) can be used in 4-12X speed DVD-RW or 1-3 X speed blue-ray disk.
  • Microstructural Characteristics and Vibration Fracture Properties of Al-Mg-Si Alloys with Excess Cu and Ni

    pp. 854-859

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    DOI:10.2320/matertrans.48.854

    This study investigated the effect of co-addition of Cu and Ni on the microstructure and vibration properties of Al-Mg-Si alloys. The results show that additions of Cu and Ni resulted in the formation of Al3(Ni,Cu) phase, a harder Al matrix and an accelerated aging rate. Nanoindentation analysis indicates that the Al3(Ni,Cu) phase exhibits a hardness of 7.7 GPa and Young’s modulus of 141.2 GPa. Due to the increased modulus by reinforcement effect of Al3(Ni,Cu), the alloyed samples possessed a higher resonant frequency. However, the damping capacity was reduced with alloying because of the hardened matrix. It was also found that since microcracks could be generated from the irregular-shaped Al3(Ni,Cu) in the vicinity of the tip of the main crack when suffering vibration deformation, the crack propagation resistance of the alloyed samples was inferior.
  • High-Resolution Electron Microscopic Study on Atomic Arrangements at Growing Tips of Martensite Plates and a Nucleating Martensite in Fe-Ni-Mn and Fe-Cr-C Alloys

    pp. 860-868

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    DOI:10.2320/matertrans.48.860

    The present work aims to clarify the atomic arrangements at the austenite/martensite interfaces for the nucleating martensite and the growing tip of martensite plates. An Fe-23Ni-3.8Mn alloy and an Fe-9Cr-1.1C alloy with the K-S orientational relationship with the {112} habit plane were observed with high resolution electron microscopy. At the very tip of the wedge-shaped growing martensite, dislocations queue up on about every six (111)f layers along the interface, with their extra-half plane in the austenite. A nucleus of the martensite was observed in the Fe-9Cr-1.1C alloy. The nucleus has the K-S orientational relationship with a habit plane of (111)f(||(011)b), a wing-like shape, and remarkably expands in the direction of [\\bar101]f(||[\\bar1\\bar11]b). The crystal structure of the nucleus shows a transient lattice region from fcc to bct toward the inside, and the transformation into the final martensite structure (bct) is still incomplete even at the center of the nucleus.
  • Mechanism of the Improvement of Shape Memory Effects in NbC Containing Fe-Mn-Si-Based Shape Memory Alloys

    pp. 869-877

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    DOI:10.2320/matertrans.48.869

    High-resolution transmission electron microscopy revealed that the NbC carbides precipitating in Fe-Mn-Si-based shape memory alloys in the orientational relationship of [100]f||[100]NbC, (001)f||(001)NbC are partially coherent with the matrix showing the misfit dislocations on every five (002)f layers. It was also found that the pre-warm rolling prior to the aging refines the NbC carbides into sizes as small as about 5 nm and produces a homogeneous distribution. It was statistically clarified that the deformation microstructures of the Fe-Mn-Si-based alloys containing finely dispersed NbC carbides exhibit nano-sized monopartial stacking martensite plates, similar to those of the conventional Fe-Mn-Si-based alloys subjected to the training treatment. These microstructural features are considered to improve the shape memory properties of the alloys.
  • Preparation of Porous Fe from Biomorphic Fe2O3 Precursors with Wood Templates

    pp. 878-881

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    DOI:10.2320/matertrans.48.878

    Porous iron with woodlike microstructures was prepared from two kinds of wood templates through a developed biotemplating method in the present work. The biomorphic iron oxide was first produced through infiltration and sintering procedures, and was then reduced to the biomorphic iron in a hydrogen atmosphere at high temperatures (600°C and 1000°C). The morphologies of iron and iron oxide products were observed using SEM and FESEM, and their crystal structures were identified using X-ray diffraction. The results indicate that the pure iron phase can be obtained after the reduction process and the products faithfully retained the microstructures of the corresponding wood templates.
  • Plastic Strain due to Isothermal Transformation from Austenite to Ferrite in IF and Low Carbon Steels

    pp. 882-885

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    DOI:10.2320/matertrans.48.882

    Apparent non-isotropic strain under external stress is quantified as a function of transformed fraction with dilatometric measurement and analysis for IF and low carbon steel. The non-isotropic strain of IF steel increases linearly with a transformed fraction, because fast transformation kinetics minimizes the contribution of creep in austenite and ferrite, and thereby the evolution of non-isotropic strain is mainly governed by transformation plasticity. For low carbon steel, the non-isotropic strain deviates from linear behavior in transformation segment where the creep in austenite and ferrite becomes remarkable due to the slow transformation kinetics. A diffusion controlled model describes well the effect of transformation kinetics on the evolution of non-isotropic strain during the transformation.
  • Thermal Diffusivity of Zr-Based Bulk Glass Alloys in the Liquid State

    pp. 886-888

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    DOI:10.2320/matertrans.48.886

    Thermal diffusivity of three alloys of Zr55Al10Ni5Cu30, Zr60Al15Ni25 and Zr65Al7.5Cu27.5 has been measured in the liquid state with a laser flash technique. The thermal diffusivity values of three Zr-based alloys in the liquid state are summarized in the linear equations with positive temperature dependency. The lower the thermal diffusivity values of Zr-based alloys at liquidus temperature, the lower the critical cooling rate to produce metallic glass phase becomes. The measured thermal diffusivity was compared with the value for Pd-based metallic glass. The results indicate that critical cooling rate to obtain metallic glass phase could be an increasing function of thermal diffusivity for each alloy system.
  • The Interfacial Reaction between Diamond Grit and Ni-Based Brazing Filler Metal

    pp. 889-891

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    DOI:10.2320/matertrans.48.889

    The main goal of this study was to examine the interfacial reaction between diamond grits and Ni-based brazing filler metal. A Ni alloy (Ni-7Cr-3Fe-3B-4Si (wt. %)) was used as the brazing filler metal. Brazing was carried out by heating up to the brazing temperature (1223, 1273 or 1323 K) and then held at this temperature for 10 min. The morphology of the interface between diamond grits and Ni-based filler metal exhibited a very good condition after this heat treatment. Cr-carbide and Ni-rich compounds were detected by XRD analysis in the vicinity of the interface between diamond grits and Ni-based filler metal after vacuum induction brazing. Chromium carbide is considered to play an important role in the high bonding strength achieved between diamonds grits and the brazing alloy.

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