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

MATERIALS TRANSACTIONS Vol. 49 (2008), No. 11

  • TD-DFT Studies on Hematoporphyrin and Its Dimers

    A. Suvitha, R. V. Belosludov, H. Mizuseki, Y. Kawazoe, M. Takeda, M. Kohno, N. Ohuchi

    pp. 2416-2419

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    DOI:10.2320/matertrans.MB200829

    Abstract

    A theoretical study has been performed on a hematoporphyrin and its dimers which are components of Photofrin, a photosensitizer. Full geometry optimizations have been carried out using the PBEPBE functional and 6-31G(d) basis set. This combination gives better agreement with X-ray crystal data of porphyrin. Among the dimers studied, the C–C linked structure is found to have the highest stability. The predicted change of free energy (ΔG=−13.9 kcal/mol) suggests that the interconversation of ester to ether would be thermodynamically favorable. The time-dependent density functional theory (TDDFT) studies show that Q-band absorption maxima undergo a less intense transition and low oscillator strength, indicating that dimers have activity when treated under higher dosage.

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  • First-Principles Calculation of Photoabsorption Spectra of Cadmium Selenide Clusters

    Momoko Nagaoka, Soh Ishii, Yoshifumi Noguchi, Kaoru Ohno

    pp. 2420-2423

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    DOI:10.2320/matertrans.MB200825

    Abstract

    Photoabsorption spectra of magic-number cluster, (CdSe)34, in a pearl-necklace geometry are calculated for the first time by a first-principles approach based on the density functional theory. Photoabsorption spectra for the (CdSe)34 isolated-cage geometry is also calculated. We confirmed the size dependence by comparing them with our former result of smaller magic-number cluster, (CdSe)13. Three different types of supercells are supposed to simulate the pearl-necklace geometry and a double-peak structure is found in a particular supercell. We found that the cluster geometry in this supercell is the most stable among the three.

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

  • A Lattice Gas Model with Tetrahedral 4-Body Interaction of FePt Alloy Clusters

    Satoru Masatsuji, Yuji Misumi, Soh Ishii, Kaoru Ohno

    pp. 2424-2428

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    DOI:10.2320/matertrans.MB200826

    Abstract

    A realistic lattice gas model with a tetrahedral 4-body interaction is derived for a system composed of Fe, Pt atoms and vacancies on the basis of first-principles calculations. Using this model, we carry out lattice Monte Carlo simulations of order-disorder phase transition in a bulk FePt alloy, aggregation into FePt clusters in vapor, and L10 ordering in FePt clusters. The order-disorder phase transition temperature of a bulk FePt is estimated to be 1970 K, which is slightly higher than the experimental value of 1572 K because of the ignorance of the off-lattice effects. The present model shows inherent atomic cohesion that leads to aggregation into clusters in a simulation starting from a random configuration in vapor. Finally for FePt alloy clusters, we find that the L10 ordered structure is maintained only for those clusters with a size (diameter) greater than 2.5 nm, in accordance with the recent experimental evidence reported by Miyazaki et al.

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  • Structural Dependence of Magnetic Shielding Properties in Al4Li4 Clusters

    Sang Uck Lee, Young-Kyu Han, Chiranjib Majumder, Rodion V. Belosludov, Hiroshi Mizuseki, Yoshiyuki Kawazoe

    pp. 2429-2436

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    DOI:10.2320/matertrans.MB200823

    Abstract

    This work demonstrates that the binding of Li atom plays an important role in the Al4Li4 clusters, which changes the structure of the Al4 ring and induces the distinct magnetic shielding properties depending on the position of Li atom. The Al4Li4 cluster possesses both aromatic (S type) and antiaromatic (L type) isomers depending on the position of Li atom with an 8.74 kcal/mol energy difference at the singlet state. The bond length alternation (BLA) values and nucleus independent chemical shift analysis of each canonical molecular orbital (NICS-CMO) analyses show that S type isomers are aromatic and L type isomers are antiaromatic as the singlet low-lying states. A cyclic reaction pathway between L and S type isomers is mapped with five low-lying and five transition states including two intermediate states.

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  • Geometries and Electronic Structures of Alkaline Earth Auride Clusters, Au4M (M=Mg, Ca, Sr, Ba)

    Fabio Pichierri

    pp. 2437-2440

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    DOI:10.2320/matertrans.MB200803

    Abstract

    Using density functional theory calculations we have investigated the geometries and electronic structures of a series of neutral alkaline earth auride clusters with chemical formula Au4M, with M=Mg, Ca, Sr, and Ba. These clusters are formally made of an Au42− unit and a doubly-charged M2+ cation. Of the three geometries investigated herein, namely planar, square-pyramidal, and lantern-type geometry, the planar structure is the most energetically favored. Because all structures are characterized by positive vibrational frequencies, these clusters represent local minima on the corresponding potential energy hypersurface.

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  • First-Principles Calculations of M10/Graphene (M = Au, Pt) Systems —Atomic Structures and Hydrogen Adsorption—

    Kazuyuki Okazaki-Maeda, T. Akita, S. Tanaka, M. Kohyama

    pp. 2441-2444

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    DOI:10.2320/matertrans.MB200812

    Abstract

    The usage of Au nano-particles as a catalytic electrode may be effective for the CO-poisoning problem in the anode of a proton-exchange membrane fuel cell (PEMFC), because Au nano-particles supported on metal oxides have novel catalytic activity of low-temperature CO oxidation or water gas-shift reaction. As the first step to examine this possibility, we have performed first-principles calculations of a Au10 cluster on graphene as well as a Pt10 cluster on graphene, based on the density functional theory (DFT). There are no strong interactions between the cluster and graphene such as substantial charge transfer or orbital hybridization, although the interaction for Pt is stronger than that for Au. We have further examined the H-atom adsorption on the clusters on graphene, and found that the adsorption energy is much larger for the Pt cluster than for the Au cluster. However, we have observed that the energy gain in the dissociation and adsorption from a H2 molecule is indeed obtained for the Au small cluster in spite of no energy gain for the Au(111) surface.

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  • Magnetic Properties of Mn Doped Armchair Graphene Nanoribbon

    Narjes Gorjizadeh, Yoshiyuki Kawazoe

    pp. 2445-2447

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    DOI:10.2320/matertrans.MB200815

    Abstract

    We investigate the electronic structure and magnetism of an armchair graphene ribbon doped with Mn by first-principles density functional calculations. Mn atoms are doped at the edge of the ribbon, with different densities. The local magnetic moment due to Mn atom is 5 μB/Mn for dilute doping and 4.5 μB/Mn for heavy doping. The structures of Mn doped at both edge of graphene ribbon were optimized in ferromagnetic and antiferromagnetic states to find the stable magnetic states of the two opposite ferromagnetic edges. Our calculations show that the ground state is ferromagnetic for heavy doping and does not have a preferable configuration for dilute doping because of the small energy difference. These structures have application in nanoelectronics and spintronics.

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  • Bonding and Magnetism in High Symmetry Nano-Sized Graphene Molecules: Linear Acenes C4m+2H2m+4 (m=2,…25); Zigzag Hexangulenes C6m**2H6m (m=2,…10); Crenelated Hexangulenes C6(3m**2−3m+1)H6(2m−1) (m=2,…6); Zigzag Triangulenes Cm**2+4m+1H6m (m=2,…15)

    Michael R. Philpott, Fanica Cimpoesu, Yoshiyuki Kawazoe

    pp. 2448-2456

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    DOI:10.2320/matertrans.MB200822

    Abstract

    Plane wave based ab initio DTF all valence electron spin polarized calculations are reported for the electronic structure and geometry of differently shaped graphene molecules. These polycyclic hydrocarbon molecules comprise four series: D2h symmetric linear polyacenes C4m+2H2m+4 (m=2,…,25); D6h hexagulenes with zigzag edges C6m**2H6m (m=2,…,10); D6h hexagulenes with crenelated edges C6(3m**2−3m+1)H6(2m−1) (m=2,…,6); D3h zigzag edged triangulenes Cm**2+4m+1H6m (m=2,…15). The systems variously display ground states that are spin paired singlet (S=0), singlet anti-ferromagnetically ordered diradical and spin polarized S=1⁄2(m−1). Molecules with zigzag edges show evidence of electron delocalization along the perimeters with some bond alternation at the corners. In the acenes the spin paired singlet state of the short members switches to a singlet diradical at m≈7–8 and this remains as the ground state for larger m. In contrast the triangulenes are magnetic and the atomic charge and spin density changes monotonically with distance from center to perimeter. In the hexagonal systems the development of a graphene core region, where the C-C bonds are 142 pm, extends to within a few C-C bonds of the perimeter atoms. Zigzag hexagulenes have a spin paired singlet ground state for m≤8 and a singlet diradical ground state for larger m. When hexagulenes are substitutionally doped with boron or nitrogen, acceptor or donor levels appear that track the valence or conduction band edges with increase in zigzag number. This result suggests the possibility of building several semiconductor device structures into the same graphene molecule.

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  • Formation and Characterization of Bulk Hetero-Junction Solar Cells Using C60 and Perylene

    Takeo Oku, Nariaki Kakuta, Atsushi Kawashima, Katsunori Nomura, Ryosuke Motoyoshi, Atsushi Suzuki, Kenji Kikuchi, Gentaro Kinoshita

    pp. 2457-2460

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    DOI:10.2320/matertrans.MB200807

    Abstract

    Polymer bulk hetero-junction solar cells were fabricated and the electronic and optical properties were investigated. C60 and perylene were used as n-type semiconductors, and copper phthalocyanine, zinc phthalocyanine and pentacene were used as p-type semiconductors. Energy levels of the molecules were calculated, and HOMO levels were localized around the main chains of the zinc phthalocyanine and pentacene. Nanostructures of the solar cells were confirmed as mixed nanocrystals by transmission electron microscopy and electron diffraction.

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  • Growth of Boron Nitride Nanohorn Structures

    Takeo Oku, Kenji Hiraga, Toshitsugu Matsuda

    pp. 2461-2464

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    DOI:10.2320/matertrans.MB200806

    Abstract

    Boron nitride (BN) nanohorns were fabricated, and their structures were investigated by transmission electron microscopy and molecular mechanics calculation. The multi-walled BN nanohorns would be stabilized by stacking of nanohorn structures. Growth of the BN nanohorn was observed at elevated temperatures, and the activation energy for the nanohorn growth was estimated to be 2.3 eV.

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  • Effect of Central Metal Ion, CoII in the FeII Spin-Crossover Complex in Emulsion Polymerization of Trifluoroethylmethacrylate Using Poly(Vinyl Alcohol)

    Atsushi Suzuki, Motoi Iguchi, Takeo Oku, Motoyasu Fujiwara

    pp. 2465-2468

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    DOI:10.2320/matertrans.MB200808

    Abstract

    To apply to magnetic memory device of nanodispersed spin crossover complex, we have studied the magnetic properties of hetero-spin crossover complex of [Fe(Htrz)3x(4-NHtrz)3−3x](BF4)2nH2O in emulsion polymerization of trifluoroethylmethacrylate using poly (vinyl alcohol) as a protective colloid. Effect of central transition metal ion of CoII ions on the spin crossover complex in the emulsion polymerization was investigated. The experimental results can be explained by theoretical consideration of electron density between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and Fe-N bond lengths, magnetic parameters, g-factor using density functional theory. This result was thought to have arisen from ligand field theory with a slight distribution of bond-length based on a slight exchange interaction due to a miner Jahn-Teller effect.

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  • Dependence of Magnetism on Doping Concentration in V-Doped Bulk ZnO

    Qian Wang, Qiang Sun, Puru Jena, Yoshiyuki Kawazoe

    pp. 2469-2473

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    DOI:10.2320/matertrans.MB200828

    Abstract

    Extensive calculations based on density functional theory have been carried out to understand the dependence of magnetic coupling on the concentration and distribution of V dopants in bulk ZnO. We considered three different doping concentration of V, namely 5.6%, 8.3% and 12.5%. At low doping concentration, ferromagnetic, anti-ferromagnetic and ferrimagnetic couplings are energetically nearly degenerate. Consequently, thermal fluctuation in samples may cause diverse magnetic behaviors. However, the ferromagnetic state becomes stable as the concentration of V increases to 12.5%. At low concentrations (5.6% and 8.3%) V atoms substitute Zn atoms uniformly in bulk ZnO, while they tend to cluster when their concentration reaches 12.5%. The present study provides an understanding of the conflicting experimental observations in V-doped bulk ZnO.

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  • Structural, Electronic and Optical Properties of the Al2O3 Doped SiO2: First Principles Calculations

    Yong Yang, Masae Takahashi, Hiroshi Abe, Yoshiyuki Kawazoe

    pp. 2474-2479

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    DOI:10.2320/matertrans.MB200831

    Abstract

    The doping effects of Al2O3 on SiO2 (α-cristobalite) have been studied by first principles calculations, with emphasis on the structural, electronic and optical properties. Compared to pure SiO2 crystal, the electronic density of states (DOS) of the Al2O3 doped SiO2 show significant changes. The electron energy states corresponding to the newly emerged sharp DOS peaks are found to exhibit localized characteristics, which are mainly attributed to the unsaturatedly bonded 2p orbitals of O atoms in the –[Al-O-Al]– linkages. The optical properties of the Al2O3 doped SiO2 are studied by calculating the frequency-dependent dielectric functions. The electric dipole moment induced by the electron states near the top of the valence band is found to have significant effect on the optical absorption spectrum.

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  • First-Principles Study on the Electronic Structure and Elastic Properties of YCu, DyCu and YAg

    Y. J. Shi, Y. L. Du, G. Chen, G. L. Chen

    pp. 2480-2483

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    DOI:10.2320/matertrans.MB200816

    Abstract

    The electronic structure and elastic properties of YCu, YAg, and DyCu were studied by full-potential linearized augmented plane wave method (FP_LAPW) on the basis of the density functional theory (DFT). The generalized gradient approximation (GGA) is applied for YCu, YAg, and the LDA+U is applied for DyCu. The density of states at the Fermi energy, N(EF), are 1.08, 1.09, and 1.04 states/(eV unit cell) for YCu, YAg and DyCu, respectively. The elastic constants were calculated. The values for Pugh’s criterion are 2.30, 2.05 and 3.00 for YCu, DyCu and YAg, respectively. All of them are larger than 1.75, indicating the ductile manner of these materials. The calculated value of the anisotropy is close to 1, indicating highly isotropic behavior.

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  • First Principles Calculation of CO and H2 Adsorption on Strained Pt Surface

    Akihide Kuwabara, Yohei Saito, Yukinori Koyama, Fumiyasu Oba, Katsuyuki Matsunaga, Isao Tanaka

    pp. 2484-2490

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    DOI:10.2320/matertrans.MB200817

    Abstract

    First principles calculations are carried out to analyze adsorption of CO and H2 molecules on a Pt (111) surface and the effect of surface strain on the adsorption energy. A CO molecule is more adsorptive on the Pt (111) surface than a H2 molecule under an ordinary condition. Surface expansion enhances CO poisoning on a Pt (111) surface. On the contrary, a compressive strain reduces adsorptive strength of a CO molecule. Similar tendency is also found in adsorption of a H2 molecule on the bridge, fcc-hollow, and hcp-hollow sites. However, H2 adsorption on the top site is less affected by the strain. As a consequence, the difference of adsorption energies between CO and H2 molecules becomes smaller when compressive strain is introduced into the Pt (111) surface. Based on thermodynamics, surface coverage ratio is quantitatively evaluated with taking into account the effect of surface strain and partial pressure of gas phase. It is revealed that compressive strain improves probability of H2 adsorption on Pt surface.

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  • First Principle Study on the Domain Matching Epitaxy Growth of Semiconductor Hetero-Interface

    Vu Ngoc Tuoc

    pp. 2491-2496

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    DOI:10.2320/matertrans.MB200818

    Abstract

    In conventional lattice-matching epitaxy with lattice misfit of less than 7–8%, the thin films grow pseudomorphically (i.e. film take lattice constant of the substrate up to some “critical thickness” of one to several monolayers). Above this misfit, it was surmised that the film will grow textured or largely polycrystalline. The recent discovery of Domain Matching Epitaxy Growth method had proposed the new growth technology using Pulsed laser deposition (PLD), by which the epitaxial growth of hetero-thin films with very large lattice mismatch is possible by matching of domains where an integer multiples of major lattice planes match across the interface. Misfit dislocation generated along the interface (i.e. critical thickness is less than one-monolayer). Based on all of these exciting technology applications, there is an urgent need to study the material properties, structure correlations and defect microstructure for this thin film growth mode. In this work, we performed an ab-initio study of the structural properties of that pseudomorphic-like growth of semiconductor hetero-interface using the well-known density functional-based tight-binding (DFTB) simulation tool. We examine the simulation study of domain matching growth of GaN(0001)/Si(111) - a Hex-on-Cub problem.

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  • Dislocation Driven Problems in Atomistic Modelling of Materials

    Duc Nguyen-Manh, Matous Mrovec, Steven P. Fitzgerald

    pp. 2497-2506

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    DOI:10.2320/matertrans.MB200827

    Abstract

    Understanding the mechanical properties of technologically advanced materials from quantum mechanical predictions based on electronic structure calculations remains one of the most challenging problems in modern computational materials science. In this paper, we illustrate this challenge from our current investigations on dislocation behaviour in bcc transition metals that are promising candidates for materials subject to fast neutron irradiations in future fusion power plants. Starting with the relationship between the brittleness and the negative Cauchy pressure of elastic constants in materials within the so-called Harris-Foulkes approximation to the density functional theory (DFT), we briefly discuss the importance of the generic form of interatomic potentials in order to reproduce a correct Cauchy pressure. The latter in turn plays an important role in predicting dislocation properties in fcc iridium and therefore allows us to explain experimental observation of the intrinsic brittleness of this material. We then investigate the behaviour of the (1/2)[111] screw dislocation that controls plastic deformation in bcc metals from atomistic simulation. Here we show the atomic phenomena associated with the non-planar core structure of dislocations in bcc iron from the Stoner tight-binding bond model. The crucial point comes from the accurate evaluation of forces implemented within the charge neutrality conditions in the treatment of the spin-polarized dependence in the electronic structure calculations. In agreement with DFT studies, the magnetic bond-order potentials predict a non-degenerate core structure for screw dislocations in Fe. Finally, a new analytic expression has been derived for the migration energy barrier for the one-dimensional (1D) motion of crowdions, which are the most stable self-interstitial atom (SIA) defects predicted by our DFT calculations. Importantly, the latter study is strongly supported by the recent observation of 1D diffusion of nanometer-sized dislocation loops, observed very recently under in situ electron microscope irradiation for bcc transition metals.

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  • Computational Study on Misfit Dislocation in Ni-Based Superalloys by Quasicontinuum Method

    Joy RP Djuansjah, Kisaragi Yashiro, Yoshihiro Tomita

    pp. 2507-2514

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    DOI:10.2320/matertrans.MB200821

    Abstract

    Misfit dislocation at the γ⁄γ′ interface of Ni-based superalloys is investigated using the quasicontinuum simulation. In order to imitate the γ′ phases, nickel embedding function is modified by changing the lattice parameter, bulk modulus and cohesive energy simultaneously. Negative and positive misfits with different magnitudes are set in the simulations. Atomic structure at the interface, spatial distance and strain energy density at the core dislocation are investigated. Shear simulation is also conducted for a flat interface of γ⁄γ′ laminates, while the dislocation propagation and it’s interaction with interface are analyzed.

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  • Thermal Expansion Calculated by Continuous Displacement Cluster Variation Method

    Tetsuo Mohri

    pp. 2515-2520

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    DOI:10.2320/matertrans.MB200802

    Abstract

    Thermal expansion of a single component system in a two dimensional square lattice is calculated by employing Continuous Displacement Cluster Variation Method. It is demonstrated that the entropy effect arising from the freedom of local atomic displacements drives the thermal expansion. The coefficient of thermal expansion curve is compared with the one calculated based on Debye-Grüneisen model within the quasi-harmonic approximation. The two curves demonstrate opposite behavior.

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  • Optical Characteristics and Nanoscale Energy Transport in Thin Film Structures Irradiated by Nanosecond-to-Femtosecond Lasers

    Kwangu Kang, Seong Hyuk Lee, Hong Sun Ryou

    pp. 2521-2527

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    DOI:10.2320/matertrans.MB200820

    Abstract

    Extensive numerical simulations are rigorously conducted for conductive and radiative heat transfer characteristics in thin silicon structures irradiated by nano-to-femtosecond pulsed lasers. The two-temperature model is used to calculate the carrier and lattice temperatures, respectively. The wave interference effects on reflectivity and absorption are considered by using the thin film optics and the electromagnetic theory. The radiation property of silicon is expressed in terms of lattice temperature and carrier density. The reflectivity of thin film structure exhibits different patterns with variation of laser pulse durations. In femtosecond laser irradiation, the energy transfer between carriers and lattice phonons mostly takes place after laser irradiation is over and then it rapidly heats the ions to much higher temperatures, compared to the long pulse cases. For nanosecond pulse lasers, the carrier and lattice temperature distributions do not show wavy patterns, whereas for subpicosecond pulse lasers, the spatial carrier and lattice temperature distributions appear to be periodic in space because of shorter pulse duration than diffusion time.

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  • Thermodynamic Analysis of the V–H Binary Phase Diagram

    Shusuke Ukita, Hiroshi Ohtani, Mitsuhiro Hasebe

    pp. 2528-2533

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    DOI:10.2320/matertrans.MB200810

    Abstract

    A thermodynamic analysis of the V–H binary system has been performed by combining first-principles calculations with the CALPHAD approach. In order to represent the order-disorder transition between the monoclinic β1 and body-centered tetragonal β2 phases arising from the ordering of H atoms located at the octahedral interstitial sites, a (V)1⁄2(H,Va)1⁄4(H,Va)1⁄4-type three-sublattice model was applied. The formation energies of the δ-VH2 hydride phase and solid solution β phases were calculated in the ground state using the Full-potential Linearized Augmented Plane Wave method, and the estimated values were introduced into a CALPHAD-type thermodynamic analysis, along with some experimental information on the phase boundaries and the hydrogen isotherms. The calculated phase diagram and hydrogen isotherms were in good agreement with these experimental results.

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  • Thermodynamic Analysis of the Phase Equilibria in the Fe-Zr-B System

    Tatsuya Tokunaga, Ken Terashima, Hiroshi Ohtani, Mitsuhiro Hasebe

    pp. 2534-2540

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    DOI:10.2320/matertrans.MB200809

    Abstract

    A thermodynamic analysis of the Fe-Zr-B ternary system has been carried out using the CALPHAD method. Among the three binary systems present in the ternary phase diagram, the thermodynamic descriptions of the Fe-Zr and Fe-B binary systems were taken from reported results and from our previous study, respectively. The thermodynamic parameters of the Zr-B binary system were evaluated using the thermochemical properties from our first-principles calculations, as well as available experimental data. In this modelling, the Gibbs energy of ZrB2 with an AlB2-type structure was represented using the two-sublattice model, in which vacancies were introduced into both the Zr and the B sublattices, following the recent data obtained from neutron diffraction experiments on NbB2 with the same structure as that of ZrB2. The optimized thermodynamic parameters of the Zr-B system enabled us to obtain reproducible calculations of the experimental data on phase boundaries and formation enthalpies obtained from first-principles calculations. The ternary parameters were determined using the experimental data on phase boundaries. The calculated results have nicely reproduced the experimental Fe-Zr-B ternary phase diagrams.

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  • Development and Implementation of Recursive Coarse-Grained Particle Method for Meso-Scale Simulation

    Ryo Kobayashi, Takahide Nakamura, Shuji Ogata

    pp. 2541-2549

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    DOI:10.2320/matertrans.MB200813

    Abstract

    A coarse-graining method has been proposed [R. E. Rudd and J. Q. Broughton: Phys. Rev. B 58 (1998) R5893–R5896] for a crystalline system of atoms, in which the inter-particle interaction is obtained through coarse-graining of the partition function of the atomic Hamiltonian in the harmonic approximation. Though the method has attractive features such as its natural incorporation of atomistic phonons, the original formulation limits its application to small periodic systems without surfaces. In this paper, we improve the method as follows: (i) we introduce a recursive coarse-graining procedure to overcome the size limitation problem, (ii) we rewrite the deformation energy in both translation and rotation invariant form to make it applicable to macroscopically deformed systems, (iii) we extend the formulation for multi-component systems, and (iv) we incorporate the thermal expansion and softening of the atomistic systems. The essentials in the code implementation are explained. The method is successfully applied to deforming nanorods of sub-micron size in both two and three dimensions, to show that it is ready for dynamics simulation of meso-scale, three-dimensional realistic systems.

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  • Multiscale Numerical Simulation of Fluid-Solid Interaction

    Yohei Inoue, Junji Tanaka, Ryo Kobayashi, Shuji Ogata, Toshiyuki Gotoh

    pp. 2550-2558

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    DOI:10.2320/matertrans.MB200814

    Abstract

    A new multiscale numerical method is developed to simulate the fluid-solid interaction. The solid motion is described by coarse grained particles which are generated by consolidation of harmonically interacting atoms, and the fluid motion is by the lattice Boltzmann method. Since the characteristic time of the fluid motion is much longer than that of the coarse grained particles, the momentum change due to the rapid collision of the coarse grained particles at the interface is accumulated over a certain time duration and then passed the fluid motion. The method is applied to an elastic rod fixed on the wall in the two dimensional Poiseuille flow. The oscillation and stress within the rod as well as the velocity and vorticity of the fluid are examined with respect to the vortex shedding at the top of the rod. Also the method is applied to the problem of fluid transfer by multiple elastic rods. It is found that the results are quite reasonable and that the present method is effective in dealing with the fluid-solid interactions.

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  • Multi-Phase-Field Model to Simulate Microstructure Evolutions during Dynamic Recrystallization

    Tomohiro Takaki, Tomoyuki Hirouchi, Yousuke Hisakuni, Akinori Yamanaka, Yoshihiro Tomita

    pp. 2559-2565

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    DOI:10.2320/matertrans.MB200805

    Abstract

    A numerical model to simulate microstructure evolution and macroscopic mechanical behavior during hot working was developed. In this model, we employed a multi-phase-field model to simulate the growth of dynamically recrystallized grains with high accuracy and the Kocks-Meching model to calculate the evolution of dislocation density due to plastic deformation and dynamic recovery. Furthermore, an efficient computational algorithm was introduced to perform the multi-phase-field simulation efficiently. The accuracy of the developed model was confirmed by comparing the migration rate of grain boundaries with the theoretical value. Also, the numerical results for a polycrystalline material are compared with those obtained from a cellular automaton simulation. Furthermore, the effects of the initial grain size, grain boundary mobility and nucleation rate on the dynamic recrystallization behavior were investigated using the developed model.

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  • Thermocapillary Convection of Liquid Bridge under Axisymmetric Magnetic Fields

    Chaobo Chen, Zhong Zeng, Hiroshi Mizuseki, Yoshiyuki Kawazoe

    pp. 2566-2571

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    DOI:10.2320/matertrans.MB200830

    Abstract

    Three-dimensional numerical simulation of thermocapillary flow in liquid bridge model is performed. The effects of the magnetic field, including both axial uniform magnetic field and axisymmetric non-uniform magnetic field generated by circle coil, on the thermocapillary flow of semiconductor melt are investigated. For a three-dimensional thermocapillary flow, the axial magnetic field and the axisymmetric non-uniform magnetic field suppress convection effectively, and the three-dimensional thermocapillary flow tends to become an axisymmetric one. Under axial magnetic field, the convection in central core region becomes very weak, and in the meantime, the energetic thermocapillary flow is squeezed toward free surface. While the axisymmetric non-uniform magnetic field generated by single coil is applied on the melt of liquid bridge, the convection structure is similar with that under axial magnetic field. By applying the axisymmetric CUSP magnetic field generated by two coils, convection structure depends on the symmetric plane position of two coils (SPPTC), the surface tension flow penetrates the whole liquid bridge and no stagnant core in the inner part of the melt is observed when SPPTC locates at z*=0.5, which is thought as a more favorable convection structure to alleviate radial dopant segregation in floating zone crystal growth.

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  • Numerical Investigation on Self-Organized Interconnection Using Anisotropic Conductive Adhesive with Low Melting Point Alloy Filler

    Jin Woon Lee, Seong Hyuk Lee, Jong-Min Kim, Jae Hyung Kim, Jung Hee Lee

    pp. 2572-2578

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    DOI:10.2320/matertrans.MB200819

    Abstract

    The present study is devoted to develop a new simulation code for the numerical investigation on coalescence characteristics in self-organized interconnection using anisotropic conductive adhesive (ACA) with low melting point alloy (LMPA) fillers. In particular, this article examines the coalescence mechanism during ACA process for different resin viscosity, particle volume fractions, and provides estimated results of conduction path growth fraction for different conditions. Starting from the motion equation of filler particles, moreover, a theoretical approach is presented to find out dominant factors affecting the formation of interconnection. The new simulation code is based on the finite volume method with the use of the continuum surface force (CSF) model and the cubic interpolated propagation (CIP) method. It is confirmed that conduction path formation depends on volume fraction, viscosity, and surface tension during the process. It is also found that the pressure-driven force effect becomes not dominant in the path formation at high resin viscosity and high filler density, the particle drift velocity becomes slow due to the increase in resin viscosity, conduction path growth fraction increases with the volume fraction, and the time for path formation is shorter with the increase of the volume fraction.

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  • The Floating Potential on the Surface of 25 mol%Na2O-SiO2 Glass Heated by Thermal Plasma of Ar

    Keiichiro Kashimura, Toru Yamashita, Kazuhiro Nagata

    pp. 2579-2583

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    DOI:10.2320/matertrans.MRA2008190

    Abstract

    Mechanisms of heat transfer need to be understood to control plasma more efficiently in industrial applications. Floating potential is defined to be the potential on molten 25 mol%Na2O-SiO2 glass surface and the dependence of transferred-type thermal plasma current on the floating potential of the glass has been studied using the Langmuir probe method. An anomalous probe voltage–current curve was found when the plasma current was applied under 3 A. It is also considered that the electrochemical reaction at the surface exists, which is dependent on the plasma current.

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  • Occurrence of Faceting for [110] Symmetric Tilt Boundaries in Cu Doped with Bi

    Nobuyuki Gokon, Masanori Kajihara

    pp. 2584-2590

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    DOI:10.2320/matertrans.MRA2008062

    Abstract

    The faceting of the grain boundary in the binary Cu-Bi system was experimentally observed by transmission electron microscopy (TEM). For the observation, Cu bicrystals with Σ33, Σ9 and Σ11 [110] symmetric tilt boundaries were doped with Bi at 1173 K for 120 h, and then homogenized at 1173 K for 48 h, followed by furnace cooling or water quenching. The misorientation angle between the [001] directions of the two single-crystals is 20.1°, 38.9° and 50.5° for the Σ33, Σ9 and Σ11 boundaries, respectively. According to the TEM observation, the grain boundary is faceted markedly in the bicrystal with furnace cooling but barely in that with water quenching. Thus, the faceting takes place during furnace cooling but not during homogenization. The faceting was analyzed quantitatively on the basis of the inclination angle dependence of the boundary energy in Cu. The analysis yields that the contribution of the torque term to the faceting is important. Comparing the boundary diffusivities of Bi and Cu in Cu, we may expect that the mobility is much greater for the grain boundary with Bi than for that without Bi. As a result, the faceting during furnace cooling takes place considerably for the grain boundary with Bi but scarcely for that without Bi.

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  • Mechanical Properties and Resonant Characteristics of Friction Stirred AZ31-Mg Alloy

    Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen, Kai-Jie Zhuang

    pp. 2591-2596

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    DOI:10.2320/matertrans.MRA2008167

    Abstract

    An annealed AZ31-Mg specimen (AZ31-O) was given a FSP (friction stir process) to obtain a AZ31-FSP specimen, whose tensile and vibration fracture mechanisms are examined in this study. As a result of FSP, the structure of the stirred zone (SZ) separated into two zones: (1) the SZ-top had a finer structure and (2) the grain size of the SZ-bottom was like the AZ31-O specimen. Because the basal plane (0002) had pressed close to the trace surface of the onion structure in the SZ, the recrystallization of FSP increased the elongation of the specimens at room temperature, but the refined grains had no contribution to tensile strength and had an unusual Hall-Petch effect. Notably, the vibration deformed resistance of the AZ31-FSP specimen was higher than that of the AZ31-O specimen. The FSP specimen not only possessed finer structures but also had a preferred orientation in the stirred zone. This led to an increase in the crack tortuosity, which in turn increased the crack propagation resistance and the vibration life.

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  • An Adaptive Time-Step Control Strategy for the Solidification Processes Based on Modified Local Time Truncation Error

    Hsiun-Chang Peng, Long-Sun Chao

    pp. 2597-2604

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    DOI:10.2320/matertrans.MRA2008067

    Abstract

    Choosing appropriate time steps to model the transient and discontinuous characteristics of solidification processes is difficult. The current study develops a modified local time truncation error (LTE)-based strategy designed to adaptively adjust the size of the time step during the simulated solidification procedure in such a way that the time steps can be adapted in accordance with the local variations in latent heat released during phase change or the effects of pure conduction in a single solid or liquid phase. The computational accuracy, efficiency and convergence of the proposed method are demonstrated via the simulation of the one-dimensional and two-dimensional solidification problems and compared with those of other uniform time step and adaptive time step methods. Consequently, the effects of latent heat release are more accurately modeled, the precision and efficiency of the computational solutions is correspondingly improved, and the computational errors are minimized. Furthermore, in solving the 2-D problem, it is shown that the line Gauss-Seidel iteration method and the proposed nonlinear iteration method can be combined to construct a highly efficient and accurate solver.

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  • Viscous Flow Behavior and Workability of Mg-Cu-(Ag)-Gd Bulk Metallic Glasses

    Y. C. Chang, J. C. Huang, C. W. Tang, C. I. Chang, J. S. C. Jang

    pp. 2605-2610

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    DOI:10.2320/matertrans.MRA2008172

    Abstract

    The thermomechanical properties and viscous flow behaviors of the Mg65Cu25−xAgxGd10 (x=0, 3, 10 at%, namely, Mg65Cu25Gd10, Mg65Cu22Ag3Gd10, and Mg65Cu15Ag10Gd10) bulk metallic glasses in the supercooled viscous region under the loading condition were investigated using the thermomechanical analyzer. In this study, the supercooled viscous temperature windows, the minimum viscosity, the fragility parameter, and the deformability parameter would all be degraded with increasing Ag addition, leading to the negative factors for the micro-forming and nano-imprinting practices. The base Mg65Cu25Gd10 alloy appears to be more promising than the Ag containing alloys when the viscous forming is under consideration.

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  • Copper Leaching Behavior of Iron-Oxide Hosted Copper-Gold Ore in Sulfuric Acid Medium

    Xiaobo Min, Hitoshi Watanabe, Yasushi Takasaki, Takahiko Okura, Muneyuki Tamura, Joe Seong-Jin, Hidekatsu Nakamura, Yoshiharu Kida

    pp. 2611-2617

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    DOI:10.2320/matertrans.M-MRA2008834

    Abstract

    Iron-oxide hosted copper-gold (IOCG) deposit is a newly recognized raw material for copper recovery. A poor understanding of its hydrometallurgical behavior has limited the development of its commercial practice for copper extraction. In this paper, the leaching behavior of IOCG ore in sulfuric acid medium containing hydrogen peroxide were studied in shaking flask and rolling-ball (RB) vessel. The dissolved copper and iron, pH and oxidation-reduction potential were monitored versus time. It was found that the IOCG ore is more difficult to leach than primary and secondary copper ores. Furthermore, some variables including sulfuric acid dosage, hydrogen peroxide addition and particle sizes were considered and investigated. The similar copper recovery was observed with the variation of the amount of sulfuric acid, and the addition of hydrogen peroxide did not enhance copper yield considerably. Although the higher copper recovery occurred with smaller particle sizes, the highest copper extraction was still not over 40% even for −0.02 mm size. The dissolved copper level behavior with time in shaking flask indicates the hindered dissolution is occurring. Moreover, more than 90% copper recovery in RB leaching confirmed the existing hindered dissolution in shaking flask. The passivation candidates of elemental sulfur was detected and confirmed by X-ray diffraction further, which were responsible for the low copper yield in shaking flask.

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  • Bubble Formation from a Two-Hole Nozzle Attached to a Top Lance

    Akira Hiratsuka, Shintaro Ooishi, Ryoji Tsujino, Masaharu Hashimoto, Kazuo Ohmi, Manabu Iguchi

    pp. 2618-2624

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    DOI:10.2320/matertrans.MRA2008128

    Abstract

    Submerged powder injection is widely used for steel refining processes. Powder is usually injected downwards through a single-hole nozzle or horizontally through a two-hole nozzle attached to a top lance into the molten metal bath with carrier gas. In this study we investigate fundamentally horizontal injection through a two-hole nozzle to enhance the refining efficiency of the processes. As a first step, experimental investigation is carried out on the bubble formation from the two-hole nozzle in the case that only gas is injected into the bath. Two types of bubble formation patterns are observed depending on the gas flow rate: synchronized and non-synchronized bubble formations. A synchronization ratio is newly introduced in this study to describe the degree of synchronization. The frequency of bubble formation at each nozzle is measured with a high-speed video camera and compared with existing empirical equations for a single-hole nozzle because no empirical equation is available for the frequency of bubble formation for a two-hole nozzle.

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

  • Free Energy Problem for the Simulations of the Growth of Fe2B Phase Using Phase-Field Method

    Raden Dadan Ramdan, Tomohiro Takaki, Yoshihiro Tomita

    pp. 2625-2631

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    DOI:10.2320/matertrans.MRA2008158

    Abstract

    The present simulation works develop phase-field method to replicate the growth of Fe2B boride from austenite phase. The present works also give a major concern on the free energy driving force problem for this transformation. In order to enhance the reliability of this study, free energy driving force is left as the only variable parameter to be optimized while other parameters were taken from experimental data. Several sets of free energy have been established based on the thermo-chemical database and the assumption that there is a parabolic relationship between free energy of boride/austenite and boron concentration. On the other hand, in order to allow the growth of single Fe2B phase, temperature of 1223 K has been chosen as the evaluated temperature. Based on the comparison of the present numerical results and available experimental data, one set of free energy has been considered to give the appropriate condition that approaching the experimental condition for the growth of Fe2B from austenite phase.

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

  • Observation of Light-Induced Drift Effect of Rubidium by Using Two Diode Lasers for Pumping and Re-Pumping

    Masaya Okamoto, Takahiro Nakamura, Shunichi Sato

    pp. 2632-2635

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    DOI:10.2320/matertrans.MRA2008193

    Abstract

    The light-induced drift (LID) of rubidium was demonstrated by using two diode lasers for the pumping and re-pumping of rubidium atoms. The isotope composition ratio for 85Rb and 87Rb was estimated by measuring the absorption spectrum of the rubidium vapor.

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  • Distribution of Cobalt between MgO-Saturated FeOx-MgO-CaO-SiO2 Slag and Fe-Cu-Co Molten Alloy

    Shin-ya Kitamura, Hideki Kuriyama, Nobuhiro Maruoka, Katsunori Yamaguchi, Akira Hasegawa

    pp. 2636-2641

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    DOI:10.2320/matertrans.MAW200831

    Abstract

    During the decommissioning phase of a nuclear reactor, most of the steel-reinforced concrete shielding around a pressure vessel is considered as low-level radioactive waste. It is highly desirable to reduce the radioactivity level of this waste to below the clearance level. Normally, the radioactivity of steel after irradiation is found to be proportional to the cobalt content. In this study, for the production of low-activation steel in steelmaking process, cobalt distribution between MgO-saturated FeOx-MgO-CaO-SiO2 slag and Fe-Cu-Co molten alloy was investigated. The results are summarized as follows: (1) the distribution ratio increases with decreasing temperature and (2) the activity coefficient of CoO decreases with increasing temperature and decreasing slag basicity. Although low temperature and low basicity are suitable conditions for refining, it is extremely difficult to decrease the Co content by an oxidation reaction, because of a very small distribution ratio of cobalt.

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  • Solvent Extraction of Mn(II) from Strong Hydrochloric Acid Solutions by Alamine336

    Man Seung Lee, M. Filiz

    pp. 2642-2647

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    DOI:10.2320/matertrans.MRA2008213

    Abstract

    Solvent extraction reaction of Mn(II) by Alamine336 from strong HCl solution up to 10 kmol/m3 was identified from the experimental data by using slope analysis method. The equilibrium constant for this solvent extraction reaction was estimated by considering the complex formation reactions between Mn(II) and chloride ion. The activity coefficients of solutes present in the aqueous phase were calculated by Bromley equation. The necessary thermodynamic parameters for the formation of MnCl+ were evaluated from the data reported in the literature. The measured distribution coefficients of Mn(II) agreed well with those calculated in this study.

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  • Pitting Corrosion Resistance of Anodized Aluminum-Copper Alloy Processed by Severe Plastic Deformation

    In-Joon Son, Hiroaki Nakano, Satoshi Oue, Shigeo Kobayashi, Hisaaki Fukushima, Zenji Horita

    pp. 2648-2655

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    DOI:10.2320/matertrans.MRA2008216

    Abstract

    The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L of AlCl3 and also by surface analysis. The time required before initiating pitting corrosion of anodized Al-Cu alloy was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. Second phase precipitates were present in Al-Cu alloy matrix and the size of these precipitates was greatly decreased by application of ECAP. The precipitates composed of Si and Al-Cu-Si-Fe-Mn were not oxidized during anodization, and the anodic oxide film were absent at the boundary between the normal oxide films and these impurity precipitates. The pitting corrosion of anodized Al-Cu alloy occurred preferentially around these precipitates, the improvement of pitting corrosion resistance of anodized Al-Cu alloy by ECAP appears to be attributable to a decrease in the size of precipitates, which act as origins of pitting corrosion.

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  • Effect of Annealing on the Pitting Corrosion Resistance of Anodized Aluminum-Magnesium Alloy Processed by Severe Plastic Deformation

    In-Joon Son, Hiroaki Nakano, Satoshi Oue, Shigeo Kobayashi, Hisaaki Fukushima, Zenji Horita

    pp. 2656-2663

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    DOI:10.2320/matertrans.MRA2008230

    Abstract

    The effect of annealing on the pitting corrosion resistance of anodized Al–Mg alloy processed by equal-channel angular pressing (ECAP) was investigated by electrochemical techniques in a solution containing 0.2 mol·L−1 of AlCl3 and also by surface analysis. The degree of internal stress generated in anodic oxide films during anodization was evaluated with a strain gauge. The ECAP decreased the pitting corrosion resistance of anodized Al–Mg alloy. However, the pitting corrosion resistance was improved by annealing after the ECAP. The internal stress present in the anodic oxide films was compressive, and the stress was higher in the alloys with ECAP than without. The compressive internal stress gradually decreased with increasing annealing temperature. Cracks occurred in the anodic oxide film on Al–Mg alloy during initial corrosion. The ECAP produces high internal stresses in the Al–Mg alloy; the stresses remain in the anodic oxide films, increasing the likelihood of cracks. It is assumed that the pitting corrosion is promoted by these cracks as a result of the higher internal stress resulting from the ECAP. The improvement in the pitting corrosion resistance of anodized Al–Mg alloy by annealing appears to be attributable to a decrease in the internal stresses in anodic oxide films.

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  • Microstructure and Thermal Properties of Squeeze Cast Aluminum Alloy Composite Reinforced with Short Potassium Titanate Fiber

    Kazunori Asano, Hiroyuki Yoneda, Yasuyuki Agari

    pp. 2664-2669

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    DOI:10.2320/matertrans.F-MRA2008833

    Abstract

    Aluminum alloy composites reinforced with the short potassium titanate fibers were fabricated to obtain a material having a low thermal expansion rate and good machinability. The composites were fabricated by the squeeze casting. The microstructure, thermal conductivity and thermal expansion behavior of the composites were investigated. Optical microscopy revealed that the fibers were homogeneously distributed in the alloy. However, the fibers were somewhat in a random planar arrangement parallel to the pressed plane when the fiber volume fraction was high. This is due to the forming of the preform by pressing the top and bottom of it. The composites were easily machined using both super alloy and diamond cutting tools. The thermal conductivity of the composite decreased as the fiber volume fraction increased. At the higher volume fraction, the thermal conductivity of the composite in the direction parallel to the pressed plane was higher than that in the transverse direction due to the random planar arrangement of the fibers. The thermal conductivity can be roughly estimated by Landauer’s model. The average thermal expansion coefficient of the composite decreased as the fiber volume fraction increased. The difference in the thermal expansion coefficient between the parallel and transverse directions to the pressed plane was slight, and the experimental values were in good agreement with the theoretical values calculated using the rule of mixture.

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  • An Effect of Addition of NiO Powder on Pore Formation in Lotus-Type Porous Nickel

    H. Onishi, S. Ueno, H. Nakajima

    pp. 2670-2672

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    DOI:10.2320/matertrans.MRA2008150

    Abstract

    Lotus-type porous nickel with cylindrical pores was fabricated by unidirectional solidification in a mixture gas of hydrogen and argon. The pore size is significantly affected by the addition of NiO powder. The pore size decreases and the number density of the pores increases by the addition of NiO. It is concluded that NiO powder can serve as nucleation sites for the pore formation in the process of the solidification.

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  • Carbide Synthesis from Graphite/molybdenum Powder Mixtures at Sub-Stoichiometric Ratios under Solar Radiation Heating to 1900°C

    Bernard Granier, Jean-Marie Badie, Fernando Almeida Costa Oliveira, Teresa Magalhães, Nobumitsu Shohoji, Luis Guerra Rosa, Jorge Cruz Fernandes

    pp. 2673-2678

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    DOI:10.2320/matertrans.MRA2008202

    Abstract

    A solar furnace at PROMES-CNRS in Odeillo (France) is with very unique capacity of heating the specimen material from ambient temperature to a target temperature exceeding 2000°C within fractions of a second in arbitrary gas environment with pressure no higher than 1 atm. In the preceding work on the Mo-C synthesis using this solar furnace with the set target temperature 1600°C, evidence of formation of η-MoC1−x besides α-Mo2C (the low temperature phase of Mo2C) was confirmed under presence of excess free carbon (graphite). The η-MoC1−x is known to be stable at temperatures between 1650°C and 2500°C with range of x between 0.25 and 0.35. Thus, in the present work, carbide synthesis experiments were carried out for compacted powder mixtures between graphite and molybdenum at C/Mo mole ratios, 2/3 and 3/4, as well as the ratios, 1/2 and 1/1, as the references in the solar furnace at Odeillo under application of the ultra-fast heating rate to the set target temperature 1900°C in search of favourable processing condition for η-MoC1−x synthesis. The gained experimental evidences indicated that, at any chosen C/Mo ratio in the starting powder compact, formation of β-Mo2C (the high temperature phase of Mo2C) took place preferentially while certain proportion of the η-MoC1−x formed besides the β-Mo2C from the powder compacts with C/Mo mole ratios, 2/3 and 3/4.

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  • Synthesis of Mg-Al Alloys by Bulk Mechanical Alloying (BMA) and Their Hydrogen Solubility

    Tohru Nobuki, Jean-Claude Crivello, Toshiro Kuji

    pp. 2679-2685

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    DOI:10.2320/matertrans.MRA2008155

    Abstract

    In this work, the Mg17Al12 phase was successfully synthesized by the Bulk Mechanical Alloying (BMA), based on repeating compression and extrusion cycles in a metallic die. After 2000 cycles of compression and extrusion, nano-structural Mg17Al12 phase was obtained in molded bulk shape.
    X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and differential scanning calorimetry (DSC) analyses were carried out to determine the morphology, phase structure of BMA-ed samples.
    The qualitative and quantitative analysis of phase abundance, evolution of microstructure and distribution of particles size were studied.
    It was shown that the Mg17Al12 alloy is able to absorb a large amount of hydrogen, higher than 3 mass% of Hydrogen.

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  • In Situ Synthesis and Compressive Deformation Behaviors of TiC Reinforced Magnesium Matrix Composites

    Wei Cao, Congfa Zhang, Tongxiang Fan, Di Zhang

    pp. 2686-2691

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    DOI:10.2320/matertrans.MRA2008157

    Abstract

    TiC reinforced magnesium matrix composites (Mg-MMCs) were successfully synthesized by spontaneously infiltrating the molten magnesium into Ti-C preforms, simultaneously in situ forming TiC particles in the liquid of magnesium alloy. The compressive deformation behaviors of TiC reinforced Mg-MMCs were further investigated by means of uniaxial compression tests at strain rates between 10−3 s−1 and 1 s−1 and temperature between room temperature and 200°C. Early fracture was observed in the low-temperature/high strain rate regime, fracture occurring by crack propagation at 45 degree with respect to the compression axis. In high-temperature/low strain rate regime, the flow curves exhibited the typical flow softening shape. The results show that with the addition of TiC particles Mg-MMCs can effectively improve compressive properties of magnesium matrix at testing temperature interval. When compared to the unreinforced counterpart, TiC reinforced Mg-MMCs need higher temperature and lower strain rate to avoid premature fracture.

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  • Influence of Rapid Homogeneous Irradiation of Electron Beam with Low Energy (RHIEBL) on Water Absorption into Nylon6

    Yoshitake Nishi, Ryuichi Suenaga, Alain Vautrin

    pp. 2692-2697

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    DOI:10.2320/matertrans.MRA2008151

    Abstract

    In order to evaluate the influence of rapid homogeneous irradiation of electron beam with low potential (RHIEBL) on absorption phenomena of boiled water into nylon6, the absorbed mass of water in nylon6 has been measured. The RHIEBL decreases the saturated mass of water absorption in nylon6 and also decreases the initial absorption rate of water, as well as the absorption mass of water in nylon6 at each treatment time. Since the RHIEBL increases the initial reaction index from 1/2 to 2/3, RHIEBL changes the initial mode of water absorption, as well as decreases the absorbed mass of water. Based on the results of ESR and XPS, the RHIEBL forms dangling bonds and then decreases the electrical polarization of nylon6 molecules, resulting in a decrease of the mass of water absorption into nylon6.

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  • Effect of Ball-Milling on the Properties of Mg2Cu Hydrogen Storage Alloy

    M. X. Tanaka, N. Takeichi, H. T. Takeshita, T. Kiyobayashi

    pp. 2698-2701

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    DOI:10.2320/matertrans.MRA2008183

    Abstract

    We investigated by differential scanning calorimetry the effect of ball milling on the hydrogenation properties of Mg2Cu, a hydrogen storage alloy, prepared by two methods: One is mechanically alloyed Mg2Cu using Mg and Cu powders as starting materials. Eight hours (=28.8 ks) of ball milling transformed the Mg:Cu=2:1 mixture into Mg2Cu single phase which reacts reversibly with hydrogen. The other is prepared by ball milling a cast Mg2Cu alloy. While the as-cast Mg2Cu undergoes neither hydrogenation nor dehydrogenation under 3 MPa of hydrogen in the temperature range of 300–773 K, just an hour of ball milling activates the inert Mg2Cu to react with hydrogen reversibly. Examining the milling period dependency of the particle size, crystallite size, activation energy and the apparent heat of dehydrogenation which reflects the fraction of activated part in a specimen, we found that the ball milling firstly influenced the particle size and the activated fraction of the sample, and then followed the effect on the crystallite size and kinetic properties. We also found that a trace amount of oxygen could significantly spoil the benefits brought by the ball milling for longer period of milling.

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  • Effects of Welding Parameters on the Mechanical Performance of Laser Welded Nitinol

    M. I. Khan, S. K. Panda, Y. Zhou

    pp. 2702-2708

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    DOI:10.2320/matertrans.MRA2008243

    Abstract

    The excellent pseudoelasticity, shape memory and biocompatibility of Nitinol has made it a leading candidate for various applications, including aerospace, micro-electronics and medical devices. Challenges associated with the welding Nitinol need to be resolved before its full potential in practical applications can be attained. The current study details the effects of process parameters on the mechanical and pseudoelastic properties of Ni-rich pulsed Nd:YAG laser welded Nitinol. The weld strength, pseudoelastic and cyclic loading properties for varying welding parameters are compared to those of the base metal. Furthermore, fracture surfaces have been analysed and detailed. Results show that process parameters greatly influence the mechanical performance and fracture mode of weldments.

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  • Hardness and Stress-Strain Curves of Al-Zn-Mg-Cu Alloy Single Crystals

    Sei Miura, Takuro Mimaki, Shinji Moriwaki, Nagato Ono

    pp. 2709-2713

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    DOI:10.2320/matertrans.MER2008178

    Abstract

    The present paper describes the variations of the mechanical properties of Al-Zn-Mg-Cu alloy single crystals with various aging times. The cylindrical single crystals of 7475 aluminum alloys were produced at 1033 K by the Bridgeman method, where the composition of initial material and the shape of carbon mold were modified for the growth of quaternary crystals. The specimens proper for tensile and hardness testing were obtained from the single crystal rod homogenized at 823 K for 900 ks using spark-cutting method. Subsequently, they were aged at 393 K for 3.6, 86.4, 900 and 2880 ks after quenching in ice water from 773 K. In the stress-strain curves of the alloy single crystals, the increase of yield stress and the decrease of elongation with an increase of aging time are seen together with a decrease in the rate of work hardening. Moreover, some serrations occur especially in the final plastic stage on the curves. Hardness of the alloy single crystals agrees with those of polycrystals due to the occurrence of multiple slips during loading. However, the alloy single crystals exhibit a marked decrease of yield strength in comparison with the polycrystals, which results from a single glide occurring in the single crystals. If we compare the increase of critical resolved shear stress (CRSS) derived from two kinds of theories of precipitation with the experimental value, both of them are roughly in agreement except for the specimen aged for 3.6 ks. The obtained results indicate that the maximum strength of Al-Zn-Mg-Cu alloy single crystals is achieved in the transitional process between the mechanism of particle cutting and the Orowan mechanism.

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  • Effect of Microstructure on the Mechanical Behavior of Reactive Magnetron Sputtered Al2O3/TiO2 Multilayer Ceramics

    A. F. Dericioglu

    pp. 2714-2722

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    DOI:10.2320/matertrans.MER2008055

    Abstract

    Mechanical characteristics of reactive magnetron sputtered Al2O3–TiO2 multilayer ceramics were studied. Tailored mechanical properties such as moderately high hardness and reasonable toughness were achieved through varying sputtering process parameters resulting in microstructural control at nano-scale. Interchanging Al2O3 and TiO2 layers with a single layer thickness of ∼65–70 nm were deposited on single crystal alumina (sapphire) substrates to form the multilayer structure composed of 10 layers. Deposition pressure was systematically changed throughout the process to obtain variety of microstructures. Nanostructured Al2O3 and TiO2 layers with a high degree of uniformity and interlayer bonding were obtained. The effect of the deposition pressure on the microstructure, and hence the ensuing physical characteristics of the multilayer ceramics were investigated. Resulting physical property sets were discussed in relation to the nanometer-order controlled microstructures. Potential of the nanostructured Al2O3–TiO2 multilayer ceramics for advanced engineering applications in terms of their processing and capacity for improved mechanical properties were addressed.

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  • Formation of Porous Intermetallic Thick Film by Ni-Al Microscopic Reactive Infiltration

    Tatsuya Ohmi, Naoya Hayashi, Manabu Iguchi

    pp. 2723-2727

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    DOI:10.2320/matertrans.MER2008188

    Abstract

    Microporous structures of nickel-aluminide thick films lining the inner wall of microchannels have been investigated. The microchannels were produced in metal bodies by a powder metallurgical process utilizing microscopic reactive infiltration. In the experiment, a nickel-powder compact containing shaped aluminum wires was sintered at a temperature between the melting points of nickel and aluminum. Infiltration and diffusion of aluminum into the surrounding nickel powder, accompanied by the reaction between the metals, occurred during the sintering and brought about the formation of microchannels lined with a NiAl intermetallic layer. In this process, nickel powder composed the device body, and the aluminum wires gave the shape of the microchannels. The intermetallic layer had a microporous structure when the diameter of the aluminum wire was 500 μm and the porosity of the compact specimen was 23.6–31.5% within the porosity range examined. When the porosity was 36.0%, such a structure, the porous thick film, was not observed. On the other hand, the porous NiAl thick film was produced in all specimens with an aluminum wire of 200 μm in diameter. The voidage of the porous thick film was maximized when the porosity of the compact specimen was 29.8%, and it reached to 53.8% in the case the diameter of the aluminum wire was 500 μm, and 60.2% in the case that was 200 μm.

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  • Room Temperature Aging Characteristic of MgLiAlZn Alloy

    Chang-Chan Hsu, Jian-Yih Wang, Shyong Lee

    pp. 2728-2731

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    DOI:10.2320/matertrans.MER2008225

    Abstract

    Making alloys of Mg and Li is quite a task as their individual melting temperatures are vastly different. However, it is thought paid off considering their extreme lightness. Basically, low melting temperature Li could cause Mg-Li alloys’ microstructures change at room temperature (R.T.). Recrystallization and aging of Li-rich solid solution phase (β) can proceed under R.T. Previously, R.T. aging phenomenon was mentioned without in-depth analysis. This paper fills up the blank by working on Mg-11.2%Li-0.95%Al-0.43%Zn (mass%), mainly due to the TEM work brought in. With this apparatus for analysis, a transition precipitate (tentatively called pre-θ phase) is revealed. This pre-θ precipitation is responsible for the distinctive strengthening in the initial stage of R.T. aging. However, it is unstable and subsequently transforms to θ or α phase. Both of these later precipitates are little effective in producing aging strengthening.

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  • Improvement of Plasticity in Pd Containing Zr-Al-Ni-Cu Bulk Metallic Glass by Deformation-Induced Nano Structure Change

    Junji Saida, Albertus Deny Setyawan, Hidemi Kato, Mitsuhide Matsushita, Akihisa Inoue

    pp. 2732-2736

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    DOI:10.2320/matertrans.MER2008162

    Abstract

    We have prepared Zr-Al-Ni-Cu-Pd bulk metallic glasses (BMGs) cast in an ambient Ar atmosphere, in which the cooling effect is enhanced. The Zr65Al7.5Ni10Cu17.5−xPdx (x=1–5) BMGs exhibit a good plasticity during the compressive deformation process. A significant plasticity of 6% plastic strain is obtained in the Zr65Al7.5Ni10Cu12.5Pd5 BMG, where the deformation mode with multi shear bands appears near the fracture surface. Nanocrystalline particles are arranged in a band-like formation in the glassy matrix around the multi shear bands, indicating the restraint of shear band propagation owing to the dynamic precipitation of the nanocrystals. The unrelaxed structure owing to the higher cooling rate in the present condition may also contribute to the good plasticity.

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  • Nanostructured CrAlN Films Prepared at Different Pulse Widths by Pulsed DC Reactive Sputtering in Facing Target Type System

    Sara Khamseh, Masateru Nose, Shohei Ueda, Tokimasa Kawabata, Takekazu Nagae, Kenji Matsuda, Susumu Ikeno

    pp. 2737-2742

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    DOI:10.2320/matertrans.MER2008249

    Abstract

    CrAlN films have been prepared using a pulsed DC reactive sputtering in FTS system with Cr/Al alloy (=50⁄50 at%) targets in a mixed atmosphere of Ar and N2. The effects of pulse width on the film structure and properties have been investigated. XRD analyses were carried out to determine the phases and texture of the films. Transmission electron microscopy studies were carried out for selected films. In order to investigate the relationship between the mechanical properties and microstructure of the films, the hardness was measured by a nanoindentation system. Films prepared at lower pulse widths, exhibited fcc-CrN structure. In contrast, films that were prepared at higher pulse widths showed a mixed structure of hcp-AlN, hcp-Cr2N and a small amount of fcc-CrN phases. Plastic hardness, Hpl, of the films ranged between 32 to 41 GPa while the Young’s modulus, EIT, of the films ranged from 320 to 340 GPa. Increasing the pulse width also resulted in an increase in the film’s internal stress. In addition, the grain size of the samples decreased with increasing pulse width.
    Consequently, the film deposited at higher pulse width exhibited high hardness of 41 GPa, H3⁄E2 ratio of ∼0.6 and relatively lower internal stress of −3.5 Gpa. These results indicated that changing the pulse width can strongly affect structure and properties of CrAlN films, resulting in a good combination of mechanical and tribological properties, under proper conditions in a pulsed DC Balanced Magnetron Sputtering system.

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  • Unusual Glass-Forming Ability of New Zr-Cu-Based Bulk Glassy Alloys Containing an Immiscible Element Pair

    Qingsheng Zhang, Wei Zhang, Akihisa Inoue

    pp. 2743-2746

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    DOI:10.2320/matertrans.MEP2008212

    Abstract

    We herein report the unusual glass-forming ability (GFA) of a new series of quinary Zr48Cu36−xNixAg8Al8 (0<x≤10 in at%) alloys, in which Ni-Ag element pair is an immiscible system with a large positive heat of mixing. Addition of Ni lowers the liquidus temperature of the quaternary Zr48Cu36Ag8Al8 alloy. By copper mold casting, an as-cast glassy rod with a diameter of 30 mm can be easily obtained for the representative alloy Zr48Cu32Ni4Ag8Al8. The possible reasons for the excellent GFA of the new quinary alloys with an immiscible element pair are discussed based on the atomic size distribution, chemical compatibility among the components and atomic structure of glassy alloys.

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  • Control of Al Content in Mg Melt by Addition of ZrCl4

    Chang Dong Yim, Bong Sun You, Hyung Kyu Park

    pp. 2747-2750

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    DOI:10.2320/matertrans.MRP2008246

    Abstract

    ZrCl4 was added into Mg-0.3Al model alloy in order to reduce the Al content in the castings below 0.005 mass%. Amount of ZrCl4 was determined by thermodynamic calculation. Various Al-Zr intermetallic compounds were formed in the melt at 1013 K. Large intermetallic compounds would be floated to melt surface by Ar bubbling and then removed by skimming before pouring. Smaller ones remained after Ar bubbling and isothermal holding would be partially removed by filter inserted into a mold during pouring. The Al content in the castings was higher than that predicted by thermodynamic calculation due to incomplete removal of Al-Zr intermetallic compounds from the melt.

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  • Differential Scanning Calorimetry Measurements of Magnesium Borohydride Mg(BH4)2

    Yigang Yan, Hai-Wen Li, Yuko Nakamori, Nobuko Ohba, Kazutoshi Miwa, Shin-ichi Towata, Shin-ichi Orimo

    pp. 2751-2752

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    DOI:10.2320/matertrans.MEP2008224

    Abstract

    Multistep dehydriding reactions of magnesium borohydride Mg(BH4)2 were studied by Differential Scanning Calorimetry (DSC) measurements. The values of the enthalpy changes of the reactions from the measurements are in good agreement with those from first-principles calculations. Kinetically restricted dehydriding reaction of Mg(BH4)2, suggested also by the measurements, was briefly discussed.

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  • Three-Dimensional Observation of Dislocations by Electron Tomography in a Silicon Crystal

    Masaki Tanaka, Masaki Honda, Masatoshi Mitsuhara, Satoshi Hata, Kenji Kaneko, Kenji Higashida

    pp. 2753-2753

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    DOI:10.2320/matertrans.E2008002

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  • © 2008 The Japan Institute of Metals and Materials

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