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

MATERIALS TRANSACTIONS Vol. 47 (2006), No. 11

  • Diffusion Monte Carlo Study of Atomic Systems from Li to Ne

    Kenta Hongo, Yoshiyuki Kawazoe, Hiroshi Yasuhara

    pp. 2612-2616

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    DOI:10.2320/matertrans.47.2612

    Abstract

    A systematic diffusion Monte Carlo (DMC) study of both neutral and charged atomic systems from Li to Ne in the ground state is performed to evaluate the correlation energy (Ec), the ionization energy (IE), and the electron affinity (EA) of these systems. The present study is based on the fixed-node approximation in which the nodal surfaces of the DMC wavefunction is assumed to be the same as those of the Hartree-Fock wavefunction. The present calculations reproduce 90±7% of the exact value of correlation energy for the cations, 91±3% for the neutral atoms, and 92±2% for the anions, respectively. The theoretical values of IE and EA in the present study are in good agreement with experimental values within an accuracy of 0.3 eV for IE and 0.1 eV for EA. The variation of Ec and IE with respect to the atomic number Z is interpreted.

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  • Quantum Monte Carlo Study of Electron Correlation in Chromium-Doped Silicon Cluster Cr@Si12

    Kenta Hongo, Vijay Kumar, Yoshiyuki Kawazoe, Hiroshi Yasuhara

    pp. 2617-2619

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    DOI:10.2320/matertrans.47.2617

    Abstract

    Electron correlation in chromium-doped silicon cluster (Cr@Si12) in its neutral, positively, and negatively charged states with different nuclear configurations is investigated by means of quantum Monte Carlo methods. It is found that the correlation energy per electron is independent of whether the state is charged or not and about −1 eV for each of these three states. The total binding energy of the neutral state per atom is 3.5 eV, which is divided into the Hartree-Fock contribution nearly equal to 1.2 eV and the correlation contribution as large as 2.3 eV. In the Hartree-Fock approximation, the ionization energy is 6.9 eV and the electron affinity is 2.7 eV. Correlation increases the ionization energy by 1.7 eV and the electron affinity by 1.4 eV.

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  • All-Electron GW Calculation for Quasiparticle Energies in C60

    Hitoshi Adachi, Soh Ishii, Kaoru Ohno, Kyoko Ichinoseki, Yoshiyuki Kawazoe

    pp. 2620-2623

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    DOI:10.2320/matertrans.47.2620

    Abstract

    By carrying out an all-electron GW calculation, we firstly obtain quasiparticle energies of C60 molecule without any experimental information. The amount of computation of GW calculation is propotional to the order of N6 (N = number of electrons) far more than the case of the standard LDA of N3 for such a large system. The GW program code has been parallelized using MPI and actual computaions are performed on several supercomputers within the Nanotechnology-VPN under ITBL environment.

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  • Theoretical Investigation of Stable Structures of Ge6 Clusters with Various Negative Charges

    Hideki Kikuchi, Masae Takahashi, Yoshiyuki Kawazoe

    pp. 2624-2628

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    DOI:10.2320/matertrans.47.2624

    Abstract

    Nine isomers of Ge6, Ge62-, Ge64-, and Ge66- have been searched for by the MP2/6-31+G(d), B3LYP/6-311+G(d), and B3LYP/LANL2DZ electronic structure calculations. Totally 16 isomers are found: six Ge6, three Ge62-, five Ge64-, and two Ge66-. We discovered that the predicted stable shapes of Ge62-, Ge64-, and Ge66- are octahedral, pentagonal pyramidal, and hexagonal, respectively, which agrees well with the Wade rule. It is concluded that the electron counting rule governs the structural preference in Ge anion clusters as well as in Si anion clusters.

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  • First-Principles Study of C6M2 (M=B, Al, Mg, Li), C7B and Related Compounds

    Kazuaki Kobayashi, Masao Arai, Kazuo Yamamoto

    pp. 2629-2637

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    DOI:10.2320/matertrans.47.2629

    Abstract

    We calculate electronic and lattice dynamics properties of C6M2 (M=B, Al, Mg, Li), C7B, AlC2, MgC2, LiC2 and LiB2 compounds. The electronic and lattice properties are optimized automatically by the first-principles molecular dynamics (FPMD) method. The present electronic structure calculation is based on the local density approximation (LDA) in the density functional theory (DFT). C6M2 (M=B, Al, Mg, Li) and C7B compounds are hypothetical hexagonal layered materials. They consist of C-C and M-C layers in a unit cell. The electronic band structures of them are found to be metallic. Several compounds have unoccupied flat bands above the Fermi level along the A-Γ line. These flat bands are similar to those of MgB2. Lattice dynamics properties (phonon frequencies) of them are calculated in order to investigate lattice stabilities in this study. Calculated phonon frequencies of them are imaginary with the exception of LiB2. Imaginary phonon frequencies imply that it is structurally unstable. Most of calculated compounds are cohesively unfavorable. Although the cohesive energy of LiB2 is positive, the value is quite small with 7.2 meV/LiB2. Cohesive energies of other compounds are positive and larger than 0.17 eV.

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  • Electronic Structure Calculations of Carbon Nanomaterials

    Shuji Obata

    pp. 2638-2645

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    DOI:10.2320/matertrans.47.2638

    Abstract

    Various carbon materials have been discovered in recent years, and their characteristics are remarkably interested in applications to new devices. In particular, the investigation of carbon nanomaterials has markedly progressed in physics and in industry. In many studies, conduction bands in carbon sheets have been treated as the antibonding states of sp2 orbitals. In contrast, in this work, excited states as in the Hubbard model are assumed and are added to the previous ground states. These excited states are set as singlet spin states composed of 2pz (3s) orbitals, which have the same character as the valence bond singlet spin state. The electronic structures of these materials are calculated on the basis of the LCVB tight-binding theory. The calculated results clearly explain the energy states of benzene. The conductive states in graphite sheets are also accurately obtained from the experimental data by including the proposed excited states. The electronic structures of nanotubes are characterized with several types of compositions related to band gaps and the Fermi levels. The characteristic sharp peak adjacent to the Fermi level in the conduction band is realistically represented in each calculation.

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  • First Principles Calculation of Defect and Magnetic Structures in FeCo

    Masataka Mizuno, Hideki Araki, Yasuharu Shirai

    pp. 2646-2650

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    DOI:10.2320/matertrans.47.2646

    Abstract

    First-principles electronic structure calculations have been performed for defect and magnetic structures in FeCo. The compositional dependence curves both of formation energies and lattice parameters are obtained by calculations employing supercells of various sizes. The vacancy formation energies are calculated with taking into account the compositional dependence of chemical potentials. Antisite atoms compensate the deviation from the stoichiometric composition both in Fe-rich and in Co-rich FeCo. The compositional dependence of magnetic moments is well explained by the electronic structures of antisite atoms. The vacancy formation energies obtained in the present work show a better agreement with the experimental value than those previously reported.

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  • First-Principles Calculation of Point Defects in Uranium Dioxide

    Misako Iwasawa, Ying Chen, Yasunori Kaneta, Toshiharu Ohnuma, Hua-Yun Geng, Motoyasu Kinoshita

    pp. 2651-2657

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    DOI:10.2320/matertrans.47.2651

    Abstract

    A first-principles calculation for uranium dioxide (UO2) in an antiferromagnetic structure with four types of point defects, uranium vacancy, oxygen vacancy, uranium interstitial, and oxygen interstitial, has been performed by the projector-augmented-wave method with generalized gradient approximation combined with the Hubbard U correction. Defect formation energies are estimated under lattice relaxation for supercells containing 1, 2, and 8 unit cells of UO2. The electronic structure, the atomic displacement and the stability of defected systems are obtained, and the effects of cell sizes on these properties are discussed. The results form a self-consistent dataset of formation energies and atomic distance variations of various point defects in UO2 with relatively high precision. We show that a supercell with 8 UO2 unit cells or larger is necessary to investigate the defect behavior with reliable precision, since point defects have a wide-ranging effect, not only on the first nearest neighbor atoms of the defect, but on the second neighbors and on more distant atoms.

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  • Solitonic Migration and Collisions of Self-Interstitial Defects in BCC Iron

    Katsuyuki Kusunoki

    pp. 2658-2662

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    DOI:10.2320/matertrans.47.2658

    Abstract

    Self-interstitial atoms in bcc iron display unusual migration behaviors; strong anisotropy toward a ⟨111⟩ direction with occasional rotation to an equivalent direction as well as retracing the same way as it has come, and also ultra-high mobility when they are clustered. These singularities cannot be explained by simple interstitial or interstitialcy diffusion mechanisms. However, some of them will be well accounted if the SIA could behave as a soliton, which makes three-dimensional movements in appearance, but essentially a serial combination of one-dimensional migration. Indeed, a crowdion, one of isomeric configurations of the self-interstitial atom, has an atomic arrangement very similar to the one-dimensional dislocation core structure, whose migration kinetics has been well modelled by a one-dimensional soliton equation. Here we report a decisive observation that both a single and colliding two crowdions really behave as solitons in iron crystals using molecular dynamics simulations. In addition, we ascertain that the present results are attributed to the intrinsic nature of the crowdion where an overall potential felt by atoms therein is very shallow and periodical along the migration direction.

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  • Study of Interaction between Au and TiO2(110) at Low Coverage

    Kazuyuki Okazaki-Maeda, Yasushi Maeda, Yoshitada Morikawa, Shingo Tanaka, Masanori Kohyama

    pp. 2663-2668

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    DOI:10.2320/matertrans.47.2663

    Abstract

    We have investigated the interaction between Au and a rutile TiO2(110) surface at low coverage, using density functional theory. We have examined Au adsorption on three types of TiO2(110) surface with different stoichiometry and structures; the stoichiometric surface, the surface formed by removing bridging-oxygen (defected surface), and the reconstructed 1×2 surface with Ti2O3 rows (added-row surface). For the stoichiometric surface, the most stable site for the Au adsorption is the on-top site above the bridging-oxygen atom. Electrons transfer from the Au adatom to the bridging-oxygen atom after adsorption. For the defected surface, the most stable adsorption site is the bridging-oxygen vacant site. For the added-row surface, the most stable adsorption site is the neighborhood of the Ti2O3 rows. For both the reduced surface, defected and added-row surfaces, electron densities between the Au and the reduced Ti atom increase after adsorption, and it seems that the Au atom covalently interacts with the reduced Ti atoms at the surface. Moreover, we compared the simulated scanning tunneling microscopy (STM) images with the experimental STM images for the added-row surface. The calculated STM images of Au adatom adsorbed near Ti2O3 rows agree with experimental images qualitatively.

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  • Electronic Structures of Ag and Au Adsorbed on TiO2(110) Surfaces by First-Principles Calculations

    Kazuyuki Okazaki-Maeda, Yoshitada Morikawa, Satoshi Ichikawa, Shingo Tanaka, Masanori Kohyama

    pp. 2669-2673

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    DOI:10.2320/matertrans.47.2669

    Abstract

    We have investigated electronic structures and charge transfers of Ag and Au supported on the TiO2(110) surface, using first-principles calculation. In order to investigate the effect of stoichiometry on the electronic structures, we examined Au and Ag adsorption on three kinds of TiO2(110) surface with different stoichiometry; the perfect stoichiometric surface, Ti-rich surface, and O-rich surface. We considered the on-top site above the bridging-oxygen atom (site A) and above the five-fold titanium atom (site B) for the perfect stoichiometric surface, the bridging-oxygen vacant site (site C) for the Ti-rich surface, and the six-fold titanium vacant site (site D) for the O-rich surface as the adsorption site. The adhesive energies between the metal layer and the TiO2(110) surface for the non-stoichiometric surfaces are much larger than that for the stoichiometric surface. And the Ag atom strongly interacts with the surface oxygen atoms at surface, while the Au atom strongly interacts with the surface titanium atoms at surface. The interaction between the metal and the TiO2(110) surface depends on the surface stoichiometry and the kind of metal species.

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  • Adsorption, Bond Formation and Graphitization of Carbon Atoms on Ni(111) Surface

    Yoshihiro Shamoto, Masato Aoki

    pp. 2674-2677

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    DOI:10.2320/matertrans.47.2674

    Abstract

    Adsorption, bond formation and graphitization of carbon atoms on Ni(111) surface are investigated using full-potential linear muffin-tin orbital method with Ni(111) surface modeled by a bilayer slab. The present calculations show that the adsorption of a single carbon atom onto the Ni surface occurs on fcc and hcp hollow sites and on the on-top site with strong C-Ni bonds. When another carbon atom approaches the adatom, they form stronger C-C bonds to form single-layer graphene. At the same time, C-Ni bonds are weakened and the graphene tends to float on the surface. The stationary properties of the floating graphene are also examined.

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  • Effects of Segregated Ga on an Al Grain Boundary: A First-Principles Computational Tensile Test

    Ying Zhang, Guang-Hong Lu, Tianmin Wang, Shenghua Deng, Masanori Kohyama, Ryoichi Yamamoto

    pp. 2678-2681

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    DOI:10.2320/matertrans.47.2678

    Abstract

    We perform a first-principles computational tensile test (FPCTT) to investigate the effect of segregated Ga (substitutional) on an Al grain boundary (GB). We show that isolated Ga segregation has little effect on the tensile strength of the Al GB, but greatly reduces the toughness and the Griffith fracture energy. The interfacial Al-Ga bond with some ionic character is suggested to be responsible for the nearly unchanged tensile strength and the toughness reduction. Based on the bond length evolution result, we further demonstrate that GB fracture is directly associated with interfacial Al-Ga bonds.

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  • Grain Boundary Decohesion by Sulfur Segregation in Ferromagnetic Iron and Nickel —A First-Principles Study—

    Masatake Yamaguchi, Motoyuki Shiga, Hideo Kaburaki

    pp. 2682-2689

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    DOI:10.2320/matertrans.47.2682

    Abstract

    Using first-principles calculations, we simulate grain boundary decohesion (embrittlement) in ferromagnetic bcc FeΣ3(111)[1\\bar10] and fcc NiΣ5(012)[100] symmetrical tilt grain boundaries by progressively adding sulfur atoms to the boundaries. We calculate the segregation energy of sulfur atom, tensile strength, and cohesive energy of the grain boundaries. We show that a certain amount of sulfur segregation (two atomic layers, 14.4 atom/nm2) is energetically possible to realize considering the calculated segregation energies. At this concentration, the tensile strength and the cohesive energy of the grain boundaries reduce by one order of magnitude comparing with no segregation case.

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  • First-Principles Calculations of Schottky Barrier Heights of Monolayer Metal/6H-SiC{0001} Interfaces

    Shingo Tanaka, Tomoyuki Tamura, Kazuyuki Okazaki, Shoji Ishibashi, Masanori Kohyama

    pp. 2690-2695

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    DOI:10.2320/matertrans.47.2690

    Abstract

    Schottky barrier heights (SBHs) of monolayer metal/6H-SiC{0001} interfaces have been calculated by the first-principles projector augment-wave (PAW) method in order to examine the dependence on metal species as well as surface termination of SiC. Generally, p-type SBHs of the C-terminated (000-1) interfaces are smaller than those of the Si-terminated (0001) interfaces, because of the interface dipoles caused by substantial charge transfer. The SBHs of the Si-terminated interfaces range within a relatively narrow energy region without clear correlation with metal electronegativity, although those of the C-terminated interfaces show rather specific dependence on metal electronegativity except for systems with Fe and Co. The different dependence on the metal species for the Si- and C-terminated interfaces has been analyzed from the interface electronic structure as compared with previous theoretical models and experiments.

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  • Influence of Interface Structure on Schottky Barrier Heights of α-Al2O3(0001)/Ni(111) interfaces: A First-Principles Study

    Siqi Shi, Shingo Tanaka, Masanori Kohyama

    pp. 2696-2700

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    DOI:10.2320/matertrans.47.2696

    Abstract

    The Schottky barrier heights (SBH) for α-Al2O3(0001)/Ni(111) interfaces have been examined using the first-principles pseudopotential method, and compared with our previous results of Al2O3(0001)/Cu(111) interfaces. Configurations with different rigid-body translations parallel to the interface for both the O-terminated and Al-terminated interfaces are examined to clarify the influence of the microscopic interfacial structure on the SBH. The averaged p-type value of the O-terminated interfaces is smaller than that of the Al-terminated interfaces, similar to the Al2O3/Cu interfaces, although the variation within each type of interface stoichiometry is also substantial. This indicates that the SBH depends on both the interface stoichiometry and the configuration, in contradiction with the conventional models, which can be explained by the different interface dipole associated with the charge transfer and configuration of each interface.

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  • First-Principles Study of Molecule/Al Interfaces

    Rachid Belkada, Yoshiyuki Shirakawa, Masanori Kohyama, Shingo Tanaka, Jusuke Hidaka

    pp. 2701-2705

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    DOI:10.2320/matertrans.47.2701

    Abstract

    The structural and electronic properties of CnH2n+2/Al(110) interfaces (n=5) have been studied by first-principles calculations using a plane-wave pseudopotential method coupled with an efficient electronic minimization scheme for large systems. We have examined the stability of vertical and parallel adsorption of a C5H12 molecule on an Al(110) surface for various adsorption sites and initial interface distances. It has been found that image interactions between the C-H polar bonds and the metal surface with physorption characters dominate the interfacial interactions for both the vertical and parallel cases of the C5H12/Al interfaces. However, for the C5H11 molecule with a dehydrogenated terminal C atom, we have observed the formation of a strong interfacial C-Al bond with both covalent and ionic characters.

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  • GBstudio: A Builder Software on Periodic Models of CSL Boundaries for Molecular Simulation

    Hiroshi Ogawa

    pp. 2706-2710

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    DOI:10.2320/matertrans.47.2706

    Abstract

    A new software GBstudio was developed for generating atomic coordinates in periodic grain boundary models composed two crystals. It was designed for modeling grain boundary structures in various geometries including coincident-site-lattice (CSL), tilt, and twist boundaries in easy and systematic ways. By this software, CSL boundaries of cubic crystals up to Σ99 can be constructed by selecting a few parameters in the candidate lists. Tilt and twist boundaries on representative rotation axes can also be generated in a similar way for cubic and non-cubic crystals. An editing menu is implemented to modify inappropriate atomic configuration at the boundary. The software is distributed via the Internet as a Java applet usable on web browsers.

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  • Molecular Dynamics Simulation of Grain Boundary Formation and Migration in Silicon

    Kenjiro Sugio, Hiroshi Fukushima, Osamu Yanagisawa

    pp. 2711-2717

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    DOI:10.2320/matertrans.47.2711

    Abstract

    Molecular dynamics simulation using Tersoff potential was carried out to investigate the formation and the migration of (010) Σ5 twist boundary in silicon. Effects of carbon atoms on the grain boundary formation and the grain boundary migration were also investigated. Amorphous thin layers remained at the twist boundary even after crystallization, and changes in the thickness of this layers caused grain boundary migration. When carbon atoms were segregated at the twist boundary, these atoms prevented shrinkage of an amorphous thin layer, and the grain boundary migration was retarded. Precipitated carbon atoms within the grain produces a strain field and this strain field possibly became driving force for the grain boundary migration.

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  • Critical Estimation of Relaxation Coefficient in TDGL Equation Based on Path Probability Method

    Munekazu Ohno, Tetsuo Mohri

    pp. 2718-2724

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    DOI:10.2320/matertrans.47.2718

    Abstract

    A hybrid scheme of Cluster Variation Method (CVM) combined with Phase Field Method (PFM) is applied to multiscale analysis of disorder-B2 transition. By comparing the relaxation curves of Long-Range-Order (LRO) parameter obtained by the present hybrid model and by Path Probability Method (PPM), a critical estimation of the relaxation constant which determines the time scale of the temporal evolution process of microstructure is attempted for B2 ordering process. It is found that both the LRO relaxation curves are well described within the autocatalytic reaction model of chemical species. That both curves coincide satisfactorily assures the existence of a scaling property between PFM and PPM. Finally, microstructural evolution process is simulated within Time Dependent Ginzburg Landau equation.

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  • Phase-Field Simulation of Austenite to Ferrite Transformation and Widmanstätten Ferrite Formation in Fe-C Alloy

    Akinori Yamanaka, Tomohiro Takaki, Yoshihiro Tomita

    pp. 2725-2731

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    DOI:10.2320/matertrans.47.2725

    Abstract

    The formation process of Widmanstätten ferrite plates during the isothermal austenite to ferrite transformation in Fe-C alloy is simulated by the phase-field method. The effects of the anisotropy of interfacial properties on the growth kinetics of Widmanstätten ferrite plates are investigated by the regularized gradient energy coefficient method, which enables us to introduce a wide range of interface anisotropy. It is found that by employing this method, a very sharp tip of the plate can be simulated and the morphology of Widmanstätten ferrite plate is in good agreement with the experimentally observed one. The simulation results of the growth of a single Widmanstätten ferrite plate suggest that the lengthening rate of the Widmanstätten ferrite plate increases with increasing strength of anisotropy, which causes the increase of interfacial energy at the tip. Furthermore, the simulations of the morphological changes of Widmanstätten ferrite from a grain boundary allotriomorph ferrite are performed. The results clarify that the growth of Widmanstätten ferrite plates from allotriomorph ferrite requires high anisotropy of interfacial energy. It is also proved that, in the early stage of the growth, the plate tips directly formed at the convex part of allotriomorph ferrite can preferentially develop into Widmanstätten ferrite plates due to the morphological instability. The distribution of Widmanstätten ferrite plates depends on the initial interface shape of the grain boundary allotriomorph ferrite.

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  • Simulation of V(CN) Precipitation in Steels Allowing for Local Concentration Fluctuations

    Javier Aldazabal, Carlos Garcia-Mateo, Carlos Capdevila

    pp. 2732-2736

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    DOI:10.2320/matertrans.47.2732

    Abstract

    From a “macroscopic” point of view, steel composition is assumed to vary smoothly along its microstructure. A closer look reveals that, at the atomic level, the material composition does not change so smoothly. Single atoms jump randomly along the crystal lattice due to their thermal energy, therefore creating sporadic zones of the crystal with higher concentration of certain elements. This composition fluctuations are responsible of many phenomena, such as precipitation, Ostwald ripening, some phase transformations. This work proposes a model to simulate the precipitation of V(CN) precipitates in microalloyed steels in the range of warm temperatures (800–900°C); when the matrix is fully austenitic (fcc), and taking into account for local composition fluctuations. The model works by dividing the space into very small cells, each containing a single fcc atomic cell. If during the random movement of atoms a small group of adjoining cells reach some critical composition, a nucleus of V(CN) appears. At the same time, if a cell touching an already existing precipitate reaches some critical vanadium composition, it is very easy to stick it to the precipitate by changing its “phase”. But it is also possible that some atoms escape from the precipitate by jumping to the austenitic matrix. The model considers both processes happening simultaneously, and which one is leading depends on the atoms energy, i.e. system temperature, leading to different possible situations, nucleation phenomena, Ostwald ripening or dissolution of precipitates.

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  • Modified Effective Specific Heat Method of Solidification Problems

    Yau-Chia Liu, Long-Sun Chao

    pp. 2737-2744

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    DOI:10.2320/matertrans.47.2737

    Abstract

    In the heat-transfer analysis of a solidification process, the effective specific heat method is conceptually simple to apply while dealing with the latent heat problem. The implementation of computer program is very easy for this method. However, in a time step, if a nodal temperature enters, leaves or jumps over the artificial mushy zone of a pure substance, it cannot calculate the released or absorbed latent heat correctly. If the latent heat is large or the temperature variation is very large, the discontinuity of the effective specific heat will make the iterative convergence difficult to reach. In this work, a modified method is proposed to solve these problems. The method modifies the relation between the temperature and effective specific heat for a solidification process by considering the effect that the temperature at either of two successive time steps is in the mushy zone. The Stefan and Neumann problems with exact solutions were used to test the modified method. The computing results will be compared with those of the effective specific heat method and the enthalpy method. Finally, the feasibility of the modified method is further testified by using a crystal growth problem of GaAs in a Bridgman furnace.

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  • Finite Element Simulation of Liquid Phase Sintering with Tungsten Heavy Alloys

    Seong Jin Park, Suk Hwan Chung, John L. Johnson, Randall M. German

    pp. 2745-2752

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    DOI:10.2320/matertrans.47.2745

    Abstract

    Densification and distortion of W-Ni-Fe tungsten heavy alloys during liquid phase sintering are modeled using constitutive laws of grain growth, densification, and deformation. The models are “calibrated” via carefully designed experiments to obtain the necessary parameters to enable modeling. Metallographic analysis of quenched samples is used to obtain grain size data as functions of time and temperature, while dilatometry and dimensional analyses are used to determine the bulk viscosity and shear viscosity. The influences of gravity, substrate friction, surface tension, and solid content on distorted shapes are shown by comparing predictions from the finite element method with experimentally measured shapes. The finite element simulations accurately predict several phenomena, including increased distortion with longer sintering times and higher liquid contents, slumping due to gravity, spheroidization due to surface tension, and friction-related distortion due to sticking of the part to the substrate.

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  • High Mechanical Properties of Polychloroprene/Montmorillonite Nanocomposites

    Meng-Heng Yeh, Weng-Sing Hwang

    pp. 2753-2758

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    DOI:10.2320/matertrans.47.2753

    Abstract

    The principal objective of this study is to improve the mechanical properties of polychloroprene through the addition of montmorillonite. Three modifying cations are tested. The polychloroprene-MMT composite is characterized by FTIR, SEM, EDX, XRD, ICP-MS and TEM. The tensile and tear strength of polychloroprene was increased significantly after the modification of montmorillonite.

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  • Electrochemical Characteristics of LiMn2O4 (Li/Ni) Cathode Materials

    Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen, Hung-Chi Liao

    pp. 2759-2764

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    DOI:10.2320/matertrans.47.2759

    Abstract

    The present study used the Pechini process with a continuous furnace to synthesize LiMn2O4 powders. After heat treatment, the particle size and lattice constant of the LiMn2O4 powder increased. For heat treatment cathode powders (LMO800), due to both the average valence of Mn cations approaching the theoretical value and the higher crystalinity, the discharge capacities are raised significantly. The charge and discharge cycling capacity of LMO800 powder was best at 25°C. Under the charge-discharge cycling test at 55°C, some Mn ions dissolved easily into the electrolyte resulting in a significant decrease in the charge and discharge capacity with increasing the cycling number. The surface modification powder (LMO-Ni) contains a surface oxidative film of lithium-nickel-manganese that not only restrains Mn ions dissolved into the electrolyte, but also improves the charge and discharge capacity at 55°C.

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  • Phase-Field Simulation of Phase Transformation in Fe-Cu-Mn-Ni Quaternary Alloy

    Toshiyuki Koyama, Kiyoshi Hashimoto, Hidehiro Onodera

    pp. 2765-2772

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    DOI:10.2320/matertrans.47.2765

    Abstract

    The phase decomposition in α(bcc) phase and the subsequent structural phase transformation from α to γ(fcc) phase during isothermal aging of an Fe-Cu-Mn-Ni quaternary alloy, which is a base alloy of the light-water reactor pressure vessel, have been simulated by the phase-field method. At the early stage of spinodal decomposition, Cu-rich α phase is formed, and the Mn and Ni, which are minor components, are partitioned to the Cu-rich phase. As the Cu composition in the precipitate is increased, the Ni atoms inside the precipitates move to the interface region between the precipitate and matrix, but Mn atoms remain inside the Cu particles. When the Cu-rich particles eventually transform to the fcc structure, the Mn atoms also move to the interface region, which results in the shell structure of the fcc Cu precipitates, where each particle is surrounded by a thin layer enriched in Mn and Ni. This microstructural change can be reasonably explained by considering the local equilibrium at the surface region of the Cu-rich particles.

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  • High Strain Rate Superplasticity of Mg Based Composites Fabricated by Friction Stir Processing

    C. J. Lee, J. C. Huang

    pp. 2773-2778

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    DOI:10.2320/matertrans.47.2773

    Abstract

    The nano-sized SiO2 particles were added into the AZ61 Mg alloys via friction stir processing (FSP) to a volume fraction of 5–10%. After four FSP passes, the 10% composites had uniform dispersion of particles and grain size of 0.8 μm. This composite exhibited high strain rate superplasticity, with a maximum ductility of 470% at 1×10−2 s−1 and 300°C or 454% at 3×10−1 s−1 and 400°C while maintaining fine grains less than 2 μm in size.

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  • Influence of Hot Rolling and Post-Tempering on the Mechanical Properties of Duplex Stainless Steel Containing Martensite and Ferrite

    Dong-Cherng Wen

    pp. 2779-2785

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    DOI:10.2320/matertrans.47.2779

    Abstract

    In this research, SUS 403 duplex stainless steel containing martensite and ferrite was processed with hot rolling at a range of reductions (15–50%) and post-tempering at a range of temperatures (473–873 K) to investigate microstructural change during tempering and mechanical properties as a function of tempering temperature and ferrite grain size. The results indicate that Cr-rich carbides precipitate when tempering at the range of 473–773 K. The precipitation of fine carbides increases the carbide-ferrite phase boundary area. Again, the hard carbides reinforce the ferrite matrix along the boundaries and, consequently, results in enhancing mechanical properties. A secondary strengthening phenomenon in stress and hardness occurs at 773 K tempered. The ferrite grain size decreases with increasing reduction. Fine grain structure leads to an increase in grain boundaries and homogeneous dispersion of carbides, which provides a dominant action against crack propagation and improves the mechanical properties. Except the hardness, the maximum mechanical properties of each rolling reduction are better than that of the specimens quenched and tempered without hot rolling.

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  • High Corrosion and Weather Resistant Anionic Resin Coating for 2014 T6 Aluminum Alloys Which Maintains Mirror Luster

    Masaaki Hara, Kenji Matsuda, Tooru Iwai, Masayoshi Kihara, Wataru Yamauchi, Yorinobu Takigawa, Kenji Higashi

    pp. 2786-2790

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    DOI:10.2320/matertrans.47.2786

    Abstract

    A new surface treatment technology for 2014 T6 aluminum alloys that exhibits not only high corrosion and weather resistance but also good mirror luster has been developed. By using this new electrode-position coating process with anion resin, the resin can preferentially permeate into cavities that are formed by dissolving of the second phase particles during a general anodizing process. In order to maintain the excellent appearance, the thickness of the anodized layer and anion resin layer was optimized to make the layers as thin as possible while keeping the high corrosion and weather resistance. Thanks to this newly developed surface treatment technology, high strength aluminum alloys featuring high corrosion and weather resistance with mirror luster are now available for industrial products.

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  • Quasi-One-Dimensional Analysis of the Effects of Pipe Friction, Cooling and Nozzle Geometry on Gas/Particle Flows in HVOF Thermal Spray Gun

    Hiroshi Katanoda

    pp. 2791-2797

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    DOI:10.2320/matertrans.47.2791

    Abstract

    The High Velocity Oxy-Fuel (HVOF) thermal spraying can make highly tough and dense coatings on a solid surface. It is experimentally recognized that the quality of the coating largely depends on the particle velocity and temperature, which depend on the gas flow in the HVOF gun. The gas flow in the gun is affected by two factors; pipe friction and cooling along the inner wall of the long gun. This paper investigates the gas/particle flow in the HVOF gun by using quasi-one-dimensional analysis including the effects of pipe friction, cooling and nozzle geometry. The standard values of the parameters, to include the effects of pipe friction and cooling are selected based on the experimental result. The nozzle length is varied in the range of 110–330 mm. The calculated results show that (1) the pipe friction decreases the particle velocity and increases the particle temperature, (2) the cooling increases the particle velocity and decreases the particle temperature, (3) the maximum particle velocity is obtained when the length of the diverging part of the nozzle is approximately equal to the length of the following non-diverging straight part, (4) the longer nozzle results in larger particle velocity at the nozzle exit. These numerical results help understand the gasdynamics occurring in the HVOF gun, and assist in the design of the gun.

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  • Effects of Reduced Pressure and Coat Permeability on Casting Characteristics of Magnesium Alloy in Evaporative Pattern Casting Process

    Kyong-Whoan Lee, Gue-Serb Cho, Kyeong-Hwan Choe, Hyung-Ho Jo, Akira Ikenaga, Sadatoshi Koroyasu

    pp. 2798-2803

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    DOI:10.2320/matertrans.47.2798

    Abstract

    A magnesium alloy was adopted to an evaporative pattern casting (EPC) process to combine advantages of each. In the present study, foam patterns were cast at a top gating system under atmospheric and reduced pressure to evaluate casting characteristics of AZ91D to develop a complete EPC process for high productivity of magnesium alloy castings. Filling time and temperature of molten metal were measured during mold filling. It was recognized that the average filling velocity was affected by the difference of the coating material and the degree of reduced pressure. The grain size of the magnesium alloy was slightly dependent on the degree of reduced pressure. It was considered that the application of the high reduced pressure, which changed the shape of melt surface from convex to concave, was related to the occurrence of internal defects such as cold shut laps or folds in the casting.

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  • Bulk Metallic Glass Formation near a Quaternary Cu-Zr-Ti-Al Eutectic Point

    Qingsheng Zhang, Wei Zhang, Akihisa Inoue

    pp. 2804-2807

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    DOI:10.2320/matertrans.47.2804

    Abstract

    The glass-forming ability (GFA) of the CuZr-based alloys with addition of equivalent atomic ratio of Ti and Al is investigated. We show that the addition of Ti and Al is effective to increase the GFA of the binary Cu50Zr50 alloy. As the content of Ti and Al increases from 0 to 10 at%, the GFA of the quaternary Cu-Zr-based alloys increases. The critical diameter of the Cu46Zr46Ti4Al4 and Cu45Zr45Ti5Al5 alloys is up to 6 mm. Moreover, we found that the critical diameter of a glassy rod is 7 mm for the Cu45.5Zr45.5Ti4.5Al4.5 alloy. The compositions of these alloys with high GFA are closer to a CuZrTiAl quaternary eutectic. However, much higher contents of Ti and Al lead to the precipitation of the simple TiAl phase, which degrades the GFA of the alloys.

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  • Microstructure and Electrical Conductivity of SrRuO3 Thin Films Prepared by Laser Ablation

    Akihiko Ito, Hiroshi Masumoto, Takashi Goto

    pp. 2808-2814

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    DOI:10.2320/matertrans.47.2808

    Abstract

    SrRuO3 (SRO) thin films were prepared by laser ablation, and the effects of deposition conditions on the microstructure and electrical conductivity of these films were investigated by changing the substrate temperature (Tsub) and deposition atmosphere. The SRO thin films deposited on quartz substrates in a high vacuum (P=10−6 Pa) and an oxygen partial pressure (PO2) of 0.13 Pa were amorphous, independent of Tsub. Pseudo-cubic SRO thin films were obtained at PO2=13 Pa and Tsub>773 K. The Sr to Ru ratio increased with increasing Tsub, and free Ru was contained in SRO films prepared at P=10−6 Pa. The crystal grain coarsened with increasing Tsub and PO2. The electrical conductivity (σ) of SRO thin films increased with increasing Tsub and PO2, and the highest σ was obtained at Tsub=973 K and PO2=13 Pa. The σ of SRO films mainly changed with the Sr/Ru ratio and the surface morphology. The change of σ associated with the magnetic phase transition was observed at 163 K.

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  • Tensile Failure Behavior of SiC/Ti-6Al-4V Composites Manufactured by Plasma Spraying Route

    Kyeong Ho Baik

    pp. 2815-2820

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    DOI:10.2320/matertrans.47.2815

    Abstract

    In this study, multi-ply SiC fiber reinforced Ti-6Al-4V composites have been manufactured by a novel plasma spraying technique and subsequent vacuum hot pressing. Two different sizes of Ti-6Al-4V feedstock powders were used for plasma spraying to form matrix. A considerable amount of oxygen from environment was incorporated into as-sprayed Ti matrix during plasma spraying, and consequently caused matrix embrittlement. The use of coarse-sized feedstock powder reduced oxygen incorporation, but tended to increase fiber spacing irregularity and fiber strength degradation. Longitudinal tensile strength and ductility of the SiC/Ti-6Al-4V composites in this study were mainly affected by Ti matrix properties. The embrittlement of Ti matrix occurred at oxygen contents higher than ∼0.4 mass%, and consequently reduced the tensile strength and ductility of SiC/Ti-6Al-4V composites.

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  • Effect of Iron Content on Hot Tearing of High-Strength Al-Mg-Si Alloy

    Hiromi Nagaumi, Satoru Suzuki, Toshimitsu Okane, Takateru Umeda

    pp. 2821-2827

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    DOI:10.2320/matertrans.47.2821

    Abstract

    The effect of iron content on hot tearing of the high-strength Al-Mg-Si alloy was systematically investigated. The alloy with higher content of iron resulted in the severe occurrence of hot tearing during direct chill (DC) casting. Mechanical properties of this alloy in which iron content was changed were investigated during solidification using an electromagnetic induction heating tensile machine. Tensile strength and elongation were discussed in relation with solidification progress of which sequence of crystallization, crystallization temperature of formed phases and their crystallized amount were calculated by a thermodynamic calculation software Thermo-Calc. In order to confirm the calculation results of solidification path, a quenching test also was carried out. Furthermore, by comparing the fracture surfaces of the tensile testing sample and DC billet, the temperature range of crack initiation of the alloy was examined. Comparing the temperature range of crack initiation with the crystallization phase and its crystallization order, iron content influenced hot tearing significantly owing to the crystallization behavior of α(AlFeMn) in high-strength Al-Mg-Si alloy.

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  • Low-Isostatic-Press Sintering of Iron Alloy Powder

    Hidekazu Sueyoshi, Shigeru Uchida, Takeru Miyanowaki, Keita Kume, Ryo Kurose

    pp. 2828-2834

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    DOI:10.2320/matertrans.47.2828

    Abstract

    An end-sealed thin stainless-steel pipe in which a high-speed steel compact was inserted was evacuated with a vacuum pump during heating at an elevated temperature using an atmosphere furnace. The sintering behavior of this low isostatic press sintering (LIPS) was examined in detail. The compact is subjected to isostatic compression stress through the deformation of stainless-steel owing to atmospheric pressure. As the gas pressure in the stainless-steel pipe is low (about 2×10−2 Pa), as the sintering temperature is high (1573 K), and as the holding time is long (4 h), densification and hardness of the LIPS compact are large (about Hv640). This is because the decomposition of FeO film formed on the surface of the as-received powder is vigorous at low gas pressure in the stainless-steel pipe and high LIPS temperature, the degree of powder contact increases because of a large plastic flow of powder particles owing to both the degradation of the strength of high-speed steel powder at a high temperature and the compression stress caused by atmospheric pressure, and Fe diffusion is encouraged by heating at high temperature for a long time. At an early stage of LIPS, pores of the center of the LIPS compact diffuse into the surface, resulting in the reduction of densification near the surface. However, by holding for a long time, the LIPS compact that has high densification from the surface to the center is obtained because of encouragement of Fe diffusion. Under optimum LIPS conditions, it is possible to obtain a homogeneous LIPS compact which has porosity and hardness levels equivalent to those of the HIP compact.

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  • Three Temperature Model for Nonequilibrium Energy Transfer in Semiconductor Films Irradiated with Short Pulse Lasers

    Seong Hyuk Lee, Hyung Sub Sim, Junghee Lee, Jong Min Kim, Young Eui Shin

    pp. 2835-2841

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    DOI:10.2320/matertrans.47.2835

    Abstract

    This article investigates numerically carrier-phonon interaction and nonequilibrium energy transfer in direct and indirect bandgap semiconductors during sub-picosecond pulse laser irradiation and also examines the recombination effects on energy transport from the microscopic viewpoint. In addition, the influence of laser fluence and pulse duration is studied by using the self-consistent three-temperature model, which involves carriers, longitudinal optical phonons, and acoustic phonons. It is found that a substantial non-equilibrium state exists between carriers and phonons during short pulse laser irradiation because of time scale difference between the relaxation time and the pulse duration. It is clear that the two-peak structure in carrier temperature exists and it depends mainly on laser pulses, fluences, and recombination processes. During laser irradiation, in particular, the Auger recombination for Si becomes dominant due to the increase in the carrier number density, whereas for GaAs, the Auger recombination process can be ignored due to an abrupt increase in SRH recombination rates at the initial stages of laser exposure.

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  • Amorphous Formation and Magnetic Properties of Nd-Fe-Co-Al Alloys by Gas Flow Type Levitation Process

    Shuji Azumo, Katsuhisa Nagayama

    pp. 2842-2845

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    DOI:10.2320/matertrans.47.2842

    Abstract

    It is reported that Nd-Fe-Co-Al amorphous alloys have high bulk amorphous formation ability and high coercivity by rapid solidification method. We have examined the undercooling solidification, bulk amorphous formation and high coercivity appearance by using containerless process. In this study, we investigated the undercooling, bulk amorphous formation and magnetic properties for Nd-Fe-Co-Al alloys which are levitated and solidified by using the gas jet flow and high cooling type electromagnetic levitation system. Therefore, the high undercooling degree was 66–152 K and the samples formed amorphous phase. The bulk samples, φ6 mm sphere, solidified at the cooling rate, about 100 K/s. In addition, the coercivity for Nd65Fe10Co15Al10 sample with bulk amorphous phase, 3.7 kOe, was the highest value in all samples. Also, the thermal stability for Nd65Fe10Co15Al10 sample was carried out by isothermal annealing experiments. The origin of high coercivity may be related to the amorphous phase.

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  • Improvement of Charpy Impact of Carbon Fiber Reinforced Polymer by Low Energy Sheet Electron Beam Irradiation

    Yoshitake Nishi, Keisuke Inoue, Michelle Salvia

    pp. 2846-2851

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    DOI:10.2320/matertrans.47.2846

    Abstract

    Effects of sheet electron beam irradiation under low potential on the Charpy impact value of carbon fiber reinforced polymer (CFRP) have been investigated. The irradiation, which is one of short-time treatments, enhances the impact value of CFRP. It probably depends on the enhancement of interfacial force, as well as the strengthening of carbon fiber and polymer.

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  • Influences of Process Condition of Magnetron Sputtering on Magnetostrictive Susceptibility of Fe2.2Sm Alloy Film

    Yoshitake Nishi, Yoshito Matsumura, Keisuke Takahashi

    pp. 2852-2859

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    DOI:10.2320/matertrans.47.2852

    Abstract

    Since morphological interface of iron-samarium alloy thin film prepared by direct current magnetron sputtering process is controlled by substrate temperature, sputtering argon gas pressure and residual gas pressure, influences of changes of morphology and its interface on compressive (negative) magnetostrictive susceptibility of Fe2.2Sm alloy films are investigated. Decreasing the pressures of sputtering argon gas enhances the magnetostrictive susceptibility. The high susceptibility is also found under the low pressures of residual (impurity) gas at each substrate temperatures (Ts) from 423 to 523 K. The clear interface cannot be observed in the densely packed amorphous phase, when the high magnetostrictive susceptibility is obtained. Since the decreasing in impurity atoms at the unclear interface easily changes the domain direction and then doesn’t prevent to move the magnetic domain wall in the amorphous phase, influences of the residual gas pressure on magnetostrictive susceptibility are explained by not only morphological interface but also its oxidation.

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  • Electrodeposited Co-Ni-Fe-C Alloys for Hydrogen Evolution in a Hot 8 kmol·m−3 NaOH

    Piotr R. Zabinski, Shinsaku Meguro, Katsuhiko Asami, Koji Hashimoto

    pp. 2860-2866

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    DOI:10.2320/matertrans.47.2860

    Abstract

    Active cobalt alloy cathodes for hydrogen evolution in 8 kmol·m−3 NaOH at 90°C was tailored by electrodeposition. Enhancement of cathodic activity of Co-Ni alloys was carried out by the formation of Co-Ni-Fe-C alloys. The addition of both iron and carbon was effective in enhancing the electrolytic hydrogen evolution activity, and the carbon addition was further effective in preventing preferential dissolution of iron and cobalt, that is, dealloying corrosion during shutdown period in the hot concentrated alkaline solution. The fcc Co-Ni-Fe-C alloys with about 15 at% iron showed the best performance with high hydrogen evolution activity and durability without dealloying corrosion. The alloys with high iron contents forming the bcc structure and showing sufficiently high activity without carbon addition suffered readily dealloying corrosion, and complete prevention of dealloying of the high iron alloys was not achieved by carbon addition.

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  • Superelastic Property of Ti-Ni Alloy Produced by Casting After SHS

    Kazuhiro Kitamura, Toshio Kuchida, Tadashi Inaba, Masataka Tokuda, Yukiharu Yoshimi

    pp. 2867-2870

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    DOI:10.2320/matertrans.47.2867

    Abstract

    The superelastic properties of cast Ti-Ni shape memory alloy (SMA) were studied. Base materials were prepared as a melting method ingot and as a self-propagating high-temperature synthesis (SHS) ingot. The composition of these ingots was Ti-50.8 at%Ni. Each ingot was cast into a rod shape by centrifugal casting. The heat-treatment conditions were 773 K for-1.8 ks and 773 K–1.8 ks → 873 K–3.6 ks. Shape memory characteristics were measured by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and a tensile test. All casting specimens have good shape memory characteristics. According to DSC measurements, the melt method specimens show gravity segregation.

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  • Influence of Electrolyte on an Energy-Saving Copper Recycling Process Using Ammoniacal Alkaline Solutions

    Tetsuo Oishi, Kazuya Koyama, Mikiya Tanaka, Jae-Chun Lee

    pp. 2871-2876

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    DOI:10.2320/matertrans.47.2871

    Abstract

    In order to make the energy-saving copper recycling process more economical by reducing the power consumption during copper electrowinning, the influence of the bath composition on the saturated concentration of cuprous ion, the electric conductivity, the cathodic current efficiency and the power consumption were studied in an ammonia-ammonium chloride-cuprous/cupric ion solution. The saturated cuprous ion concentration increased with the ammonia and ammonium chloride concentrations. The electric conductivity of the solution increased in proportion to the ammonium chloride concentration, because ammonium chloride acts as a supporting electrolyte. When the ammonia concentration increased from 3 to 10 kmol·m−3 or when the cuprous ion concentration increased from 0.5 to 2 kmol·m−3, the cathodic current efficiency decreased by 5–10% at a current density higher than 500 A·m−2. This results from an increase in the cupric ion concentration formed by the unavoidable oxidation and the disproportionation of cuprous ions. The low current efficiency, however, had little influence on the power consumption compared to the influence of the electric conductivity that was the dominant factor determining the power consumption. Actually, when the concentration of ammonium chloride increased from 2 to 4 kmol·m−3, because of its function of increasing the electric conductivity of the solution, the power consumption was reduced by half. Based on this study, a suitable bath composition for the energy-saving copper recycling process was determined to be 3–10 kmol·m−3 ammonia, 4–5 kmol·m−3 ammonium chloride and 1–2 kmol·m−3 cuprous ions.

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  • Improvement in the Microstructure and Tensile Properties of Inconel 718 Superalloy by HIP Treatment

    Shih-Chin Lee, Shih-Hsien Chang, Tzu-Piao Tang, Hsin-Hung Ho, Jhewn-Kuang Chen

    pp. 2877-2881

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    DOI:10.2320/matertrans.47.2877

    Abstract

    Hot Isostatic Pressing (HIP) is a process that uniquely combines higher pressure and temperature to produce materials and parts with substantially better properties than those by other methods. The aim of this paper is to discuss the methods and to find a suitable process of HIP for Inconel 718 superalloy. In this study, the HIP process parameters considered were; temperatures: 1423, 1448, 1453 and 1478 K, pressures: 100, 150, 175 and 200 MPa, and soaking times of 2, 3 and 4 hours. The Inconel 718 superalloy is used throughout this study. To evaluate the effects of microstructure and tensile properties of 718 alloy by HIP process, tensile test at two different strain rates at room and high temperature were evaluated. The microstructure, TEM and XRD inspections were performed.
    The experiment results show that at 1453 K, 175 MPa, 4 hours of HIP treatment for Inconel 718 superalloy was optimal. It can improve the microstructure and tensile properties of 718 castings. Through the optimal HIP treatment, the grain sizes are uniform and the segregated structure is improved. At fast strain rate (0.001 s−1), it increased the tensile strength by 31% at 298 K, 27% at 813 K, and 24% at 923 K. The 0.2% yield strength increased 40% at 298 K, 31% at 813 K, and 28% at 923 K. Meanwhile the elongation increased 100% at 298 K, 130% at 813 K, and 60% at 923 K after tension tests. When the strain rate was very slowly (0.0001 s−1), it also increased the tensile strength by 24% at 298 K and 20% at 813 K. The 0.2% yield strength increased 29% at 298 K and 27% at 813 K. The elongation increased 54% at 298 K and 282% at 813 K.

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  • Formation and Thermal Stability of Cu46.25Zr44.25Al7.5Er2 Bulk Metallic Glass with a Diameter of 12 mm

    Hua Men, Junying Fu, Shujie Pang, Chaoli Ma, Tao Zhang

    pp. 2882-2884

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    DOI:10.2320/matertrans.47.2882

    Abstract

    Effect of substituting a small amount of Er for Zr in Cu46.25Zr46.25AI7.5 alloy on glass-forming ability was investigated. The addition of 2 at% Er effectively improves glass formation and glassy rod with a diameter of at least 12 mm was formed by copper mold casting.

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  • Coincidence Doppler Broadening of Positron Annihilation Radiation for Detection of Helium in Irradiated Ni and Cu

    Q. Xu, T. Ishizaki, K. Sato, T. Yoshiie, S. Nagata

    pp. 2885-2887

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    DOI:10.2320/matertrans.47.2885

    Abstract

    A new composition analysis method, namely, coincidence Doppler broadening (CDB) of positron annihilation radiation, was employed to detect He atoms in ion irradiated Ni and neutron irradiated Cu. The results of positron lifetime and transmission electron microscopy (TEM) show that microvoids and voids were formed in ion-irradiated Ni and neutron-irradiated Cu, respectively. The results of CDB measurements indicate that He atoms were present in the microvoids and voids, even in microvoids annealed at 1273 K in ion-irradiated Ni. Coincidence Doppler broadening measurement, which is a nondestructive technique for testing materials, is effective for detecting He atoms.

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  • © 2006 The Japan Institute of Metals and Materials

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