MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 49 , Issue 9
Showing 1-43 articles out of 43 articles from the selected issue
  • Haruhiko Morito, Hisanori Yamane, Takahiro Yamada, Shu Yin, Tsugio Sat ...
    2008 Volume 49 Issue 9 Pages 1929-1933
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    SiC porous granules were synthesized from activated granular charcoal and Si powder at 973 K by using a Na flux. The SiC granules maintained the shape of the charcoal with a dimension of about 5 mm in diameter and 7–10 mm in length. X-ray diffraction showed the structure of the formed SiC to be cubic β-type. Agglomerates of a few dozen nm of SiC grains and an electron diffraction ring pattern of β-SiC were observed with a transmission electron microscope. A micropore size distribution of <4 nm and mesopores in the range of 20–40 nm were shown by a nitrogen adsorption technique. The SiC granules had a specific surface area of 3.4±1.0 m2/g and a pore volume of 0.006±0.002 cm3/g. The fracture stress of the SiC porous granules was evaluated to be 47 MPa by a compressive test at room temperature. The Vickers hardness of the granule surface was 13.1±1.0 GPa.
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  • Y. L. Du, Z. M. Sun, H. Hashimoto, W. B. Tian
    2008 Volume 49 Issue 9 Pages 1934-1936
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 09, 2008
    JOURNALS FREE ACCESS
    We have investigated the carbon mono-vacancy in Ta4AlC3 by first-principles calculations. We identify the 2a sites as the probable carbon vacancy sites in Ta4AlC3 based on the energetics of vacancy formation. It was found that introducing carbon vacancies decreased the phase stability of Ta4AlC3. There are no significant changes in volume by introducing carbon vacancy. However, the bulk modulus decreased when introducing carbon vacancy. The differences in density of states of Ta4AlC3 with and without carbon vacancies are analyzed. Some vacancy peaks near the Fermi level were observed. Additionally, the density of states at the Fermi level increases by introducing carbon vacancies, which may be of benefit to the electron transport in Ta4AlC3.
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  • Jae-hwa Lee, Takashi Fukuda, Tomoyuki Kakeshita
    2008 Volume 49 Issue 9 Pages 1937-1940
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
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    We have investigated the kinetics of successive γ→ε′→α′ martensitic transformation in a SUS304L stainless steel by isothermal holding experiments. An in-situ optical micrograph observation suggests that the γ→ε′ martensitic transformation has so-called isothermal kinetics while the ε′→α′ martensitic transformation has so-called athermal kinetics. The TTT diagram corresponding to the formation of 0.5 vol% of α′-martensite via ε′-martensite from γ-phase shows a C-curve with a nose temperature located at about 103 K, due to the isothermal kinetics of the γ→ε′ transformation.
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  • Katsuya Inoue, Kozo Shinoda, Shigeru Suzuki, Yoshio Waseda
    2008 Volume 49 Issue 9 Pages 1941-1946
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 24, 2008
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    Green rust (GR) consisting both of Fe(II) and Fe(III) was formed in an aqueous solution with a relatively low electrochemical potential. In order to understand both the reduction and oxidation reactions of copper in a GR suspension, the aqueous solution containing Green Rust 2(SO42−) (GR2(SO42−)) was mixed with a copper sulfate solution and it was subsequently oxidized by passing a gas containing oxygen at room temperature. X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy were used for characterizing the reaction products. Copper ions were found to be reduced to metallic copper in the GR2(SO42−) suspension, while a part of GR2(SO42−) was oxidized to be transformed to α-FeOOH. The pH and oxidation-reduction potential values of the aqueous solution were measured during the reactions. The importance of the reduction of Cu(II) to metallic copper occurred in the GR2(SO42−) suspension, and the oxidation processes of the suspension containing metallic copper was suggested as distinct reaction stages. These reaction stages are considered to be attributed to the different electrochemical potential of Cu(II)/Cu(0) and Fe(III)/Fe(II) in solution.
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  • Hidetoshi Somekawa, Alok Singh, Yoshiaki Osawa, Toshiji Mukai
    2008 Volume 49 Issue 9 Pages 1947-1952
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Six kinds of Mg-2.5 at%Zn-0.5 at%RE (RE: rare earth element, Y, Gd, Tb, Dy, Ho and Er) alloys with grain size of 1∼2 μm and containing a quasicrystalline icosahedral phase were prepared by casting and extrusion. These alloys had high strength and high fracture toughness balances, due to the synergetic effect of grain refinement and the dispersion of quasicrystalline phase particles. Microstructural observations showed a ductile fracture pattern, and that the origin of void nucleation was not the quasicrystalline phase particles but the conventional precipitates and the W-phase particles, because of the difference in the interface structure between the matrix and the particles.
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  • Masaki Tanaka, Masaki Honda, Masatoshi Mitsuhara, Satoshi Hata, Kenji ...
    2008 Volume 49 Issue 9 Pages 1953-1956
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from −60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl)=220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. The observed dislocations were reconstructed by simultaneous interactive reconstruction technique, exhibiting a 3-D configuration of dislocations introduced by the three-point bending.
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  • Daigo Itoh, Yoshihiro Terada, Tatsuo Sato
    2008 Volume 49 Issue 9 Pages 1957-1962
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
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    Tensile creep tests have been carried out for the die-cast AM50 + xCa (x=0.47, 0.95 and 1.72 mass pct) alloys in the temperatures between 423 and 523 K to elucidate the effect of calcium additions on creep properties for the AM50 alloy. The creep curve for the AM50 + xCa alloys is characterized by a minimum in the creep rate followed by an extended accelerating stage, and the decrease in creep rate during transient stage becomes pronounced with calcium concentration. The creep strengthening by calcium addition is emphasized at lower stresses and lower temperatures, resulting in the positive dependence of creep parameters, n and Qc, against calcium concentration. It is found that the eutectic intermetallic phase covering the primary α grains detected in the AM50 + xCa alloys prevents the dislocation annihilation at grain boundaries. The creep strengthening by the addition of calcium results from both the solid solution strengthening of the α matrix by solute calcium and the retardation of dislocation annihilation attributed to the eutectic intermetallic phase.
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  • Tadayoshi Odahara, Hiroaki Matsumoto, Akihiko Chiba
    2008 Volume 49 Issue 9 Pages 1963-1969
    Published: September 01, 2008
    Released: August 25, 2008
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    In order to examine the mechanical properties of a biomedical Co-33Cr-5Mo-0.3N alloy at elevated temperatures, tensile tests have been conducted in the temperature range from room temperature to 1373 K at initial strain rates of 1.0×10−1 s−1 and 1.4×10−4 s−1. The 0.2% proof stress and the tensile strength as a function of temperature have the plateau and the hump, respectively, at intermediate temperatures. The elongation to fracture increases at intermediate temperatures and abruptly decreases at higher temperatures. The decrease of the elongation at higher temperatures arises from the intergranular fracture, possibly caused by the equilibrium segregation of harmful elements such as sulfur. The serrations on the stress-strain curves are observed at intermediate temperatures. The temperature range where the elongation is enhanced and the serrations appear is shifted to lower temperatures at a low strain rate. The 0.2% proof stress does not increase with increasing strain rate and the strain rate sensitivity exhibits negative values at intermediate temperatures. It is considered that a serration leading to large elongation results from the dynamic strain aging.
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  • Sahar Farjami, Takashi Fukuda, Tomoyuki Kakeshita
    2008 Volume 49 Issue 9 Pages 1970-1974
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
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    We have investigated the effect of magnetic field on microstructure formation through the disorder-order transformation in an Fe-55Pd (at%) alloy. The Curie temperature of the disordered phase is 740 K and that of the ordered phase is 670 K. When the ordering heat-treatment is made without applying magnetic field, three lattice corresponding variants of L10-phase form equivalently. On the other hand, when the ordering heat-treatment is made under a magnetic field of 4 T and higher applied in the [001] direction of the disordered phase, a single variant whose easy axis lies in the field direction is realized. Considering the present results obtained, we also suggest that magnetic field is especially effective at the early stage of ordering for the selective formation of preferable variant in Fe-Pd, as in Co-Pt previously studied [Scr. Mater. 58 (2008) 811].
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  • Akito Ishii, Fuminobu Hori, Akihiro Iwase, Yuka Fukumoto, Yoshihiko Yo ...
    2008 Volume 49 Issue 9 Pages 1975-1978
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 06, 2008
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    Relaxation of free volume in Zr50Cu40Al10 bulk metallic glass during isothermal annealing below Tg (glass transition temperature) has been investigated by using positron annihilation lifetime and coincidence Doppler broadening (CDB) techniques. The mean positron lifetime decreases with increasing annealing time at each annealing temperature. The decrease in lifetime is due to shrinkage and annealing out of the free volume. The relaxation kinetics of free volume obeys the stretched exponential function (KWW: Kohlrausch-Williams-Watts law). An adjustable parameter of the KWW exponent β depending on temperature was determined. The electron momentum distribution around free volume derived from a CDB spectrum during annealing showed no appreciable change at each temperature. These results suggest that long-range atomic diffusion and rearrangement, particularly around the free volume, do not occur essentially during relaxation below Tg.
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  • Yorinobu Takigawa, Masayoshi Honda, Tokuteru Uesugi, Kenji Higashi
    2008 Volume 49 Issue 9 Pages 1979-1982
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
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    The effect of initial grain size on dynamically recrystallized grain size (DRX grain size) is examined in AZ31 magnesium alloy with four kinds of initial grain sizes. When the average grain size after the high-temperature compression test is plotted against Zenner-Hollomon parameter (Z-parameter), initial grain size dependence on DRX grain size appears only in the specimen with large initial grain size in the low Z region, but not in the specimen with small grain size or in high Z region. When the grain size measured only in recrystallized region is plotted against Z-parameter, initial grain size dependence on DRX grain size does not appear. From these results, it is concluded that there is no initial grain size dependence on DRX grain size when the DRX proceeds to some degree, because the DRX grain size becomes constant for a given Z-value. The initial grain size dependence on DRX grain size observed in the low Z region would be related to the rotation of basal plane perpendicular to the compression axis during deformation before the DRX grains have been developed sufficiently.
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  • Hiroshi Ogawa, Akinori Tezuka, Hao Wang, Tamio Ikeshoji, Masahiko Kata ...
    2008 Volume 49 Issue 9 Pages 1983-1986
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
    JOURNALS FREE ACCESS
    Hydrogen storage in a model b.c.c. metallic nanoparticle was simulated by molecular dynamics method by changing length and energy parameters of metal-H bonds. A global image of hydrogen storage from the gas phase into the metallic nanoparticle was successfully reproduced by a single simulation. In case of weak metal-H bonds, hydrogen atoms rapidly diffuse into the particle and distribute homogeneously. The amount of absorbed hydrogen is maximized at optimized bond length, and decreases for both longer and shorter bonds. In case of strong metal-H bonds, hydrogen atoms localize in a shell-like layer near the particle surface and their inward diffusive motions are suppressed. Such a trapping phenomenon of hydrogen atoms near the surface is caused by low hydrogen diffusivity and lattice deformation due to the hydrogen absorption.
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  • Kazuyuki Kohama, Kazuhiro Ito, Susumu Tsukimoto, Kenichi Mori, Kazuyos ...
    2008 Volume 49 Issue 9 Pages 1987-1993
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
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    In our previous studies, Ti atoms in Cu(Ti) alloy films were found to segregate at the film surface and the interface between Cu(Ti) alloy films and dielectric layers after annealing in Ar atmosphere at elevated temperatures. Such self-formed Ti-rich interface layers can act as a diffusion barrier layer. This technique was called “self-formation of the diffusion barrier,” which is attractive for the fabrication of ultra-large scale integrated interconnects. In the present study, we investigated the growth of Ti-rich barrier layers in Cu(Ti)/dielectric-layer samples with a low Ti content (1 at%) after annealing in ultra high vacuum (UHV). Ti atoms were found to segregate only to the Cu(Ti)/dielectric-layer interface under annealing in UHV. The microstructures were analyzed by transmission electron microscopy and Rutherford backscattering spectrometry, and correlated with the electrical properties of the Cu(Ti) films. It was concluded that Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The Ti-rich interface layers were identified to consist of TiC or TiSi in addition to Ti oxides. The growth of the Ti-rich interface layers consisting of TiC was faster than those consisting of TiSi. Similarly, the resistivities of Cu(Ti)/dielectric-layer samples in which the TiC formation was observed were quickly reduced and those in which the TiSi formation was observed were gradually reduced. Compositions of the self-formed Ti-rich interface layers were concluded to be determined by the C concentration in the dielectric layers rather than by the enthalpy of formation. The growth of the self-formed Ti-rich interface layers consisting of TiC may be controlled by C diffusion in the Ti-rich interface layer. The composition of the dielectric layers was concluded to play an important role on the growth of the Ti-rich interface layers.
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  • Shun Fujieda, Asaya Fujita, Kazuaki Fukamichi
    2008 Volume 49 Issue 9 Pages 1994-1997
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Since La0.75Ce0.25(Fe0.85Mn0.03Si0.12)13 itinerant-electron metamagnet exhibits large magnetocaloric effects at low temperatures because of the itinerant-electron metamagnetic (IEM) transition, the reduction of hysteresis loss Eh estimated from the enclosed area between the ascendant and descendant magnetization has been investigated. We have found that Eh associated with the IEM transition of La0.75Ce0.25(Fe0.85Mn0.03Si0.12)13 is remarkably reduced from 78 to 3 J/kg by a slight adjustment of compositions, that is, the increase of the Ce concentration up to z=0.35 and the decrease of the Fe concentration down to x=0.84. What is important is that such improvement is achieved without a striking decrease of the isothermal magnetic entropy change ΔSm at low temperatures.
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  • Yuta Okimori, Tomonari Inamura, Hideki Hosoda, Kenji Wakashima
    2008 Volume 49 Issue 9 Pages 1998-2005
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
    JOURNALS FREE ACCESS
    We propose a high-temperature actuator composite material composed of a high temperature shape memory alloy (HTSMA) TiAu with a high martensitic transformation temperature (Ms=880 K) and ferromagnetic cobalt with a high Curie temperature (TC=1388 K). This actuator material can be driven by magnetic field in a bending mode due to ferromagnetic force acting on the Co-layer and generates a large actuation strain which originates from the HTSMA. The purposes of this work are (1) to fabricate the composite materials laminated as TiAu/Co/TiAu by a diffusion bonding method through hot pressing, (2) to characterize the microstructure near the bonding interface between TiAu and Co layers, (3) to evaluate growth behavior of the diffusion layer, and (4) to determine the optimum condition for the fabrication. The composite materials were fabricated by hot pressing at 1073, 1173 and 1273 K for 10 h. The bonding interface between TiAu and Co was observed by a scanning electron microscope and concentration profiles were measured by an energy-dispersive X-ray spectroscopy. In order to evaluate the growth behavior of the diffusion layer, the TiAu/Co composites were aged at 773, 1073, 1173 and 1273 K for 24 h. It was found that, after the hot pressing, TiAu and Co layers were successfully bonded, and that two reactant intermetallic compounds were formed near the TiAu/Co interface. The intermetallic compounds were identified to be C11b Ti(Au,Co)2 and C36 (Ti,Au)Co2. As for the growth behavior, the thickness of the diffusion layer was not changed by aging at 773 K. However, the thickness was increased by increasing the aging temperature above 1073 K. The apparent activation energy for the growth of the diffusion layer was estimated to be 280±20 kJ/mol in a temperature range of 1073–1273 K. Using the values of the activation energy and the diffusion constant, the thickness of the diffusion layer was predicted to be sufficiently thin: 12 μm by the hot pressing at 1073 K for 10 h. This predicted value was in good agreement with the experimental result of 7 μm.
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  • Masuo Yamada, Moritaka Hida, Takehide Senuma
    2008 Volume 49 Issue 9 Pages 2006-2011
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 24, 2008
    JOURNALS FREE ACCESS
    Quenching and annealing experiments with electrical resistivity measurements were applied to magnesium to investigate the formation of thermal vacancies. Two specimens made from materials differing in impurity contents were examined. One of the specimens quenched in a methanol bath at −80°C from elevated temperatures ranging from 160°C to 500°C revealed a significant decrease in electrical resistance after annealing for 10 min in the bath. Based on the annealing behaviors at low temperatures (−100°C to −60°C) after the quenching from 200°C, this decrease is thought to be due to the presence of hydrogen in solution. The other specimen, presumably containing smaller amounts of hydrogen, was quenched in iced water from elevated temperatures (200°C–560°C) which yielded results characterized by two thermal activation processes. These processes had the activation energies 54.1 kJ/mol (0.56 eV) and 89.8 kJ/mol (0.93 eV) for the lower and higher quenching temperature ranges, respectively. The former is ascribed to the formation energy of a vacancy interacting with hydrogen and the latter to the intrinsic formation energy of a vacancy. The difference between these energies, 35.7 kJ/mol (0.37 eV), is the binding energy between a vacancy and a hydrogen atom.
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  • Kazuyuki Ueda, Kazuya Yasuda
    2008 Volume 49 Issue 9 Pages 2012-2015
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    In cooling process of Pt(111) in an ultra high vacuum (UHV), hydrogen segregates and saturates on the surface. A time-of-flight type electron-Stimulated desorption (TOF-ESD) spectroscopy measures hydrogen ions desorbed from Pt(111) surface. The H+ signal intensity decreases with increasing of CO exposures on the H-saturated Pt(111) surface. After saturation of CO adsorption, TOF-ESD measures various intensities of the H+ and O+ (from CO) depending on specimen temperature. From the TOF-ESD results in the CO saturated surface, hydrogen is hidden under the subsurface due to CO adsorption. Desorption of hydrogen under layer of CO necessitates 80 K higher temperatures compared with CO free layer on Pt(111).
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  • Oleg D. Sherby, Jeffrey Wadsworth, Donald R. Lesuer, Chol K. Syn
    2008 Volume 49 Issue 9 Pages 2016-2027
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    A model is developed to describe the formation and crystal structure of martensite in quenched Fe-C steels based on the extensive published literature on the subject. Unique changes in the properties and structure of martensite are shown to occur at 0.6 mass% C, designated as the H-point. The concept of primary and secondary martensite is introduced in order to indicate that two different, sequential, martensites will form during quenching of Fe-C steels above 0.6 mass% C. Below 0.6 mass% C, only primary martensite is created through the two sequential steps FCC → HCP followed by HCP → BCC. Primary martensite has a lath structure and is described as BCC iron containing a C-rich phase that precipitates during quenching. The HCP transition phase is critical in interpreting the two martensite structures based on the premise that the maximum solubility of C in the HCP phase is 0.6 mass%. Primary martensite continues to form at compositions greater than 0.6 mass% C with the creation of a carbon-rich BCT phase. This is followed by the start of secondary martensite which forms at the MS (martensite start temperature) and creates the traditional BCT plates adjoining retained austenite. Both martensites are predicted to co-exist at the highest C contents. A quantitative model, based on the specific volume of the various phases obtained after quenching, has been used to calculate the composition of the precipitated C-rich phase for a 0.88 mass% C steel. It is predicted that the carbon-rich phase is either diamond or η (Fe2C) carbide.
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  • Meie Li, Jinxiong Zhou
    2008 Volume 49 Issue 9 Pages 2028-2032
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Atoms on solid surfaces may self-assemble into ordered nanophases. The phase field method in combination with semi-implicit Fourier spectral method provides an ideal tool to simulate this dynamic process. The appearance of surface stress term in the evolving kinetic equations, however, may lead to divergence of simulation if standard spectral method is used. A stabilized scheme is proposed in this paper and a second-order approach is given to perform long time simulation with rather large time step. The scheme is used to simulate the self-assembly of binary epilayers with different average concentrations on a solid substrate. The results indicate that the self-assembly patterns are influenced by the average concentration, which agrees well with the experimental results. Based on the validated scheme, simulations of self-assembly guided by closed pre-patterns are performed. It is found that the closed pre-patterns can guide to form isolated closed loops after long time of evolution. This procedure provides a possible strategy to fabricate microelectronic devices and circuits.
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  • P. G. Xu, Y. Tomota, H. Suzuki, T. Suzuki, S. Machiya, F. X. Yin
    2008 Volume 49 Issue 9 Pages 2033-2039
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    {110}, {200} and {211} neutron diffraction profiles of an interstitial-free annealed steel sheet were measured on 5×5 degrees stereographic angle grids, and several evaluation methods of diffraction intensity were employed to calculate the bulk texture, including the peak intensity at a constant 2theta angle, the simply summed intensity in a constant 2theta angle spread and the Gaussian integrated intensity obtained by single peak fitting of each profile. The comparison among differently evaluated bulk textures shows that a stronger {111}⟨uvw⟩ fiber component and a weaker {001}⟨110⟩ rotated cube component appear in the texture of investigated steel and the Gaussian integrated intensity method with proper coefficient constraints possesses a higher sensitivity to both weak texture components and strong ones. The crystallographic orientation maps obtained from electron backscattering diffraction and the bulk textures estimated from X-ray diffraction confirm the feasibility of the neutron bulk texture based on the Gaussian integrated intensity, suggesting that it can be suitably utilized to evaluate the global orientation distribution characteristics of heterogeneous materials.
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  • Rong Tu, Takashi Goto
    2008 Volume 49 Issue 9 Pages 2040-2046
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 16, 2008
    JOURNALS FREE ACCESS
    Highly thermally stable anatase films were prepared by metal-organic chemical vapor deposition (MOCVD) using Ti(O-i-Pr)2(dpm)2 as precursor. The effect of heat treatment on the microstructure, transmittance, optical band gap and refractive index of anatase films was investigated. Anatase films in a single phase were obtained at Tsub (substrate temperature) < 723 K. By heat-treating the anatase film at 1273 K, no phase transformation was observed without changing the transmittance and optical band gap, whereas the refractive index increased. A small amount of rutile phase was identified in the anatase film by heat-treating at 1323 K. The anatase films transformed into rutile in a single phase by heat-treating at 1373 K, resulting in a decrease in transmittance and optical bandgap and an increase in refractive index.
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  • Akira Yamauchi, Tatsuya Sasaki, Akira Kobayashi, Kazuya Kurokawa
    2008 Volume 49 Issue 9 Pages 2047-2053
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 16, 2008
    JOURNALS FREE ACCESS
    In order to improve the oxidation resistance of WSi2 at 873–1473 K, B added WSi2 was fabricated by a spark plasma sintering method and oxidation tests were carried out in air. The fabricated B added WSi2 consists of WSi2, Si and W2B5. The addition of B into WSi2 leads to the formation of a protective borosilicate scale, resulting in improvement of the oxidation resistance. Requisite concentration of B for the formation of a protective borosilicate scale decreases as the temperature is raised. Consequently, the addition of 2 or 3 mass% B is the most effective for improvement of the oxidation resistance of WSi2 in the temperature range of 873–1473 K. Such effect of B on high-temperature oxidation of WSi2 is also discussed.
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  • Shin-ichi Hasegawa
    2008 Volume 49 Issue 9 Pages 2054-2057
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 16, 2008
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    To establish a rapid trace-quantification scheme for elements contained in highly purified tungsten, we studied the most suitable conditions for separating the elements using solid-phase-extraction as a pretreatment for inductively coupled plasma-mass spectrometry (ICP-MS). We used chemically bonded silica gels belonging to the functional group of benzylsulfonic acid as extracting agent. Tungsten was anionized by adding hydrogen peroxide solution to a sample that had been decomposed with acid. We separated the cation trace impurities that were present in the chemically bonded silica gel of the ion-exchange type. The target elements retained in the chemicals were then eluted using 10 cm3 of 2 kmol/m3 nitric acid. Quantities of the obtained target elements were determined using ICP-MS.
    Highly sensitive quantification was established for 15 trace elements in highly purified tungsten, and for Be, Al, Mg, Mn, Fe, Co, Ni, Cu, Zn, Ga, Cd, In, Tl, Pb, and Bi with the following detection limits [3σ; ng/g (ppb)]: Be 0.11, Al 0.14, Mg 0.12, Mn 0.15, Fe 1.81, Co 0.086, Ni 0.082, Cu 0.092, Zn 0.12, Ga 0.074, Cd 0.012, In 0.069, Tl: 0.082, Pb 0.071, and Bi 0.036.
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  • Keisuke Iwata, Yoshitake Nishi
    2008 Volume 49 Issue 9 Pages 2058-2062
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
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    The effect of electron-beam (EB) irradiation on the impact value of silica glass was studied by means of a standard Charpy impact test. When it performed in short bursts to maintain a low temperature, EB irradiation at a dosage of less than 0.216 MGy increased the impact value of the glass. Because the EB irradiation generated dangling bonds in the silica glass, partial relaxation of residual strain probably occured around these dangling bonds in the network structure. If this relaxation resulted in optimization of the interatomic distance of the silicon–oxygen pairs to minimize the potential energy, it would increase the bonding energy of the network structure. The increased impact value was therefore mainly due to an increase in the bonding energy for the silicon–oxygen atomic pairs in the atomic network structure, as well as to the relaxation of the network structure.
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  • Hidekazu Sueyoshi, Hisayoshi Fukudome
    2008 Volume 49 Issue 9 Pages 2063-2067
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 24, 2008
    JOURNALS FREE ACCESS
    Carbon material/nickel/copper system was heated under a compressive stress of 13 MPa in a vacuum at 1073 K for different keeping times, and the bending strength of the joint, the microstructure, hardness and carbon concentration near the joining interface were examined. Thermal stress induced in the joint was estimated by a finite element method. In carbon material/copper system solid state bonding is difficult. However, good solid state bonding becomes feasible when nickel is used as an insert metal. Axisymmetric thermoelastic finite element analysis reveals that the maximum tensile thermal stress is induced on the surface of carbon material near the joining interface, and it decreases with increasing nickel thickness. The maximum residual tensile thermal stress in practical joints is less than the maximum tensile thermal stress calculated by finite element method because the thermal stress is released.
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  • Hiroshi Kato, Hirotsugu Kobayashi
    2008 Volume 49 Issue 9 Pages 2068-2075
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 06, 2008
    JOURNALS FREE ACCESS
    Copper plates of 1 mm in thickness were joined with a solder layer (60 μm in thickness) of Sn-3.8 mass% Ag-1.2 mass% Cu alloy, and then subjected to the shear fatigue testing. At required numbers of fatigue cycles, the specimen was subjected to the acoustic microscopy to measure the shape and the size of the bonded region. After fatigue testing, the fracture surface was observed through scanning electron microscope to verify the distribution of fine penny-shaped cracks in the bonded region. The area of the bonded region estimated from the acoustic image monotonically decreased with increasing number of fatigue cycles. The larger the initial bonded region, the longer was the fatigue life. The density of the penny-shaped crack in the bonded region decreased with the distance from the edge of the bonded region, and increased with the number of fatigue cycles. The average size of the penny-shaped crack slightly increased with the distance from the edge of the bonded region, but showed no dependence on the number of fatigue cycles. The numerical calculation was also conducted with a simple model to obtain the bonded area as a function of the number of fatigue cycles. The calculated change in the bonded area with the number of fatigue cycles agreed well with the estimated one from the acoustic image. Calculated distributions of the density and the average size of the penny-shaped crack explained the change in the measured ones with the distance from the edge of the bonded region.
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  • Fengping Lai, Rong Tu, Takashi Goto, Jingfeng Li
    2008 Volume 49 Issue 9 Pages 2076-2081
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 16, 2008
    JOURNALS FREE ACCESS
    Ferroelectric NaxK1−xNbO3 (NKN) films were prepared on quartz and Pt/SrTiO3(100) substrates by pulsed laser deposition. The effects of composition and preparation conditions on the crystal structure and ferroelectricity of the NKN films were investigated by changing the Na content (x), substrate temperature (Tsub), oxygen partial pressure (PO2), target-to-substrate distance (Dt-s) and laser energy density (EL). The permittivity values of the NKN films were 390 to 520 at room temperature and 100 kHz, showing a maximum at x=0.5. The maximum remnant polarization value was 8.2×10−2 C m−2 at x=0.5.
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  • Sara Khamseh, Masateru Nose, Tokimasa Kawabata, Atsushi Saiki, Kenji M ...
    2008 Volume 49 Issue 9 Pages 2082-2090
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 24, 2008
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    CrAlN films were prepared by a pulsed DC magnetron sputtering in FTS mode with Cr-Al alloy targets (Cr/Al = 30 at%/70 at%) in a mixed atmosphere of Ar and N2. Effects of different deposition conditions (frequency, duty cycle, nitrogen flow rate and pulsed DC power) on the films structure and phase formation have been investigated. XRD analyses were carried out to determine the phases of the films. The surface morphology was observed using FE-SEM. 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. All films exhibited mixture of fcc-CrN and hcp-AlN structures with changing the sputtering conditions. With increasing pulse frequency, the relative percent of fcc-CrN phase decreased from ∼100% to ∼20%. In the current study it was found that there is an optimal duty cycle (around 82%) where the fcc-CrN relative% reaches to its highest value (about 98%). On the other hand, grain size of the films kept in the range of 20–25 nm below 82% of duty cycle, then increased up to ∼50 nm with increasing duty cycle. Changing the nitrogen flow rate affected the fcc-CrN relative % and films morphology. Under optimal nitrogen flow rate, fcc-CrN relative % reached to about 100% in addition to the formation of micro columnar morphology, which resulted in the highest plastic hardness of the films. It seems that the mechanical properties of the CrAlN films are directly influenced not only by fcc/hcp phase ratio, but also by morphology. These results suggest that the dominant fcc-CrN phase and high hardness of CrAlN films containing high Al content (Cr:Al=3:7) can be obtained under the restricted condition by the pulsed DC magnetron sputtering in FTS mode.
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  • Satoko Kuwano, Takeshi Fujita, Deng Pan, Ke Wang, Mingwei Chen
    2008 Volume 49 Issue 9 Pages 2091-2095
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
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    Ultra-large compressive plasticity at room temperature has recently been observed in electrodeposited nanocrystalline nickel (nc-Ni) under micro-scale compression (Pan, Kuwano, Fujita, Chen, Nano Letters 7, 2108 (2007)). The evolution of microstructure of nc-Ni during ultra-large deformation is outlined at a variety of strain levels, with TEM observations in combination with a TEM sample preparation technique using focused ion beam (FIB).
    This paper demonstrates focused ion beam (FIB) technique to prepare transmission electron microscopy (TEM) samples from microcompressed specimens. There has been a demand to prepare TEM samples from a point of interest to study microstructures on atomic scales. Conventional techniques used to make TEM samples, such as chemical polishing or ion-sputtering milling, cannot provide reliable opportunity to make TEM samples from a point of interest. With this technique, the deformation mechanism on atomic scales can be fairly connected with the result of microcompression test, which is available for size-limited materials.
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  • Masahide Kohzu, Shota Nakatsuka, Kenji Higashi
    2008 Volume 49 Issue 9 Pages 2096-2099
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
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    The rolling textures evolution of AZ31 magnesium alloy sheets is investigated by the eccentric-rolls drawing as a simulated rolling. The eccentric-rolls provides a sheet continuously changing in rolling reduction, and a exact processing temperature is ensured by uniformly heating the free-rotatable rolls together with a test piece in a furnace. The formed textures at the different rolling rates of 10 and 100 mm·s−1 showed no significant differences in any temperature and rolling reduction. The double peak texture, which appreciably improves low-temperature formability of this alloy, was obtained under rolling reduction of 22% or above at 423–523 K. On the other hand, at 573 K, the texture was typically concentric circle.
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  • Sang-Mok Lee, Byeung-Gee Kim, Young-Ho Kim
    2008 Volume 49 Issue 9 Pages 2100-2106
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
    JOURNALS FREE ACCESS
    Chip-on-glass (COG) bonding using a nonconductive adhesive (NCA) and the entrapment of NCA and fillers in the COG joints were studied. Sn was used as a bump material because it has a higher propensity of plastic deformation than an Au bump. Three types of Sn bumps were fabricated, electroplated Sn bumps, reflowed Sn bumps, and coined Sn bumps. Three types of NCAs were applied during COG bonding. The reflowed bump had the least amount of trapped NCA with fillers among the bumps studied. The NCA with the lowest viscosity was trapped the least compared to the other NCAs. The electrical test results showed that contact resistance increased with increasing amounts of trapped NCA with fillers in the COG joint.
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  • Young Sam Park, Jung Wook Lim, Woo Seok Yang, Seung-Yun Lee, Sung-Min ...
    2008 Volume 49 Issue 9 Pages 2107-2111
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    The unique solution to the stress reduction of Ge2Sb2Te5 phase-change material has been known to cap a layer with an inherently huge compressive stress. In this paper, another approach to the stress reduction is firstly presented in view of the compositional change of Ge2Sb2Te5, particularly due to oxygen diffusion. During thermal cycles, we measured the radius changes using four kinds of samples and calculated their stress-changes using Stoney equation. In case of basic specimen, more oxygen in Ge2Sb2Te5 and larger stress-change are observed as cycling temperature increases. In the rest of samples, the stress-change is reduced compared with the basic one, only when a capping layer on Ge2Sb2Te5 blocks the oxygen penetration effectively. The stress increase by the oxygen diffusion is considered to be due to the lattice distortion of Ge2Sb2Te5.
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  • Victor Montenegro, Hiroyuki Sano, Toshiharu Fujisawa
    2008 Volume 49 Issue 9 Pages 2112-2118
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Most of the dust generated from the copper smelting process in Chili has been stored after the stabilization by hydrometallurgical process because it contains high concentration of arsenic. However, in recent years, the generation of dust has increased because of degrading the quality of concentrate. In addition, the environmental regulations become stricter. On the other hand, valuable metals such as copper and zinc are contained in the dust at high concentrations and it is desirable to recover them. In this study, the effect of recirculation of dust to the smelting process was examined in order not only to decrease the amount of dust but also to recover copper. The generation of dust and the distribution of arsenic, lead, zinc and so on among the matte, slag and gas phases were evaluated as a function of the amount of recirculated dust, partial pressure of oxygen and temperature. It was found that the direct return of dust to the smelting process was quite effective for the recovery of copper and the reduction of dust amount, but the acceptable amount of returnable dust was limited by the produced matte quality.
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  • Masami Tsunekawa, Yuta Sasaki, Yoshiaki Nakamura, Mayumi Ito, Naoki Hi ...
    2008 Volume 49 Issue 9 Pages 2119-2123
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
    JOURNALS FREE ACCESS
    Methyl ethyl ketone (MEK) is a good solvent for polyvinyl chloride (PVC) and it has been proposed for use in PVC recycling. In the recycling process, fine particles of 3PbO·PbSO4·H2O, used as a thermal stabilizer in PVC products, are dispersed and not dissolved in the solvent. To establish methods for removing of 3PbO·PbSO4·H2O particles from the solvent, factors affecting the dispersion-flocculation behavior of the particles in MEK were investigated.
    The zeta potential and particle distribution of 3PbO·PbSO4·H2O particles in MEK solutions containing known amounts of H2O were measured. Above 5 vol%H2O in MEK solutions, the zeta potential of 3PbO·PbSO4·H2O particles approached zero and the flocculation of particles was achieved. In addition, it was found that Pb2+ and Cl affect the zeta potential of the particles. These results indicate that the dispersion-flocculation behavior of lead particles can be influenced by the concentration of H2O, Pb2+, and Cl in MEK.
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  • Shun Myung Shin, Jin Gu Kang, Dong Hyo Yang, Jeong Soo Sohn, Tae Hyun ...
    2008 Volume 49 Issue 9 Pages 2124-2128
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 06, 2008
    JOURNALS FREE ACCESS
    This paper describes the ammoniacal ammonium carbonate leaching behavior of zinc and manganese from spent zinc-carbon batteries. For selective extraction of Zn from the spent zinc-carbon battery, leaching tests were carried out as a function of process parameters such as concentration of (NH4)2CO3, ammonia, temperature, time and pulp density. Physical methods of separation such as crushing was applied to reduce the material to 10–20 mm size followed by magnetic separation to separate iron with a recovery about 10 mass% leaving most of Zn and Mn in the non-magnetic fraction. Non-magnetic fraction was further subjected to sieving to separate 2.46 mm over and under size fractions. The oversize material was processed by eddy current separation to recover zinc sheet and carbon rods and plastics. The under size material with chemical composition of Zn 15.5 mass%, Mn 17.5 mass%, and Fe 1.4 mass% was used for leaching studies. Under the optimum leaching conditions (2.0 kmol/m3 (NH4)2CO3 and 4.0 kmol/m3 ammonia, 40°C, 100 g/L pulp density, 30 min and 250 rpm), the leaching efficiency of zinc and manganese was 80.2% and less than 0.1%, respectively, indicating the selective recovery of zinc from the spent zinc-carbon battery. An overall zinc recovery is about 88%.
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  • Katsunari Sasaki, Takayoshi Nakano, Joseph D. Ferrara, Jee-Wook Lee, T ...
    2008 Volume 49 Issue 9 Pages 2129-2135
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Two-dimensional quantitative analysis of point focus X-ray beam diffraction (XRD) was performed using a transmission optics system to examine the biological apatite (BAp) orientation in the femurs of an osteopetrotic (op/op) mouse and a normal mouse. The Mo Kα (wavelength: 0.07107 nm) was used as characteristic X-ray radiation as a substitute for conventional Cu Kα (wavelength: 0.15418 nm) radiation. At first a theoretical calculation concerning with X-ray absorption and peak resolution was performed, and subsequently X-ray diffraction measurements were carried out to confirm the usefulness of the transmission X-ray method by Mo Kα radiation. The distribution of the preferential orientation of the BAp c-axis was finally measured and calculated as an integrated intensity ratio of (002)/(310) in a plane roughly containing the bone longitudinal axis. The result resembled analysis from a conventional reflection X-ray diffraction method by Cu Kα radiation but this transmission optics system was more convenient for the screening of BAp orientation in bones without sectioning.
    The distribution of the preferential alignment of the BAp c-axis was measured as a function of the longitudinal axis in the femurs of a 12-week mutant osteopetrotic (op/op) mouse and a littermate control mouse. The preferential alignment of the BAp c-axis along the longitudinal direction is much lower in the op/op mouse than in the control mouse in all analytical positions. The transmission optics system using Mo Kα radiation in this study provides a fuss-free method for analyzing BAp orientation as a bone quality parameter.
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  • Chiang-Hao Li, Lung-Jen Chiang, Yung-Fu Hsu, Wen-Hsiung Wang
    2008 Volume 49 Issue 9 Pages 2136-2140
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 06, 2008
    JOURNALS FREE ACCESS
    A multi-stage transformation (MST) has been observed in cold-worked Ti–50.3 at%Ni shape memory alloy by differential scanning calorimetry (DSC). When thickness reduction reaches about 5% strain, the phenomenon is able to occur in 50.3 at%Ni alloy. The multi-stage transformation behavior is due to interior microstructure variation, i.e., texture formation and defects aggregation which caused localized stress fields and affected the phase transformation behavior.
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  • Q. S. Zhang, W. Zhang, X. M. Wang, Y. Yokoyama, K. Yubuta, A. Inoue
    2008 Volume 49 Issue 9 Pages 2141-2146
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    Bulk glassy alloy rods with a diameter of 16 mm and a length of 40 to 45 mm were produced for Zr65Al7.5Ni10Cu17.5 alloy by a tilt casting method. The alloy specimens taken from the different sites which are away by about 10 mm, 15 mm and 30 mm from the bottom surface of the cast rod consist of a glassy phase and their thermal stability, mechanical properties and fracture mode are almost independent of the specimen sites. The glass transition temperature, temperature interval of supercooled liquid region before crystallization and heat of crystallization are about 643 K, 102 K and 55 J/g, respectively, for the specimens taken from the three different sites. Besides, Young’s modulus, yield strength, fracture strength, yield strain and plastic strain of the specimens are about 87 GPa, 1540 MPa, 1580 MPa, 0.018 and 0.005, respectively. The fracture mode consisting of shear plastic deformation along the maximum shear stress plane, followed by an instantaneous final rupture is also independent of the specimen sites. These data indicate that the cast glassy alloy rod with a diameter of 16 mm has nearly the same characteristics, though the cooling rate is significantly dependent on sample sites. The knowledge of producing the Zr-based bulk glassy alloy rod with nearly the same characteristics in the large diameter range up to 16 mm is encouraging for future applications of bulk glassy alloys as a new type of engineering material.
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  • Byung-Su Kim, Eun-young Kim, Ho-Suck Jeon, Hoo-In Lee, Jae-Chun Lee
    2008 Volume 49 Issue 9 Pages 2147-2152
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    The reduction of MoO2 powder by hydrogen is one of the most important steps for manufacturing ferromolybdenum alloy and molybdenum powder. The results of experiments on the kinetics of this reaction are presented in this paper. The experiments were carried out under nonisothermal condition in hydrogen atmosphere using TGA equipment. The nonisothermal experiments were carried out at various linear heating rates up to 1273 K. It was found that the reduction reaction is very fast under the whole heating rate until the reduction ratio of MoO2 approaches to about 0.92. The reduction ratio of MoO2 was about 0.98 after finishing the reduction reaction at a heating rate of 4 K/min. Kinetics of the reaction was analyzed from the dynamic TGA data by means of Coats and Redfern equation. The nucleation and growth model yielded a satisfactory fit to these experimental data.
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  • Heeman Choe, Susan Abkowitz, Stanley M. Abkowitz
    2008 Volume 49 Issue 9 Pages 2153-2158
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    7.5 mass% TiC and 7.5 mass% W powder blends were densified with Ti-6Al-4V blends by combined cold and hot isostatic pressing (CHIP) method to result in three types of composites with differing processing histories, namely hot isostatic pressing (HIPping), extrusion, and casting, which were compared with their monolithic counterparts. Tensile and microhardness tests, along with compressive testing, were carried out to investigate the mechanical properties of powder metallurgy (P/M) Ti-6Al-4V-7.5%TiC-7.5%W composites at ambient temperature. Dissolution of W powder in the Ti-6Al-4V matrix during consolidation seems to be limited by the presence of TiC particles, which can in turn influence mechanical properties of the composites. Cast Ti-6Al-4V-7.5%TiC-7.5%W composite exhibits superior hardness, yield strength, and tensile strength, with a decrease in ductility, compared to its monolithic counterpart and other composites.
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  • Kai Tao, Xianglin Zhou, Hua Cui, Jishan Zhang
    2008 Volume 49 Issue 9 Pages 2159-2162
    Published: September 01, 2008
    Released: August 25, 2008
    JOURNALS FREE ACCESS
    In this paper, a high-performance nanostructured NiCrC alloy coating was synthesized by HVAF spraying of nanostructured feedstock powder, which was prepared using cryogenic ball milling (cryomilling) method. The morphology and microstructure of the powder and coating were characterized by metallographic microscope, scanning electron microscope and transmission electron microscope. A Vickers microhardness tester was employed to determine the mechanical properties of the coating. The corrosion resistance was tested with thermogravimetric method, and the thermal stability of the coating was examined as well. The experimental results indicated that the nanostructured NiCrC coating possessed a very dense and uniform microstructure and exhibited sufficient thermal stability during long time heat treatment. Furthermore, the mechanical and anti-corrosion properties were enhanced so much compared with its conventional coarse-grained counterpart. The excellent performances make this HVAF sprayed nanostructured coating a hopeful candidate for improving boiler tubes protection.
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  • D. Shi, D. Li, G. Gao, L. Wang
    2008 Volume 49 Issue 9 Pages 2163-2165
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: August 13, 2008
    JOURNALS FREE ACCESS
    A relationship between the surface tension of cast iron and the graphite shape has been proven by experimental analysis and thus the graphite shape can be forecast by the surface tension. A specific relation between the surface tension and the graphite shape has been established by experiments. When the surface tension is above 1385 mN/m, nodular graphite occurs. When the surface tension is between 1283 mN/m and 1385 mN/m, vermicular and nodular graphite occurs. When the surface tension is between 1108 mN/m and 1283 mN/m, vermicular graphite occurs. When the surface tension is between 990 mN/m and 1108 mN/m, flake and vermicular graphite occurs. When the surface tension is below 990 mN/m, flake graphite occurs.
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  • Jung-Yeul Yun, Jae-Ho Jeon, Suk-Joong L. Kang
    2008 Volume 49 Issue 9 Pages 2166-2168
    Published: September 01, 2008
    Released: August 25, 2008
    [Advance publication] Released: July 30, 2008
    JOURNALS FREE ACCESS
    Sodium niobate (NaNbO3) powder was successfully synthesized by high-energy milling of commercially available Na2CO3 and Nb2O5 powders. The powder mixture was subjected to a mechanochemical treatment of up to 300 min using a ZrO2 vial and ZrO2 or WC balls. The formation of NaNbO3 was monitored by X-ray diffraction. Use of WC balls reduced the time required for synthesis. It was possible to synthesize NaNbO3 within 120 min when using WC balls. The mechanochemically synthesized powder consisted of agglomerates of nano size particles of 10–20 nm, whereas the size of powders prepared by conventional calcination was 100–600 nm.
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