MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 44 , Issue 1
Showing 1-33 articles out of 33 articles from the selected issue
  • Rodolfo Ariel Perez, Hideo Nakajima, Fanny Dyment
    2003 Volume 44 Issue 1 Pages 2-13
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Impurity diffusion in α-Ti and α-Zr is characterized by fast interstitial diffusion of small atoms and slow substitutional diffusion of large atoms. The mechanism of the fast diffusion is discussed on the basis of the several features: the effect of α-β phase transformation, the diffusion anisotropy, the atomic size effect and the correlation between solubility and diffusivity. The temperature dependence of the diffusion coefficients of all the solutes and solvent Ti studied in α-Ti follows the Arrhenius law, whereas in α-Zr, all the elements studied with exception of Ti show downward curvatures that follow the self-diffusion behaviour in α-Zr. The influence of ultra-fast diffusion impurities on the diffusion process in these matrices, as well as the possibility that different mechanism acts in each matrix is analyzed.
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  • Christian Herzig, Sergiy V. Divinski
    2003 Volume 44 Issue 1 Pages 14-27
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    An overview on recent progress in grain boundary (GB) diffusion study is presented with emphasis on physical phenomena encountered in GB diffusion experiments such as the linear and non-linear segregation effects. Systematic investigations on pure and alloyed poly- and bicrystals gave conclusive information on the solute segregation behavior and allowed to extract the segregation isotherm solely from GB diffusion studies. Recent progress in fundamental understanding of diffusion processes in two-scale materials with two types of short-circuit diffusion paths is discussed on the basis of GB self-diffusion experiments and Monte-Carlo simulations in powder sintered nanocrystalline material.
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  • Tomonori Watanabe
    2003 Volume 44 Issue 1 Pages 28-33
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    In order to reveal the microscopical mechanism which causes the plastic deformation induced by the vacancy diffusion process, we model and analyze mathematically the motion of the atom with the vacancy in an atomic chain. We describe the dynamics of the atom with the vacancy by a kind of the diffusion equation which includes the essential effects on the plastic deformation, namely, the thermal effect, the interactions of atoms, the friction of the environment and the external force. Stripping off the fluctuation of the prime motion by the perturbation expansion, we can get the situation where the essential motion of the atom with the vacancy is represented by the propagation of the kink wave which responds to the external force and the temperature, though the system is described by the diffusion process. Then deriving the strain of the atomic chain, we show the strain against time behaves viscoelastically like the typical response, for instance, that of the Voigt model. The properties of the temperature and the applied stress coincide with the well-known results of the primary creep phenomenon.
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  • Yoshitaro Nosé, Teruyuki Ikeda, Hideo Nakajima, Hiroshi Numakur ...
    2003 Volume 44 Issue 1 Pages 34-39
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The tracer diffusion coefficient of Fe and the chemical diffusion coefficient in L12-ordered Pt3Fe have been measured at temperatures below the order-disorder transition temperature. The tracer diffusion coefficient of Fe in a nearly stoichiometric alloy is curved upwards in the Arrhenius plot on approaching the order-disorder transition temperature. The chemical diffusion coefficient is about 10–30 times larger than the diffusion coefficient of Fe. The tracer diffusion coefficient is influenced by composition, namely, it increases with increasing the concentration of Fe through the stoichiometric composition, but this trend almost vanishes at higher temperatures. The chemical diffusion coefficient is virtually independent of composition. The tracer diffusion coefficient of Pt has been estimated from the Darken-Manning relation. At 1223 K, it is in between the chemical diffusion coefficient and the tracer diffusion coefficient of Fe.
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  • Tien-Fu Chen, Gyanendra Prasad Tiwari, Yoshiaki Iijima, Kiyoshi Y ...
    2003 Volume 44 Issue 1 Pages 40-46
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Volume and grain boundary diffusion of chromium in Ni–16 mass%Cr–7 mass%Fe alloys containing 0.004, 0.015 and 0.07 mass% of carbon have been measured using radioactive tracer 51Cr over the temperature range of 858–1424 K by serial radio-frequency sputter-microsectioning technique. While the volume diffusion coefficients are largely unaffected by the presence of carbon, the increase in carbon content markedly reduces the mobility of chromium atoms along the grain boundaries. As a result, the difference between the activation energy for lattice and grain boundary diffusion decreases with increase in carbon content. In fact, for 0.07 at% carbon, the activation energies for volume and the grain boundary diffusion are nearly same. Among all three alloys, the difference between the volume diffusion coefficient, Dv, as well as δDgb (δ = grain boundary width; Dgb = grain boundary diffusion coefficient) decreases gradually in a regular manner with the rise of temperature. Grain bounadry energy is reduced by addition of carbon and enhanced by temperature. At higher temperatures, there is no difference between the grain boundary energies of the three alloys.
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  • Takanari Ogata, Mitsuo Akabori, Akinori Itoh
    2003 Volume 44 Issue 1 Pages 47-52
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Two types of diffusion couples, U–23 mol%Zr with U–23 mol%Zr–1.3 mol%Ce and U–95 mol%Zr with U–23 mol%Zr–1.3 mol%Ce, were annealed isothermally at 1123 K and 1023 K in order to provide basic data on Ce diffusion in U–Zr alloys, which are the fuel forms for advanced nuclear reactors. Because the Ce solubility in the U–23 mol%Zr alloy is less than 1 mol% in this temperature range, Ce-rich precipitates were formed and dispersed in the U–23 mol%Zr–1.3 mol%Ce alloy. The concentration profiles of Ce in the U–23 mol%Zr/U–23 mol%Zr–1.3 mol%Ce couples were analyzed based on the theoretical solutions of the one-dimensional diffusion equation for the semi-infinite diffusion couple, either side of which is supersaturated with the diffusing substance. From this analysis, the diffusion coefficients of Ce in the U–23 mol%Zr solid solution (γ–U, β–Zr) were estimated to be ∼2×10−13 m2/s at 1123 K and ∼6×10−14 m2/s at 1023 K, which are between the values extrapolated from the reported self-diffusion coefficients of γ–U and β–Zr. In the U–95 mol%Zr/U–23 mol%Zr–1.3 mol%Ce couples annealed at 1123 K and 1023 K, the concentration profiles showed up-hill diffusion of Ce. The interdiffusion coefficients in this quasi-binary U–Zr system containing Ce were obtained from the U or Zr concentration profile and compared with the reported interdiffusion coefficients in the binary U–Zr system without Ce. The result indicated that Ce does not have significant influence on interdiffusion in the U–Zr solid solutions.
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  • Hisanori Tanimoto, Seiji Sakai, Hiroshi Mizubayashi
    2003 Volume 44 Issue 1 Pages 53-58
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    High-density nanocrystalline (n-) Au was prepared by the gas deposition method. Various anelastic and plastic creep processes associated with the grain boundary (GB) regions were observed. The vibrating reed measurements at 102 Hz with strain amplitude of 10−6 show a very broad internal friction peak near 95 K, Qp,95 K−1, and a steep increase in the anelastic strain above 200 K, εa-I,>200 K. The tensile tests show a steep increase in the anelastic strain above 200 K, εa-II,>200 K, for the stress beyond a few MPa and a linear plastic creep strain above 200 K, εpc-1, for stress range between 30 MPa and 150 MPa. The activation parameters, 1⁄τ0 of 3×1011 s−1 and E of 0.16 eV, are found for Qp,95 K−1, where τ0 and E are a pre-exponential factor and an activation energy of the relaxation time τ. We surmise that simple relaxation processes are responsible for Qp,95 K−1. The values of 1⁄τ0 and E found for εa-I,>200 K and εa-II,>200 K decrease with increasing the applied stress or the temperature, indicating that their atomic processes are the same feather. Further, E found for εpc-1 is similar to or slightly smaller than that of εa-II,>200 K. These observations indicate that the atomic motions in the GB regions of n-Au develop in scale in the order of the underlying processes for εa-I,>200 K, εa-II,>200 K and εpc-1, and are so different from those in the conventional polycrystalline Au.
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  • Ayako Kushida, Katsushi Tanaka, Hiroshi Numakura
    2003 Volume 44 Issue 1 Pages 59-62
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Diffusion in FePt has been studied with emphasis on the effect of order-disorder transition by interdiffusion experiments below and above the L10–A1 transition temperature. The chemical diffusion coefficient in the disordered state obeys the Arrhenius law with the effective activation energy of 3.1 eV (1 eV=1.6×10−19 J). Anisotropy of diffusion in the ordered state has been examined using monovariant single-crystals of the tetragonal L10 structure. The coefficient of diffusion in the a-axis direction is slightly lower than the extrapolation of the diffusivity from the disordered state, while that of diffusion in the c-axis direction deviates significantly toward lower values. The apparent activation energy for the diffusion in the two directions is 3.2 and 3.8 eV, respectively.
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  • Yoritoshi Minamino, Yuichiro Koizumi, Nobuhiro Tsuji, Toru Yamada, Tom ...
    2003 Volume 44 Issue 1 Pages 63-71
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Binary, ternary and quaternary interdiffusion experiments have been investigated in cobalt solid solutions including Al, Cr, and Ni elements at 1423 K. The direct interdiffusion coefficients of Al, Cr and Ni are positive. Among them, the coefficients of Al are the largest, and those of Ni are the smallest. The indirect interdiffusion coefficients between Al and Cr are positive, but those between Al (or Cr) and Ni are negative. The addition of Al element to Co solid solution largely enhances diffusion but the addition of Cr and Ni elements slightly enhances diffusion. The effect of the addition of elements on interdiffusion are evaluated quantitatively from the factors related to the solidus temperature of Co solid solutions, the diffusivity of elements in pure Co and the interaction parameters between solute elements. The evaluated values of interdiffusion coefficients are in good agreement with the experimental ones.
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  • Dae-Gon Kim, Jeong-Won Yoon, Chang-Youl Lee, Seung-Boo Jung
    2003 Volume 44 Issue 1 Pages 72-77
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The reaction diffusion between indium solder and Au deposited (Ni and Cu) substrates was investigated. For the identification of intermetallic compounds, both Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD) were employed. Experimental results showed that the intermetallic compounds, such as Cu11In9 and In27Ni10, were observed for different substrates, respectively. Additionally, the growth rate of these intermetallic compounds was increased with the reaction temperature and time. We found that the growth of the intermetallic compound follows the parabolic law, which indicates that layer growth of the intermetallic compound was mainly controlled by volume diffusion over the temperature range. The apparent activation energies for intermetallic compound growth were 37.06 kJ/mol for Cu11In9 and 86.14 kJ/mol for In27Ni10, respectively.
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  • Ryusuke Nakamura, Yoshihiro Yamazaki, Yoshiaki Iijima
    2003 Volume 44 Issue 1 Pages 78-82
    Published: 2003
    Released: September 06, 2005
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    Interdiffusion coefficient in the B2 FeAl phase at 46–50 at%Al has been measured in the temperature range from 1173 to 1473 K under the pressure from 0.1 MPa to 5 GPa. The activation volume for interdiffusion, Δ\\ ildeV, derived from the pressure dependence of interdiffusion coefficient is found to be 0.58–0.90Vm (Vm: molar volume of alloys), which is comparable to or larger than 0.4–0.6Vm for the monovacancy mechanism in bcc pure metals or random alloys. The value of Δ\\ ildeV increases with increasing temperature and also with deviating from stoichiometry, suggesting that divacancy contributes to the diffusion in higher temperatures and in the region of off-stoichiometry.
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  • Osamu Taguchi, Gyanendra Prasad Tiwari, Yoshiaki Iijima
    2003 Volume 44 Issue 1 Pages 83-88
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The growth kinetics of the β-Ti solid solution phases in several pure metal diffusion couples have been investigated. The layer growth of β-Ti solid solution phases is observed to obey the parabolic law, indicating that the rate controlling process is diffusion. The temperature dependence of the rate constant of the layer growth shows a linear relationship in the Arrhenius plots at higher temperatures. On the other hand, it deviates from the linearity at low temperatures. This deviation from the linearity is shown to be related to the variation of compositional range of the β-Ti solid solution with temperatures. Additionally, the activation energy for the layer growth is found to be equal to sum of the activation energy for interdiffusion and the formation enthalpy of β-Ti solid solution in the eutectoid temperature range.
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  • Takeshi Aoki, Teruyuki Ikeda, Hideo Nakajima
    2003 Volume 44 Issue 1 Pages 89-93
    Published: 2003
    Released: September 06, 2005
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    Lotus-type porous brass has been fabricated by utilizing solid-state diffusion of zinc into porous copper which has been made by unidirectional solidification in pressurized hydrogen gas. The Zn diffusion has been carried out by thermal annealing of the porous copper. Zn was deposited by electroplating or vapor deposition method. It has been shown that the diffusion method is a very efficient way to synthesize the lotus-type porous alloys with a suitable composition.
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  • Hisanori Tanimoto, Seiji Sakai, Eiji Kita, Hiroshi Mizubayashi
    2003 Volume 44 Issue 1 Pages 94-103
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Nanocrystalline (n-) Au specimens with the density of 19400±200 kg/m3 were prepared by the gas deposition method. Since rearrangement of n-Au particles on the specimen surfaces takes place just after landing, the grain boundary energy of (0.3±0.15) J/m2 is comparable with 0.45 J/m2 reported for the bulk polycrystalline (p-) Au, and the concentration of vacancy type defects is about 15×10−4 in the as deposited state decreasing with the grain growth. The Young modulus observed at 10 K is almost the same to that estimated under the condition that stresses applied to the constituent crystallites are equal among all the crystallites while strains are variable.
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  • Hongwei Qin, Jifan Hu, Juan Chen
    2003 Volume 44 Issue 1 Pages 104-106
    Published: 2003
    Released: September 06, 2005
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    A series of perovskite-type compounds La0.7Sr0.3Mn1−xCuxO3 have been synthesized by solid state reaction with x=0,0.03,0.05,0.08,0.10,0.15,0.20,0.25,0.30. The Curie temperature and transition temperature of metal-insulator decreases when x value increases from 0 to 0.20. There is an enhancement of magnetoresistance ΔRR0 of compounds La0.7Sr0.3Mn1−xCuxO3 at room temperature which may be connected with the shift of Curie temperature and transition temperature of metal-insulator through Cu atom substitution. On the contrary, the increase of resistivity is due to the reduction of the double-exchange interaction.
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  • Eiji Yano, Yousuke Tamura, Tetsuichi Motegi, Eiichiro Sato
    2003 Volume 44 Issue 1 Pages 107-110
    Published: 2003
    Released: September 06, 2005
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    Grain refinement of cast magnesium alloys containing Al is attained by the well established technique of adding carbon materials. However, C2Cl6 as a grain refiner generates dioxin. Therefore, it is impossible to use grain refiners containing chloride. This study was performed to investigate grain refinement by adding carbon powder instead of harmful C2Cl6. Carbon is an important element for grain refining of commercial AZ91 magnesium alloy. Pure carbon powder was blown into the molten AZ91E magnesium alloy of 99.9% purity argon gas. Fine grains were obtained by adding the carbon powder. Foreign substances that functioned as nucleants could be observed in the center of each grain. The result of electron microprobe analysis indicated that the foreign substances were composed of Al, C and O.
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  • Byung-Kee Kim, Gook-Hyun Ha, Dae-Hwan Kwon
    2003 Volume 44 Issue 1 Pages 111-114
    Published: 2003
    Released: September 06, 2005
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    The TaC/VC inhibitor was added in nanophase WC/Co powders by either a mechanical or chemical doping method. The microstructure and mechanical properties have been investigated for the WC/Co hard alloys which were sintered with these powders. After sintering, most of the WCs maintained their original round morphology and fine microstructure. In the mechanically doped alloy, exaggerated and abnormal local grain growth was observed which was supposed to be caused by the non-uniform distribution of the TaC/VC dopant. However, such an abnormal grain growth problem does not appear in the alloy when the inhibitors were chemically doped into the powders. Due to relatively fine and homogeneous microstructure, the nanophase WC/Co doped by the chemical method showed a higher hardness and better transverse rupture strength than that doped by the mechanical method.
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  • ZhengMing Sun, Brigitte Weiss
    2003 Volume 44 Issue 1 Pages 115-117
    Published: 2003
    Released: September 06, 2005
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    By means of local measurement with a laser interferometry technique, the difference in fatigue crack opening evaluation results was revealed when the measurements were conducted at different locations along the length of a fatigue crack in an aluminum alloy. It was found that the crack opening stress increases when the measuring location approaches the crack tip. The experimental study leads to a suggestion that the fatigue crack closure result evaluated with the data obtained from a location far from the crack tip will underestimate the closure effect.
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  • Manabu Tamura, Hisao Esaka, Kei Shinozuka
    2003 Volume 44 Issue 1 Pages 118-126
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    An exponential type creep equation has been developed for heat resistant steels by the authors. This equation was induced assuming both a thermally activated process for a mobile dislocation and rather high applied stress. The applicability of the new creep equation was examined for a pure iron, two kinds of Ni-base super alloys and an eutectic solder alloy in a Pb–Sn system which were tested at relatively high temperatures and under very low stresses. All of the data obtained were completely explained by the new creep equation. The data for each alloy were classified into a few groups, where a deformation mechanism may be different with each other. The new creep equation is valid for stresses higher than the half value of the slope in a logarithm of time to rupture vs. linear stress diagram.
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  • Feng Wang, Kiyoshi Itoh, Tohru Watanabe
    2003 Volume 44 Issue 1 Pages 127-132
    Published: 2003
    Released: September 06, 2005
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    The crystallographic structures and surface morphologies of Fe–P binary alloy films electrodeposited at different bath concentrations and different electrodeposition conditions have been studied in detail by means of XRD, HRTEM and SEM. The crystallization sequences of deposited films under the heat-treatment were analyzed with the help of XRD. The crystallographic structures of Fe–P deposited films were also compared with the Fe–P thermal equilibrium phase diagram. The results indicate that the crystallographic structures of Fe–P deposited films gradually change from crystalline to amorphous phase with increasing P content in the deposited films. The deposited film exists as α-Fe supersaturated solid solution when the P compositions in deposited film are below 20.5 at%, whereas it exists as a homogenous amorphous phase when the P compositions in the deposited films are from 22.2 at% to 30.1 at%. Accordingly, the composition of boundary between the crystalline and homogenous amorphous regions can be determined at about 21.4 at% P content.
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  • JaeHo Jun, KyooYoung Kim, JoongHwan Jun
    2003 Volume 44 Issue 1 Pages 133-137
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The purpose of this study is to evaluate the lifetime of an Al–Fe coating that has been applied to separators of molten carbonate fuel cells (MCFC). In order for the Al–Fe coating to maintain its protective function for the durability requirement of 4×104 h, it needs to contain enough aluminum to form a protective LiAlO2 layer. If, however, aluminum content in the Al–Fe coating is reduced to a critical level where the protective LiAlO2 layer is not stable, it can be interpreted that the Al–Fe coating loses its protective function and reaches the lifetime of the coating. The aluminum content in an Al–Fe coating can be depleted by two different processes; one is by corrosion reaction at the surface between the aluminum source in the coating and molten carbonate, and the other is inward-diffusion of aluminum atoms within the coating into a substrate. In these two respects, therefore, the decreasing rate of aluminum concentration in an Al–Fe coating was measured, and then the impacts of these two conditions on the Al–Fe coating’s lifetime were investigated, respectively.
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  • Satoru Ishihara, Wei Zhang, Hisamichi Kimura, Mamoru Omori, Akihisa In ...
    2003 Volume 44 Issue 1 Pages 138-143
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Consolidation of Fe67Co9.5Nd3Dy0.5B20 glassy powders has been tried by spark-plasma sintering (SPS) at around the glass transition temperature in order to synthesize a hard magnetic bulk material with a nanocomposite structure. The glassy powders were consolidated into bulk forms with relative densities above 97% by the sintering at 788 K and over. The sample sintered for 420 s at 788 K had a nearly full density of 99.1% and still kept a glassy single phase. The increase in the sintering temperature and time caused crystallization and the formation of Fe3B phase. These as-sintered samples exhibited soft magnetic characteristics, but the soft magnetism changed to a hard type by annealing to form Nd2Fe14B, Fe3B and α-Fe phases. The remanence, coercivity and maximum energy product for the bulk compact sintered for 420 s at 788 K, followed by annealing for 600 s at 913 K were 1.03 T, 277 kA/m and 83.1 kJ/m3, respectively.
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  • Keizo Kobayashi, Akihiro Matsumoto, Toshiyuki Nishio, Kimihiro Ozaki
    2003 Volume 44 Issue 1 Pages 144-147
    Published: 2003
    Released: September 06, 2005
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    Ti–2 at%Fe–10 at%Si, Ti–4 at%Fe–10 at%Si and Ti–6 at%Fe–10 at%Si powders were synthesized by mechanical alloying (MA) of pure Ti, Fe and Si powders using a planetary ball milling for 720 ks. The amount of collectable powder milled for 720 ks decreased with increasing Fe content in the MA powder. An amorphous phase was generated for all of the powders milled for 720 ks. The crystallization temperature of Ti–2 at%Fe–10 at%Si powder synthesized by MA for 720 ks was higher than that of the other MA powders. Ti–2 at%Fe–10 at%Si powder prepared by milling for 720 ks, which contained amorphous phase, was consolidated using a pulsed current sintering apparatus under a high pressure. The compact consolidated at 673 K under a pressure of 1500 MPa was almost densified with the retention of amorphous phase. The pulsed current sintering under a high pressure is a powerful technique to consolidate amorphous powder into a bulk material.
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  • Tomoyuki Nishida, Hidekazu Sueyoshi
    2003 Volume 44 Issue 1 Pages 148-154
    Published: 2003
    Released: September 06, 2005
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    C/C composites were bonded to nickel in a vacuum, using an RF-induction furnace, with joining temperature, keeping time and joining compressive stress as variables. C/C composites with different carbon fiber orientations and heat treatment temperatures were used. The bending strength of the C/C composite/nickel joints was investigated. The fracture surface of the joints was observed using a scanning electron microscope. X-ray diffraction was performed on the joining surface of C/C composites. Changes in the microstructure and hardness of nickel near the joining interface were investigated. On the basis of the results of these experiments, the influences of carbon fiber orientation and graphitization on the solid-state bonding of C/C composite to nickel were examined. A large difference in thermal expansion coefficients between the longitudinal section of carbon fiber and nickel results in delamination at the interface. In the bending test, when the longitudinal section of carbon fiber is parallel to the joining surface, slip due to crystallographic anisotropy occurs. Therefore, good bonding between the longitudinal section of the carbon fiber and nickel is not achieved. On the other hand, good bonding to nickel along the cross section perpendicular to the carbon fiber axis becomes feasible. Therefore, in plain woven carbon fiber-reinforced carbon composite/nickel joints, the bending strength is low, while in unidirectional carbon fiber-reinforced carbon composite/nickel joints, the bending strength is equivalent to that of C/C composite. The degree of graphitization affects joinability. Strong bonding of C/C composite to nickel is accomplished with the progress of graphitization. The bending strength of the joint is equivalent to that of C/C composite. The bending strength of C/C composite/nickel joints is affected by the joining temperature, keeping time and joining compressive stress, because these factors are related to full contact of joining surfaces and diffusion of carbon atoms from C/C composite into nickel.
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  • Tomoya Nagira, Mikio Ito, Shigeru Katsuyama
    2003 Volume 44 Issue 1 Pages 155-160
    Published: 2003
    Released: September 06, 2005
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    The polycrystalline NaxCo2O4 thermoelectric materials were synthesized by the polymerized complex (PC) method and subsequently hot-pressed. The microstructure and thermoelectric properties of these samples were evaluated, and their differences between the sample prepared by the conventional solid-state reaction (SSR) method and the PC method were investigated. The shape of the calcined powders prepared by the PC method was flat and plate-like. For the annealed PC sample after hot-pressing at 1073 K for 3.6 ks with the nominal composition of Na1.6Co2O4, no impurity phases were observed based on a X-ray diffraction analysis and scanning electron microscopy (SEM). The crystal grain size of the sample was as small as the calcined powders and was remarkably smaller than that of the sample prepared by the SSR method. The degrees of c-axis orientation of the samples prepared by both methods were equivalent. The electrical resistivity increased and the lattice contribution to the thermal conductivity decreased compared with the sample prepared by the SSR method because of the enhancement of the carrier and phonon scattering caused by its small grain size.
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  • Gjergj Dodbiba, Atsushi Shibayama, Toshio Miyazaki, Toyohisa Fujita
    2003 Volume 44 Issue 1 Pages 161-166
    Published: 2003
    Released: September 06, 2005
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    The objective of this study was to triboelectrostatically separate artificial plastic mixture of three kinds of components (i.e. ABS, PS and PP mixture). The mixture is charged by friction in tribo-cyclone. After a given period of time inside the tribo-cyclone, the charged plastic flakes fell down freely through a horizontal electric field into collection bins. The DC electric field of maximum 400 kV/m is created by using two parallel plate electrodes made of Cu and having a given cross-section configuration. The plastic flakes of the mixtures are drawn to either positive or negative electrode according to the polarity of the charge and are separated by falling in different bins. The purification of three-component mixture is accomplished by a two-step triboelectrostatic process. Separation tests in a batch laboratory triboelectrostatic separator showed that the efficiency of the separation is strongly depended on tribocharging time, air inlet velocity, and electric field strength. Products of ABS, PS and PP with a grade of 92.1%, 84.9% and 90.0% respectively have been achieved with recoveries above 73.0%.
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  • Norihiro Itsubo, Atsushi Inaba
    2003 Volume 44 Issue 1 Pages 167-172
    Published: 2003
    Released: September 06, 2005
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    Weighting in LCIA (life cycle impact assessment) can be classified into two types; midpoint and endpoint. To improve the transparency and reliability of impact assessment, the development of the endpoint approach has been required internationally in recent years. A methodology that enables the assessment of physical damage for Japanese products has to be developed, because the actual damage is dependent on the emission area and exposed area. Regarding LCIA for materials, though some studies have already been performed, there is no consensus among the results of various methods because of the lack of reliability and transparency in conventional methodologies. This paper describes the results of a case study for steel sheets applying the Japanese endpoint-type LCIA method. We adopted the DALY concept to indicate the damage to human health. It is found that the subjective judgments can be reduced maximally by applying the endpoint approach.
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  • Hung-Mao Lin, Truan-Sheng Lui, Li-Hui Chen
    2003 Volume 44 Issue 1 Pages 173-180
    Published: 2003
    Released: September 06, 2005
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    The effect of silicon content on intergranular embrittlement of ferritic spheroidal graphite cast irons after suffer a certain number of thermal cycles is investigated. The tensile elongation tends to increase with the number of thermal cycles, and increased silicon content leads to eventual embrittlement. The fracture surface of a 2.9Si specimen changes from dimple pattern feature to intergranular fracture, whereas the fracture surfaces of both 4.0Si and 4.3Si specimens change from the brittle cleavage to intergranular fracture that following with increasing the number of thermal cycles. The intergranular cracking path will initiate and propagate through the eutectic cell boundaries due to the presence of micro-segregated inclusions that clustered in the eutectic cell boundary region. These inclusions are oxides that mainly contain magnesium, phosphorus and cerium. Experimental analysis detected that the magnesium elements not only segregated in the vicinity of eutectic cell boundaries, but also the annealed ferritic grain boundaries. However the embrittlement resulted from cyclic heating is strongly dependent on the morphology of clustered inclusions and is pertaining to the variation of silicon content. The observed magnesium-containing inclusions located in the central region of the matrix may profoundly affect the overall tensile fracture behavior of heat resistant used SG cast irons.
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  • Seong Taek Lim, Il Sang Eun, Soo Woo Nam
    2003 Volume 44 Issue 1 Pages 181-187
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Microstructural evolutions, especially for the coarse equilibrium phases, M-, T- and S-phase, are investigated in the modified aluminum alloy 7175 during the primary processing of large ingot for thick forging applications. These phases are evolved depending on the constitutional effect, primarily the change of Zn:Mg ratio, and cooling rate following solutionizing. The formation of the S-phase (Al2CuMg) is effectively inhibited by higher Zn:Mg ratio rather than higher solutionizing temperature. The formation of M-phase (MgZn2) and T-phase (Al2Mg3Zn3) is closely related with both constitution of alloying elements and cooling rate. Slow cooling after homogenization promotes the coarse precipitation of the M- and T-phases, but becomes less effective as the Zn:Mg ratio increases. In any case, the alloy with higher Zn:Mg ratio is basically free of both T and S-phases. The stability of these phases is discussed in terms of ternary and quaternary phase diagrams. In addition, the modified alloy, Al–6Zn–2Mg–1.3%Cu, has greatly reduced quench sensitivity through homogeneous precipitation, which is uniquely applicable in 7175 thick forgings.
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  • Chaoli Ma, Akihisa Inoue
    2003 Volume 44 Issue 1 Pages 188-196
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    By incorporating small amounts (0≤5 at%) of transition metals (TM) of Cr, Mo, Fe and Ta into Pd40Cu30Ni10P20 alloy that has been considered to be the best glass former so far, in-situ composites consisting of a glassy phase and nano- and/or micro-sized crystalline particles were prepared by copper-mold casting. The nano- and micro-sized particles identified to be phosphides are homogeneously dispersed in a glassy matrix. The formation of such a characteristic structure is attributed to a primary crystallization reaction with high nucleation rate and limited growth rate in the undercooled Pd40Cu30−xNi10P20TMx melt. The TM atoms interact preferentially with the clusters of Pd–Ni–P, one kind of atomic units in the deeply undercooled Pd–Cu–Ni–P liquid, and result in the formation of the TM–Ni–P or TM–Ni–P–Pd clustered units in the undercooled melt, which act as nucleation sites during solidification. With the addition of Cr, Mo, Fe and Ta atoms into Pd40Cu30Ni10P20 alloy, the first phosphide phases precipitated from these melts are Ni33Cr33P34, MoNiP, Fe33Ni33P34, and (Pd,Ta)NiP, respectively. These phases possess the same hexagonal structure as Fe2P (hP9). The dispersed particles have a volume fraction ranging from 9 to 18% for the alloys investigated. The compressive strength and ductility of these glassy composites are not significantly improved by the dispersion of the nano- and micro-sized particles. These glassy composites deformed by an inhomogeneous shear slip mode and fractured by an adiabatic shear mechanism. The nucleation behavior and the effect of dispersed particles on the deformation and fracture behavior are discussed.
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  • Xuyue Yang, Hiromi Miura, Taku Sakai
    2003 Volume 44 Issue 1 Pages 197-203
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Dynamic grain evolution of a magnesium alloy AZ31 was studied in compression at 673 K (0.73Tm) by optical and SEM/OIM microscopy. The flow curve shows rapid hardening accompanied by a stress peak at a relatively low strain (εp=0.12), followed by strain softening and then a steady state flow stress at high strains. Fine grains evolved at corrugated grain boundaries at around εp and developed rapidly during strain softening, finally leading to a full structure of equiaxed fine grains. Such characteristics of new grain evolution and flow behavior are apparently similar to those in conventional, i.e. discontinuous, dynamic recrystallization (DRX). On the other hand, kink bands were observed frequently near corrugated grain boundaries and also in grain interiors, even around εp. The misorientation of the boundaries of the kink bands increases rapidly during strain softening and approaches a saturation value of around 43° at high strains. The average size of the regions fragmented by kink bands is almost the same as that of the new grains. It is concluded, therefore, that new grain evolution in this alloy is controlled by a deformation-induced continuous reaction, i.e. continuous DRX.
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  • Kenichi Yamaguchi, Shoji Ishida, Setsuro Asano
    2003 Volume 44 Issue 1 Pages 204-210
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    In the Ni2MnGa based alloys with additions of transition element Ni–Mn–Ga–X, the martensitic transformation temperature TM was observed as a function of the valence electron concentration per atom ea. The TM(ea) strongly depends on ea and increases with increasing ea. In this paper, to examine the effect of X atom on the phase transformation in Ni–Mn–Ga–X alloys, the electronic structures for six systems were calculated for four phases, that is, the paramagnetic cubic, the paramagnetic monoclinic, the ferromagnetic cubic and the ferromagnetic monoclinic phases. Moreover, the total energy differences ΔE(ea) between two phases among four phases were calculated as a function of ea. The variations of TM(ea) were predicted by the difference ΔE(ea) between the cubic and monoclinic structures in a ferromagnetic state. It was found that their correspondence is good for some systems and that the features of TM(ea) reflect the changes of the density of states of X atoms.
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  • X.J. Hao, Hideyuki Ohtsuka, Patricia DE Rango, Hitoshi Wada
    2003 Volume 44 Issue 1 Pages 211-213
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Structural alignment in Fe–0.4C alloy transformed in high magnetic field has been evaluated by quantitative microscopy analysis. An aligned two-phase structure is formed in high magnetic field by austenite to ferrite transformation during slow cooling. Ferrite grains are elongated and connected with each other along the direction of magnetic field. The degree of alignment can be evaluated by measuring the number of intersections between test lines and ferrite/austenite phase boundaries. Results of measurement show that the degree of alignment increases continuously with increasing magnetic field strength up to 10 Tesla.
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