MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 44 , Issue 9
Showing 1-44 articles out of 44 articles from the selected issue
  • Tatsuya Tokunaga, Kazumasa Nishio, Hiroshi Ohtani, Mitsuhiro Hasebe
    2003 Volume 44 Issue 9 Pages 1651-1654
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    A thermodynamic study has been carried out on the Ni–Si–B ternary system, which is an important system in view of the development of Ni-base filler metals. A regular solution approximation based on the sublattice model was adopted to describe the Gibbs energy for the individual phases in the binary and ternary systems. Thermodynamic parameters for each phase have been evaluated using the available experimental information on phase boundaries and other related thermodynamic properties. Thermal analysis experiments have also been conducted on several ternary alloys to re-examine the available ternary experimental data on phase boundaries. The set of evaluated parameters in this study enables reproducible calculations of the liquidus and solidus temperatures and vertical section diagrams satisfactorily.
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  • Shigeru Suzuki, Katsuyuki Yanagihara, Shuichi Yamazaki, Yoshio Waseda
    2003 Volume 44 Issue 9 Pages 1655-1658
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Secondary ion mass spectrometry (SIMS) has been used for characterizing penetration of gold, which was deposited on the surface of Fe–3 mass%Si (011) single crystal and subsequently penetrated into its bulk by annealing under the low partial pressure of oxygen. The degree of gold penetration was evaluated using an effective diffusion coefficient of gold in Fe–3 mass%Si, which was apparently estimated from a SIMS depth profile. The effective diffusion coefficients of gold in the surface layer of Fe–3 mass%Si were found to be larger than those in the bulk iron. The gold penetration is likely to be correlated with the distribution of silicon oxides, which is formed by selective oxidation of silicon in the surface layer of Fe–3 mass%Si. This indicates that silicon oxides formed in the surface layer of Fe–3 mass%Si act as a path for the gold penetration, which is presumably the interface between the iron matrix and a network of silicon oxides.
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  • Mazhar Mehmood, Nobuaki Kawaguchi, Hideki Maekawa, Yuzuru Sato, Tsutom ...
    2003 Volume 44 Issue 9 Pages 1659-1662
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Attempts to prepare tantalum coating on tungsten have been performed in 55 mol%LiF–35 mol%NaF–10 mol%CaF2 melt containing K2TaF7. Electrolytic deposition of tantalum was carried out by galvanostatic polarization. A conproportionation reaction also occurred that interfered with the electrodeposition and resulted in decrease in current efficiency. However, the product of this reaction was soluble, which diffused away from the electrode without contaminating the deposit. Hence, a compact electrodeposited tantalum coating was obtained on tungsten substrate. An excellent interface was possible when coating was performed in the melt containing 2 mol% K2TaF7.
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  • Hiroshi Senoh, Nobuhiko Takeichi, Hiroyuki T. Takeshita, Hideaki Tanak ...
    2003 Volume 44 Issue 9 Pages 1663-1666
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Some hydrogen storage materials with the hexagonal CaCu5-type crystal structure have two pressure plateaux during hydrogen absorption and desorption processes. To clarify the correlation of hydrogenation properties between two plateaux, we investigated the pressure-composition isotherms of several binary RNi5 (R = La, Ce, Pr, Nd and Sm) intermetallic compounds at pressures up to 35 MPa and at temperatures ranging from 196 to 423 K by use of a modified Sieverts’ method. We also determined the unit cell volume of the compounds to correlate the hydrogenation properties with the crystal structure. It was found that RNi5 compounds had qualitatively similar hydrogenation properties in that two well-separated plateaux indicated the existence of two hydrides with the compositions of RNi5H3–4 (β phase) and RNi5H6–7 (γ phase) except CeNi5. Similar to the lower plateau pressure, the higher plateau pressure increases with increasing the atomic number of R element or with decreasing the unit cell volume of these compounds. For LaNi5–H2 system, the pressure gap between two plateaux expands with increasing temperature, indicating that the absolute value of enthalpy of dehydrogenation (|ΔH|) of β hydride is smaller than that of γ hydride or |ΔH(β)|<|ΔH(γ)|. On the other hand, for other RNi5–H2 systems the pressure gap expands with decreasing temperature; that is, the |ΔH| values of both hydrides show the opposite tendency or |ΔH(β)|>|ΔH(γ)|. The maximum hydrogen content of each RNi5 compound exceeds six hydrogen atoms per formula unit and some compounds absorb the hydrogen to reach the hydride composition of RNi5H7 without new plateau.
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  • Shuji Tada, Zheng Ming Sun, Hitoshi Hashimoto, Toshihiko Abe
    2003 Volume 44 Issue 9 Pages 1667-1670
    Published: 2003
    Released: September 06, 2005
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    A traveling zone heating technique was examined with the aim of creating a long dense rod by means of pressurized pulse discharge sintering. Based on local heating enabled by electric power supplied perpendicular to the loading axis through a terminal board, a one-direction continuous sintering process was successfully achieved, in which the terminal board was able to slide along the side wall of the cylinder in the direction of the loading axis while remaining in continuous contact with it. The heating zone was limited to within the range corresponding to the thickness of the board. Aluminum powder of 9.54 g, 99.9% in purity with an average size of 20 μm was placed in a graphite cylinder of inner diameter 15 mm. Electric power was then supplied through a 12 mm thick terminal board to sinter the powder. Power supply was provided to the board, which was moved upwards three times by a distance of 8 mm. A 20 mm long rod with a relative density of 99.2% was successfully sintered by means of this procedure. Similarly, four successive local heatings over a range 30 mm wide while moving the heating zone distances of 20 mm led to the production of a 55 mm long aluminum rod with a relative density of 99.7%. The present results suggest that much longer rods can be sintered well by expanding the moving range of the heating zone. The new sintering technique proposed in this study will enable the production of long rods with high density.
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  • Fuxing Yin, Kotobu Nagai, Kenji Watanabe, Kohji Kawahara
    2003 Volume 44 Issue 9 Pages 1671-1674
    Published: 2003
    Released: September 06, 2005
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    The temperature and frequency dependent damping behavior of Ni added Mn–Cu alloys were investigated. Ni addition not only increased the magnitude of the phase-transformation damping peak, but also decreased its frequency dependence. A decreased transformation temperature was found in the Ni added Mn–Cu alloys under the same treating condition, which suggested a retarding effect of Ni on the decomposition of γMn phase during the slow-cooling process. The characteristic twin-boundary damping peak of Mn–Cu alloys was enlarged and broadened with the addition of Ni. According to the relaxation damping models the twin-boundaries in Ni added alloys had the larger activation energy, and also exhibited a broader distribution of relaxation time during the stress induced movement. In Ni added Mn–Cu alloys, the FCT γMn phase showed a larger axis ratio, ca and the Cu-rich γMn phase coexisting with the FCT phase showed the similar lattice constants at ambient temperature. These microstructural features in Ni added Mn–Cu alloys might contribute to the improved damping behavior of the twin-boundary damping peak.
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  • Feng Wu, Hideyuki Murakami, Hiroshi Harada
    2003 Volume 44 Issue 9 Pages 1675-1678
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The oxidation behavior of iridium-modified aluminide (Ir–Al) coating obtained by a two-step process was investigated. A pure Ir layer was first electrodeposited on the nickel-base single crystal superalloy TMS-75, and then the Ir-coated TMS-75 was treated by a conventional low activity pack-cementation aluminizing process. The oxidation resistance of the Ir–Al coated TMS-75 and the simply aluminized TMS-75 was evaluated by a cyclic oxidation test at 1373 K in air. The results showed that the Ir–Al coated TMS-75 had better thermal cyclic oxidation resistance than the simply aluminized TMS-75. The existence of Ir in the Ir–Al coatings may promote the formation of dense and adherent Al2O3 scale and thus retard the degradation of β-(Ir, Ni)Al phase during oxidation process.
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  • Hiroaki Ishii, Kenji Ohkubo, Seiji Miura, Tetsuo Mohri
    2003 Volume 44 Issue 9 Pages 1679-1681
    Published: 2003
    Released: September 06, 2005
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    E21-Fe3AlC carbide (κ) in the Fe–Al–C ternary system is known to have ductility at room temperature. It forms a lamellar structure similar to the pearlite with a ferrite (α) phase through a eutectoid-like reaction from an austenite (γ) phase and improved mechanical properties are expected by replacing cementite to κ phase. The mechanical properties of α+κ two-phase lamellar structure were investigated through micro-Vickers hardness measurements and compression tests at room temperature in order to compare with those of pearlite steels. A typical mean inter-lamellar spacing of Fe–8 at%Mn–13 at%Al–7 at%C alloy aged at 773 K for 100 h was 60 nm and its yield stress and micro-Vickers hardness were 1880 MPa and 580 HV, respectively. Yield stress and micro-Vickers hardness of these specimens were higher than those of pearlite steels regardless of the mean inter-lamellar spacing. Those results seem to be rationalized by taking the solid solution hardening of ferrite phase into account.
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  • Takashi Kawasaki, Masahiro Itoh, Ken-ichi Machida
    2003 Volume 44 Issue 9 Pages 1682-1685
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Nd–Fe–B sintered magnet scraps were reproduced as the corresponding sintered magnets from the ground powders (mean particle ≤3 μm) by using a binary alloy blending technique. Although the magnets re-sintered from the as-ground powders only provided poor magnetic properties, especially the observed coercivity values (∼20 kAm−1), the magnetic properties were considerably improved compared with the as-ground powders by adding an Nd-rich alloy (80 and 20 mass% for Nd and Fe, respectively) with the mass ratio of 90 (scrap powders) to 10 (Nd-rich alloy). Typical magnetic parameters of the recovered magnets were Br=∼1.21 T, HcJ=∼1.6 MAm−1 and (BH)max=∼251 kJm−3. It was found that the Nd–Fe–B sintered magnet scraps were reproduced as the practically usable magnets by the above process.
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  • Kenji Komiya, Shigeyuki Ito, Hiroshi Yukawa, Masahiko Morinaga, Kensuk ...
    2003 Volume 44 Issue 9 Pages 1686-1689
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Niobium metal forms two kind of hydrides, NbH and NbH2, by hydrogenation, and the corresponding plateau region appears at low and high hydrogen permeable regions in the PCT curve of the Nb–H system. However, alloying effects have never been investigated in this system. In the present study, alloying effects were firstly investigated with various binary Nb–3 mol%M and Nb–5 mol%M alloys. Here M’s were 4d transition metals, Zr, Mo, Ru, Rh and Pd, all of which were soluble in bcc Nb. The stability of each hydride was found to be varied with the addition of a small amount of alloying elements into niobium metal. For example, the β (NbH) phase became most unstable by the addition of Ru, whereas δ (NbH2) phase became most unstable by the addition of Mo. These data will be useful for the design of hydrogen permeable niobium-based membranes.
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  • Yonosuke Murayama, Shuji Hanada, Yoshiharu Waku
    2003 Volume 44 Issue 9 Pages 1690-1693
    Published: 2003
    Released: September 06, 2005
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    The microstructure and crystallographic texture of a directionally solidified Al2O3/YAG eutectic composite were studied by field emission scanning electron microscopy (FE-SEM), electron backscatter pattern (EBSP) method and X-ray diffraction (XRD). The high-temperature strength of the composites was investigated by compression test. The Al2O3/YAG eutectic composite with characteristic microstructure shows highly accumulated texture with preferred growth orientations of ⟨300⟩ for Al2O3 and ⟨420⟩-⟨800⟩ for YAG. The growth directions of Al2O3 are concentrated around ⟨100⟩ and ⟨010⟩ directions in twin-related variants, along the interphase boundaries. The composite strength is dependent on both compression direction and strain rate at 1773 and 1873 K, which is attributable mainly to the strain rate and orientation dependence of strength for constituent Al2O3.
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  • Marat Shagiev, Yoshinobu Motohashi, Fanil Musin, Rustam Kaibyshev, Gor ...
    2003 Volume 44 Issue 9 Pages 1694-1697
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Superplastic properties of an Al–Li–Mg–Cu–Sc alloy subjected to hot rolling at 573 K with a reduction of 90% were examined in the temperature range of 673–798 K and an initial strain rate of 1.4×10−2 s−1. It was found that partially recrystallized microstructure evolved under the hot rolling resulting in slight anisotropy of superplastic behavior. The maximum elongation-to-failure of 415% appeared in the rolling direction at 723 K while in the transverse direction the maximum ductility of 385% was achieved at a higher temperature of 773 K. Microstructure evolution and cavitation during superplastic deformation were examined.
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  • Marat Shagiev, Yoshinobu Motohashi, Fanil Musin, Rustam Kaibyshev, Gor ...
    2003 Volume 44 Issue 9 Pages 1698-1701
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    A novel commercial Al–Li–Mg–Cu–Sc alloy was fabricated by casting and subjected to intense plastic deformation through equal-channel angular extrusion at 598 K to a total strain of ∼16. Superplastic properties of this alloy were studied in the temperature range of 623–773 K and at strain rates of 1.4×10−3–1.4×10−1 s−1. The highest elongation-to-failure of 650% appeared at 723 K and a strain rate of 1.4×10−3 s−1 with corresponding coefficient of strain rate sensitivity of 0.42. The microstructure evolution and cavitation during superplastic deformation were examined.
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  • Yoshinori Ono, Tetsumi Yuri, Hideshi Sumiyoshi, Saburo Matsuoka, Toshi ...
    2003 Volume 44 Issue 9 Pages 1702-1705
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    High-cycle fatigue properties were investigated for Ti–5%Al–2.5%Sn extra low interstitial alloy with a mean α grain size of 80 μm, which had been used for liquid hydrogen turbo-pump of Japanese-built launch vehicle. The fatigue strengths at cryogenic temperatures of 4 K and 77 K do not increase in proportion to increments of the ultimate tensile strength, and come to be lower than that at 293 K around 107 cycles. Observations by optical microscopy and scanning electron microscopy reveal that fatigue cracks initiate in the specimen interior and grow transgranularly, not depending on the test temperature. At the subsurface crack initiation sites, several facet-like structures are formed at cryogenic temperatures, while there are no facet-like structures at 293 K. Since localized deformation occurs at cryogenic temperatures, the subsurface cracks form facet-like structures and are supposed to initiate in the early stage of the fatigue life. As the result, the fatigue strength deteriorates at cryogenic temperatures.
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  • Yoshiyuki Nakata
    2003 Volume 44 Issue 9 Pages 1706-1708
    Published: 2003
    Released: September 06, 2005
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    The crystal structure and some magnetic properties of Fe3Pt martensite are investigated by first principle calculations. The crystal structure is optimized in such a way that the atom positions are changed according to the force acting on the nuclei. The positions are repeatedly changed until the forces are all less than 0.257 eV/nm. The final structure obtained is the same as expected from simple Bain distortion of austenite with L12 ordered structure. The magnetic moments of two kinds of Fe atoms in this structure are 2.6 and 2.8 Bohr magneton, and that of a Pt atom is 0.45. The magnetic moments of Fe atoms in Fe3Pt martensite are considerably larger than those in bcc Fe.
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  • Yibin Xu, Junichi Kinugawa, Koichi Yagi
    2003 Volume 44 Issue 9 Pages 1709-1712
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The thermal conductivity of Mo fiber-reinforced Al2O3 composite was calculated using analytical solutions for effective thermal conductivity. The deviation between calculated and literature data was less than 10%. The influence of constitution on thermal conductivity of dispersion composites was investigated by simulation based on analytical solutions. When the reinforcements are unidirectionally arrayed, their volume, shape and thermal conductivity greatly affects the thermal conductivity of the composite, and the effects on the thermal conductivity parallel to the reinforcement orientation are bigger than those on the thermal conductivity along the perpendicular direction. As the orientation of reinforcements becomes increasingly random, the anisotropy of thermal conductivity becomes smaller and smaller.
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  • Tetsuji Saito
    2003 Volume 44 Issue 9 Pages 1713-1716
    Published: 2003
    Released: September 06, 2005
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    The microstructures and magnetic properties of Co90−xZr10+x (x=0–20) alloy ingots and those melt-spun ribbons were examined in order to clarify the phase and microstructure of the Co–Zr system alloys. The Co90Zr10 alloy ingot and melt-spun ribbon consisted of Co, Co23Zr6, and Co11Zr2 phases. Although the Co80Zr20 alloy ingot consisted of Co, Co23Zr6, and Co11Zr2 phases as was the case for the Co90Zr10 alloy ingot, those melt-spun ribbon consisted of metastable Co5Zr phase together with Co and Co23Zr6 phases. The Co70Zr30 alloy ingot and melt-spun ribbon consisted of Co2Zr phase. Among the alloy ingots and those melt-spun ribbons, only the Co80Zr20 melt-spun ribbon with the metastable Co5Zr phase exhibited a high coercivity. This study confirmed that the hard magnetic phase was not the Co11Zr2 phase but the metastable Co5Zr phase.
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  • J. R. Vargas Garcia, Takashi Goto
    2003 Volume 44 Issue 9 Pages 1717-1728
    Published: 2003
    Released: September 06, 2005
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    This article reviews the progress in the chemical vapor deposition of iridium, platinum, rhodium and palladium metals. In the course of the last decade the number of articles on CVD of this group of metals has increased significantly. A wide variety of metal organic complexes have been investigated as potential precursors and appreciable results have been obtained. However, some aspects such as low deposition rates and impurity incorporation into the films still remain as concerns in this area. The representative results on CVD of these metals are presented according to the type of metal organic complexes used.
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  • Hirokazu Ohno, Tetsumori Shinoda, Yoshihiro Oya-Seimiya
    2003 Volume 44 Issue 9 Pages 1729-1735
    Published: 2003
    Released: September 06, 2005
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    Formation of A15 type Nb3Al phase at the interface between solid Nb and liquid Al in a bulky Nb/Al composite has been studied at as high temperatures as from 1873 to 2073 K. The A15-phase layer grows keeping the interfaces planar when heated at 2023 K or lower, whereas the interface adjacent to Nb solid solution, NbS.S, becomes “nonplanar” when heated at 2073 K. It is suggested that the formation process of A15 phase consists of three stages; the rapid dissolution of Nb into liquid Al until nucleation of A15 phase at the Nb/Al interface, and the following two stages (1st and 2nd ones) for growth of A15 phase. The planar growth rate of A15-phase on the 1st stage is considerably faster than that on the 2nd one. A model for the planar growth rate of A15-lphase on the 2nd stage has been presented. The model is based on the unidirectional inter-diffusion fluxes of Nb and Al atoms in the three sequential regions of NbS.S, A15 and σ-phases. The “nonplanar” growth of A15-phase will be detailed in Part II of the present study.
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  • Hirokazu Ohno, Tetsumori Shinoda, Yoshihiro Oya-Seimiya
    2003 Volume 44 Issue 9 Pages 1736-1740
    Published: 2003
    Released: September 06, 2005
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    At the interface between A15-phase layer and Nb solid-solution (NbS.S) region in a bulky Nb/Al composite, a layer of two-phase structure of Nb3Al plus NbS.S is formed when the composite is heated at 2073 K, whereas it is not formed when heated at 2023 K or less. The morphology and width of the two-phase structure layers are significantly influenced by the cooling rate from 2073 K and by the heating time at that temperature. These facts, as well as the theoretical consideration, suggests that the two-phase structure is formed during the cooling process from 2073 K. When cooled more slowly from 2073 K than a certain cooling rate, there observed anomalous growth of A15-phase, which is strongly correlated with formation of the two-phase structure. Most favorite performance of the bulky Nb/Al composite as the super-conducting material is obtained by cooling it at the slowest cooling rate after 1 h heating at 2073 K as far as the present study is concerned.
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  • Jafar Mahmoudi, Michael Vynnycky, Patrik Sivesson, Hasse Fredriksson
    2003 Volume 44 Issue 9 Pages 1741-1751
    Published: 2003
    Released: September 06, 2005
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    An experimental and numerical study was carried out to investigate the solidification process in a copper continuous strip casting process. Heat flow and solidification process has been experimentally studied. Cooling curves during solidification were registered using a thermocouple of type “K” connected to a data acquisition system. Temperature measurements in the mould and cooling water were also performed. The numerical model considers a generalized set of mass, momentum and heat equations that is valid for the solid, liquid and solidification interval in the cast. A k−ε turbulence model, produced with the commercial program CFX, is used to analyse the solidification process of pure copper in the mould region of the caster. The fluid flow, temperature and heat flux distributions in the mould region of the caster were computed. The shape and location of the solidification front were also determined. The effects of the parameters such as heat transfer coefficient, casting speed, casting temperature, heat of fusion and specific heat on the shape and location of the solidification front and the heat transport at the mould-cast interface were investigated. The predicted temperature and heat flux distributions were compared with experimental measurements, and reasonable agreement was obtained.
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  • Nikola Nikolov, Alain Reza Yavari
    2003 Volume 44 Issue 9 Pages 1752-1759
    Published: 2003
    Released: September 06, 2005
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    This paper represents a view at the field of Glass Forming Ability (GFA) of Hf-alloys from positions of the planning of experiment, and by the tools of mathematical modeling and optimization. On the basis of real physical experiments carried out with aim achievement of large GFA, the mathematical models of few chosen characteristics for GFA (Tg, Tx, ΔTx, TgTm, TgTl) are drawn up by Regression analysis with two-rate polynomial. A comparison between modeled results and experimental ones is completed. With aims enlargement of the GFA four two-criteria and three-parametrical optimization tasks are formulated and solved. On the basis of their compromise decisions obtained by searching for maxima of Complex Objective Function following the Method of Deformable Simplex (of Nelder-Mead), the optimal values for ZrxTix-, Gay(Ge2Si)-additions (x=0–10%, y=0–3%) and addition of element with maximal atomic radii rat in interval 0.150–0.2013 nm are found depending on the importance of optimization criteria. It is found mathematically that increase of ZrxTix-addition and addition of element with atomic radii approximate to 0.200 nm decrease the supercooled liquid region ΔTx with 30% and increase the ratios TgTl, TgTm with 5.5% and 8.3%, respectively. Addition of Gay(Ge2Si) increases ΔTx and decreases TgTl and TgTm. After comparisons with other conclusions obtained by experimental results the conclusions are drawn that the approach proposed in this paper and obtained modeled results can be used as a basis for formulation and solving of other problems in the field of Bulk Metallic Glass forming.
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  • Rubén Santamarta, Dominique Schryvers
    2003 Volume 44 Issue 9 Pages 1760-1767
    Published: 2003
    Released: September 06, 2005
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    A low dispersion of micrometric particles embedded in the amorphous matrix is obtained by controlled thermal treatments in an initially amorphous Ti50Ni25Cu25 melt-spun ribbon. The microstructure and crystallography of the crystalline particles have been investigated by means of TEM. Many of these particles are nearly spherical and exhibit a single crystallographic grain of austenite, the crystalline-amorphous interfaces revealing a stepped surface with preferential crystallographic planes. In addition to this, some particles with several grains in austenite have also been observed, most of them showing rather planar interfaces between adjacent grains in TEM images and twinning relationships in SAEDP. The experimental results indicate that the growth of the particular grains does not occur independently, and suggest that additional topological conditions, different from the twinning planes, yield the interfaces.
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  • Ryosuke Kainuma, Ikuo Ohnuma, Kiyohito Ishida
    2003 Volume 44 Issue 9 Pages 1768-1773
    Published: 2003
    Released: September 06, 2005
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    Microstructure and grain growth characteristics of pre-deformed Al–Bi alloys annealed at 773 K were investigated mainly by scanning electron microscopic (SEM) observation. In addition to very fine liquid-Bi particles in the grains, large Bi particles were observed on the grain boundaries, and non-precipitation zones are mainly formed in the vicinity outside of the curved grain boundaries. This result suggests that the Bi particles on the grain boundaries were dragged by the grain boundaries. The grain growth is significantly retarded by the effect of this dragging, the origin of which can be explained by the decrease of the interfacial energy of the intragranular Bi particles. Quantitative analysis showed that the diffusion of Al atoms in the liquid Bi particles on the grain boundaries is the rate-determining process of this dragging.
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  • Kenzaburo Marukawa, Masayuki Tabuchi
    2003 Volume 44 Issue 9 Pages 1774-1782
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    In order to clarify the mechanism of the bainitic transformation, a new technique utilizing interference fringes in transmission electron micrographs was applied for observations of bainitic precipitates in copper alloys. Based on the theoretical consideration of image formation, the appearance of these fringes along the interface of a precipitate was taken to be evidence of the existence of a shear-type transformation strain. From the analysis on the spacing of interference fringes, the direction and magnitude of the shear strain were obtained. It was found that the shear strain associated with bainites has almost the same crystallographic direction and magnitude as the one associated with martensites in the same alloy. On the basis of these findings, a new model on the transformation mechanism is presented, in which the dislocation motion bringing about the lattice transformation is controlled by the atomic diffusion through a local concentration change. This model consistently explains both of existence of the transformation strain and the diffusion-control nature of the transformation.
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  • Jae-Hwan Pee, Takahiro Akao, Shigeru Ohtsuka, Motozo Hayakawa
    2003 Volume 44 Issue 9 Pages 1783-1789
    Published: 2003
    Released: September 06, 2005
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    The high temperature tetragonal phase of zirconia containing 1.40–1.60 mol% Y2O3 were successfully quenched in at room temperature by rapid cooling of small spherical specimens. On these metastable specimens, the isothermal transformation behavior into the monoclinic phase was studied by dilatometric method. The transformation start time exhibited a C-curve in a TTT diagram. The C-curve shifted toward short time side as well as toward high temperature side with decreasing yttria content or increasing grain sizes. A study of the pre-aging effect during the incubation period on the subsequent isothermal transformation suggested consecutive growth of embryos, but alternative interpretation was also possible. The activation energy was evaluated to be ∼50 kJ/mol.
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  • Takashi Sugizaki, Hidehiro Nakao, Takashi Kimura, Tohru Watanabe
    2003 Volume 44 Issue 9 Pages 1790-1796
    Published: 2003
    Released: September 06, 2005
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    The BGA jointing properties including the joint strength and the interfacial structure have been investigated in detail between the lead-free solders containing Sn–8.8Zn and Sn–8.0Zn–3.0Bi with low melting temperature and the immersion gold plated film on the electroless nickel-phosphorus deposits. The results indicate that both Sn–8.8Zn and Sn–8.0Zn–3.0Bi solders can be readily jointed with the substrate in the same way as the conventional Sn–37Pb solder at the peak temperature of 230°C. The joint strength of Sn–8.8Zn solder is higher than that of Sn–8.0Zn–3.0Bi solder, and both of them are higher than that of Sn–37Pb under same surface finishing. Moreover, γ2(AuZn3) intermetallic compound occurs as the reaction layer at Sn–8.8Zn and Sn–8.0Zn–3.0Bi joints, and the bismuth crystals occur at Sn–8.0Zn–3.0Bi joint. The hot bump pull testing results clearly show that the fracture of solder ball occurs along the reaction layer of γ2(AuZn3) intermetallic compound since this reaction layer or bismuth crystals in the joint causes the decrease of joint strength.
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  • Wen Yang, Hiroshi Araki, Akira Kohyama, Chumphol Busabok, Quanli Hu, H ...
    2003 Volume 44 Issue 9 Pages 1797-1801
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    A SiC/SiC composite in a disc preform of 120 mm in diameter and 3.2 mm in thickness was fabricated by the chemical vapor infiltration (CVI) process. The composite was reinforced with plain-woven high-crystalline Tyarnno-SA fiber. Microstructure examinations and density measurements indicated a quite dense and very good space homogeneous matrix deposition in the composite. The fracture behavior and statistic reliability of the flexural strength upon three-point bending loading were investigated. The composite had an average flexural strength 597 MPa with a standard deviation 70 MPa. The statistic analysis of the strength showed good consistency among the bending specimens, with a Weibull modulus of 10.2, which is much higher than that for the Nicalon and Hi-Nicalon fibers reinforced CVI-SiC matrix SiC/SiC composites.
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  • Takeshi Nakajima, Stefano Spigarelli, Enrico Evangelista, Takao Endo
    2003 Volume 44 Issue 9 Pages 1802-1808
    Published: 2003
    Released: September 06, 2005
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    The previous work showed that the precipitate coarsening of T91 (Modified 9Cr–1Mo steel) was described by an empirical relationship depending on applied stress. However, there is another possibility that the stress dependent coarsening is merely apparent and strain dependent actually. In the present paper, an attempt was made to re-analyze the previous data based on a model in which the effective diffusivity of solute is strain dependent. The result of analysis suggests strongly that the dislocation dragging solute atmosphere causes the enhancement of solute diffusivity and leads to the promoted growth of precipitates.
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  • Takuo Shoji, Yoshihito Kawamura, Yasuhide Ohno
    2003 Volume 44 Issue 9 Pages 1809-1816
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    In order to establish metallurgical bonding technology of bulk metallic glasses, friction welding of Zr41Be23Ti14Cu12Ni10 bulk metallic glass with a wide supercooled liquid region and high glass forming ability has been tried. The Zr41Be23Ti14Cu12Ni10 bulk metallic glass has successfully welded to the same bulk metallic glass together. Moreover, the effects of friction-welding conditions such as friction time, rotational speed and upsetting pressure have been investigated under a wide range of conditions, no crystallization and no defects were observed in the interface.
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  • Takahiro Miki, Fujio Ishii, Mitsutaka Hino
    2003 Volume 44 Issue 9 Pages 1817-1823
    Published: 2003
    Released: September 06, 2005
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    Relation between the activity coefficient expressed by Darken’s quadratic formalism and the excess Gibbs energy change of mixing described by Redlich-Kister type polynomial was discussed in Si deoxidation of Ni alloy. The activity coefficients of Si and O in metal expressed by quadratic formalism have been converted into formula using interaction parameters Ωij under the condition where concentration of Si and O are dilute. Numerical analysis on Si deoxidation of molten Ni and Ni–Cu alloy has been carried out. It has been found to be outstanding in the agreement of equilibrium Si and O contents in molten Ni and Ni–Cu alloy analyzed in the present work with the experimental results. The deoxidation equilibrium of not only pure metal but also alloy can be analyzed numerically using the formula determined in the present work.
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  • Sachiko Hiromoto, Takao Hanawa, Kazuyuki Ogawa
    2003 Volume 44 Issue 9 Pages 1824-1829
    Published: 2003
    Released: September 06, 2005
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    The thermodynamic structural stability and anodic polarization behavior in Hanks’ solution of cast amorphous Zr65Al7.5Ni10Cu17.5 alloy rods with a diameter of 2.0 mm and 2.5 mm and a length of 35 mm were evaluated. The change of the magnitude of the super-cooled liquid region owing to structural relaxation was obtained from the differential scanning calorimetry (DSC) curve. Since the super-cooled liquid region of the distant region from the sprue of mold was larger than that of the proximate region to the sprue, the structural stability was lower in the distant region than in the proximate region. It was revealed that the structural stability varies along the distance from the sprue. In electrochemical analysis in a simulated body fluid, the specimens sampled from the distant region showed higher open-circuit potential, lower passive current density, and lower pitting potential than those from the proximate region. In other words, the amorphous structure with low stability shows higher passivity but lower pitting corrosion resistance than that with high stability. Consequently, the corrosion behavior of zirconium-based amorphous alloy sensitively depends on the structural stability in a biological environment.
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  • Masaaki Nakai, Yoshinori Murata, Masahiko Morinaga, Ryokichi Hashizume
    2003 Volume 44 Issue 9 Pages 1830-1838
    Published: 2003
    Released: September 06, 2005
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    The dependence of steam oxidation resistance on the sulfur content has been investigated systematically in both ferritic and austenitic steels. It is found that the presence of impurity S, being considered as a harmful element in the past, improves significantly the steam oxidation resistance of high Cr steels. However, such a beneficial S effect is not so remarkable in low Cr steels, indicating that the S effect is related strongly to the Cr content in the steels. However, in case of high Cr ferritic steels containing more than 0.3%Si, the S effect is still less remarkable. These results are probably caused by the difference in the affinity of S for Cr atom and for Si atom. Since S has a strong affinity for Cr, Cr is enriched in the vicinity of the segregated-S on the specimen surface even after the steam oxidation test for a short time. The enriched Cr layer obstructs the formation of any island-like Fe oxides on the surface because of the easy formation of the passive Cr2O3 oxide layer on this area. On the other hand, Si segregates onto the iron surface faster than S, but a part of the segregated-Si on the surface is replaced by S. Therefore, it is considered that the formation of SiO2 is difficult in the case when the S content is too higher in the steel. As a result, the S effect does not appear so significantly in the Si-containing steels.
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  • Takeshi Wada, Tao Zhang, Akihisa Inoue
    2003 Volume 44 Issue 9 Pages 1839-1844
    Published: 2003
    Released: September 06, 2005
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    The thermal stability of supercooled liquid in the temperature range before crystallization was examined in Zr55Al45−xyCoxCuy alloys without Ni element and the large supercooled liquid region exceeding 80 K was obtained at the compositions around Zr55Al20Co20Cu5 and Zr55Al15Co7.5Cu22.5. By choosing the alloy composition of Zr55Al20Co20Cu5, we have formed bulk glassy alloys in rod and sheet forms by copper mold casting and melt-clamp die forging. The maximum diameter and sheet thickness were 5 mm and 3 mm, respectively. The Tg, ΔTx and TgTl are 746 K, 84 K and 0.61, respectively, being independent of sample thickness. The bulk alloy sheet exhibits Young’s modulus of 92 GPa, elastic elongation limit of 2.1% and high tensile strength of 1960 MPa. These strength values are considerably higher than those for the other Zr-based bulk glassy alloys reported up to date. The synthesis of the new Zr–Al–Co-based bulk glassy alloy with high glass-forming ability, large supercooled liquid region and high tensile strength approaching 2000 MPa is expected to result in a future extension of application fields as a high strength material.
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  • Hua-nan Liu, Michiru Sakamoto, Kazushi Kishi, Kazuhisa Shobu, Tatsuo T ...
    2003 Volume 44 Issue 9 Pages 1845-1850
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Thermographic imaging under steady-state heat flow was used to nondestructively detect the defects in thermal barrier coatings (TBCs). The finite element method (FEM) analyses and the experimental thermography observations were performed using artificially grooved ZrO2 plates and the indentation-tested TBC-metal specimens. The FEM results show that: (1) Defects (nonuniformity or internal cracks) of the TBC can be effectively detected by the thermographic imaging method; (2) The apparent thermal images would be far greater than the real sizes of the defects, but the half-height sizes of the temperature profile were found to give good estimates for the latter; and (3) The higher value of heat flow would contribute to the detections. Besides these results, the influence of the defect situations (morphology, size and position) on the thermal images was also predicted by the FEM analysis. Although, due to some difficulties in preparing the test specimens, the quantitative comparison between each FEM result and that of the actual measurement was not performed, however, the experimental results of the grooved ZrO2 plates were found to be in good agreement with the FEM predictions. For the thermographic experiments of the indentation-tested specimens, both the internal-cracks and the thickness-nonuniformity of the TBCs were successfully observed, and the smallest cracks detectable had a diameter far less than 1 mm.
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  • Taek-Soo Kim, In-Cheol Kang, Takashi Goto, Byong-Taek Lee
    2003 Volume 44 Issue 9 Pages 1851-1856
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    A continuously porous alumina sintered body was successfully fabricated using by the fibrous monolithic process, in which carbon and flour were used as a pore forming agent. An equation was driven for anticipating the microstructural change during extrusion as a function of the extrusion ratio, and it was identified that the resultant microstructure obtained from using the fibrous monolithic process agreed well with the calculated size using the equation. The third passed and sintered alumina body includes continuous pores of about 42.5 μm in diameter at an intended direction, while the second one consists of 228 μm. Fine pores were also found to form along the alumina surfaces with 0.1–10 μm in diameter. There was no shape change during binder burning out and sintering processes.
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  • Akihiro Mizutani, Yoshitake Nishi
    2003 Volume 44 Issue 9 Pages 1857-1860
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Carbon fiber reinforced plastics (CFRPs), with their advantages of light weight and high strength, are increasingly being applied as structural materials in the fields of aerospace engineering and rapid transport engineering. To strengthen CFRPs, electron beam (EB) irradiation is performed homogeneously. EB irradiation enhances the bending fracture stress and the bending fracture strain, and also slightly enhances the bending elasticity of CFRP. The analysis based on the Law of Mixture Strength for composites suggests that EB strengthening of CFRPs is chiefly attributable to ductility enhancement of the epoxy resin and carbon fiber.
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  • Janakarajan Ramkumar, Santa Kumar Malhotra, Ramalingam Krishnamurthy, ...
    2003 Volume 44 Issue 9 Pages 1861-1865
    Published: 2003
    Released: September 06, 2005
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    To study dry sliding wear behavior and its relation to microstructure, Ti–50Al alloys and Ti–47Al–3W alloy and its composite with varying reinforcement of Ti2AlC were prepared by reactive arc-melting. Dispersion of fine B2 particles is obtained by the addition of tungsten to TiAl alloy, which improves both the hardness and wear resistance of the matrix. By adding carbon to Ti–47Al–3W alloy, composite can be produced having a random distribution of reacted rod-like Ti2AlC particles and smaller Ti2AlC precipitates with fine B2 particles in the matrix. The Ti–47Al–3W/3.5 vol%Ti2AlC intermetallic composite features excellent wear resistance compared to 10 and 18 vol% composites, and fine dispersion of the Ti2AlC and B2 particles in the matrix has improved the wear resistance properties.
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  • Tomoya Nagira, Mikio Ito, Shigeru Katsuyama, Shigeta Hara
    2003 Volume 44 Issue 9 Pages 1866-1871
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    NaxCo2O4 powders were synthesized using the polymerized complex (PC) method and then the polycrystalline samples were prepared by the spark plasma sintering (SPS) method. The microstructure and thermoelectric properties of these samples were evaluated, and their differences due to the preparation process of the polycrystalline NaxCo2O4 samples were investigated. The crystal grain sizes of the annealed PC samples after SPS at 1073 K and 1173 K were much smaller than that of the sample prepared by the conventional solid-state reaction (SSR) method and the sintered PC sample without pressure. Their relative densities were greater than 99%. We have obtained the dense sintered NaxCo2O4 samples with a finer microstructure. In the case of the annealed PC sample after SPS at 1073 K, the thermoelectric power, α, was remarkably higher than that of the SSR sample, and the α value was as high as that of the PC sample without pressure. The electrical resistivity, ρ, increased because of its finer crystal grains compared to the SSR sample and the sintered PC sample without pressure. In the case of the annealed PC sample after SPS at 1173 K, the ρ was the lowest of all samples in spite of its finer microstructure. Based on these results, the power factors of the annealed PC samples after SPS at 1073 K and 1173 K were markedly higher than that of the SSR sample over the entire temperature range. For the annealed PC sample after SPS at 1073 K, the maximum power factor, 1.4×10−3 W/mK2, was obtained at 1073 K.
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  • Masaki Sumida, Akiyoshi Matsumoto, Hiroaki Kumakura
    2003 Volume 44 Issue 9 Pages 1872-1876
    Published: 2003
    Released: September 06, 2005
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    In this paper, effect of the cooling process is examined for the superconductive properties of high Tc Bi-2223/Ag tapes prepared by dip-coating. The short tapes are cooled after the isothermal heat treatment at a controlled temperature profile, which can refine the microstructure. The cooling rate and the slow cooling range are varied, showing that the optimum condition is found where the enhanced Jc is obtained compared to that of normal furnace cooling. Contrarily, Tc did not show an optimum under this condition but increased monotonously with a decrease in the cooling rate and an increase in the slow cooling range. From phase identification, microscopic observation, and quantitative analysis, the microstructure formation in the polycrystalline oxide layer during this process and its relation to these properties are discussed.
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  • Keiko Sasaki, Tagiru Ogino, Yuji Endo, Kunihiko Kurosawa
    2003 Volume 44 Issue 9 Pages 1877-1884
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    The mechanism of surface water remediation in a natural wetland that is receiving heavy metal-rich acidic mine drainage was investigated. Selective sequential extraction was useful to derive the mechanisms of heavy metal removal in the wetland. In the upstream portion of the wetland, dissolved Fe was removed mainly as oxide-bounded mineral phases, such as hydroxides. These are important for the subsequent removal of other heavy metals. Other ion-exchangeable and carbonate-bounded heavy metals are also observed in the upstream, associated with Fe oxides. Organic matter and Fe–Mn oxides in the upstream remove Cu and Zn ions from the drainage, respectively. In the middle of portion of the wetland the removal of heavy metal ions in relatively low concentrations occurs by the emergent vegetation. Greater clay abundance and higher microbial activity of sulfate reducing bacteria in the downstream parts achieved low-level removal of metals. Multi-cell wetlands are recommended for the treatment of acidic metal bearing surface water drainage, if sufficient land area and expenses are available to construct.
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  • Shin-ichi Yamaura, Yoichiro Shimpo, Hitoshi Okouchi, Motonori Nishida, ...
    2003 Volume 44 Issue 9 Pages 1885-1890
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    We prepared the melt-spun (Ni0.6Nb0.4)100−xZrx (x=0 to 40 at%) and other amorphous alloy membranes and examined the permeation of hydrogen through those alloy membranes. The interatomic spacing in the Ni–Nb–Zr amorphous structure increased with increasing Zr content. The crystallization temperature of the Ni–Nb–Zr amorphous alloys decreased with increasing Zr content. The hydrogen flow increased with an increase of the temperature or the difference in the square-roots of hydrogen pressures across the membrane, Δ\\sqrtp. At relatively higher temperature up to 673 K or at relatively higher hydrogen pressure difference, Δ\\sqrtp up to 550 Pa1⁄2, the hydrogen flow was more strictly proportional to Δ\\sqrtp. This indicates that the diffusion of hydrogen through the membrane is a rate-controlling factor for hydrogen permeation. The permeability of the Ni–Nb–Zr amorphous alloys was strongly dependent on alloy compositions and increased with increasing Zr content. However, it was difficult to investigate the hydrogen permeability of the (Ni0.6Nb0.4)60Zr40 amorphous alloy in this work due to the embrittlement during the measurement. The maximum hydrogen permeability was 1.3×10−8 (mol·m−1·s−1·Pa−1⁄2) at 673 K for the (Ni0.6Nb0.4)70Zr30 amorphous alloy. It is noticed that the hydrogen permeability of the (Ni0.6Nb0.4)70Zr30 amorphous alloy is higher than that of pure Pd metal. These permeation characteristics indicate the possibility of future practical use of the melt-spun amorphous alloys as a hydrogen permeable membrane.
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  • Tsutomu Tanaka, Hiroyuki Watanabe, Kenji Higashi
    2003 Volume 44 Issue 9 Pages 1891-1894
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Experiments were conducted to evaluate the grain refinement in Zn–22Al alloys subjected to equal-channel-angular extrusion (ECAE) under three different conditions. In the first condition (Route 1), ECAE was performed during the phase transformation at room temperature. In the second condition (Route 2), ECAE was carried out after the phase transformation at room temperature. In the third condition (Route 3), ECAE was performed after the phase transformation at 373 K. The average grain sizes after ECAE exhibited 0.35, 0.3 and 0.6 μm for Route 1, 2 and 3, respectively. Route 1 was efficient to develop the material with a finer microstructure, and reduce the processing time. It was also verified that reasonably equiaxed and homogeneously distributed grains were obtained by ECAE after solution treatment without rolling process.
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  • Shin-ichi Yamaura, Hisamichi Kimura, Akihisa Inoue
    2003 Volume 44 Issue 9 Pages 1895-1898
    Published: 2003
    Released: September 06, 2005
    JOURNALS FREE ACCESS
    Amorphous alloys in the Mg–Pd binary system were formed in a composition range of 10 to 35 at%Pd by melt-spinning technique. The crystallization temperature and tensile strength of the amorphous Mg100−xPdx (x=10, 20 and 30 at%) alloys are in the range from 417 to 535 K and 440 to 650 MPa, respectively. There is a tendency for the crystallization temperature and the tensile strength to increase with increasing Pd content. Vickers hardness also increased with increasing Pd content. Their compositional dependence is attributed to an increase in the number of Mg–Pd atomic pairs with large negative mixing enthalpy. Crystallized structure of the Mg–Pd amorphous alloys was also examined in correlation with equilibrium phases.
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