MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 51 , Issue 9
Showing 1-39 articles out of 39 articles from the selected issue
  • Kazuaki Kobayashi, Shojiro Komatsu
    2010 Volume 51 Issue 9 Pages 1497-1503
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    We calculated the electronic and lattice properties of 30H-BN which are sp3-bonded compounds. The 30H polytype has various over 6000000 structures. Their possible symmetries and hexagonalities (H[%]) are P63mc and P3m1, and 6.7%∼93.3%, respectively. Hexagonality is a ratio of the number of hexagonal (h) character and the total number of cubic (c) and h characters in a unit cell. Two structures in the 30H polytype are considered in this study. Their stacking sequences (ABC notation) are ABCABCABCABCABCACBACBACBACBACB (P63mc, H=6.7%) and ABCBCBCBCBCBCBCBCBCBCBCBCBCBCB (P3m1, H=93.3%). Their lattice properties were optimized automatically by the total energy pseudopotential method. Calculated total energies of 30H-BN are in the order of ABCABCABCABCABCACBACBACBACBACB (6.7%) < ABCBCBCBCBCBCBCBCBCBCBCBCBCBCB (93.3%). Values in parentheses are hexagonalities (%). This means the former is energetically more favorable than the latter. The total energy of the BN polytype increases with increasing hexagonality. We calculated their electronic band structures, the band gap values, the valence band maximum (VBM), and conduction band minimum (CBM). Their electronic band structures are non-metallic and band gaps are indirect.
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  • Junyoung Park, Yoji Shibutani, Masato Wakeda
    2010 Volume 51 Issue 9 Pages 1504-1509
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 11, 2010
    JOURNALS FREE ACCESS
    This study explores the plastic deformability of highly density-fluctuated states due to the different thermal quenching process of the binary amorphous metals, Zr67Cu33, with embedded nanocrystals, Zr2Cu. To know the effect of local structural fluctuation, we prepare 5 computational models with Zr2Cu-nanocrystals that undergo rapid heat up and cool down. The region of nanocrystals is corresponding to the dense area because the intrinsic density of crystal is greater than that of amorphous structure. Due to the distribution of nanocrystals, the artificially constructed models have highly density-fluctuated structures (called “structural-inhomogeneity”). Strain localization during plastic deformation is much retarded at structural-inhomogeneous model in tensile loading. We found that structural-inhomogeneity promotes more homogenous deformation (call “deformable-homogeneity”, that is, retarded strain localization) even in globally recognized elastic region, while structural-homogeneity (almost close to pure amorphous structure) makes catastrophic inhomogeneous deformation (catastrophic shear band).
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  • Toshio Itami, Junpei Okada, Yuki Watanabe, Takehiko Ishikawa, Shinichi ...
    2010 Volume 51 Issue 9 Pages 1510-1515
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 19, 2010
    JOURNALS FREE ACCESS
    To study the supercooling of many liquid metals with high melting temperatures, the investigation was performed for the cooling curves of electrostatic levitation (ESL) experiments, which had been originally obtained for the measurements of many physical properties. The largest supercooling over the literature values was found for liquid Ru (428 K), Ta (721 K), W (601 K), and Ir (438 K), where temperatures in the parentheses mean the supercooling of respective liquid metals. This indicates the validity of ESL for the supercooling experiments of liquid metals and alloys because of being rather free from the heterogeneous nucleation. This ESL was applied to the study of supercooling of homogeneous liquid phase in the composition range from 29 at% Nb to 71 at% Nb of eutectic Ni-Nb system, whose eutectic point is present at 40.5 at% Nb and 1448 K. The experimental result shows a poor supercooling tendency of homogeneous liquid phase around the eutectic composition in spite of large supercooling far apart from this eutectic composition. This characteristic feature was discussed based on the classical nucleation theory coupled with the knowledge recently found, the existence of concentration fluctuations in the homogeneous liquid phase near the eutectic point.
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  • Masayuki Kamaya
    2010 Volume 51 Issue 9 Pages 1516-1520
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    Electron backscatter diffraction in conjunction with scanning electron microscopy is used to assess local misorientation. However, measurement errors cause the distribution of misorientation to be scattered. To reduce the errors in local misorientation identification and obtain a smooth map, a data processing procedure is proposed. By taking the average of the crystal orientation of surrounding points, the distribution of the local misorientation became smoother and clearer. Moreover, the obtained local misorientation was shown to be valid for quantitatively evaluating the degree of plastic strain induced in Type 316 stainless steel.
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  • K. Sato, S. Takizawa, T. Mohri
    2010 Volume 51 Issue 9 Pages 1521-1525
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 07, 2010
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    We investigate temperature dependency of the activation free energy for the atomic diffusion in the fcc Lennrad-Jones system within the transition states theory based on the quasi-harmonic approximation. The activation free energy consists of the static activation energy and the vibrational free energy difference between the saddle point and the equilibrium state, and it is shown that both of them strongly depend on the system volume and the temperature. The temperature dependencies of both quantities exhibit opposite tendencies, i.e., the static activation energy decreases, while the free energy difference increases with increasing temperature. As a result, the activation free energy shows a weak temperature dependency. We discuss the effects of anharmonicity on the activation free energy by comparing the activation free energy obtained by the quasi-harmonic and harmonic approximations.
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  • Liren Cheng, Zhanyi Cao, Ruizhi Wu, Milin Zhang, Dongmei Jiang
    2010 Volume 51 Issue 9 Pages 1526-1530
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    Samples of (A) Mg-6.86Li-3.02Al-1.12Ce-0.7Ca, (B) Mg-8.15Li-3.07Al-1.12Ce-0.72Ca and (C) Mg-10.54Li-3.54Al-1.23Ce-0.94Ca alloys are prepared by casting and extrusion process. The microstructure and mechanical properties of alloys are characterized. The results indicate that the as-cast specimens of (A) and (B) have α+β dual phase structure and the as-cast (C) alloy has β phase (Li), α+β eutectic structure. Bulk and rod-like Al2Ce and Al2Ca compounds are found in matrix and boundaries in all the alloys. The orientation relationship between a type of Al2(Ce, Ca) phase and the α phase is confirmed, i.e., [\\bar112]||[7\\bar2\\bar53]α, (1\\bar11)||(01\\bar1\\bar1)α. For the extruded alloys, the microstructures are refined and the β phase has the effect of coordination during deformation. The long rod-like and bulk compounds become short rods and fine clumps distributing evenly in the extruding direction. The microstructure of extruded Mg-10.54Li-3.54Al-1.23Ce-0.94-Ca alloy testifies the existence of the eutectic structure. The tensile strength and yield strength of Mg-6.86Li-3.02Al-1.12Ce-0.7Ca (UTS: 12.5%, YS: 36%) and Mg-8.15Li-3.07-Al-1.12Ce-0.72Ca (UTS: 24%, YS: 46%) alloys have improved after extruding process.
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  • Yasushi Kato, Masatoshi Ito, Yoshimine Kato, Osamu Furukimi
    2010 Volume 51 Issue 9 Pages 1531-1535
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    The effect of Si was investigated on the precipitation behavior and the amount of Nb in solid solution at temperature ranging from 1073 to 1173 K in high purity 17Cr-0.5Nb steels. Adding Si promoted the precipitation of the Nb Laves phase and then decreased the solubility of Nb in steels. The Nb Laves phase which was composed of Fe, Cr and Nb could be expressed as (Fe, Cr)2Nb in a 0.002 mass% Si steel. On the other hand, in a 0.5 mass% Si steel the Nb Laves phase which was composed of Fe, Si, Cr and Nb could be expressed as (Fe, Si, Cr)2Nb. Based on calculations from the experimental results assuming the Laves phase is Fe2Nb, the standard free energy change of the Fe2Nb precipitation reaction was about −61 k J/mol for a 0.002 mass% Si steel.
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  • Takaomi Itoi, Takeru Suzuki, Yoshihito Kawamura, Mitsuji Hirohashi
    2010 Volume 51 Issue 9 Pages 1536-1542
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 11, 2010
    JOURNALS FREE ACCESS
    Ternary Mg-Zn-Y alloy sheets with several volume fractions of a Mg12ZnY phase were prepared by hot-rolling at 623 K. Volume fraction of the Mg12ZnY phase was increased with increasing of Zn and Y contents in the Mg100−xyZnxYy (x=1∼6, y=2∼9 at%) alloys, and achieved more than 85% in an Mg85Zn6Y9 alloy. (002) pole figures showed both of basal planes of the Mg12ZnY and Mg phases have a tendency to incline toward parallel to the sheet surface. However, it was considered that the formation of a basal plane texture in the Mg12ZnY phase is difficult compared with that in the Mg phase, due to a kink deformation. An Mg90.5Zn3.25Y6.25 alloy sheet exhibited a 0.2% proof strength, an ultimate tensile strength, and an elongation of 353 MPa, 400 MPa, and 5%, respectively, at room temperature, and 279 MPa, 375 MPa, and 12%, respectively, at 523 K. Although elongation was slightly less than those in the commercial Mg sheets, the Mg90.5Zn3.25Y6.25 alloy sheet showed high strength over a wide temperature range compared to those in commercial Mg alloys.
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  • Shigeki Morita, Nobuyoshi Ohno, Fujio Tamai, Yuji Kawakami
    2010 Volume 51 Issue 9 Pages 1543-1546
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 22, 2010
    JOURNALS FREE ACCESS
    This paper describes the fatigue crack propagation behavior of rolled and extruded AZ31B magnesium alloys (grain size: approximately 20 and 15 μm, respectively). Fatigue crack propagation tests were performed on center cracked plate tension specimens at a stress ratio of R=0.1 and a frequency of 10 Hz at room temperature. Loading axes were parallel to the rolling and extrusion directions; fatigue cracks propagated parallel to the transverse direction (L-T specimen of rolled AZ31B), parallel to the short transverse direction (L-S specimen of rolled AZ31B), and perpendicular to the extrusion direction (E-R specimen of extruded AZ31B). The crack growth rate (dadN) of the L-S specimen was approximately 10 times lower than that of the L-T specimen in the examined stress intensity factor (ΔK) range. Fracture surfaces of the L-T and L-S specimens showed many steps parallel and perpendicular, respectively, to the macroscopic crack growth direction. The plot of the dadN versus the ΔK range for the E-R specimen shows two regimes with different slopes in the examined ΔK range. The fracture surface was covered by various directional steps independent of macroscopic crack growth direction, and the fracture surface roughness at low ΔK was larger than that at high ΔK. SEM-EBSD observations revealed that the c-axis direction is unfavorable for the fatigue crack propagation in rolled AZ31B magnesium alloy. Free deformation twins were observed around the fatigue crack path in the L-T, L-S, and E-R specimens.
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  • Hyung-Ki Park, Se-Jong Kim, Heung Nam Han, Chan-Hee Han, Nong-Moon Hwa ...
    2010 Volume 51 Issue 9 Pages 1547-1552
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 11, 2010
    JOURNALS FREE ACCESS
    In an effort to explain the selective Goss abnormal grain growth in Fe-3%Si steel based on the sub-boundary enhanced solid-state wetting, we investigated why sub-boundaries are formed exclusively in Goss grains after primary recrystallization. In order for Goss grains to have sub-boundaries exclusively, they should undergo only recovery without recrystallization whereas other grains undergo recrystallization. For this, Goss grains should have the lowest stored energy after cold rolling. Goss and rotated cube orientations have the same and the lowest Taylor factor among the grains formed after cold rolling, implying that they should have the lowest stored energy. The stored energy between Goss and rotated cube orientations was compared by the crystal plasticity finite element calculation, which showed that the stored energy of the Goss orientation was lower than that of the rotated cube orientation after plane strain deformation.
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  • T. Nishimura, S. Tamilselvi, X. H. Min, K. Tsuzaki
    2010 Volume 51 Issue 9 Pages 1553-1559
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    The corrosion resistance of an aging heat-treated Ti-8Mo-5Fe alloy was investigated by electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDAX). The sample subjected to solution heat treatment (ST) featured a single β-phase microstructure, and the samples subjected to aging heat treatments at 600–700°C showed α-phase precipitates in the β-phase matrix. EIS results showed that the corrosion resistance of the aging heat-treated samples was lower than that of the ST sample, but much higher than that of pure Ti in a long-term immersion test in an acidic 10 mass% NaCl solution (pH 0.5) at 97°C. Laser micrographs of the aging heat-treated samples indicated susceptibility to selective corrosion of α-phase at the grain boundary and in the grains, causing selective dissolution in the NaCl solution. The results of TEM combined with EDAX analyses showed the presence of the β-phase matrix composed of 5.3 mass% Mo and 4.8 mass% Fe, and α-phase of 0.7 mass% Mo and 0.1 mass% Fe in the sample aged at 600°C. Thus, the Mo-poor α-phase precipitates were selectively dissolved in the 10 mass% NaCl solution (pH 0.5) at 97°C. In the results, the ST sample of only β-phase microstructure showed the highest resistance, and the aging heat-treated samples containing α-phase precipitates (0.7 mass% Mo) showed higher values than that of pure Ti in the corrosion test. Addition of Fe did not decrease the corrosion resistance of the alloy under the ST condition. Moreover, as Fe was involved in the β phase with Mo which showed remarkable increase in corrosion resistance, the addition of Fe did not decrease the corrosion resistance of the aging heat-treated Mo-Fe-Ti alloy.
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  • Youhei Nasukawa, Tosihide Fujikawa, Ryoji Tsujino, Manabu Iguchi
    2010 Volume 51 Issue 9 Pages 1560-1565
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    Experimental investigations are carried out on the bath surface oscillations caused by horizontal air injection through an L-shaped lance into a cylindrical bath. Several types of bath surface oscillations are observed depending on the gas flow rate, the lance exit location, and so on. A bath surface oscillation map is drawn to identify the occurrence conditions of the oscillations. Particular attention is paid to the deep-water wave type swirl motion because of its practical importance. Empirical equations are newly proposed to describe the occurrence condition of the swirl motion. The measured values of the period and amplitude of the swirl motion compare favorably with their respective empirical equations proposed previously for bottom gas injection.
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  • Akira Kudo, Takeshi Fujita, Xingyou Lang, Luyang Chen, Mingwei Chen
    2010 Volume 51 Issue 9 Pages 1566-1569
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    We reported novel nanoporous gold (NPG) with surface modified by TiO2 nanoparticles. The as-fabricated sample showed larger effective area than bare NPG. Microstructure characterization demonstrated that the TiO2 nanoparticles effectively suppressed the coarsening of the nanoporous structure by the reaction with gold ligaments. The resultant porous nanocomposite with rough ligament surfaces was proofed to spontaneously possess enhanced catalytic performance towards methanol oxidation. This result would yield an effective and inexpensive method to improve NPG’s catalytic activity.
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  • Daisuke Maruoka, Makoto Nanko
    2010 Volume 51 Issue 9 Pages 1570-1573
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    The oxidation kinetics of 5 vol% nano-Ni dispersed Al2O3 with Si-doping (nano-Ni/Al2O3-Si) was studied in the present paper. The starting powder mixture was prepared by drying aqueous slurry consisting of alumina with nickel nitrate and Si (OCH3)4. The powder mixture was reduced at 600°C for 12 h in a stream of Ar-1%H2 gas mixture. Nano-Ni/Al2O3-Si was densified by pulsed electric current sintering. The oxidation test was conducted at 1200–1350°C for 1–14 d in air. Oxidized zone consisted of Al2O3 matrix and NiAl2O4 as the oxidation product. Growth of the oxidized zone followed a parabolic manner. A thin NiAl2O4 layer was also observed on the sample surface. Si-doping decreases growth rate of oxidized zone effectively at lower temperatures such 1200°C.
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  • Yoshihiko Hangai, Osamu Kuwazuru, Takayuki Yano, Takao Utsunomiya, Yoz ...
    2010 Volume 51 Issue 9 Pages 1574-1580
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 14, 2010
    JOURNALS FREE ACCESS
    The geometric features of clustered shrinkage pores (CSP) in ill-conditioned aluminum alloy die castings were revealed and their effect on the fatigue strength was discussed. To obtain the geometric features of CSP, an observation using a commercial microfocus X-ray computed tomography (X-ray CT) system was carried out and the position and size of CSP were confirmed. However, the detailed geometry of the CSP could not be clearly observed by X-ray CT, because each pore in the CSP was too small to observe owing to the insufficient resolution of the CT image. We developed a serial sectioning system with a polishing machine and an optical microscope. Observation using the serial sectioning system clearly showed that a CSP consists of many interconnected small pores, which formed an extremely complicated shape. The CSP was thought to grow from relatively large gas pores, which connect to small pores and consequently generate a cavity with a huge volume and a complicated geometry. The complex geometry of CSP resulted in the concentration of stress around CSP, and significantly undermines mechanical properties such as tensile strength and fatigue strength.
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  • Masahiro Komaki, Tsunehiro Mimura, Yuji Kusumoto, Ryurou Kurahasi, Mas ...
    2010 Volume 51 Issue 9 Pages 1581-1585
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    Some amorphous Fe-Cr-P-C coating films having high hardness and high corrosion resistance have been produced by a newly developed thermal spraying technique. In order to control the temperatures of the powder particles in the flame spray and the substrate, a newly developed cylindrical nozzle, with external cooling nitrogen gas, was mounted to the front end of the thermal spraying gun. Fe70Cr10P13C7 films with various external cooling gas velocities between 20 m/s and 40 m/s exhibited entire amorphous structure without oxides and/or unmelted particles. Corrosion-resistance of the films was observed in immersion tests using various corrosive liquids. An amorphous film was formed on the surface of the shaft sleeve of the slurry pump by using the cylindrical nozzle. This shaft sleeve was installed in the slurry pump of chemical fertilizer maker’s production line and the life test was done under the real operation condition for two months.
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  • Chau-Jeng Su, Jaw-Min Chou, Shih-Hsien Liu
    2010 Volume 51 Issue 9 Pages 1586-1593
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    A water model was adopted to physically simulate the bottom gas stirring inside an ironmaking smelter. The water model experiments were conducted to investigate the erosion of the bottom refractory lining near the tuyere tip under different gas bottom blowing conditions. In experiments, the major parameters are the gas flow rate, and the inside diameter and placement of bottom blowing tuyeres.
    The purpose of this study is to provide a design and operation reference of the gas bottom blowing system for CSC’s Ironmaking Smelter. A transparent acrylic water model, which is 60% of the actual furnace’s size, is used to study the erosion of the bottom refractory lining near the tuyere tips. The experiments suggested that the erosion rate of specimens near the tuyere tips reduced with a decrease in the gas flow rate. In the case of the triangle-corners-center placement of four bottom blowing tuyeres, the lowest erosion rate of boric acid specimens was found at a 15 mm tuyere size. In the case of the square-corners placement of four bottom blowing tuyeres, the lowest erosion rate of boric acid specimens was found at a 10 mm tuyere size. With the same blowing conditions, the erosion rate appears to decrease with a decrease in tuyere numbers. It was shown that the erosion rate of the square-corners placement case was lower than that of the triangle-corners-center at the same bottom blowing condition. The results imply that the conditions for the lowest erosion rate of specimens is a bottom blowing gas flow rate for each tuyere of 80 L/min, a tuyere inner diameter of 15.0 mm and three bottom blowing tuyeres, all of which should be in the range of the experimental parameters described above.
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  • Chau-Jeng Su, Jaw-Min Chou, Shih-Hsien Liu, Cheng-Hsueh Chiang
    2010 Volume 51 Issue 9 Pages 1594-1601
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    To aid efficient use of the gas flow rate for a smelting reduction furnace, this study investigates the effect of gas bottom blowing and stirring on the mixing time of the molten iron phase. In this study, transparent acrylic is used to construct a water model, which is 60% as big as the original experimental melting reduction furnace of the China Steel Corporation. The mixing time of the molten iron phase in the water model is measured by using gas bottom blowing and changing the number of tuyeres (from three to five), the tuyere placement, the tuyere size (6.0–15.0 mm), and the gas flow rate per tuyere (80–120 NL/min).
    The mixing trials adopt KCl as an indicator and use water filtrated using reverse osmosis (RO) in place of liquid iron to investigate the effect of gas bottom blowing conditions on mixing of the molten iron phase. The experimental results indicate that in the cases of four tuyeres in the square-corner and triangle-corner-center placements, 10.0 mm tuyeres yield the shortest mixing time (and thus the best mixing effect) under different total gas flow rates. In the case of five tuyeres in the square-corner-center placement, 10.0 mm tuyeres also have the shortest mixing time under total gas flow rates of 400 NL/min and 500 NL/min. However, 12.5 mm tuyeres have the shortest mixing time under a total gas flow rate of 600 NL/min. In addition, in the case of three tuyeres in the triangle-corner placement, 12.5 mm tuyeres have the shortest mixing time under different total gas flow rates. When the gas flow rate per tuyere is 80 NL/min, the fewer the tuyeres, the shorter the mixing time. Depending on tuyere placement, some of the energy injected by the gas may be counteracted. For example, when a bottom-blowing tuyere exists in the center, the gas injection from that tuyere may be counteracted by that of adjacent tuyeres such that energy dissipates. In contrast, a tuyere placement without a center tuyere may yield better mixing effects. In this study, the best combination for mixing in the liquid phase is four 10.0 mm tuyeres in the square-corner placement and a total gas flow rate of 480 NL/min.
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  • Chau-Jeng Su, Jaw-Min Chou, Shih-Hsien Liu
    2010 Volume 51 Issue 9 Pages 1602-1608
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    This study uses a water model experiment to investigate the effects of gas bottom blowing conditions on fluid flow phenomena and the mixing time of molten iron within an ironmaking smelter. Our experimental setup adopted four tuyeres in a square-corner placement. The parameters for trials include bottom-blowing tuyere size (7.5∼15.0 mm) and the bottom blowing gas flow rate (320∼480 NL/min). Experimental results show that the bubble size decreased and the invading depth became deeper as the tuyere size decreased and the total gas flow rate increased. Consequently, the spout height of the liquid surface became higher. The results of the mixing experiment indicate that under any bottom blowing gas flow rates, the 10.0 mm tuyere has the shortest mixing time. Except for the 7.5 mm tuyere, the 10.0 mm, 12.5 mm, and 15.0 mm tuyeres had shorter mixing times and better mixing effects as the gas flow rate increased. Therefore, the best combination for mixing iron phase in a smelter is to use a 10.0 mm tuyere and a gas flow rate of 480 NL/min, which has the appropriate intensity of the total blown energy and the degree of stirred liquid bath.
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  • Sung-chul Kim, Shin-ichi Yamaura, Yuta Shimizu, Koji Nakashima, Takano ...
    2010 Volume 51 Issue 9 Pages 1609-1613
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    In this study, the newly designed bipolar plate for proton exchange membrane fuel cells (PEMFC) was produced by spray-coating the Ni65Cr15P16B4 metallic glassy alloy on Al plate. The Ni65Cr15P16B4 metallic glass was adopted as a coating material because of its excellent corrosion resistance and the high velocity oxy-fuel (HVOF) spray coating was used for the metallic glass deposition on the Al plates having a bipolar plate flow field.
    The corrosion resistance of the Ni65Cr15P16B4 glassy alloy film produced by the HVOF spray-coating was studied under simulated PEMFC environments. As a result, the Ni65Cr15P16B4 glassy alloy film showed lower corrosion current density than the high-corrosion-resistant stainless steel SUS316L. Then, the electricity generation tests with the single cell having the Ni65Cr15P16B4 glassy alloy-coated bipolar plates produced in this study were conducted. As a result, the single cell with the metallic glass-coated bipolar plates showed very high I-V performance as well as the cell with the carbon bipolar plates. The long time durability tests for 24 h were also conducted at the constant current density of 200 mA·cm−2. As a result, the single cell with the glass-coated bipolar plates showed no voltage drop during the test. So, it was found in this study that the Ni65Cr15P16B4 glassy alloy-coated bipolar plate produced by the HVOF spray-coating have a potential for practical use for the fuel cells.
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  • Ho Won Lee, Yong-Taek Im
    2010 Volume 51 Issue 9 Pages 1614-1620
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 11, 2010
    JOURNALS FREE ACCESS
    In this study, a cellular automata technique was developed to simulate a dynamic recrystallization process of pure copper. Moore’s neighboring rule was applied with partial fraction and time step control in the current approach to represent the grain growth kinetics more accurately. The cellular automata model developed in this study was applied to a simulation of the dynamic recrystallization of pure copper during hot deformation and compared with the experimental flow stresses and grain sizes determined from hot compression tests for validation. The predicted results were in reasonably good agreement with the experimental results. The grain coarsening and refinement phenomena were also investigated in detail. Finally, the effects of the process parameters on the microstructure and flow stress were investigated from various simulation results.
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  • Akihiro Nino, Ayumi Tanaka, Shigeaki Sugiyama, Hitoshi Taimatsu
    2010 Volume 51 Issue 9 Pages 1621-1626
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 11, 2010
    JOURNALS FREE ACCESS
    This study measured the Vickers hardness of the sintered refractory carbides B4C, Mo2C, NbC, TiC, V8C7, W2C, WC, WC–SiC, and ZrC over a wide range of test forces between 0.49 and 196 N. The results showed an indentation size effect (ISE), with hardness values that increased with decreasing test force for the carbides. The test force dependence of the hardness was analyzed by the proportional specimen resistance (PSR) model. The value of the a1 term that reflects the elastic resistance in the model was obtained for the carbides and compared with their measured elastic, shear, and bulk moduli. It was not clear what type of modulus related strongly to the a1 term. There was a strict correlation between the hardness at an infinite test force and at a test force of 9.8 N. However, the hardness at a test force of 0.49 N a little poorly reflected the hardness at an infinite test force. The hardness at low test forces must be corrected using the a1 value in comparing it with the hardness at a test force of 9.8 N recommended for the Vickers hardness test by the Japanese Industrial Standard.
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  • Shuji Uehara, Kazuhiro Ito, Kazuyuki Kohama, Takashi Onishi, Yasuharu ...
    2010 Volume 51 Issue 9 Pages 1627-1632
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 07, 2010
    JOURNALS FREE ACCESS
    Low-resistivity and excellent-adhesion Cu(Ti) alloy films were prepared on glass substrates. Cu(0.3∼4 at%Ti) alloy films were deposited on the substrates, and subsequently annealed in vacuum at 400°C for 3 h. Resistivity of the annealed Cu(Ti) alloy films was significantly reduced to about 2.8 μΩcm. Tensile strength of the Cu(Ti)/glass interface increased to about 60 MPa after annealing. The low resistivity and excellent adhesion resulted from Ti segregation at the film surface and the Cu(Ti)/glass interface. The segregated Ti atoms reacted with atmospheric oxygen at the surface and with oxygen in glass and/or from atmosphere at the interface, and formed a TiO2 layer at the surface and a TiO2 layer with a small amount of Ti2O3 and TiO at the interface. The layers were non-crystalline. Columnar grains in the alloy films were seen to enhance Ti segregation and subsequent Cu grain growth. The Cu grain growth also contributed to low resistivity of Cu(Ti) alloy films.
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  • Yui Yamashita, Yunping Li, Emi Onodera, Hiroaki Matsumoto, Akihiko Chi ...
    2010 Volume 51 Issue 9 Pages 1633-1639
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    In order to examine the dynamic recrystallization (DRX) behaviors of Co-29Cr-6Mo alloy with additions of both C and N (hereafter CCMCN alloy), uniaxial compression tests in the temperature range of 1273 to 1473 K and strain rates of 0.01 to 30 s−1 were carried out. The influence of hot forging conditions (i.e., temperature, strain rate, and strain) on the microstructure of deformed sample was investigated in detail by means of electron backscattering diffraction (EBSD) and optical microscopy (OM). The results revealed that the initial microstructure is a stable γ face-centered cubic (FCC) phase with a large number of M23C6 precipitates both inside the grains and at grain boundaries. The DRXed grains were observed to be uniformly distributed and to decrease with strain. The high volume fraction of Σ3 boundaries after the DRX was observed, indicating a close relation between the DRX mechanism and Σ3 boundary formations. In addition, the activation energy Q of CCMCN alloy was observed to be higher as compared to those of alloys without C or N addition and that with N addition.
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  • Masaaki Hirano, Michiaki Yamasaki, Koji Hagihara, Kenji Higashida, Yos ...
    2010 Volume 51 Issue 9 Pages 1640-1647
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 22, 2010
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    The effects of alloy extrusion parameters, such as extrusion ratio, temperature, and speed on the mechanical properties at room and elevated temperatures and the microstructure evolution were investigated in the production of high strength Mg-Zn-Y alloys. The alloy used is a Mg97Zn1Y2 (at%) which is engineered to acquire a long-period stacking ordered (LPSO) structure phase to increase alloy-strength. The microstructure of the extruded Mg97Zn1Y2 alloy consists of hot-worked and dynamically recrystallized (DRXed) α-Mg grains that includes a fiber-shaped LPSO phase elongated along the direction of extrusion. Whereas an increase in average equivalent strain promotes the DRX of α-Mg matrix and the dispersion of the fiber-shaped LPSO phase, an increase in average metal flow rate is conductive to the DRX of α-Mg grains, but is not to the dispersion of LPSO phase. The mechanical properties of the extruded Mg-Zn-Y alloys are affected by changes in the area fraction of the DRXed grains and the dispersion of the fiber-shaped LPSO phase. As the extrusion ratio and extrusion speed increase, overall DRX bringing grain growth in its train in the α-Mg matrix phase decreases the tensile strength of alloys, but the dispersed fiber-shaped LPSO phase remaining in the DRXed grains region makes good the adverse effect of overall DRX followed by grain growth.
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  • Yoshifuru Mitsui, Keiichi Koyama, Wataru Ito, Rie Y. Umetsu, Ryosuke K ...
    2010 Volume 51 Issue 9 Pages 1648-1650
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    The structural properties of metamagnetic shape memory alloy Ni40Co10Mn34Al16 were investigated by X-ray powder diffraction measurements in the temperature range from 283 to 473 K and magnetic fields up to 5 T. With increasing temperature from 283 K, the alloy undergoes the reverse martensitic transformation from the tetragonal L10-type structure with the lattice parameter at=0.3853 nm and ct=0.3299 nm into the B2-type cubic structure with the lattice parameter ac=0.2924 nm at As=383 K. At 408 K (>As), we directly observed the field-induced reverse martensitic transformation.
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  • Pattira Homhuan, Surasing Chaiyakun, Rattaporn Thonggoom, Nurot Panich ...
    2010 Volume 51 Issue 9 Pages 1651-1655
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    Nanostructured Cr-Zr-N thin films were grown on Si(100) substrates in a mixture of Ar and N2 plasma. The nitrogen partial pressure was varied to produce and control the stoichiometric forms obtained. All the Cr-Zr-N films exhibited a nanostructure with an average grain size of less than 10 nm, as determined by X-ray diffractogram analysis, and were formed in the solid-solution. As the contents of nitrogen in the film increased, it lead to changes in the crystal texture and competitive growth. The maximum root mean square roughness was 7.87 nm at a 20% nitrogen partial pressure and the roughness tended to decrease as the grain size decreased. The nano-indentation showed that the films grown at a 20% nitrogen partial pressure and annealed at 700°C had the highest reduced modulus and hardness at 349.2 and 35.1 GPa, respectively. The mechanical properties of films can be improved by a post-annealing heat treatment. With respect to the electrical properties of these films, the sheet resistance, which is related to the defect level, tended to increase as the nitrogen partial pressure increased.
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  • Toshimitsu Tetsui, Toshiharu Kobayashi, Takashi Mori, Tatsuya Kishimot ...
    2010 Volume 51 Issue 9 Pages 1656-1662
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 28, 2010
    JOURNALS FREE ACCESS
    In seeking cost reductions for precision cast parts made of TiAl alloy, application of induction melting using a ceramic crucible would be highly effective. Accordingly, consideration was given to the applicability of yttria as the material basis for such a ceramic crucible. Crucible specifications were first investigated, and a prototype crucible was fabricated with a suitable mixture ratio of raw materials from the standpoint of satisfactory thermal shock resistance and low reactivity with TiAl molten metal. As a result of induction melting testing of Ti-46 at%Al alloy, the developed crucible was found to facilitate substantially less contamination of the TiAl alloy, with lower oxygen concentration and hardness as compared with other conventional ceramic crucibles.
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  • Shojiro Ochiai, Hiroshi Okuda, Michinaka Sugano, Masaki Hojo, Kozo Osa ...
    2010 Volume 51 Issue 9 Pages 1663-1670
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 04, 2010
    JOURNALS FREE ACCESS
    Critical current of bent-damaged Bi2223 composite tape differs from specimen to specimen. To describe the distributed critical current values of specimens, the three-parameter Weibull distribution function has been employed and has been demonstrated to describe the experimental results. In the present work, the reason for this was discussed by modeling analysis of the experimental results in a round robin test of VAMAS/TWA16. The distribution of the measured normalized critical current values was described well by using the damage evolution approach, in which the difference in damage evolution among the specimens was correlated to the distribution of critical current values. From this approach, the three-parameter Weibull distribution function for critical current values was derived, which gave almost the same parameter values for the minimum critical current, scale parameter and shape parameter as those obtained by the direct application of the Weibull distribution function to the experimental results. Based on this result, the reason why the normalized critical current values of bent-damaged composite tape is described by the three-parameter Weibull distribution function was accounted for in a quantitative manner by the difference in damage evolution among the specimens.
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  • Faiza M. Al Kharafi, Nouria A. Al-Awadi, Ibrahim M. Ghayad, Ragab M. A ...
    2010 Volume 51 Issue 9 Pages 1671-1676
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    A new method was proposed for the application of azole corrosion inhibitors on the surface of copper. This method depends on the vacuum pyrolysis of the inhibitor in the presence of copper specimens. Three azole inhibitors namely; benzotriazole (Azole (1)), N-[Benzotriazol-1-yl-(phenyl)-methylene]-N-phenyl-hydrazine (Azole (2)) and N-[Benzotriazol-1-yl-(4-methoxy-phenyl)-methylene]-N-phenyl-hydrazine (Azole (3)) were tested. After pyrolysis copper samples were electrochemically tested in sulfide polluted salt water and compared to the behavior of copper tested in the sulfide polluted salt water containing dissolved benzotriazole. Results showed that copper specimens treated in the presence of Azoles (2) and (3) exhibit excellent corrosion resistance. Those samples could resist the poisoning effect of sulfide ions. Azole (1) shows good resistance at low sulfide concentration and failed at the high concentration. Surface investigation support the results of electrochemical tests.
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  • Chien-Hsuan Yeh, Li-Shin Chang, Boris Straumal
    2010 Volume 51 Issue 9 Pages 1677-1682
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    The microstructural evolution of tin–rich indium-based alloys after the grain boundary wetting phase transition in the (liquid + γ) two-phase region of the tin–indium phase diagram and its influence on the electrical conductivity were investigated. Five tin–indium alloys, Sn75In25, Sn70In30, Sn65In35, Sn60In40, and Sn55In45, were annealed between 393 and 454 K for 24 h. The melted area of the grain boundary triple junctions and grain boundaries increased with increasing the annealing temperature. The microstructures of as-prepared specimens of Sn75In25 and Sn70In30 alloys had different amounts of completely wetted grain boundaries after annealing. The XRD results show the changes in phases that underwent the eutectic transformation during quenching from various annealing temperatures. The electrical conductivity of annealed tin–indium specimens with various microstructures was measured. It increased with both annealing temperature and tin content.
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  • Shih-Hsien Chang, Shih-Chin Lee, Kuo-Tsung Huang
    2010 Volume 51 Issue 9 Pages 1683-1688
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    In our previous work, the parameters of solid-solution treatment for 718 alloy were discussed. The results showed that a solution temperature of 1020°C is optimum. The Laves and δ phase can complete solution after 1020°C, 1 h solid-solution treatment. The aim of this study is to discuss the effect of various aging treatments for as-HIP treated 718 alloy. In the experiment, seven different aging treatments were used: 720°C for 2, 4, 8 and 16 h, furnace cooled to 620°C, soak for 8 h, and air cooled to room temperature; 720°C for 8 h, furnace cooled to 620°C, soak for 2, 4, 8 and 16 h, and air cooled to room temperature. Experimental results showed that 1020°C solid-solution, 720°C for 8 h and 620°C for 4 h of aging treatment for as-HIP treated 718 alloy is optimum. All the precipitations are MC carbides; the dimension of γ″ precipitations is 30.41 nm, which with a maximum tensile strength (1407.2 MPa) and elongation (14.5%) at room temperature.
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  • Jung G. Lee, S. J. Hong, J. J. Park, M. K. Lee, V. V. Ivanov, C. K. Rh ...
    2010 Volume 51 Issue 9 Pages 1689-1693
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 19, 2010
    JOURNALS FREE ACCESS
    Highly dense and homogeneous yttria (Y2O3) thin-wall tubes have been successfully fabricated by applying tape-casting and radial magnetic pulsed compaction (RMPC) followed by thermal sintering. Since a homogeneous density distribution was obtained in the RMPCed compact, by using the Y2O3-based tape instead of a stuck of raw powder, cracking and bending were inhibited throughout the process up to the final sintered body. The relative density of the resultant tube reached 99.9%, and the structure was very fine with grain sizes of 2∼5 μm. Moreover, when the granulated powder was used as the precursor of the tape, the thermal densification was promoted due to its enhanced sinterability as compared to the raw powder.
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  • Wantae Kim, Doyoung Choi, Sangbae Kim
    2010 Volume 51 Issue 9 Pages 1694-1698
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 19, 2010
    JOURNALS FREE ACCESS
    Sonochemical synthesis of zeolite A has been conducted by ultrasonic irradiation of mixtures of metakaolinite and NaOH solution. The hydrothermal synthesis at conventional synthesis conditions was undertaken to determine the sonochemical reliability. The enhancement of nucleation and crystallization rate of zeolite A was achieved by ultrasound. In the ultrasonic field, zeolite A once formed in the suspension has been converted into hydroxysodalite and losod as sonicating proceeded. Comparing the results with those of conventional methods, this heterogeneous reaction was particularly accelerated by ultrasound, leading to improved reactivity of solid reactant through intensive mixing. The use of ultrasound enables us to prepare well-dispersed fine zeolite A particles with mean particle size of around 1 μm. The cation exchange capacity values of the products increased as the synthesis reaction for zeolite A proceeded. The high solid concentration in the suspension, however, hindered the ultrasound from intense agitating, resulting in the decrease of zeolite A yield.
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  • Seong-Ho Ha, Kyosuke Yoshimi, Kouichi Maruyama, Rong Tu, Takashi Goto
    2010 Volume 51 Issue 9 Pages 1699-1704
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 19, 2010
    JOURNALS FREE ACCESS
    The phase formation behavior during solidification in the Mo-Si-B system was experimentally examined around the triple junction point (T) of the Mo solid solution (Moss), Mo5SiB2 (T2) and Mo2B primary phases in the Mo-Si-B liquidus projection suggested by Yang and Chang through thermodynamic calculations, and the solidification routes of the Mo-Si-B alloys were reconsidered based on the obtained results. Alloys of four different compositions around the T point were produced by arc-melting. The primary phases observed in these alloys were in excellent agreement with the liquidus projection proposed by Yang and Chang. The solidification routes were basically Moss (primary) → Moss + Mo2B → Moss + T2 eutectic → Moss + T2 + Mo3Si (A15), T2 (primary) → Moss + T2 eutectic → Moss + T2 + A15, or Mo2B (primary) → Moss + T2 eutectic → Moss + T2 + A15, depending on the composition. However, a quantitative EPMA analysis indicated the compositions of the Moss-T2 eutectic and Moss + T2 + A15 phases differed from the reported liquidus projection. This is due to the difficulties interpreting the unusual solidification routes in the Mo-Si-B system and their as-cast microstructures.
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  • Masao Morishita, Hiroaki Yamamoto, Shinichi Shikada, Minoru Kusumoto, ...
    2010 Volume 51 Issue 9 Pages 1705-1708
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: August 11, 2010
    JOURNALS FREE ACCESS
    Relative partial molar Gibbs energies of the Mg component substituted into the Zn site, Δ\\barGMgMg on Zn site, in the intermediate phases of Mg0.48Zn0.52 and Mg0.4Zn0.6 in the Mg-Zn binary system were directly evaluated, assuming that change in the chemical potential of magnesium, ΔμMg, as a function of the composition in a narrow solubility limit is caused by anti-site substitution of Mg atoms at the Zn site. At 298 K, the Δ\\barGMgMg on Zn site values of Mg0.4Zn0.6 and Mg0.48Zn0.52 were found to be 1.254 and 0.163 MJ·mol−1, respectively, consistent with about the same order of internal energy of the Fe components substituted into the Pt site, ΔUFeFe on Pt site, in the ordered phase of L10-Fe1−xPtx calculated by theoretical calculation (=0.101 MJ·mol−1). When the symmetric atomic configuration at the stoichiometric composition was violated by anti-site substitution, the relative partial molar thermodynamic value of lattice defect was found to be very large.
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  • Jae Bong Lee, Hyuk Rok Gwon, Seong Hyuk Lee, Minhaeng Cho
    2010 Volume 51 Issue 9 Pages 1709-1711
    Published: September 01, 2010
    Released: August 25, 2010
    [Advance publication] Released: July 14, 2010
    JOURNALS FREE ACCESS
    Hydrophobicity and wetting transition behavior of water droplets were investigated on microstructured hydrophobic rough surfaces with pillar arrays, fabricated by self-replication with hydrophobic polydimethylsiloxane(PDMS) together with the use of CNC machine. The surfaces consist of microscale pillars(diameter: 105 μm, height: 150 μm) with varying spacing-to-diameter ratio (sd) ranging from ∼1.0 to ∼3.3. A de-ionized(DI) water droplet of 4.3 μl was placed on hydrophobic surfaces and contact angles(CA) were measured by the digital image processing algorithm. A wetting transition from the Cassie state to the Wenzel state was demonstrated depending on the values of sd, from ∼1.81 to ∼2.95. In the transition regime, a partial penetration of liquid meniscus which moves downward in the groove formed by four pillar posts was observed. It was also found that the contact angle prediction using the Cassie-Baxter equation showed fairly good agreement with experimental data, whereas in the transition regime, the rapid decrease in CA was found.
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  • Kaichi Saito, Masahiko Nishijima, Kenji Hiraga
    2010 Volume 51 Issue 9 Pages 1712-1714
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    Stabilization of Guinier-Preston zones (GP-zones), which have been found in an Mg97Gd2Zn1 alloy annealed at 200°C for 150 h, is studied. Single formation of the GP-zones without other precipitates is found in Mg98Gd1Zn1 and Mg97.5Gd1.5Zn1 alloys annealed at 200°C for 100 h. The GP-zones at this aging stage are distributed widely and separately from each other, but they change into many groups of band-shaped GP-zones by prolonged annealing.
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  • Jin Onuki, Kunihiro Tamahashi, Takashi Namekawa, Yasushi Sasajima
    2010 Volume 51 Issue 9 Pages 1715-1717
    Published: September 01, 2010
    Released: August 25, 2010
    JOURNALS FREE ACCESS
    Low resistivity Cu wires were obtained by high heating rate, short time, and low temperature annealing even at a temperature 100 K lower and for a time 67% shorter than the conventional H2 annealing temperature and time. This was due to promotion of the grain growth by the release of grain boundary energy when the heating rate to the peak temperature was set at 1.7 K/s. Resistivity of Cu wires made by the new process at 573 K was lower than that of wires made by conventional H2 annealing at 673 K for 30 min.
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