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MATERIALS TRANSACTIONS Vol. 49 (2008), No. 4

ISIJ International
belloff
オンライン版ISSN: 1347-5320
冊子版ISSN: 1345-9678
発行機関: The Japan Institute of Metals and Materials

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キーワードランキング

22 Dec. (Last 30 Days)

MATERIALS TRANSACTIONS Vol. 49 (2008), No. 4

Electrical Percolation during Codeposition of Fe and Si Clusters by a Dual Source PGCCD System

Nobuyuki Shinohara, Ryoji Katoh, Kenji Sumiyama

pp. 693-697

DOI:

10.2320/matertrans.MBW200708

抄録

Random assemblies of Fe and Si clusters have been prepared using a dual source plasma gas condensation cluster deposition system and their conductivities were measured for various compositional ratios. The size distributions of Fe and Si clusters are obtained by transmission electron microscopy (TEM) observations and the volume fraction of Fe clusters, fFe, is estimated from the chemical analysis and packing fraction of cluster assemblies. Electrical conductivity, σ, of Fe and Si cluster assemblies obeys a power law of fFe. The dramatic change at around fFe=fc, indicates that the percolation of Fe clusters takes place at the threshold value, fc=0.16. It is consistent with the Links-Nodes-Blobs model calculated for a three dimensional percolation network.

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Microstructural Changes at the Ultra-Precision Raster Milled Surface of Zn-Al Based Alloy

S. To, Y. H. Zhu, W. B. Lee

pp. 698-703

DOI:

10.2320/matertrans.MRA2007626

抄録

The microstructural changes and phase decomposition at the surface of a ultra-precision raster milled Zn-Al based alloy were studied using optical microscopy, back-scattered electron microscopy and X-ray diffraction techniques. The phase decomposition and the related crystal orientation were examined after ultra-precision raster milling with various processing parameters. UPRM induced phase decomposition and the structural recovery were discussed in relation to the structural evolution of the chips. The effect of UPRM on the hardness of the surface of the alloy specimen was studied.

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Parallel Computer Simulation of Three-Dimensional Grain Growth Using the Multi-Phase-Field Model

Yoshihiro Suwa, Yoshiyuki Saito, Hidehiro Onodera

pp. 704-709

DOI:

10.2320/matertrans.MRA2007225

抄録

We have performed computer simulations of normal grain growth in three-dimension by using the multi-phase-field (MPF) model. For the purpose of the acceleration of computation, we have applied both the active parameter tracking algorithm and parallel coding techniques to the MPF model. The simulation results have been compared with those obtained in previous simulations and a theoretical treatment. We have reconfirmed that the MPF is a powerful tool for simulating grain growth. Especially, the procedure described in this paper is highly efficient.

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Analyses on Compression Twins in Magnesium

L. Meng, P. Yang, Q. Xie, W. Mao

pp. 710-714

DOI:

10.2320/matertrans.MRA2007242

抄録

The orientation relationships between the compression twins and their matrices in magnesium were investigated using EBSD technique. Schmid factor analyses were applied to determine the orientation dependency of compression twins and the condition for double twinning. Results show that thin compression twin bands of {10\\bar11} type lose easily their exact twin relation of 56°⟨11\\bar20⟩ to ∼40°⟨11\\bar20⟩ due to the instability of twin orientation and immobility of twin boundaries. And the basal orientation with TD-rotation tends to induce tension twinning in compression twins.

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Influence of Temperature Dependence of Solubility on Kinetics for Reactive Diffusion in a Hypothetical Binary System

Masanori Kajihara

pp. 715-722

DOI:

10.2320/matertrans.MRA2007316

抄録

Influence of temperature dependence of solubility for each phase on kinetics of reactive diffusion has been theoretically analyzed for a hypothetical binary system consisting of two primary solid-solution phases (α and γ) and one compound phase (β). For the analysis, we consider that the β phase is produced owing to the reactive diffusion between the α and γ phases in a semi-infinite diffusion couple and the growth of the β phase is controlled by volume diffusion. In such a case, the parabolic relationship holds good between the thickness l of the β phase and the annealing time t as follows: l2=Kt. Here, the parabolic coefficient K is mathematically expressed as a function of the interdiffusion coefficients and the solubility ranges of the α, β and γ phases. The temperature dependencies of the parabolic coefficient K, the solubility range Δyθ and the interdiffusion coefficient Dθ of the θ (θ=α,β,γ) phase are described by Arrhenius equations of K=K0exp(−QK⁄RT), Δyθ=Δy0θexp(−Qθ⁄RT) and Dθ=D0θexp(−QDθ⁄RT), respectively. The analysis indicates that QK is close to QDβ+Qβ at QDβ≤QDα and QDβ≤QDγ but greater than QDβ+Qβ at QDβ>QDα or QDβ>QDγ. As a consequence, the temperature dependency of the parabolic coefficient is directly related with those of the interdiffusion coefficient and the solubility range of the compound phase in the former case but not in the latter case.

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Direct Evidence of Polycrystalline Silicon Thin Films Formation during Aluminum Induced Crystallization by In-Situ Heating TEM Observation

Seiichiro Ii, Takeshi Hirota, Kensuke Fujimoto, Youhei Sugimoto, Naoki Takata, Ken-ichi Ikeda, Hideharu Nakashima, Hiroshi Nakashima

pp. 723-727

DOI:

10.2320/matertrans.MRA2007312

抄録

The formation behavior of polycrystalline silicon thin films during the aluminum induced crystallization (AIC) process was investigated by scanning transmission electron microscopy (STEM) and in-situ heating transmission electron microscopy (TEM) observations. The STEM observation and electron dispersive X-ray spectroscopy (EDS) analysis of ex-situ heat-treated specimen revealed that the a-Si layer and Al layer switched the positions with each other during the heat treatment, resulting the crystallization of the a-Si layer. Furthermore, the in-situ heating TEM observation and EDS analysis of as-deposited specimen revealed the mixed state of Si and Al in an a-Si/Al film and the lateral growth of crystalline Si grain during the heating. The mechanism of AIC and switching layers were also discussed from the experimental results and the binary phase diagram of Al-Si system.

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Quantitative Analysis of Aluminum Dross by the Rietveld Method

A. Gómez, N. B. Lima, J. A. Tenório

pp. 728-732

DOI:

10.2320/matertrans.MRA2007129

抄録

Aluminum white dross is a valuable material principally due to its high metallic aluminum content. The aim of this work is to develop a method for quantitative analysis of aluminum white dross with high accuracy. Initially, the material was separated into four granulometric fractions by means of screening. Two samples of each fraction were obtained, which were analyzed by means of X-ray fluorescence and energy dispersive spectroscopy in order to determine the elements present in the samples. The crystalline phases aluminum, corundum, spinel, defect spinel, diaoyudaoite, aluminum nitride, silicon and quartz low were identified by X-ray diffraction. The quantitative phase analysis was performed by fitting the X-ray diffraction profile with the Rietveld method using the GSAS software. The following quantitative results were found: 77.8% aluminum, 7.3% corundum, 2.6% spinel, 7.6% defect spinel, 1.8% diaoyudaoite, 2.9% aluminum nitride, and values not significant of quartz and silicon.

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A New Approach to Predict the Thermal Conductivity of Composites with Coated Spherical Fillers and Imperfect Interface

Yong Kuk Park, Jae-Kon Lee, Jin-Gon Kim

pp. 733-736

DOI:

10.2320/matertrans.MRA2007135

抄録

An examination of the concept of a microgeometry proposed by Benveniste reveals that the thermal conductivity of the concentric sphere adopted by generalized self-consistent model (GSCM) is equal to that of the composite. It is also noted that the thermal conductivities of the composite with spherical fillers predicted by GSCM and modified Eshelby model (MEM) are the same. These equivalencies enable to propose a simple and alternative approach for determining the thermal conductivity of the composite with multiply coated spherical fillers by applying MEM repeatedly. The present result is compared and shows the exact agreement with the results from literatures.

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Tensile Properties of Forged Direct-Squeeze-Cast Al-(6.0∼8.0 mass%)Si-(0.3∼0.52 mass%)Mg Alloy

Teng-Shih Shih, Po-Chen Chen, Wei-Shian Tsai

pp. 737-745

DOI:

10.2320/matertrans.MRA2007132

抄録

The effects of lubricants on the quality of squeeze-cast Al-(6.0∼8.0 mass%)Si-(0.3∼0.52 mass%)Mg alloys were studied. Different melts with varying amounts of Si and Mg were prepared and then directly squeeze-cast into cakes. Different lubricants and two different pressures, 60 and 120 MPa, were used in the production of the cakes. These squeeze-cast cakes were then forged and heat-treated. Tensile specimens prepared from the forged and heat-treated cakes were tested to determine their tensile properties. Among all the variables tested, the Weibull modulus (in ultimate tensile strength, UTS) was the largest (m=53.7) for the cakes squeeze-cast at 120 MPa using water-based BN powder (∼4 μm in size) as a lubricant. After polishing and ultrasonic-vibration treatment, oxide films appeared as foggy films on the chilled blocks and forged cakes. Reaction films were also observed on the tensile fracture surfaces of the tested bars. They were particularly apparent on the bars produced from cakes that had been prepared using an oil-based lubricant. The area ratios of the foggy films and reaction films on the samples were calculated. The Weibull modulus (in UTS) of the forged cakes after T6 treatment was significantly affected by both the pore count and the total area ratio covered by reaction films and foggy films.

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Fusion Zone Microstructure Evolution of Al-Alloyed TRIP Steel in Diode Laser Welding

Mingsheng Xia, Zhiling Tian, Lin Zhao, Y. Norman. Zhou

pp. 746-753

DOI:

10.2320/matertrans.MRA2007271

抄録

TRansformation Induced Plasticity (TRIP) steels are promising materials to achieve a better combination of formability and strength than conventional steels due to their unique microstructural makeup. Though welding is a vital part of auto body manufacturing, the weldability of TRIP steels has some complex and poorly understood features, which has served to retard the growth of its applications in the automotive industry. In this study, autogeneous welds were carried out on Al-alloyed TRIP steel using a 4 kW diode laser. Both fusion zone solidification behavior and subsequent austenite transformation products were investigated with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. In terms of solidification behavior, fusion zones solidified with high temperature δ-ferrite as the primary phase. Fusion zone microstructure at room temperature was composed of ferrite with a skeletal morphology characteristic of solidification, and austenite decomposition products almost all having a lath morphology. Skeletal ferrite covered about 30% fusion zone area. Upper bainite laths separated by retained austenite films comprised most of the transformed microstructure, about 65% of the fused area. Lower bainite with carbide particles dispersed in an aligned way, chunk shaped retained austenite, lath martensite and twinned martensite were also occasionally observed. The Al content was considered to be for a dominant influence on fusion zone microstructure evolution.

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Hydrogen Permeation of Thin Pd-25Ag Membranes Prepared by Cold Rolling and Microsystem Technology

Yi Zhang, Jian Lu, Ryutaro Maeda, Chikashi Nishimura

pp. 754-759

DOI:

10.2320/matertrans.MRA2007260

抄録

Hydrogen permeation of thin Pd-25Ag membranes with the thickness down to 1.2 μm was investigated by conventional gas permeation method within the temperature range of 473–673 K. The thin Pd-25Ag membranes with the thickness down to 51 μm were prepared by cold rolling method. The 1.2 μm-thick Pd-25Ag membrane was prepared by microsystem technology. The hydrogen permeation of the prepared Pd-25Ag membranes was independent of the membrane thickness until down to 51 μm. The 51 μm-thick Pd-25Ag membrane had the hydrogen permeability lower by 60% than that of the bulk Pd-25Ag metal. It mainly resulted from slow surface reaction and lower hydrogen solubility near the surface of the 51 μm-thick Pd-25Ag membrane. The hydrogen permeability of the 1.2 μm-thick Pd-25Ag membrane was one order lower than that of bulk Pd-25Ag metal because the hydrogen permeation was mainly limited by surface reaction. However, literature review indicated that the microfabricated 1.2 μm-thick Pd-25Ag membrane had the hydrogen permeability superior to those conventional Pd-25Ag membranes supported by porous materials, suggesting attractive advantages of the microsystem technology in hydrogen-separation membrane applications.

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Disbonding in Joint of Carbon to Nickel

Tomoyuki Nishida

pp. 760-765

DOI:

10.2320/matertrans.MRA2007227

抄録

Carbon samples heat-treated at different temperatures of 1273 to 3273 K were bonded to nickel in the solid state in a vacuum using an RF induction furnace. The bending and shearing strengths of the joints were investigated. The feasibility of disbonding of the joints was investigated by heating in a vacuum. The fracture surfaces for the joints were also observed using a scanning electron microscope. Based on the results, the effects of the heat treatment of carbon on the interface strength of a joint were examined. With increasing heat treatment temperature, the joint strength of carbon to nickel is improved. Utilizing this property, the heat treatment of carbon is performed to adjust the interface strength of a joint. Moreover, by the selection of carbon materials heat-treated at a specific temperature (2023 or 2123 K), the design of the joining system with both bonding and disbonding properties is feasible.

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Numerical Study of Fluid Flow Behaviors in an Alkali-Free Glass Melting Furnace

Chien-Chih Yen, Weng-Sing Hwang

pp. 766-773

DOI:

10.2320/matertrans.MRA2007259

抄録

In this study, fluid flow behavior of molten glass in a melting furnace, which is characterized by the stirring range of gas bubbles and trajectories of tracer particles, is investigated by a reduced physical model and a mathematical model. The reduced physical model was made of an acrylic tank, which was similar in shape of the actual glass melting furnace but one fifth in size, with heating electrodes and air bubbling devices. The gas flow rates were set at 8.27, 10.42 and 14.75 Ncm3/sec based on similarity conversions. The electrode temperatures were set at 25°C and 150°C. The mathematical model was based on the SOLA-VOF technique, which incorporated a Quasi-single Phase method to accommodate the gas bubbling phenomena. Results from the physical model showed that the trajectories of tracer particles and minimum residence time (MRT) increase with gas flow rates. This is caused by the increase in stirring range of gas bubbles, which was demonstrated by the physical model as well as the mathematical model. The trajectories of tracer particles at the electrode temperature of 150°C were observed to be longer than those for the electrode temperature of 25°C from the physical model. This is due to the free convection induced by the heating electrodes, which is also shown by the mathematical model.

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Reliability of Laser Welding Process for ZE41A-T5 Magnesium Alloy Sand Castings

Haider Al-Kazzaz, Xinjin Cao, Mohammad Jahazi, Mamoun Medraj

pp. 774-781

DOI:

10.2320/matertrans.MRA2007622

抄録

Laser welding is a promising joining method for magnesium alloys. The process reliability of 2-mm ZE41A-T5 butt joints welded by a 4 kW Nd:YAG laser was investigated from weld geometries, defects and mechanical properties using Weibull statistical distribution. Smooth, geometrically regular and macroscopically defect-free sound joints were obtained. However, sag, undercut, surface misalignment, and some variations in weld width and fusion zone area were also observed. The results indicated that tensile strength and elongation at fracture can be more accurately described by Weibull distribution. The modulus values of 31.98 and 22.52 were obtained for tensile strength in the as-welded and the aged conditions, respectively, indicating that tensile strength becomes more scattered after artificial aging. The aging treatment does not significantly affect mechanical properties, although it can provide stress relief. After laser welding, there is some degradation in tensile properties, especially elongation at fracture.

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Quantitative Evaluation of Porosity in Aluminum Die Castings by Fractal Analysis of Perimeter

Yoshihiko Hangai, Soichiro Kitahara

pp. 782-786

DOI:

10.2320/matertrans.MRA2007314

抄録

In the die-casting process, the formation of pores in components is unavoidable. This porosity has a harmful effect on the strength and pressure tightness of die castings. To eliminate the porosity in components, its predominant cause has to be identified as being due to either shrinkage or gas. In practice, however, it is frequently difficult to tell the difference between porosity due to shrinkage and that due to gas from observing die castings. Accurate identification enables die casters to take corrective action. To identify the porosity accurately and to take corrective action in the die-casting process, the quantitative estimation of the morphology of pores such as their shape or spatial distribution can be a source of useful information. In this study, two types of fractal analyses are proposed to characterize the porosity in terms of the shape of individual pores and the spatial distribution of multiple pores. It is shown that these are indicators of whether the predominant cause of the porosity is shrinkage or gas. These parameters are expected to indicate the action that should be taken to manufacture pore-free die castings.

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Analysis of Uniaxial Alignment Behavior of Nonmagnetic Materials under Static Magnetic Field with Sample Rotation

Jun Akiyama, Hidefumi Asano, Kazuhiko Iwai, Shigeo Asai

pp. 787-791

DOI:

10.2320/matertrans.MRA2007326

抄録

A high magnetic field is a useful tool to control the crystal alignment of nonmagnetic materials such as metals, ceramics and polymers. However, the uniaxial alignment of hexagonal crystals with a magnetic susceptibility of χc<χa cannot be achieved under a static magnetic field, because the c-axis could lie along any arbitrary direction in the plane perpendicular to the direction of the magnetic field. For the uniaxial alignment of these materials, the imposition of a rotating magnetic field during a slip casting process has been proposed.
In this study, both theoretical analysis and model experiment have been conducted for the elucidation of the crystal alignment phenomena under a rotating magnetic field and for the quantitative clarification of the optimum operating parameters such as magnetic field strength and viscosity of the medium surrounding the crystals. It has been found that the alignment time decreased with the magnetic field strength and/or with an increase in the viscosity of the surrounding medium. This relation is in contrary to the case of the crystal alignment under the static magnetic field. The result of the model experiment agrees well with that obtained by the theoretical analysis.

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Diffusion and γ′ Phase Coarsening Kinetics in Ruthenium Containing Nickel Based Alloys

Efendi Mabruri, Shingo Sakurai, Yoshinori Murata, Toshiyuki Koyama, Masahiko Morinaga

pp. 792-799

DOI:

10.2320/matertrans.MRA2007283

抄録

The present paper reports the interdiffusion of Re, W, Ru and Co in the binary and pseudo-binary Ni based alloys at 1523 K and the γ′ phase coarsening kinetics of model superalloys at 1324 K. Both Re and W concentration gradients caused Ru uphill diffusion in the respective pseudo-binary diffusion couple, whereas Ru concentration gradient promoted uphill diffusion for W but not for Re. Interestingly, Re uphill diffusion occurred under the influence of Co concentration gradient but the reverse effect was not observed. The cross interdiffusion coefficients qualitatively determined from the uphill diffusion profiles were in reasonable agreement with those reported previously. Comparison of the interdiffusion coefficients in the binary and the pseudo-binary diffusion couples showed that Ru and W decreased the diffusivity of each other whereas Co appeared to be more powerful barrier atoms than Ru to decrease the Re diffusivity. Furthermore, it was evident that the coarsening kinetics of the γ′ phase in both Ru-free and Ru-containing model superalloys were controlled by diffusion and Ru was found to have no effect on the rate constant of the γ′ phase coarsening.

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Machinability of Experimental Ti-Cu Alloys

Masafumi Kikuchi, Masatoshi Takahashi, Osamu Okuno

pp. 800-804

DOI:

10.2320/matertrans.MRA2007285

抄録

This study is an investigation of the machinability of experimental Ti-Cu alloys (2, 5, and 10 mass% Cu) as new dental titanium alloy candidates for CAD/CAM use. The alloys were slotted with a vertical milling machine and carbide square end mills under two cutting conditions. Their machinability was evaluated through cutting force using a three-component force transducer fixed on the table of the milling machine. The horizontal cutting forces of the Ti-Cu alloys tended to increase as the concentration of copper increased. The feed force for Ti-10%Cu was more than twice as large as that for titanium under both cutting conditions. Alloying with copper reduced the machinability of titanium under the present cutting conditions. The adverse effect on the cutting force was attributed to the higher degree of tensile strength and hardness of the Ti-Cu alloys than of titanium.

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Active Hydroxyl Groups on Surface Oxide Film of Titanium, 316L Stainless Steel, and Cobalt-Chromium-Molybdenum Alloy and Its Effect on the Immobilization of Poly(Ethylene Glycol)

Yuta Tanaka, Haruka Saito, Yusuke Tsutsumi, Hisashi Doi, Hachiro Imai, Takao Hanawa

pp. 805-811

DOI:

10.2320/matertrans.MRA2007317

抄録

The concentrations of hydroxyl groups located inside and on the surface oxide films of a commercially pure titanium, cp-Ti, a type 316L austenitic stainless steel, SS, and a cobalt-chromium-molybdenum alloy, Co-Cr-Mo, were evaluated using X-ray photoelectron spectroscopy, XPS, and a zinc-complex substitution technique. As a result, the concentrations of the hydroxyl groups detected by the zinc-complex substitution technique, defined as active hydroxyl groups, were much larger than those detected by other conventional techniques. The concentration of the active hydroxyl groups on Co-Cr-Mo was significantly larger than those on cp-Ti and SS. Poly(ethylene glycol), PEG, is a biofunctional molecule that inhibits the adsorption of proteins. The immobilization of PEG to metal surfaces by electrodeposition or immersion is an important technique to biofunctionalize the metals. The amounts of the PEG layer immobilized on the metals were governed by the concentrations of the active hydroxyl groups on each surface oxide in the case of electrodeposition; it was governed by the relative permittivity of the surface oxide in the case of immersion. The estimation of active hydroxyl groups on the surface oxide film with the zinc-complex substitution technique is useful for the elucidation of reactions between metal substrates and immobilized molecules.

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AFM Observation of Microstructural Changes in Fe-Mn-Si-Al Shape Memory Alloy

Motomichi Koyama, Masato Murakami, Kazuyuki Ogawa, Takehiko Kikuchi, Takahiro Sawaguchi

pp. 812-816

DOI:

10.2320/matertrans.MRA2007321

抄録

We analyzed the surface relief caused by stress-induced hcp martensitic transformation in Fe-30Mn-5Si-1Al shape memory alloy by atomic force microscopy. The alloy exhibits a good shape memory effect and an improved ductility due to a small addition of Al to a conventional Fe-30Mn-6Si shape memory alloy. The orientation of an austenite matrix was determined with surface traces of four {111}f planes, which enabled us to determine the surface tilt angles for all twelve variants of hcp martensites and deformation twins. On the basis of these values, stress-induced martensite and deformation twin coexisting in the same grain were identified by studying the surface tilt angles. The surface relieves caused by the stress-induced martensite recovered after heating above the reversed transformation temperature, however some relieves originating from the deformation twin remained.

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Effects of Heat Treatment and Hot Forging on Microstructure and Mechanical Properties of Co-Cr-Mo Alloy for Surgical Implants

Yoshimitsu Okazaki

pp. 817-823

DOI:

10.2320/matertrans.MRA2007274

抄録

The effects of heat treatment and hot forging on the microstructure and mechanical properties of Co-Cr-Mo alloy for implant applications were examined. In an alloy annealed at 1200°C for 1 h, M23C6 carbides precipitated along the grain boundary in the γ phase matrix containing a small amount of ε phase. The 0.2% proof strength (σ0.2%PS), ultimate tensile strength (σUTS), total elongation (T. E.), and reduction of area (R. A.) of annealed alloy were 553±2 MPa, 928±41 MPa, 21±2%, and 15±1%, respectively. The σ0.2%PS and σUTS of the Co-Cr-Mo alloy hot-forged at a starting temperature of 1100°C increased linearly with an increase in reduction in area, whereas T. E. gradually decreased with an increase in the reduction. The σ0.2%PS, σUTS, T. E., and R. A. of 57% hot-forged alloy were 715±86 MPa, 1109±61 MPa, 8±1%, and 10±1%, respectively. In the 57% hot-forged Co-Cr-Mo alloy, a large amount of M23C6 carbide and a small amount of M6C carbide were observed in the γ phase matrix containing the ε phase. In the light of these results, it appears that hot forging with a starting temperature of approximately 1100°C provided excellent mechanical properties to the alloys.

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Synthesis of Spinel-Type Magnesium Cobalt Oxide and Its Electrical Conductivity

Natsumi Kamioka, Tetsu Ichitsubo, Tetsuya Uda, Susumu Imashuku, Yu-ki Taninouchi, Eiichiro Matsubara

pp. 824-828

DOI:

10.2320/matertrans.MBW200721

抄録

This work devotes to investigate synthesis and electrical properties of spinel MgCo2O4 that is considered as a candidate of the cathode materials of magnesium-ion batteries in future. Samples were synthesized by two types of techniques: solid-state reaction and wet process. The crystal structures of the samples were analyzed by X-ray diffraction, and their electrical conductivities were obtained through the dc resistance and ac impedance measurements. By solid-state reaction, sample of a single MgCo2O4 phase was not obtained; a sample synthesized at 800°C for 24 h after milling of Co3O4 and MgO powder was comprised of dual phases of spinel-type and rocksalt-type structures, and samples synthesized at temperatures higher than 880°C showed a single rocksalt-type phase without electrical conductance. The former sample showed p-type semiconducting behavior as well as spinel-type Co3O4, but its electrical conductivity around room temperature was shown to exceed that of Co3O4. In contrast, a sample consisting of a single spinel-type phase was successfully synthesized by wet process, which exhibited an electrical conductivity of the order 10−2 Scm−1, being much higher than those of the samples synthesized by solid-state reaction. Thus, substitution of Co2+ in Co3O4 with Mg2+ is found to enhance the electrical conductivity of the spinel-type phase.

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Reduction of Functionally Graded Material Layers for Si3N4-Al2O3 System Using Three-Dimensional Finite Element Modeling

Jae Chul Lee, Jong Ha Park, Sae Hee Ryu, Hyun Jung Hong, Doh Hyung Riu, Sung Hoon Ahn, Caroline Sunyong Lee

pp. 829-834

DOI:

10.2320/matertrans.MRA2007319

抄録

Numerical analysis method was used to reduce the number of functionally graded material (FGM) layers for joining Si3N4-Al2O3 using polytypoid interlayer by estimating the position of crack. In the past, hot press sintering of multi-layered FGMs with 20 layers of thickness 500 μm each have been fabricated successfully. In this paper, thermal residual stresses were calculated using finite element method (FEM) to find the optimized number of layers and its thicknesses of FGM joint. The number of layers for FGM was reduced to 15 layers from 20 layers. Thicknesses were varied to minimize residual stresses within the layers while reducing the number of FGM layers. The damage caused by thermal residual stress was estimated using maximum principal stress theory and maximum tensile stress theory. The calculated maximum stress was found to be axial stress of 430 MPa around 90% 12H/10% Al2O3 area. For each case, calculated strength of each FGM layer by linear rule of mixture was compared with computed thermal residual stresses. Thermal analysis results correctly predicted the position of crack, and this position agreed well with fabricated joints. Therefore, this numerical analysis method can be applied to reduced FGM layers of crack free joint. Finally, new composition profile of crack free joint was proposed using FGM method.

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Removal of Arsenate in Acid Mine Drainage by a Permeable Reactive Barrier Bearing Granulated Blast Furnace Slag: Column Study

Keiko Sasaki, Shunsuke Nukina, Wahyu Wilopo, Tsuyoshi Hirajima

pp. 835-844

DOI:

10.2320/matertrans.M-MRA2008801

抄録

Immobilization of arsenate in groundwater impacted by acid mine drainage was investigated using a permeable reactive barrier (PRB) column bearing granulated blast furnace slag (GBFS) to compare with iron granules which are commonly used. Sorption capacity of arsenate onto the GBFS was quite lower than iron granules in the amount of sorbed arsenate per unit surface area of sorbents (mmol/m2) at the equilibrium, Q′, in two orders of magnitude in batch tests, however, the amount of sorbed arsenate per unit amount of sorbents (mmol/kg) at the equilibrium, Q, were comparative to each other, because of much higher porosity in the GBFS. Results of column performance showed that 15 mg/L of As was decreased to be less than 0.4 mg/L for more than 18 pore volumes (pv) in the GBFS-PRB by sorption, co-precipitation and presumably formation of hydrated calcium arsenate, and less than 0.04 mg/L for more than 17 pv in the iron bearing PRB probably by co-precipitation with iron (oxyhydro)oxides. Additionally 15 mg/L of Mn2+ ions was also decreased to less than 0.3 mg/L and 0.03 mg/L, respectively, in iron bearing and the GBFS bearing PRB columns, probably caused by sorption and precipitation of oxides and carbonates. The GBFS has advantages to compensate its low reactivity with high porosity, to facilitate the industrial handling with low density, and to utilize industrial wastes for more valuable applications, emphasizing a potential of alternative reactive materials instead of iron granules in PRB for immobilization of arsenic and manganese in acid mine drainage.

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Optimum pH for Oxidation of Mn(II) Ions in Model and Actual Manganese Drainages by a Mn-Oxidizing Fungus, Phoma sp. Strain KY-1

Keiko Sasaki, Hideki Tachibana, Yuuki Ogawa, Hidetaka Konno

pp. 845-849

DOI:

10.2320/matertrans.M-MRA2008802

抄録

A Mn-oxidizing fungus, Phoma sp. strain KY-1, showed a Mn-oxidizing activity of more than 1.82 mol m−3 of Mn(II) at an optimum pH 6.8. Controlling the pH at between 6.5 and 7.3 was necessary for fungal oxidation of Mn(II). This is probably due to inactivation of the Mn-oxidizing enzyme by decrease in pH during the reaction. Carbon fiber was found to catalyze the oxidation of Mn(II), most significantly under more unfavorable conditions such as high Mn concentrations, coexisting inhibitive components, or lacking nutrients. Examinations of fungus used for actual Mn-rich mine drainage containing more than 1.46 mol m−3 of Mn showed that organic nourishments and pH-buffering agents are both essential to obtain acceptable Mn removal rates and that the time required to attain the 10 mg dm−3 (0.182 mol m−3), which is the maximum acceptable concentration of Mn in discharged wastewater in Japan, was about 170 h in the presence of carbon fiber.

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Effects of Aging Treatment on the Bending Strength in AZ91D/Al18B4O33w Composite

W. G. Wang, W. L. Li, K. C. Chang, K. Matsugi, G. Sasaki

pp. 850-853

DOI:

10.2320/matertrans.MER2007302

抄録

Aluminum borate whisker (Al18B4O33w, denoted by ABOw) reinforced AZ91D (Mg-Al-Zn) magnesium alloy composites were prepared by squeeze casting. The composite was solution-treated at 683 K for 345.6 ks in argon atmosphere and then water-quenched. Aging treatment was carried out at 443 K in oil-bath. While the composite was cooled from the solution temperature of 683 K to room temperature, large thermal residual stress (TRS) was formed due to the mismatch of thermal expansion coefficient between ABOw and AZ91D matrix. The TRS of AZ91D matrix in as-quenched AZ91D/ABOw composite was measured with X-ray diffraction (XRD) and it was 103 MPa. After aging for 115.2 ks, the TRS relaxed and decreased to 45 MPa. Owing to the formation of precipitates, the bending strength of peak-aged composite (aged for 115.2 ks) was enhanced. Nevertheless, when the composite was aged for 345.6 ks, the bending strength decreased greatly. Even the bending strength of over-aged composite was lower than that of as-quenched composite. It is attribute to the coarsening of continuous precipitate within composite matrix close to whiskers.

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Thermodynamic Interactions of Nb and Mo on Ti in Liquid Iron

Tae-In Chung, Joong-Beom Lee, Jin-Goo Kang, Jong-Oh Jo, Bo-Ho Kim, Jong-Jin Pak

pp. 854-859

DOI:

10.2320/matertrans.MER2007286

抄録

Thermodynamic interactions of niobium and molybdenum on titanium in liquid iron were studied in the temperature range of 1873∼1973 K by measuring the effects of niobium and molybdenum on the solubility product for TiN formation in liquid iron using the metal-nitride-gas equilibration technique. The experimental results were thermodynamically analyzed using Wagner’s interaction parameter formalism to determine the first-order interaction parameters of niobium and molybdenum on titanium in liquid iron as 0.0495±0.0049 and 0.01±0.0026, respectively, at 1873 K. Temperature dependence of these parameters was also determined as follows. e_Ti^Nb = 1160/T - 0.570, e_Ti^Mo = 0.01 (1873∼1973 K)

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The Effect of Temperature on Microstructure, Magnetic Properties and Reaction Kinetics of Ni0.5Co0.5Fe2O4 Reduction in Hydrogen Atmosphere

M. Bahgat, Min-Kyu Paek, Jong-Jin Pak

pp. 860-868

DOI:

10.2320/matertrans.MER2007268

抄録

Nickel cobalt ferrite (Ni0.5Co0.5Fe2O4) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of nickel oxide, cobalt oxide and iron oxide at 1100 and 1200°C. The produced powders of Ni0.5Co0.5Fe2O4 were isothermally reduced in pure hydrogen at 800–1100°C. Based on thermogravimetric analysis, the reduction behavior of nickel cobalt ferrite and the kinetics reaction mechanism were studied. The initial ferrite powder and the various reduction products were characterized by XRD, pore size, SEM, VSM and reflected light microscope to reveal the effect of hydrogen reduction on composition, microstructure and magnetic properties of produced Fe-Ni-Co alloy. Microstructure of partially and completely reduced samples was studied and the activation energy values were calculated from Arrhenius equation. The approved mathematical formulations for the gas solid reaction were applied and it was found that the initial reaction stages are controlled by the combined gaseous diffusion and interfacial chemical reaction mechanisms with high contribution to gas diffusion while the final reaction stages is controlled by chemical reaction mechanism. Complete reduction of Ni0.5Co0.5Fe2O4 was achieved with synthesis of nanocrystalline (18–20 nm) Fe-Ni-Co alloy.

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Phase Transition of Shock-Loaded ZrTiCuNiBe Bulk Metallic Glass under Continuous Heating

Chao Yang, Weiping Chen, Zaiji Zhan, Mindan Chen, Junyi Yang, Liang Guo, Xinyu Zhang, Riping Liu, Wenkui Wang

pp. 869-873

DOI:

10.2320/matertrans.MER2007218

抄録

Phase transition of Zr41.9Ti14.7Cu13.1Ni10.1Be20.2 bulk metallic glasses (BMGs) treated by shock loading (transition from a solid state to a solid state) and prepared by shock-wave quenching (transition from a solid state to a liquid state to a solid state) are investigated by in situ X-ray diffraction measurements under continuous heating conditions. The thermal properties, precipitation phases and phase transitions of the shock-loaded and shock-wave-quenched BMGs are found to be different from those of water-quenched BMGs. The differences are probably due to different structures between the BMGs induced by complex effects of shock loading.

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Laser Raman Spectroscopic Study on Magnetite Formation in Magnetotactic Bacteria

Shingo Watanabe, Masaharu Yamanaka, Akira Sakai, Ken Sawada, Tatsuo Iwasa

pp. 874-878

DOI:

10.2320/matertrans.MER2007333

抄録

Magnetotactic bacteria have one or more chains of magnetosome, consisting of nano-sized magnetic crystal covered with a phospholipid bilayer and use it to sense the geomagnetic fields. In order to elucidate the molecular process to make magnetosome from the iron compounds found in the bacteria, laser Raman spectroscopic measurements were performed with the magnetotactic bacterium, Magnetospirillum magnetotacticum MS-1 and the fractions separated from it. The major Raman signals at 662 cm−1 and 740 cm−1 were observed. The former was assigned to the Raman signal of magnetite and the latter, to that of ferrihydrite. The Raman signal of ferrihydrite was observed not only in the membrane fraction, but also in the cytoplasmic fraction. Based on the results, the role of ferrihydrite in magnetosome synthesis in the magnetotactic bacteria was discussed.

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Microstructural Control of the TiO2-SnO2 Binary System and Synthesis of SnO2 Nanowhiskers by Microwave Irradiation

Takuya Aoyagi, Yamato Hayashi, Hirotsugu Takizawa

pp. 879-884

DOI:

10.2320/matertrans.MER2007327

抄録

SnO2 single crystals (columnar crystals and silver grass-like nanowhiskers) were synthesized by selective microwave heating of a TiO2-SnO2 mixture. The shape of the as-grown SnO2 crystals is strongly dependent on the atmosphere during microwave irradiation. This is due to the difference in growth mechanisms, as revealed by in-situ surface observation under microwave irradiation, in addition to scanning and transmission electron microscopy observations of irradiated specimens. In a N2 atmosphere, silver grass-like SnO2 nanowhiskers were obtained. On the other hand, columnar SnO2 crystals were obtained in air or an O2 atmosphere. Photoluminescence and absorption spectra of the as-grown SnO2 crystals were examined. Based on the analysis of a TiO2-SnO2 pellet, it was found that the bottom was selectively heated, and SnO2 sublimated by microwave irradiation. A density gradient texture of the sample pellet was formed.

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Microstructures and Mechanical Properties of Double-Friction Stir Welded 2219 Al Alloy

Chang-Yong Lee, Don-Hyun Choi, Won-Bae Lee, Sun-Kyu Park, Yun-Mo Yeon, Seung-Boo Jung

pp. 885-888

DOI:

10.2320/matertrans.MRP2007249

抄録

The microstructure, mechanical properties and thermal stability of double friction stir welded 2219 Al alloy were investigated. The grain size of the double friction stir zone was about 0.8 μm, which was smaller than that of the single friction stir zone. The dissolution of the very fine strengthening particles resulted in a decrease of the hardness values in the single and double friction stir zone. Following the post weld heat treatment (PWHT), the grain structure of the double-FSW joints was found to be more unstable than that of the single-FSW joints, owing to the finer grain size, higher fraction of sub-grains and lower particle density.

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Equal Channel Angular Extrued Bi0.5Sb1.5Te3 Thermoelectric Compound

CheolHo Lim, KyungTaek Kim, YongHwan Kim, ChangHun Lee, ChiHwan Lee

pp. 889-891

DOI:

10.2320/matertrans.MEP2007297

抄録

The effects of equal channel angular extrusion (ECAE) process parameters on microstructure and thermoelectric properties of the p-type Bi0.5Sb1.5Te3 compound have been investigated. ECAE was carried out under various temperatures (653 K, 693 K, 733 K) and ram speeds (0.5 mm/s, 1 mm/s, 2 mm/s). Fraction of recrystallized grains and grain size was found to be increase with lower ram speed and higher deformation temperature. As a result, Seebeck coefficient increased, and electrical resistivity and thermal conductivity decreased. The decrease in thermal conductivity was attributed to the decrease of lattice thermal conductivity (κph) which is independent of electrical properties. Maximum figure-of-merit (2.87×10−3 K−1) was achieved in as-ECAE’ed specimen at 733 K and at ram speed of 0.5 mm/s. This value was found to be 6% higher than that of as-sintered specimen.

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