MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 47 (2006), No. 9

  • Fabrication of Lotus-Type Porous Ni3Al with and without Boron

    pp. 2116-2119

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    DOI:10.2320/matertrans.47.2116

    Ni3Al with and without boron was melted and unidirectionally solidified in pressurized hydrogen atmosphere by using a continuous zone melting method. For Ni3Al without boron, cylindrical pores elongated in the direction parallel to the solidification direction, are formed in Ni3Al matrix. On the other hand, no pore is formed in Ni3Al with 0.23 mol% B solidified under the same condition. This result suggests that the solubility gap of hydrogen between liquid and solid Ni3Al with boron is extremaly small.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effect of Hydrogen Pressure on Moisture-Based Fabrication of Lotus-Type Porous Nickel

    pp. 2120-2124

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    DOI:10.2320/matertrans.47.2120

    Lotus-type porous nickel, which has long straight pores aligned in one direction, was fabricated by utilizing moisture during unidirectional solidification in argon atmosphere. We studied the effect of the quantity of hydrogen in the atmosphere on the fabrication of lotus-type porous nickel. Adding hydrogen in the atmosphere, it was expected that the porosity of the lotus-type porous nickel with a smaller pore diameter became larger because not only the moisture but also hydrogen gas in the atmosphere were the supply source of hydrogen bubble. However, in fact, the pore diameter and the porosity of lotus-type porous nickel gradually decreased as the hydrogen partial pressure increased up to a point. When hydrogen was further added to the atmosphere, the pore diameter and porosity increased while the number of pores decreased dramatically. As a result of the fabrication under various pressures, the partial pressure of hydrogen at the border was 0.05 MPa. No moisture can be dissociated when a large amount of hydrogen is dissolved in the molten nickel.
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  • Producing Technology of Aluminum Foam from Machined Chip Waste

    pp. 2125-2130

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    DOI:10.2320/matertrans.47.2125

    The present study focuses on the investigation of the possibility of producing aluminum foam from low cost machined chip waste. To produce highly porous aluminum, manufacturing process of precursor, the effect of TiH2 content and the effect of ceramic particle addition were examined. In the study of precursor manufacturing processes, precursors fabricated by extrusion process did not expand sufficiently and the pore morphology was very irregular. In contrast, precursors fabricated by compressive torsion processing satisfactorily expanded and the pore morphology was uniform. There was an adequate range of TiH2 addition. The increase of TiH2 content more than 3 mass% was not an effective way to produce highly porous aluminum foam. Addition of fine Al2O3 particle resulted in a significant increase in foam expansion.
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  • The Role of Foaming Agent in Structure and Mechanical Performance of Al Based Foams

    pp. 2131-2136

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    DOI:10.2320/matertrans.47.2131

    The effect of the novel foaming agent, calcium carbonate in comparison with the conventional titanium hydride on structure and energy absorbing ability of the aluminium based foams was studied. Mechanical testing Alporas foams of Al and wrought alloy Al-5.5Zn-3Mg-0.6Cu-0.5Mn (similar to alloy 7075) doped by small amount (<0.6 mass%) of Sc and Zr was undertaken under compression with static strain rate of 1.5·10−3 s−1. The influence of Ca additive on the cell wall structure and deformation behaviour of two kinds of the foams was recognised. Significant advantages in mechanical performance of the aluminium foams processed with CaCO3 were found and attributed to fine cellular structure and favourable microstructure of the cell wall material.
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  • Powder-Metallurgical Process for Producing Metallic Microchannel Devices

    pp. 2137-2142

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    DOI:10.2320/matertrans.47.2137

    We investigated a simple and economical method for producing free-form microchannels in metal bodies. The concept for our process is based on a microscopic infiltration phenomenon that often occurs during liquid phase sintering of a mixture of metal powders with different melting points. A shaped compound of the metal powder with lower melting point and an organic binder are used as the sacrificial core that gives the shape of the microchannel. A body-metal powder compact that includes the sacrificial core is sintered at a temperature between the melting points of the sacrificial-core metal and body metal. The organic binder is removed during heating of the powder compact, and infiltration of molten sacrificial-core metal into the body-metal powder produces a microchannel and a lining layer. We examined following combinations of metal powders: titanium-aluminum, nickel-aluminum, copper-tin, and iron-copper. Metallographic observations confirmed that microchannels were produced in the metallic bodies in all these systems. Furthermore, in the case of the titanium body metal with an Al-Cu alloy sacrificial-core metal, the inner wall of the microchannel was smoother than the case of titanium with aluminum. The copper content of the sacrificial-core metal influenced the composition and structure of the microchannel lining.
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  • Preparation of Metallic Porous Materials by Oxide-Reduction Liquid Phase Sintering of Fe-SnO2 Mixture

    pp. 2143-2147

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    DOI:10.2320/matertrans.47.2143

    Green compacts of mixture of iron and tin oxide powders were heated at 773–973 K in a hydrogen atmosphere to produce a metallic porous material. Tin oxide in a green compact was not reduced sufficiently to tin after 3.6×103 s at 673 K. Even at 773 K, some tin oxide was not reduced to tin by reduction after 3.6×103 s. At 873 K, a sintered body with sufficient strength was obtained using the reduction processing for 3.6×103 s, and fine FeSn crystals were generated on the iron powder surface. The compression strength of the sintered body obtained at 873 K was 45.1 MPa. It was confirmed that the FeSn crystals connected the each iron powder particles. At 973 K, although a sintered body was obtained, it had low strength because the FeSn on the iron powder surface grew to form large crystals. Results demonstrated that the open porous metal can be manufactured through tin-oxide reduction liquid phase sintering for 3.6×103 s at 873 K.
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  • Processing and Characterization of a New Composite Metal Foam

    pp. 2148-2153

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    DOI:10.2320/matertrans.47.2148

    New closed cell composite metal foam has been processed using both casting and powder metallurgy (PM) techniques. The foam is comprised of steel hollow spheres packed into a dense arrangement, with the interstitial spaces between spheres occupied with a solid metal matrix. Using the casting technique, an aluminum alloy infiltrates the interstitial spaces between steel spheres. In the PM technique, steel spheres and steel powder are sintered to form a solid, closed cell structure. The measured densities of the Al-Fe composite foam, low carbon steel foam, and stainless steel foam are 2.4, 2.6, and 2.9 g/cm3 with relative densities of 42, 34, and 37%, respectively.
    The composite metal foams composite materials developed in this study displayed superior compressive strength as compared to any other foam being produced with similar materials. The compressive strength of the cast Al-Fe foam averaged 67 MPa over a region of 10 to 50% strain, while the low carbon steel PM foam averaged 76 MPa over the same strain region, and the stainless steel PM foam averaged 136 MPa over the same region. Densification began at approximately 50% for the cast foam and ranged from 50 to 55% for the PM foams. The strength to density ratio of the product of both techniques exceeded twice that of foams processed using other techniques with similar materials.
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  • Wire Formed Cellular Metals

    pp. 2154-2160

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    DOI:10.2320/matertrans.47.2154

    The authors have noted that wires could be the best candidate material to create truss PCMs, because they can easily obtain high strength as in piano wires, are simple to be fabricated, and can be controlled for good quality. Seven new ideas to fabricate truss PCMs using wires, namely, straight bulk octet, bulk woven Kagome, circular spring Kagome, hexagonal spring Kagome, dual wired octet, and dual wired Kagomes are presented. The assembly process, the geometry, features and benefit of each idea are described. Also, the analytic solutions of the stiffness or strength, and the constraints for selecting proper materials are discussed.
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  • Development of an Electrophoretic Sol-Gel Coating Process for Porous Metals

    pp. 2161-2166

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    DOI:10.2320/matertrans.47.2161

    An electrophoretic sol-gel coating process was developed for applying to surface modification of metallic materials with complicated shapes such as porous metals. In this process, sol-gel transformation is directly induced on the substrates. In the present work, the formation of TiO2 coating layer on SUS 304 substrates is discussed as a practical example of the coating process. The colloidal particles derived from hydrolysis of titanium tetraisopropoxide in ethanol can be deflocculated using a small amount of CaCl2 to form a transparent solution. When a dc voltage of 1–5 V was applied between the substrate (cathod) and counter electrode in this solution, the gel film was formed on the substrate. After subsequent water-soaking and annealing processes, the coating layers with no cracking were obtained successfully on the substrate. As the results of X-ray photoelectron spectroscopy, the coating layers were found to consist of TiO2 doped with Ca2+ ions.
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  • Effect of Silica Additive on the Formation of Lotus-Type Porous Alumina under Unidirectional Solidification

    pp. 2167-2171

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    DOI:10.2320/matertrans.47.2167

    Effect of silica additive on the formation of lotus-type porous alumina on the unidirectional solidification was examined. Lotus-type porous alumina with 44% porosity was formed by unidirectional solidification using the optical floating zone method under a hydrogen atmosphere when low purity alumina was used as the feed rod. However, non-porous alumina was prepared in argon atmosphere. The formed pores possessed a drop-like shape and were elongated along the solidification direction in porous alumina. Gas bubbles evolved in the molten zone and was trapped by the solid/liquid interface during the unidirectional solidification. On the other hand, lotus-type porous alumina could not be obtained when high purity alumina was used as the feed rod. The porosity of the solidified porous alumina increased with increasing silica contents in the feed rods.
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  • Effects of Processing Parameters on Pore Morphology of Combustion Synthesized Al-Ni Foams

    pp. 2172-2177

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    DOI:10.2320/matertrans.47.2172

    Intermetallic (Al-Ni) foams were fabricated by a combustion reaction of the blended powder compacts consisting of nickel and aluminum. The foaming agents (titanium and B4C powders) were added to the nickel and aluminum blended powder to produce foams with high porosity by increasing the combustion temperature. The effects of the size of elemental powders (aluminum and nickel), the powder blending ratio, the amount of foaming agent and compacting conditions on the porosity and pore morphology of the foams were investigated. The size of nickel powder was an important factor to produce foams by the combustion synthesis and it should be small enough to achieve high porosity. The size of the aluminum powder was not such an important factor. The uniform pore morphology in the foam was obtained only when the powder blending ratio was adequate. The proper addition of the foaming agent increased the porosity and the size of pores, and also stabilized the uniformity of the pore morphology. There was a threshold density of the precursor to achieve sufficient foaming. The pore diameter of a synthesized foam is increased with increasing precursor compacting temperature and pressure. An attempt was made to disperse fine ceramic particles in the foam materials. It was revealed that the addition of ceramic particles did not affect the porous structure.
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  • Foaming and Filling-in Behavior of Porous Aluminum in Hollow Components

    pp. 2178-2182

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    DOI:10.2320/matertrans.47.2178

    Porous aluminum (aluminum foam) was fabricated by a powder processing route. TiH2 powder was blended with Al powder as a blowing agent. The blended powder was then consolidated to make a precursor. When the precursor was heated, the TiH2 powder started to decompose and hydrogen gas expanded in molten aluminum. Physical properties of the porous aluminum strongly depend on both porosity and pore morphology. In this research, pore morphology was characterized by an image analyzing software. Manufacturing temperature and heating time affected the pore morphology significantly. The manufacturing temperature should be in an adequate range. When the manufacturing temperature was low, the precursor did not expand sufficiently. The life-time of the pores became shorter when the temperature was too high. Although the pores at the initial stage of the blowing process were small (<0.5 mm) and relatively spherical, the pores become larger and irregular as the heating time became longer. A molding technique of porous aluminum in hollow parts becomes indispensable when porous aluminum is applied to automobile components The precursor was heated in a hollow pipe and the specimen was cut in both vertical and horizontal sections to investigate the filling-in behavior of the precursor. In the beginning of the expansion, the precursor expanded in a radial direction of the pipe. After the cross section of the pipe was filled, then the precursor expanded along the longitudinal axis. Heating profile was one of the most important factors which determines the possibility of filling-in behavior and the porosity of porous aluminum. Another important factor turned out to be an aspect ratio of the precursor.
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  • Influence of Ultrasonic Agitation on Pore Formation and Growth during Unidirectional Solidification of Water-Carbon Dioxide Solution

    pp. 2183-2187

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    DOI:10.2320/matertrans.47.2183

    We studied the influence of agitation by ultrasonic vibration on pore formation and growth during the unidirectional solidification of water-carbon dioxide solution. The agitation of liquid affects the pore formation and growth, and the morphology of pores formed during solidification depends on the magnitude of agitation; the agitation of liquid during unidirectional solidification shortens the length of cylindrical pores in lotus metals. This is because the agitation decreases the concentration of carbon dioxide near the solid-liquid interface.
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  • Integral Foam Moulding of Light Metals

    pp. 2188-2194

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    DOI:10.2320/matertrans.47.2188

    Integral foam moulding (IFM) is an economical way to produce castings with integrated cellular structure, i.e. a solid skin and a foamed core. IFM has been known for polymers for more than four decades and is well established in industrial production. Polymer integral foam parts are accepted as a material system with own properties which simplifies designs, reduces production costs and weight, and increases stiffness and overall strength. On the other hand, integral foam moulding for metals is a new field of research. The development of metal based integral foam moulding processes at WTM moves along analogous paths as that of polymers by transferring and adapting successful moulding technologies for polymer integral foam to metals. Two moulding techniques for metal integral foam are presented, a low and a high pressure process. In the low pressure process, the molten metal charged with blowing agent is injected into a permanent steel mould without completely filling it. In this case, the mould gets eventually filled by foam expansion.
    In the high pressure process foaming is initiated by expansion of the mould cavity after it has been filled completely with the mixture of the metal melt and the blowing agent. The moulded parts are characterized with respect to their cellular structure, density profile and pore size distribution. Mechanical properties such as stiffness and damping behaviour are discussed.
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  • Open Celled Material Structural Properties Measurement: From Morphology To Transport Properties

    pp. 2195-2202

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    DOI:10.2320/matertrans.47.2195

    Metallic foams are highly porous materials which present complex structure of three-dimensional open cells. The effective transport properties determination is essential for these widely used new materials. The aim of this work is to develop morphology analysis tools to study the impact of foams structure on physical transport properties. The reconstruction of the solid-pore interface allows the visualization of the 3D data and determination of specific surface and porosity. We present an original method to measure the geometrical tortuosity of a porous media for the two phases. A centerline extraction method allows us to model the solid matrix as a network of linear connected segments. The thermal conductivity of metallic foams is determined by solving energy equation over the solid phase skeleton. Results obtained on a set of nickel foams covering a wide range of pore size are discussed.
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  • Size Effects on Tensile Strength of Lotus-Type Porous Copper

    pp. 2203-2207

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    DOI:10.2320/matertrans.47.2203

    Effects of specimen thickness on the tensile strength of lotus-type porous copper were investigated. The ultimate tensile strength in the direction perpendicular to the longitudinal axis of pores hardly depends on the thickness of a specimen when the width of the specimen is large enough compared with the pore diameter, while the ultimate tensile strength increases with an increase in the thickness when the width is not large enough compared with the pore diameter. The 0.2% offset strength in the direction and strain at the peak stress depend on the thickness of specimens; the 0.2% offset strength decreases with an increase in the thickness, and the strain at peak stress increases with the increase in the thickness.
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  • Effect of Pore Morphology on Compressive Yield Strength of Lotus-Type Porous Copper with Various Specimen Sizes

    pp. 2208-2212

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    DOI:10.2320/matertrans.47.2208

    Lotus-type porous copper with long cylindrical pores aligned in one direction parallel to the solidification direction was fabricated by unidirectional solidification of the melt in a mixed gas of hydrogen and argon. Compression tests were performed in the direction parallel to the cylindrical pores in order to investigate the relationship between the specimen size and compressive yield strength. The compressive yield strengths and the standard deviation decrease with an increase in specimen size. Increments of the standard deviation are caused by the standard deviation of porosity occurred by inhomogeneous pore diameter and irregular pore arrangement.
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  • Space-Filling Polyhedra as Mechanical Models for Solidified Dry Foams

    pp. 2213-2218

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    DOI:10.2320/matertrans.47.2213

    The simulation of the mechanical behavior of idealized cellular structures is important as it gives insight into the principal deformation mechanisms that govern the mechanical behavior of real cellular structures, such as polymer foams or metallic foams, making accessible at least qualitative information about properties that are difficult to determine otherwise, for example the effective strength under hydrostatic loading. For capturing the mechanics of a closed-cell foam material in a meaningful way, three-dimensional models are employed in the context of the Finite Element method. The modeling approach presented in this paper employs generic, periodic unit cell models with the extension of providing physically sound microstructures by basing these models on surfaces of minimal energy calculated with the program Surface Evolver. This program is able to minimize the energy of a surface subject to given constraints, for example a prescribed initial geometry and, where required, periodicity. Accordingly, space-filling polyhedra with cells being separated by walls of minimal total area can be predicted, such as Lord Kelvin’s tetrakaidecahedra or the Weaire-Phelan partition, the latter being energetically more favorable. These physics-based configurations are good representations of solidified (dry) foams. The results obtained by Finite Element stress and deformation analyses comprise the full tensor of elasticity and its dependence on the effective density; the non-planar faces resulting from the surface energy minimization are shown to influence the behavior for very low effective densities. By studying the behavior up to the onset of yielding on the effective, macro-mechanical level including the effects of multi-axial loading conditions, valuable information for the homogenized representation of closed-cell foams is obtained.
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  • Fracture Behavior of Metal Foam Made of Recycled MMC by the Melt Route

    pp. 2219-2222

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    DOI:10.2320/matertrans.47.2219

    Metal foam was made from recycled MMC precursor by the melt route. The original starting material was an Al-9Si alloy containing 20 vol% of SiC particles (10 μm), which are used to stabilize the foam during the foaming process. The starting material has been used to make foam parts from which the residue was recycled and refoamed. During the (re)foaming process Fe is present in the melt. During solidification of the foam, β-AlSiFe plates are formed with the surplus of Si and Al present in the alloy. These plates run through the entire thickness of the cell wall (40–50 μm) and their length ranges between 50 and 200 μm. During in-situ tensile tests fracture initiates in the β-AlFeSi plates and propagates through other β-AlFeSi plates leading to brittle fracture of the cell walls.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Superplastic Forming and Foaming of Cellular Aluminum Components

    pp. 2223-2228

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    DOI:10.2320/matertrans.47.2223

    Liquid and semi-solid state foaming processes have been widely used as a manufacturing method of closed-cell metal foams. These metal foams usually have large pores as well as high porosity. Large pores and inhomogeneous pore distribution often cause a decrease in mechanical properties. Therefore, microcellular foams are desirable for engineering applications. In the present study, solid-state foaming process under superplastic conditions is examined in order to manufacture microcellular aluminum foams. The superplastic flow during the high temperature foaming accelerates the foaming rate and increases the porosity. Commercial SP5083 aluminum alloy sheets were used as a starting material because they are typical superplastic material. Preform sheet containing titanium hydride particles was produced through accumulative roll-bonding (ARB) processing. Heating the preform sheet under superplastic conditions, we obtained aluminum foam with small oblate pores. The thermal conductivity was quite small because of the oblate pore shape. Superplastic flow enabled to produce a thin sandwich panel and porous bulge structures. These panel and bulge with oblate spheroidal pores parallel to the surface are industrially important because of their excellent thermal insulation. Present experimental results of superplastic forming and foaming (SPFF) processing has potential for near net-shape forming of microcellular aluminum foams.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Electrochemical Behaviour of Lotus-Type Porous SUS304L and SUS316L Stainless Steels

    pp. 2229-2232

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    DOI:10.2320/matertrans.47.2229

    Lotus-type porous metals are expected to be used in various applications such as lightweight structural materials and biomedical materials. Lotus-type porous stainless steel is particularly promising as a structural material because stainless steel has useful properties such as high corrosion resistance, high workability, low cost and so on. However, there is a possibility that dissolved hydrogen or the microstructure of lotus-type porous stainless steel affects its corrosion behaviour. In this study, the electrochemical corrosion behaviour of lotus-type porous SUS304L and SUS316L stainless steels fabricated by the continuous zone melting technique under pressurized hydrogen was investigated using a potentiodynamic polarization in 0.1-kmol/m3 sulphuric acid solution. The current density of lotus-type porous SUS304L was higher than that of nonporous SUS304L at around −100 mV (−100 mV peak), while it was similar to that of nonporous stainless steel in the passive and transpassive regions. The specific current peak observed for the porous SUS304L at around −100 mV disappears when the pores are filled with epoxy resin or the specimens are dehydrogenated. Thus, it is concluded that the −100 mV peak is attributed to the dissolved hydrogen at pore surface. In the case of lotus-type porous SUS316L, corrosion behaviour is similar to that of SUS304L.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Evaluation of Bone Quality near Metallic Implants with and without Lotus-Type Pores for Optimal Biomaterial Design

    pp. 2233-2239

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    DOI:10.2320/matertrans.47.2233

    The stress shielding effect often degrades the quality and quantity of bones near implants. Thus, the shape and structure of metallic biomaterials should be optimally designed. A dominant inorganic substance in bones is a biological apatite (BAp) nanocrystal, which basically crystallizes in an anisotropic hexagonal lattice. The BAp c-axis is parallel to elongated collagen fibers. Because the BAp orientation of bones is a possible parameter of bone quality near implants, we used a microbeam X-ray diffractometer system with a beam spot, which had a diameter of 50 or 100 μmφ, to evaluate the BAp orientation of bones.
    Two animal models were prepared: (1) a nail model (φ: 3.0 mm, SUS316L), which was used to understand the stress shielding effect in a rabbit tibial marrow cavity, and (2) a model of a lotus-type porous implant (φ: 3.4 mm, mean pore diameter: 170 μm, SUS304L), which was used to understand the effect of the unidirectional-elongated pore direction in an anisotropic bone tissue of a beagle mandible. The porous implants were implanted so that the pore direction was parallel or perpendicular to the mesiodistal axis of mandible.
    For the porous implant model, new bone formation strongly depended on the elongated pore direction and the time after implantation. For example, four weeks after implantation, new bone formed in pores of the implants, but the BAp orientation degree in the new bone was more similar to that in the original bone in the elongated pores parallel to the mesiodistal direction than that in the perpendicular pores. These differences in bone formation inside the parallel and perpendicular pores may be closely related to the anisotropy of original bone tissues such as the orientations of collagen fiber, BAp, and blood vessels. The orientation degree of BAp also changed in the nail model. The stress shielding effect decreased the orientation degree of the BAp c-axis in the tibia along the longitudinal axis.
    Thus, optimal design of metallic biomaterials such as implant shape, pore size, elongated pore direction, etc., should be based on the anisotropy of the bone microstructure.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Development of Lotus-Type Porous Copper Heat Sink

    pp. 2240-2247

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    DOI:10.2320/matertrans.47.2240

    Lotus-type porous copper with many straight pores is produced by precipitation of supersaturated gas when the melt dissolving gas is solidified. Lotus-type porous copper is attractive as a heat sink because a higher heat transfer capacity is obtained as the pore diameter decreases. The main features of lotus-type porous metals are as follows; (1) the pores are straight, (2) the pore size and porosity are controllable, and (3) porous metals with pores whose diameter is as small as ten microns can be produced. We developed a lotus-type porous copper heat sink for cooling of power devices. Firstly we investigated the effective thermal conductivity of the lotus copper, considering the pore effect on heat flow. Secondly, we investigated a straight fin model for predicting the heat transfer capacity of lotus copper. Finally, we examined experimentally and analytically determined the heat transfer capacities of three types of heat sink with conventional groove fins, with groove fins having a smaller fin gap (micro-channels) and with lotus-type porous copper fins. The lotus-type porous copper heat sink were found to have a heat transfer capacity 4 times greater than the conventional groove heat sink and 1.3 times greater than the micro-channel heat sink at the same pumping power.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Numerical Simulation of Laser Fusion Zone Profile of Lotus-Type Porous Metals

    pp. 2248-2253

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    DOI:10.2320/matertrans.47.2248

    Lotus-type porous metals, whose pores are aligned in one direction by unidirectional solidification, have a unique combination of properties. These are expected as innovative engineering materials with anisotropy of the properties. A reliable joining technology such as welding is required for the industrial application of the lotus-type porous metals as well as processing technology. We have already investigated the melting property of the lotus-type porous copper and magnesium by laser beam irradiation and have pointed out that these materials possessed anisotropy of melting property with the pore direction perpendicular and parallel to the specimen surface, especially remarkable anisotropy was obtained for the lotus-type porous copper owing to the difference of the laser energy absorption to the specimen surface. In this study, three-dimensional finite element calculations of temperature distribution for the lotus-type porous copper as well as the lotus-type porous magnesium under the non-steady-state conditions were performed in order to investigate the effect of the anisotropy of the laser energy absorption comparing with the anisotropy of thermal conductivity inherent to lotus type porous metals. The effect of these factors on the profile of fusion zone by comparing the results of numerical simulation and the experimental observations were discussed.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Laser Welding of Lotus-Type Porous Iron

    pp. 2254-2258

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    DOI:10.2320/matertrans.47.2254

    A lotus-type porous iron (AISI 1018) that is fabricated by unidirectional solidification using the continuous zone melting technique in a nitrogen atmosphere under a pressure of 2.5 MPa, was welded by a Nd:YAG laser. The melting property of this was investigated to evaluate its melting characteristics at different laser powers and welding speeds. The weld bead surface of the lotus-type porous iron was rough with pits and dents irrespective of the pore growth direction. The remarkable effect of the pore growth direction on the penetration depth of the weld bead was not observed. This was due to the unstable weld bead formation caused by the relatively large-sized pores and the blowing of the remaining gas from the closed pores as well as the smaller anisotropy of the thermal diffusivity as compared to the copper and magnesium cases.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Tribological Behaviour of Lotus-Type Porous Cast Iron

    pp. 2259-2263

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    DOI:10.2320/matertrans.47.2259

    Tribological behaviours of lotus-type porous cast iron under oil lubrication were investigated with reciprocal motion friction testing equipment. Lotus-type porous cast iron was fabricated by unidirectional solidification in mixture gas of hydrogen and argon at high pressure up to 2.8 MPa. The porosity is controlled by partial pressures of hydrogen and argon during melting and solidification. The friction coefficient was improved by about 20%, and the seizure resistance was also improved by about double, and the abrasion resistance was decreased by about 20%, compared with that of non-porous cast iron. Thus, such improvement of wear resistance and seizure resistance of lotus cast iron may be attributed to the hardness and tribological behaviour of lotus-type porous cast iron.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Magnetic Properties of Mechanically Milled Sm-Co Permanent Magnetic Materials with the TbCu7 Structure

    pp. 2264-2268

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    DOI:10.2320/matertrans.47.2264

    The magnetic properties of Sm(Co,Fe,Cu,Zr)7 compound with the TbCu7 structure are studied for the mechanically milled samples. The coercivity could be varied, without affecting the saturation magnetization, from 44 kA/m for the micron sized particles to 280 kA/m by reducing the particle size to sub-micron size (600–900 nm) using high-energy ball milling. The enhancement in the coercivity is attributed to the particles approaching single domain size. The presence of dipolar coupling suggests that the grain sizes are well above the exchange length for the milled samples. The thermal measurements indicate that the compound with the TbCu7 structure is not stable at high temperatures beyond 743 K.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Evolution of Microstructural Banding during the Manufacturing Process of Dual Phase Steels

    pp. 2269-2276

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    DOI:10.2320/matertrans.47.2269

    The segregation of manganese during solidification from casting is responsible for banding problems of dual phase steels. Microstructural banding lasts during all the manufacture process, producing the deterioration of the material, so the final ductility and impact toughness of the sheets are decreased due to the high level of anisotropy. To avoid or reduce the problem of microstructural banding, it is proposed to modify the hot rolling parameters so the formation of ferrite-pearlite microstructures is avoided and thus the presence of banding. The study of the microstructural evolution during the whole manufacturing process reveals that the increase of the cooling rate during the hot rolling leads to a significant decrease of martensite banding in the microstructure of dual phase steels for sheets used in the automotive industry.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Kinetic Features of Reactive Diffusion between Sn–5Au Alloy and Ni at Solid-State Temperatures

    pp. 2277-2284

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    DOI:10.2320/matertrans.47.2277

    In order to examine microstructure evolution at the interconnection between the Sn-base solder and Au/Ni/Cu multilayer conductor alloys during energization heating, the kinetics of the reactive diffusion between a binary Sn–5 at% Au alloy and pure Ni was experimentally observed at solid-state temperatures. Sandwich (Sn–Au)/Ni/(Sn–Au) diffusion couples were prepared by a diffusion bonding technique, and then isothermally annealed at temperatures of T=433, 453 and 473 K for various periods up to 1057 h. During annealing, AuNiSn8 and Ni3Sn4 compound layers are formed along the (Sn–Au)/Ni interface in the diffusion couple. The total thickness of the compound layers is expressed as a power function of the annealing time. The exponent of the power function is close to 0.5 at T=453–473 K, and equal to 0.7 at T=433 K. Therefore, volume diffusion is the rate-controlling process for the growth of the compound layers at T=453–473 K, but interface reaction contributes to the rate-controlling process at T=433 K. The growth of the compound layers occurs slower for the reactive diffusion between the Sn–5Au alloy and Ni than for that between Sn and Au, but faster for that between the Sn–5Au alloy and Ni than for that between Sn and Ni.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Coarsening Behavior of Al3Sc Precipitates in an Al–Mg–Sc Alloy

    pp. 2285-2291

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    DOI:10.2320/matertrans.47.2285

    The coarsening of Al3Sc precipitates in an Al–1 mass%Mg–0.27 mass%Sc alloy aged at 673 to 748 K has been studied by measuring both the precipitate size by transmission electron microscopy (TEM) and the Sc concentration in the Al matrix by electrical resistivity measurements. The growth and coarsening of Al3Sc precipitates occur concurrently prior to the beginning of coarsening. The Al3Sc precipitates grow more slowly at the coarsening stage than at the mixed stage of growth and coarsening. The Al/Al3Sc interface energy γ and the diffusivity D of Sc in Al have been independently derived from data obtained by TEM and electrical resistivity measurements using a coarsening model developed by Kuehmann and Voorhees for ternary systems. The estimates of γ and D are in agreement with those determined by the Lifshitz-Slyozov-Wagner theory from data on coarsening of Al3Sc precipitates in an Al–0.28 mass%Sc alloy. The experimentally obtained value of γ is insensitive to the change in coherency between the Al3Sc precipitate and Al matrix. Whether the precipitates are coherent or semi-coherent with the matrix, the obtained value of γ is then 0.23 J/m2.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Two-Dimensional Time-Resolved X-ray Diffraction Study of Directional Solidification in Steels

    pp. 2292-2298

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    DOI:10.2320/matertrans.47.2292

    In situ characterization of directional solidification process during welding was carried out using the time resolved X-ray diffraction technique utilizing intense synchrotron radiation. Then, behaviour of dendrites in steels under welding conditions of a practical manufacturing process were investigated using the TRXRD method for in-situ weld observation with the uniquely-sensitive two-dimensional pixel detector. Consequently, the crystal growth during the rapid cooling was caught in detail and employed a systematic peak profile analysis in order to acquire the essential information for controlling the weld microstructure. Our results would suggest the microstructure formation process of low alloy in directional solidification during rapid cooling. Simultaneously, we discuss the possibility of detecting the nucleation.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Texture of Electroplated Copper Film under Biaxial Stress

    pp. 2299-2301

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    DOI:10.2320/matertrans.47.2299

    The stresses and the textures of electroplated copper films were studied using the X-ray diffraction analysis. The results show that the stresses in the films are always tensile. The films have (110) fiber texture at different thickness from 8 to 60 μm. From strain energy minimization point of view, the grains with (110) orientation should be favorable in these films. A further planar texture on top of the fiber texture was developed. It could be explained by elastic anisotropy at different orientation in grain.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effect of Boron Nitride Precipitation at Cavity Surface on Rupture Properties

    pp. 2302-2307

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    DOI:10.2320/matertrans.47.2302

    Compositions of type 304 austenitic stainless steels were modified with additions of boron, cerium and titanium. The additions of cerium and titanium removed free sulfur almost completely by formation of sulfides (Ce2O2S2 and Ti4C2S2), and led to precipitation of boron nitride onto creep cavity surfaces during creep exposure. Chemistries of the creep cavity surfaces, exposed by breaking creep exposed specimens at liquid nitrogen temperature under impact loading, were examined by Auger electron spectroscopy. The Auger spectra revealed the presence of boron nitride precipitating onto creep cavity surfaces. It was indicated that the boron nitride suppressed creep cavity growth and provided the steel with higher rupture strength and higher rupture ductility.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Temperature-Time-Transformation Curve and Viscous Flow Deformation of Zr55Cu30Al10Ni5 Bulk Glassy Alloy

    pp. 2308-2311

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    DOI:10.2320/matertrans.47.2308

    The temperature-time-transformation curve of a Zr55Cu30Al10Ni5 bulk glassy alloy was obtained by isothermal DSC measurements. High temperature compression tests were carried out to investigate the viscous flow behavior of the Zr55Cu30Al10Ni5 bulk glassy alloy. The influence of four process parameters (temperature, time, initial stress, strain rate) on viscous flow deformation of the bulk glassy alloy was studied. X-ray diffractometry (XRD) was used to examine a glassy state of the glassy alloy samples subjected to viscous flow deformation. Appropriate parameters of viscous flow leading to a good deformation process were proposed. The relative displacement over 80% was obtained by compressing for 200 s at 723 K under a pressure of 160 MPa with a strain rate of 1.32×10−2 s−1. The XRD results showed the absence of crystal peaks after viscous flow deformation under the condition being suggested.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effect of Nano-Scale Copper Sulfide Precipitation on Mechanical Properties and Microstructure of Rapidly Solidified Steel with Tramp Copper Element

    pp. 2312-2320

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    DOI:10.2320/matertrans.47.2312

    Copper is one of the main residual elements in steel, especially in recycled scrap steel, whereas sulfur is one of the main impurities in steel. A large quantity of slag and CO2 is produced during the process of removing the sulfur from the steel. However, copper and sulfur may combine to form copper sulfide, especially during the rapid cooling process. In this paper samples containing and not containing fine copper sulfide are prepared by the rapid solidification process. The microstructure, sulfide precipitates, and the mechanical properties of the samples are investigated by optical microscopy, Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), and the tensile testing. A large difference in the yield strength between the samples containing and not containing copper sulfides is observed. Each contribution of solid solution strengthening, grain refining strengthening, and sulfide precipitates strengthening in the samples with and without copper sulfide has been discussed. Particular attention has been paid to effect of the nano-scale copper sulfides, that is, main factor contributing to the alloy strengthening. Contribution of reduction of the copper sulfide particle size has also been discussed by comparing the results of two rapid solidification processes with different cooling rates.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Be Effect on Glass-Forming Ability and Mechanical Properties of Ti-Cu-Co-Zr-Sn Bulk Metallic Glasses

    pp. 2321-2325

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    DOI:10.2320/matertrans.47.2321

    A series of Ti44Cu44−xCo4Zr6Sn2Bex bulk metallic glasses with x=0–5.1 has been systematically investigated in terms of glass-forming ability and mechanical properties at room temperature. With the small amount of Be addition, the glass forming ability as well as ductility can be significantly increased leading to the fully amorphous rod having the diameter larger than 4 mm and ductility larger than 10%. Upon compressing the bulk metallic glass Ti44Cu38.9Co4Zr6Sn2Be5.1, a work hardening-like behavior that may be attributed to structural heteorgeniety was observed.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Nanoscopic Strength Analysis of Work-Hardened L-Grade Austenitic Stainless Steel, 316(NG)

    pp. 2326-2334

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    DOI:10.2320/matertrans.47.2326

    Stress corrosion cracking (SCC) occurs in shrouds and piping of L-grade austenitic stainless steels at nuclear power plants. A work-hardened layer, where the transgranular SCC initiates, is considered to be one of the probable cause for this occurrence. In order to clarify the microstrucural characteristics of work-hardened layer at the surface of shrouds or piping, the strengthen analysis of L-grade austenitic stainless steel, 316(NG), rolled at the reduction in area, RA, of 10, 20, 30, 40 and 50% at room temperature were conducted on a nanoscopic scale, using an ultra-microhardness tester, TEM and SEM. TEM and SEM observation showed that the microstructural parameters are the dislocation cell size, dcel, coarse slip spacing, lcsl, and austenitic grain size, dγ. Referring 10dcel and 10lcsl, Vickers hardness, Hv, corresponding to macro strength was expressed as Hv=Hv*bas+Hv*sol+Hv*dis+Hv*cel+Hv*csl. Hv*bas (=100) is the base hardness, Hv*sol is the solid solution strengthening hardness, Hv*dis is the dislocation strengthening hardness in the dislocation cell, and Hv*cel and Hv*csl are the fine grain strengthening hardness due to the dislocation cell and coarse slip. Hv*sol was about 50, independently of RA. Hv*dis was zero at RA<30% and increased at RA>30%. Hv*cel and Hv*csl increased with increasing in RA and were kept constant at about 50 and 120 at RA=20 and 30%, respectively. It was suggested from these results that all dislocations introduced by rolling might be dissipated for the creation of dislocation cells and coarse slips at RA<30% and that the microstructure contributing to the fine grain strengthening due to the dislocation cell and coarse slip might be accomplished at RA=30%. The dislocation strengthening in the dislocation cell might begin to operate at RA>30%.
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  • Synthetic Process of Environmentally-Friendly TiO2 Coating on Magnesium by Chemical Conversion Treatment

    pp. 2335-2340

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    DOI:10.2320/matertrans.47.2335

    Titanium dioxide (TiO2) coatings were prepared by chemical conversion treatment of magnesium in (NH4)2[TiO(C2O4)2] with H2O2, then, anatase type TiO2 coatings were prepared by sintering. To identify the coating structure, coating analysis was carried out using an infrared absorption spectrum analyzer. Based on the infrared absorption results, a component of the coating was found in the hydrolysis product of peroxo-titanium compound. Furthermore, the coating analysis was carried out using X-ray diffractometry (XRD), and non-sintered coating was amorphous; however, the coating sintered at more than 573 K was anatase-type titanium dioxide.
    In the forming process of the conversion treatment in (NH4)2[TiO(C2O4)2] with H2O2, first, magnesium was dissolved because H+ in the bath reacted with the magnesium. Hydrogen ions on the magnesium surface were consumed to generated hydrogen gas. Thus, the pH of the interface became alkali. The hydrolysis of the peroxo-titanium compound was deposited on the magnesium because pH increased on the surface. From the XPS results and the TG-DTA results, a component of the coating is a hydrolyzation product of a peroxo-titanium compound and Mg(OH)2. Because Mg(OH)2 is generates in pH more than 11, it is considered that the pH on the magnesium surface is more than 11.
    The coating sintered at 573 K had the highest photocatalytic activity. The photocatalytic activity of the coating sintered at 623 K was lower than the coating heated at 573 K, which is attributed to growth of TiO2 particle. This forming process of the coating is low cost because of the useless electrolytic decomposition process and increasing the speed of the treatment. It is possible to treat complicated form of the substrate metal, so this method can be expected to use in various fields. Therefore this method is expected to practical use for environmental purification.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Growth Behavior of Coatings Formed by Vapor Phase Aluminizing Using Fe-Al Pellets of Varying Composition

    pp. 2341-2347

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    DOI:10.2320/matertrans.47.2341

    Growth behavior of coatings formed by AlF3 activated vapor phase aluminizing on an Ni-base superalloy substrate was investigated at 1353 K for up to 4 h using FeAl, FeAl2, Fe2Al5, and FeAl3 pellets as aluminum donors, with an aim of understanding the kinetics under the different aluminum activities. The coatings consist of an outer δ-Ni2Al3 layer, a middle β-NiAl layer, and an inner diffusion layer of γ′-Ni3Al. The thickness of the δ-Ni2Al3 layer remarkably increases with an increase of the coating time and of the aluminum content of the donor pellet. Contrarily, the aluminum concentration at the coating surface increases only a little, which might be due to the strong dependence of the aluminum activity on composition of solid Ni-Al alloys. The amount of aluminum deposition shows parabolic time dependence in all the cases, and the deposition rate becomes higher for the donor pellet of higher aluminum content. Except for the case of the FeAl pellet, the parabolic rate constants are similar to the reported value calculated from the diffusion rate of aluminum in solid Ni-Al alloys. This suggests that the rate of aluminum deposition is dominantly controlled by solid diffusion in the coating. However, the rate falling occurs in the last stage due to the phase transformations of FeAl3 → Fe2Al5 → FeAl2 → FeAl caused by the depletion of aluminum in the pellet. It is supposed that the gaseous diffusion of aluminum or the other process might contribute to the rate-controlling when a sufficiently thick FeAl layer covers the pellet surface.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Titanium Mesh/Rod Joined by Pulse Electric Current Sintering: Effect of Heating Rate

    pp. 2348-2352

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    DOI:10.2320/matertrans.47.2348

    Ti mesh was bonded to a solid titanium substrate using pulse electric current sintering (PECS) to fabricate a porous surface of potential use in a titanium implant. We investigated the effect of heating rate on the bonding strength, deformation of the mesh and deformation of the entire construct. During the PECS process, there was a temperature gradient between the Ti mesh and Ti rod, which increased with increasing the heating rate. At the same bonding temperature, a rapidly heated mesh showed a higher temperature than when heating was slow, and caused the strongest bonding.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Microstructure and Mechanical Properties of W-C-B Ceramics Containing VC

    pp. 2353-2357

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    DOI:10.2320/matertrans.47.2353

    We prepared WC-based W-C-B ceramics by reactive resistance-heated hot pressing at 1600 to 1800°C from a B4C-5W-80WC (molar ratio) powder mixture containing a small amount of VC, and examined the effect of VC on sinterability and the mechanical properties of the ceramics. The sintered bodies were composed mainly of WC and small quantities of W2C, WB, W2B and VC. Slight amounts of V were detected at the boundaries between WC grains. VC raised the sintering temperature necessary for obtaining dense bodies, and strongly suppressed the growth of WC grains. Young’s modulus for the dense bodies was slightly smaller than that without VC because of the low modulus value of VC. The suppressive effect of VC on the growth of WC grains avoided reducing hardness with increasing sintering temperature.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Synthesis and Thermal Stability of New Ni-Based Bulk Glassy Alloy with Excellent Mechanical Properties

    pp. 2358-2362

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    DOI:10.2320/matertrans.47.2358

    The thermal stability, glass-forming ability (GFA) and mechanical properties of the Ni-Ta-Ti and Ni-Ta-Ti-Zr glassy alloys have been investigated. As the Ti content increases, the supercooled liquid region ΔTx(=TxTg) and reduced glass transition temperature (TgTl) of Ni60Ta40−xTix glassy alloys increase, showing maximum values of 63 K at 20%Ti and 0.59 at 25 at%Ti, respectively, and then gradually decrease. The addition of Zr to Ni-Ta-Ti alloys is effective for the increase in ΔTx and TgTl. The maximum ΔTx and TgTl values of 73 K and 0.60, respectively, are obtained for Ni60Ta15Ti20Zr5 alloy. The Ni-Ta-Ti-Zr glassy alloys were formed in the rod form with diameters of over 1.0 mm by copper mold casting. The Ni-Ta-Ti-Zr bulk glassy alloys exhibit excellent mechanical properties, i.e., the compressive fracture strength (σc,f) of 3180–3220 MPa and the compressive plastic elongation (εc,p) of 0.2–0.4%.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Pore Defect Control in Die Casting by Compression Loading

    pp. 2363-2367

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    DOI:10.2320/matertrans.47.2363

    Although die casting enables high productivity, pore defects in the die castings are unavoidable. These pore defects influence the mechanical properties or air leakage efficiency of the products. To reduce the number of pore defects, we performed compression tests on the front housings of car air conditioners made by ADC12 aluminum alloy die casting at room temperature. Because of plastic deformation, the porosity rate of the die castings decreases as the compression strain of the specimen increases, particularly in the middle of the specimens where the porosity rate is high. However, the efficiency of the reduction in the porosity rate and damage of the products differs depending on the compression load. Consequently, it is necessary to investigate the conditions of the compression load to enable this method to be applied in practice.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effect of β-TCP Size on Bone-Like Layer Growth and Adhesion of Osteoblast-Like Cells in Hydroxyapatite/β-TCP Composites

    pp. 2368-2372

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    DOI:10.2320/matertrans.47.2368

    Hydroxyapatite (HAp)-20 vol% β-tricalcium phosphate (β-TCP) composites were prepared. The effect of β-TCP size on bone-like layer growth and adhesion of osteoblast-like cells on the composites was systematically studied in vitro. When the composites were soaked in a simulated body fluid, the formation and growth rates of the bone-like layer increased with increasing β-TCP size, even if the volume fraction of β-TCP was constant. Moreover, selective dissolution of β-TCP phase and formation of the bone-like layer around the phase were frequently observed. Higher Ca2+ concentration due to the fast dissolution of β-TCP beneath the sample surface resulted in faster formation and growth of the bone-like layer, especially in the samples containing β-TCP powders larger than 100 μm. MC3T3-E1 osteoblast-like cells preferentially adhered to β-TCP phase in HAp/β-TCP composites because of the enrichment of Ca2+ ions around β-TCP.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Magnetic Properties of Palladium and Palladium–Platinum Alloy of Various Hydrogen Content

    pp. 2373-2376

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    DOI:10.2320/matertrans.47.2373

    Magnetic properties of palladium and palladium-platinum alloy (Pd-Pt) of different hydrogen content were measured in a hydrogen atmosphere at ambient temperature using a superconducting quantum interference device (SQUID) magnetometer. It was found that the magnetic susceptibility of Pd and Pd-Pt alloy decreased with increasing hydrogen content. These results were attributed to a change in the electronic structure of the valence band. Increasing hydrogen content in Pd and Pd-Pt alloy causes the Fermi level to rise and the density of states at Fermi level to decrease. Since the magnetic susceptibility is proportional to the density of states at the Fermi level, the magnetic susceptibility decreases with increasing hydrogen content. The magnetic susceptibility of Pd-Pt was smaller than that of Pd over the whole hydrogen content range. This was ascribed to the higher position of the Fermi level of Pd-Pt than that of Pd.
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  • FCC/HCP Martensitic Transformation and High-Temperature Shape Memory Properties in Co-Si Alloys

    pp. 2377-2380

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    DOI:10.2320/matertrans.47.2377

    The microstructure, martensitic transformation temperatures and shape memory properties of Co-Si binary alloys were investigated by means of optical and transmission electron microscopy, differential scanning calorimetry and a shape memory test. The ε martensite phase with a hexagonal close-packed (hcp) structure was observed to coexist with the face-centered cubic (fcc) γ parent phase at room temperature. The γ⁄ε martensitic transformation temperatures linearly increased with Si content up to 4 mol%, but the trend flattened beyond 4 mol%Si while the transformation hysteresis and intervals monotonously increased. The Co-Si alloys exhibited shape recovery at high temperatures up to 900°C and a relatively high thermal stability up to 600°C. These results suggest that Co-Si alloy system has a possibility for high-temperature shape memory alloys.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effect of Alloying Elements on fcc/hcp Martensitic Transformation and Shape Memory Properties in Co-Al Alloys

    pp. 2381-2386

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    DOI:10.2320/matertrans.47.2381

    Effects of alloying elements (Si, Ti, V, Cr, Mn, Fe, Ni, Nb, Mo, Ta and W) on γ (fcc)/ε (hcp) martensitic transformation, ductility and shape memory (SM) properties of Co90Al10 alloy were investigated by means of differential scanning calorimetry, X-ray diffraction method, cold-rolling and an SM test. The addition of Ti, V, Mn, Fe, Ni, Nb, Mo, Ta or W decreased the volume fraction of the ε martensite phase (Vm), resulting in improvement of the ductility due to the stabilization of the γ phase, and the addition of Si or Cr, known as hcp stabilizing elements, slightly decreased Vm. The relationship between the martensitic transformation temperatures and Vm was determined in Co-Al and Co-Al-Fe alloys. Co-Al alloys showed behavior different from that of other alloys. The SM effect decreased with decreasing Vm and the Co-Al binary alloys showed the highest SM effect in this study, whereas the transformation temperatures and the ductility could be controlled by the alloying element.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Fabrication of the Crystal-Oriented Thermoelectric Material Bi2Te3 by Slip Casting under a High Magnetic Field

    pp. 2387-2392

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    DOI:10.2320/matertrans.47.2387

    It is well known that the electric and thermal conductivities of materials depend largely on their crystal orientation. Meanwhile, the imposition of a high magnetic field is a very effective method of obtaining highly crystal-aligned structures. Recently, thermoelectric materials, that is, materials which can directly convert electrical energy to thermal energy and vice versa, have attracted significant attention for their potential uses in solving environmental problems.
    In this study, highly crystal-aligned structures of Bi2Te3 compact were prepared by introducing crystal alignment into a green sample by conducting slip casting under a high magnetic field, followed by compaction by pulse-discharge sintering (PDS). By aligning the crystal orientation, electric resistivity was reduced, while the Seebeck coefficient maintained a value nearly identical to that of non-aligned crystals. The reference value of a dimensionless figure of merit as high as 1.3 at 323 K was obtained.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Microstructure and Mechanical Properties of Common Straight Carbon Steels Strengthened by TiC Dispersion

    pp. 2393-2398

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    DOI:10.2320/matertrans.47.2393

    TiC particles have been synthesized in common straight steels with three different carbon contents by in situ reaction during melting process. Experimental results show that the distribution of TiC particles in the steels containing 0.55 mass%C and 0.8 mass%C is uniform, however, slight segregation of TiC particles has been observed in the steel containing 1.4 mass%C. With the formation of TiC more ferrite precipitates from the steel with 0.55 mass%C, while the TiC formation inhibits the precipitation of secondary cementite in the steel containing 1.4 wt%C. In the present investigation a proper technique of heat treatment has been designed, after which good mechanical properties as well as high wear resistance have been obtained from the steel with TiC additions. However the effect of TiC addition on wear resistance is weakened with the increase of carbon concentration.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effects of Zr and C Additions on Magnetic Properties and Microstructures of α-Fe/Nd2F14B Nanocomposite Magnets

    pp. 2399-2404

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    DOI:10.2320/matertrans.47.2399

    The effects of Zr and C additions on the magnetic properties and microstructures of melt-spun Nd8Fe85−xZrxB7−yCy (x=0–3,y=0,1) alloy ribbons were investigated. The cooling rates of melts and the heat treatment conditions were varied to optimize the hard magnetic properties. The C addition improved remanence and the Zr addition suppressed the undesirable crystallization of Nd2Fe17Cx during heat treatment. The (BH)max of 135 kJ/m3 was obtained for an optimally heat-treated Nd8Fe83Zr2B6C1 ribbon.
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    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Effect of Dynamically Recrystallized Grain Size on the Tensile Properties and Vibration Fracture Resistance of Friction Stirred 5052 Alloy

    pp. 2405-2412

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    DOI:10.2320/matertrans.47.2405

    5052H34 Al-Mg plates were annealed and then friction stir processed at various rotation speeds ranging from 500 to 1500 rpm to investigate the tensile properties and vibration fracture resistance. The experimental results indicate that grain refinement could be observed at the stir zone with an average grain size varying from 5–16 μm. Based on the observed microstructure and tensile deformation resistance data, the ky slope value of the Hall-Petch equation can be determined. A refined grain size in the stir zone is a common feature of the friction stirred specimens. Different rotation speeds have different corresponding grain sizes and this can be attributed to dynamic recrystallization during friction stir processing (FSP). The effect of grain size on vibration fracture resistance in the stir zone was also examined. Results show that the vibration fracture resistance of the stir zone decreases with increasing the rotation speed. An increase in grain size due to higher rotation speed is detrimental to the vibration propagation resistance, and a small variation in grain size can result in significant changes in the duration of stage I of the D-N curves. The inward crack propagation behavior was found to be the main controlling factor on vibration fracture resistance. This result agrees with the variation in crack propagation rate.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Temperature Simulation of Pb-Free Sn-9Zn Elements for a Low Voltage Fuse

    pp. 2413-2420

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    DOI:10.2320/matertrans.47.2413

    The distribution of the temperature was estimated by combination of electrical and thermal calculations on the basis of Ohm’s and Fourier’s laws in the fuse element-connector-electric wire system in order to design Pb-free Sn-9Zn fuse elements used in electric power line. The temperature distributions in fuses were obtained on the basis of the amount of Joule’s heat generation and heat transfer depending on the ratio of the length and diameter of fuse elements. Main requirements for AC-low voltage fuses were satisfied on the promising fuse element with the size designed on the basis of the heat generation and transfer calculations. The promising size was the diameter of 2.5 mm and length of 10 mm in the smaller diameter part of two step cylindrical fuse elements. In contrast, the electrical potential and temperature distributions can be also estimated by this calculation method, regardless of a kind and shape of the fuse elements, connectors and electric wires.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • A Kinetic Study of the Carbothermic Reduction of Zinc Oxide with Various Additives

    pp. 2421-2426

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    DOI:10.2320/matertrans.47.2421

    Most processes for recovering zinc from electric arc furnace (EAF) dust employ carbon as a reducing agent for zinc oxide in the dust. In the present work, the reduction reaction of zinc oxide with carbon in the presence of various additives was kinetically studied. The effects of temperature and the additives of Fe2O3, mill scale, and CaCO3 on the kinetics of the reduction reaction were measured in the temperature range of 1173–1373 K under nitrogen atmosphere. The mill scale is one of byproducts generated from the steel rolling process. It was found from the experimental results that all three additives enhance the reaction rate of zinc oxide with carbon, but the effect of CaCO3 addition is the highest. The increase in the reaction rate is because Fe2O3, mill scale, and CaCO3 in the reduction reaction promote the carbon gasification reaction. The spherical shrinking core model for a surface chemical reaction control was also found to be useful in describing the kinetics of the reaction, which had an activation energy of 224 kJ/mol (53 kcal/mol) for ZnO-C reaction system, 175 kJ/mol (42 kcal/mol) for ZnO-Fe2O3-C reaction system, 184 kJ/mol (44 kcal/mol) for ZnO-mill scale-C reaction system, and 161 kJ/mol (39 kcal/mol) for ZnO-CaCO3-C reaction system.
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    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • The Precipitation Behavior of α1-Plate and γ Phase in Cu-Zn-Sn Shape Memory Alloys

    pp. 2427-2433

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    DOI:10.2320/matertrans.47.2427

    A DSC scan of a Cu-33.5Zn-4Sn (mass%) alloy shows two exothermic peaks at around 250 and 300°C. The first peak is associated with the precipitation of α1-plates with M9R structure, and the second peak is associated with the formation of γ precipitates. For the first peak, the α1-plates start to nucleate at grain boundaries and grow dendritically upon heating. The primary and secondary arms of the dendritic α1-plates grow in two preferred directions, namely, [110]B2 and [100]B2 of the β′ matrix. However, the stacking faults in the two arms are parallel and differ from those with the structure of the twin-accommodating variants. As the thickness and number of α1-plates increase, the hardness of the alloy increases significantly; however, the recovery strain reduces dramatically. Additionally, the γ precipitates nucleate heterogeneously at the interface between the α1-plate and the β′ matrix on heating above 300°C. The volume fraction of the γ precipitates increases with temperature, resulting in a reduction in the ductility of the alloy and a complete loss of its shape memory effect.
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    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
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  • Experimental Investigation on Earing Behavior of Aluminum/Copper Bimetal Sheet

    pp. 2434-2443

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    DOI:10.2320/matertrans.47.2434

    The effect of post-annealing treatment on the texture evolution of an Al/Cu bimetal sheet as well as on the earing behavior was investigated. The earing behavior was tracked by means of measuring plastic anisotropy and deep drawing. The analysis texture evolution for as-rolled and annealed samples was performed by X-ray diffraction. The study results show that Δr⁄\\barr value increases and becomes positive when annealing temperature rises up to 300°C, in the meanwhile, a transition was observed from 45 to 0/90° earings. The mismatch in texture evolution between Al-side and Cu-side specimens was investigated. The typical recrystallization texture of Cu-side specimens mainly consists of a cube-orientation with its twins (CT) and cube texture develops at anneal temperature higher than 200°C. However, cube texture becomes the main component in Al-side specimen annealed at the temperature higher than 300°C. The mismatch in texture evolution between aluminum and copper has profound effect on the earing behavior of Al/Cu bimetal sheet. The analysis results of texture and plastic anisotropy were inductively reasoned to construct a prediction model of a Al/Cu bimetal material on earing. The earing behavior of Al/Cu bimetal material is depicted as a compromised result of the growth and decline in some certain texture components, which is agreement with the experimental findings obtained in this study.
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    Readers Who Read This Article Also Read

    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6
  • Fatigue Property of Ti-5Al-13Ta Alloy Dental Castings in 0.9% NaCl Solution

    pp. 2444-2447

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    DOI:10.2320/matertrans.47.2444

    The purpose of this study was to evaluate the fatigue property of Ti-5Al-13Ta alloy castings for dental application since dental prostheses are used under repetitive stress condition. Dumbbell-shaped cast specimens were prepared with a centrifugal casting machine and a magnesia-based mold material. Fatigue test was performed at 310 K in 0.9% NaCl solution under repetitive loading condition with the maximum cycles at 107. As a result, fatigue limit of Ti-5Al-13Ta alloy castings in NaCl solution was about 220 MPa, which was higher than those of CP-Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys, previously reported. Clear striation was observed at the crack propagation area on the fracture surface. The ratio of fatigue limit to UTS was suggested to be 30% for Ti-5Al-13Ta alloy castings; this value was higher than those for Ti-6Al-4V and Ti-6Al-7Nb alloys. It was concluded that Ti-5Al-13Ta alloy castings showed good fatigue property in 0.9% NaCl solution as an α+β high-strength titanium alloy for dental prostheses.
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    Readers Who Read This Article Also Read

    1. Mechanical Properties of Melt-Spun Amorphous Ni-Nb-Zr Alloys after Hydrogen Charging MATERIALS TRANSACTIONS Vol.47(2006), No.6
    2. Compressive Deformation Behavior of Nanocrystalline Al Alloys at High Temperatures MATERIALS TRANSACTIONS Vol.47(2006), No.6
    3. High Temperature Deformation of ZrC Particulate-Reinforced Nb-Mo-W Composites MATERIALS TRANSACTIONS Vol.47(2006), No.6

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