MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 47 , Issue 9
Showing 1-50 articles out of 56 articles from the selected issue
  • Takuya Ide, Masakazu Tane, Soong-Keun Hyun, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2116-2119
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Hirofumi Onishi, Soong-Keun Hyun, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2120-2124
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Satoshi Tsuda, Makoto Kobashi, Naoyuki Kanetake
    2006 Volume 47 Issue 9 Pages 2125-2130
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Aleksandra V. Byakova, Svyatoslav V. Gnyloskurenko, Alexander I. Sirko ...
    2006 Volume 47 Issue 9 Pages 2131-2136
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Tatsuya Ohmi, Masashi Takatoo, Manabu Iguchi, Kiyotaka Matsuura, Masay ...
    2006 Volume 47 Issue 9 Pages 2137-2142
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Teruo Takahashi
    2006 Volume 47 Issue 9 Pages 2143-2147
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Afsaneh Rabiei, Lakshmi Vendra, Nick Reese, Noah Young, Brian P. Nevil ...
    2006 Volume 47 Issue 9 Pages 2148-2153
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Ji-Hyun Lim, Ki-Ju Kang
    2006 Volume 47 Issue 9 Pages 2154-2160
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Masahiro Inoue, Soong-Keun Hyun, Katsuaki Suganuma, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2161-2166
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Shunkichi Ueno, Li Ming Lin, Soong Keun Hyun, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2167-2171
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Makoto Kobashi, Rui-Xue Wang, Yoshikazu Inagaki, Naoyuki Kanetake
    2006 Volume 47 Issue 9 Pages 2172-2177
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Makoto Kobashi, Ryosuke Sato, Naoyuki Kanetake
    2006 Volume 47 Issue 9 Pages 2178-2182
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Masakazu Tane, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2183-2187
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Carolin Körner, Markus Hirschmann, Harald Wiehler
    2006 Volume 47 Issue 9 Pages 2188-2194
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Jérôme Vicente, Frédéric Topin, Jean-Vincen ...
    2006 Volume 47 Issue 9 Pages 2195-2202
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Hidekazu Sueno, Masakazu Tane, Jae-Soung Park, Soong-Keun Hyun, Hideo ...
    2006 Volume 47 Issue 9 Pages 2203-2207
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Jae-Soung Park, Soong-Keun Hyun, Hidekazu Sueno, Masakazu Tane, Hideo ...
    2006 Volume 47 Issue 9 Pages 2208-2212
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Thomas Daxner, Robert D. Bitsche, Helmut J. Böhm
    2006 Volume 47 Issue 9 Pages 2213-2218
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Emiel Amsterdam, Norbert Babcsán, Jeff T. M. De Hosson, Patrick ...
    2006 Volume 47 Issue 9 Pages 2219-2222
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Koichi Kitazono
    2006 Volume 47 Issue 9 Pages 2223-2228
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Minoru Fuseya, Takuji Nakahata, Soong-Keun Hyun, Shinji Fujimoto, Hide ...
    2006 Volume 47 Issue 9 Pages 2229-2232
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Takayoshi Nakano, Tomoko Kan, Takuya Ishimoto, Yoshio Ohashi, Wataru F ...
    2006 Volume 47 Issue 9 Pages 2233-2239
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Tetsuro Ogushi, Hiroshi Chiba, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2240-2247
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Takuya Tsumura, Taichi Murakami, Hideo Nakajima, Kazuhiro Nakata
    2006 Volume 47 Issue 9 Pages 2248-2253
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Hiroyasu Yanagino, Takuya Tsumura, Hideo Nakajima, Soong-Keun Hyun, Ka ...
    2006 Volume 47 Issue 9 Pages 2254-2258
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Takeshi Kato, Takuji Nakahata, Hideo Nakajima
    2006 Volume 47 Issue 9 Pages 2259-2263
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Raphael Justin Joseyphus, Alwarramanujam Narayanasamy, Raghavan Gopala ...
    2006 Volume 47 Issue 9 Pages 2264-2268
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Francisca G. Caballero, Andrea García-Junceda, Carlos Capdevila ...
    2006 Volume 47 Issue 9 Pages 2269-2276
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Yu-ichi Yato, Masanori Kajihara
    2006 Volume 47 Issue 9 Pages 2277-2284
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Chihiro Watanabe, Daizen Watanabe, Ryoichi Monzen
    2006 Volume 47 Issue 9 Pages 2285-2291
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Mitsuharu Yonemura, Takahiro Osuki, Hidenori Terasaki, Yuichi Komizo, ...
    2006 Volume 47 Issue 9 Pages 2292-2298
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Bo Hong, Chuan-hai Jiang, Xin-jian Wang
    2006 Volume 47 Issue 9 Pages 2299-2301
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Norio Shinya, Junro Kyono
    2006 Volume 47 Issue 9 Pages 2302-2307
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Shengli Zhu, Xinmin Wang, Fengxiang Qin, Katsuhiro Abe, Hisamichi Kimu ...
    2006 Volume 47 Issue 9 Pages 2308-2311
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Zhongzhu Liu, Yoshinao Kobayashi, Jian Yang, Kotobu Nagai, Mamoru Kuwa ...
    2006 Volume 47 Issue 9 Pages 2312-2320
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • X. F. Zhang, X. D. Wang, K. B. Kim, S. Yi
    2006 Volume 47 Issue 9 Pages 2321-2325
    Published: 2006
    Released: September 23, 2006
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    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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  • Nobuo Nagashima, Saburo Matsuoka
    2006 Volume 47 Issue 9 Pages 2326-2334
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Takayoshi Fujino, Teppei Matzuda
    2006 Volume 47 Issue 9 Pages 2335-2340
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Yuki Matsuoka, Yasuo Matsunaga, Kiyokazu Nakagawa, Yoshihiro Tuda, Shi ...
    2006 Volume 47 Issue 9 Pages 2341-2347
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Airu Wang, Osamu Ohashi
    2006 Volume 47 Issue 9 Pages 2348-2352
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Shigeaki Sugiyama, Hitoshi Taimatsu
    2006 Volume 47 Issue 9 Pages 2353-2357
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Katuyoshi Arai, Wei Zhang, Fei Jia, Akihisa Inoue
    2006 Volume 47 Issue 9 Pages 2358-2362
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Yoshihiko Hangai, Soichiro Kitahara, Shigeyasu Amada
    2006 Volume 47 Issue 9 Pages 2363-2367
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Hiroyuki Y. Yasuda, Mitsuhiro Aoki, Yohei Fujita, Wataru Fujitani, Yuk ...
    2006 Volume 47 Issue 9 Pages 2368-2372
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Masanori Hara, Junichi Sakurai, Satoshi Akamaru, Kuniaki Watanabe, Kat ...
    2006 Volume 47 Issue 9 Pages 2373-2376
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Toshihiro Omori, Wataru Ito, Keisuke Ando, Katsunari Oikawa, Ryosuke K ...
    2006 Volume 47 Issue 9 Pages 2377-2380
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Keisuke Ando, Toshihiro Omori, Jun Sato, Yuji Sutou, Katsunari Oikawa, ...
    2006 Volume 47 Issue 9 Pages 2381-2386
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • Toshiyuki Kuribayashi, Mun-Gyu Sung, Takashi Itoh, Kensuke Sassa, Shig ...
    2006 Volume 47 Issue 9 Pages 2387-2392
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • QianLin Wu, Yangshan Sun, Caiding Yang, Feng Xue, Fengming Song
    2006 Volume 47 Issue 9 Pages 2393-2398
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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  • H. Takehara, H. Ino, T. Ohkubo, K. Hono
    2006 Volume 47 Issue 9 Pages 2399-2404
    Published: 2006
    Released: September 23, 2006
    JOURNALS FREE ACCESS
    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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