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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 3

  • Surface Properties of a Nano-Quasicrystalline Forming Ti Based System

    pp. 278-286

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    DOI:10.2320/matertrans.48.278

    Two decades of intense research on quasicrystalline materials have suggested their potential use as surface coatings, considering their low coefficient of friction, high hardness, good corrosion and wear resistances and low surface energy. In that sense, quasicrystals could be introduced into the field of biomaterials since biomolecules are well known to be sensitive to solid surface properties. In this paper we report on investigations of the early stage of oxidation of the quasicrystals forming Ti45Zr38Ni17 alloy and its surface reactivity with respect to an amino-acid. After analysing the microstructure of as-quenched ribbons both by transmission electron microscopy and X-ray diffraction, surface oxide layers were characterized by X-ray Photoelectron Spectroscopy (XPS). Oxidation of Ti45Zr38Ni17 results in the formation of a ZrO2/TiO2 barrier oxide layer, avoiding toxic Ni release. This latter is mainly present at the oxide/alloy interface. Thereafter, adsorption of L-glutamic acid has been investigated by infrared spectroscopy. Even if this biomolecule is found to adsorb to each substrate, it seems to display different adsorption mechanisms on quasicrystalline ribbons compared to that on pure titanium (CpTi) or on pure zirconium (Zr), leading to a weaker signal on Ti45Zr38Ni17. We discuss these results along with the affinities of each alloying metal to oxygen and with the peculiar electronic properties of quasicrystals which could affect the surface properties of Ti45Zr38Ni17.
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    1. Formation of Titania/Hydroxyapatite Composite Films by Pulse Electrolysis MATERIALS TRANSACTIONS Vol.48(2007), No.3
    2. Fabrication of Functionally Graded Ti3SiC2–TiC Binary-Phase Material MATERIALS TRANSACTIONS Vol.48(2007), No.2
    3. Electron Irradiation Induced Crystallization of Supercooled Liquid in Zr Based Alloys MATERIALS TRANSACTIONS Vol.48(2007), No.2
  • Determination of the Immobilization Manner of Amine-Terminated Poly(Ethylene Glycol) Electrodeposited on a Titanium Surface with XPS and GD-OES

    pp. 287-292

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    DOI:10.2320/matertrans.48.287

    Poly(ethylene glycol), PEG, is a biofunctional molecule that inhibits the adsorption of proteins. Therefore, the immobilization of PEG on a metal surface is an important step in making metal surfaces biofunctional. The bonding manner of PEG to a titanium surface is significant for the design of PEG-immobilized materials; however, there are few characterization techniques for the determination of the immobilization manner of PEG. In this study, PEG terminated at one or both terminals with amine bases was immobilized on a titanium surface with electrodeposition and immersion. The electrodeposition was carried out with −5 V for 300 s. The immobilization manner of PEG was characterized using X-ray photoelectron spectroscopy (XPS) with an angle-resolved technique and glow discharge optical emission spectroscopy (GD-OES). As a result, not only electrodeposition but also immersion led to the immobilization of PEG onto a titanium surface. However, more terminated amines combined with titanium oxide as an ionic NH-O with electrodeposition, while more amines randomly existed as NH3+ in the PEG molecule with immersion. Moreover, the difference in the amine termination resulted in a different manner of bonding. The PEG terminated at both terminals immobilized in a U shape, and the PEG terminated at one terminal immobilized a brush. Characterization with XPS and GD-OES is useful to determine the immobilization mode of PEG to a solid surface.
  • Bioactive Ceramic Surface Modification of β-Type Ti-Nb-Ta-Zr System Alloy by Alkali Solution Treatment

    pp. 293-300

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    DOI:10.2320/matertrans.48.293

    Biomedical β-type titanium alloys have been developed or are under development all over the world. In particular, researchers in Japan have been developed Ti-29Nb-13Ta-4.6Zr alloy (TNTZ)—β-type titanium alloy—for biomedical applications. Bioactive ceramic surface modification is effective for further improvement in the biocompatibility of TNTZ. Calcium phosphate ceramics such as hydroxyapatite (Ca10(PO4)6OH2; HAP), β-calcium pyrophosphate (β-Ca2P2O7; CPP), and β-tricalcium phosphate (β-Ca3(PO4)2; β-TCP) exhibit bioactivity. In this study, the formability and morphology of HAP on the surface of TNTZ, covered with sodium titanate film by alkali solution treatment were investigated before and after immersion in a simulated body fluid (SBF).
    A reticulate structure with a considerable number of large cracks and mainly composed of sodium titanate and niobate films having a thickness of 400 nm to 800 nm is formed on the specimen surface of TNTZ after immersing in 3, 5, and 10 kmol·m−3 NaOH solutions for 86.4 and 172.8 ks. As the concentration of the alkali solution and the immersion time are increased, the formability of HAP improves because of the presence of a large amount of oxygen and the sodium in sodium titanate and niobate film. HAP is completely formed on the entire specimen surface of TNTZ immersed in the SBF for 1209.6 ks after immersing in 5 and 10 kmol·m−3 NaOH solutions for 172.8 ks. Alkali treatment at 333 K in 5 kmol·m−3 NaOH solutions for 172.8 ks is proposed to be an excellent condition to rapidly form HAP and fully cover the specimen surface of TNTZ with it. The bonding strength between TNTZ (alkali treatment at 333 K in 5 kmol·m−3 NaOH solutions for 172.8 ks) and HAP is around 2 MPa, which was half or less than half the value required for biomedical applications. The inclusion of a baking treatment after the alkali treatment in order to improve the bonding strength degraded the HAP formability. Furthermore, the formability decreases with an increase in the baking temperature.
  • Inhibition Effect of Zirconium Coating on Calcium Phosphate Precipitation of Titanium to Avoid Assimilation with Bone

    pp. 301-306

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    DOI:10.2320/matertrans.48.301

    In order to control of the calcium phosphate precipitation of Ti in body fluid, which might result in assimilated bone re-facture during removal operation of implanted devices such as femoral nails and bone screws after healing, vacuum vapor deposition of Zr on Ti Substrate was carried out. The calcium phosphate precipitation was evaluated through the immersion test into the Hanks’ solution. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were conducted to evaluate inhibition effect of coated Zr layer.
    Calcium phosphate particle were observed on the Ti with and without 90-nm thick Zr coated layer by SEM. On the other hand, on the specimens with 130-nm thick Zr coated layer and those of Zr sputter-coated, no calcium phosphate particle was observed. By the surface analysis of the specimens Zr sputter-coated, Ca was not identified. It was considered to form zirconium phosphate instead of calcium phosphate by immersion in the Hanks’ solution. It was suggested that Zr coating technique can be applied to orthopedic devices to avoid re-fracture of bone by calcium phosphate precipitation during removal operation.
  • Evaluation of Calcium Phosphate Coating Films on Titanium Fabricated Using RF Magnetron Sputtering

    pp. 307-312

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    DOI:10.2320/matertrans.48.307

    Calcium phosphate coating films fabricated on commercially pure titanium (CP-Ti) substrates using radiofrequency (RF) magnetron sputtering were evaluated in vivo and in vitro for investigating their applications in dental and medical implants. For the in vitro evaluations of the calcium phosphate coating films, the bonding strength and alkaline phosphatase (ALP) activity were examined. The bonding strength of the coating films to a polished titanium plate exceeded 60 MPa. When compared with an uncoated titanium plate, the increase in the ALP activity of SaOS-2 cells (a well-characterized osteosarcoma human cell line exhibiting osteoblast-like properties) on a titanium plate coated with a calcium phosphate film was confirmed by a culture test. Titanium cylinders coated with an amorphous calcium phosphate film were implanted into the mandibles of beagle dogs. The percentage of bone-implant contact in coated titanium was greater than that in uncoated titanium.
  • Control of β-Tricalcium Phosphate Formation in Macroporous Phosphate Glass-Ceramic Composites

    pp. 313-316

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    DOI:10.2320/matertrans.48.313

    A macroporous phosphate invert glass-ceramic (PIGC) was derived from the mother glass with a composition of 60CaO-30P2O5-3TiO2-7Na2O in mol%. The mother glass powders were coated on a polymer sponge skeleton and subsequently sintered at 850°C for 1 h through burning off the sponge, resulting in the preparation of macroporous PIGC. The resulting macroporous PIGC consists predominantly of β-tricalcium phosphate (β-TCP) and β-calcium pyrophosphate and has large-sized pores of 300–1000 μm in diameter and small-sized pores of several tens micrometer in diameter. A new type of composite containing a large amount of β-TCP was also prepared by heating the mixture of the mother glass powders with Ca(OH)2 at 800°C for 1 h. The amount of β-TCP in the crystalline phase of the composites increased with increasing the Ca(OH)2 amount. The β-TCP-containing glass-ceramic composites can be prepared by firing at a considerably lower temperature than a conventional β-TCP ceramics. The amount of β-TCP in the composites is controllable by variation of the Ca(OH)2 amount. The composites showed higher solubility in an acetic acid solution at 37°C with an initial pH value of 5.0 in comparison with PIGC. The solubility of one of the composites was comparable with that of pure β-TCP. The composites are expected to be applicable for biodegradable scaffold for bone tissue engineering.
  • Effects of Cross-Linking Agent on Apatite-Forming Ability and Mechanical Property of Organic-Inorganic Hybrids Based on Starch

    pp. 317-321

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    DOI:10.2320/matertrans.48.317

    So-called bioactive ceramics can directly bond to living bone through the apatite layer formed on their surfaces in the body. However, hard and brittle character of ceramics limits their clinical applications to low loaded portions. The apatite deposition on the bioactive ceramics is known to be triggered by a catalytic effect of silanol (Si-OH) groups formed on their surfaces and by release of calcium ions (Ca2+) that increases degree of supersaturation of the surrounding fluid with respect to the apatite. It is expected that organic modification of these components would produce bioactive materials with mechanical properties analogous to natural bone. We previously reported that bioactive organic-inorganic hybrids can be prepared from starch by modification with glycidoxypropyltrimethoxysilane (GPS) that provides with Si-OH groups and calcium chloride that releases calcium ions. In this study, we examined effect of synthetic conditions of the hybrids on their bioactivity and mechanical properties. We prepared several hybrids with different content of divinylsulfone as a cross-linking agent. Their bioactivity was examined in simulated body fluid (SBF, Kokubo solution) with inorganic ion concentrations nearly equal to those of human extracellular fluid. Materials that form the apatite on their surfaces in SBF are known to have a potential to show the bone-bonding. It was found that the added cross-linking agent did not decrease apatite-forming ability of the hybrids in SBF. Mechanical properties of the hybrids were further evaluated by a tensile test. Tensile strength and Young’s modulus increased with increasing content of divinylsulfone.
  • Formation of Titania/Hydroxyapatite Composite Films by Pulse Electrolysis

    pp. 322-327

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    DOI:10.2320/matertrans.48.322

    The aim of this study was to examine the formation of titania (TiO2)/hydroxyapatite (HAp) composite films on a titanium substrate using anodic-cathodic pulse electrolysis. The TiO2/HAp composites were coated on commercially pure titanium plates (surface area: 1.0 cm2) using pulse electrolysis in an autoclave in an aqueous solution that consisted of 0.3 mM Ca(H2PO4)2 and 0.7 mM CaCl2 and pH=5.5 at 120°C. The pulse potentials were applied at +8.7 V vs. Ag/AgCl sat. KCl as anodic potential and −9.3 V as cathodic. The total electrolysis time was 1800 s. We examined the effects of the electrolysis cycle (60∼600 s) and duty ratio on such properties of the coatings as the surface morphology, the amount of precipitated HAp, and the size of the HAp crystals. Prior to the pulse electrolysis, cathodic and anodic electrolysis experiments were also conducted. With pulse electrolysis, we could obtain TiO2/HAp composite films with fine HAp particles dispersed uniformly on a thin TiO2 coating.
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    3. Microstructure and Corrosion Resistance of Ti–Zr–Cu–Pd–Sn Glassy and Nanocrystalline Alloys MATERIALS TRANSACTIONS Vol.48(2007), No.2
  • Osteoinductivity of Titania/Hydroxyapatite Composite Films Formed Using Pulse Electrolysis

    pp. 328-331

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    DOI:10.2320/matertrans.48.328

    Titania (TiO2)/hydroxyapatite (HAp) composite films were prepared on commercially pure titanium rods (2 mm in diameter, 5 mm in length) by anodic-cathodic pulse electrolysis in an aqueous solution consisting of 0.3 mM Ca(H2PO4)2 and 0.7 mM CaCl2 and pH=5.5. The electrolysis was carried out in an autoclave at 120°C for 30 min. using +8.7 V vs. Ag/AgCl sat. KCl as the anodic potential and −9.3 V as the cathodic potential, and changing the electrolysis cycle (60∼600 s) and duty ratio. We obtained TiO2/HAp composite films in which fine HAp particles were uniformly dispersed on a thin TiO2 layer. The coated rods were implanted in the tibiae of 10-week-old male rats. The constructs were retrieved 14 days postimplantation and examined for new bone formation and tissue response in the cancellous and cortical bone. They were compared with HAp-coated titanium rods, TiO2-coated rods (anodizing in an aqueous solution), TiO2/HAp-coated rods formed by the high temperature oxidization of specimens coated with HAp by cathodic electrolysis, and uncoated titanium rods. Fourteen days after implantation, new bone had formed on all the coated samples (HAp, TiO2, and TiO2/HAp) and noncoated titanium rods in the cancellous bone and cortical bone. In particular, TiO2/HAp composite films prepared by pulse electrolysis had very high osteoinductivity, which resulted from a synergistic effect of HAp and TiO2 on the bioactivity.
  • Effect of Titania Doping on Phase Stability of Zirconia Bioceramics in Hot Water

    pp. 332-336

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    DOI:10.2320/matertrans.48.332

    The effect of titania doping on tetragonal to monoclinic (t-m) phase transformation of zirconia bioceramics is evaluated by ageing in hot water at 413 K. The examined materials are 3 mol%Y2O3 stabilized tetragonal zirconia polycrystal (3Y-TZP) and 1.5, 3.0 and 7.7 mol%TiO2-doped 3Y-TZP. The t-m phase transformation of 3Y-TZP is accelerated by titania doping in all the specimen examined. However, 7.7 mol%TiO2-doped TZP shows better phase stability than 1.5 or 3.0 mol%TiO2-doped one. This change in phase stability of 7.7 mol%TiO2-doped TZP cannot be simply explained from the difference of grain size or the change in the axial ratio, ca. XRD analysis reveals that the distance between nearest neighbor anion and cation site significantly decreases only in 7.7 mol%TiO2-doped TZP. This result indicates that the binding energy between dopant and oxygen vacancy affects the phase stability as well as the change in the axial ratio, ca.
  • Areal Distribution of Preferential Alignment of Biological Apatite (BAp) Crystallite on Cross-Section of Center of Femoral Diaphysis in Osteopetrotic (op/op) Mouse

    pp. 337-342

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    DOI:10.2320/matertrans.48.337

    Osteoclasts are nearly non-existent in mutant osteopetrotic (op/op) mice due to defects in the expression of the macrophage colony-stimulating factor (M-CSF). Thus, areal distribution of the biological apatite (BAp) c-axis in a femoral cross-section of an op/op mouse was investigated using a microbeam X-ray diffraction system to understand the role of osteoclasts on formation of BAp preferential alignment.
    The incident X-ray beam is focused to 20 μm in diameter. The diffraction analysis is performed at 20 μm displacement intervals from the periosteal surface along the radial axis of the anterior portion at a cross-section of the femoral diaphysis. The osteopetrotic (op/op) mouse and its normal littermate used as a control were 12 weeks old.
    The lack of osteoclasts induces both abnormality of the skeletal system and calcification of the medullary cavity, which are typical features of osteopetrosis. Preferential alignment of the BAp c-axis in the osteopetrotic (op/op) mouse always shows a lower degree than that in the control mouse, regardless of the distance from the periosteum. Moreover, areal distributions of preferential alignment of the BAp c-axis on the femoral cross-section show quite different tendencies between the op/op and control mice. The preferential alignment of BAp gradually increases towards the periosteal surface in the op/op mouse due to the intramembranous ossification, while that in the control mouse is the lowest near the cortical envelope on the cross-section. This is because the decrease in the number of osteoclasts suppresses the normal modeling or remodeling, resulting in degradation of preferential alignment of the BAp c-axis as a bone quality parameter in the op/op mouse.
  • Two-Dimensional Quantitative Analysis of Preferential Alignment of BAp c-axis for Isolated Human Trabecular Bone Using Microbeam X-ray Diffractometer with a Transmission Optical System

    pp. 343-347

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    DOI:10.2320/matertrans.48.343

    Two-dimensional quantitative analysis of microbeam X-ray diffraction (XRD) was performed using a transmission optical system to examine biological apatite (BAp) orientation in an isolated trabecula of a human fourth lumber vertebral body. The incident X-ray beam is 20 μm in diameter, which is small enough for the isolated trabecula despite a slight beam divergence of 0.2°. Integrated intensities of (002) and (310) are obtained separately by different incident angles and detector positions. Distribution of the preferential orientation of the BAp c-axis is finally calculated quantitatively as an integrated intensity ratio of (002)/(310) in a plane containing the trabecular direction.
    Preferential alignment of the BAp c-axis was finally determined to be perfectly parallel to the fiber direction in a rod-shaped trabecula, since accurate one-dimensional alignment is different from the alignment in the femoral cortical bone as a long bone that shows the local maximum of preferential alignment perpendicular to the longitudinal bone axis. For example, the integrated intensity ratio of (002)/(310) has a maximum value of 16 along the trabecular fiber and a minimum value of 0.09 in the perpendicular direction.
    Using this method, the anisotropy of BAp orientation in the trabecular bone can be quantitatively evaluated in the plane including the trabecular fiber. Thus, we successfully obtained a methodology that two-dimensionally analyzes the distribution of the BAp c-axis along all axes within a plane in a bone specimen.
  • Immobilized Heparin onto TiNi Shape Memory Alloy Modified with Acrylamide by UV-Induced Grafting

    pp. 348-351

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    DOI:10.2320/matertrans.48.348

    SiC:H organic-like thin films are deposited on Ti50Ni50 shape memory alloy by DC-pulsed plasma enhanced chemical vapor deposition (PECVD) in the gas mixture of Hexamethyldisilazane (HMDSN) and Ar at room temperature. The organic-like thin films containing peroxides or free radicals can be successfully grafted with hydrophilic polymer acrylamide (AAm) by UV-induced grafting polymerization. After grafting, a new dense organic and slippery surface with low friction coefficient is obtained. Heparin is finally immobilized onto grafted-AAm thin films to take TiNi SMA into the anti-thrombin biomaterials.
  • Evaluation of Biocompatibility for Titanium-Nickel Shape Memory Alloy in Vivo and in Vitro Environments

    pp. 352-360

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    DOI:10.2320/matertrans.48.352

    This study was conducted to evaluate the biocompatibility of titanium-nickel shape memory alloy used as a medical implant material. The authors carried out the following electrochemical corrosion test and in vivo and in vitro biological tests for the alloy and some metal and alloys clinically used previously to compare the intensities concerned with the biological reactions, that is, (1) anodic polarization test for the alloy in a quasi-body fluid, (2) cell proliferation tests for pure titanium (cp Ti), pure nickel (cp Ni), SUS316L stainless steel, titanium-6 mass% aluminium-4 mass% vanadium (Ti-6Al-4V), and titanium-55 mass% nickel (Ti-55Ni) by using of L929 fibroblastic cells, (3) Lactate dehydrogenaze (LDH), human interlukin-1β (hIL-1β), and human tumor necrosis factor-α (hTNF-α) biochemical assays by using of U937 human macrophages administered the corrosion products of these alloys for the cells, (4) measurement of the mount of excretions of the metallic corrosion products of Ti-55Ni, SUS316L stainless steel, and Ti-6Al-4V with urine and feces injected into the abdomen cavity of Wistar rats, and (5) tissue reaction observations for SUS316L, Ti-55Ni, and cp Ni wires implanted along the femoral bone axis of the rats.
    The following results were obtained. (1) The pitting corrosion potentials of Ti-55Ni alloy was drastically improved by the aging treatment. (2) In the case of Ti-55Ni alloy, the inflammatory cytokines, hIL-6β and hTNF-α were suppressed to lower levels compared with Ti-6Al-4V alloy. (3) Corrosion products prepared from the titanium alloys were stable in the body. Then it is very hard to eliminate the titanium ions with urine and feces. (4) Ti-55Ni alloy was shown an excellent biocompatibility evaluated by the in vivo implantation test, because of the stable passive film formed on the surface and protected the metal ion release to the surrounding tissue.
  • Cytocompatibility Evaluation of Ti-Ni and Ti-Mo-Al System Shape Memory Alloys

    pp. 361-366

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    DOI:10.2320/matertrans.48.361

    Cytocompatibility of nickel-free Ti-Mo-Al shape memory alloys was evaluated and compared with that of a conventional Ti-Ni shape memory alloy. Two types of cytotoxicity tests were performed; in static and dynamic conditions. In the static condition, human normal diploid fibroblast HEL299 was cultured on the disks of the three materials and cell growth was examined. In the dynamic condition, the disks were rotated in extraction medium with zirconia balls at 37°C for 14 days, and the collected extraction medium was added into HEL299 culture to examine its inhibitive effect on cell growth. Quantification of metallic elements in the collected extraction medium was also performed. The results showed that Ti-Mo-Al alloys had a rate of cell growth similar to that of Ti-Ni alloy in the static condition. The extraction medium of Ti-Ni alloy, however, tended to inhibit cell proliferation more than those of Ti-Mo-Al alloys. Nickel was detected in all of these extraction media, but that of Ti-Ni alloy was about three times higher than those of Ti-Mo-Al alloys. These facts indicate that developed Ti-Mo-Al alloys have higher cytocompatibility than the Ti-Ni alloy.
  • Orthodontic Tooth Movement in Rats Using Ni-Free Ti-Based Shape Memory Alloy Wire

    pp. 367-372

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    DOI:10.2320/matertrans.48.367

    The purpose of this study was to evaluate the performance and the usefulness of a newly developed Ni-free Ti-based shape memory alloy (SMA) wire in orthodontic tooth movement by comparing with a nickel-titanium (Ni-Ti) alloy wire. A Titanium-niobium-aluminum (Ti-24Nb-3Al) SMA wire, which was considered to be biocompatible because it contained no nickel, was newly developed and mechanical property of this new alloy was improved by severe cold rolling reduction. Twenty-one male Wistar-strain rats (age; 6 weeks) were used in the animal experiment. A Ti-Nb-Al alloy wire and an orthodontic superelastic wire (Ni-Ti alloy wire) were set in the oral cavities of rats, and orthodontic palatal movement of maxillary first molars was performed with an initial load of 15 gf. The amount of tooth movement was measured and periodontal structures were histologically examined. The Ti-Nb-Al alloy wire was effective for palatal tooth movement without any adverse reaction in rats. There was no significant difference in the amount of tooth movement between the Ti-Nb-Al group and the Ni-Ti group. Histological observation of the periodontal tissues revealed no differences between the two groups. These results indicate that Ti-Nb-Al alloy wire has excellent mechanical properties suitable for orthodontic tooth movement, suggesting that Ti-Nb-Al wire may be used as a practical nickel-free shape memory and superelastic alloy wire for orthodontic treatment as a substitute for Ni-Ti alloy wire.
  • Microstructure and Mechanical Properties of Alumina-Dispersed Magnesium Fabricated Using Mechanical Alloying Method

    pp. 373-379

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    DOI:10.2320/matertrans.48.373

    In order to improve the mechanical properties of magnesium, dispersion strengthening with α-alumina particles (pAl2O3) is experimentally investigated as an application of powder metallurgy. The trial process consists of milling, compacting and hot-pressing. The microstructure of hot-pressed discs of magnesium composites were investigated using optical microscopy, scanning electron microscopy, x-ray diffraction (XRD) and electron probe micro analysis, and the density, surface hardness, and bending stress for deflection were also examined. All of the mechanically alloyed (MA) prepared powders were composed of only magnesium (Mg) and alumina (Al2O3). Although the particle size of the MA powders varied, the mean values were approximately 80 μm and were approximately the half size of the raw Mg powder. Not only Mg powder, but also pAl2O3 became finer with processing, and the pAl2O3 was almost uniformly dispersed in the Mg powder. In addition, the fine pAl2O3 was almost uniformly dispersed within the Mg of the pAl2O3 dispersion strengthened (ODS) magnesium discs. For all discs, a small quantity of magnesium oxide (MgO) was identified along with Mg and Al2O3. However, in only the 22.7 vol% pAl2O3/Mg disc, an XRD peak assigned to an Al–Mg intermetallic compound (Al12Mg17) was detected, in addition to Mg, Al2O3 and MgO. It is proposed that Al12Mg17 was produced by the solid-state reaction of Mg and Al2O3, and appeared at the interface between the regions of only Mg and regions where pAl2O3 is dispersed in Mg. The density of the discs was above the theoretical density for all pAl2O3 content; the density for the highest pAl2O3 content of 22.7 vol% was approximately 0.8 times greater than that of practical Al alloys. The 22.7 vol% pAl2O3 disc had a maximum hardness value of 280 HV. This value is much higher than that of both pure Mg ingot and AZ91D. The bending stress for deflection decreased with an increase in the pAl2O3 content. The reason for this is considered to be that the discs become harder and more brittle, and voids are more easily formed in the discs; therefore, cracks that are generated on the specimen surface propagate more easily.
  • Comparison of Various Properties between Titanium-Tantalum Alloy and Pure Titanium for Biomedical Applications

    pp. 380-384

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    DOI:10.2320/matertrans.48.380

    The mechanical properties, corrosion resistance and biocompatibility of the titanium-tantalum alloys together with pure titanium are comparatively studied for biomedical applications in this study. The experimental results confirm the previous theoretic investigation that tantalum has a potential to enhance the strength and reduce the elastic modulus of titanium alloys at the same time, and indicate that the titanium-tantalum alloys are more suitable than pure titanium for biomedical applications because of their lower elastic modulus, higher strength and enhanced corrosion resistance than pure titanium used as a standard metallic biomaterial, and the same excellent compatibility to pure titanium.
  • Effects of Aging on Phase Constitution, Lattice Parameter and Mechanical Properties of Ti-4 mol%Au Near-Eutectoid Alloy

    pp. 385-389

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    DOI:10.2320/matertrans.48.385

    Effects of aging on phase constitution, lattice parameters and mechanical properties of Ti-4 mol%Au near-eutectoid alloy were investigated. The alloy was fabricated by Ar arc-melting method, followed by homogenization at 1273 K for 3.6 ks. The ingot was cold-rolled with 95% reduction in thickness, solution treated at 1173 K for 0.9 ks and quenched into ice water. It was found that the apparent phase after the solution treatment was a supersaturated solid solution of α (hcp) phase. This supersaturated α-phase is termed αm, hereafter. The apparent phase of the aged alloys was αm regardless of the aging temperature from 373 to 1073 K for 3.6 ks. The 0.2% flow stress was decreased as the aging temperature increased. On the other hand, by the isothermal aging at 973 K, Ti3Au with A15 structure was formed and the volume fraction of Ti3Au increased with increasing aging time. The 0.2% flow stress of the materials was decreased as the volume fraction of Ti3Au increased. This indicates that the Ti3Au precipitations are not effective on strengthening of the Ti-Au alloy.
  • The Effect of Al Content on Tensile and Fatigue Properties of Solution-Treated and Quenched Ti-13Cr-1Fe Alloys

    pp. 390-394

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    DOI:10.2320/matertrans.48.390

    The effect of Al content on tensile and fatigue properties of Ti-13Cr-1Fe alloys was investigated by measurement of electrical resistivity and Vickers hardness, X-ray diffractometry (XRD), and tensile and fatigue tests. Only β reflection was detected by XRD in all alloys quenched from 1173 K. Resistivity at room and liquid nitrogen temperatures increased monotonically with Al content. Vickers hardness slightly increased with Al content up to 4.5 mass%. In 6.0 mass%Al, the Vickers hardness increased dramatically. In 0 mass%Al and 3.0 mass%Al, the tensile strength (σB) and 0.2% proof stress (σ0.2) remained almost constant. Above 4.5 mass%, σB and σ0.2 increased with increasing Al content. S-N curves in high cycle fatigue test of 0 mass%Al and 3.0 mass%Al showed almost the same behavior. The stress at 107 cycles, i.e. the fatigue strength, was around 460 MPa.
  • Damping Capacity of Ti-Nb-Al Shape Memory β-Titanium Alloy with {001}β⟨110⟩β Texture

    pp. 395-399

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    DOI:10.2320/matertrans.48.395

    Damping capacity (tanδ) of Ti-24 mol%Nb-3 mol%Al (Ti-Nb-Al) shape memory alloy (SMA) with {001}β⟨110⟩β texture was examined upon cooling from 423 K to 123 K by dynamic mechanical analysis (DMA) in a tensile mode. The {001}β⟨110⟩β texture was well developed by a cold-rolling with reduction in thickness of 99% followed by a heat treatment at 873 K for 3.6 ks. The apparent phase of the material at room temperature was the β-phase (bcc) containing small amount of α-phase (hcp) and the martensite start temperature (Ms) of the β-α″(C-orthorhombic) thermoelastic martensitic transformation was about 250 K. The β-phase was equiaxed and averaged grain size was 2 μm. The angle between the longitudinal direction of the DMA specimens and the rolling direction (RD) was defined as φ and was 0, 30, 45, 60 and 90 degrees on the normal plane. Damping capacity, tanδ, depended on the stress-amplitude (σo) and φ. The peak height of tanδ during the martensitic transformation, Δtanδ, was proportional to σo for each φ and also proportional to the maximum transformation strain along the loading direction (εMAX) which is determined by the crystallography of the transformation. A proportional relationship between Δtanδ and σoεMAX was found and indicated that the interaction between the transformation and the applied stress plays an important role in the damping of the textured SMA.
  • Martensitic Transformation and Superelasticity of Ti-Nb-Pt Alloys

    pp. 400-406

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    DOI:10.2320/matertrans.48.400

    Shape memory properties and martensitic transformation of Ti-Nb-Pt alloys were investigated in order to develop Ni-free biomedical superelastic alloys. The effect of Pt addition on the transformation strain was investigated by measuring the lattice constants of the parent and martensite phases of Ti-Nb-Pt alloys. The Ti-Nb-Pt alloys were fabricated by arc melting. The ingots were cold-rolled up to 99% reduction in thickness. The cold-rolled specimens were heat treated at 873 K for 0.6 ks. The shape memory effect and/or superelastic behavior were observed in the Ti-Nb-Pt alloys. The martensitic transformation temperature decreases by about 160 K with a 1 at% increase of Pt in the Ti-Nb-Pt alloys. The addition of Pt as a substitute of Nb was effective to increase the transformation strain when compared with compositions which reveal similar transformation temperatures. An aging treatment at 573 K was effective for increasing the stress for inducing the martensitic transformation and the critical stress for plastic deformation, resulting in good superelasticity.
  • Effect of Boron Concentration on Martensitic Transformation Temperatures, Stress for Inducing Martensite and Slip Stress of Ti-24 mol%Nb-3 mol%Al Superelastic Alloy

    pp. 407-413

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    DOI:10.2320/matertrans.48.407

    Effects of boron (B) addition on martensitic transformation temperature, stress for inducing martensite and slip stress of a Ti-24 mol%Nb-3 mol%Al (TiNbAl) superelastic alloy were investigated in a composition range from 0 to 0.10 mass%B. It was found that a second phase is formed by the B addition being higher than 0.05 mass%B. This second phase was estimated to be TiB. The averaged grain size of TiNbAl was decreased by the B addition being higher than 0.05 mass%B. This decrease must be explained by the suppression of grain growth by the second phase. The second phase plays a role of pining sites of grain boundary movement during the solution treatment. The martensitic transformation temperatures (Ms) measured by differential scanning calorimetry were decreased by the B addition. Superelastic behavior was evaluated by a cyclic loading-unloading tensile test at room temperature with a constant strain increment of 1%, and it was found that superelasticity appeared regardless of the amount of B addition. It was also found that stress for inducing martensitic transformation (σSIM) increased with increasing B concentration up to 0.05 mass%B. This increase of σSIM by the B addition can be explained by the lowering of Ms by the B addition. The critical stress for slip (σSLIP) increased with increasing the B concentration being up to 0.05 mass%B. The increase of σSLIP by B addition was evaluated to be 3 GPa/mass%B, and it was significantly higher than that of σSIM (500 MPa/mass%B) when the B concentration was less than 0.05 mass%B. These results indicate that B addition is effective to reduce the permanent unrecoverable strain introduced during deformation.
  • Effect of Cu Addition on Shape Memory Behavior of Ti-18 mol%Nb Alloys

    pp. 414-421

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    DOI:10.2320/matertrans.48.414

    Shape memory characteristics of Ti-18 mol%Nb alloys containing 3, 4, 5 and 6 mol%Cu (termed Ti18Nb3Cu, Ti18Nb4Cu, Ti18Nb5Cu and Ti18Nb6Cu, respectively) were investigated and effects of Cu addition on shape memory behavior was clarified. The alloys fabricated by Ar arc-melting method were cold-rolled with 98% reduction thickness and solution-treated at 1273 K for 1.8 ks followed by quenching into water. It was found by θ-2θ X-ray diffraction analysis (XRD) at room temperature (RT) that Ti18Nb3Cu is composed of α″ (c-centered tetragonal)martensite phase and β (bcc) parent phase. The other alloys with higher Cu contents are β single phase. These results indicate that 6 mol%Cu is completely dissolved in Ti-18 mol%Nb alloys. Besides, the lattice parameter of β phase is decreased by Cu addition with a rate of 0.2×10−3 nm/mol%Cu, and then, the atomic radius of Cu in Ti-18 mol%Nb alloys is estimated to be 0.130 nm. By tensile test it was found that (1) shape recovery strain of Ti18Nb3Cu reaches 3% by heating after deformation, (2) Ti18Nb4Cu exhibits superelasticity at RT, and (3) either shape memory effect or superelasticity does not appear at RT for Ti18Nb5Cu and Ti18Nb6Cu. Besides, the stress for slip deformation is increased by Cu addition with a rate of 50 MPa/mol%Cu. By tensile tests at cryogenic temperatures, the martensitic transformation start temperature (Ms) of Ti18Nb5Cu is determined to be 75 K, and the Cu addition to Ti-18 mol%Nb alloys decreases Ms with a rate of 100 K/mol%Cu. Moreover, more than 5% in transformation strain is observed for Ti18Nb5Cu at 173 K. It was concluded that Cu is an effective additional element in order to improve shape memory and superelastic properties of Ti-Nb alloys.
  • Superelastic Behavior under Cyclic Loading for Coil Spring of Ti-Ni Shape Memory Alloy

    pp. 422-427

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    DOI:10.2320/matertrans.48.422

    The superelastic behavior of coil springs of a Ti-Ni shape memory alloy was investigated using loading-unloading cycling tests under isothemal temperatures. The effects of the Ni content and shape memory treatment temperatures on the cyclic behavior in the superelastic deformation were investigated. The deformation behavior within the elastic region of the parent phase scarcely changes during tensile cyclic loading. However, when a martensitic phase is induced by the stress, the deformation behavior changes considerably during cyclic loading. The critical shear stress for inducing martensites and the dissipated strain energy per cycle decrease with an increase in the number of cyclic loadings. Such changes in the superelastic behavior under cyclic loading become large with a decrease in the Ni content of the Ti-Ni shape memory alloy and the increase in the shape memory treatment temperature.
  • Bending Property of Super-Elastic Ti-Ni Alloy Dental Castings with Different Heat Treatments

    pp. 428-431

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    DOI:10.2320/matertrans.48.428

    Bending property of Ti-Ni alloy dental castings was evaluated in comparison with that of Co-Cr alloy in a cantilever test. Heat treatment effect on the bending property was also investigated in relation to phase transformation. Ti-50.85Ni (mol%) alloy was used, and the shape of bending test specimens was half-rounded in cross section, 2.0 mm in diameter. The bending test was carried out at 310 K. Distance between the loading point and the grip edge was 5.0 or 10.0 mm. Maximum bending deflection was 0.50 mm. Thermal behavior accompanying phase transformation of Ti-Ni alloy was examined by differential scanning calorimetry. Load-deflection diagrams of Ti-Ni alloy castings in the bending test showed elastic and super-elastic deformation, while those of Co-Cr castings showed elastic and permanent deformation. Maximum bending load and residual deflection of the Ti-Ni castings were lower than those of the Co-Cr castings and were decreased by heat treatment under a high-stress condition at the 5-mm loading point. Transformation temperature was increased by heat treatment, which was thought to influence the change in bending property. Super-elasticity of the Ti-Ni alloy castings in bending was shown to be improved by heat treatment, offering the potential to improve the design and clinical performance of cast dental prostheses.
  • Microstructural Evolution during Isothermal Aging in Ni-Rich Ti-Zr-Ni Shape Memory Alloys

    pp. 432-438

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    DOI:10.2320/matertrans.48.432

    Microstructural evolution during isothermal aging at temperatures ranging from 673 K to 773 K was investigated by transmission electron microscopy (TEM) for Ni-rich Ti-Zr-Ni alloys. It was revealed that the aging is a two-stage process: the first stage is characterized by circular diffuse scattering in electron diffraction patterns, most likely attributed to short range ordered structure with no significant microstructural change. Second stage is characterized by a fine coherent precipitation followed by the coarsening. The precipitates had a lenticular shape and their habit was {100}B2. The electron diffraction pattern of the sample containing the precipitates exhibited satellite spots at 1⁄3⟨110⟩B2 and 1⁄4⟨210⟩B2 positions. High resolution TEM observations and fast Fourier transformation analysis revealed that the ⟨100⟩B2 electron diffraction pattern was composed of the reflection from 4 variants of the precipitates. The two-stage microstructural evolutions coincide well with the previously reported changes in mechanical properties and martensitic transformation behavior.
  • Effect of Heat Aging on Thermal and Mechanical Properties of Ti-Ni-Nb Shape Memory Alloy

    pp. 439-444

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    DOI:10.2320/matertrans.48.439

    This paper describes the effect of heat aging on thermal and mechanical properties of shape memory alloy. The materials used in this study are Ti-Ni-(6–12 at%)Nb shape memory alloy. The tensile tests at 173 K and the heating-cooling tests under constrained strain condition were carried out using the specimens aged at 561 K for between 20 h and 1000 h in normal water chemistry. The martensite start temperature rapidly decreases in the initial short aging time, but there is little further decrease of the martensite start temperature with aging time more than 100 h. The recovery stress gradually increases with aging time, but on the contrary, the aging time of more than 500 h causes reduction of the recovery stress.
  • Effect of Nb Content on Martensitic Transformation Temperatures and Mechanical Properties of Ti-Ni-Nb Shape Memory Alloys for Pipe Joint Applications

    pp. 445-450

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    DOI:10.2320/matertrans.48.445

    Several Ti-Ni-Nb shape memory alloys (SMAs) with various Nb contents (0∼15 mol%) or Ni/Ti atomic ratios (1.0∼1.1) were tested to investigate the martensitic transformation temperatures and mechanical properties. The martensitic transformation temperatures (Ms, Mf, As and Af) of the solution-treated Ti-Ni-Nb alloys at 1173 K for 300 seconds with Ni/Ti ratio of 1.0 decrease with increasing the Nb content. These transformation temperatures also depend on the Ni/Ti ratio, heat treatment condition and cold working rate. Furthermore, in the alloy with Nb content of 6 mol% and Ni/Ti atomic ratio being less than 1.05, the fracture stress and fracture strain reached about 1,000 MPa and over 20%, respectively. Based on the obtained results, several processing conditions such as the chemical composition, fabrication process and heat treatment are optimized for the Ti-Ni-Nb SMAs to develop SMA pipe joints.
  • Magnetic Entropy Changes of SmMn2Ge2 under High Pressure

    pp. 451-454

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    DOI:10.2320/matertrans.48.451

    In order to obtain the information about magnetic states of reentrant ferromagnet, SmMn2Ge2, we have studied the pressure effect on magnetocaloric properties by magnetization measurements under high pressures up to 1.2 GPa in the temperature range from 5 to 300 K. Using the Maxwell relation, we estimated the magnetic entropy change |ΔSM| to be 0.65 JK−1mol−1 at T1 (=100 K) and 0.53 JK−1mol−1 at T2 (=150 K) under 0.1 MPa. By applying pressures up to 0.5 GPa, |ΔSM(T1)| is enhanced (2.0 JK−1mol−1), while |ΔSM(T2)| is slightly suppressed (0.4 JK−1mol−1). The obtained values of |ΔSM| were discussed on the basis of a mean field theory using a two-sublattice model.
  • Molecular Dynamic Simulation of Coalescence between Silver and Palladium Clusters

    pp. 455-459

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    DOI:10.2320/matertrans.48.455

    The coalescence between 135-Ag and 16-Pd clusters was studied through constant temperature molecular dynamic (MD) simulations at 300 K. Initially, the surface energy reduction was dominant. Later, some of the Pd atoms at the surface penetrated into the cluster and induced a further energy decrease. Surface atoms were rearranged to a local five-folded icosahedron structure (Ihp). Pd atoms gradually penetrated the cluster but did not segregate into the cluster core. As a result, a core-shell cluster structure was not observed, which could be explained by the strong mixing nature between Ag and Pd atoms and low kinetic energy.
  • Sample Length Dependence of Giant Magnetoimpedance in FeCuNbSiB Nanocrystalline Ribbons

    pp. 460-464

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    DOI:10.2320/matertrans.48.460

    In this work the sample length dependence of giant magnetoimpedance for Fe73.5Cu1Nb3Si13.5B9 nanocrystalline ribbons was investigated. The longitudinal magnetoimpedance ΔZZ0 for Fe73.5Cu1Nb3Si13.5B9 nanocrystalline ribbons decreases with the decreasing of sample length L due to the demagnetization effects. The demagnetization field lowers the permeability, especially for the very shorter sample. The magnetoimpedance ΔZZ0 experiences a peak under a field Hp due to the existence of transverse anisotropy. Different from the saturation behavior of Hp at high frequencies for longer sample with L=40 mm, there is a maximum phenomenon of peak field HP at about 700∼900 kHz for shorter sample with L=13 mm. With increasing ac frequency, the peak-magnetoimpedance (ΔZZ0)p also experiences a maximum value for both longer and shorter samples. The maximum peak-magnetoimpedance [(ΔZZ0)p]max shifts to lower frequency with reduction of sample length.
  • Crystal Structure and Magnetic Properties of Cr-Doped AlN Films with Various Cr Concentrations

    pp. 465-470

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    DOI:10.2320/matertrans.48.465

    We have studied the crystal structure and magnetic properties of Cr-doped AlN (Al1−xCrxN) films in the range of Cr concentration (x) of 0.04–0.37. The film changes from a wurtzite-type AlN phase for x=0.04–0.20 to a wurtzite-type AlN phase and zinc-blende-type AlN mixed phase for x=0.24, and further to only the zinc-blende-type AlN phase with increasing x. The Cr atoms are considered to occupy Al sites in spite of the change of AlN phase with x. Room-temperature (RT) ferromagnetism is not observed at any x. The magnetic state at 10 K of the film is considered to change from a paramagnetic state to a paramagnetic state or a superparamagnetic state, and further to a paramagnetic state as x increases. Ferromagnetic state is not observed at 10 K regardless of x.
  • Local Oxide Growth Mechanisms on Nickel Films

    pp. 471-475

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    DOI:10.2320/matertrans.48.471

    The oxidation characteristics of nickel thin films were investigated by atomic force microscopy (AFM) anodization. The anodization parameters, such as anodized voltages, oxidation times, pulse voltage periods and how they affected the creation and growth of the oxide nanostructures were explored. The results showed that the height of the nickel oxide nanodots grew as a result of either the anodization time or the anodized voltage being increased. The oxide growth rate was dependent on the anodized voltage and on the resulting electric field strength. Furthermore, as the electric field strength was at an order of 2×109 Vm−1, the anodization rate decreased quickly and the oxide dots stopped growing.
  • Transmission Electron Microscopy for Precipitate Phases in Rapidly Solidified Mg-2 at%Ce-1 at%Zn and Mg-2 at%Ce Alloys

    pp. 476-480

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    DOI:10.2320/matertrans.48.476

    Precipitate phases in Mg-2 at%Ce-1 at%Zn (Mg97Ce2Zn1) and Mg-2 at%Ce (Mg98Ce2) alloys, prepared by a melt-quenching method, have been examined by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). A precipitate phase formed at grain boundaries has an ordered structure with a hexagonal unit cell of \\sqrt3a0 and c0, in which a0 and c0 are lattice parameters of an h.c.p. structure of the Mg-matrix. On the other hand, a precipitate phase embedded in Mg-matrix grains has a long-period modulated structure formed by the appearance of two-dimensional anti-phase boundaries with a hexagonal symmetry in the fundamental hexagonal structure with lattice constants of \\sqrt3a0 and c0.
  • Microstructual Study of the Dissimilar Joints of Alloy 690 and SUS 304L Stainless Steel

    pp. 481-489

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    DOI:10.2320/matertrans.48.481

    This study was to characterize the microstructure of Alloy 690-SUS 304L stainless steel dissimilar weldments with Inconel 52 and 82 filler metals (I-52 and I-82). The weldments were butt-welded with gas tungsten arc welding. Microstructural analyses were conducted on the samples prepared from the middle of each fusion zone. Precipitates observed in the interdendritic region and along the grain boundary of the I-52 fusion zone were TiNs, while Ti-Nb-rich phases were detected in the I-82 fusion zone. In the root regions, Cr-carbides precipitated abundantly in the I-52, whereas few Cr-carbides were found in the I-82. The Cr content of the grain boundary was higher than 9 mass% in the root regions of both I-52 and I-82 welds. Owing to the dilution with base metal Alloy 690, the average Cr content was higher in the I-82 root region than in the cap region.
  • Influence of Frequency on the High-Temperature Fatigue Crack Growth Behavior of 17-4 PH Stainless Steels

    pp. 490-499

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    DOI:10.2320/matertrans.48.490

    The influence of frequency on fatigue crack growth (FCG) behavior was investigated for three differently heat-treated 17-4 PH stainless steels, namely unaged “Condition A,” peak-aged “Condition H900,” and overaged “Condition H1150,” at 673 and 773 K, and at frequencies ranging from 0.002 to 20 Hz. At 773 K, all heat-treated conditions exhibited similar FCG behavior in which no frequency effect was observed at frequencies higher than 2 Hz and the fatigue crack growth rates (FCGRs) increased with decreasing frequency below 2 Hz. The increase in FCGR at a lower frequency at 773 K was thought to be caused by a time-dependent, oxidation-assisted cracking mechanism. At 673 K, for a given heat-treated condition, the FCGRs increased with decreasing frequency at higher frequencies and leveled off at lower frequencies. Such an anomalous FCG behavior was attributable to a dynamic strain aging (DSA) effect. At a given frequency, when the temperature was increased from 673 to 773 K, the FCGR increased in Condition H1150, but decreased in Conditions A and H900 due to an in-situ overaging and precipitate-coarsening effect during the FCG test for the latter.
  • Dynamic Shear Behaviour of Unweldable Aluminum-Scandium (Al-Sc) Alloy

    pp. 500-509

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    DOI:10.2320/matertrans.48.500

    This study uses a torsional split-Hopkinson bar to investigate the shear response and fracture characteristics of unweldable Al-Sc alloy during mechanical testing at shear strain rates of 800 s−1, 1500 s−1, 2200 s−1 and 2800 s−1 and temperatures of −150°C, 25°C and 300°C. The experimental results show that both the shear strain rate and the temperature have a significant effect on the shear properties of the Al-Sc alloy. At a constant temperature, the shear stress, fracture shear strain, work hardening rate, yielding shear strength, work hardening coefficient, strain rate sensitivity and temperature sensitivity all increase with increasing strain rate. However, inverse tendencies are observed with increasing temperature at a constant strain rate. It is found that the Kobayashi and Dodd constitutive equation provides accurate predictions of the high strain rate shear plastic behaviour of unweldable Al-Sc alloy. SEM fractographic observations reveal that the fracture surfaces are characterized by a dimple-like structure. The density of the dimples increases with increasing strain rate at a constant temperature or with increasing temperature at a constant strain rate. SEM observations indicate that specimen fracture initiates at the interface of the matrix and the Al3Sc precipitates. Finally, twisted shear bands are observed on the equatorial plane of the gauge length section of the deformed specimens. The microhardness of these shear bands increases with increasing strain rate, but decreases with increasing temperature.
  • Microstructural Stability of Friction Stirred AA 2218 Alloy on Tensile Properties at Elevated Temperature

    pp. 510-514

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    DOI:10.2320/matertrans.48.510

    The microstructural features of Al-Cu 2218 alloy after FSP were composed mainly of equiaxed 4 μm grains as well as a much more random orientation in SZ comparing to the extruded base metal. In this investigation, tensile properties of FSP specimens displayed an advanced performance than base metal. Furthermore, it should be noted that the FSP specimens possessed great elongation which even more than 100% at 400 °C. As the test temperature over 450 °C, the deterioration of the elongation could be responsible to second phase particles coarsening during tensile deformation process as well as abnormal grain growth. Ductility was commonly degenerated in both base metal and FSP specimens at 500 °C, whole grains within FSP sample grew into large ones that conducted the seriously descent of ductility. It is rational to deduce that the tensile strain promoted the coarsening of particles that would resulted from Ostwald ripening phenomenon. The declination of elongation could be ascribed mainly to the microstructural stability problem at elevated temperature.
  • Fabrication and Corrosion Property of Novel Ti-Based Bulk Glassy Alloys without Ni

    pp. 515-518

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    DOI:10.2320/matertrans.48.515

    New Ni-free bulk glassy alloys in the Ti47.5Zr2.5+xCu37.5−xPd7.5Sn5 (x=0,5,7.5) system were fabricated by copper mold casting with diameters from 1 to 3 mm, which are expected to be applied as biomaterials. The structure, thermal stability and corrosion resistance were investigated by X-ray diffraction, differential scanning calorimetry and electrochemical measurement, respectively. Surface information after immersion in Hanks’ solution was also characterized by using XPS. The results indicate that the bulk glassy alloys examined are spontaneously passivated. By anodic polarization, they show the passive current densities between 10−2 and 10−3 A/m2. The higher corrosion resistance for the Ti-based bulk glassy alloys is attributed to the formation of stable and protective passive films enriched with titanium and zirconium.
  • Corrosion of CrN-Coated Steels in Liquid Pb-Bi

    pp. 519-525

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    DOI:10.2320/matertrans.48.519

    Corrosion tests of CrN-coated steels were conducted in liquid lead-bismuth (Pb-Bi) at 450°C and 550°C for 3000 h to investigate the applicability of CrN coating to a liquid Pb-Bi environment. CrN coatings on F82H (Fe-8Cr-2W-0.3V-0.04Ta-0.1C) and 316SS exhibited good compatibility in liquid Pb-Bi during corrosion test at 450°C. The CrN coating layer suffered heavy damage such as cracking and spalling, and showed no effectiveness as a protective layer in corrosion test at 550°C. Nickel and chromium in 316SS dissolved into Pb-Bi through the damaged coating layer at 550°C. It is considered that stresses caused by the difference of thermal expansion coefficients between CrN and steels led to cracking and spalling of the CrN coating through corrosion attack by liquid Pb-Bi at 550°C.
  • Submicron Structure of Rhenium-Base Diffusion Barrier Coating Layer on a Nickel-Base Superalloy

    pp. 526-530

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    DOI:10.2320/matertrans.48.526

    Cross sectional structure of a Re-based diffusion barrier layer coated on a Ni-based single-crystal superalloy has been investigated in sub-micron scale. The barrier layer was prepared by electroplating of a Ni-73 at%Re film onto the alloy substrate, followed by a Cr-pack cementation in a mixture of Ni-30Cr and Al2O3 powders at 1573 K for 36 ks in vacuum. The diffusion barrier containing 38 at%Re, 35 at%Cr, 16 at%Ni and few amount of Al was identified to be topologically close-packed σ-phase using electron backscattered diffraction method. Voids formed with precipitates in the diffusion barrier layer. Poly-crystallization and γ′-phase coarsening occurred in the superalloy substrate close to the Re-based alloy layer.
  • Microwave Heating of Thin Au Film

    pp. 531-537

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    DOI:10.2320/matertrans.48.531

    Thin Au film was prepared by sputtering and evaporation methods with a quartz substrate, followed by microwave irradiation in air (frequency of microwave: 2.45 GHz, incident flux of microwave: 563 W, irradiation time: 600 s). As a result, it was confirmed that microwave heating of thin Au film is feasible. The growth of crystalline and particles due to microwave heating was confirmed from AFM observation and XRD analysis.
    Thin Au film is continuously heated during microwave irradiation, regardless of a preparation method of thin film. Microwave heating depends on the amount of microwave absorption on a thin Au film, which is related to the thickness and microstructure of the thin Au film. The rate of temperature rise depends on the ratio of a thickness to resistivity of thin Au film.
  • Effect of Electromagnetic Vibration Frequency and Temperature Gradient on Grain Refinement of Pure Aluminum

    pp. 538-543

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    DOI:10.2320/matertrans.48.538

    The electromagnetic vibrations are applied to grain refinement of pure aluminum (99.7 mass%) and the effects of electromagnetic vibration frequency and temperature gradient on grain refinement are investigated. As the pure aluminum melt has been subjected to electromagnetic vibrations with a frequency range from 150 to 500 Hz, crystal grain has become small with increase of vibration frequency. To the contrary, the effect of refinement has become weak at the vibration frequency more than 1 kHz and this microstructure is similar to one of nonvibrated state. When the longitudinal temperature gradient in the specimen becomes gradual, refined area is remarkably extends. It is assumed that refinement by the electromagnetic vibrations is significantly affected by the temperature gradient.
  • Properties of Metal Injection Molded Products Using Titanate-Containing Binders

    pp. 544-549

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    DOI:10.2320/matertrans.48.544

    MIM parts usually require a green strength high enough to withstand handling, particularly after molding and before sintering. Thus, it is necessary to develop a binder system that can provide a high green strength without impairing molding and debinding properties. In this study, a titanate coupling agent was evaluated as a processing aid. The results showed that a higher green strength and a lower amount of swelling during solvent debinding were attained. Due to the presence of Ti atoms in the coupling agent, the sintered density and hardness also increased slightly. Scanning electron microscope observations confirmed that the presence of the titanate coupling agent resulted in improved bonding between the metal powder and the binder.
  • Determination of Cyclic-Tension Fatigue of Al-4Cu-1Mg Alloy Using Ultrasonic Shear Waves

    pp. 550-555

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    DOI:10.2320/matertrans.48.550

    Cyclic-tension fatigue of aluminum alloy, Al-4Cu-1Mg, was determined by an analysis of diffracted SH and SV waves, passing through the surface and reflecting the bottom of the specimen, respectively. The propagation time of SH waves and the internal friction of SV waves begins to decrease and increase from fatigue damage ratio (=NNf) of 0.5, respectively, suggesting noticeable increase of movable dislocation. From the analysis of SH waves along the direction to the loading axis, the damping ratio decreases and the phase advances with increasing of the degree of fatigue. Assumed from SH wave flux model, the former behavior correlates well with increasing of the residual stress by cyclic tension. The latter may be characterized by viscoelasticity. These results show that ultrasonic transmission method is useful probe for evaluation of fatigue in aluminum alloy.
  • Gas Emission Properties of the MgHx-Zn(BH4)2 Systems

    pp. 556-559

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    DOI:10.2320/matertrans.48.556

    The gas emission properties of MgH2-Zn(BH4)2 and Mg-Zn(BH4)2 systems have been investigated to design a new Metal-B-H system which has superior hydrogen storage properties. Thermal decomposition properties of two-layered samples with MgH2 on Zn(BH4)2, Mg on Zn(BH4)2, the mixture of Mg and Zn(BH4)2 and the mixture of MgH2 and Zn(BH4)2 were investigated by DTA-MS. The experimental results indicated that the B2H6 emission decreases in the case of the two-layered samples and the mixtures when compared with that of Zn(BH4)2, as a result of reaction of the solid MgH2 or Mg with B2H6. Then, the reactions between Mg and Zn(BH4)2 as well as MgH2 and Zn(BH4)2 were exothermic. In the case of the Mg-Zn(BH4)2 mixture, the reaction between Mg and Zn(BH4)2 surprisingly proceeded below 100°C before the decomposition of Zn(BH4)2 occurred. This indicates that the reaction between Mg and Zn(BH4)2 proceeds by a solid-solid reaction.
  • Kinetics of Hydrogen Isotope Absorption for Well-Annealed Palladium-Platinum Alloys

    pp. 560-565

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    DOI:10.2320/matertrans.48.560

    Absorption kinetics of protium and deuterium for Pd, Pd-4 at%Pt and Pd-8 at%Pt were studied in a dilute hydrogen concentration region in a temperature region from 274 to 357 K by means of constant volume method, where samples were annealed well at 973 K under vacuum before measurements to remove defects induced by sample preparation. It was found that protium had larger rate constants for adsorption, lower rate constants for desorption and larger diffusion constants than those of deuterium within the examined temperature region. The activation energy of hydrogen absorption for both hydrogen isotopes was almost null for all of the samples used. The activation energy of desorption for deuterium was smaller than that for protium. It was attributed to the difference in the enthalpy of hydrogen absorption into metal in dilute hydrogen concentration region between protium and deuterium. These features and trends observed in the alloying effect were supported by the ab initio calculations for small clusters.
  • Atom Probe Investigation of Ruthenium Distributions around Rhenium, Molybdenum and Tungsten in a Gamma Phase of 5th-Generation Nickel-Base Single-Crystal Superalloys

    pp. 566-569

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    DOI:10.2320/matertrans.48.566

    The three-dimensional atom-probe microanalysis was performed to investigate Ru distributions around Re, Mo and W in the γ phase of a fifth-generation nickel-base single crystal superalloys. Ru-concentration-frequency distributions within Re-, Mo- and W-centered spheres of 100 atoms in the γ phase were analyzed. Any concentration deviation of Ru around Re, Mo and W were not detected under the condition employed in the present study.
  • Effects of Inclusions on Fracture Toughness of Reduced-Activation Ferritic/Martensitic F82H-IEA Steels

    pp. 570-573

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    DOI:10.2320/matertrans.48.570

    Reduced activation ferritic/martensitic steels (RAFs) are recognized as the primary candidate structural materials for fusion blanket systems. F82H is the RAF which has been developed and studied in Japan, and F82H-IEA heat, one of the world’s first 5 ton heats of RAF, was provided and evaluated in various countries as a part of the IEA collaboration on fusion materials development. A problem with the steel is that some fracture toughness values obtained by 1T type of compact tension (1TCT) specimens showed very low values in ductile brittle transition region. There might be several reasons for the scatter, and one of them could be related to the microstructural inhomogeneity of F82H-IEA. In the present study, this possibility was investigated focusing on inclusions formed in a plate of F82H-IEA steel by scanning (SEM) and transmission electron microscopy (TEM) equipped with EDS.
    The plates examined in this study were obtained from F82H-IEA heat no. 9753, nominally Fe-7.5Cr-2W-0.15V-0.02Ta-0.1C, in mass%. Analyses by SEM and TEM for the plates revealed that Ta does not form MX precipitates, but instead, it forms composite Al2O3 – Ta(V,Ti)O oxide, or single phase Ta(V)O oxide. The composite inclusions are rather dominant in the plate obtained from the bottom of the ingot, but not in the plate from the middle of the ingot. SEM observations also revealed that composite oxide tended to be observed at the crack-initiation site. These results suggest that the scatter of toughness values may be correlated with this microstructural inhomogeneity.
  • Development of Methodology for Quantifying Collection Rate of Post-Consumer Products Based on Material Flow of Steel

    pp. 574-578

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    DOI:10.2320/matertrans.48.574

    Currently, some post-consumer products are not collected appropriately and remain or are disposed of by unknown ways. In order to conserve resources, the collection rate of such products should be increased. To date, few definitive methods to quantify the collection rate have been developed due to the difficulties in monitoring the amounts of the uncollected products. We have no other choice but to estimate the collection rate. In this paper, a new statistical method was developed to quantify the collection rate of post-consumer products. This method is based on the identification of dynamic material flow of steel used in several kinds of products. The steel-contained products were categorized into six categories: buildings, civil engineering, machines, automobiles, containers, and “others.” The collection rates of buildings, civil engineering, and machines were estimated. As the denominator of the collection rate, the amount of discarded post-consumer products during a year was calculated dynamically from their lifetime distributions and production history in which steel was used prior to that year. As the numerator of the collection rate, the amount of collected steel scraps for recycling domestically and exports was obtained from statistics. Furthermore, uncertainty derived from the lifetime distributions was considered in the calculations. The estimated collection rates obtained with these methods were 1.00 for buildings, 0.00 to 0.22 for civil engineering, and 0.39 to 0.52 for machines.
  • X-ray Diffraction Analysis of Rust Layer on a Weathering Steel Bridge with Surface Treatment Using Synchrotron Radiation

    pp. 579-583

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    DOI:10.2320/matertrans.48.579

    We have examined the structure of rust layer formed on a weathering steel bridge, to which the surface treatment, employing the effect of Cr2(SO4)3 sophisticatedly designed to form the protective goethite (α-FeOOH) rust layer which contains a certain amount of Cr, Cr-goethite, was applied in 1996, using X-ray diffraction at SPring-8 synchrotron radiation facility. It was shown that the formation of α-FeOOH was promoted and/or crystal growth of γ-FeOOH was suppressed by the surface treatment. The increase in the protective ability index (PAI) of the rust layer indicates that the protective goethite was predominantly formed under the effect of the surface treatment. In conclusion, it can be said that the surface treatment worked well to promote the formation of the protective goethite rust layer on the weathering steel bridge during the 10-year exposure.
  • Thermal Properties and Phase Stability of Zn-Sn and Zn-In Alloys as High Temperature Lead-Free Solder

    pp. 584-593

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    DOI:10.2320/matertrans.48.584

    The potential of newly-designed Zn-xSn (x=40, 30, and 20 mass%) and Zn-30 mass%In alloys as high temperature lead-free solders was evaluated, with particular focus on the fundamental thermal properties and phase stability during thermal and humidity exposure. From DSC results, the melting temperature of Zn-Sn alloys increased with decreasing Sn content, and the final undercooling was about 3 °C. The liquid fraction of the alloys calculated using Scheil’s model is lower than that of the alloys calculated according to the phase diagram by approximately 10 mass% at the eutectic temperature and 250 °C. The coefficients of thermal expansion (CTE) of Zn-Sn alloys increased with decreasing Sn content, i.e. 29.2×10−6·K−1 to 33.2×10−6·K−1 in the temperature range of −50 °C to 200 °C for Zn-Sn alloys and 31.3×10−6·K−1 in the temperature range of −50 °C to 140 °C for Zn-30In alloy. With increasing temperature above eutectic temperature, all alloys began to deform, indicating the formation of a liquid phase. The thermal deformation of Zn-Sn alloys decreased with increasing Sn content. The ultimate tensile strength (UTS) and 0.2% proof stress of the as-cast Zn-Sn alloys were almost the same, but the elongation of the as-cast Zn-Sn alloys decreased with increasing Sn content. After thermal and humidity exposure for 1000 h (85 °C/85% Relative Humidity), only the outer surface of Zn-Sn alloys oxidized. However, Zn-30In alloy rusted quite seriously resulting in Zn oxidation after 1000 h. The UTS and 0.2% proof stress of Zn-Sn alloy slightly decreased with increasing exposure time. The elongation of Zn-Sn alloys decreased with decreasing Sn content for 100 h exposure. However, the elongation of Zn-Sn alloys showed no further degradation beyond 100 h exposure.
  • Pb-Free Silver Conductive Paste with High Reliability

    pp. 594-599

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    DOI:10.2320/matertrans.48.594

    We have been engaged in developmental activities aimed at improving the properties of Ag conductive paste which can be used for various kinds of electronic components including circuit boards and both chip and high frequency components. By applying the uniform ceramic coating technology to Ag powder, we produced a variety of options to achieving the goal of lead elimination. The properties, namely solder leaching, adhesives strength (aging, heat cycles, strength in high heat and humidity) and migration, have successfully been improved to a level which is the same or higher than those of Ag/Pd (80/20) and Ag/Pt (99/1), which are currently used for conductive paste material. In this study, we succeeded in eliminating not only lead, but also frit, which, as a result, paves the way for the application of Ag conductive paste to high-frequency components, LTCC (Low Temperature Co-fired Ceramic) terminations and surface electrodes.
  • Effects of Microstructure on the Mechanical Properties and Stress Corrosion Cracking of an Al-Zn-Mg-Sc-Zr Alloy by Various Temper Treatments

    pp. 600-609

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    DOI:10.2320/matertrans.48.600

    The high strength Al-Zn-Mg alloy used in the aerospace industry is strengthened by coherent G.P. zones and semicoherent η′ phase. However, this series of aluminum alloys are susceptible to stress corrosion cracking (SCC), particularly when aged to the peak-aged state of T6 temper. In this study, the effect of microstructure on mechanical properties and stress corrosion cracking of the alloy was investigated for alloys tempered to T6, RRA, Two-Step and T7 conditions by tensile test in air, SCC test and polarization test in a 3.5%NaCl solution. It is shown that the improvement in SCC resistance correlates very well with the size of matrix precipitates and grain boundary precipitates. T7 temper can produce larger sizes of both the matrix precipitates and grain boundary precipitates than that of T6, RRA and Two-step tempers, causing a decrease in the length and density of dislocation lines, which results in the decrease of stress concentration at grain boundary and greatly improving the SCC resistance. The addition of Sc and Zr to high strength Al-Zn-Mg alloys has been found to simultaneously improve the tensile strength and SCC resistance.
  • Variation of Microstructure and Electrical Conductivity of Amorphous AgInSbTe and SbTe Films during Crystallization

    pp. 610-617

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    DOI:10.2320/matertrans.48.610

    Two kinds of chalcogenide films with similar Sb/Te atomic ratios, AgInSbTe (AIST) and SbTe (ST) were deposited on alkali-free glass using the RF sputtering method. The microstructure characteristics of both ST and AIST films were demonstrated to correlate with the electrical properties. TEM observation and GI-XRD profiles revealed that the structures of as-deposited AIST and ST films were amorphous characteristics. The sheet resistance of the as-deposited AIST films was twice as high as that of ST films and the effect of Ag and In additives was proposed. After annealing at 523 K for 1 h, the sheet resistance of both chalcogenide films decreased by four orders of magnitude due to crystallizations and the sheet resistance of crystallized AIST film was still twice as large as that of crystallized ST film. DSC measurement was used to determine the crystallization temperature of AIST films as 476 K and that of ST films as 445 K. The activation energies of crystallization were determined using Kissinger’s method, and 0.94 eV and 0.84 eV were obtained for AIST and ST films, respectively. TEM observations showed that AgSbTe2 phase exists in the AIST film after heat treatment in addition to δ-Sb phase. No indium compounds were discovered in the AIST film by the energy dispersive spectroscopy (EDS) and XRD measurements.
  • Microstructural Evolution of Friction Stir Processed Cast Mg-5.9 mass%Y-2.6 mass%Zn Alloy in High Temperature Deformation

    pp. 618-621

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    DOI:10.2320/matertrans.48.618

    Cast Mg-Y2-Zn1 alloy was friction stir (FS) processed to obtain fine grain structure. Then the elevated temperature tensile tests were carried out to investigate the deformation behavior of the FS processed alloy. The starting structure for FS processing was coarse dendritic microstructure (secondary dendrite arm spacing ca. 75 μm) with a plate-like second phase, which developed from inter-dendritic eutectic pockets after homogenization heat treatment. The α-Mg matrix and second phases were broken mechanically and distributed homogeneously by FS processing. The refined grain size at the fully stirred zone had the average size of ca. 2.0 μm. Different deformation behavior occurred as a result of varying microstructural evolution according to temperatures (623 K and 723 K).
  • Influence of Grain Size Distributions on the Resistivity of 80 nm Wide Cu Interconnects

    pp. 622-624

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    DOI:10.2320/matertrans.48.622

    The grain length distributions in the longitudinal direction of 80 nm wide Cu interconnects as a function of interconnect height and grain size influence on the resistivity have been investigated. Cu interconnects with 300 nm and 500 nm height had very similar average grain lengths when the trench depth was less than 260 nm, while for the 500 nm high Cu interconnect, larger grains were dominant when the trench depth was above 260 nm. Resistivity of the 80 nm wide Cu interconnect with 500 nm height was 10% lower than that for the 300 nm high interconnect.
  • Effect of Oxygen Partial Pressure on Structure and Dielectric Property of BaTi2O5 Films Prepared by Laser Ablation

    pp. 625-628

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    DOI:10.2320/matertrans.48.625

    BaTi2O5 ferroelectric films were prepared on MgO (100) substrates by laser ablation at various oxygen partial pressures (PO2). The effect of PO2 on the orientation, composition, surface morphology and dielectric property of the films was investigated. The molar ratio of Ti to Ba was independent of PO2, almost in agreement with the stoichiometric composition of BaTi2O5. The BaTi2O5 films showed the orientation of (710) and (020) depending on PO2. At PO2=12.5 Pa, (020) oriented BaTi2O5 film with an elongated granular and perpendicularly crossing texture was epitaxially grown on MgO (100) substrates. The BaTi2O5 film prepared at PO2=12.5 Pa exhibited a sharp permittivity maximum (ε′≈2000) at 750 K.
  • Preparation of Cu36Zr48Ag8Al8 Bulk Metallic Glass with a Diameter of 25 mm by Copper Mold Casting

    pp. 629-631

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    DOI:10.2320/matertrans.48.629

    The Cu36Zr48Ag8Al8 alloy exhibits very high glass-forming ability. We have succeeded in synthesizing a Cu36Zr48Ag8Al8 bulk glassy alloy with a diameter of 25 mm using the conventional copper mold injection casting. The absence of a crystalline phase was confirmed by X-ray diffraction and differential scanning calorimetry examinations. The critical cooling rate for formation of a glassy phase for the Cu36Zr48Ag8Al8 alloy was estimated to be less than 6.4 K/s. High glass-forming ability and high strength might contribute to its commercial application for the Cu36Zr48Ag8Al8 bulk metallic glass.
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  • Microstructural Changes during Microwave Heating of Ni52.5Zr15Nb10Ti15Pt7.5 Metal Glasses

    pp. 632-634

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    DOI:10.2320/matertrans.48.632

    This letter presents microwave sintering of Ni52.5Zr15Nb10Ti15Pt7.5 glassy alloy powder. It was observed that the alloy was heated well in the magnetic field maximum, while it was not heated enough in the electric field maximum. A sintered sample with a glassy structure was obtained at 843 K in an inert atmosphere (Ar).
  • Hydrogenation and Dehydrogenation Properties of [AlN-Pd]/Y and [AlOx-Pd]/[AlN-Pd]/Y Films

    pp. 635-636

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    DOI:10.2320/matertrans.48.635

    We report hydrogenation and dehydrogenation properties of the [AlN-Pd]/Y and [AlOx-Pd]/[AlN-Pd]/Y films. The [AlN-Pd] and [AlOx-Pd]/[AlN-Pd] composite cap layers were deposited on yttrium layers by a rf-magnetron sputtering method. The cap layers were used to protect the Y layers from oxidation. Electrical resistivity of the films was measured during a few cycles of hydrogen loading and unloading in order to monitor the hydrogenation and dehydrogenation of the Y layers. As repeating the cycles, the amplitude of resistivity change was gradually reduced for the [AlOx-Pd]/[AlN-Pd]/Y film. On the other hand, the [AlOx-Pd]/[AlN-Pd] protective layer showed much better stability against the high temperature steam than the [AlN-Pd] layer.

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