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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 1

  • Nanoscale Evaluation of Strength and Deformation Properties of Ultrahigh-Purity Aluminum

    pp. 1-5

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    DOI:10.2320/matertrans.48.1

    In order to investigate the strength and the deformation properties of metals in nearly perfect crystals, the nanoindentation test is performed on aluminum samples with various purities: 99.9999% (6 N), 99.99% (4 N) and 99% (2 N). It is widely known that the strength decreases with increasing purity of metals. On the nanoscale, however, the strength has been revealed to be close to the ideal shear strength, because a nanoscale area is expected to behave as a perfect crystal. In this study, a nanoindentation system that is able to provide indentation load vs penetration depth curves is employed. The experiment is performed on ultrahigh-purity aluminum (99.9999%), and high-purity aluminum (99.99%) and commercial-purity aluminum (99%) so as to discuss the relationship between the purity level and the mechanical properties at room temperature. It is revealed that the penetration depth decreases with increasing purity, and the critical shear stress estimated from the experimental results is close to the ideal shear strength. These results suggest that a perfect crystal is harder than an imperfect crystal. Furthermore, the indentation load vs penetration depth curves indicate a discontinuous deformation of the metals. It is considered that these discontinuities are caused by the existence of impurities or the initiation and the multiplication of dislocations in these samples.
  • Investigation on the Giant Magnetoimpedance of Fe89−xZr7B4Alx (x=0 and 2.5) Nanocrystalline Ribbons

    pp. 6-9

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    DOI:10.2320/matertrans.48.6

    In the present work, annealing effects upon the crystallization and giant magnetoimpedance (GMI) of Fe86.5Zr7B4Al2.5 ribbons were investigated, in comparison with the case of Fe89Zr7B4 ribbons. Annealing at 720°C for Fe89Zr7B4 results in the formation of mixture of α-Fe and Fe3Zr, and the appropriate addition of Al can restrain the Fe3Zr precipitation. The optimum annealing temperature for obtaining the largest magnetoimpedance is 650°C for Fe89Zr7B4, and is 720°C for Fe86.5Zr7B4Al2.5, where the permeability reaches its maximum value. The GMI effect depends not only on the permeability change with field, but also on the magnitude of the permeability itself. The reduction of the permeability and GMI at high annealing temperature is due to the occurrence of Fe3Zr precipitation and the coarsening of α-Fe grains. The maximum magnetoimpedance (ΔZZ0)max under applied magnetic field H=7162 A/m can reach −43.3% for Fe89Zr7B4, and −45.8% for Fe86.5Zr7B4Al2.5. The appropriate Al addition in Fe-Zr-B ribbon not only lowers the transverse anisotropy, but also improves the change slope of impedance at low fields (H<1000 A/m).
  • Structural Changes of Precipitates in an Mg-5 at%Gd Alloy Studied by Transmission Electron Microscopy

    pp. 10-15

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    DOI:10.2320/matertrans.48.10

    Structural changes of precipitates in an Mg-5 at%Gd (Mg95Gd5) alloy by aging at 200°C and 250°C have been studied by ordinary high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). In the early stage of precipitation by aging at 200°C up to 5 h, a short-range ordered structure exists in Gd-enriched regions with an about 2 nm size, and nuclei of an Mg7Gd structure (β′ phase) occur in the short-range ordered structure by aging at 200°C for 5 h. The β′ phase with the Mg7Gd structure is formed as definite precipitates by aging at 200°C for 10 h. The β′ precipitates are joined along the b-axis and form a plate-shape with a thickness of about 20 nm along the a-axis, and lengths of about 200 nm along the b-axis and 200 nm along the c-axis, and the connection of planar precipitates along the three directions, which are parallel to the [210]m-typed directions of the Mg-matrix, forms a two-dimensional cell structure, by top-aging at 200°C for 100 h.
  • Influence of Preservation in Two Kinds of Formaldehyde Solutions on the Fracture Characteristics of Bovine Femoral Compact Bones

    pp. 16-20

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    DOI:10.2320/matertrans.48.16

    For the evaluation of the physical properties of bones, specimens are often either deep-frozen or chemically fixed with reagents such as formaldehyde (formalin) or ethanol for antisepsis and sterilization. However, formalin contains formic acid, which dissolves bone minerals such as Ca and P. To suppress this bone mineral elution, we tested neutral buffered formalin as a fixative. In this study, we investigated the influence of formalin and the neutral buffered formalin fixation on the fracture characteristics of bovine femoral compact bones over a relatively long-term preservation period. In both the formalin and the neutral buffered formalin fixation, bone minerals migrated rapidly into the fixatives. Thus, some aqueous solutions such as a normal saline solution may also dissolve bone minerals. In the neutral buffered formalin fixation, fine calcium phosphate grains precipitated on the surface of the soft tissues of blood vessels in the Haversian canal, as observed by scanning electron microscopy. An element analysis with energy-dispersive X-ray spectroscopy also demonstrated the presence of Ca and P. Thus, the precipitated grains are assumed to be hydroxyapatite. In this study we evaluated the influence of formalin preservation, which reduces the fracture toughness of bovine femoral compact bones, and concluded that due to the formation of chemical bridges from the reaction of formaldehyde with the collagen fibers in the bones, the collagen fibers are cured and hardened, resulting in a reduction in the fracture toughness of the bovine femoral compact bones.
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  • Pitting Corrosion Resistance of Anodized Aluminum Alloy Processed by Severe Plastic Deformation

    pp. 21-28

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    DOI:10.2320/matertrans.48.21

    The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al and Al-Mg alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L of AlCl3 and by surface analysis. The time required for initiating pitting corrosion of anodized Al was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. However, in anodized Al-Mg alloy, the pitting corrosion occurred earlier with ECAP than without, showing that the corrosion resistance was worse with ECAP than without. SEM and EPMA observation revealed that pitting corrosion of anodized Al occurred around the impurity precipitates and that the size of the impurity precipitates decreased as a result of the ECAP. The improvement in pitting corrosion resistance of anodized Al by ECAP appears to be attributable to a decrease in the size of impurity precipitates. On the other hand, in anodized Al-Mg alloy, cracks occurred in the anodic oxide films during initial corrosion and the cracks were larger with ECAP than without. It is assumed that the pitting corrosion was promoted by the cracks due to the higher internal stress resulting from ECAP.
  • Preparation of ATO Nanoparticles from a New Composite Complex Salt

    pp. 29-31

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    DOI:10.2320/matertrans.48.29

    A new composite complex salt—(NH4)1.8(Sn0.9Sb0.2)Cl6 was synthesized at room temperature from the starting materials SnCl4·5H2O and SbCl3. Its XRD pattern was indexed. The ATO nanoparticles were then obtained by sintering the composite complex salt at various temperatures. Analyses revealed the obtained ATO nanoparticles are single phase belonging to tetrahedral rutile structure.
  • Influence of Porosity and Pore Size on Electrical Resistivity of Porous Aluminum Produced by Spacer Method

    pp. 32-36

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    DOI:10.2320/matertrans.48.32

    Porous Al specimens with a pore size range from 212–300 to 850–1000 μm and a porosity range from 77 to 90% were produced by the powder-metallurgical spacer method, and their electrical properties were experimentally investigated. The electrical resistivity increased with an increase in porosity; on the other hand, it was negligibly affected by the pore size when the pore size was sufficiently small. The experimental results agreed with the theoretical results obtained using the unit-cell model in which size of apertures at cell walls are taken into consideration. However, at the maximum pore size in the range investigated, the measured value was much higher than the calculated one. This is likely to be related to the large variation in the local density of the cross section.
  • Fine Pitch and Low Temperature Bonding Using Solder Bumps and the Assessment of Solder Joint Reliability

    pp. 37-43

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    DOI:10.2320/matertrans.48.37

    We developed a bonding at low temperature using fine pitch Sn and In bumps at 120°C, and studied the reliability of the fine pitch In-Sn solder joints. The 30 μm pitch Sn and In bumps were joined together without flux at 120°C for 2 minutes under 70.2 MPa. A non conductive adhesive (NCA) was applied during solder joining. Thermal cycling test (0°C–100°C, 2 cycles/h) of up to 2000 cycles and 1000-h temperature and humidity test (40°C/95%) were carried out to evaluate the reliability of the solder joints. The bondability was evaluated by measuring the contact resistance (Rc) of the joints through the four point probe method. The solder joints were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy. Joints between the In and Sn bumps were successfully made at 120°C. The average contact resistance of the In/Sn solder joints was 10–14 mΩ before thermal cycling. Without the NCA, the solder joints between the Si chip and glass substrate failed electrically in the early stages of the thermal cycling test. The failure in the solder joint during thermal cycling was attributed to the thermal expansion mismatch between the Si chip and glass substrate. In contrast, no electrical failures were observed in the joints with applied NCA even after 2000 cycles. The flip chip joints with applied NCA were stable up to 1000 hours in the temperature and humidity test.
  • Effect of Post Weld Heat Treatment on Microstructures and Mechanical Properties of AZ31B Friction Welded Joint

    pp. 44-52

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    DOI:10.2320/matertrans.48.44

    AZ31 magnesium alloy was welded by friction welding and the effect of post weld heat treatment on microstructures and mechanical properties were investigated. Fine grained microstructure whose minimum grain size is approximately 1 μm was formed at the weld interface by dynamic recrystallization due to hot-heavy working. Although abnormal grain growth which is often found in stir zone in friction stir welding occurred near weld interface where the material was work hardened, the area was limited and did not affect the mechanical properties of weld interface. The tensile and fatigue strength of as weld joints were equal to those of base metal and did not decrease until grain size increased to approximately 15 μm. The decrease in the Hall-Petch slope was found when the grain size decreased less than 3 μm in grain size in terms of yield stress.
  • Effect of Electromagnetic Vibrations on Fe-Co-B-Si-Nb Bulk Metallic Glasses

    pp. 53-57

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    DOI:10.2320/matertrans.48.53

    It is known that cooling rate from the liquid state is an important factor for producing the bulk metallic glasses. However, almost no other factors such as electric and/or magnetic fields were investigated. The present authors have reported that a new method for producing Mg-Cu-Y bulk metallic glasses by using electromagnetic vibrations is effective in forming the metallic glass phase. Moreover, the present authors have reported that the glass-forming ability of Fe-Co-B-Si-Nb alloys also is enhanced with increasing the electromagnetic vibration force. Thus, this study aims to investigate effects of the electromagnetic vibrations on Fe-Co-B-Si-Nb bulk metallic glasses in order to investigate further. Half round lines which consist of fine crystal particles in a glassy phase were observed in the boundary part of the molybdenum electrode for the alloy with the electromagnetic vibrations. It was considered that the reactants of the molybdenum electrode which were solid at 1573 K were moved into the sample by the electromagnetic vibrations and caused the nuclei of crystal particles which composed the half round lines. If tungsten was used as the electrodes, there was no influence of electrodes in the center of the samples. When molybdenum or tungsten was used as the electrodes, the effect of the electromagnetic vibrations was found to be the same, namely the electromagnetic vibrations act on decreasing the number of crystal nuclei.
  • Microstructures and Electrical Properties of Ru-C Nano-Composite Films by PECVD

    pp. 58-63

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    DOI:10.2320/matertrans.48.58

    Ruthenium-Carbon (Ru-C) nano-composite films were prepared by plasma-enhanced chemical vapor deposition (PECVD) and the effects of deposition conditions on the microstructure and electrical properies were investigated. The films consisted of agglomerated grains of 10 to 20 nm in diameter, in which Ru particles of 2.5 to 3.5 nm in diameter were dispersed in a C matrix. The C content of the films was about 90 vol%. The electrical properties of Ru-C nano-composite films as a catalytic electrode for an yttria-stabilized zirconia (YSZ) solid electrolyte were evaluated by AC impedance spectroscopy. The interfacial electrical conductivity at the Ru-C/YSZ interface was 0.2×10−3 Sm−1 at 500 K and increased with increasing temperature. The activation energy of the interfacial electrical conductivity was about 70 kJ/mol, implying an oxygen diffusion limited process at the interface.
  • Singular Effect of Carbon Fiber on the Oxidation of Dissolved Mn(II) Ions by a Fungus Genetically Related to Phoma sp.

    pp. 64-67

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    DOI:10.2320/matertrans.48.64

    Oxidation of Mn(II) ions in model drainages by a fungus genetically related to Phoma sp. was carried out in the presence of polyacrylonitrile-based carbon fiber, pitch-based carbon fibers formed at different heat treatment temperatures, and bamboo charcoal, aiming to understand the morphological effect of carbon materials on the microbiological activity of the manganese-oxidizing fungus. From the experimental results obtained so far, it was reasonably concluded that only carbon fiber accelerates the oxidation of dissolved Mn(II) ions by this fungus. When the carbon fiber shortened below certain length, the promoting effect was lost. The results strongly suggest that the shape of carbon, specifically the fibrous shape having flexibility, is a crucial factor in the promoting effect on the manganese oxidation by the present fungus.
  • Formation and Properties of New La-Based Bulk Glassy Alloys with Diameters up to Centimeter Order

    pp. 68-73

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    DOI:10.2320/matertrans.48.68

    New La-based bulk glassy alloys with superior glass-forming ability (GFA) were synthesized in La-Al-Ag-(Cu,Co,Ni) system. The addition of 5 at%Ag to La-Al-Cu ternary base system greatly increases the stability of supercooled liquid as well as the GFA. The largest supercooled liquid region and largest diameter in La-Al-Cu-Ag quaternary system were of 83 K and 6.0 mm, respectively, for La62.5Cu20Al12.5Ag5 alloy. The addition of Ni or Co to La-Al-Cu-Ag alloy is effective for the further increase in GFA. The maximum sample diameter of over 12 mm was fabricated for La62.5Al12.5Cu10Ni5Co5Ag5 alloy. The GFA has better correlation with reduced glass transition temperature. The new La-based bulk glassy alloys exhibit high fracture strength of 640–858 MPa with distinct plastic strains of 0.2–0.4%.
  • Preparation of Fe–Pt–Si Amorphous Ribbons and Their Coercivity after Crystallization

    pp. 74-79

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    DOI:10.2320/matertrans.48.74

    FexPtySiz (x=60–90, y=10–70, z=10–40) ribbons were prepared using a melt-spinning technique. Fully amorphous ribbons were obtained for alloys containing approximately 20–30 at%Si. Crystallization of the amorphous ribbons yielded composite structures of L10 FePt and Pt–Si intermetallic compounds for Fe45Pt35Si20 and Fe47Pt28Si25. Fe45Pt35Si20 amorphous ribbons were annealed at 700 K for 180 min, producing a grain size of approximately 40 nm in diameter, and a maximum coercivity of 160 kA/m.
  • WC/Co Coating on a Mild Steel Substrate through Underwater Shock Compaction Using a Self Combustible Material Layer (WC/Co Coating through Underwater Shock Compaction)

    pp. 80-83

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    DOI:10.2320/matertrans.48.80

    The explosive compaction technique has been applied to consolidate WC/Co powder to make a coating layer on a steel substrate, and the microstructure and some properties are investigated. Explosive compaction was performed using an improved method through underwater shock compression. Two types of assemblies, open and closed types were used for the experiments for generating relatively low and high pressure respectively. The effect of a thin nitrocellulose layer placed above the powders and the effect of the following heat treatment were investigated. In most of the experiments, the WC/Co layer was successfully recovered without cracks. The effects of applying higher underwater shock pressure, role of nitrocellulose as self combustible material and the following heat treatment showed positive effect to improve the properties by the increase of hardness as well as wear resistance of the coating layer.
  • Characterization of β′ Precipitate Phase in Mg-2 at%Y Alloy Aged to Peak Hardness Condition by High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM)

    pp. 84-87

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    DOI:10.2320/matertrans.48.84

    The β′ phase precipitated in an Mg-2 at%Y (Mg98Y2) alloy aged to a peak hardness condition at 200°C for 336 h has been studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). The β′ precipitates have an about 20 nm size and definite facets parallel to the (010) plane, and Y-enriched double atom planes parallel to the (010) plane grow long and sometimes individually along the [100] and [001] directions. This morphology of the β′ precipitates in the Mg98Y2 alloy is remarkably different from that in an Mg95Gd5 alloy.

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