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

MATERIALS TRANSACTIONS Vol. 46 (2005), No. 2

  • Deformation and Recrystallization in Lightly-Rolled Aluminum Single Crystals of Cube Orientation

    pp. 141-144

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    DOI:10.2320/matertrans.46.141

    Deformation and recrystallization of 17%- and 34%-rolled aluminum single crystals of cube orientation were studied. Most slip bands observed in the TD surface were straight and the occurrences of cross-slip were small. There was a relatively large orientation variation in the TD surface and the deviation from the initial orientation reached 10° in the 34%-rolled sample. After annealing, recrystallized grains were formed both at the rolled surfaces and around the middle of the thickness of the sample. Two thirds of the recrystallized grains had ⟨111⟩-rotation relationships with the deformed matrix. Although all ⟨111⟩-rotation relationships were found, their occurrences were not the same. Above results are compared with those obtained in tensile-deformed aluminum single crystals with the same initial orientation.
  • Eutectic Phase Investigation in a Ca-added AM50 Magnesium Alloy Produced by Die Casting

    pp. 145-147

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    DOI:10.2320/matertrans.46.145

    The eutectic phase in a 1.72 mass pct calcium added AM50 die-cast alloy homogenized at 673 K has been investigated by X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The XRD and EDS experiments indicate that the eutectic phase consists of a Al2Ca phase with the C15 structure and contains 10.76 atomic pct magnesium in the equilibrium state. The solubility lobe of the Al2Ca phase lies parallel to the equi-66.7 at%Al composition line in the Mg-Al-Ca ternary grid, indicating that magnesium preferentially substitutes the calcium site of the Al2Ca phase.
  • Thermal Conductivity of Unidirectionally Aligned SiC Whisker Reinforced Al Alloy Matrix Composite with Interfacial Thermal Resistance

    pp. 148-151

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    DOI:10.2320/matertrans.46.148

    The effective thermal conductivities of unidirectionally aligned SiC whisker reinforced aluminum alloy matrix composites with different whisker diameters and volume fractions were measured from room temperature to 700 K. The thermal conductivity values parallel to the whiskers were found to be significantly higher than those in the normal direction. The thermal conductivities decrease as the whiskers’ volume fraction is increased or their diameter is decreased. Effective-medium theory was used to calculate the effective thermal conductivity of the composites with consideration of the interfacial thermal resistance. The calculated values are in good agreement with the experimental ones.
  • Appearance of a Novel Pressure Plateau in RNi5-H (R = Rare Earth) Systems

    pp. 152-154

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    DOI:10.2320/matertrans.46.152

    We investigated the hydrogen storage properties in a HoNi5-H system combined with TbNi5-H and DyNi5-H systems. Pressure-composition (P-C) isotherms in the HoNi5-H system show one reversible pressure plateau during hydrogen absorption and desorption with a hysteretic phase transition. The maximum hydrogen storage capacity was found to be H/HoNi5=ca. 2, and no second plateau similar to that observed in other RNi5-H (R: rare earth) systems was observed, even at 196 K. Two pressure plateaux found in light rare earth-based RLNi5-H (RL=La, Pr, Nd, Sm and Gd) systems tend to disappear in TbNi5-H and DyNi5-H systems and are scarcely present in HoNi5-H system. On the other hand, a novel pressure plateau appears at low hydrogen content in these systems due to the presence of a new hydride phase, and the plateau region extends from TbNi5-H and DyNi5-H to HoNi5-H systems. Contrary to the other plateaux, the pressures of the novel plateau during both hydrogen absorption and desorption decrease with decreasing unit cell volume of RNi5 compounds or with increasing atomic number of the R element in RNi5-H systems. To clarify the effect of 4f electrons in the R element in RNi5-H systems on the novel plateau, we have evaluated the hydrogen storage properties in an YNi5-H system. Our results show that YNi5 compound with lattice constants similar to those of TbNi5 and DyNi5 compounds has a similar P-C isotherm, suggesting that 4f electrons has no direct influence on the appearance of the novel plateau.
  • Effect of Silicate Ions on Conversion of Ferric Hydroxide to β-FeOOH and α-Fe2O3

    pp. 155-158

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    DOI:10.2320/matertrans.46.155

    Ferric hydroxide (Fe(OH)3) gel, prepared from FeCl3 and NaOH solutions, was aged at 100°C in the presence and absence of silicate ions to examine the effect of silicate ions on the conversion process of condensed Fe(OH)3 gel to iron oxides. The aged suspensions containing colloidal particles in each stage were separated into solid particles and supernatant solutions by centrifugation. X-ray diffraction measurements and transmission electron microscopic observations of the solid particles revealed that β-FeOOH was formed from the Fe(OH)3 gel and subsequently converted into α-Fe2O3, and the addition of silicate ions in the Fe(OH)3 gel decreased the conversion rate to β-FeOOH and α-Fe2O3 particles. IR measurements of the solid particles and inductively coupled plasma analyses of the supernatant solutions showed that the adsorption of silicate ions on specific plane of the solid particles was decisive factor for the suppression of the conversion process.
  • Atomic Structures and Magnetic Behavior of Small Ruthenium Clusters

    pp. 159-162

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    DOI:10.2320/matertrans.46.159

    Magnetism in clusters having upto 14 atoms of non-magnetic element, Ru is studied using the ab initio ultrasoft pseudopotential plane wave method and generalized gradient approximation for the exchange-correlation energy. The lowest energy structures are found to have no atom at the center upto n=14. The well known icosahedral structure for 13 atoms does not have the lowest energy. The calculated magnetic moments are in better agreement with experiments and tend to vanish faster as compared to Rh with an increase in size.
  • Diffusion of Refractory Elements in Ni-Al-X (X:Re,W) Ternary Alloys

    pp. 163-166

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    DOI:10.2320/matertrans.46.163

    In order to investigate the diffusivity of both W and Re in Ni-based superalloys, interdiffusion coefficients in Ni-Al-X (X=Re, W) ternary system, which is the fundamental system of Ni-based superalloys, were measured by an experiment using diffusion couples. A modified ternary Boltzmann-Matano method was employed for the evaluation of the interdiffusion coefficients. In the γ phase of Ni-2.5Al-4.3Re and of Ni-2.4Al-3.3W (mol%), the major interdiffusion coefficients were estimated to be \\ ildeDReReNi=2.2×10−15 m2/s and \\ ildeDWWNi=9.9×10−15 m2/s. It is found that \\ ildeDReReNi is much smaller than \\ ildeDWWNi. Also cross interdiffusion coefficients, |\\ ildeDReAlNi|<|\\ ildeDWAlNi| and \\ ildeDReAlNi,\\ ildeDWAlNi<0 were obtained in the γ phase. The interdiffusion coefficients give the Wagner’s interaction parameter between Re and Al, and between W and Al as εReAlWAl<0, indicating that the ordering tendency exists between Al and Re, and between Al and W.
  • Improvement in Oxidation Resistance of Cu-Al Dilute Alloys by Pre-annealing in H2 and Ar Atmospheres

    pp. 167-170

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    DOI:10.2320/matertrans.46.167

    The formation of protective Al2O3 thin layers on Cu-Al dilute alloys and their effect on the oxidation resistance has been investigated at high temperatures. Since selective and preferential oxidation of Al in Cu-Al alloys would take place under the very low oxygen pressures, Cu-Al (Al: 0.2∼2 mass%) alloys were annealed at various temperatures in H2 and/or Ar atmosphere. Continuous stable Al2O3 thin layers were formed on the specimens annealed in Ar after H2 annealing. Owing to the protective thin Al2O3 layers, the high temperature oxidation rates decreased to about 1/20 to 1/40 times lower than that of pure Cu.
  • Effect of Ammonia on the Crystal Morphology of Nickel Oxalate Precipitates and their Thermal Decomposition into Metallic Nickel

    pp. 171-174

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    DOI:10.2320/matertrans.46.171

    Morphology- and size-controlled nickel powder was synthesized via the thermal decomposition of nickel oxalate, which was prepared by mixing a solution containing nickel chloride hexahydrate (NiCl2·6H2O) and aqueous ammonia (NH3·H2O) with a solution of sodium oxalate (Na2C2O4) under controlled conditions. Nickel precursors ca. 1 μm long and 0.05 μm wide were obtained using 1.2 mol dm−3 aqueous ammonia and 0.2 mol dm−3 nickel chloride hexahydrate, pH 9.5, and 293 K. The morphology of the precursor changed from granular to needle-like with increasing aqueous ammonia concentration. Large dispersed needle-like particles were obtained at 353 K. Nickel metal powder was obtained that was needle-like or filament in shape depending on the heat treatment temperature of the needle-like nickel precursor.
  • Electronic Structure and Structural Transformation of Co1−xNi1+xAl (x=0, ±1⁄2)

    pp. 175-177

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    DOI:10.2320/matertrans.46.175

    To expand our knowledge of the martensitic transformation from a B2 to an L10 structure for ferromagnetic shape memory Co-Ni-Al alloys, we have performed first-principles band calculations for the supercell structures corresponding to Co1−xNi1+xAl (x=0, ±1⁄2) in a nonmagnetic state. From the investigation of total energy vs ca, we have found that the total-energy gain for x=0 due to the distortion is 3∼4 times as large as those for x=±1⁄2. This result indicates that the stabilization of an L10 structure becomes weak in a rich Co or Ni region compared with the composition of Co:Ni:Al = 1:1:1. We have discussed the result in terms of band energy and such components as CoAl, NiAl, CoNi and etc., which compose Co1−xNi1+xAl.
  • The Continuous Pressurized Sintering of a Metallic Powder Assisted by a Stepped Mold

    pp. 178-181

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    DOI:10.2320/matertrans.46.178

    A new industrial technique for the continuous pressurized sintering of metallic powders was proposed. A unique open mold with a step in its sintering room was employed in order to make the continuous production of sintered rods possible. This step added pressure to a powdered material in the mold, and the amount of pressure was controlled by a sectional reduction ratio at the step. Tin powder was extruded repetitiously into the mold, which was heated by a band heater attached near the step. It was confirmed that the above procedure successfully generated a stable pressure on the powdered material during sintering when it was fed into the mold. This sintering resulted in the production of a tin rod with a relative density of 99%. The longest sample produced in this study was about 70 mm, since in the case of longer samples the push rod was broken in the middle of the sintering by the friction due to the powder in the gap between the push rod and the mold. This failure must be avoided by improving the strength and precision of this system. It was indicated that the proposed sintering system has the potential for the continuous production of dense metallic rods.
  • High-Temperature Friction and Wear Properties of X-BaSO4 (X: Al2O3, NiAl) Composites Prepared by Spark Plasma Sintering

    pp. 182-185

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    DOI:10.2320/matertrans.46.182

    X-BaSO4 (X: Al2O3, Ni-Cr alloy and NiAl) composites were prepared by spark plasma sintering, and their friction and wear properties were investigated from at temperatures ranging from room temperature to 1073 K in air. The friction coefficients of the Al2O3-50 mass% BaSO4 composites varied from 0.2 to 0.4 at the temperature range. The NiAl-50 mass% BaSO4 composites and Ni-Cr alloy-based composites containing 50 mass% BaSO4 showed low friction coefficients at temperatures over 873 K, although their friction coefficients were higher than 0.5 at 473 K and 673 K. The wear rates of the Al2O3-50 mass% BaSO4 composites were much higher than those of the NiAl-50 mass% BaSO4 composites and Ni-Cr alloy-based composites containing 50 mass% BaSO4 at room temperature. In order to improve the wear resistance of the Al2O3-50 mass% BaSO4 composites, it would be necessary to use fine Al2O3 and BaSO4 powders and to add some sintering additives to the composites.
  • Effect of Sintering Temperature on Compressive Properties of Porous Aluminum Produced by Spark Plasma Sintering

    pp. 186-188

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    DOI:10.2320/matertrans.46.186

    Porous aluminum with a porosity of 78% and pore sizes of 850–1000 μm was produced by the spacer method including spark plasma sintering (SPS) at various sintering temperatures of 773–853 K and the dissolution of space-holding sodium chloride particles. The effect of sintering temperature on the compressive properties of porous Al was investigated. The stress-strain curves for the specimens fabricated at 813 K and higher exhibited a plateau region with a nearly constant flow stress to a large strain of about 40%. However, the specimens fabricated at less than 813 K showed no plateau regions, although there were no significant differences in the characteristics of the pores by macroscopic observation between the porous Al specimen fabricated at 843 K and that fabricated at 773 K. Microscopic observation revealed that there were large voids in the cell wall of the specimens fabricated at 773 K, showing that sintering was insufficient and the connection of Al powder was poor. Furthermore, the fully-dense Al specimen fabricated at 793 K exhibited poor ductility in tension. Therefore, poor ductility in tension of cell walls may be responsible for the lack of plateau regions in the specimens fabricated at less than 813 K.
  • Physicochemical Properties of Single Phase La2Zr2O7 Powder

    pp. 189-192

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    DOI:10.2320/matertrans.46.189

    Powders of La2O3 and ZrO2 in ethanol based suspension were planetary ball milled at 200 rpm for 12 hours, dried and then heat treated at 1500°C for one hour to synthesize single phase of La2Zr2O7 which is a very promising thermal barrier coating material. Planetary milling results to particle diminution together with an increase in surface area with increasing milling time as investigated by FE-SEM, particle size analyses and BET method. The formation of single phase La2Zr2O7 with pyrochlore structure was confirmed by X-ray diffraction and TEM analyses. DSC investigation on the milled powders revealed the dehydroxylation reaction at around 320°C and complete disintegration of ethanol including decarboxylation at around 500°C. The absence of these peaks in the thermal plot for the single phase material confirms its thermal stability at 1500°C sintering temperature.
  • Heat Treatment Effects on Microstructures and DBTT of F82H Steel Doped with Boron and Nitrogen

    pp. 193-195

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    DOI:10.2320/matertrans.46.193

    Effects of doping with 60 ppm B and/or 200 ppm N and heat treatments on the microstructures and the ductile-brittle transition temperature (DBTT) have been studied for ferritic/martensitic steel F82H. Prior austenitic grain size of standard F82H decreased from about 120 to 30 μm and also the DBTT decreased by about 50°C when the normalizing temperatures were changed from 1040 to 950°C. In case of F82H doped with B (F82H+B) normalized at 950°C the grain size increased from 30 to 40 μm and the DBTT increased by about 50°C as compared with that of the standard F82H. In case of F82H co-doped with B and N (F82H+B+N) the grain size and DBTT, however, were comparable to each one of the standard F82H. Localization of B and C with the size of a few μm at grain boundaries was observed in the F82H+B by using a time of flight-secondary ion mass spectroscope, but not in the F82H+B+N. The results indicated that the degradation of fracture toughness in F82H+B was caused mainly by the localization of B at the grain boundaries. The DBTT of F82H+B+N steels normalized at the temperatures from 950 to 1040°C was changed from −96 to −73°C, but the prior austenitic grain size remained nearly unchanged. The precipitate size, however, depended on the normalizing temperature. It was shown that the change of DBTT was related to the change in the mean size of the precipitates in the F82H+B+N steels.
  • Thermal Desorption of Hydrogen at the Titanium Hydride-Oxide Interface

    pp. 196-198

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    DOI:10.2320/matertrans.46.196

    Changes in hydrogen distribution in δ-phase titanium hydrides (TiH1.92∼1.95), covered with titanium oxide layers (TiO and TiO2), were investigated by elastic recoil detection analysis (ERDA) after isochronal and isothermal annealing experiments. The hydrogen concentration near to the surface of the hydride exponentially decreased as a function of annealing time in the temperature range from 423 to 523 K. The result shows that the thermal desorption of hydrogen from the hydride is governed by first-order reaction kinetics and greatly depends on the thermal detrapping process. The thermal detrapping rates of hydrogen at the hydride-oxide interface were estimated and their activation energy was determined to be 1.3±0.2 eV.
  • High-Temperature Plastic Flow in Pre-Annealed Zr-Al-Ni-Cu Bulk Metallic Glass in a Supercooled Liquid Region

    pp. 199-202

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    DOI:10.2320/matertrans.46.199

    High-temperature plastic flow in pre-annealed Zr65Al10Ni10Cu15 bulk metallic glass is examined in a supercooled region, in order to clarify the effect of the change in microstructure on high-temperature plastic flow. The specimen without annealing exhibits significant necking, but the elongation of 550% is obtained in the tensile test at 673 K and in a constant true strain rate of 1×10−2 s−1. In contrast, the specimen annealed at 673 K for 1.8 ks before the tensile test exhibits uniform deformation, and large tensile ductility of 1100% is obtained. In the specimen, initial stress decreases in comparison with that of the specimen without annealing, but apparent strain hardening arise during deformation. XRD analysis reveals that no crystalline phase is detected in the specimen without annealing even after deformation. In contrast in the specimen annealed at 673 K for 1.8 ks, the peaks from icosahedral phase are observed only in gage section but not in grip section after deformation. Strain hardening due to the precipitation and growth of icosahedral phase, which is enhanced by deformation, must make a positive contribution to neck stability, and results in the large elongation in the annealed specimen.
  • Formation of c-axis Aligned Polycrystal Hydroxyapatite Using High Magnetic Field with Mechanical Sample Rotation

    pp. 203-206

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    DOI:10.2320/matertrans.46.203

    It is possible to control the crystal alignment of non-magnetic materials such as anisotropic ceramics and polymeric materials using a high magnetic field. However, the alignment of the c-axis direction in hexagonal crystals, with a magnetic susceptibility of χca,b, is uncontrollable using a static magnetic field, because the c-axis can rotate in the plane perpendicular to the direction of the magnetic field. In this study, a high magnetic field and mechanical rotation are simultaneously imposed on a sample in order to align crystals parallel to that axis (c-axis) which has small magnetic susceptibility. This process of alignment was applied to hydroxyapatite (HAp) crystals and a sample was obtained, in which the c-axis of the HAp crystals aligned in a particular direction.
  • Effect of Heat Treatment on Cohesion of Films on Alkali-Treated Titanium

    pp. 207-210

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    DOI:10.2320/matertrans.46.207

    The cohesiveness of films on titanium was evaluated by a scratch test. The films were formed on titanium by immersion in an aqueous solution of NaOH (hereafter referred as “alkali-treated”) followed by heating at 500–700°C for 3.6 ks. The cohesion of the alkali-treated film was increased by the heat treatment, and the maximum cohesion was obtained by heating at 500°C. The film on alkali- and heat-treated titanium consisted of both microporous films and dense films. The microporous film furthest from the titanium surface was barely cohesive, whereas the dense film showed cohesion with titanium. The cohesion of film formed by alkali-treatment was increased on heating, but the formation of TiO2 (rutile) at the film–titanium interface on heating at and above 600°C caused a deterioration in the cohesion.
  • Effect of Zr Addition on Dynamic Recrystallization during Hot Extrusion in Al Alloys

    pp. 211-214

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    DOI:10.2320/matertrans.46.211

    The presence of Al3Zr precipitates promotes continuous dynamic recrystallization in Al-Zn-Mg alloys during hot extrusion, resulting in a fine-grained structure. The mechanism for this phenomenon was investigated by observing the change in microstructure under hot extrusion using high resolution EBSP. In the rear of the extrusion die mouth, grain boundary mobility is low since the flow stress is comparatively low and grain boundary migration is inhibited by Al3Zr particles. Thus, in order to reduce the deformation-induced high dislocation density, continuous dynamic recrystallization occurs, which does not involve long-range grain boundary migration, resulting in a finer-grained structure. The flow stress, and hence, the mobility of the grain boundary increase near the die mouth. This promotes long-range grain boundary migration, which reduces the dislocation density. Continuous dynamic recrystallization is not observed under these conditions. Since Al3Zr precipitates inhibit long-range grain boundary migration, increase of the Al3Zr precipitate content expands the region where continuous dynamic recrystallization occurs towards the die mouth, resulting in a finer-grained structure.
  • Oxidation Resistance of Mo Coated with Mo(Si,Al)2 Layer Prepared by Dipping into Liquid of Al-25 mass%Si alloy

    pp. 215-218

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    DOI:10.2320/matertrans.46.215

    A homogeneous layer of molybdenum alumininosilicide Mo(Si,Al)2 with C(40) structure was made on the sample surface of molybdenum by dip-coating technique using Al-25 mass%Si liquid at 1123 K. Adherent Al-Si was removed by soaking the dipped samples in the NaOH saturated hydraulic solution. The Mo samples coated with the Mo(Si,Al)2 layer were found to have excellent oxidation resistance in air even at 1473 K due to formation of a dense alumina film on the sample surface during oxidation. The formation of Mo5(Si,Al)3 layer was also observed at the interface between the Mo substrate and the Mo(Si,Al)2 layer.
  • Sedimentation of Substitutional Solute Atoms in In-Pb System Alloy under Strong Gravitational Field: Experiments and Simulations

    pp. 219-224

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    DOI:10.2320/matertrans.46.219

    Ultracentrifuge experiments were performed on a miscible alloy of In-Pb system to study the sedimentation of atoms and phase equilibrium under a strong gravitational field (maximum acceleration: 106 g level, temperature: below melting point (solid), starting state: intermediate α-phase (fct, c0a0<1), time duration: 30–150 h). All centrifuged samples formed graded structure. The Pb content continuously increased, and conversely, the In content decreased in the direction of gravitational field. For the centrifuged sample of 100 hours in time duration, Pb-rich phase (fcc) and In-rich phase (fct, c0a0>1) appeared at the strong- and weak-gravitational field sides of the sample, respectively, from starting state of α-phase, and the continuous changes in lattice parameters were observed in each phases. These observation results showed that the graded structure was continuous in atomic scale, and was formed by the sedimentation of substitutional solute atoms. Composition profiles of the centrifuged samples for 31.3 h, 60 h and 150 h showed that the composition change reached the steady state within 60 hours. As a result of the simulation of sedimentation process, the diffusion coefficient for sedimentation was estimated to be about 8 times larger than that for usual diffusion. The present result indicated that the diffusion mechanism of the sedimentation in this system was different from the conventional ones.
  • Giant Magnetoimpedance in As Cast Fe84Nb3.5Zr3.5B9−xCux Ribbons

    pp. 225-227

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    DOI:10.2320/matertrans.46.225

    In the present work the giant magnetoimpedance of Fe84Nb3.5Zr3.5B9−xCux as cast ribbons was reported. With increasing Cu content, the magnetoimpedance increases at first, experiences a maximum value at about x=3, and then decreases again at high Cu content. The value of magnetoimpedance ΔZZ0=(Z(H)−Z(0))⁄Z(0) for Fe84Nb3.5Zr3.5B6Cu3 (x=3) as cast ribbon is −37.5% under H=7162 A/m at 700 kHz. The large magnetoimpedance for Fe84Nb3.5Zr3.5B6Cu3 is connected with the strong change of transverse permeability. The grain size of α-Fe derived from (200) peak based on Scherrer’s equation is 19 nm for Fe84Nb3.5Zr3.5B6Cu3 (x=3), 13 nm for Fe84Nb3.5Zr3.5B5Cu4 (x=4) and 11 nm for Fe84Nb3.5Zr3.5B4Cu5 (x=5), respectively. The high Cu addition in Fe-(Nb,Zr)-B-Cu not only enhances the nucleation of α-Fe in as cast ribbon, but also reduces its grain size. The present experimental results indicated that Fe-(Nb,Zr)-B-Cu nanocrystalline materials with large magnetoimpedance can be fabricated with melting-spinning method without annealing.
  • Calcium Hydroxyapatite Thin Films on Titanium Substrates Prepared by Ultrasonic Spray Pyrolysis

    pp. 228-235

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    DOI:10.2320/matertrans.46.228

    Calciumhydroxyapatite thin films have been prepared by ultrasonic spray pyrolysis deposition on titanium substrate. The surface morphologies of the films formed at different deposition times were analysed by using SEM. The mechanism of the films formation was investigated in relation to the observed film morphology during the first stages of its formation, as well as to its consolidation to the final form. The chemical homogeneity of the synthesized films was determined by using EDS analysis, whereas the phase composition was determined by using XRD measurements and IR spectroscopy. The roughnesses and the thicknesses of the films were analysed by using surface profiler method. The continuous morphology films are obtained only for samples deposited more than 1.5 h.
  • The Effect of Silver Content on the Precipitation of the Al-4.6Cu-0.3Mg Alloy

    pp. 236-240

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    DOI:10.2320/matertrans.46.236

    The effect of Ag concentrations of up to 0.9 mass% on the precipitation of the strengthening phases in Al-4.6Cu-0.3Mg casting alloy were investigated. Microstructural features were elucidated by optical microscopy, electron probe X-ray microanalysis, measurement of electrical conductivity and differential scanning calorimetry. The microstructure was correlated with Rockwell hardness. The results revealed that the addition of Ag at a concentration of under 0.6 mass% promoted the precipitation of the Ω and θ′ phases and the augmentation of hardness of T7 tempered alloys. 0.9 mass% Ag caused the extensive precipitation of the Ω phase, but only mildly suppressed the precipitation of the θ′ phase, slightly increasing the hardness. The high density of the precipitates of the Ω phase is responsible for the excellent thermal stability and mechanical properties of the microstructure. The Ω precipitates out before the θ′ phase, and does so more quickly, during the aging process.
  • Characterisation of Precipitate Microstructures of Natural and Artificial Ageing in Al-Mg(-Ag) Alloys

    pp. 241-250

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    DOI:10.2320/matertrans.46.241

    In order to improve fundamental understanding of the ageing behaviour in Al-Mg(-Ag) alloys, the effects of trace additions of Ag on the precipitate microstructures of the Al-Mg alloys aged at temperature range 20 and 90°C was examined.
    The fine-scale and uniformly distributed spheroidal precipitate particles were formed in the ternary Al-10Mg-0.5Ag (mass%) alloy during the natural ageing process of periods of 16 months, while no precipitate particles were observed in the binary Al-10 mass% Mg alloy under the same ageing conditions. These fine scale, spheroidal precipitate particles observed in the ternary Al-10Mg-0.5Ag (mass%) alloy were identified as the β″ phase which has the ordered L12 structure with the lattice parameter of a=0.408 nm. The orientation relationship between the β″ phase and the aluminium matrix was of the form: (100)L12||(100)α, [001]L12||[001]α. The spheroidal precipitate particles having the ordered L12 structure in the Ag-modified alloys were unstable when the specimen was aged at 90°C.
    The plate-like precipitate particles were formed in binary alloys aged from 30 days at 90°C. The plate-like particles had habit planes of {100}α, and were identified as the β′ phase which is consistent with the metastable β′ phase (Al3Mg2, a=1.002 nm, c=1.636 nm) in Al-Mg alloys.
  • Grain-Size Strengthening in Equal-Channel-Angular-Pressing Processed AZ31 Mg Alloys with a Constant Texture

    pp. 251-258

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    DOI:10.2320/matertrans.46.251

    The effects of ECAP temperature and post-ECAP annealing on grain size, texture and mechanical behavior have been examined. The softening of ECAPed Mg alloys despite the considerable grain size refinement has been ascribed to the texture change during ECAP. The strength of the ECAPed AZ31 Mg alloys, however, increased with decrease in grain size following the standard Hall-Petch relation when the similar texture could be retained. Based on the present analysis, it could be concluded that it was practically hard to improve the strength of the Mg alloys significantly by grain-size refinement when ECAP was used, because texture softening effect was often more dominant over the grain strengthening effect.
  • Solvent Extraction of Gd from Chloride Solution with PC88A

    pp. 259-262

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    DOI:10.2320/matertrans.46.259

    Solvent extraction experiments of Gd from chloride solution with PC88A were conducted at different extraction conditions. Solvent extraction reaction was identified from the experimental results using a graphical method, and the corresponding effective equilibrium constant was determined by analyzing the ionic equlibria in a GdCl3 solution. In the experimental ranges investigated in this study, i.e., [GdCl3]≤0.3 kmol/m3, [PC88A]org≤3.0 kmol/m3 and initial pH≤2.3, solvent extraction reaction of Gd with PC88A and the corresponding effective equilibrium constant were obtained as follows Gd3++2H2A2,org=GdA3HAorg+3H+, Kex,eff=2.8×10−1.
  • Effects of Degassing and Fluxing on the Quality of Al-7%Si and A356.2 Alloys

    pp. 263-271

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    DOI:10.2320/matertrans.46.263

    A covering flux is commonly used to prevent an aluminum melt from reacting with the surrounding atmosphere or from re-oxidizing. In this study, melts were degassed with and without a covering flux using a porous bar diffuser. After degassing and holding, the melts were then poured to obtain chilled samples, reduced pressure samples and permanent mold castings. The chilled samples were polished and treated by ultrasonic vibration to reveal any foggy marks and the area of the foggy marks and the pore count were measured. The densities of the chilled samples and the reduced pressure sample were also measured to compute the relative porosities. The factors influencing the relative porosities of the aluminum alloy castings were then discussed. Rotational bending fatigue tests were also conducted to assess the effect of the pore count and the relative porosity on the fatigue life cycles of the A356 alloy castings.
  • Production of Tantalum Powder by External Continuous Supply of Feed Materials and Reductant

    pp. 272-276

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    DOI:10.2320/matertrans.46.272

    In order to produce high-quality tantalum powder of spherical shape with a uniform particle size and a high purity using a metallothermic reduction process, it is important to control the reaction temperature and reaction rate. In this study, we developed a metallothermic reduction method using a system supplying materials continuously from an external unit where the feed materials of K2TaF7 and the reductant Na were continuously supplied to control the reaction temperature and reaction rate.
    The characteristics of tantalum powder produced by the continuous supply system were compared with those of tantalum powder produced by a batch system in which, all of the feed materials and reductant were supplied into the reaction vessel at one time. We could obtain tantalum powder with a spherical shape and a uniform particle size with a diameter of 2∼3 μm because we used the external continuous supply system where the reaction temperature and reaction rate could be well controlled.
    After deoxidation, dehydration, and heat treatments, the purity of the tantalum power reached 99.5 mass% level of the reagent grade. The yield of tantalum powder increased from 80% in the batch system to 90% in the external continuous supply system.
  • Effects of Sputter Order and Oxide Layer on Amorphous Formation of Zr-Ni Thin Film System

    pp. 277-280

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    DOI:10.2320/matertrans.46.277

    Effects of the sputtering order and the presence of an oxide layer on an amorphous metal layer formation of zirconium-nickel bilayer thin films annealed at 623 K (350°C) have been investigated. Nickel species are found to diffuse preferentially from the nickel layer into the zirconium layer in Zr/Ni bilayer thin film. From this diffusion, the amorphous phase and voids are formed. However, by the change of the sputtering order and with the formation of a Zr oxide layer, the amorphous and voids are not formed. This indicates that nickel species migrate into the amorphous layer by means of vacancies. Vacancies are supplied from the zirconium-free surface.
  • Formation of Poly(2-vinylpyridine) Films on Zn by Galvanostatic Electropolymerization

    pp. 281-286

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    DOI:10.2320/matertrans.46.281

    Poly(2vinylpyridine) films were deposited on Zn substrate by electropolymerization using a galvanostatic technique at 30°C in pH 5 aqueous solution containing methanol. Films were also formed by employing cyclic voltammetry and potentiostatic techniques; these were compared with those formed using galvanostatic electrolysis. The thickness of films formed by galvanostatic electrolysis increased in proportion to the amount of charge passed during electropolymerization but decreased with increasing current density because of increased hydrogen evolution. The FT-IR spectra and the color of the films suggested that the structure of poly(2-vinylpyridine) films changed from the non-branched to the branched chain type at higher current densities. The anodic current density for Zn dissolution in 3% NaCl solution was significantly decreased by coating with poly(2-vinylpyridine) films. After electropolymerization at 50 A m−2, the anodic reaction was most inhibited, showing excellent corrosion resistance. Although the electrochemical techniques employed had no influence on the thickness or the structure of films, the films formed by galvanostatic electrolysis contained the fewest cracks and gave the best corrosion resistance.
  • Changes of Shape and Stress Distribution during Free Bulging in Axisymmetrically Blow-Formed Superplastic Sheet

    pp. 287-291

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    DOI:10.2320/matertrans.46.287

    Changes in the shape and stress distributions during free bulging in axisymmetrically blow-formed superplastic sheets are analyzed. Generally, the shape is assumed to be spherical and the stress distribution is a function satisfying only boundary conditions without any theoretical bases, because of the nonlinear constitutive equations of superplasticity. An assumed stress distribution function gives a particular pressure distribution on the workpiece. If the pressure distribution is uniform, the function represents a true distribution of stress. Such a function is proposed in this paper and is verified by the analysis without these additional assumptions. With progress in forming, all areas except those in the neighborhood of the periphery approach the equi-biaxial tensile stress state and the entire shape approaches that of a hemisphere.
  • Bonding Characteristics of Various Metals by DC Pulse Resistance Heat Pressure Welding

    pp. 292-297

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    DOI:10.2320/matertrans.46.292

    The characteristics of various metals bonded by DC pulse resistance heat pressure welding using spark plasma sintering (SPS) process are investigated. As the results of the experiments, the SPS process is found to complete heat pressure welding in a much shorter processing time than the conventional hot pressing process because the SPS process supplies the electric resistance energy directly to the specimens. In addition, the following conclusions are obtained: (1) Bonding strengths of 130∼200 MPa between Al-11.5 mass%Si alloy and Al-20.0 mass%Si alloy including SiC particles can be obtained with the application of titanium powder at the interface. (2) For the combinations of similar metal, complete bonding, that is, a bonding ratio of approximately 100%, can be obtained. However, sufficient bonding strength cannot be obtained for the combination of cemented carbide. (3) Dissimilar steels can be bonded with a bonding ratio of more than 70%. (4) A bonding strength is reduced for the combinations of titanium alloy and other metals, because of the formation of some intermetallic compounds at the interface.
  • Effect of Heating Rate and Phase Transformation on the Dimensional Control of Ferrous PIM Compacts

    pp. 298-302

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    DOI:10.2320/matertrans.46.298

    Powder injection molded (PIM) parts usually show large amounts of shrinkage after sintering due to the low powder loading, resulting in poor dimensional stability. This problem is further aggravated when a high shrinkage rate occurs or when the furnace temperature is not uniform. To alleviate this dimensional control problem, the effects of the phase transformation, sintering temperature, and heating rate were investigated. The results show that when an abrupt volume change occurs, as happens during the α→γ phase transformation of iron, the dimensional stability deteriorates. This problem gets worse when the density of the part is low. By slowing down the heating rate in the region where the high shrinkage rate occurs, avoiding the phase changes, and adding alloying elements to broaden the temperature range of the phase transformation, the dimensional control of ferrous PIM compacts can be improved.
  • Induction Brazing of γ-TiAl to Alloy Steel AISI 4140 Using Filler Metal of Eutectic Ag-Cu Alloy Coated with Ti Film

    pp. 303-308

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    DOI:10.2320/matertrans.46.303

    The induction brazing of TiAl to alloy steel AISI 4140 was carried out using a filler metal of eutectic Ag-Cu alloy coated with Ti film. The brazement was comprised of Ag-rich, Ti-rich, CuTi and CuTi2 phases at a brazing temperature of 1073 K. Two reaction layers, AlCuTi and AlCu2Ti phases, were observed between the filler metal and TiAl. The consumption of Cu to form these intermetallic compounds during brazing resulted in the increasing amount of Ag-rich and Ti-rich phases in the brazement with increasing the brazing temperature and time. The maximum tensile strength of the joints, 294 MPa, was achieved at 1073 K for 60 s, which was 71% of that of the TiAl base metal. The mechanical strength of the joint decreased with increasing the brazing temperature and time due to the growth of brittle reaction products at the interface. The fracture mode of the specimen brazed at 1073 K for 60 s was a mixed mode, consisting of 16% TiAl base metal fracture and 84% interface fracture through the AlCu2Ti and AlCuTi phases. However, the fracture location shifted toward the interfacial reaction layers with increasing the bonding temperature and time.
  • Nanocrystalline Manganese-Molybdenum-Tungsten Oxide Anodes for Oxygen Evolution in Acidic Seawater Electrolysis

    pp. 309-316

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    DOI:10.2320/matertrans.46.309

    In an attempt to tailor new oxygen evolution anodes for acidic seawater electrolysis, manganese-molybdenum-tungsten oxide anodes were prepared by anodic deposition on IrO2/Ti substrate using 0.2 kmol m−3 MnSO4-(0.00–0.006) kmol m−3 Na2MoO4-(0.0–0.03) kmol m−3 Na2WO4 electrolytes at pH −0.1∼+1.0 and 363 K at 600 Am−2. The deposits consist of a nanocrystalline single γ-MnO2 type phase in the form of triple Mn1−xyMoxWyO2+x+y oxide. Anodic deposition in 0.2 kmol m−3 Mn2+-0.003 kmol m−3 Mo6+-0.006 kmol m−3 W6+ electrolyte at pH 0.0 resulted in the formation of an electrode with 100% and 99.8% oxygen evolution efficiencies before and after electrolysis for 691.2 ks in 0.5 kmol m−3 NaCl solution of pH 2 at 1000 Am−2. Thus, Mn1−xyMoxWyO2+x+y electrodes were promising oxygen evolving anodes for acidic seawater electrolysis. It has been concluded that additions of both tungsten and molybdenum beneficially bring about an increase in the real electro-catalytic activity along with the formation of deposits with optimum thickness and good adherence to the IrO2/Ti substrate.
  • A Comparison of Low-cycle Fatigue Properties in Stainless Steel Types 347N and 316N

    pp. 317-322

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    DOI:10.2320/matertrans.46.317

    The low-cycle fatigue (LCF) properties of an Nb-stabilized grade, type 347N, and an unstabilized grade, type 316N, of austenitic stainless steels containing approximately 0.1 mass% nitrogen were evaluated at ambient temperature and at the operating temperature of a nuclear power plant (330°C). Type 347N exhibited a shorter fatigue life than type 316N. The difference in the fatigue lives of the two grades of steel was greater at ambient temperature than at 330°C. The inferior LCF resistance of type 347N compared to that of type 316N was largely attributed to the presence of carbo-nitride particles in type 347N, which exhibited a bimodal size distribution. Fine particles induced strong secondary cyclic hardening by pinning dislocation cell walls at ambient temperature, whereas no secondary hardening occurred at 330°C. The hardening caused a higher stress concentration at the tip of the fatigue crack at constant strain amplitude, which resulted in a lower fatigue life at ambient temperature. Coarse particles acted as material defects that deteriorated the fatigue resistance by creating voids on the surface of the propagating fatigue crack, regardless of the testing temperature. An observation of the outer surface showed that the two types of steel exhibited different crack initiation modes on the surface. In type 316N, the crack initiation mode was predominantly intergranular at a high strain amplitude but transgranular at lower strain amplitude. In type 347N, the crack initiation mode was always intergranular, regardless of the strain amplitude.
  • Kinetics of the Volatilization Removal of Lead in Electric Arc Furnace Dust

    pp. 323-328

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    DOI:10.2320/matertrans.46.323

    The selective removal of lead and chlorine with minimizing zinc loss from electric arc furnace (EAF) dust is very important in the process for recovering high purity zinc from the EAF dust by high temperature metal recovery (HTMR) processes. In this study, the volatilization reaction of lead contained in the EAF dust was investigated at reaction temperatures between 973 and 1223 K in air. The main volatilization reaction equation of lead was found as follows: 2NaCl+PbO+2SiO2+Al2O3=PbCl2(g)+2NaAlSiO4In the reaction time of 90 min at 1223 K, the volatilization ratio was about 98% for both lead and chlorine, while that was about 1% for zinc. Jander rate expression was found to fit reasonably well the volatilization reaction rate over the entire temperature range. The volatilization reaction rate of lead in the EAF dust is controlled by solid-solid diffusion and has an activation energy of 175 kJ/mol (41.8 kcal/mol).
  • Characterization of Rust Layer Formed on Fe, Fe-Ni and Fe-Cr Alloys Exposed to Cl-Rich Environment by Cl and Fe K-Edge XANES Measurements

    pp. 329-336

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    DOI:10.2320/matertrans.46.329

    Chloride in atmosphere considerably reduces the corrosion resistance of conventional weathering steel containing a small amount of Cr. Ni is an effective anticorrosive element for improving the corrosion resistance of steel in a Cl-rich environment. In order to clarify the structure of the protective rust layer of weathering steel, Cl and Fe K-edge X-ray absorption near edge structure (XANES) spectra of atmospheric corrosion products (rust) formed on Fe, Fe-Ni and Fe-Cr alloys exposed to Cl-rich atmosphere were measured. The Fe K-XANES measurements enable the characterization of a mixture of iron oxides such as rust. The chemical composition of the rust was determined by performing pattern fitting of the measured spectra. All the rust is composed mainly of goethite, akaganéite, lepidocrocite and magnetite. Among these iron oxides, akaganéite in particular is the major component in the rust. Additionally, the amount of akaganéite in the rust of Fe-Ni alloy is much greater than that in rust of Fe-Cr alloy. Akaganéite is generally considered to facilitate the corrosion of steel, but our results indicate that akaganéite in the rust of Fe-Ni alloy is quantitatively different from that in rust of Fe-Cr alloy and does not facilitate the corrosion of steel. The shoulder peak observed in Cl K-XANES spectra reveals that the rust contains a chloride other than akaganéite. The energy of the shoulder peak does not correspond to that of any well-known chlorides. In the measured spectra, there is no proof that Cl, by combining with the alloying element, inhibits the alloying element from acting in corrosion resistance. The shoulder peak appears only when the content of the alloying element is lower than a certain value. This suggests that the generation of the unidentified chloride is related to the corrosion rate of steel.
  • Structure Analysis of Cation Selective Cr-goethite as Protective Rust of Weathering Steel

    pp. 337-341

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    DOI:10.2320/matertrans.46.337

    We have performed extended X-ray absorption fine structure (EXAFS) analysis for artificial Cr-goethite to elucidate the local structure around Cr in Cr-goethite. The spectra were obtained using synchrotron radiation X-rays at the Photon Factory in Tsukuba. The first shell contributions were isolated by Fourier filtering the EXAFS data, and the inverse Fourier transformed single-shell data were analyzed using a curve fitting method. The results show that Cr is coordinated with (7±1) O2− ions. The protective characteristics of the Cr-goethite protective rust layer on weathering steel can be interpreted in terms of the O2− coordination around Cr3+ resulting in the creation of negative fixed charge in the Cr-goethite particles.
  • Rolling and Recrystallization Textures of Ag-10 mol% Pd Alloy Substrate for Superconducting Tapes

    pp. 342-348

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    DOI:10.2320/matertrans.46.342

    In order to demonstrate the effect of deformation temperature on texture formation in silver alloy sheet for superconducting tapes, the rolling and annealing textures of Ag-10 mol% Pd alloy rolled at the temperatures from −196 to 160°C and subsequently annealed were examined in detail.
    The rolling texture for all deformed specimens rolled at temperatures from −196 to 160°C consisted of a certain component near the Brass {110}⟨112⟩ orientation with some weak components. During annealing procedure, the characteristic components of deformation texture disappeared quickly in specimens rolled at room temperature or −196°C but slowly in those warm-rolled at 120°C or 160°C. The Copper component was found to be formed by higher temperature annealing in specimens warm-rolled at 160°C and those rolled at room temperature. Above all, a single {112}⟨111⟩ Copper type texture with high intensity in ODFs has been realized in three different specimens, which were rolled by 92% at room temperature or warm-rolled by 92% or 95% at 160°C and subsequently annealed as 200°C-10 min + 500°C-30 min + 800°C-180 min + 950°C-180 min respectively. From the experimental results obtained here, a metallurgical processing to get a sharp single orientation type texture in Ag-10 mol% Pd alloy was presented for the development of new technology on oriented superconducting substrate tapes.
  • Development of Sharp {011}⟨211⟩ Textured Silver Substrate for Superconducting Tapes

    pp. 349-354

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    DOI:10.2320/matertrans.46.349

    Texture formation in pure silver was investigated in order to obtain sharply Brass {011}⟨211⟩ type textured silver sheet that can be used as a substrate for Y-123 superconducting coated tapes without any buffer layers.
    The feature of recrystallization texture after the two-step annealing appeared as two peaks close to Goss {011}⟨100⟩ orientation and Brass {011}⟨211⟩ orientation respectively with other weak components along α-fiber in specimens rolled at room temperature, and only one peak close to Brass {011}⟨211⟩ orientation with weak components limited to cube orientation, rotated cube orientation and orientation close to Copper {112}⟨111⟩ orientation in those warm rolled at 150°C. By using the improved metallurgical processing, a very sharp Brass {011}⟨211⟩ type texture has been successfully realized in specimen, which was cast in vacuum, warm rolled by 92% at 150°C and subsequently annealed as 200°C–20 min + 800°C–180 min in nitrogen. There are some critical conditions on the formation of sharp Brass {011}⟨211⟩ type recrystallization texture: a low oxygen content in the starting material, elevated rolling temperature, and the selection of lower primary recrystallization temperature of two-step annealing process.
  • Deep Potential Effect on Magnetism of Binary Including Spintronic Material

    pp. 355-360

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    DOI:10.2320/matertrans.46.355

    Magnetic moments on transition elements strongly depend on their circumstances. Generally, the magnetic moments, surrounded by neighbor atoms having deep potential, seem to be enhanced. For example, the moment on Iron (Fe) is indeed enhanced in the Ni3Fe and Ni-Fe-Ga as shown in the previous calculation. \\citerf1 In both alloys, the nearest neighbors of Fe are Nickel (Ni) atoms, having deeper potential than Fe.
    To examine the effect of surrounding deep potential, the electronic structures of binary alloys between 3d-transition-metal elements are calculated for the B2 and L12 structure. The surrounding deeper potential draw the electronic states of the subject atoms into lower energy range and bring the various moments and interesting features. In other words, the effects of surrounding potential can control energy level of DOS peak or the band gap. Were the structure of Cu3V to be the L12, the magnetic moment on V would become unusually large (1.99 μB). Some alloys calculated show the high spin polarization at the Fermi level (EF). The values of the spin polarization at the EF evaluated from the density of states (DOS) for Ni3Cr, Ni3Co and CoFe are 0.94, −0.86 and −0.88 respectively. To control the energy level of DOS peak or the band gap would give us another means for finding new spintronic materials. The relations between whole magnetic moment and the valence electron concentration show the Slater-Pauling like behavior.
  • Dislocation Structure in Rapidly Solidified Mg97Zn1Y2 Alloy with Long Period Stacking Order Phase

    pp. 361-364

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    DOI:10.2320/matertrans.46.361

    Dislocation structure in rapidly solidified Mg97Zn1Y2 ribbon with the long period stacking order (LPSO) phase is investigated by conventional transmission electron microscopy. In the grain with the LPSO phase there are no a dislocations lying on the basal plane, and a number of c+a dislocations are visible. On the other hand, in the grain without the LPSO phase there are many straight a dislocations lying on the basal plane. These facts indicate that the critical resolved shear stress of the basal plane increases by the formation of the LPSO phase and the non-basal slip is activated by the prevention of the basal slip. In other words, the former directly contributes to the strengthening and the latter relates to the improvement of ductility with the increment of the number of the slip system. Therefore, it is concluded that the LPSO phase plays a unique role which overcomes the conflicting properties of strength and ductility in the mechanical property of the present alloy.
  • Formation of Quasicrystalline Particles in an Isothermally Aged Al-10 Mg-0.5 Ag (mass%) Alloy

    pp. 365-368

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    DOI:10.2320/matertrans.46.365

    The trace additions of Ag to binary Al-Mg alloys promote precipitation of a phase in the under-aged condition. The structures of the phase in an Al-10 Mg-0.5 Ag (mass%) alloy have been characterised using transmission electron microscopy and electron microdiffraction. An icosahedral quasicrystalline phase, which is identified by the electron microdiffraction patterns, has been found in the Al-10 Mg-0.5 Ag (mass%) alloy after solution treatment, water quenched and then aged during the time between 20 and 40 min. at 240°C. The orientation relationship between the quasicrystalline phase and the α-Al matrix is as follows; i5||⟨011⟩α and i3||⟨111⟩α. A uniform distribution of finer-scale (typically 20 nm), faceted precipitate particles was observed within the core of the grains, but the precipitates became coarser (60–80 nm) approaching the grain boundary precipitate-free zone.
  • Plastic Deformation of Mg-Zn-Y Icosahedral Quasicrystals under Confining Pressure

    pp. 369-371

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    DOI:10.2320/matertrans.46.369

    Deformation experiments of Mg-Zn-Y icosahedral quasicrystals under a hydrostatic confining pressure have been performed to investigate their deformation mechanism in a low temperature range. The temperature dependence of the yield stress has been successfully measured, for the first time, down to room temperature. An irregular behavior has been found in the temperature dependence: the yield stress increases rapidly with lowering temperature down to 373 K and it becomes almost constant in the temperature region lower than 373 K. The origin of such an irregular temperature dependence is discussed in terms of possible transition between two different dislocation processes: glide and climb.
  • Underwater Explosive Shock Consolidation of Nanocomposite Pr2Fe14B/α-Fe Magnetic Powders

    pp. 372-375

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    DOI:10.2320/matertrans.46.372

    Dynamic consolidation of powders was studied to fabricate exchange-coupled Pr2Fe14B/α-Fe nanocomposite bulk magnets, using explosively generated shock waves transmitted through water. The planar shock wave propagating into the powder had a peak pressure calculated to be ∼12 GPa. Extensive plastic deformation of the powders and solid-state interfacial bonding of the ribbon flakes was obtained during shock compaction, resulting in fabrication of bulk compacts with nearly full density. Retention of nano-scale structure, and in fact further refinement of the grain size, ensured exchange coupling between the hard and soft phases, resulting in magnetic properties better than those of resin-bonded commercially available magnets. Post-shock annealing of the compacts at 750 and 850°C resulted in deterioration of the magnetic properties due to slight grain growth and decoupling of exchange interactions between hard and soft phases. The results illustrate that dynamic shock consolidation employing explosive loading is a viable method for fabricating bulk nanocomposite magnets and the rapid thermal excursions can be controlled to minimize and in fact eliminate the detrimental effects otherwise observed during high temperature sintering and annealing of the powders.
  • Formation of Bulk Pd-Cu-Si-P Glass with Good Mechanical Properties

    pp. 376-378

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    DOI:10.2320/matertrans.46.376

    Glassy Pd85−xCuxSi10P5 (x=5–12 at%) alloys with a supercooled liquid region (ΔTx) of 51–73 K were synthesized despite the low metalloid content. The glassy Pd79Cu6Si10P5 alloy exhibits the largest ΔTx of 73 K in the present alloy system and its critical diameter for glass formation reaches 5 mm by copper mold casting. For the bulk glassy Pd79Cu6Si10P5 alloy, the Young’s modulus, compressive yield strength and maximum compressive strength are 82 GPa, 1475 MPa and 1575 MPa, respectively. Distinct compressive plastic strain of 3.5% and a vein pattern morphology on the fracture surface indicate the ductile nature of the bulk glassy Pd-Cu-Si-P alloy.
  • Structural Analysis of Melt-Spun MgxPd100−x (x=70, 80, 85 and 90) Amorphous Alloys

    pp. 379-381

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    DOI:10.2320/matertrans.46.379

    MgxPd100−x (x=70, 80, 85 and 90) amorphous alloys were prepared by the single-roller melt-spinning technique and X-ray diffractometry was performed with synchrotron radiation using the large Debye-Scherrer camera installed at SPring-8. As a result, it has been shown that a medium-range order (MRO) exists in each of the amorphous alloys and that the MRO decreases monotonously with increasing the Mg content. Additionally, it has also been shown that the atomic distances of first neighbor pairs hardly vary although the rate of the coordination numbers varies monotonously with the alloy composition.

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