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

MATERIALS TRANSACTIONS Vol. 51 (2010), No. 5

  • EcoAudit: a Renewed Simplified Procedure to Facilitate the Environmentally Informed Material Choice Orienting the Further Life Cycle Analysis for Ecodesigners

    pp. 832-837

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    DOI:10.2320/matertrans.MH200918

    Design process determines 80% of the whole environmental impact generated by a product or service. This paper intends to describe a simplified renewed procedure for the analysis and selection of materials capable of providing fast and reliable information to those designers that are interested to minimize the life-cycle environmental burden of products and services, the so called EcoAudit. The here presented EcoAudit procedure assesses the burden associated to a component/product by means of a customized set of environmental impact indicators, without exploring all parameters that are usually provided by a LCA study.
    The set of environmental impact indicators that are here adopted for this purpose are the energy consumption (energy breakdown in terms of direct and indirect contributors, MJ per functional unit), the global warming potential (in terms of CO2 equiv per functional unit) and the end of life possibilities (in terms of effective practicable scenarios, i.e. of recycling). The first two indicators may be intended as “key environmental performance indicators” (“KEPIs”).
    This approach allows a fast preliminary ranking of materials and processes identifying the most relevant critical phases of a system, making the ecodesign process really starting. The integration within the Cambridge Engineering Selector 2009 EcoAudit tool allows to search and browse materials data, calculating the environmental load in a real time.
  • Removal of Magnesium from Molten Aluminum Scrap by Compound-Separation Method with Shirasu

    pp. 838-843

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    DOI:10.2320/matertrans.MH200914

    The removal of magnesium from the molten aluminum scrap containing magnesium was examined by compound-separation method using Shirasu as an additive. When Sirasu is added to the molten aluminum scrap, which is followed by agitation, MgAl2O4 and MgO are formed by the reactions among SiO2 and Al2O3 in Shirasu and magnesium in the molten scrap. It is feasible to remove magnesium by separating these reaction products as dross. The effect of addition temperature of Shirasu on magnesium removal is smaller than that of the agitation time. In the case of the addition of flaky Shirasu with 63–150 μm of particle size, the amount of magnesium removed increases linearly with agitation time because the over-all reaction is mainly controlled by a surface-controlled reaction. In the case of the addition of granular Shirasu with 300–590 μm of particle size, the amount of magnesium removed increases parabolically with agitation time because the over-all reaction is mainly controlled by a diffusion-controlled reaction. The amount of magnesium removed can be controlled by changing the amount of Shirasu added.
  • Synthesis of β-SiAlON-AlN-Polytypoid Ceramics from Aluminum Dross

    pp. 844-848

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    DOI:10.2320/matertrans.MH200913

    Aluminum dross is one of the main secondary wastes during aluminum recycling procedure. It is utilized to synthesize β-SiAlON-AlN-polytypoid ceramics by the reduction-nitridation method in this paper. The effects of the reaction parameters, such as the Si/Al ratio, reaction temperature and holding time are studied in detail. The results indicate that the synthesized products are mainly composed of β-SiAlON and Mg-AlN-polytypoid at 1450°C to 1650°C for 6 h. As the Si/Al ratio changes from 1.0 to 2.5, the amount of β-SiAlON increases while the amount of Mg-AlN-polytypoid decreases. At 1750°C, the samples consist mainly of AlN and AlN-polytypoid because SiO gas is significantly evaporated. With the increment of synthesis temperature, the growth of elongated Mg-AlN-polytypoid grains is significantly accelerated. SEM and EDS analysis results for the samples formed at 1650°C for 6 h show that the β-SiAlON grains display a short platelet morphology, and Mg-AlN-polytypoid grains possess needle or lath morphology. This study suggests that it is possible to synthesize the low cost SiAlON ceramics with high toughness from aluminum dross.
  • Conversion of Waste Sandstone Cake into Crystalline Zeolite X Using Alkali Fusion

    pp. 849-854

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    DOI:10.2320/matertrans.MH200905

    Waste sandstone cake, which is discharged as industrial waste, was converted into crystalline zeolite-X using alkali fusion. The cake was transformed into a soluble phase via alkali fusion, and then agitated in distilled water at room temperature to give an intermediate solid, followed by synthesis at 80°C to give the final product. The effects of the agitation and synthesis times on the product phase were investigated with a view to obtaining a single crystalline zeolite-X. Hydroxysodalite was synthesized from the intermediate solid obtained without agitation, and with increasing agitation times for the intermediate solid, the amount of zeolite-X in the product increased, because of the increased Si content in the intermediate solid and the decrease of interference from impurities in the synthesis of zeolite crystals. The observed concentrations of Si and Al in the solution during the reaction explain the crystallization of the zeolite phase. The equilibrium adsorption capacity of the product for Sr2+ was almost the same as that of commercial zeolite-X in a low concentration Sr2+ solution, and the maximum adsorption capacity of the product, calculated using the Langmuir isotherm model, was 0.46 mmol/g.
  • Development of Lead-Free Machinable Brass with Bismuth and Graphite Particles by Powder Metallurgy Process

    pp. 855-859

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    DOI:10.2320/matertrans.MH200907

    The aim of this paper was to produce a lead-free machinable brass dispersed with bismuth and graphite particles by powder metallurgy process. The effect of the machinable elements on the elongation and machinability of extruded materials was investigated. The Cu-40 mass%Zn (Cu-40Zn) brass powder with 0∼3.23 mass% bismuth additions were produced by rapid solidification process, having a mean particle size of 150 μm. It was found that bismuth were uniformly dispersed as the island of about 5 um in the brass powder matrix, and appeared at the brass powder surface after heat treatment over the melting point of bismuth. When 2.2 mass% or more bismuth was added, the quantity of bismuth appearing at the brass powder surface increased because of saturated quantity of bismuth elements in the brass powder. There were bismuth islands of tens of microns in the extruded brass with 2.2 mass% or more bismuth addition. These bismuth islands were depressed the elongation of extruded materials. The graphite particles with mean particle size of 5 μm were also used as raw powder. 0∼0.5 mass% graphite particles were mixed with the as-atomized brass powder by dry process. The elongation of the extruded brass alloy with both bismuth and graphite particles additions increased comparing with that of extruded brass with bismuth addition. The extruded brass using the as-atomized brass powder with 2.2 mass% bismuth and 0.5 mass% graphite particles indicated excellent machinability as well as the conventional leaded brass. Synergy effect of bismuth and graphite particles on the improvement of elongation and machinability of brass alloys was much useful compared with the brass containing only bismuth or graphite particles.
  • Preparation of Single-Phase ZnSb Thermoelectric Materials Using a Mechanical Grinding Process

    pp. 860-862

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    DOI:10.2320/matertrans.MH200902

    Single-phase zinc antimonide (ZnSb) was prepared using a mechanical grinding (MG) process. The ZnSb source ingots were prepared by direct melting of the constituent elements. Two processes were used to prepare the ingots. One of the processes involved quenching the molten material in water in an evacuated quartz ampoule. In the other process, an additional step consisting of heating for 100 h at 723 K was performed after quenching. The ground materials were obtained by mechanically grinding the resultant ingots and then hot-pressing at 673 K. The materials were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), and thermoelectric property measurements. The results indicated that the materials were crack free and single phase. The thermal conductivity of the ground materials was 1.41 Wm−1K−1 at room temperature. This value was lower than that reported in the available data for materials prepared by conventional melt growth and powder metallurgy methods. The ZnSb single phase was found to have a dimensionless figure of merit of 0.6–0.8 at 573 K.
  • Thermoelectric Properties and Scattering Factors of Finely Grained Bi2Te3-Related Materials Prepared by Mechanical Alloying

    pp. 863-867

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    DOI:10.2320/matertrans.MH200901

    Fine grained samples with a nominal composition of Bi0.5Sb1.5Tex (x=3.0 to 3.4) were prepared by mechanical alloying (MA). Average grain sizes were found to range from 1.0 to 2.1 μm. Tellurium precipitation at x=3.1 was observed by scanning electron microscopy (SEM), X-ray diffraction and differential thermal analysis (DTA). Electrical conductivity as well as Hall and Seebeck coefficients were measured from 300 to 470 K. Using the relationship between Hall mobility and temperature, carrier scattering factors of the Bi0.5Sb1.5Tex samples were estimated to range from r=−0.9 to −2.0. The thermal conductivities of the samples were found to range from 0.94 to 1.00 Wm−1K−1 at room temperature. Excess tellurium was recognized to be responsible for the decrease in thermal conductivity. The Lorenz number and the carrier component of thermal conductivity were calculated from the scattering factor and the Fermi integral. The phonon component of thermal conductivity was dominant in the Bi0.5Sb1.5Tex samples. The Seebeck coefficient of the Bi0.5Sb1.5Tex samples was higher than that from the available data which means that the absolute scattering factor of the Bi0.5Sb1.5Tex samples was large. A maximum figure of merit of 7.02×10−3 K−1 was obtained at 310 K for the Bi0.5Sb1.5Te3.1 sample. This high figure of merit results from an enhanced Seebeck coefficient that is due to an increased absolute scattering factor. High thermoelectric performance can, therefore, be established by a reduction in the phonon component of the thermal conductivity and also by an enhanced Seebeck coefficient, which results from an increased absolute scattering factor for finely grained Bi0.5Sb1.5Tex samples that were prepared by MA.
  • Thermoelectric Performance of p-Type Mg2Si0.25Sn0.75 with Li and Ag Double Doping

    pp. 868-871

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    DOI:10.2320/matertrans.MH200906

    The single-phase of p-type Mg2Si0.25Sn0.75 with Li and Ag double doping were prepared by the liquid-solid reaction and hot-pressing methods. All samples thus obtained were identified by XRD as single-phase solid solutions with an anti-fluorite structure. The effects of Li and Ag double doping on thermoelectric performance were investigated at temperature differences (ΔT) of 0 to 500 K. The thermoelectromotive force (E) of the Li-25000 ppm single-doped sample was determined to be 88 mV at ΔT=500 K. For the Li-20000 ppm and Ag-5000 ppm double-doped sample, the E value became larger (92 mV) after Ag substitution. A maximum E value of 97 mV was obtained for the Ag-25000 ppm single-doped sample and the Li-5000 ppm and Ag-20000 ppm double-doped sample. Mean resistivity (rm) at ΔT=500 K decreased by double doping and showed a minimum value of 2.94×10−5 Ωm for the Li-5000 ppm and Ag-20000 ppm double-doped sample. The maximum effective power (P=E2⁄4rm) increased with ΔT. The P values of single-doped samples at ΔT=500 K were 38 Wm−1 for Li single-doped and 72 Wm−1 for Ag single-doped samples. P for the Li-20000 ppm and Ag-5000 ppm double-doped sample was 64 Wm−1, which was an improvement of about 90% compared with the Li single-doped sample. The maximum value of P at ΔT=500 K was 80 Wm−1 for the Li-5000 ppm and Ag-20000 ppm double-doped sample, which was an improvement of about 10% compared with the Ag single-doped sample.
  • Texture and Mechanical Properties of Mg-3Al-1Zn-0.5Mn-1.5Ca Alloy Produced by Torsion Extrusion

    pp. 872-877

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    DOI:10.2320/matertrans.MH200909

    Torsion extrusion was carried out on Mg-3Al-1Zn-0.5Mn-1.5Ca (in mass%) alloy (AZ31+1.5Ca alloy). The annealed torsion-extruded AZ31+1.5Ca alloy exhibited higher elongation compared with the annealed extruded AZ31+1.5Ca alloy without torsion. The ductility enhancement was attributed to a unique texture with ⟨10\\bar10⟩ direction inclined 30° from the extrusion direction and low pole density. Besides, the annealed torsion-extruded AZ31+1.5Ca alloy exhibited higher strength compared with the annealed torsion-extruded Mg-3Al-1Zn-0.5Mn (in mass%) alloy (AZ31 alloy). In the extruded AZ31+1.5Ca alloy, the fine second phase particles, which contributed to a suppression of the grain growth during extrusion and annealing, were observed. The enhanced strength of the annealed torsion-extruded AZ31+1.5Ca alloy was likely attributed to not only grain refinement but also strengthening by the presence of the second phase particles.
  • Structural Properties of Heavily B-Doped SiGe Thin Films for High Thermoelectric Power

    pp. 878-881

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    DOI:10.2320/matertrans.E-M2010806

    Heavily B-doped SiGe thin films was reported to have large thermoelectric power and power factor at room temperature after annealing. In this paper, we investigated the structures that give rise to the large thermoelectric power and power factor. The thin films were prepared by ion-beam sputtering method. The annealing temperature dependence of structural properties was investigated. The thin films exhibited large thermoelectric power (1.4 mVK−1) and power factor (6.8×10−3 Wm−1K−2) at room temperature after annealing at around 900 K. At that region, crystallite diameter was below 10 nm. The structure changed from amorphous to microcrystalline over 900 K. It is considered that quantum size effect enhances the thermoelectric power and power factor.
  • Effect of Rh Substitution for Co on the Thermoelectric Properties of CoSb3

    pp. 882-886

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    DOI:10.2320/matertrans.E-M2010808

    CoSb3 is known as a skutterudite compound that could exhibit high thermoelectric figure of merit. However, the thermal conductivity of CoSb3 is relatively high. In order to enhance the thermoelectric performance of this compound, we tried to reduce the thermal conductivity of CoSb3 by substitution of Rh for Co. The polycrystalline samples of (Co1−xRhx)Sb3 (x=0, 0.1, 0.2, and 0.3) were prepared and the thermoelectric properties such as the Seebeck coefficient, electrical resistivity, and thermal conductivity were measured in the temperature range from room temperature to 750 K. The Rh substitution for Co reduced the lattice thermal conductivity, due to the alloying scattering effect. The minimum value of the lattice thermal conductivity was 4 Wm−1K−1 at 750 K obtained for (Co0.7Rh0.3)Sb3.
  • SEM Electron Channeling Contrast Imaging of Dislocation Structures in Fatigued [017] Cu Single Crystals Oriented for Critical Double Slip

    pp. 887-891

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    DOI:10.2320/matertrans.M2009439

    Dislocation structures in fatigued [017] critical double-slip-oriented Cu single crystals were studied using the electron channeling contrast technique in scanning electron microscopy. It was found that the dislocation structures are strongly dependent upon the applied plastic strain amplitude γpl. As γpl falls into the quasi-plateau region in the cyclic stress-strain curve of the [017] crystal, a special “two-phase” dislocation structure, i.e., persistent slip band ladder-like structures and matrix labyrinth structures, was observed. When γpl≥3.0×10−3, which is beyond the quasi-plateau region, two types of deformation bands denoted DBI and DBII were observed. The dislocation microstructures in DBI and DBII consist mainly of well-developed regular labyrinth structures and densely-aligned dislocation walls, respectively, and the microstructures at the intersection region of DBI and DBII comprise dislocation walls together with a number of dislocation cells. The orientation dependence of microstructures in DBI and DBII is further summarized and discussed.
  • Effect of Electric Current on the Inclusions in a Cu-Zn Alloy

    pp. 892-895

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    DOI:10.2320/matertrans.M2009389

    The effect of electric current pulse (ECP) treatment on lead inclusions in a Cu-Zn alloy was studied in present work. It was found that with the application of a critical high current density, the coarse and random distributed lead inclusions transferred into grain boundaries or defects in dispersed small particles. The reason was ascribed to the specific electric effect of electric current on the grain refinement and the reduction of the diffusive activation energy of lead inclusions. Therefore, the high current density ECP treatment might be an effective method to refine inclusions of bulk materials.
  • An Interpretation of Martensitic Transformation in L12-Type Fe3Pt from Its Electronic Structure

    pp. 896-898

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    DOI:10.2320/matertrans.M2009400

    Partly ordered Fe3Pt is one of ferromagnetic shape memory alloys exhibiting a large magnetic field-induced strain in its martensite phase formed by a second-order-like martensitic transformation from the L12-type structure to the so-called FCT martensite (L60-type structure). We have investigated the origin of this transformation from their electronic structures calculated in the present study. A characteristic feature in the electronic structure is the existence of a relatively high peak in the density of states of the minority spin band just below the Fermi energy. This peak splits into two peaks by tetragonal distortion, and one of them shifts to lower energy by the distortion, suggesting that the band Jahn-Teller effect is the main cause for the transformation.
  • Shape-Strain Analysis of Martensite in Ceria-Doped Zirconia

    pp. 899-905

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    DOI:10.2320/matertrans.M2009296

    We use the scanning-electron-microscope–electron-backscattering diffraction (SEM-EBSD), atomic force microscopy (AFM), and calculations based on the phenomenological theory of martensite crystallography (PTMC) to study two types of martensite observed in ceria-doped zirconia. The results indicate that a plate-type martensite has various habit planes such as {301}t, {100}t, and {10 1 0}t, which suggests the association of different lattice correspondences and lattice-invariant shears in PTMC. A pyramid-type martensite has only {301}t habit plane. The shape strains of the variants associated with these habit planes are effective in accommodating the shape strains of the transformation in the near-surface region, as proposed by Deville et al. (2004). Although pyramidal structures appear predominantly on surfaces near the (001)t plane, they also appear on surfaces near (100)t and (010)t planes. These results are understood from the shape strains calculated by the PTMC.
  • Premartensitic State of Ti-Pd-Fe Shape Memory Alloys Studied by Electrical Resistivity, Magnetic Susceptibility and Specific Heat Measurements

    pp. 906-910

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    DOI:10.2320/matertrans.M2009412

    Transformation behavior in Ti-(50-x)Pd-xFe shape memory alloys has been investigated by electrical resistivity, magnetic susceptibility and specific heat measurements. The alloys with x=14, 16 and 18 exhibit an obvious first order martensitic transformation, but the alloys with x=19, 20 and 22 exhibit no first order transformation down to 4.2 K. However, the latter alloys show a negative temperature coefficient in electrical resistivity below a temperature Tmin, which decreases with increasing x. The increase in resistivity with decreasing temperature is associated with a decrease in magnetic susceptibility. Also, specific heat measurements at cryogenic temperatures have revealed that the electronic specific heat coefficient of the latter alloys (x=19, 20 and 22) is significantly larger than that of the former alloys (x=14, 16 and 18). These results suggest that the so-called precursor phenomena observed in Ti-Pd based shape memory alloys are caused by the instability of electronic structure of the B2-phase, as in the Ti-Ni based alloys previously studied by our group.
  • Characteristics of the Cold-Rolling Texture in a Multi-Layered Material Composed of SUS301 and SUS420J2 Steels

    pp. 911-917

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    DOI:10.2320/matertrans.MG200906

    A multi-layered composite material composed of alternating SUS301 and SUS420J2 steels, prepared by hot-rolling bonding, shows a superior strength and ductility balance than the components. Few researches have been addressed on texture features of structural multi-layered materials during cold-rolling. In the present work, cold-rolling with three reductions (20%, 40% and 65%) in thickness was conducted on both the two monolithic steels (SUS301 and SUS420J2) and the multi-layered material consisting of SUS301 and SUS420J2 components. Texture and microstructure development during the cold-rolling deformation in both the monolithic steels and multi-layered material were investigated by using EBSD technique. It was found that austenite phase in SUS301 component of the multi-layered material showed weaker ⟨110⟩//ND texture as compared to the monolithic SUS301 steel although the similar texture characteristics appeared in both conditions. On the other hand, the martensite phase in SUS420J2 component of the multi-layered material showed stronger {112}⟨110⟩ texture components than the ⟨111⟩//ND and ⟨100⟩//ND texture components that were dominant in the monolithic SUS420J2 steel. It is considered that the constraint condition and shear stress at component layer interfaces are significant for the formation of Brass component observed as the final stable orientation of austenite phase of the SUS301 steel in the multi-layered samples, and the formation of the {112}⟨110⟩ texture of martensite phase of the SUS420J2 steel in the multi-layered samples during the cold-rolling deformation.
  • Effect of Preheating Temperature on ECAP Formability of AC4CH Aluminum Casting Alloy

    pp. 918-924

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    DOI:10.2320/matertrans.L-M2010805

    Effects of preheating treatment on the microstructural features and the ECAP formability at room temperature were investigated for an AC4CH aluminum alloy. The preheating treatment at the temperature range from 260 to 560°C improved the ECAP formability at room temperature, especially at around 350°C the occurrence of cracks was inhibited effectively. When the preheating treatment was carried out at 410°C or less the hardness of primary α-Al decreased with rise in preheating temperature, while the increase of the hardness was observed for the test pieces preheated at above 470°C. The observation on the eutectic Si particles showed that the mean cross-sectional area and the spherical coefficient were constant at the preheating temperatures below 410°C but increased clearly at 470°C and higher. In addition to the above, when the hardness of the primary α-Al reached to a specified value due to a strain hardening by the repetitive ECAP press, the cracks occurred in the test piece and the ECAP process became impossible. These experimental results implied that the hardness of the primary α-Al gave a useful indication for the ECAP formability at room temperature. Cracks at the rear section of the test piece initiated on the inner side of ECAP channel angle and propagated preferentially along the solidification cell regions, that is, not only at the interface between aluminum matrix and eutectic Si particles but also at the transcrystalline cracking of eutectic Si particles.
  • Change of Young’s Modulus with Increasing Applied Tensile Strain in Open Cell Nickel and Copper Foams

    pp. 925-932

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    DOI:10.2320/matertrans.M2009384

    The change of Young’s modulus with increasing applied tensile strain in the open cell nickel and copper foams, fabricated by the slurry foaming process at Mitsubishi Materials Corporation, Japan, was investigated experimentally and analytically. Stress-strain curves were measured at room temperature, in which the loading-unloading-reloading process was performed on the sample at various applied strains. For measurement of the strain of the sample itself accurately, the non-contact extensometer was employed. The Young’s modulus values at various applied tensile strains were estimated from the slope of the elastic region in the stress-strain curve in the unloading process. It was revealed that two competitive factors affect on the Young’ modulus value. One is the irreversible morphology-change of cells arising from the plastic deformation of the metal as a results of which, the cells are elongated and struts are straight forwarded in the tensile direction. This factor acts to raise the Young’s modulus with increasing applied strain. Another factor is the failure of struts, which tends to reduce the Young’s modulus with increasing applied strain, especially beyond the strain where the struts are failed successively. Accordingly, due to the competition of the former and latter factors, the Young’s modulus increases, reaching maximum and then decreases with increasing applied strain in both of the foams. The increase in Young’s modulus with increasing applied strain due to the change of geometry of struts was confirmed by the experimental test of micro-samples composed of several struts and nodes and by the simulation based on the finite element analysis using a model micro-sample.
  • Mechanical Properties of Nanometric Al2O3 Particulate-Reinforced Al-Al11Ce3 Composites Produced by Friction Stir Processing

    pp. 933-938

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    DOI:10.2320/matertrans.M2009406

    Aluminum matrix composites reinforced with nanometer sized Al2O3 particles were produced from powder mixtures of Al and CeO2 by the use of friction stir processing (FSP). This approach has combined hot working nature of FSP and exothermic reaction between Al and oxide. In the composites, Al2O3 particles (∼10 nm in size) and Al11Ce3 intermetallic compound were formed in situ by oxide-aluminum displacement reaction. The aluminum matrix of the composites has an average grain size about 400 nm. The composites produced exhibit high strength both at ambient and elevated temperatures. It is mainly attributed to the uniform dispersion of nanometer sized Al2O3 particles, which not only contribute significantly to the strength by the Orowan mechanism but also stabilize the fine structure at elevated temperatures.
  • Electrochemical Properties of Titanium in PEFC Bipolar Plate Environments

    pp. 939-947

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    DOI:10.2320/matertrans.M2009402

    In order to assess the applicability of titanium as a bipolar plate for polymer electrolyte fuel cells (PEFCs), the electrochemical surface characteristics of commercially available pure titanium were examined in simulated PEFC conditions. The results of the electrochemical tests showed that the cathode operating potential of PEFC, 0.64 V (vs. Ag/AgCl(3.33 kmol·m−3 KCl)), lay in the anodic passivation region for titanium. The operating potential of the PEFC anode, −0.36 V, lay in the cathodic region or the cathodic to anodic transition region. Under the PEFC cathode condition, a barrier-type film with high charge transfer resistance and high contact resistance formed on the specimen. Under the PEFC anode condition, an oxide film with low charge transfer resistance and low contact resistance formed by a dissolution-precipitation mechanism.
  • Effect of Current Density and Organic Additives on the Texture and Hardness of Ni Electrodeposited from Sulfamate and Watt’s Solutions

    pp. 948-956

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    DOI:10.2320/matertrans.M2009361

    Ni electrodeposition was galvanostatically conducted over the current density range 500–2000 A/m2 in unagitated sulfamate and Watt’s solutions at 323 and 313 K, respectively, to examine the effect of current density and organic additives on the texture, crystal orientation, and hardness of the deposited Ni. The overpotential for Ni deposition increased by the addition of polyethylene glycol (PEG) or saccharin in both sulfamate and Watt’s solutions. The degree of increase in the overpotential in a PEG-containing solution was larger than that in a saccharin-containing solution. Ni deposited from an additive-free solution showed a morphology of field oriented texture type with the preferred orientation of the {100} plane, while Ni obtained from a PEG- or saccharin-containing solution had the unoriented dispersed type without a preferred orientation in the region of some current densities. The region of the current density that resulted in the unoriented dispersed type in Watt’s solution was larger than that in a sulfamate solution. The particle size of the deposited Ni decreased with the addition of PEG and saccharin. The hardness of the deposited Ni increased with PEG and saccharin, and was higher for the unoriented dispersed texture than for the field oriented texture. In additive-containing solutions, the hardness of Ni deposited from Watt’s solution was higher than that from a sulfamate solution.
  • Fabrication of AlN Coatings by Reactive Atmospheric Plasma Spray Nitriding of Al Powders

    pp. 957-961

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    DOI:10.2320/matertrans.T-M2010804

    Atmospheric Plasma Spray (APS) is well-established process and is widely used to produce various coatings with high deposition rate for structural and functional applications. Aluminum nitride is a promising material due to its outstanding properties. In this study, AlN coatings were synthesized by APS process through reactive plasma nitriding of Al powders by nitrogen plasma. Al powders were supplied into the plasma stream by Ar carrier gas and reacted with the surrounding plasma, then were deposited onto substrate. The obtained coatings were cubic-AlN/Al mixture with 100 μm of thickness at 150 mm of spray distance. Since the nitride content increases gradually with spray distance, the coating almost consists of AlN at 300 mm. However, the thickness of the coatings decreased with increasing spray distance, it was less than 10 μm at 300 mm spray distance. The nitriding reaction was investigated and it indicated that Al particles may react during flight and after deposition on the substrate surface. Completing the nitriding during flight (formation of AlN in-flight) decreases the coatings thickness. We can conclude that enhancing the nitriding reaction after deposition at short spray distance may enable to fabricate thick AlN based coatings.
  • Residual Stress Behavior of Rolled Aluminum Alloy A2024T3 in a Thin Plate During Cyclic-Tension Fatigue Studied Using Ultrasonic Horizontally Polarized Shear Waves

    pp. 962-968

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    DOI:10.2320/matertrans.M2009356

    The cyclic-tension fatigue in a rolled thin-plate of aluminum alloy Al–4Cu–1Mg was evaluated nondestructively using a horizontally polarized shear wave (SH) transmission method under optimized measuring and analyzing conditions. The propagation time of the SH waves, which contained elements of reflected waves, had three distinct stages, the first, middle and final ones, during the fatigue process. The variation of the propagation time was dominated by the residual-stress field during the fatigue progress, as an acoustoelastic effect. The change in the stage of the variation can be elucidated by balance points for the redistribution of the residual stress, which clearly told us the degree of progression of the fatigue in the thin plate.
  • Redistribution of Solute during Cellular Solidification of Single Phase Alloys

    pp. 969-976

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    DOI:10.2320/matertrans.M2009392

    Computer simulation of the upward cellular solidification of Al–Cu alloy was carried out considering the solidification to be a reaction controlled by diffusion. In the simulation, direct solving method of differential equation was applied to the diffusion in solid and liquid in contact with each other during cooling. The results of simulation showed that the solute distribution in liquid groove ahead of the solid-liquid interface is parabola whose bottom zenith lies at cell boundary. This result, together with the negligible diffusion in solid, induced that Scheil’s equation is approximately applicable to the solute distribution in the solid cell after the solidification. Numerical analysis of the simulated results induced also a general equation which expresses the parabolic relationship between cooling rate and the cell size. The validity of thus induced equation was verified by the experimental results obtained by other researchers. The transition of planar/cellular interface in solidification was also investigated from the standpoint of the diffusion controlled solidification.
  • Plastic Flow and Strain Homogeneity of an Equal Channel Angular Pressing Process Enhanced through Forward Extrusion

    pp. 977-981

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    DOI:10.2320/matertrans.M2009407

    The plastic deformation behavior of forward extrusion, equal channel angular pressing, and a combination of the forward extrusion and equal channel angular pressing processes are analyzed by the finite element method. Simulations were carried out under realistic conditions by considering the strain hardening of the material and the degree of friction. Strain homogeneity in the combined processes is also compared to that of the individual forward extrusion and equal channel angular pressing processes. The plastic flow is more complicated and the strain induced is non-uniform in the combined processes. However, the combined processes show no corner gap formation. Moreover, it led to the development of higher strains in a single step compared to the individual processes. In addition, the load requirements for the combined processes are higher than the summation of loads of the individual processes.
  • Aluminizing of Nickel-Based Superalloys Grade IN 738 by Powder Liquid Coating

    pp. 982-987

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    DOI:10.2320/matertrans.M2009382

    Nickel-based superalloy grade IN738 has superior creep resistance, however, oxidation resistance is the main limitation of this alloy for practical applications at high temperature. Coating of nickel aluminide compounds which have high oxidation resistance on the IN738 alloys surface can remarkably increase the oxidation resistance by formation of Al2O3 film as protective layer. Aluminizing by powder liquid coating methods is applied in this research. Mixed slurries of Al and Al2O3 powders are pasted onto IN 738 samples and heated at 1273 K in argon atmosphere for 3.6 to 14.4 ks (1 to 4 h). Slurries can be classified into four different ratios of Al:Al2O3: 10:0, 7:3, 5:5 and 3:7. The microstructure was investigated by scanning electron microscope (SEM) and optical microscope. Phases in the coated layer are characterized by Glancing Incident-angle X-ray Diffractometer (GIXD) and Electron Probe Micro Analysis (EPMA). The results show that the coated layer is formed by dissolution of nickel into liquid aluminum at aluminizing temperature resulting in formation of intermetallic compound layer. The coated layer consists of Ni2Al3 as a main phase with small amount of NiAl3 and AlCr2. AlCr2 exists mostly at the layer adjacent to the top surface. For 8.1 and 14.4 ks (2.25 and 4 h) holding time, formation of AlCr2 at the interface of matrix and coated layer occurs due to diffusion of aluminum from coated layer into nickel matrix. The effect of time shows that longer aluminizing time leads to formation of a uniform coated layer. The Al:Al2O3 ratio of either 10:0 or 7:3 will create a uniform coated layer with thickness more than 200 μm.
  • Thermoelectric Properties of Binary Semiconducting Intermetallic Compounds Al2Ru and Ga2Ru Synthesized by Spark Plasma Sintering Process

    pp. 988-993

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    DOI:10.2320/matertrans.E-M2010807

    The authors report the electrical and thermal transport properties of binary semiconducting intermetallic Al2Ru and Ga2Ru compounds from 373 to 973 K. We synthesized sintered pellets of Al2Ru and Ga2Ru by the spark plasma sintering (SPS) method, resulted in a removal of small amount of a secondary phase and of cracks. The maximum Seebeck coefficient of Al2Ru and Ga2Ru shows a large positive value of 200 μV/K and 360 μV/K, respectively. In particular, a large power factor ∼2.8 mW/m-K2 was obtained at 773 K in Ga2Ru compound. The dimensionless figures of merit ZT of sintered Al2Ru and Ga2Ru samples monotonically increase with increasing temperature and reach a maximum value of 0.20 and 0.45 at about 873 K and 773 K, respectively.
  • Reversible Bending Motion of Unimorph Composites Driven by Combining LaNi5 Alloy Powders Dispersed Polyurethane and Thin Supporting Copper Sheet under Partial Hydrogen Gas Pressure

    pp. 994-1001

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    DOI:10.2320/matertrans.M2009420

    The polyurethane composites dispersed with powders mixture of LaNi5 hydrogen storage alloy (35 vol% of LaNi5) and Pd-Al2O3 catalyst powders were prepared by solution cast method, which easily controlled the shape and mixed ratio of the composites. In order to generate the bending strain of reversible up motions at vertical and horizontal directions, the unimorph (PU+LaNi5/Cu) sheet constructed with the driving polyurethane composite and supporting copper thin sheet of 10 μm thickness with high specific stiffness (apparent hardening modulus per specific weight) was prepared.
    Although the bending motion of the unimorph sheet operated by hydrogenation under 0.3 MPa H2 gas was irreversible, the reversible motion was detected under 0.2 MPa H2 gas. The maximum strain of reversible bending motion (εmax) of the PU+LaNi5/Cu sheet is more than 1520 and 1120 ppm on vertical and horizontal directions, respectively. The εmax of the PU+LaNi5/Cu sheet at vertical direction was slightly higher than that of the ABS resin unimorph (ABS+LaNi5/ABS) sheet constructed with the driving ABS resin composites and pure ABS resin supporting sheet, whereas it was slightly lower than that of the silicone rubber unimorph (SR+LaNi5/SR) sheet constructed with the driving silicone rubber composites and pure silicone rubber supporting sheet. It can be estimated that the responsiveness (dε⁄dt) of cyclic motion of the (PU+LaNi5/Cu) sheet is slightly higher than ABS+LaNi5/ABS sheet.
  • Catalytic Properties of Cold-Rolled Ni3(Si,Ti) Intermetallic Foils for Methanol Decomposition

    pp. 1002-1010

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    DOI:10.2320/matertrans.M2009438

    Methanol decomposition tests were carried out for the first time on cold-rolled Ni3(Si,Ti) foils in a temperature range of 513–793 K to investigate their potential catalytic properties for hydrogen production. The catalytic activity was observed at temperatures above 713 K. At 793 K, the catalytic activity changed with the reaction time in three stages: low-activity incubation, rapid spontaneous activation and high-activity state. Surface analysis revealed an intensive formation of fine Ni particles on the foil surfaces after the second stage where rapid spontaneous activation was observed. The formation of the fine Ni particles was considered to be induced by the selective oxidation of Si in Ni3(Si,Ti). The catalytic activity in the second and third stages was due to the fine Ni particles formed by the spontaneous activation.
  • Effects of Zr Addition on the Microstructure of 14%Cr4%Al ODS Ferritic Steels

    pp. 1011-1015

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    DOI:10.2320/matertrans.MBW200923

    Oxide dispersion-strengthened (ODS) ferritic steels have a good radiation resistance, high creep strength and a good swelling resistance. In such alloys, Zr is used to improve the creep properties by stabilizing the grains boundaries. The influence of the zirconium on the microstructure will be discussed is this study. The addition of Zr reduces strongly the number density of the inclusion distribution. The reduction factor is between 4 (transverse direction) to 15 (longitudinal direction). The addition of Zr reduces the formation of Al and Y oxides (micro scale). The carbide composition is also different according to the material composition. Zr-free material forms W/Ti carbides and Zr-added material forms Zr/Ti carbides without formation of W carbides (free enthalpy). Zr addition may be considered as very good in term of strength and corrosion resistance.
  • High-Resolution TEM Observations of the Decomposition of NaAlH4

    pp. 1016-1019

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    DOI:10.2320/matertrans.MBW200902

    Sodium alanate (NaAlH4) was ground in a glove box in inert gas and transferred to a microscope without exposing the samples to air, using a plastic bag method. The results of in-situ electron beam diffraction showed that NaAlH4 decomposed to Na3AlH6 and Al, and then to NaH and Al when heated to 150°C and then 200°C. The decomposition of NaAlH4 was observed by ex-situ transmission electron microscopy (TEM) at 1250 keV. Porous structures appeared when the samples were heated and dehydrogenated. These are likely due to structural defects or are cavities due to volume changes between phases. The Na3AlH6 and Al particles were found to distribute around the pores.
  • Electromigration Behavior of through-Si-via (TSV) Interconnect for 3-D Flip Chip Packaging

    pp. 1020-1027

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    DOI:10.2320/matertrans.M2009367

    The electromigration of conventional Sn-37Pb (in mass%) solder bumps was investigated with a current density of 2.0×104 A/cm2 at 393 K using three-dimensional (3-D) flip-chip specimens comprised of an upper Si chip and a lower FR-4 substrate. Electromigration failure of the Sn-37Pb solder bumps occurred with complete consumption of electroless Ni immersion Au (ENIG) under bump metallization (UBM) and void formation at the cathode side of the solder bump. Cross-sectional studies were conducted with scanning electron microscopy (SEM). Ni3Sn4 intermetallic compound (IMC) layers were formed in both interfaces, while a typical eutectic structure of Pb- and Sn-rich phases was formed within the solder region. After 11 h current stressing, separation of the Pb- and Sn-rich phases occurred in the solder bump, while a void was formed in the cathode-side bump. After 18 h current stressing, the solder joints catastrophically failed due to the re-melting of the solder bump.
  • Effect of Pin Shapes on Joint Characteristics of Friction Stir Spot Welded AA5J32 Sheet

    pp. 1028-1032

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    DOI:10.2320/matertrans.M2009405

    The joint strength of friction stir spot welded 5J32 Al alloy was investigated according to the tool shape (threaded pin tool: TPT; cylindrical tool: CT; cylindrical tool with projection: CTP) and tool penetration depth. With increasing tool penetration depth, the vertical joint deformation increased in TPT and CT, whereas the joint diameter increased in TPT. The tensile shear load of the joint using TPT and CT did not vary with tool penetration depth, because the decreased upper plate thickness impeded the increase of the tensile shear load. That of CTP, however, rapidly increased with increasing tool penetration depth to produce a maximum tensile shear load of 4.6 kN. CTP, with its shoulder comprising a slight, broad projection, retarded the vertical joint deformation and produced good mechanical properties.
  • Microstructure and Compressive Properties of In-Situ Martensite CuZr Phase Reinforced ZrCuNiAl Metallic Glass Matrix Composite

    pp. 1033-1037

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    DOI:10.2320/matertrans.M2010031

    In-situ micro-level martensite CuZr phase reinforced Zr50.5Cu27.45Ni13.05Al9 metallic glass matrix composite was synthesized by copper mold casting. Microstructure and compressive properties of the composite are investigated. The martensite CuZr phase possesses numerous coherent twin boundaries, and holds strong interfacial cohesion with the matrix. They both effectively induce the seeding and branching of shear bands during compression. The compressive properties of the composite are therefore improved. The fracture strength and plastic strain of composite with a diameter of 3 mm is up to 2190 MPa, 5.7% respectively.
  • Effect of Braking Speeds on the Tribological Properties of Carbon/Carbon Composites

    pp. 1038-1043

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    DOI:10.2320/matertrans.M2009390

    This paper describes the tribological properties of carbon/carbon composites used as braking materials under various braking speeds, in which the materials with three kinds of microstructures were used: rough lamina (sample A), smooth lamina (sample B), and the mixture of rough lamina and smooth lamina (sample C), respectively. Friction tests were carried out through a laboratory dynamometer. Polarized optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure and worn surface. Results indicated that the friction coefficient of sample A reached a peak value at braking speed lower than that in both sample B and sample C. However, when the friction coefficients reached to the peak values the temperature inside the worn surface was observed to be approximately 250°C for all of the samples. The weight losses in all of the samples were observed to increase with increasing braking speed; however, the oxidation losses at speed of 28 m·s−1 are higher than that of 30 m·s−1 for all of the samples.
  • Microstructure and Mechanical Properties of Friction Stir Spot Welded Galvanized Steel

    pp. 1044-1050

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    DOI:10.2320/matertrans.M2009337

    Joints of galvanized steel were obtained by friction stir spot welding (FSSW) with lap configuration using CPS design tool. No mechanically mixed layer was formed between the top and bottom plates at the weld nugget due to the limited tool penetration and the lower pin height of the welding tool than the steel plate thickness. A deformed region, in which ZnO particles were detected, was observed in the joint. The formation of this deformed region was attributed to the explosion of the Zn coating layer due to friction heating and tool compression. With increasing tool penetration depth, the tensile shear strength of the joint increased to a maximum value of 3.07 kN at a tool penetration depth of 0.52 mm.
  • Universal Plot for Hardness Variation in Pure Metals Processed by High-Pressure Torsion

    pp. 1051-1054

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    DOI:10.2320/matertrans.M2009431

    Various pure metals (Al, Au, Ag, Cu, V, Pt, Ni, Fe, Co, Ti, Zr, Hf, Mo) including Cu-30%Zn are processed by high-pressure torsion. Most of Vickers microhardness (HV) values are expressed by a universal plot when they are normalized as (HVG)(TTm) and plotted against εPG, where G, TTm, ε and P are the shear modulus, homologous temperature, equivalent strain and pressure, respectively. Deviations to this plot are for Al (99.99%), Ti, Zr, Hf and Cu-30%Zn and for when P is below a critical pressure.
  • Etching Effect on Microstructural Behavior of Gas Atomized Al-20 mass%Si Alloy Powder

    pp. 1055-1058

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    DOI:10.2320/matertrans.M2010008

    In this research, a metallographic investigation of as atomized Al-20 mass%Si alloy powders, etched at surface and cross-section, was conducted by scanning electron microscopy. The surface micrographs of the etched powders showed the existence of primary Si and eutectic Si on the microstructure of the powder surface, and satellite particles adhering to the larger particles, while it was impossible to observe the surface microstructure in the case of the non-etched powder surface. The coarse primary Si phases in these powder particles were not present, indicating that their formation was effectively suppressed by the rapid solidification. In addition, it was possible to observe the microstructure of satellite powder surface such as fine cellular or featureless structure due to surface etching.

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