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

MATERIALS TRANSACTIONS Vol. 50 (2009), No. 10

  • Microstructural Evaluation of Nd-Fe-B Jet-Milled Powders

    pp. 2347-2350

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    DOI:10.2320/matertrans.MAW200915

    Nd-Fe-B sintered magnets have high energy products and are used for various applications. Motors of hybrid vehicles (HEVs) are one of the major applications. For usage of HEVs, Dy is added to Nd-Fe-B magnets to maintain coercivity at high temperature environment. However, due to low natural resources of Dy, Dy-free or Dy-lean Nd-Fe-B sintered magnets are strongly required. To achieve high coercivity, it is necessary that microstructure of sintered magnets is consisted of both fine main phase particles and homogeneously distributed Nd-rich phases around the main phase. In this study, the microstructure of Nd-Fe-B jet-milled powders and the distribution of the Nd-rich phase were investigated. The distribution of the Nd-rich phase was evaluated by the ratio of grains which contain the Nd-rich phase. With decreasing size of the jet-milled Nd-Fe-B powder, the Nd-rich phase tends to aggregate and its distribution becomes inhomogeneous. The powder size of Nd-Fe-B jet-milled powder is much smaller than the average lamella interval of strip cast alloys.
  • Effect of Prior Deformation on Creep Behavior of a Die-Cast Mg-Al-Ca Alloy

    pp. 2351-2354

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    DOI:10.2320/matertrans.MAW200901

    The creep of die-cast Mg-Al-Ca alloys is characterized by the pronounced decrease in creep rate during the transient region. Higher creep rates immediately after the stress application for the alloys can result in the degradation of bolt-load retention in the automotive powertrain applications. In this study, the effect of prior deformation on creep behavior was investigated for the Mg-Al-Ca AX51 (X representing calcium) die-cast alloy, where the prior deformation was introduced by using the creep machine at temperatures of 423 and 473 K. The creep curves of the specimens with the prior deformation were compared with that of the as die-cast specimen at the creep testing condition of 423 K and 80 MPa. It was found that the prior deformation introduced by the creep machine is not effective to decrease the creep rates for the alloy. The obtained results of creep behavior are discussed on the basis of dislocation movements during creep.
  • Effect of Pre-Introduced Shear Bands Direction on Deformation Behavior in Zr55Al10Ni5Cu30 Bulk Metallic Glass

    pp. 2355-2358

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    DOI:10.2320/matertrans.MAW200920

    We investigated the effect of pre-introduced shear bands direction on compressive deformation behavior in Zr55Al10Ni5Cu30 bulk metallic glass. The compressive deformation behavior varied with the difference of the direction of pre-introduced shear bands with respect to loading direction. The specimen in which shear bands were introduced at an angle of 45 degree to the loading direction showed largest plastic strain. This large plasticity was achieved due to the activity of pre-introduced shear bands and formation of multiple shear bands. The direction of pre-introduced shear bands is an important factor to improve the plasticity in bulk metallic glasses.
  • Conditions of Electronic Structure to Obtain Large Dimensionless Figure of Merit for Developing Practical Thermoelectric Materials

    pp. 2359-2365

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    DOI:10.2320/matertrans.M2009143

    The highest value of the dimensionless figure of merit ZT obtainable from a given electronic structure was quantitatively estimated from the linear response theory by considering the normalized spectral conductivity. It was found, by calculating ZT from the possible electronic structures, that the bulk materials with the electronic structure consisting of two bands overlapping together near the Fermi level have potential to possess a large ZT-value exceeding unity.
  • Thermally Formed Oxides on Al-2 and 3.5 mass% Mg Alloys Heated and Held in Different Gases

    pp. 2366-2372

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    DOI:10.2320/matertrans.M2009155

    Weight changes in Al-2 and 3.5 mass% Mg alloy samples were measured by thermogravimetric analysis. X-ray diffractometer tests were used to investigate the progressive development of thermally formed oxide films on the samples. Both samples were first heated in a dry air atmosphere. The oxide film formed on the Al-2 mass% sample comprised γ-alumina, MgO, MgAl2O4, and gibbsite. The film formed on the Al-3.5 mass% sample contained large quantities of MgO, but no MgAl2O4.
    The samples were then heated in a nitrogen gas atmosphere for <1.9 h. The Al-3.5 mass% sample contained greater amounts of gibbsite and γ-alumina than did the Al-2 mass% sample. The latter yielded a greater amount of AlN (and/or MgO). After an extended holding time (∼6 h), the Al-3.5 sample contained a greater amount of AlN (and/or MgO), and its weight increased remarkably. The as-cast samples containing the Al-3.5 mass%Mg cube had a higher percentage of foggy film compared to those containing an Al-2 mass%Mg cube. Oxide films that are readily formed during melting tend to be trapped in aluminum alloy castings.
  • Molecular Dynamics Simulation of Void Generation during Annealing of Copper Wiring

    pp. 2373-2377

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    DOI:10.2320/matertrans.MRA2008477

    In the production of LSIs, annealing is necessary to coarsen the crystal grains in the wires. In this process, wiring breakdown is frequently caused by defect generation at the T-shaped buried wire. To overcome this difficulty, we investigated the conditions for defect generation and the atomic behavior during the annealing process by molecular dynamics simulation. We focused on the influence of the adhesion strength between substrate and wire materials on void generation. As samples for the simulation, a Cu single crystal was buried in three different substrates, Si, Ti, and W. After structural relaxation at low temperature (50 K), the movements of individual Cu atoms were simulated for different annealing temperatures using the molecular dynamics method. The strain of the buried wire was also varied where the thickness of the covered layer, the width and the height of the wire were fixed. We found that the system with strong adhesion strength between substrate and wire materials suppressed void generation.
  • Microstructures and Mechanical Properties in Friction Stir Zone of Thixo-Molded AS41 Mg Alloy

    pp. 2378-2383

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    DOI:10.2320/matertrans.M2009122

    The friction stir weldability of thixo-molded AS41 Mg alloy was investigated, and the microstructures and mechanical properties in friction stir zones were examined and evaluated. The non-destructive inspection by means of X-ray radiography shows that the optimum FSW condition range of AS41 alloy exists between AZ61 and AE42 alloys, and it seems that the optimum welding condition range increases with decreasing Al content in the Mg alloys. There are mainly three kinds of compounds, i.e. Mg2Si, MnSi and Al12Mg17, in the thixo-molded AS41 base metal, while only two kinds of compounds are found in SZ except Al12Mg17 phase. This is because of the decomposition of Al12Mg17 phase at the higher temperature caused by the FSW heat input. Furthermore, the average diameter of compounds in SZ decreases with increasing the traveling speed at constant rotation speed due to less heat input. The hardness in SZ is higher than that in BM, and tensile strength and elongation are both improved after welding because the stirring refines and uniforms the microstructure and intermetallic compounds.
  • Martensitic Transformation of Ti50Ni25−XPd25−YCuX+Y Quaternary Shape Memory Alloys with X, Y≤10 at%

    pp. 2384-2390

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    DOI:10.2320/matertrans.M2009196

    Ti50Ni25−XPd25−YCuX+Y high temperature shape memory alloys (HTSMAs) with X, Y≤10 at% have been studied by DSC, XRD, TEM/EDS, hardness and cold-rolling workability tests. Experimental results show that all these HTSMAs exhibit B2 ↔ B19 martensitic transformation with Ms temperature can be predicted by the linear regression as: Ms (K)=424.2+2.7X−9.7Y. The substitution of Ni/Pd by Cu affects the lattice constants of B19 martensite, the hardness and the cold-rolling workability which can be explained by the different atomic radii of Ni, Cu and Pd. Ti50Ni15Pd25Cu10 HTSMA annealed at 523 K up to 9 weeks and thermal-cycled up to 100 times still has quite good thermal stability. However, Ti50Ni15Pd25Cu10 HTSMA annealed in between 723 K∼923 K shows obvious decrease for both Ms temperature and ΔHc value, especially at 823 K due to Ti2Pd and Ti(Cu,Pd)2 precipitated during annealing.
  • Axial Compression and Post-Deformation Annealing of ⟨011⟩ Aluminum Single Crystal

    pp. 2391-2395

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    DOI:10.2320/matertrans.M2009194

    In order to study the formation of deformation bands (DBs) and its relation to recrystallization, an aluminum single crystal was compressed along the ⟨011⟩ direction and subsequently annealed. In the present crystal, the four slip systems having the largest Schmid factors were on two slip planes that were symmetrically arranged with respect to the direction of observation. The overall deformation was consistent with the arrangement of these two major slip planes. In the central region of the observed surface, the major slip planes were activated to form a double-slip pattern. On the other hand, at the corner regions, many DBs were formed. After annealing, recrystallization occurred in the regions containing the DBs. Recrystallized grains had a ⟨111⟩-rotation relationship with the DBs. The experimental results were compared with those in tensile-deformed aluminum single crystals having the same crystallographic orientation.
  • The Effect of Preheating on Notch Fracture of Ti-4.5Al-3V-2Fe-2Mo Laser Welds

    pp. 2396-2402

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    DOI:10.2320/matertrans.M2009141

    Notched tensile strength (NTS) and impact fracture toughness were determined for Ti-4.5Al-3V-2Fe-2Mo laser welds subjected to post-weld heat treatment (PWHT) at distinct temperatures. In the welding process, the specimens were preheated at 300°C to reduce the cooling rate of the welds, and the results were compared with the non-preheated welds. Generally, the preheated welds had coarser α+β structures and showed slower responses to age-hardening in PWHTs than the non-preheated welds. The decreased hardness and accompanied ductility enhancement resulted in the improved notch brittleness and impact toughness of the preheated welds, relative to the non-preheated welds. As the PWHT temperature of the welds increased, the coarsening of grain boundary α assisted grain boundary sliding and formed intergranular dimple fractures on the fracture surface.
  • Effects of Structures of Substrates on Sn Whisker Formation Using Substitutionally-Deposited Sn Films

    pp. 2403-2409

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    DOI:10.2320/matertrans.M2009045

    The effects of the microstructure of Cu foils, used as a copper pattern for flexible printed circuits (FPC), on Sn whisker formation as well as on the structure of substitutionally-deposited Sn films were investigated. In particular, the relationship between the grain size of the Cu foil and the amount of intermetallic compound deposits formed at the interface between the substitutionally-deposited Sn films and Cu foils as a function of aging was examined. Two types of Cu foils were used as substrates in this study. One had granular-shaped grains 0.5∼1.0 μm in size while the other had pillar-shaped grains about 5.0 μm in size. We called the former “With the gelatin additive” and the latter “With the Cl ion additive”. The grain size of the Cu foil with the gelatin additive was smaller than that of the Cu foil with the Cl ion additive. The structures of the Sn whiskers, Sn films and Cu foils were investigated using TEM and SEM. The number of whiskers formed on the Sn-deposited film increased after aging. The number of whiskers formed on the substitutionally deposited Sn film on the Cu foil with the gelatin additive was larger than that with the Cl ion additive. Cross-sectional structures of the Sn-deposited films and Cu foils were observed using TEM. Analysis of TEM selected-area diffraction patterns obtained from the samples after aging indicated the presence of Cu6Sn5 intermetallic compound deposits at the interface between the deposited Sn films and the Cu foils. The amount of intermetallic compound deposits formed with a gelatin additive was larger than that with a Cl ion additive. The structure of the intermetallic compound deposits was classified either as nodular-shaped or as layer-shaped. The difference between the amount of nodular-shaped intermetallic compound deposits between the Cu foils with the gelatin additive and the Cu foils with the Cl ion additive were examined.
  • Temperature Dependence of Corrosion of Ferritic/Martensitic and Austenitic Steels in Liquid Lead-Bismuth Eutectic

    pp. 2410-2417

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    DOI:10.2320/matertrans.M2009173

    Corrosion tests of ferritic/martensitic (F/M), austenitic stainless and Si-added austenitic steels were conducted at 450 to 600°C for 2000 h or 3000 h in oxygen-saturated lead-bismuth eutectic (LBE) to clarify temperature effect on corrosion behavior. While the corrosion depth is small at 450°C because of oxide film formation with low growth rate, it increases at 500°C due to additional grain boundary corrosion/internal oxidation and node formation. At 550°C, extensive grain boundary corrosion/internal oxidation is observed in F/M steels. Ferritization characterized by selective dissolution of Ni and Cr, and LBE penetration occurs in austenitic stainless steels, JPCA and 316SS. Corrosion attack becomes very severe for most steels at 600°C. LBE penetration follows grain boundary corrosion/internal oxidation in F/M steels and ferritization advances deeply in JPCA and 316SS. The compound corrosion layer of oxidation, dissolution and LBE penetration often peels off. Addition of Si to austenitic steels is useful to improve corrosion resistance.
  • Modeling of Elution Curves in Preparative Chromatography Using Anion-Exchange Resin for Cobalt Purification

    pp. 2418-2426

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    DOI:10.2320/matertrans.M2009095

    There have been many studies on the modeling of elution and breakthrough curves of ion-exchange chromatography. A precise representation of elution curves using an appropriate mathematical model is significant for the application and expansion of ion-exchange chromatography. The significance of precise modeling particularly increases when the yield and purity of the product are important. However, no previous studies have proposed a model that can perfectly represent experimental elution curves. We investigated the purification of various metals by anion-exchange separation and determined an optimum condition for purification of an element through trial and error. An appropriate model replicating the elution curves accurately is greatly needed to reduce the testing phase. Consequently, this paper proposes a novel model called the plate theory in multi-path mode, in which three virtual paths are assumed. The results show that this model well represents the experimental elution curves. In addition, the model was validated by comparing the distribution coefficients obtained from the fitting results with those determined by previously reported batch experiments.
  • Effects of Powder Shape and Processing Parameters on Heat Dissipation of Heat Pipes with Sintered Porous Wicks

    pp. 2427-2434

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    DOI:10.2320/matertrans.M2009152

    The thermal performance of sintered-type heat pipes can be determined from their permeability, capillary pressure, and capillary speed. These characteristics are closely related to the pore structure, which is influenced by the powder used. To investigate the effects of powder shape on the heat dissipation of a heat pipe, gas atomized, water atomized, and electrolytic copper powders were used in this study. The results showed that the gas atomized spherical powder, despite having the lowest porosity, provided the highest permeability and capillary speed and thus the best heat dissipation. The water atomized irregular powder had a smaller permeability, slightly higher capillary speed, and better thermal performance compared to dendritic electrolytic powder. These results suggest that capillary speed is favorable over the permeability for evaluating whether a copper powder is suitable for heat pipe applications or not. The geometrical factor in the Kozeny-Carman permeability equation, which takes into account the effective pore length, pore surface roughness, and tortuosity, could vary from the 250 of the spherical powder to the 3108 of the dendritic powder for compacts with similar permeabilities, showing the effect of powder shape. The processing parameters, compacting pressure and sintering temperature, were also important. Compacts that were loose-powder-sintered at high temperatures showed higher permeability than those using compaction and low temperature sintering due to the differences in the pore surface roughness. These results demonstrate that the thermal performance of heat pipes is closely related to the powder shape and the process used, in addition to the effects of particle size and particle size distribution.
  • Effects of Cr3C2 and V8C7 on the Microstructure and Mechanical Properties of WC-SiC Whisker Ceramics

    pp. 2435-2440

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    DOI:10.2320/matertrans.M2009169

    WC-SiC whisker ceramics (5 vol% SiC) containing Cr3C2 and/or V8C7 with no metallic binders were prepared by resistance-heated hot pressing at 1650°C and were examined with regard to sinterability, microstructure and mechanical properties. The addition of Cr3C2 or V8C7 brought about an increase or decrease in the sinterability. For equal molar amounts of Cr and V, V8C7 more strongly inhibited the growth of WC grains than Cr3C2. The hardness of the ceramics was dependent on the WC grain size which was influenced by the nature or quantity of the additives. The hardness values are consistent with the Hall-Petch-type relationship between hardness and WC grain size estimated for WC phases in WC-Co cemented carbides.
  • Ni-Rich Bulk Metallic Glasses with High Glass-Forming Ability and Good Metallic Properties

    pp. 2441-2445

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    DOI:10.2320/matertrans.MRA2008453

    Glass-forming ability, thermal behavior and mechanical properties of Ni80−xPdxP20 (10at%≤x≤35at%) glassy alloys have been investigated. The alloys with Pd contents higher than 25 at% exhibit high glass-forming ability, as is evidenced from the formation of a cylindrical Ni50Pd30P20 glassy rod with a diameter of 21 mm. The Ni-rich bulk metallic glasses show relatively high strength in compression and tension tests. More notably, plastic strains exceeding 2% were obtained for all the metallic glasses at room temperature in compression test.
  • Fabrication of Ti-Ni-Zr Shape Memory Alloy by P/M Process

    pp. 2446-2450

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    DOI:10.2320/matertrans.M2009213

    This work focuses on the fabrication of Ti-Ni-Zr high-temperature shape memory alloy by powder metallurgy (P/M) process. The effects of fabrication conditions on the microstructure and shape memory characteristics of Ti-50.2 mol%Ni-5 mol%Zr alloy were investigated. In this research, elemental Ti, Ni and Zr powders were used. These powders were mixed by a planetary ball mill at a rotational speed of 500 rpm for milling times of 0.6 ks (mixed powder) and 720 ks (MAed powder). The mixtures were sintered by a pulse-current pressure sintering equipment at 1153 K for sintering times of 1.8 ks and 1.2 ks. The solution treatment was carried out at various temperatures between 1073 K and 1273 K to homogenize the microstructure of the as-sintered alloy. The microstructure of the alloy became more homogeneous with an increase in solution-treatment temperature. In the case of the mixed powder, however, Zr-rich phases were observed in the microstructure of the solution-treated alloy. The alloy solution-treated at 1173 K showed a yielding behavior in the stress-strain curve, and the tensile strength and elongation of the alloy were more than 350 MPa and 2.5%, respectively. On the other hand, in the case of the MAed powder, the microstructure of the as-sintered alloy was homogeneous. The P/M alloy showed higher transformation temperatures than those of the wrought alloy. But, the alloy showed no shape memory effect and poor tensile property due to contamination of the MAed powder.
  • Enhancement of Strength and Corrosion Resistance of Copper Wires by Metallic Glass Coating

    pp. 2451-2454

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    DOI:10.2320/matertrans.M2009157

    Metallic glass was coated on copper (Cu) wires for enhancing their strength and corrosion resistance. The metallic glass coating has strong cohesion to the copper, and can effectively protect the wires from external forces and corrosive environments. Compared with bare Cu wires, the yield strength and the elastic strain limit of the coated wires have been significantly increased. The excellent corrosion resistance of the metallic glass coating has also provided essential shielding of the wires from chloride-containing electrolyte environments. The experimental results present a new technique for strengthening and enhancing the corrosion resistance of copper wires.
  • Precipitation Behavior in a Hanks’ Solution on Ca-P-O Films Prepared by Laser CVD

    pp. 2455-2459

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    DOI:10.2320/matertrans.M2009160

    Ca-P-O films were prepared by laser CVD using Ca(dpm)2 and (C6H5O)3PO metal organic precursors. The crystal phase of Ca-P-O films changed depending on deposition temperature (Tdep), total pressure (Ptot), laser power (PL) and molar ratio of Ca to P (RCa/P). β-TCP films in a single phase were obtained in a P-rich and high Tdep region, while HAp films in a single phase were obtained in a Ca-rich and low Tdep region. The β-TCP films had a (220) orientation with an elongated and angular roof-shaped surface texture, whereas HAp films had a (300) orientation with a granular surface texture. Both the β-TCP film and the HAp film had a dense cross section. The Ca-P-O films were immersed in a Hanks’ solution for 6 h to 7 d. Particle-shaped precipitates were observed on the β-TCP and HAp films after 3 d immersion. Needle-shaped precipitates covered the whole surface of HAp film after 7 d immersion.
  • Giant Bending Strain of Reversible Motion of Uni-Morph Soft Mover Composites Driven by Hydrogen Storage Alloy Powders Dispersed in Polyurethane Sheet

    pp. 2460-2465

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    DOI:10.2320/matertrans.M2009178

    In order to generate the bending motion operated by pressure change in hydrogen gas, soft uni-morph composites were prepared, in which composites dispersed with not only driving particles of LaNi5 hydrogen storage alloy with Pd-Al2O3 catalyst powders to get high responsiveness, were piled up on a simple polyurethane sheet. Since the highest values of irreversible bending strain at the first hydrogenation (ε1) under 0.3 MPa H2 gas and the maximum irreversible bending strain during hydrogenation cycles (εm) were remarkably obtained at the 35 vol% of LaNi5 powders dispersed in polyurethane composites, the bending strain of reversible motion was detected from the first to the 8th hydrogenation (εr1 and εr8) under 0.2 MPa H2 gas. The bending strain of reversible motion of polyurethane composites sheet is more than 2000 ppm, which was approximately equal to that of silicone rubber composites and is extremely larger than that (300 ppm) of ABS resin composites. Responsiveness (dε⁄dt) of cyclic motion of elastic deformed mover composites, which were constructed with 35 vol%LaNi5 dispersed powder and matrix of polyurethane or silicone rubber, were more than 10 times higher than that of ABS composite.
  • Effects of Phase Constitution of Zr-Nb Alloys on Their Magnetic Susceptibilities

    pp. 2466-2472

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    DOI:10.2320/matertrans.M2009187

    The magnetic susceptibilities and microstructures of Zr-Nb binary alloys were investigated to develop a new metallic biomaterial with a low magnetic susceptibility for magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, and the microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). Zr-Nb alloys as-cast showed a minimum value of magnetic susceptibility between 3 and 9 mass% Nb, and the value abruptly increased up to 20 mass% Nb, followed by a gradual increase with the increase of the Nb content. XRD, OM, and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal ω phase in the β phase. Since the magnetic susceptibility of Zr-3Nb alloy consisting of an α′ phase was as low as that of Zr-9Nb alloy consisting of the β and ω phases, that of the ω phase was lower than that of the α′ and β phases. When Zr-16Nb alloy was heat-treated, the isothermal ω phase appeared, and, simultaneously, the magnetic susceptibility decreased. Therefore, the ω phase contributes to the decrease of the magnetic susceptibility, independently of the formation process of the ω phase. The magnetic susceptibility of the Zr-3Nb alloy as-cast was almost one-third that of Ti-6Al-4V alloy, which is commonly used for medical implant devices. Zr-Nb alloys are useful for medical devices used under MRI.
  • Effect of Tellurium Doping on the Thermoelectric Properties of ZnSb

    pp. 2473-2475

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    DOI:10.2320/matertrans.M2009201

    N-type tellurium doped ZnSb was prepared by direct melting at 923 K after which it was quenched in water within an evacuated quartz ampoule. All the ingots were heat treated at 723 K for 100 h. The resultant samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and by measurement of their Seebeck and Hall coefficients. XRD and DTA indicated that the solubility limit of tellurium in ZnSb was less than 3 atomic%. The samples with 0, 1 and 3 atomic% tellurium were p-type while those with 1.90 and 2.06 atomic% tellurium were n-type. These results indicated that n-type ZnSb samples can be obtained by the proper doping of tellurium. Excess doping with tellurium resulted in precipitation of the ZnTe phase and a change in conduction from n- to p-type. The maximum power factor for the 2.06 atomic% tellurium doped n-type sample was found to be 0.84×10−3 W m−1K−2 at 573 K.
  • Adsorption of Toxic Gases on Iron-Incorporated Na-A Zeolites Synthesized from Melting Slag

    pp. 2476-2483

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    DOI:10.2320/matertrans.M2009175

    Iron incorporated zeolites were prepared from Na-A type zeolite synthesized from melting slag and FeCl3 solution and applied as adsorbents for NH3 and H2S gases. Iron incorporated zeolite was pelletized, calcined and used for gas adsorption experiment. XRD analyses of the zeolite revealed that Fe3+ concentration of solution more than 90 mM could destruct the zeolite network structure. It was observed that the gas adsorption capacities of these zeolite pellets depend significantly on iron concentration of solution and calcination temperature. The type of binders affected a little on gas adsorption capacities. From adsorption results, adsorption capacity for NH3 was proportional to Fe3+ concentration and it was increased with calcination temperature up to 500°C, but it was decreased over 600°C. Pellets prepared from 56 mM Fe3+ solution calcined at 500°C showed highest ammonia adsorption capacity (3.7%). This iron incorporated Na-A type zeolites showed much higher adsorption capacities for NH3 (2.4∼3.7%) than commercially available activated carbons (0.16∼0.44%) and zeolites (0.23∼0.60%). In the case of adsorption capacities for H2S, adsorption capacity was proportional to Fe3+ concentration and inversely proportional to calcination temperature. Pellets prepared from 78 mM Fe3+ solution calcined at 200°C showed highest hydrogen sulfide adsorption capacity (1.5%). Adsorption capacity (0.2∼1.5%) was found to be lower than that of the commercial activated carbons (1.2∼2.4%) and higher than that of commercial zeolites 4A (0.15%) and 13X (0.91%). Higher ammonia adsorption in iron incorporated Na-A zeolites could be possibly due to development of number of acid sites on the zeolites surface due to incorporation of Fe3+ ion.
  • Research on TiAl Alloy Porous Metal Flow Restrictors

    pp. 2484-2487

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    DOI:10.2320/matertrans.M2009120

    For the restriction application, the uniformity of pore size and connectivity of pore channels are much more important for TiAl restrictor. TiAl porous materials have expansion phenomenon during reaction sintering for the Kirkendall Effect, and the pores were generated by its partial diffusion. In this paper, elemental powders blending and reaction sintering methods were adopted to prepare TiAl porous flow restrictor materials. The influence of particle size, the fraction of Ti and Al powder, pressing pressure, sintering temperature on the pore character of TiAl porous flow restrictor was studied. The results show that the maximum pore size and expansion coefficient increased with the increase of Al powder particle size, the porosity and permeability increased only when the Al powder particle size is larger than −400/+600 mesh. With the decrease of larger particle Al powder fraction, the porosity and permeability decreased, but the maximum pore size shows little change. With the increase of fraction of fine Al powder, the porosity and permeability increased to a certain value then decreased. With the increase of pressing pressure, maximum pore size, porosity and permeability decreased. When the sintering temperature is lower than 800°C, the porosity and permeability increased with the increase of sintering temperature. At above 800°C, the porosity and permeability decreased with the increase of sintering temperature.
  • Matrix Microstructure and Its Micro-Analysis of Constituent Phases in As-Cast Fe-Cr-C-V Alloys

    pp. 2488-2492

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    DOI:10.2320/matertrans.M2009002

    The as-cast matrix microstructure in 19 mass%Cr-2.8 mass%C white cast iron with up to 4.7 mass% V additions has been studied. Type and degree of the austenite transformation in the course of cooling after solidification in Fe-Cr-C-V alloys appeared to be dependent on the content of carbon and other alloying elements. Results obtained by EDS analysis of the phases in the tested Fe-Cr-C-V alloys indicated that vanadium is present in both matrix and carbide. Increasing the vanadium content in the alloy, its concentration increases in the matrix, whereas the concentration of carbon decreases. The precipitation kinetic of carbides in austenite was found dependent on the vanadium content. The volume fraction of M23C6 carbides was larger when the vanadium content was higher. TEM analysis revealed that both twinned and dislocation type martensites were present around secondary carbides. The transformation of austenite into martensite in the Fe-C-Cr-V alloys seems to be closely related to the precipitation of secondary carbides.
  • Orientation Characterization of Columnar-Grained Aluminum at Triple Junctions

    pp. 2493-2497

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    DOI:10.2320/matertrans.M2009159

    In this study, we used the digital-image-correlation (DIC) technique to investigate microstrain distribution after 5% deformation. Electron backscatter diffraction (EBSD) was also investigated in the orientation maps at triple junctions for an aluminum polycrystal after annealing at 360°C for 5, 20, 40, and 80 min, respectively. The results of the strain distribution demonstrated that strong deformation heterogeneities occur in the form of macroscopic shear localizations and that the average orientation spread or misorientation increases during annealing. Further, grain boundary migration was observed even at grain boundaries with the smallest differences in the orientation spread.
  • Mechanical Properties of Friction-Stir-Welded Inconel 625 Alloy

    pp. 2498-2501

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    DOI:10.2320/matertrans.M2009200

    The present study was carried out to evaluate the microstructural and mechanical properties on friction stir welded Inconel 625 alloy. For this work, friction stir welding was performed at a tool rotation speed of 200 rpm and a traveling speed of 100 mm/min. As a result, the grain refinement was achieved from 10.3 μm in the base material to 2.1 μm in the stir zone at an average grain size, accompanied by the dynamic recrystallization. This grain refinement has an effect on the increase of mechanical properties so that microhardness and tensile strength were significantly increased than that of the base material, more than 40% and 15% in fraction, respectively.
  • Comments on the Paper “Production of Zr55Cu30Ni5Al10 Glassy Alloy Rod of 30 mm in Diameter by a Cap-Cast Technique” (Yoshihiko Yokoyama, Enrico Mund, Akihisa Inoue and Ludwig Schultz, Mater. Trans. 48 (2007) 3190–3192.)

    pp. 2502-2503

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    DOI:10.2320/matertrans.M2009156

    The authors of the title paper under discussion state the importance of low oxygen content in producing an amorphous top half in slowly cooled arc-melted buttons. Since the cooling rate does not favor the amorphous state in top half of the button, more evidence is needed to support the claim. Further, the authors made a liquid quenching machine to enhance the cooling speed to make larger ingots of the same alloy. It is not clear why a new machine with higher cooling rate is needed if the amorphous state can be achieved at lower cooling rates. Lack of essential details of the “cap-cast method” does not permit a critical assessment of the new process. The nature and quality of optical micrographs and HREM pictures are a cause of concern.
  • Reply to Comments by Tsuyoshi Kajitani on Our Paper Titled ‘Production of Zr55Cu30Ni5Al10 Glassy Alloy Rod of 30 mm in Diameter by a Cap-Cast Technique (by Y. Yokoyama, et al., Mater. Trans. 48 (2007) 3190–3192)’

    pp. 2504-2506

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    DOI:10.2320/matertrans.M2009258

    Our paper (Mater. Trans. 48 (2007) 3190–3192) reports (1) the importance of controlling the impurity oxygen content during the manufacture of Zr55Cu30Ni5Al10 bulk metallic glasses (BMGs) and (2) the successful fabrication of a BMG rod of 30 mm diameter rod by our newly developed ‘cap casting’ technique. In response to Kajitani’s comments, where he questions the validity of the proposed method through his eight specific criticisms, we have made our assertion from an academic viewpoint. He has rightly pointed out a typographical error, where the TEM apparatus has been typed as JEOL 4000 FX instead of JEM-4000EX, for which we apologize. Nevertheless, our TEM, JEM-4000EX has indeed better resolution than that of ‘FX’ and, thus, this typographical error does not diminish the scientific significance of our results.
  • Production of Zr55Cu30Ni5Al10 Glassy Alloy Rod of 30 mm in Diameter by a Cap-Cast Technique

    pp. 2506a-2506a

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    DOI:10.2320/matertrans.ERM200905

  • Editor’s Announcement

    pp. 2506b-2506b

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    DOI:10.2320/matertrans.ERM200906

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