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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 9

  • Phase Equilibria in Ni-Rich Portion of Ni-Si System

    pp. 2259-2262

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    DOI:10.2320/matertrans.MB200702

    The phase equilibria of the Ni-rich portion in the Ni-Si system were investigated. The phase boundaries between liquid and fcc phases were established by the diffusion couple method and those of fcc and β1 or β2 were determined by the SEM-EDX measurement of two-phase alloys. The liquidus of the present work well agrees with the previous experimental data determined by a thermal analysis. The solidus data are rather different from the previous experimental data, but agree with the thermodynamic calculated phase diagram. This result suggests that the present solidus and liquidus data are consistent with thermodynamic data. The solubility of Si in the fcc phase agrees with some previous experimental data, but disagrees with the thermodynamic calculated phase diagram. This fact suggests that the thermodynamic reassessment for this system is necessary by the CALPHAD approach.
  • Thermodynamic Analysis of the Phase Equilibria in the Nb-Ni-Zr System

    pp. 2263-2271

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    DOI:10.2320/matertrans.MB200713

    A thermodynamic study of phase equilibria in the Nb-Ni-Zr system has been carried out experimentally and using the CALPHAD method. To enable the thermodynamic description of the constituent binary systems, the results from a previous evaluation were adopted for the Nb-Ni, Ni-Zr and Nb-Zr systems. However, some modifications of the thermodynamic parameters of the Ni-Zr system were made based on recent experimental data on the binary and ternary phase equilibria. The phase boundaries involving the liquid phase in the Nb-Ni-Zr ternary system at the constant 60 mol%Ni and 20 mol%Zr were determined experimentally using differential scanning calorimetry (DSC). The thermodynamic parameters of the Nb-Ni-Zr ternary system were evaluated by combining the experimental results from DSC with reported phase boundaries of the isothermal sections at 773 and 1073 K. The calculated results reproduced the DSC results as well as the experimental isothermal sections. Furthermore, the amorphous-forming ability of Nb-Ni-Zr ternary alloys was evaluated by incorporating the thermodynamic properties from the phase diagram calculations into the Davies-Uhlmann kinetic formulations. The calculated critical cooling rates in the observed metallic glass forming compositional range were found to be lower than those in the observed amorphous forming range by one or more orders of magnitude.
  • Cellular and Dendritic Growth in Constrained Solidification

    pp. 2272-2279

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    DOI:10.2320/matertrans.MB200701

    A theoretical model is developed to predict the characteristics of a needle (cellular or dendrite) interface during the controlled and arrayed solidification of binary alloys. Both heat and mass transport fields near a growing needle front have been considered. The effect of solute, diffused from nearby dendrites, on dimensions of needle is also taken into account. Minimum undercooling criterion of tip of interface has been developed to select a solution to determine the dimensions, satisfying the local equilibrium conditions at the interface. Solutions are classified into two categories; one is responsible to the cellular growth and the other to the dendrite growth. Good correlations are obtained between theory and experiments.
  • Phase-Field Simulation of Free Dendrite Growth of Aluminum-4.5 mass% Copper Alloy

    pp. 2280-2284

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    DOI:10.2320/matertrans.MB200708

    The free dendrite growth of aluminum-4.5 mass%copper alloy has been investigated using a three-dimensional phase-field model with thin-interface-limit parameters. The dendrite growth velocity and the tip radius of curvature are measured for a given value of anisotropy intensity of the interface energy, and the stability parameters are determined at different degrees of undercooling. The dendrite growth velocities are compared with those obtained by LKT (Lipton, Kurz and Trivedi) model, and the role of the stability parameter is quantitatively discussed.
  • Faceted Crystal Growth of Silicon from Undercooled Melt of Si-20 mass%Ni Alloy

    pp. 2285-2288

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    DOI:10.2320/matertrans.MB200709

    Two-dimensional faceted crystal growth of silicon from undercooled melt of Si-20 mass%Ni alloy was experimentally investigated, in which a droplet sample from 10 to 100 mg was undercooled on a single-crystal sapphire and growing crystals were observed in situ. Observed crystals were classified according to the shapes of square, wedge and irregular shapes. The growth velocity was measured for different undercooling conditions. The growth velocity of square shaped crystals was about half times smaller than that of wedge shaped crystals. The growth of square shaped crystals is regarded to be two-dimensional and it is compared with the results of two-dimensional phase-field simulations. Growth velocity in both is in good agreement and the linear kinetic coefficient is estimated to be 0.002 m/sK.
  • Extra Nodes Added on the Solid/Liquid Interface to Solve the Mass Transfer Problem in a Directional Solidification Process

    pp. 2289-2296

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    DOI:10.2320/matertrans.MB200711

    In a directional solidification process, since the liquid solubility is higher than the solid one, the surplus solute will be released from the solid/liquid interface into the liquid, which is the main source of increasing the liquid solute. The release of solute at the moving interface is like that of latent heat. Except the growth rate, the release of extra solute also depends on the liquid concentration at the interface, which is not fixed. Consequently, the numerical treatment of the solute release is not so easy as that of the latent-heat one. If the effect of solute release is not handled appropriately, the concentration solutions will diverge very easily. In this paper, extra nodes added on the solid/liquid interface in a fixed grid system are proposed to solve the mass transfer problem in the directional solidification process. A one-dimensional problem is firstly used to test the proposed method. The computing results are compared with those of other fixed grid methods and the analytical solutions from the literature. Finally, the feasibility of the proposed method is further testified by applying it to solve the concentration field of the crystal growth of GaAs in a Bridgman furnace.
  • Theoretical Considerations for Thermal Control over Solid Fraction of Aluminum Alloy Slurry Prepared by Cup-Cast Method

    pp. 2297-2303

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    DOI:10.2320/matertrans.MB200751

    Currently, semi-solid metal (SSM) processing has been established as a common technique of manufacturing net-shape components. Among different techniques available for SSM processing, Cup-Cast method is a recently developed technique that produces semi-solid slurry with appropriate properties in the easiest way. In Cup-Cast method due to variation in the alloy and cup, solid fraction and heat transfer condition would change. Consequently, the process would be more robust if the suitable cup for specific alloy can be predicted. For this purpose a dimensionless number γ has been introduced to determine the fraction solid and its variations, and it also can apply to find the condition with homogeneous temperature in the cup. By calculating fraction solid variations as a function of the dimensionless number γ, suitable range of cup for experimental test can be predicted.
  • Prediction of Thermal Properties In A Solidification Process

    pp. 2304-2311

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    DOI:10.2320/matertrans.MB200712

    In solidification models, the uncertainty of thermal properties will influence the computing results. In this paper, a non-linear inverse method is proposed to predict the thermal properties of materials according to the temperature data measured in solidification processes. With the proposed method, the solid and liquid thermal conductivities and specific heats of materials can be computed simultaneously. Furthermore, with the effective specific heat method, the inverse scheme can be utilized to calculate the latent heat. Stefan and Neumann problems are used to test the proposed method. From the computing results, it is proved that the properties can be predicted accurately. After that, the method is applied to the casting experiments, in which Al, Sn, 90 mass% Sn-10 mass% Pb alloy and A356 aluminum alloy are taken as testing materials. The computed thermal properties are very close to the values reported in the literature. From these results, it is shown that the proposed method provides an easy way to predict thermal properties with simple casting experiments.
  • Effects of Shaping Conditions on the Microstructure and the Mechanical Property of the Al2O3-YAG Eutectic Composite Produced by Melting the Al2O3-YAP Eutectic Structure

    pp. 2312-2315

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    DOI:10.2320/matertrans.MB200705

    When the Al2O3-YAP metastable eutectic system was heated above the metastable eutectic temperature but below the equilibrium eutectic temperature, undercooled melt was formed. Solidification in the equilibrium path accompanied the melting of the metastable eutectic system, resulting in a fine and uniform eutectic structure. A novel solidification process using undercooled melt formation was developed. In this paper, the influences of the initial Al2O3-YAP eutectic particle size, forming pressure and holding time at the maximum temperature on the microstructure and/or the mechanical property of the Al2O3-YAG compact were examined to optimize the forming conditions. The Al2O3-YAG compact produced from the Al2O3-YAP eutectic particles with diameters less than 20 μm exhibited a higher flexural strength and the smaller porosity as compared to that produced from Al2O3-YAP eutectic particles with diameters ranging from 20 μm to 45 μm. The volume fraction of the porosity was approximately 4% under a forming pressure of 10 MPa and a holding time of 60 s. The flexural strength of the Al2O3-YAG compact decreased with the increase in the holding time due to the increase in the lamellar spacing. For Al2O3-YAP eutectic particles with diameters less than 20 μm, a low forming pressure of 10 MPa and a short holding time of 60 s were sufficient to synthesize a dense Al2O3-YAG compact. Thus, the solidification technique that uses undercooled melt produced by melting the Al2O3-YAP metastable eutectic system has good advantages for shaping.
  • Inconel 690 Alloy Crystal Growth Orientation under Different Vibration Waveforms

    pp. 2316-2318

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    DOI:10.2320/matertrans.MB200719

    The crystal growth orientation of Inconel 690 alloy solidified under the application of additional kinetic energy was studied. By using an eccentric-mass electric motor for transmitting the kinetic energy to a melting pool, liquid atoms attained kinetic energy that enabled them to strike the solid-liquid interface during solidification. Due to unequal upper and lower amplitudes of the waveform, three types of states of the applied kinetic energy were discussed: (1) the kinetic energy required for the attachment of an atom is greater than that for detachment, (2) the kinetic energy for attachment is less than that for detachment, and (3) the kinetic energy for attachment is equal to that for detachment. The results reveal that unequal kinetic energies for attachment and detachment will encourage epitaxial growth in the (100) direction. Only when the kinetic energies for atom’s attachment and detachment are equal will the degree of epitaxial growth in the (100) direction will decrease.
  • Characterization and Mechanism of 304 Stainless Steel Vibration Welding

    pp. 2319-2323

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    DOI:10.2320/matertrans.MB200706

    Gas tungsten arc welding (GTAW) was performed on AISI 304 stainless steel; steady-state vibration was produced by a mass-eccentric motor. The vibration weld shows a very small δ-ferrite structure, uniform composition distribution, less residual stress and less δ-ferrite content relative to the weld without vibration. The results illustrate that the vibration reduces the micro supercooling and improves the nucleation of δ-ferrite to form a grain refined structure. Vibration-induced stacking faults are identified as the major cause of the line broadening of X-ray diffraction profile. Correlating the literature and the result in the study, the mechanism of vibratory stress relief can be represented as the breakdown of dislocation into a pair of partial dislocations. This mechanism can comprehensively explain all the phenomena that take place during vibratory stress relief.
  • Microstructure and Wear Characteristics of Hypoeutectic, Eutectic and Hypereutectic (Cr,Fe)23C6 Carbides in Hardfacing Alloys

    pp. 2324-2328

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    DOI:10.2320/matertrans.MB200716

    This study investigates the microstructure and wear characteristics of hypoeutectic, eutectic and hypereutectic (Cr,Fe)23C6 carbides in hardfacing alloy cladding by using gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to clad ASTM A36 steel substrates. These coatings were specially designed to vary the size and proportion of the (Cr,Fe)23C6 carbides that are present in the microstructure at room temperature. Depending on the amount of graphite used in the alloy filler, a hypoeutectic, eutectic or hypereutectic microstructure was obtained on the coated surface. The wear behavior indicated that the abrasive wear resistance is not only simply related to the hardness of the deposit but that it is also determined by the carbides and matrix structure of the coating. The hypereutectic carbides have the largest (Cr,Fe)23C6 carbide content and the maximum hardness; however, they show the worst wear resistance due to the large particles were dug out during wearing.
  • Creep Parameters in a Die-Cast Mg-Al-Ca Alloy

    pp. 2329-2335

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    DOI:10.2320/matertrans.MAW200701

    Tensile creep tests were conducted to determine the creep parameters for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) in a temperature range from 423 to 498 K. The stress exponent of the minimum creep rate, n, increases at the yield stress of the alloy, and it lowers at higher temperatures. The activation energy for creep, Qc, decreases with increasing applied stress typically below the yield stress. The change in the creep parameters, n and Qc, is associated with the decreased creep strength caused by the collapse of the eutectic intermetallic phase covering the primary α-Mg grains during creep. The thermally activated component of Qc is evaluated to be 143 kJ/mol below the yield stress, which is very close to the activation energy for the lattice self-diffusion of magnesium. It is deduced that the creep for the alloy is controlled by the high-temperature climb of dislocations.
  • Comparison of Mechanical Properties of Thin Copper Films Processed by Electrodeposition and Rolling

    pp. 2336-2339

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    DOI:10.2320/matertrans.MAW200708

    Thin copper films with grain sizes of 31 nm and 3.3 μm were processed by electrodeposition, and their mechanical properties were compared with those of a rolled copper film. The hardness and strength for the electrodeposited copper with a grain size of 3.3 μm were lower than those of the rolled copper with a grain size of 6.3 μm, however, the elongation to failure for the former was larger than that for the latter. Intense (111) texture formation was found for the rolled copper. Therefore, it is suggested that the difference in mechanical properties between the electrodeposited and rolled copper films are related to the texture formation. The electrodeposited copper with a grain size of 31 nm showed higher strength and larger elongation than the rolled copper. The very small grain size of 31 nm gave rise to the excellent mechanical properties.
  • Fabrication and Characterization of GaP Photonic Crystals for Terahertz Wave Application

    pp. 2340-2342

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    DOI:10.2320/matertrans.MAW200728

    We have fabricated GaP two-dimensional photonic crystals (PCs) for terahertz (THz) wave generation by a reactive ion etching in Ar/Cl2 gas chemistries. We performed 75-μm-deep etching of GaP, in which Al2O3 layer is applied as a hard mask with its selectivity as high as 125. We demonstrated the THz-wave generation from the fabricated GaP slab waveguide with the PC structure as a cladding layer under a collinear phase-matched difference frequency generation. In the frequency dependence of THz output power for the PC slab waveguide is seen at around 1.1 THz. From the in-plane transmission spectrum of THz-wave, we confirmed that the THz output characteristics had relation with the photonic structure for THz wave.
  • Deformation and Anelastic Recovery of Pure Magnesium and AZ31B Alloy Investigated by AE

    pp. 2343-2348

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    DOI:10.2320/matertrans.MAW200720

    Extruded pure magnesium and AZ31B alloy were compressed parallel and vertical to extrusion direction. Deformation behavior was investigated in monotonous compression by acoustic emission (AE). Anelastic recovery behavior was observed in cyclic compression-quick unloading-recovery process. AE method was applied in each recovery process to investigate detwinning behavior at different strain levels. It was found that twinned samples vertically compressed easily detwin compared to parallel samples in both pure magnesium and AZ31B alloy. Compared to pure magnesium, twinning in AZ31B alloy is more stable and shows weaker psuedoelasticity. A model of strain dependence on cumulative AE counts from detwinning was proposed and fitting results are in good agreement with experimental data.
  • Computation of Interfacial Thermal Resistance by Phonon Diffuse Mismatch Model

    pp. 2349-2352

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    DOI:10.2320/matertrans.MAW200717

    The thermal resistances of 1250 kinds of interface were computed at room temperature based on the phonon diffuse mismatch model. The result shows that the ratio of Debye temperature and the ratio of average sound velocity can be approximately used to characterize the difference of two materials in terms of interfacial thermal resistance. The high interfacial thermal resistances are composed of high and low Debye temperature materials. The low interfacial thermal resistances are composed of both similar Debye temperature materials, and their Debye temperatures are very high. The relation between the interfacial thermal resistance with the ratio of average sound velocity is similar to that of the ratio of Debye temperature.
  • Evaluation of the Potential Amounts of Dissipated Rare Metals from WEEE in Japan

    pp. 2353-2357

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    DOI:10.2320/matertrans.MAW200781

    The potential amounts of dissipated rare metals (Au, Ag, B, Ba, Cr, In, Ni, Pb, Sb, Sn, Sr, Ta, Zn and Zr) in WEEE (Cathode Ray Tube TV, liquid-crystal display TV, plasma display panel TV, refrigerator, air conditioner, washing machine, microwave oven and cleaner) have been estimated. For the estimation, the number of WEEE was also estimated using the population balance model. The composition of the WEEE were examined by interviews and the measurement using energy dispersive X-ray diffractometer. The estimated amounts of the dissipation were evaluated by both the ratio of the dissipation to domestic demand and the weight amount of the dissipation by “total materials requirement” (TMR).
  • Local Structure around Pd Atoms in Pd42.5Ni7.5Cu30P20 Excellent Glass-Former Studied by Anomalous X-ray Scattering

    pp. 2358-2361

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    DOI:10.2320/matertrans.MAW200715

    In order to study local structure around the Pd atoms in Pd42.5Ni7.5Cu30P20 excellent metallic glass-former, an anomalous X-ray scattering (AXS) experiment was performed at energies close to the Pd K absorption edge at the beamline BM02 of the European Synchrotron Radiation Facility. The differential structure factor, ΔPdS(Q), was obtained with a good statistical quality, which demonstrates that a pre-shoulder at about 20 nm−1, indicating the existence of an intermediate-range order, originates from the Pd-Pd atomic correlation. The first peak in the differential pair correlation function, ΔPdg(r), shows a longer inter-atomic length around the Pd atoms than the average value. The local structure around the Pd atoms is discussed in detail by comparing to the previous experiments of AXS and electronic structure.
  • Validity of Activation Energy for Vacancy Migration Obtained by Integrating Force–Distance Curve

    pp. 2362-2364

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    DOI:10.2320/matertrans.MAW200714

    Kuramoto et al. calculated the activation energy for dislocation loop migration by integrating the force–distance curve. Their method has a great potential for the determination of migration energy in many cases. However, the validity of the application of their method to point defect migration has not yet been proved, because the migration of point defects is a thermally activated process and the physical meaning of the force in the force–distance curve has not been clarified. In this study, the validity was investigated by three methods to calculate the vacancy migration energy. In the first method, the migration energy was obtained by definition from the difference in potential energy between the equilibrium configuration before migration and the saddle point configuration (Method 1) using a statistic lattice relaxation method. The second method involved a molecular dynamics simulation based on an absolute reaction rate theory (Method 2). The third method involved the integration of the force–distance curve obtained by the statistic lattice relaxation method mentioned above (Method 3). The calculation model used was a two-dimensional hexagonal lattice and the Morse potential for Cu was used. The migration energies obtained by Methods 1, 2 and 3 were 0.391 eV, 0.394±0.009 eV and 0.392 eV, respectively. As these values were similar, the validity of Method 3 was demonstrated.
  • Substance Flow Analysis of Indium for Flat Panel Displays in Japan

    pp. 2365-2369

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    DOI:10.2320/matertrans.MAW200702

    Substance flow analysis (SFA) of indium has been conducted in this study. The purpose of this study is to identify the relevant issues for the development of an efficient indium recycling system by performing SFA of indium supplied for indium-tin oxide (ITO) processing as transparent electrodes, which accounts for 86.9% of the total indium demand. In this study, as part of the development of substance and material flow data, (1) data on the flow of indium was collected and reviewed, (2) the amount of dissipated indium associated with the production of flat-panel displays (FPDs) were estimated and (3) its environmental impact was also assessed.
    The major conclusions are (a) 470 t-In is used in ITO for transparent electrodes, out of which 220 t-In is dissipated or potentially dissipated in Japan, and (b) 220 t-In of dissipated indium is equivalent to 11.4 TJ of energy consumption, 0.5×103 t of CO2 emissions, and 1.0×106 t of Total Materials Requirement (TMR).
  • Structural Analysis of Polycrystalline BiFeO3 Films by Transmission Electron Microscopy

    pp. 2370-2373

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    DOI:10.2320/matertrans.MAW200782

    A multiferroic polycrystalline BiFeO3 film has been fabricated by a chemical solution deposition followed by the post deposition annealing at 823 K in air. The nanostructure of the BiFeO3 film was characterized by transmission electron microscopy (TEM). The nano-beam electron diffraction and the fast Fourier transform pattern image from the high resolution TEM image were compared with the electron diffraction patterns of the multislice simulation, and it was revealed that the BiFeO3 has R3c rhombohedral structure. Formation of any additional phase or phases was not found in the sample. The BiFeO3 film shows the small saturation magnetization of 5.2 emu/cm3 without spontaneous magnetization at room temperature, which behavior is typical for the weak ferromagnetic materials. The ferroelectric hysteresis loop of the BiFeO3 film was measured at low temperature in order to reduce the leakage current. The remanent polarization and the electric coercive field at 90 K were 52 μC/cm2 and 0.51 MV/cm at an applied electric field of 1.4 MV/cm, respectively. The structure-magnetic properties relationship is also discussed.
  • Synthesis of Fine Ceramic Particles in Molten Aluminum by Combustion Reaction

    pp. 2374-2377

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    DOI:10.2320/matertrans.MAW200783

    Ceramic particles (TiB2 and TiC) dispersed aluminum alloy was synthesized by a combustion reaction. Starting materials were aluminum, titanium, boron and boron carbide. The heat of reaction between Ti/B and Ti/B4C was too high to maintain the original configuration of the blended powder compact. Aluminum was added to the blended powder mixture to control the adiabatic temperature of the reaction. Aluminum could successfully control the adiabatic temperature and prevented the collapse of the precursor. The average size of the TiB2 and TiC particles strongly depended on the amount of aluminum added as the diluents of the heat of reaction. By increasing the aluminum addition to the powder phase, the average size of TiB2 and TiC particles synthesized by the combustion reaction decreased. The TiB2 and TiC particles were extracted from aluminum matrix, and confirmed to have submicron size under the suitable conditions.
  • Improvement of Soft Magnetic Properties in (Fe0.85B0.15)100−xCux Melt-Spun Alloys

    pp. 2378-2380

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    DOI:10.2320/matertrans.MAW200730

    The Cu content dependence of magnetic properties in annealed (Fe0.85B0.15)100−xCux alloys fabricated by melt-spinning was discussed. The value of Hc markedly decreases with increasing x between x=1.0 and 1.5, accompanied with significant reduction of crystalline grain size. The alloy with x=1.5 showed excellent magnetic properties such as a small Hc of about 7 A/m and a high Bs of more than 1.8 T. For the present alloy system, more than 1.0% addition of Cu is effective for the formation of nano-scale grains and for the improvement of the soft magnetic properties.
  • Preparation of Open-Cell Porous Zr-Based Bulk Glassy Alloy

    pp. 2381-2384

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    DOI:10.2320/matertrans.MAW200707

    A Zr-Nb-Al-Ni-Cu porous bulk glassy alloy was prepared by a melt infiltration technique using La2O3 compact. The alloy has open-cell structure with a pore size of about 50 micrometer and roughened cell wall structure. The yield strength and Young’s modulus of the porous alloy are 180 MPa and 17 GPa, respectively, which are coincident with those for human cortical bone. The porous alloy exhibited good corrosion resistance in a simulated human body fluid, indicating the possibility of application as biomaterials.
  • Formation and Thermal Stability of Ni-Based Bulk Metallic Glasses in Ni-Zr-Nb-Al System

    pp. 2385-2389

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    DOI:10.2320/matertrans.MAW200705

    An Al element was selected as an alloying metal to improve the glass-forming ability (GFA) of Ni-Zr-Nb alloys. The thermal stability and glass-forming ability of Ni-Zr-Nb-Al alloys were investigated. It was found that the partial substitution of Nb by Al led to significant shift of the onset crystallization temperature Tx and the liquidus temperature Tl, while the glass transition temperature Tg was less composition sensitive. The supercooled liquid region, ΔTx (=TxTg), the reduced glass transition temperature (TgTl) and γ=Tx⁄(Tg+Tl) increased with increasing Al content up to 5 at%. The best GFA was found at Ni60Zr20Nb15Al5 with a critical diameter of 3 mm. The characteristic parameters are: ΔTx=54 K, TgTl=0.615 and γ=0.405. The maximum values of ΔTx and TgTl were 72 K and 0.617, respectively, at Ni60Zr25Nb10Al5. The compression tests showed that the Ni60Zr20Nb15Al5 BMG possessed high fracture strength of 2900 MPa, Young’s modul of 152 GPa, and plastic elongation of 2.5% at room temperature.
  • Effects of Ta on Microstructure and Mechanical Property of Ti-Zr-Cu-Pd-Ta Alloys

    pp. 2390-2394

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    DOI:10.2320/matertrans.MAW200704

    The effects of Ta on microstructure and mechanical property of Ti-Zr-Cu-Pd-Ta alloys without toxic element were investigated in this paper. The results revealed that with increasing Ta content, the glass-forming ability of examined alloys decreased. Nano-crystalline composites were obtained with 1% and 3% Ta addition. Higher strength and distinct plastic deformation comparing with Ti-Zr-Cu-Pd base alloy were achieved in 1% Ta-containing alloys due to the nano-particles existing in the glassy matrix which inhibit the deformation of shear bands. Dendrite enriched with Ta was also observed in the 5% Ta-containing alloy by SEM. No plastic deformation was observed for 3% and 5% Ta-containing alloys with the high volume fractions of crystallization over 50%.
  • Hydrogen Storage Properties and Corresponding Phase Transformations of Mg/Pd Laminate Composites Prepared by a Repetitive-Rolling Method

    pp. 2395-2398

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    DOI:10.2320/matertrans.MAW200726

    Mg/Pd laminate composites (Mg/Pd = 6) prepared by a repetitive-rolling method can reversibly absorb and desorb a large amount of hydrogen, up to 1.47 H/M (4 mass%) at 573 K. Pressure-composition isotherms of the Mg/Pd laminate composites show two plateaux, PL=0.2 MPa and PH=2 MPa, during hydrogen absorption and desorption. To clarify the correlation between hydrogen storage properties and phase transformations, we investigated structural changes of the Mg6Pd intermetallic compound with in-situ XRD. The low-pressure plateau PL corresponds to the decomposition of Mg6Pd into Mg5Pd2 and MgH2, and the high-pressure plateau PH to the decomposition of Mg5Pd2 into MgPd and MgH2. In subsequent dehydrogenation processes, part of the MgH2 reformed Mg, and the Mg and MgPd form Mg5Pd2 at the high-pressure plateau PH and then the remaining MgH2 reformed Mg, and the Mg and Mg5Pd2 form Mg6Pd at the low-pressure plateau PL. According to this mechanism, the Mg6Pd can absorb and desorb hydrogen through reversibly disproportionation and recombination processes.
  • Effects of Transmutation Elements on Neutron Irradiation Hardening of Tungsten

    pp. 2399-2402

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    DOI:10.2320/matertrans.MAW200722

    Tungsten (W) is a candidate material for Plasma facing materials of fusion reactors. During fusion reactor operation, not only irradiation damages but also transmutation elements such as rhenium (Re) and osmium (Os) are produced by neutron irradiation. As a result, the original pure tungsten changes to W-Re or W-Re-Os alloys. Thus, the mechanical and physical properties are expected to change. The aim of this study is to investigate the effects of transmutation elements on neutron irradiation hardening and microstructure changes of tungsten.
    To simulate the effects of transmutation elements, tungsten base model alloys were used in this study. The examined compositions of the alloys were selected from the calculated changes in solid solution area of W-Re-Os alloy. Neutron irradiation was performed in fast test reactor JOYO in JAEA. The irradiation damages and temperature ranges were 0.17–1.54 dpa and 400–750°C respectively. After the irradiation, Vickers hardness test and TEM observation were performed.
    There were clear differences between Re and Os in effects on irradiation hardening. In the case of W-Re alloys, when damages were less than 0.40 dpa, the irradiation hardenings were nearly equal to those of pure tungsten independent of Re addition. But when the damage was 1.54 dpa, the irradiation hardenings increased lineally with Re content. Microstructural observations showed that precipitations mainly formed in W-Re alloys. In the case of W-Os alloys, the irradiation hardenings (ΔHv) of W-3Os alloys were larger than those of pure tungsten. And the differences were about 400 independent of dpa and irradiation temperature. Effects of Re and Os on irradiation hardening based on the microstructural observations were discussed.
  • Mechanical Properties of Co-Based L12 Intermetallic Compound Co3(Al,W)

    pp. 2403-2408

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    DOI:10.2320/matertrans.MAW200734

    Mechanical properties of L12-Co3(Al,W) polycrystalline sample are investigated by compression testing at various temperature ranging from room temperature to 1193 K. It was found that at room temperature the 0.2% flow stress is 410 MPa and the compressive ductility is higher than 10%, whereas at 1193 K the 0.2% flow stress is 382 MPa and the compressive ductility is about 10%. Two candidates for the reaction scheme of the Co-rich region of the Co-Al-W ternary phase diagram are proposed by combining the results of microstructure observation, X-ray diffractometry and the previous report.
  • Effects of Size and Volume Fraction of Precipitated Crystalline Phase Induced by Friction Stir Processing on Hardness in Zr–Al–Ni–Cu Bulk Metallic Glass

    pp. 2409-2413

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    DOI:10.2320/matertrans.MAW200733

    The effects of the size and volume fraction of the precipitated crystalline phase induced by friction stir processing (FSP) on the hardness in Zr–Al–Ni–Cu bulk metallic glass (BMG) was examined. The microstructure in the friction zone (FZ) exhibits an amorphous “band-like” structure with a small number of nanoscale crystalline particles. On the other hand, the microstructure in the FZ near the finishing point of the process exhibits a large number of nanocrystalline particles with a size of less than 20 nm and amorphous phase. The difference in the microstructures of FSP regions is explained in terms of differences in the heat input by FSP. The hardness in both FSP regions is greater than that of heat-treated specimens with almost the same volume fraction of the crystallized phase. Control of the size and volume fraction of precipitated crystalline phase induced by FSP offers the possibility of further improvement in the mechanical properties of BMGs.
  • Magnetic Phase Transition of MnBi under High Magnetic Fields and High Temperature

    pp. 2414-2418

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    DOI:10.2320/matertrans.MAW200721

    Magnetization measurements and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in magnetic fields up to 14 T and in 300–773 K, in order to investigate the magnetic phase transition. The magnetic phase transition temperature (Tt) at a zero magnetic field is 628 K and linearly increases with increasing fields up to 14 T at the rate of 2 KT−1. A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above Tt. The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in 626–623 K, which relates to the metamagnetic transition. The obtained results were discussed on the basis of a mean field theory.
  • Molecular Dynamics Simulation of Thermal Conductivity of Silicon Thin Film

    pp. 2419-2421

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    DOI:10.2320/matertrans.MAW200710

    We computed the thermal conductivity of silicon single crystal thin film with a thickness of 25 nm–134 nm at room temperature by non-equilibrium molecular dynamics simulation. The thermal conductivity was shown to depend on the thickness of the film, and is markedly lower than that in bulk silicon. The phonon classical thermal conductivity theory, incorporating the Boltzmann transport equation, was used to establish a phonon scattering model for size dependence. The results show that boundary scattering is very strong for phonon transport in silicon thin film.
  • Effect of Hf Addition on Oxidation Properties of Pt-Ir Modified Aluminide Coating

    pp. 2422-2426

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    DOI:10.2320/matertrans.MAW200723

    In the present study, the effect of Hf addition on oxidation kinetics of Pt-Ir modified aluminide coatings was investigated. Pt-15 at%Ir and Pt-15 at%Ir with trace amount of Hf films with 7∼8 μm thick were deposited on a Ni-based single crystal superalloy TMS-82+ using magnetron sputtering, followed by a diffusion treatment and conventional Al pack cementation. While there were no significant microstructual differences observed in as aluminized specimens, cyclic oxidation test at 1423 K revealed clear advantages of Hf addition. Hf containing coatings showed smaller mass change with retarded surface rumpling during cyclic oxidation test. These results confirmed the beneficial effects of Hf addition reported for other alloy systems such as Pt modified γ-γ′ coatings and Pt modified aluminide coatings.
  • Strengthening of Titanium Silicon Carbide by Grain Orientation Control and Silicon Carbide Whisker Dispersion

    pp. 2427-2431

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    DOI:10.2320/matertrans.MAW200718

    Strengthening of titanium silicon carbide (Ti3SiC2) was investigated by the grain orientation control and silicon carbide (SiC) whisker dispersion. Ti3SiC2 with preferentially oriented grains was prepared by hot-pressing of milled Ti3SiC2 powder. Composites were also fabricated by hot-pressing of a blend of the milled Ti3SiC2 powder and SiC whiskers. During hot-pressing, the preferential orientation of Ti3SiC2 grains was achieved while the precipitation of titanium carbide (TiC) occurred. As a result, 4-point bending strength of preferentially-oriented Ti3SiC2 was approximately 1.5 times the randomly-oriented pure Ti3SiC2 in a temperature range from room temperature to 1073 K. The bending strength of Ti3SiC2 with 15 vol% whiskers reached approximately 1 GPa, approximately 3 times the randomly-oriented pure Ti3SiC2, in the range to 1073 K. The results in this study indicate that the strengthening effect on Ti3SiC2 was contributed from the orientation control, TiC precipitation and SiC whisker dispersion.
  • Mechanical Behavior of Ti3AlC2 Prepared by Pulse Discharge Sintering Method

    pp. 2432-2435

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    DOI:10.2320/matertrans.MAW200703

    Almost single-phase ternary compound Ti3AlC2 was successfully synthesized by pulse discharge sintering (PDS) from Ti/Al/TiC powder mixtures with molar ratio of 2:2:3. The typical microstructure of Ti3AlC2 was found to consist of plate-like grains with mean size of 9.5 μm in length. Four-point bending testing results revealed that the fracture behavior is brittle below 1200°C, and some characteristics of plastic deformation were observed at higher testing temperatures. The polycrystalline Ti3AlC2 synthesized by PDS technique shows good strength at high temperatures.
  • Outflow of Resources from Japan focusing on End-of-life Vehicles

    pp. 2436-2444

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    DOI:10.2320/matertrans.MAW200712

    In order to examine the risk to resource security in Japan, this paper quantifies the outflow of base metals (iron, aluminum, copper, lead, and zinc) through export of end-of-life vehicles (ELVs) from Japan from 1988 to 2005 using the Trade Statistics of Japan and vehicles composition data. Estimates were also made for engine-related rare metals (manganese, nickel, chromium, and molybdenum), under statistical restrictions. This analysis shows that 24% of iron, 38% of aluminum, 13% of copper, 53% of lead, 11% of zinc, and 38% of rare metals in ELVs in Japan were not recycled and flowed out of the country, mostly in the form of used vehicle and parts. The destinations of these metals were mainly developing countries with rudimentary recycling technology. These results strongly indicate that many metal resources that could be utilized domestically from automobiles in Japan were instead scattered and lost overseas.
  • New TiZrCuPd Quaternary Bulk Glassy Alloys with Potential of Biomedical Applications

    pp. 2445-2448

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    DOI:10.2320/matertrans.MRA2007086

    In this paper, we have developed TiZrCuPd quaternary bulk glassy alloys which seem to be favorable for future application as biomaterials because of the absence of toxic elements such as Ni, Al and Be. A series of (TiZr)50(CuPd)50 bulk glassy alloys exhibit high glass-forming ability (with critical diameters of 6 and 7 mm) and relatively large supercooled liquid region (ΔTx) of over 50 K. This alloy system follows the three empirical rules for stabilization of supercooled liquid. The thermal stability of Ti40Zr10Cu36Pd14 bulk glassy alloy was also examined in correlation with the origin for the high glass-forming ability.
  • Surface Free Energy Effects in Sputter-Deposited WNx Films

    pp. 2449-2453

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    DOI:10.2320/matertrans.MRA2007095

    WNx thin films have attracted much attention for semiconductor IC packaging molding dies and forming tools due to their excellent hardness, thermal stability. WNx thin films with WN0.46, WN1.03, WN1.52, WN1.91, WN2.54 were prepared using radio frequency (RF) sputtering. The experimental results showed that the contact angle at 20°C go up with raising N2 content to 116.7° at beginning, corresponding to WN1.91, and then drop off. In addition, the contact angle components decreased with increasing surface temperature. Because increasing surface temperature disrupts the hydrogen bonds between water, Diiodomethane, Ethylene glycol and the films and these liquids vaporize gradually. The total SFE at 20°C decrease with N2 content to raise to 37.6 mN/m(WN1.91) at the start, and then increase. Because a larger contact angle means that a weaker hydrogen bonding, resulting in a lower SFE. The polar SFE component has same trend with total SFE, but the dispersive SFE component is on the contrary exactly. The polar SFE component is also lower than the dispersive SFE component. This is resulting from hydrogen bonding being polar. The total SFE, dispersive SFE and polar SFE of WNx films decreased with increasing surface temperature. This is because liquids evaporation on the surface, disrupted hydrogen bonds and surface entropy increasing with increasing temperature. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. Because SFE and surface roughness can be expressed as a function in direct ratio.
  • Changes in Hydrogen Permeability and Microstructures of Nb-(Ti, Zr)Ni Alloys by Cold Rolling and Annealing

    pp. 2454-2458

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    DOI:10.2320/matertrans.MRA2007096

    Maximum cold rolling reduction rates of as-cast Nb40Ti30−xZrxNi30 alloys were measured to evaluate ductility by measuring the change in the thickness. 50% or higher reduction rates were obtained for the alloys containing the Zr content of 12 mol% or less, but lower values were obtained for the alloys substituted with more Zr. Changes of hydrogen permeability (Φ) and microstructures of the Nb40Ti18Zr12Ni30 alloy caused by cold-rolling and subsequent vacuum annealing were investigated. Φ of this alloy was reduced to the half of the as-cast one by the 50% reduction rate, but recovered to 3.23×10−8 [molH2m−1 s−1 Pa−0.5], which is 1.13 times higher than that of as-cast one, by a subsequent annealing for 360 ks at 1273 K. Although the eutectic phase disappeared and was replaced by a small spherical (Nb, Ti, Zr) phase embedded in the (Ti, Zr)Ni matrix after rolling and subsequent annealing, these alloys showed good resistance to the hydrogen embrittlement at 523 K or more.
  • Annealing-Induced Devitrification Behavior of a Ti47.4Zr5.3Ni5.3Cu42.0 Glassy Alloy

    pp. 2459-2463

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    DOI:10.2320/matertrans.MRA2007033

    We have investigated devitrification behavior, accompanied by glass transition and precipitation of crystallites, as a function of annealing temperature and time for a Ti47.4Zr5.3Ni5.3Cu42.0 glassy alloy sheet, together with embrittlement behavior using bending fracture strain test. From kinetic analysis in one DSC profile under a constant heating rate, we can easily estimate the devitrification with temperature and time upon annealing. The glassy alloy became brittle during progressive devitrification in accordance with kinetic estimation. In sharp contrast with a Zr55Al10Ni5Cu30 glassy alloy, all the precipitations of crystallites (Cu4Ti3, Ti and CuTi) occur above glass transition temperature (Tg). We found that the Ti-based glassy alloy has large structurally and thermally stable area, which does not brittle up to 1.10×104 s at 650 K and 1.29×1010 s at 600 K, by experiment and kinetic estimation, respectively.
  • Preparation of TiO2 Nanotubes and Their Photocatalytic Properties in Degradation Methylcyclohexane

    pp. 2464-2466

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    DOI:10.2320/matertrans.MRA2007616

    The tubular TiO2 photocatalysts were successfully synthesized by hydrothermal method. The external tube diameters fall in 8 and 12 nm and the internal diameters are between 5 and 8 nm. Moreover, the lengths of the nanotubes are up to 500 nm and the specific surface area increases to 330 m2/g, while TiO2 powders are 78 m2/g. Methylcyclohexane (MCH) was selected as the target pollutant to investigate the photocatalytic performance. The results indicate that TiO2 nanotubes accelerate the degradation of MCH under the same conditions, comparing with TiO2 nanoparticles. Finally, the degradation reaction shows a first order kinetics.
  • Morphology of Intermetallic Compounds in Al-Si-Fe Alloy and Its Control by Ultrasonic Vibration

    pp. 2467-2475

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    DOI:10.2320/matertrans.F-MRA2007874

    Iron impurity in aluminum alloys forms coarse needle-shaped intermetallic compounds during solidification and hampers the recycling process. To control the morphology of the material microstructure, an experiment was carried out where ultrasonic vibration was applied to the melt during solidification. Aluminum-Silicon-Iron alloys containing 4 mass% iron were melted and solidified. The primary crystals that formed from the melts were intermetallic compounds that were identified as Al3Fe, α-AlSiFe (Al7.4SiFe2) and β-AlSiFe (Al9Si2Fe2). The refinement of these intermetallic compounds was thought to occur with the application of ultrasonic vibration. Accurate results were obtained when the vibration was applied at the liquidus temperature. The liquidus temperatures of the Al-6∼15Si-4Fe alloys were in the range of 945 to 955 K regardless of the silicon content and that of the Al-18Si-4Fe alloy was 977.2 K.
    Coarse plate-like intermetallic compounds formed in Al-6 mass%Si-4 mass%Fe and Al-12 mass%Si-4 mass%Fe alloys, which can be refined by the application of ultrasonic vibration on crossing the liquidus temperature on cooling. The coarse columnar structure of an Al-18 mass%Si-4 mass%Fe alloy was modified to a fine grained structure.
  • A Scheme to Design Multi-Component Bulk Metallic Glasses in Ideal Glass-Forming Liquids

    pp. 2476-2482

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    DOI:10.2320/matertrans.MJ200762

    In this study, we have proposed to use binary eutectics, rather than individual constituent elements, as basic units for designing complex multi-component bulk metallic glasses (BMGs), based on a novel physical concept of “ideal” glass-forming liquids. An innovative approach to designing multi-component BMGs in these ideal liquids was thus established and the reliability and usefulness of the current approach of this strategy has been confirmed in the Zr-Fe-Cu-Al metallic systems. As a result, several new BMGs with superior GFA in this system were successfully developed.
  • Effect of Die Surface Roughness on Deformation Characteristics and Cavitation during Blow Forming in a Superplastic 5083 Alloy

    pp. 2483-2488

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    DOI:10.2320/matertrans.MRA2006319

    Effect of die surface roughness on deformation behavior of a superplastic material has relatively been less examined, though it is important for industrial application during die design. In this paper, a superplastic 5083 Al alloy under bi-axial deformation was investigated by deforming the sheet into a rectangular die cavity with different degrees of die surface roughness. It was found that reducing the interfacial friction by use of a die with a smaller surface roughness improved the metal flow after the deformed sheet had made contact with the die bottom surface. Changes of the metal flow during forming not only developed a better thickness distribution of the formed part, but also reduced the cavitation levels.
  • Three Dimensional Analysis of Thermal Stress and Prediction of Failure of Polytypoidally Joined SI3N4-AL2O3 Functionally Graded Material (FGM)

    pp. 2489-2493

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    DOI:10.2320/matertrans.MRA2007092

    Three-dimensional analysis methods to calculate residual stress for functionally graded material (FGM) sample using sialon polytypoids to join silicon nitride and Alumina are introduced in this paper. The various multilayered FGM samples with 3, 9, and 20 layers were sintered to fabricate a crack-free joining of heterogeneous ceramics. To calculate three-dimensional thermal stresses of those fabricated FGM samples, a finite element analysis tool, ALGOR, was used. The Von Mises failure criterion and the maximum stress criterion were applied to predict failures in the FGM samples. For each case, calculated strength of each FGM layer by rule of mixture was compared with predicted thermal residual stresses. The Von Mises failure criterion predicted the locations of cracks more precisely than the maximum stress criterion. Such analyses are especially useful for graded FGM samples where the residual stresses are very difficult to measure experimentally.
  • Study of Solid Accretion Formation inside Pyrometallurgical Vessels by a Wax Model and Similarity Conversion for Gas Bottom-Blown Process

    pp. 2494-2500

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    DOI:10.2320/matertrans.MRA2007107

    In this study, a wax model with an extra low temperature (−110°C) gas blown-in system was established to simulate the phenomena inside ironmaking and steelmaking vessels and investigate the effects of gas bottom-blown conditions on the shape and dimensions of solid accretion sitting on the refractory lining near gas tuyeres.
    The experiments were conducted with the gas flow rate set in the range of 30–90 Nl/min. The results show that increasing gas flow rate or decreasing wax temperature increases the sizes of the wax accretion. Not only accretion size but also formation time and growth rate increase with gas flow rate and decreases with wax temperature. The results also show that final height of accretion is directly proportional to its growth rate and square of the formation time.
    In addition, Accretion Similarity Conversion Method (ASCM) was developed for correlating conditions of the accretion formation in the similar systems. A cone-shaped accretion was assumed to increase the accuracy of ASCM. The results indicate that the accretions sizes inside the wax model under a specific condition can be reasonably estimated by modified ASCM with the observed results of the water model from a previous study.
  • Dissimilar Friction Stir Welded Joints between 2024-T3 Aluminum Alloy and AZ31 Magnesium Alloy

    pp. 2501-2505

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    DOI:10.2320/matertrans.MRA2007093

    Dissimilar alloys such as 2024-T3 Al alloy and AZ31 Mg alloy of plates in 3 mm thickness has been friction stir butt welded. The welding was carried out at a constant rotation speed of 2500 min−1 and welding speeds of 200, 300, 400 and 550 mm/min. Effects of welding speeds on microstructures and hardness distributions of the joints were investigated. Distribution of phases in the stir zone (SZ) was analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS).
    Increasing welding speed brought about a redistribution of phases in SZ where the regions occupied by 2024 Al alloy concentrated in the lower portion of SZ while AZ31 Mg alloy concentrated in the upper region beneath the tool shoulder. The laminated structure was formed in the SZ near the boundary between SZ and TMAZ on the advancing side of 2024 Al alloy regardless of the welding speed. The hardness value fluctuates in the SZ due to formation of intermetallic compounds that formed by constitutional liquation during welding.
  • Fabrication and Thermal Properties of Carbon Nanotube/Nickel Composite by Spark Plasma Sintering Method

    pp. 2506-2512

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    DOI:10.2320/matertrans.MRA2007084

    Multiwall carbon nanotube (MWNT) materials are attractive because they possess excellent thermal conductivity and mechanical properties. However, few reports exist that focus on improving the thermal conductivity of MWNT by combining it with a metal matrix. Thus to improve the thermal conductivity, a nickel-matrix composite with MWNT was prepared by slurry mixing process using ethanol as a solvent. Using spark plasma sintering (SPS), MWNT/Nickel nanocomposites were fabricated and the fabrication conditions were investigated. The sintered relative densities of the composites containing up to 5 vol% of MWNT were above 99%. The thermal and electrical behaviors of the MWNT/Nickel composites were determined using the laser flash and van der Pauw methods, respectively, and were found to be anisotropic. The thermal conductivity was found to increase by 10% for the composition with 3 vol% MWNT.
  • Numerical Analysis for Electromigration of Cu Atom

    pp. 2513-2517

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    DOI:10.2320/matertrans.MRA2007082

    The electromigration of Cu interconnection was investigated to solve the Huntigton’s equation by numerical analysis. The Cu atoms moved toward anode from cathode and accumulated at the anode end. This result was in good agreement with the result previously derived by our theoretical analysis. The accumulation rate of Cu atoms increased with increasing in current density, but it was not so influenced by temperature.
    The characteristic of the rate of electromigration showed a liner relationship with current density and exponential relationship with temperature. This result agreed with the equation experimentally derived by Black. This result proved that numerical analysis of atom transport equation enables to predict of electromigration failure time.
  • Dynamic Substance Flow Analysis of Aluminum and Its Alloying Elements

    pp. 2518-2524

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    DOI:10.2320/matertrans.MRA2007102

    Aluminum demand in Japan has grown significantly during the last few decades. For most uses, small amounts of other metals are added to the primary aluminum to make harder alloys, which are classified by the nature and concentrations of their alloying elements. Aluminum scraps from end-of-life products, which are used as raw materials for secondary aluminum, are often mixtures of several alloys. Therefore, not only the amount of scrap but also the concentrations of their alloying elements must be taken into account when assessing the maximum recycle rate of aluminum scraps.
    This paper reports a dynamic substance flow analysis of aluminum and its alloying elements in Japan, focusing on the alloying elements Si, Fe, Cu and Mn. We devised eight categories of aluminum end uses and 16 types of aluminum alloys. The amount of each alloy in each end-use category was estimated from statistical data. We then estimated future quantities of discarded aluminum in each of the eight categories using the population balance model. At the same time, we calculated the concentrations of the alloying elements in each of the end uses.
    It was estimated that the amount of aluminum recovered in Japan would be about 1800 kt in 2050, which is 2.12 times that recovered in 1990. Calculated concentrations of alloying elements in aluminum scraps showed good correlation with those of the measured data.
  • Effects of Strain Rate and Temperature on the Deformation and Fracture Behaviour of Titanium Alloy

    pp. 2525-2533

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    DOI:10.2320/matertrans.MRA2007607

    The deformation response and fracture behaviour of Ti alloy under strain rates of 8×102 s−1 to 8×103 s−1 at temperatures ranging from 25°C to 900°C are studied using split-Hopkinson pressure bar. The mechanical properties and fracture features of the alloy are found to be significantly dependent on both the strain rate and the temperature. At a constant temperature, the flow stress increases with increasing strain rate. However, at a given strain rate, the flow stress reduces as the temperature increases. Furthermore, the fracture strain decreases with increasing temperature prior to phase transformation at 785°C, but increases thereafter as the temperature is further increased. As the strain rate increases, the strain rate sensitivity increases, but the activation volume decreases. However, as the temperature increases, the strain rate sensitivity decreases and the activation volume increases. Optical microscopy (OM) and scanning electron microscopy (SEM) observations reveal that the alloy specimens fracture primarily as the result of the formation of adiabatic shear bands. The fracture surfaces of the impacted specimens exhibit both dimple-like and cleavage-like features. The density of the dimples reflects the toughness of the alloy specimen and is found to vary directly as a function of the strain rate and the temperature.
  • Correlation between sp2/sp3 Ratio or Hydrogen Content and Water Contact Angle in Hydrogenated DLC Film

    pp. 2534-2538

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    DOI:10.2320/matertrans.MER2007044

    Water contact angle has been measured to indirectly assess the sp2/sp3 ratio and hydrogen content of DLCH film under post N2 annealed treatment with O2 content under 100 ppm. XPS spectrum is used to measure the C1s bonding type and calculate the sp2/sp3 ratio. The surface morphology of DLCH film was examined by SEM and AFM. From experimental results, it seems the surface morphology was not a critical factor on water contact angle value, at least for DLCH film. A quantitative correlation between water contact angle and sp2/sp3 ratio of DLCH film is established from which the hydrogen content can be estimated by the sp2/sp3 ratio as well as Angus equation.
  • Enhanced Grain Refinement by Mechanical Twinning in a Bulk Cu-30 mass%Zn during Multi-Directional Forging

    pp. 2539-2541

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    DOI:10.2320/matertrans.MRP2007123

    A bulk Cu-Zn alloy was multi-directionally forged at 77 K and 300 K to a cumulative strain of ΣΔε=6.0. With increasing strain, the initial grains subdivided gradually to ultrafine grains. Mechanical twins enhanced the grain fragmentation. The formed twins were further subdivided by the other variants of twins. The grain size obtained at ΣΔε=6.0 was about 17 nm at 77 K and 26 nm at 300 K.
  • Unusual Plasticity of the Particulate-Reinforced Cu-Zr-Based Bulk Metallic Glass Composites

    pp. 2542-2544

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    DOI:10.2320/matertrans.MEP2007099

    We report a particulate-reinforced bulk metallic glass composite with high strength and unusual plasticity, which consists of Ta particles homogenously distributed in Cu36Zr48Al8Ag8 glassy matrix. The glassy matrix remains amorphous even after adding up to 15 vol.% of Ta particles. A largest plastic strain of up to 31% was obtained for the 10% Ta-containing composite. Ta particles seed the initiation of multiple shear bands and block the shear band propagation, leading to a net-like homogeneous distribution of the shear bands.

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