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

MATERIALS TRANSACTIONS Vol. 54 (2013), No. 6

  • PREFACE

    pp. 859-859

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    DOI:10.2320/matertrans.MPR2013903

  • Bondability of Copper Joints Formed Using a Mixed Paste of Ag2O and CuO for Low-Temperature Sinter Bonding

    pp. 860-865

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    DOI:10.2320/matertrans.MD201202

    The bondability of copper joints formed using a mixed paste of silver oxide (Ag2O) and copper oxide (CuO) that contained reducing solvents was evaluated in order to achieve bonds that exhibited high migration tolerance and could serve as Pb-free alternatives to the conventional bonds formed using high-melting point solders in electronics packaging. The Ag2O particles reduced into silver nanoparticles at 150°C, whereas the CuO reduced into copper nanoparticles about 300°C. The joints formed using the Ag2O/CuO mixed paste, when heated to the appropriate levels, exhibited bondability superior to that of conventional Pb–5Sn joints. The oxide film formed on the copper substrate was reduced by the combustion of polyethylene glycol 400, and bonding was achieved between the sintered layer and the copper substrate. A longer period resulted in the oxidisation of a few layers of sintered copper layers into Cu2O. The ion-migration tolerance of the Ag2O/CuO mixed paste was approximately four times that of a layer of pure sintered silver.
  • Effect of Polyethylene Glycols with Different Polymer Chain Lengths on the Bonding Process Involving In Situ Formation of Silver Nanoparticles from Ag2O

    pp. 866-871

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    DOI:10.2320/matertrans.MD201201

    The need for lead-free alternatives to conventional solders for metal-bonding processes has prompted the development of processes based on metal nanoparticles. In this study, the low-temperature bondability of silver oxide (Ag2O) pastes containing polyethylene glycols (PEGs) with different polymer chain lengths was investigated. Bonding was achieved because of the low-temperature sinterability of silver nanoparticles that form in situ through redox reactions between Ag2O and PEGs. It was found that PEGs with shorter chain length provide superior bondability at low bonding temperatures. Thermogravimetric-differential thermal analysis and thermomechanical analysis showed that shorter PEGs resulted in less residual organic material in the sintered silver layer and contributed to form a larger amount of silver nanoparticles. Therefore, pastes with shorter PEGs afforded well-sintered, high-density silver joints and exhibited superior bondability even at lower temperatures. Using ethylene glycol, which has the shortest chain length, the tensile strength achieved was 11 MPa for bonding at 150°C.
  • Mechanism of Low Temperature Sintering-Bonding through In-Situ Formation of Silver Nanoparticles Using Silver Oxide Microparticles

    pp. 872-878

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    DOI:10.2320/matertrans.MD201231

    In this paper, a low temperature sintering-bonding process through in-situ formation of silver (Ag) nanoparticles using silver–oxide (Ag2O) microparticles was studied. The Ag2O powders were mixed with triethylene glycol (TEG) to form a paste, which was used to bond the Ag-coated copper (Cu) bulks. The results revealed that high temperature was helpful to increase the bond strength, and the joints average shear strength can reach 21.9 MPa at 523 K under 2 MPa for 5 min. And the mechanism of the reaction and sintering bonding process were basically made clear by using TGA-FTIR, FE-SEM and XRD, further, a reasonable sintering-bonding model was proposed.
  • Metal–Metal Bonding Process Using Cu+Ag Mixed Nanoparticles

    pp. 879-883

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    DOI:10.2320/matertrans.MD201222

    The Cu+Ag mixed nanoparticles were prepared based on the chemical reduction method. The polymer coated on the Cu+Ag mixed nanoparticles can protect Cu nanoparticles from oxidation. The metal–metal joint of silver plated Cu bulks was investigated with the use of Cu+Ag mixed nanoparticles. The bonding experiments show that joint with shear strength about 20 MPa was formed at the bonding temperature above 250°C under 5 MPa using Cu+Ag mixed nanoparticles. The strength of bonding using Cu+Ag mixed nanoparticles is lower than that of bonding using pure Ag nanoparticles. This may be due to the fact that the sintering between the Cu nanoparticles and Ag nanoparticles is more difficult than the sintering between Ag nanoparticles.
  • Molecular Dynamics Simulation of Sintering and Surface Premelting of Silver Nanoparticles

    pp. 884-889

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    DOI:10.2320/matertrans.MD201225

    Sintering of Ag nanoparticles (NPs) is increasingly being used as a driving mechanism for joining in the microelectronics industry. We therefore performed molecular dynamics simulations based on the embedded atom method (EAM) to study pressureless sintering kinetics of two Ag NPs in the size range of (4 to 20 nm), and sintering of three and four Ag NPs of 4 nm diameter. We found that the sintering process passed through three main stages. The first was the neck formation followed by a rapid increase of the neck radius at 50 K for 20 nm particles and at 10 K for smaller NPs. The second was characterized by a gradual linear increase of the neck radius to particle radius ratio as the temperature of the sintered structure was increased to the surface premelting point. Different than previous sintering studies, a twin boundary was formed during the second stage that relaxed the sintered structure and decreased the average potential energy (PE). The third stage of sintering was a rapid shrinkage during surface premelting of the sintered structure. Based on pore geometry, densification occurred during the first stage for three 4 nm particles and during the second stage for four 4 nm particles. Sintering rates obtained by our simulation were higher than those obtained by theoretical models generally used for predicting sintering rates of microparticles.
  • Interfacial Nanostructure and Electrical Properties of Ti3SiC2 Contact on p-Type Gallium Nitride

    pp. 890-894

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    DOI:10.2320/matertrans.MD201206

    In the present study, the interfacial nanostructure and electrical properties of Ti3SiC2 formed by depositing a Ti–Si–C ternary film with a composition stoichiometrically equivalent to Ti3SiC2 on p-type GaN and subsequent annealing at 1073 K were analyzed by X-ray diffraction, transmission electron microscopy and direct current conduction test. The results reveal that structural changes occur by the annealing. Polycrystalline Ti3SiC2 is formed at most of the contact interface area and single crystal Ti3SiC2 at small area of the contact interface. Furthermore, other than Ti3SiC2 phase, polycrystalline Ti5Si3 and TiSi2 with different grain sizes are also formed, resulting in a formation of three-layered film after the annealing. By all these structural change, the electric conduction profiles show that the Schottky barrier height (SBH) is reduced. The estimated SBH of the Ti3SiC2 contact on p-type GaN is 0.70 eV, which is 1.73 eV lower than the theoretically predicted value.
  • Effect of Argon Ion Irradiation on Ohmic Contact Formation on n-type Gallium Nitride

    pp. 895-898

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    DOI:10.2320/matertrans.MD201217

    This paper describes electrical properties at the interface between n-type GaN and Ti contact layers formed by RF magnetron sputter deposition under various time of Ar+ irradiation. The conductance increases proportionately to the extension of the Ar+ irradiation time, indicating that Ar+ irradiation enhances the formation of nitrogen vacancies and consequently Schottky barrier width is narrowed. On the other hand, extensive Ar+ irradiation for 3600 s and longer does not show further increase of conductance. Extensive selective sputtering of nitrogen atoms out of GaN has induced the phase transformation from GaN to Ga at the surface of GaN. The Ga phase enhances the formation of Ga–Ti compounds during the deposition of Ti, and it increases the height and width of the Schottky barrier.
  • Surface Mounting Process Using Hybrid Resin Sheet Including Self-Organizable Solder Particles

    pp. 899-904

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    DOI:10.2320/matertrans.MD201204

    To ensure the robustness of surface-mount technology, underfill resin should be applied between the chip device and the substrate. However, this application process is time consuming. Therefore, a novel chip surface-mounting process using hybrid resin containing solder particles is proposed to shorten the underfill application process. The hybrid resin consists of semicured thermoset epoxy resin containing a reducing reagent, Sn–Bi solder particles, and thermoplastic polyester thin resin film. Viscosity and reduction ability of the hybrid resin were investigated via various techniques. The semicured epoxy resin fabricated at lower temperature showed better bondability. Acetic acid was effective in reducing the oxide film on the solder particles. The coalescence behavior of molten solder particles depended on both the reduction reaction and the viscosity of epoxy resin at the bonding temperature. The epoxy resin with low viscosity was mounted on the substrate via an overcoat of the polyester film. A conductive path covered with the resin formed between the chip resistor and the substrate via the hybrid resin.
  • Thermal and Mechanical Properties of Flip Chip Package with Au Stud Bump

    pp. 905-910

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    DOI:10.2320/matertrans.MD201209

    The Au stud bumps offer a low cost flip chip solution for low I/O (input/output) count ICs and fine pitch packaging applications. The thermo-mechanical reliability of the flip chip package with Au stud bump was investigated in this study. Flip chip solder joints were fabricated using the Au stud bumps and Sn surface finish. And two different types of reliability test was done with and without the underfill process. Isothermal aging study was performed to investigate the formation and growth of the intermetallic compound (IMC) layer at the solder/metallization interface. The micro structural change of the Au stud solder joints were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy. Results showed that before aging for 250 h, AuSn4 and (Cu,Au)3Sn IMC formed and after aging for 250 h Cu3Sn IMC formed and grew as the aging time got longer. Effect on the mechanical reliability of the Au stud solder joints was also studied using shear (bonding) tester, and the temperature cycle test was chosen for the thermo-mechanical reliability evaluation of the Au stud solder joints.
  • Evolution of Interfacial Shear Force during Ultrasonic Al Ribbon Bonding

    pp. 911-915

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    DOI:10.2320/matertrans.MD201207

    An Al ribbon was bonded to SiO2 substrate with a 60 kHz ultrasonic wedge bonder. The shear force applied at the interface between the ribbon and the substrate was measured with a piezoelectric load-cell. Simultaneously, the vibration amplitude at the tip of bonding tool was monitored with a laser-Doppler vibrometer. It was suggested from experimental results that the maximum interfacial shear force was 6.4 times larger than the bonding force, i.e., the friction coefficient at the interface could be significantly high during ultrasonic bonding. The evolution and the transmission of the interfacial shear force were discussed, based on numerical simulations. The purpose of the present study is to reveal the evolution of interfacial shear force at the interface during ultrasonic ribbon bonding.
  • Deformation Behavior of Thick Aluminum Wire during Ultrasonic Bonding

    pp. 916-921

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    DOI:10.2320/matertrans.MD201210

    The deformation behavior of thick Al wires and the expansion behavior of the bond area during ultrasonic wedge bonding to Al–Si, Si and SiO2 substrates were measured simultaneously in detail with a high-speed measuring system. The deformation of the wire by the application of the bonding force is completed immediately. The deformation restarts by the application of the ultrasonic vibration. The deformation induced by applying the bonding force consists of only elastic component, whereas that by ultrasonic vibration consists of only plastic component. The Al wire is not work-hardened by the plastic deformation during application of ultrasonic vibration. The adhered area expands to the direction perpendicular to the ultrasonic vibration. The evolution of the wire deformation behavior and the expansion of the adhered area show an intimate correlation with each other.
  • Investigation on Microwelding of Microchip by Laser without Solder

    pp. 922-925

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    DOI:10.2320/matertrans.MD201211

    Laser reflow soldering is of great importance in surface mount technology for the advantages of non-contact, local fast heating and cooling. Compared with Sn–Pb solder, lead-free solder has higher melting point and poorer wetability and becomes deterioration easily in the air. This undoubtedly brings new challenges for reflow soldering. In this paper fiber laser with high energy density was used to weld three microchips (QFP-44, SSOP-48, SOP-14) without solder at the parameter of 20 kHz repetition rate, 18 W in average power and 20 mm/s of the speed. The properties of micro-joints of laser welding without solder were analyzed including electric property test, X-ray nondestructive test, 45° pull test for tensile strength as well as SEM and EDS for fracture surface analyses. It shows the properties can meet the requirement of welding joint for microchips.
  • Femtosecond Laser Direct Joining of Copper with Polyethylene Terephthalate

    pp. 926-930

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    DOI:10.2320/matertrans.MD201229

    We succeeded in directly joining Cu with polyethylene terephthalate (PET) using femtosecond laser pulses, which were focused through PET onto the Cu surface which was thermally adhered to PET prior to the laser irradiation. A maximum tensile strength of 5.5 MPa was obtained. X-ray photoelectron spectroscopic spectra of the fractured surface suggested the chemical bonding of Cu with PET. TEM images of the sample showed no voids or no cracks. They also showed the mechanical mixture of Cu with PET around the interface of the joint. We suggest that the ultrashort pulse width of the laser enables the direct joining of these dissimilar materials, thereby avoiding graphitization of the polymeric material.
  • Diffusion Bonding of Cu–Cu with Al–Ni Nano Multilayers

    pp. 931-933

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    DOI:10.2320/matertrans.MD201221

    The paper examines the joinability, microstructures and thermal behaviors of the Al–Ni nano multilayers. The results reveal the transitions and possible compositions of the nano multilayers when heating. Nanoscale Al–Ni multilayers could be used in Cu–Cu diffusion joining though the process and preparation method need to be optimized.
  • Grain Refinement during Rapid Solidification of Aluminum–Zirconium Alloys Using Electrospark Deposition

    pp. 934-939

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    DOI:10.2320/matertrans.MD201228

    Electrospark deposition (ESD) was applied to Al–Zr binary system in order to study the possible change of solidification structure from the stable D023 tetragonal equilibrium phases to the cubic L12, when high cooling rates and undercooling conditions are involved. The results show that a supersaturated solid solution was formed for the alloy containing 0.5 at%Zr, while a two-region layered structure was developed for the alloys with 1–1.5 at%Zr. These layers are composed of refined equiaxed grains, with a smaller particle size distribution for the region where the L12 precipitates were present.
  • The Formation of Molecular Junctions between Graphene Sheets

    pp. 940-946

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    DOI:10.2320/matertrans.MD201213

    Based on molecular dynamics simulations, the formation possibility of molecular junctions between two tailored graphene sheets under ultrafast laser irradiation was investigated. It was found that single layer graphene sheet can survive under significantly high intensity of laser beam. The fluctuations of graphene sheets in the plane and out of plane under laser irradiation provided the “driving power” for the possible joining process. The relative position of two graphene sheets can influence the joining difficulties and this influence was found to be attributed to the dangling bonds of edges. The saturation of dangling bonds can prompt the self-assembly of carbon networks in the joining area and lead to the connection of two graphene sheets.
  • Fabrication and Optical Spectral Characterization of Linked Plasmonic Nanostructures and Nanodevices

    pp. 947-952

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    DOI:10.2320/matertrans.MD201227

    Linked plasmonic nanoparticles made of noble metal materials exhibit significant enhancement of the amplitude of electromagnetic-field and strongly frequency-selective response at visible ranges which are distinct from that of individual nanoparicles. We introduce recent progress in the fabrication processes to achieve linked plasmonic nanostructures with various configurations. It includes the synthesis of ultrathin gold nanosheets composed of steadily linked nanoparticles using magnetron sputtering and lift-off processes, shaped gold nanopartocles films linked by surfactant, self-assembled silver nanoparticle films at water-organic interface assisted by phase transfer catalysts, large scale silver nanoplate films using self-assembly method, and silver nano-flags fabricated by chemical two-step synthesis methods. The morphologies and optical characteristics of these nanostructures are shown, respectively. These plasmonic nanostructures with special optical responses show a great potential in the applications of optical communications, photovoltaics and biochemical sensing.
  • Effects of Transition Metal (TM: Co, Rh, Ni and Pd) Substitution for Ru on Thermoelectric Properties for Intermetallic Compound RuGa2

    pp. 953-957

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    DOI:10.2320/matertrans.E-M2013804

    The effects of substituting transition metals (TM: Co, Rh, Ni and Pd) on the Ru site with respect to the electrical conductivity and Seebeck coefficient for the binary semiconducting intermetallic compound RuGa2 have been investigated above room temperature. Only Rh substituted RuGa2 exhibited a higher electrical conductivity compared with undoped RuGa2. The sign of the Seebeck coefficient at 373 K for all doped samples is negative and their magnitudes exhibit rather large values of 150 < |S373K| < 350 µVK−1, indicating that Co, Rh, Ni and Pd work as n-type dopants. However, the sign changes from negative to positive at high temperature. This implies that the effective carrier doping is insufficient to obtain a high efficiency n-type material. To investigate the effect of TM substitution on the electronic density of states, the Korringa-Kohn-Rostoker Green’s function method under a coherent potential approximation has been employed. The calculation indicates that the dopant d-states at the conduction band affect the transport properties.
  • Effects of Indenter Tilt on Nanoindentation Results of Fused Silica: an Investigation by Finite Element Analysis

    pp. 958-963

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    DOI:10.2320/matertrans.M2012400

    In reality, it is a common phenomenon to perform nanoindentation test while the indenter is not perpendicular to the sample, which would cause the properties such as hardness and elastic modulus of sample to be somehow different from the true values. In this paper, the effects of indenter tilt on the results of nanoindentation were studied by finite element analysis (FEA) simulation. The results were compared with indenter perpendicularly penetrating into a flat surface. Conclusions show that when the tilt indenter penetrates into specimen, the projected contact area varies widely. The tilt indentation could significantly influence the tendency of the force-displacement curves, and could also affect the hardness and elastic modulus of the specimen that obtained from the results. Finally, a simple method is given to correct the values of projected area, hardness and elastic modulus once tilt indentation happens.
  • A Numerical Method for Simulation of Nonlinear Eddy Current Testing Signals Based on Transient Ar Formulation

    pp. 964-968

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    DOI:10.2320/matertrans.M2013034

    To explore the principle and to optimize the nonlinear Eddy Current Testing (ECT) system, a forward numerical analysis code for nonlinear ECT signal simulation is indispensable. In this paper, an edge element numerical code of the transient Ar (reduced A) formulation is developed for this purpose. The nonlinear feature of the permeability in each element is taken into account at every time step during step by step numerical integration procedure. The dependence of the third harmonic component of the response signals on the initial permeability is investigated by using the developed code. The qualitative agreement of the simulation and the experimental results demonstrated the feasibility of the proposed simulation method and the corresponding numerical code.
  • Magnetic and Structural Properties of Mn1.8Co0.2Sb under High Magnetic Fields

    pp. 969-973

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    DOI:10.2320/matertrans.M2012415

    Magnetization, electrical resistivity and X-ray diffraction measurements were carried out for Mn1.8Co0.2Sb with a tetragonal structure in 4.2 ≤ T ≤ 280 K and in field B up to 16 T. For B = 0 T, anisotropic structural deformation occurred at Tt ∼ 140 K for zero-field cooling (ZFC), accompanied by a first-order magnetic transition from the ferrimagnetic (FRI) to antiferromagnetic (AFM) phases. In this deformation, the lattice parameters a and c changed by Δa/a = +0.15% and by Δc/c = −0.44%, respectively. By applying magnetic fields of 5 T, Tt decreased to 60 K with thermal hysteresis of 35 K. The two-phase coexistence of the AFM and residual FRI phases was observed even at 10 K for field cooling of 5 T, while a single phase of AFM was confirmed for ZFC. At B = 16 T, the transition did not occurs. In addition, a field-induced structural deformation was observed, accompanied by the metamagnetic transition just below Tt. The obtained results are discussed from a viewpoint on entropy change for the transition.
  • Neutron Diffraction on LPSO Structure in Mg–Zn–Y Alloys

    pp. 974-976

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    DOI:10.2320/matertrans.MI201215

    Crystal structure, phase fraction and texture of long period stacking ordered structure (LPSO) phase in ternary Mg–Zn–Y alloys have been investigated by analysis on time-of-flight (TOF) neutron diffraction profiles using the Rietveld method. It has been shown that the LPSO phase in the alloys is 18R-type structure of space group P3212 with a = 1.1182(0) nm and c = 4.7032(5) nm. The LPSO phase shows very strong [10\bar{1}0] texture parallel to the growth direction in a directionally-solidified crystal alloy.
  • Microstructural and Mechanical Study of the Al–20Sn (mass%) Alloy Processed by Equal-Channel Angular Pressing by Route C

    pp. 977-983

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    DOI:10.2320/matertrans.M2012378

    In this work, the feasibility of an Al–20Sn (mass%) alloy to improve its mechanical properties through the Equal Channel Angular Pressing (ECAP) process is presented and discussed. Al–20Sn (mass%) alloy samples with a square section of 16 × 16 mm and a length of 100 mm were subjected to the ECAP process through route C (i.e., rotation of 180 degrees between each pass). The characterization of the samples was carried out using X-ray diffraction and the sin2(ψ) method for residual stresses. Scanning Electron Microscopy (SEM) was used to analyze the morphology and grain size. Vickers microhardness was carried out to analyze the homogeneity of the states of deformation and tensile testing to evaluate the yield strength, ultimate tensile strength and elongation. The results showed that the residual stresses were relatively low, confirming the effect of Sn as stress reliever. The grain size was refined to a sub-micron scale and a ribbon-like morphology was observed. The microhardness values of the severely deformed samples showed a significant increase when compared to the as-cast sample. The tensile tests showed an increase in the yield strength after the first pass, that doubled the yield strength of the as cast sample. A marginal increase in the yield strength after the fifth pass was observed; whilst the ductility remained very similar from 1 to 5 passes.
  • Specimen Dimension and Grain Size Effects on Deformation Behavior in Micro Tensile of SUS304 Stainless Steel Foil

    pp. 984-989

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    DOI:10.2320/matertrans.M2013016

    Size effects are the main problem in micro-forming process and material behavior with miniaturization of feature size. In the paper, size effects of grain size and foil thickness on deformation behavior and fracture were investigated by using micro tensile test of SUS304 foil. The results show that the yield strength of SUS304 stainless foil increases with the decrease of foil thickness and grain size in micro tensile tests. Meanwhile, the fracture mechanism of SUS304 foil changes from ductile fracture with lots of dimples to ductile fracture with slip separation with the decrease of foil thickness. A compound material model by considering grain size, foil thickness and surface effects is proposed and constitutive relation of SUS304 foil is established. The calculation curves well match with experimental results.
  • Effects of 4 GPa Pressure Heat Treatment on Microstructure and Micro-Mechanical Properties of LC4 Aluminum Alloy

    pp. 990-993

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    DOI:10.2320/matertrans.M2013040

    Microstructure and micro-mechanical properties of LC4 aluminum alloy were studied before and after treating the samples at 4 GPa pressure. The hardness, elastic modulus and plastic deformation were measured by nanoindenter and the microstructure of the LC4 aluminum alloy was observed by metalloscope and scanning electron microscope. The results show that the microstructure of the LC4 aluminum alloy can be refined and compacted after 4 GPa pressure treatment. The micro-mechanical properties of LC4 aluminum alloy can be improved effectively.
  • Fracture Toughness Evaluation of Thin Fe–Al Intermetallic Compound Layer at Reactive Interface between Dissimilar Metals

    pp. 994-1000

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    DOI:10.2320/matertrans.M2012425

    The fracture toughness of Fe–Al intermetallic compounds (IMCs), FeAl and Fe2Al5, that form as a thin layer on steel substrate was investigated. A model for evaluating the fracture toughness of a brittle thin layer on an elastoplastic substrate was applied, and the fracture toughness was evaluated from the thickness of the IMC layer and the crack interval in the IMC layer after uniaxial tensile testing. The phase and microstructure of the IMC layer were varied to investigate their effects on the fracture toughness of the IMC. The relationship between layer thickness and crack interval was in a good agreement with the theoretical model, and the fracture toughness was evaluated adequately using the model. It was clarified that FeAl has higher fracture toughness than Fe2Al5, and that fine-grained Fe2Al5 has higher fracture toughness than coarse-grained Fe2Al5.
  • Stress Corrosion Cracking Behavior of Zirconium in Boiling Nitric Acid Solutions at Oxide Formation Potentials

    pp. 1001-1005

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    DOI:10.2320/matertrans.M2012341

    Zirconium has been utilized in nuclear fuel reprocessing plants because of its superior corrosion resistance in nitric acid solutions. However, stress corrosion cracking (SCC) susceptibility of zirconium has been reported in boiling nitric acid solutions at the passivity breakdown potential. However, it has not been clear the SCC initiation and propagation behavior of zirconium.
    In this study, to clarify the SCC initiation and propagation behavior of zirconium, constant load tensile tests were carried out in boiling nitric acid solutions.
    From the results, many cracks were initiated under the oxide film and maximum crack led to rupture in the potentials that nobler than passivity breakdown potential. These results showed that the SCC of zirconium in boiling nitric acid solutions is due to the oxide formation. And this SCC behavior suggests that the SCC behavior of zirconium can be attributed to tarnish rupture model.
  • Molten Salt Pulse Electrodeposition of Silicon on Low Silicon Steel

    pp. 1006-1011

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    DOI:10.2320/matertrans.M2012257

    Low silicon steel was siliconized by pulse electrodeposition from KCl–NaCl–NaF–SiO2 molten salts and high silicon steel containing 6.5 mass% Si was prepared by followed diffusion annealing. The composition depth profile, the cross-section micrograph and the phase structure of the siliconized layer were characterized with glow discharge optical emission spectroscopy (GDOES), optical microscope (OM), scanning electron microscopy (SEM) with an X-ray energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The textures of substrate, deposited sample and high silicon steel were analyzed by the orientation distribution function (ODF). The results showed that Si was almost homogeneously distributed in the siliconized layer. The siliconized layer had a two-layer structure. The top layer composed of columnar grains and a layer with equiaxed grains close to the substrate. The phase structure of the layer was composed of Fe3Si with (110) preferred orientation. After diffusion annealing the undesirable γ-fiber type texture {111}<110> and {111}<112> weakened, both easy magnetization direction Goss texture ({110}<001>) and cube texture {100}<001> were intensified.
  • Fabrication of an Al Foam/Dense Steel Composite by Friction Welding

    pp. 1012-1017

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    DOI:10.2320/matertrans.M2012390

    Al foam is lightweight with superior shock-absorbing properties but has low tensile and bending strengths. This has spurred efforts to form composites of Al foam with dense materials. In this study, we examined the possibility of fabricating composite structures of Al foam and dense steel with strong metal bonding by employing friction welding. The use of friction welding is expected to facilitate the fabrication of Al foam/dense steel composites by a simple process with low environmental impact. It is shown that this procedure is capable of fabricating an Al foam/dense steel composite in which the Al foam completely fills the hollow in the dense steel. An Fe–Al intermetallic compound (IMC) layer with a thickness on the order of 10 µm was found throughout almost the entire interface between the Al foam and the dense steel. Therefore, it is shown that an Al foam/dense steel composite with strong metal bonding can be fabricated.
  • Microstructure and Charge–Discharge Characteristics of Ag–AgCl Coated Natural Bamboo Carbon

    pp. 1018-1024

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    DOI:10.2320/matertrans.M2012254

    Bamboo carbon decomposed by low temperature has a high surface area and contains micro-holes; it belongs to one of the amorphous carbon materials. Due to the large lithium storage space and high discharge performance rate, lithium batteries enjoy high power consumption. However, there are also some defects of the first higher irreversible capacity and voltage delay. In this study, a natural bamboo carbon powder was used as an experimental material. After adding AgNO3 and treating the surface with heat at 450 and 650°C, fine Ag/AgCl phases are coated on the surface of carbon powders. C–Ag and C–AgCl are formed to increase the capacity and reduce the first irreversibility. Also, the concentration of Ag on the carbon surface increased with the increment of temperature from 450 to 650°C. This not only increased the conductivity but also enhanced the surface bonding of C–Ag powders to promote the performance of charge–discharge cycles.
  • Formation of Anti-Reflection Coating by Hydrothermal Treatment of Aluminum Films and Their Stabilization by Dehydration

    pp. 1025-1028

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    DOI:10.2320/matertrans.M2013026

    Anti-reflection coating, which exhibits higher transmittance than that of glass substrate itself, has been obtained by hydrothermal treatment of Al film in ultrapure water and hydrothermally-treated Al film was consisted of transparent boehmite (aluminum oxyhydroxide) (J. Appl. Phys. 106 (2009) 023524). However the stability of the hydrothermally-treated film is not enough, as boehmite contains water in its crystal structure. In this study, we examined the heat-treatment of such boehmite film. According to transmission electron microscopy and transmission Fourier-transform infrared spectroscopy, dehydration was observed at above 673 K for 1 h and boehmite transformed to a stable phase of γ-alumina. Though the structural change took place, the optical property of high transmittance remained and/or even improved.
  • Preparation and Characterization of a Cylinder-Type Adsorbent for the Recovery of Lithium from Seawater

    pp. 1029-1033

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    DOI:10.2320/matertrans.M2013028

    In this work, a spinel lithium manganese oxide (LMO) used as a lithium adsorbent was prepared with a conventional solid state reaction using lithium carbonate and manganese carbonate as the reactants. A cylinder-type LMO was prepared using water glass (sodium silicate solution) as a binder together with the reactants and examined for its lithium adsorption capacity. The effect of the preparation condition on the adsorption capacity of the LMO powder was investigated. The optimum heating condition for the LMO powder, determined to be 500°C for 4 h, was applied to prepare the cylinder-type LMO. The cylinder-type LMO showed a maximum adsorption capacity of 15.06 mg/g when immersed in lithium-enriched seawater, whereas LMO powder showed a maximum adsorption capacity of 27.62 mg/g under identical conditions. The cylinder-type LMO generally maintained its structure after the acid treatment and the Li adsorption process. Thus, the cylinder-type LMO developed in this study can overcome the limits associated with powder-type adsorbents and may be appropriate for multiple adsorption runs in seawater.
  • Improvement of Mechanical and Electrical Properties on the Sintered Ni–50 mass% Cr Alloys by HIP Treatment

    pp. 1034-1039

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    DOI:10.2320/matertrans.M2013018

    This study investigated Ni–50 mass% Cr alloys produced by the vacuum sintering and hot isostatic pressing (HIP) of powder metallurgy technology. The experimental results showed that the relative density of Ni–50 mass% Cr alloys reached 98.67%, the apparent porosity decreased to 1.33%, transverse rupture strength (TRS) increased to 454.29 MPa and electrical resistivity decreased to 4.284 × 10−4 Ω·cm after 1345°C sintering for 1 h. Meanwhile, laminar eutectic precipitations appeared in the sintered Ni–50 mass% Cr alloys. In addition, the relative density increased to 99.73%, the apparent porosity decreases to 0.27% and TRS was obviously enhanced to 1181.4 MPa after 1260°C 175 MPa 4 h HIP treatment. Moreover, the electrical resistivity decreased to 3.346 × 10−4 Ω·cm after the optimal HIP treatment. This study showed that the HIP process is effective in eliminating internal pores and improving the mechanical and electrical properties of the sintered Ni–50 mass% Cr alloys, thus obtaining the high density and optimum properties of the sintered materials.
  • Aging Effect on Adhesion Strength between Electroless Copper and Polyimide Films

    pp. 1040-1044

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    DOI:10.2320/matertrans.M2013044

    The effect of atmospheric aging on the adhesion strength between electroless copper and polyimide films was investigated. 100 nm thick electroless copper was plated on polyimide film and 10 µm of copper electroplating was performed successively. Aging was allowed to occur at room temperature in atmosphere for designated times: either between electroless deposition and electroplating or between electroplating and the peel test. The adhesion strength between copper and polyimide film increased and then saturated as aging progressed for about 1 d, with rapid increase from 0.2 to 0.5 d. Among the samples with equivalent total aging time, samples that were electroplated later showed higher adhesion strength. Inter-diffusion and chemical bonding between copper and polyimide were observed after aging and additionally applied electrical current increased the adhesion strength. It could be suggested that the atmospheric aging and additionally applied current enhance the inter-diffusion and the chemical bonding between electroless copper and polyimide film.
  • A Novel Process for Extracting Precious Metals from Spent Mobile Phone PCBs and Automobile Catalysts

    pp. 1045-1048

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    DOI:10.2320/matertrans.M2013051

    A novel process to simultaneously extract the precious metals such as gold, silver, platinum, palladium and rhodium from spent mobile phone printed circuit boards (PCBs) and honeycomb-type auto catalysts by smelting using waste-copper slag without adding any collector metals or by-products such as dross, matte and slime has been developed. In the process, waste-copper slag which is an industrial waste discharged from copper smelter is used not only as a flux for controlling slag composition, but also as a collector metal for capturing precious metals, and a plastic component contained in spent mobile phone PCBs is done as a reducing agent of iron oxides contained in the waste-copper slag. Using the developed process, up to 95% of gold, silver, platinum, palladium and rhodium contained in the raw materials were extracted in a Cu–Fe–Sn alloy phase, respectively.
  • Mechanochemical Synthesis and Rapid Consolidation of Nanocrystalline Al2O3–2.25Co Composite by High-Frequency Induction Heating and Its Mechanical Properties

    pp. 1049-1052

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    DOI:10.2320/matertrans.M2013008

    This study focused on synthesizing nanopowders of Co and Al2O3 from Co3O4 and Al powders and fabricating nanocrystalline Al2O3 reinforced Co composite to improve its mechanical properties. Nanopowders of Co and Al2O3 were synthesized from Co3O4 and Al by high-energy ball milling. A highly dense nanostructured 2.25Co–Al2O3 composite was consolidated by high-frequency induction heated sintering method within 3 min from the mechanically synthesized powders (2.25Co–Al2O3) under the 80 MPa pressure. The advantage of this process is that it allows for very quick densification to near theoretical density and prohibits grain growth in nanostructured materials. The grain sizes of Co and Al2O3 in the composite were calculated. And the average hardness and fracture toughness values of nanostuctured Co–Al2O3 composite were investigated.
  • Thermal Fatigue Behavior Evaluation of Shot-Peened JIS SKD61 Hot-Work Mold Steel

    pp. 1053-1056

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    DOI:10.2320/matertrans.M2013019

    Thermal fatigue cracking is one of the most important failure mechanisms in hot work die steels. Shot-peening can be used in a much wider field to obtain higher static strength, as well as better fatigue resistance. This study investigates the shot-peening effect on the microstructure and mechanical properties of hardened JIS SKD61 hot-work steel. The thermal fatigue test is based on cyclic induction heating and water cooling. A non-peened specimen with a hardness of 510 HV0.05 was used as the reference material. The scanning electron microscopic observations showed craters on the surface and a severely worked hardened area in the shot-peened specimen subsurface. The microhardness values of the shot-peened surface are about 720 and 750 HV0.05 for the Almen intensity of 15 A (typical shot-peened specimen) and 18 A (severe shot-peened specimen), respectively. The work hardening depths of typical shot-peened and severe shot-peened specimens are about 20 and 30 µm, respectively. The thermal fatigue properties of shot-peened specimens, including the mean crack length and crack distribution density, are better than those of non-peened specimens. Only a slight improvement in thermal fatigue properties occurred for the severe shot-peened specimen compared with typical shot-peened specimen.
  • Effect of Die Material on Compressive Properties of Open-Cell Porous Aluminum Fabricated by Friction Powder Compaction Process

    pp. 1057-1059

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    DOI:10.2320/matertrans.M2013081

    Porous Al was fabricated by combining a sintering dissolution process and a friction powder compaction process. Porous Al fabricated using a Cu die exhibited superior mechanical properties to that fabricated using an Al die and had a fine pore structure, which is attributed to the high load and temperature during the sintering process when using the Cu die.
  • Nanostructured CeO2–Al2O3 Catalytic Powders for m-Xylene and Toluene Combustion

    pp. 1060-1062

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    DOI:10.2320/matertrans.M2013056

    The bee’s nest-like nanostructured CeO2–Al2O3 powders were synthesized by combustion method using polyvinyl alcohol as a fuel and their catalytic activity were tested in the m-xylene and toluene combustion. The results showed that the catalytic reaction temperature increased monotonically from 200 to 250°C and from 250 to 300°C for the 90% conversion of m-xylene and toluene, respectively, with the calcination temperature in the range of 450–850°C. For both combustions, the sample calcined at 450°C with a bee’s nest-like nanostructure and average pore size of 800 nm exhibited the highest catalytic activity. Among the samples calcined at 850°C, the lowest catalytic reaction temperature for the 90% conversion of m-xylene and toluene of 250 and 300°C, respectively, was found with the sample having the equimolar ratio of Ce/Al.
  • Low-Temperature Bonding of Silver Derived from Silver–Oxide Particles to Nickel

    pp. 1063-1065

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    DOI:10.2320/matertrans.M2013083

    Silver was bonded to nickel by using silver–oxide particles with cetyl alcohol as a bonding material for bonding at 350°C under H2. The shear strength of the bonds formed with the joining medium of silver oxide/cetyl alcohol was 27.1 MPa. Sintered silver was bonded to nickel without the oxide layer that ensured the sintered silver was strongly bonded to nickel, which was confirmed by cross-sectional transmission electron microscopy.

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