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

MATERIALS TRANSACTIONS Vol. 57 (2016), No. 6

  • Special Issue on Advanced Spintronic/Nano-Magnetic Materials

    pp. 759-759

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    DOI:10.2320/matertrans.MPR2016902

  • Finely Controlled Approaches to Formation of Heusler-Alloy/Semiconductor Heterostructures for Spintronics

    pp. 760-766

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    DOI:10.2320/matertrans.ME201503

    We present recent progress of the low-temperature growth of Heusler-alloy/silicon(Si) or Heusler-alloy/germanium(Ge) heterostructures and of their applications for spintronics. First, a concept of the realization of the low-temperature heteroepitaxy for high-quality Heusler alloy/Si or Heusler alloy/Ge heterostructures is shown. Despite very low-growth temperatures, B2 or L21 ordered full-Heusler alloys are achieved. Next, by applying this concept to the growth of Ge on a Heusler alloy or a Heusler alloy on another Heusler alloy, we can also achieve unusual heterostructures for the possibility of novel spintronics applications. Finally, we demonstrate the pure spin current transport in Cu and Ge using these Heusler-alloy spin injectors and detectors. Our approaches will open new avenues for developing high-performance spintronic applications with Heusler alloys.
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  • Spin Injection, Transport, and Detection in a Lateral Spin Transport Devices with Co2FeAl0.5Si0.5/n-GaAs, Co2FeSi/MgO/n-Si, and CoFe/MgO/n-Si Junctions

    pp. 767-772

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    DOI:10.2320/matertrans.ME201502

    We demonstrate spin injection, transport, and detection in a lateral spin transport devices with Co2FeAl0.5Si0.5/n-GaAs, Co2FeSi/MgO/n-Si, and CoFe/MgO/n-Si junctions. Non-local four- and three-terminal Hanle-effect signals indicate large spin injection/detection efficiency in Si for Co2FeSi/MgO/Si on insulator (SOI) devices compared with CoFe/MgO/SOI devices, whereas the preparation methods of MgO layers on SOI are exactly same in both devices. The estimated spin injection/detection efficiency in GaAs is 0.06 at 4.2 K, which is also larger than those of the devices with Fe and CoFe electrodes. Different properties in the bias voltage dependences on the amplitude of spin accumulation signals are also observed between Co2FeSi/MgO/SOI and CoFe/MgO/SOI devices. These results indicate that the species of ferromagnetic material definitely influences the amplitude and the behavior of the spin signals.
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    Readers Who Read This Article Also Read

    1. Magnetic Properties of Spinel Ferrite Thin Films Grown by Reactive Sputtering MATERIALS TRANSACTIONS Vol.57(2016), No.6
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  • Interface Magnetic Anisotropy of Pd/Co2FexMn1−xSi/MgO Layered Structures

    pp. 773-776

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    DOI:10.2320/matertrans.ME201505

    Interface magnetic anisotropy of Co2FexMn1−xSi Heusler alloy thin films were studied quantitatively. Films of Co2MnSi (x = 1, CMS), Co2Fe0.5Mn0.5Si (x = 0.5, CFMS), and Co2FeSi (x = 1, CFS) were fabricated onto MgO (001) substrates with an epitaxially grown Pd (001) under layer, and were capped by an MgO layer. The maximum thickness for the perpendicular magnetization was 0.8 nm for CMS and CFMS, and it was 0.6 nm for CFS. The interface anisotropy energies (Ks) were 1.5, 1.5, and 1.2 erg/cm2 for CMS, CFMS, and CFS, respectively. The difference in Ks probably originated from the different alloying conditions at the bottom interface between Pd and Co2FexMn1−xSi layers.
  • Magnetic Properties of Spinel Ferrite Thin Films Grown by Reactive Sputtering

    pp. 777-780

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    DOI:10.2320/matertrans.ME201504

    We report the crystal structure and magnetic properties of spinel ferrite thin films of magnetite, maghemite, and cobalt ferrite grown by reactive magnetron sputtering. The magnetic properties of spinel ferrite films, in particular saturation magnetization, are affected by the growth conditions, even when no significant difference is found in the crystal structures. Comparing films grown by molecular beam epitaxy with those produced by reactive magnetron sputtering, we found that the latter technique produces larger saturation magnetization than the bulk. Therefore, sputtering can be considered the suitable method for preparing various spinel ferrite compounds.
  • Perpendicular Exchange Bias and Magneto-Electric Control Using Cr2O3(0001) Thin Film

    pp. 781-788

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    DOI:10.2320/matertrans.ME201506

    Antiferromagnets themselves do not generate either stray fields or spontaneous magnetization. However, if an antiferromagnet is coupled with a ferromagnet, unique and useful characteristics appear. Exchange bias is one such characteristic that is utilized in spintronic devices like spin-valve films. To date, exchange bias has been used to induce static effects in devices; however, the exchange bias has not been switchable in these devices. Recently, switchable exchange bias has been developed using Cr2O3, which exhibits a magnetoelectric effect in an antiferromagnetic layer. The promising features of this effect are (1) the strength of the exchange bias is high and its direction is perpendicular to the film, and (2) the switching is triggered by an electric field. In this overview, we will summarize our recent results on the unique temperature dependence of high, perpendicular exchange bias and magnetoelectric switching of the induced perpendicular exchange bias.
  • Anomalous Hall Effect Measurement on Nanostructure with Magnetic Pulse Fields

    pp. 789-795

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    DOI:10.2320/matertrans.ME201507

    Characterization of magnetic properties is one of the key issues for development of future magnetic and spintronic devices. The dimension and the operation frequency of those devices has reached nanoscale and GHz regime, respectively, so that it is required to realize new measurement technique with such sensitivity and time resolutions. The anomalous Hall effect (AHE) can be adopted as a probe capable to approach magnetization behavior in nanoscale structure. We have developed AHE measurement technique for nanostructure and investigated magnetization reversal behavior of perpendicularly magnetized dot in dynamic field. In this article, we overview the capability of AHE measurement as a probe for magnetic characterization and the experimental results of magnetization behavior of Co/Pt multilayer dots in pulse fields with nanoseconds durations.
  • Special Issue on Frontier Researches Related to Interconnection, Packaging and Microjoining Materials and Microprocessing for Such Materials

    pp. 796-796

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    DOI:10.2320/matertrans.MPR2016901

  • Molten Lead-Free Solder Deposited by Inkjet Printing for Bonding of Thin-Film Solar Cell Modules

    pp. 797-804

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    DOI:10.2320/matertrans.MD201501

    In this study we deposited Sn-3.0Ag-0.5Cu solder alloy as a bonding material in lead-free soldering by utilizing inkjet printing to improve the electrical interconnections of solar cell modules. Sn-3.0Ag-0.5Cu solder was successfully printed to bond thin-film solar cell modules. The improved interface wetting behavior between the adhesive surface of the aluminum electrode and lead-free solder joints in silicon thin-film solar cell modules was investigated with respect to reflowing at 240°C for 30 s by using an optical microscope and mean contact angle. The results show that the peel strength of the Sn-3.0Ag-0.5Cu solder alloy is better than that of silver paste when the dot spacing of solder droplets is lower than 200 µm (a density of over 50 µg/mm2). The findings also show that the contact resistance of the solder alloy is better than that of silver paste when the dot spacing of solder droplets is lower than 100 µm. This results in a low power loss of solar cells of 1.1%, and a good photovoltaic conversion efficiency of over 8.3%. This study thus demonstrates the feasibility of decreasing the efficiency loss of solar cells by employing the proper spacing of lead-free solder droplets by inkjet printing.
  • Thermal Fatigue Life Evaluation of Epoxy Resin/Si Joint under Mineral Oil Condition

    pp. 805-809

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    DOI:10.2320/matertrans.MD201506

    Thermal fatigue life of epoxy resin/Si joint under mineral oil condition including impurities was evaluated by diffusion-structure coupled FEM analysis. The mass of the mineral oil impurities in epoxy resin increases with an increase in the number of thermal cycles by the diffusion phenomenon. An increase in the mass of the impurities in the resin causes swelling, which increases the stress intensity factor range ΔKi at the joint interface. ΔKi under the mineral oil condition increases by 1.5 times compared to that under air atmosphere. Swelling significantly shortened the thermal fatigue life under the mineral oil condition. Thus, swelling by diffusion of mineral oil impurities into epoxy resin becomes a dominant factor over thermal fatigue life of the joint.
  • Effect of Interfacial Hardness on Failure Modes of Liquid Phase Diffusion Bonded Sn/Sn with Bi Filler

    pp. 810-814

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    DOI:10.2320/matertrans.MD201507

    To examine the effect of Bi filler metal on bond strength of the Sn/Sn bonded joint interface, the interfacial microstructures and fractured surfaces of joint were observed by using SEM. After Bi filler metal had been deposited to the surface, the diffusion bonding was carried out in a vacuum chamber at bonding temperature of 413~463 K. The application of filler has decreased bonding temperature by 20 K or more which the bonded joints obtained bond strength comparable to the base metal. As the bonding temperature increases, the thickness of the Bi diffusion layer increases as well. Moreover, the interfacial hardness has decreased with a rise in bonding temperature, and the failure mode changes from brittle to ductile. The changes in the interfacial eutectic reaction layer between Sn and Bi accompanied by the expansion of the contact area between Sn metal surfaces are considered as the contributing factor to the increase in the bond strength.
  • In Situ Observation of Self-Annealing Behaviors of (001)-Oriented Electrodeposited Silver Film by EBSD Method

    pp. 815-818

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    DOI:10.2320/matertrans.MD201505

    The self-annealing behaviors of an electrodeposited silver film preferentially oriented in the (001) direction were investigated by in situ electron backscatter diffraction pattern (EBSD) analysis. It was confirmed that there are fine grains with crystallite sizes of approximately 20 nm in an as-electrodeposited silver film by X-ray diffraction (XRD) analysis. Self-annealing starts after storage for about 2 h at room temperature (R.T.) and recrystallization is almost complete after storage for 6 h. The area fraction of (001)-oriented grains rapidly increases after storage for about 2 h at R.T. and saturates in the range from 70% to 80% after storage for 6 h. In the initial stage of self-annealing, (001)-oriented and (212)-oriented recrystallized grains nucleate. Moreover, (001)-oriented grains mainly grow during subsequent storage.
  • Plastic Deformation Behavior and Mechanism of Bismuth Single Crystals in Principal Axes

    pp. 819-823

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    DOI:10.2320/matertrans.MD201503

    Tensile tests of single-crystal bismuth were performed for the a1-axis [2110], a2-axis [1210] and c-axis [0001]. The mechanism of the a1-axis and a2-axis plastic deformation at 298 K is twinning deformation at the initial deformation stage. Subsequent plastic deformation mechanism is the slip deformation that occurs by the changes in the crystallographic orientation inside twin crystals that is advantageous to the slip. The mechanism of the c-axis plastic deformation at 298 K is slip deformation, where the secondary slip system becomes activated. On the other hand, the slip deformation is the primary deformation mechanism and twinning deformation is not observed for any axes at 423 K.
  • Application of Spark Sintering to Preparation of Zn-50Sn-Al2O3/Cu Joints for AC-Low Voltage Fuse Elements Without Lead

    pp. 824-832

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    DOI:10.2320/matertrans.MD201512

    After the casting and cold drawing of fuse alloys, the joint between fuse alloys and Cu has been soldered using their parts for fabrication of AC-low voltage elements used in electric power line, which means to complex fabrication processes. As case study for the power saving, the Zn-50mass%Sn-8vol%Al2O3 and Cu was directly joined using their powders by spark sintering, for development of Pb-free fuse elements, which led to the keep of initial microstructural state because of the un-melting without soldering. The sintering of their powders showed a low sinter-ability because of the large difference in their melting points, which meant the difficulty in application of spark sintering to the fabrication of their joints. However, the joints of Zn-Sn-Al2O3 fuse alloy and Cu connectors were prepared successfully by controlling the maximum holding temperature of 433–473 K. The joints were sintered at the solid state of 433 K, showed a little of reaction area at the interface between the fuse alloy and Cu. In contrast, the joints with high relative density which were sintered at the liquid state, showed much amount of reaction area at the interface. The temperature dependence of specific resistivity, thermal conductivity and specific heat was measured for electrical and thermal calculations. The joint sintered at the solid state showed the close values in their properties to the solidified alloy as the reference. Both the melt and un-melt down performance for AC-low voltage fuse elements could be satisfied on the joints of fuse alloy and Cu sintered at the solid state, which resulted in the same performance shown in the standard alloys by complex fabrication processes consisting of casting and soldering as previously manufacturing method.
  • Microstructure and Shear Strength of Low-Silver SAC/Cu Solder Joints during Aging

    pp. 833-837

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    DOI:10.2320/matertrans.MD201508

    A new type of low-silver hypoeutectic SAC lead-free solder was prepared, and then hot dip soldering was used to form the joints of copper. The microstructure evolution of IMCs and the variation of shear strength of solder joints were investigated. The results have shown that the thickness of the IMC layer increased over time and the scallop-type IMC became a hump like shape during the aging process. The growth rates of the IMC layer were 0.61 × 10−14 cm2/s, 2.06 × 10−14 cm2/s, 4.83 × 10−14 cm2/s at 348 K, 373 K and 423 K respectively. The shear strength of solder joint fell sharply at first and then became slow, finally dropped from 40.94 MPa to 29.73 MPa after aging at 423 K for 12 days. Moreover, the fracture mode changed from ductile fracture to local brittle fracture with the increasing of aging time.
  • Observation on Isothermal Reactive Diffusion between Solid Ni and Liquid Sn

    pp. 838-845

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    DOI:10.2320/matertrans.MD201510

    The kinetics of the reactive diffusion between solid Ni and liquid Sn was experimentally examined using Ni/Sn diffusion couples. The diffusion couples were prepared by an isothermal bonding technique and then immediately annealed in the temperature range of T = 533–623 K for various times up to t = 14.4 ks (4 h). During annealing, a compound layer of Ni3Sn4 is formed at the original Ni/Sn interface in the diffusion couple and grows mainly into the liquid Sn specimen. The mean thickness of the compound layer is proportional to a power function of the annealing time. The exponent n of the power function takes values between 0.31 and 0.43. Since there is no systematic dependence of n on T, we may consider that n is insensitive to T within experimental uncertainty. When growth of a compound layer with uniform thickness is controlled by volume diffusion, n is equivalent to 0.5. If boundary diffusion contributes to the layer growth and grain growth occurs in the compound layer, however, n becomes smaller than 0.5. Since grain growth practically takes place in the compound layer, it is concluded that the layer growth of Ni3Sn4 is mainly controlled by boundary diffusion at T = 533–623 K.
  • Effect of Zinc Addition on Void Formation in Solid-Liquid Interdiffusion Bonding of Copper

    pp. 846-852

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    DOI:10.2320/matertrans.MD201509

    Solid–liquid interdiffusion bonding of Cu was carried out at 573 K with deposited Sn and Cu films. The effect of Zn addition to the faying surfaces was investigated to reduce Kirkendall voids. At the beginning of the reaction, molten Sn reacted with Cu to form Cu6Sn5, and Cu3Sn successively formed between the Cu6Sn5 and the Cu. Many voids formed in the Cu3Sn phase, especially close to the Cu3Sn/Cu interface. When Zn was added in the faying surfaces, Zn was segregated near the interface of Cu/Cu3Sn and the grain boundaries of Cu3Sn. The Zn segregation inhibited diffusion of Cu due to the effect of solute drag, which also delayed growth of the Cu3Sn layer. As a result, the fluxes of Cu and Sn via the Cu3Sn phase were balanced out, which reduced the Kirkendall void formation.
  • Effect of Strain Rate and Temperature on Micro Fatigue Crack Propagation of Bi-Sn Eutectic Alloy

    pp. 853-859

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    DOI:10.2320/matertrans.MD201504

    Effects of strain rate and temperature on fatigue crack growth of Bi-Sn eutectic alloy were investigated. The micro fatigue crack propagation rate decreases with a decrease in strain rate and an increase in temperature when compared with in the same strain range. This is an opposite trend to the effect of strain rate and temperature observed in common high temperature fatigue fractures. The result is attributed that fatigue crack propagation does not increase even by strain reduction and temperature increase, since cavity formation is suppressed by viscous deformations of grain interior. Fatigue crack propagation rate is controlled only by strain energy which is the driving force for crack propagation. As a result, the rate of crack propagation and the number of crack initiation cycles can be assessed by ΔJ, not by strain rate and temperature.
  • Reliable Material Properties of Aluminum Pads with Strong Delamination Toughness in Gold - Aluminum Wire Bonding

    pp. 860-864

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    DOI:10.2320/matertrans.MD201502

    Au/Al wire bonding is the traditional bonding method of circuits of electronic packages, and still a very important bonding technique. Bonding strength was measured by the shear test of a gold ball on an aluminum pad. Delamination behavior was categorized into three types, cohesive fracture in the gold ball, interfacial delamination between the gold ball and the aluminum pad, and fracture from inside of the aluminum pad. The cohesive fracture in the gold ball is the most reliable in these three types of fracture. We investigated the mechanisms causing the different types of fracture from the shear test. First, we observed the surface of aluminum pads using a scanning electron microscope (SEM) and measured the orientation of crystal grains using the electron backscatter diffraction (EBSD). A porous structure was observed on the surface of the aluminum pad that caused the fracture from the inside of the pad. Almost all of the crystal grains on the aluminum pads were aligned (111). Then, we measured the material properties of aluminum pads using a nano-indenter. Aluminum pads with stiff surfaces showed interfacial fracture. Aluminum pads with soft surfaces and large absorbed plastic energy showed cohesive fracture of the gold balls.
  • Evolution of Electrical Conductivity in Silver-Loaded Electrically Conductive Adhesives Composed of an Amine-Cured Epoxy-Based Binder

    pp. 865-872

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    DOI:10.2320/matertrans.MD201511

    To investigate interfacial phenomena related to the evolution of electrical conductivity in electrically conductive adhesives containing silver fillers, the curing processes of model adhesives composed of an amine-cured epoxy-based binder were examined using several analytical methods. Shrinkage of the adhesives during curing was not a predominant factor in determining the electrical resistivity. Rearrangement of the fillers occurred at the onset of gelation. Afterwards, the electrical conductivity evolved in the adhesives through the following two steps: development of conduction paths during gelation of the epoxy-based binder, and microstructural evolution between the silver fillers. The use of adipic acid as a surfactant enhanced the first of these steps during gelation. The latter process occurred concurrently with cross-linking of binder molecules to increase the elastic modulus. In this step, the amine molecules probably reacted with silver fillers to induce necking between the fillers. Because interfacial chemical phenomena probably influence the electrical conductivity evolution, the conventional hypothesis, which is based on the mechanical contact concept for inter-filler contacts in electrically conductive adhesives, needs to be expanded.
  • Effect of Strain Rate and Temperature on Tensile Properties of Bi-Based Lead-Free Solder

    pp. 873-880

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    DOI:10.2320/matertrans.MD201517

    Tensile properties of three Bi-based lead-free solder which are pure Bi, Bi-1.0Ag-0.3Sn-0.03Ge (mass%), and Bi-2.5Ag (mass%) were investigated and compared with that of Pb-rich Pb-2.5Ag-2.5Sn (mass%) solder. Tensile strength of pure Bi is the minimum among solder investigated regardless of the temperature and strain state. Although tensile strength of Bi-based solder is lower than that of Pb-2.5Ag-2.5Sn at 25℃, those of Bi-1.0Ag-0.3Sn-0.03Ge and Bi-2.5Ag improve and become analogous and higher than that of Pb-2.5Ag-2.5Sn at a temperature of 125℃ or more. The effect of strain rate on elongation is negligible in solder investigated. Although elongations of Bi-based lead-free solder are lower than that of Pb-2.5Ag-2.5Sn at 25℃, they increase with increasing temperature. While the elongation of Pb-2.5Ag-2.5Sn relatively stable at approximately 20–30% regardless of temperature, elongations of Bi-1.0Ag-0.3Sn-0.03Ge and Bi-2.5Ag become a same level with that of Pb-2.5Ag-2.5Sn at 125℃ and 175℃. In particular, the ductility of pure Bi which is about 5% improves drastically at temperatures of 75℃ or more and the elongation rises to approximately 60%. From microstructure observation results, it was confirmed that the addition of small amount of Sn and Ge is effective to form fine microstructure. From fracture surface observation results, it was confirmed that brittle fracture occurs at 25℃ and the fracture mode changes to ductile fracture when the temperature increases and the ductility improves.
  • Effects of Metal Surface Conditions on Interfacial Characteristics between Metal and Epoxy Resin

    pp. 881-886

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    DOI:10.2320/matertrans.MD201516

    Conductive adhesives are alternatives to solder joints and are of interest because of their high bonding strength, low thermal resistance, and low electrical resistance. In this paper, we focused on the dependence of the metal surface conditions on the surface processing and clarified the effect of different metal surface finishes on the bonding strength and thermal characteristics. The effects of air exposure and silane coupling agent processing on the adhesive strength between the metal and resin were investigated. The thermal resistance after repeated bending was measured to determine the effect of different metal surface finishes on the thermal resistance.
  • Interfacial Reactions in Sn-57Bi-1Ag Solder Joints with Cu and Au Metallization

    pp. 887-891

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    DOI:10.2320/matertrans.MD201514

    This paper investigated interfacial reactions in two Sn-57Bi-1Ag (mass%) solder joints, bonded to Cu and Au metallization. As the melting point of Sn-57Bi-1Ag is 138℃, bonding was conducted at 170℃ and the bonding time was varied from 1 min to 60 min. The melting properties and microstructure of each solder joint were investigated. Results indicated that the melting point of the Sn-57Bi-1Ag solder joint bonded to Cu was approximately 140℃ even after heating at 170℃ for 60 min, and that the lamellar structure of Sn and Bi phases was similar to the structure at an initial state. Conversely, the melting start point of the Sn-57Bi-1Ag solder joint bonded to Au metallization was approximately 230℃ after heating at 170℃ for 60 min and the differential scanning calorimeter peak at 138℃ disappeared. The microstructure of the solder joint did not show the lamellar structure of Sn and Bi phases, but rather consisted of an Au-Sn intermetallic compound, Bi phase, and Ag3Sn phase. The occurrence of voids in the solder joint was possibly suppressed by optimum loading.
  • Magneto-Optical Enhancement and Chemical Sensing Applications of Perpendicular Magnetic CoPt/Ag Stacked Structures with a ZnO Intermediate Layer

    pp. 892-897

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    DOI:10.2320/matertrans.M2015395

    The magneto-optical (MO) properties of perpendicular magnetic Co80Pt20/Ag stacked films with ZnO intermediate layers of different thickness were investigated by polar Kerr measurements. The insertion of a thin ZnO layer at the CoPt/Ag interface improved the perpendicular magnetic properties and MO enhancement at the plasma edge of Ag. The CoPt/Ag stacked films with a 2-nm-thick ZnO layer exhibited an ideal square out-of-plane hysteresis loop with a relatively large Kerr angle of approximately 1.4° in the ultraviolet region. The peak position of the MO plasma enhancement shifted to longer wavelength as the thickness of the ZnO layer increased, and a new peak appeared consistent with the band-gap energy of ZnO. Moreover, the CoPt/ZnO/Ag stacked layer acted as a Fabry–Pérot etalon when the thickness of the ZnO layer was the sub-wavelength of incident light. As a result, a MO cavity was realized in the stacked films, and an ideal square MO loop with a large Kerr rotation angle of approximately 20° was obtained in the visible region. The MO enhancement factor reached approximately 200. We demonstrated that the stacked films were sensitive to changes in the optical conditions at the film surface. The developed MO cavity can act as a highly accurate chemical and biological sensing system under simple measurement conditions.
  • Magnetically Retarded Recovery and Recrystallization in Cold Rolled Pure Copper

    pp. 898-902

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    DOI:10.2320/matertrans.M2015320

    The effects of magnetic field annealing on the micro-hardness and recrystallization microstructures in a cold-rolled pure copper sheet were studied. The results showed that the micro-hardness in the specimens subjected to magnetic field annealing were higher than those annealed without the magnetic field. There are significant differences in the microstructure during the recovery and early stage of recrystallization for the specimens annealed with and without the field. Magnetic annealing leads to the retarded recovery and delayed primary recrystallization. This effect is attributed to the decreasing of stored energy, which provides the driving force for the recovery and early stage of recrystallization being retarded by the application of a magnetic field in the cold-rolled pure copper sheets.
  • Electric Evolution in Sputter-Deposited SncSnSi1−cSn Alloy Films

    pp. 903-906

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    DOI:10.2320/matertrans.M2016029

    SncSnSi1−cSn alloy films (cSn : the chemical composition) have been prepared by rf sputter-deposition. X-ray diffraction measurement indicate that almost pure bct Sn and amorphous Si phases coexist for 0.28 ≤ cSn < 1.0. The electrical resistivity (ρ) measurement indicate that the alloy films are semiconducting above 10 K for cSn ≤ 0.47 and metallic for cSn ≥ 0.57, whereas they are superconducting below 4 K for cSn ≥ 0.38. When cSn is transformed to the volume fraction, vSn, the electrical conductivity, σ versus vSn plot shows clear inflection at around vSn = 0.41. This semiconductor to metal transition threshold (vp ≅ 0.41) is much larger than 0.16 for the 3 dimensional site percolation theory, 0.21~0.25 for the partially coalesced Sn-core/Si-shell cluster assemblies and 0.33 for the effective medium theory, but smaller than 0.5 for the granular materials in which metal grains are heavily coated by small insulator grain layers. Temperature dependence of ρ also reveals a transition from a simple energy gap type conduction to a thermally assisted electron tunneling type one with increasing vSn.
  • Electric and Magnetic Evolution in Sputter-Deposited FexSi1−x Alloy Films

    pp. 907-912

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    DOI:10.2320/matertrans.M2016046

    FexSi1−x alloy films have been prepared by an rf sputter-deposition method. X-ray diffraction patterns indicate that an amorphous phase is formed for x < 0.8. Temperature dependence of electrical resistivity indicates the following electric evolution. Carrier-excitation from the impurity to the conduction (or valence) bands is dominant for x < 0.2 (the semiconductor regime), the band conduction is affected by strong impurity- and random-scatterings for x > 0.4 (the metallic regime), and the carrier-excitation between the impurity band and the mobility edge is retained due to the electron-localization effect in the amorphous structure for 0.2 < x < 0.4 (the transition region). The thermomagnetic- and magnetization-curves indicate the following magnetic evolution. The ferromagnetic phase appears at x ≅ 0.3 and the Curie temperature rapidly increases with increasing x. The magnetic (spin- or cluster-) glass region is very narrow (x = 0.3 ∼ 0.55) at low temperature. These magnetic behaviors are ascribed to the instability of Fe magnetic moments and the depression of RKKY interactions in the low x range.
  • Effects of Cerium Addition on the Microstructure, Mechanical Property and Creep Behavior of AM60B Magnesium Alloy

    pp. 913-917

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    DOI:10.2320/matertrans.M2016064

    The effects of cerium addition on the microstructure, mechanical property and creep behavior of AM60B alloy were investigated. The results indicate a little Ce addition can refine the microstructure, and with the increase of Ce addition, intermetallic compound Mg17Al12 formation in AM60B was restricted and substituted by new intermetallic compound Al11Ce3. Ce was beneficial to the mechanical property of AM60B except for elongation when Ce addition is further increased. The high temperature stability of AM60B is poor owing to the precipitation of Mg17Al12. With the addition of Ce, the creep property of AM60B was improved notably, mainly due to the stability of intermetallic Al11Ce3 at high temperature.
  • Three-Dimensional Imaging of a Long-Period Stacking Ordered Phase in Mg97Zn1Gd2 Using High-Voltage Electron Microscopy

    pp. 918-921

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    DOI:10.2320/matertrans.M2016021

    Spatial configurations and lateral morphology of the 14H long-period stacking ordered (LPSO) phase have been studied by single tilt-axis electron tomography using high-voltage scanning transmission electron microscopy (STEM) operated at 1 MV. A “Quonset hut-like” lateral shape of the LPSO was found in a tomogram of a specimen as thick as 1.7 μm. The reconstructed volume reveals spatial distribution of residual particulate precipitates of (Mg, Zn)3Gd phase 20–30 nm in diameters. The precipitates act as a source of solute elements for the formation and growth processes of 14H LPSO. 1 MV-STEM realizes enough resolution for imaging the morphology of LPSO as well as high electron transmittance (~4.1 μm) without any obvious electron irradiation damages on microstructures.
  • Simulation of the Si Precipitation Process in Mg2Si Using a Phase-Field Kinetic Model

    pp. 922-926

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    DOI:10.2320/matertrans.M2015479

    The Si precipitation process in an Mg2Si matrix has been simulated by the phase-field kinetic model, considering the eigen strain at the interface between precipitates and the matrix. We observed that the shape of the precipitate changed during the course of heat treatment from circular to lenticular. As the Si precipitate grew larger, the adjacent precipitate aggregated to form a lamellar microstructure. This microstructure is suitable for thermo-electric materials because the scattering of phonons will frequently occur at the interface between the Si precipitates and the Mg2Si matrix. Our present simulation suggests drastic improvements of thermo-electric properties of this type of material are possible due to the eigen strain.
  • Grain Refinement and Ductility Improvement by Hot Extrusion Using a Heteromorphic Die with Small Holes

    pp. 927-934

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    DOI:10.2320/matertrans.M2016005

    It has been shown using an Al–4.0mass%Cu alloy as a demonstration material that hot extrusion with the use of a specially–designed die leads to grain refinement and improvement in ductility. The specially–designed die is called in this study the “heteromorphic die” and it consists of two plates and one spacer. One plate is called the “strain–giving die” and has six small round holes of 5 mm in diameter, while the other plate is called the “shape–giving die” and has one big rectangular hole of 9 mm × 15 mm. The spacer separates these two plates at a distance of 10 mm and provides a space between them. The Al–Cu alloy billet was hot–extruded through the six small round holes of the strain–giving die to produce six thin round rods, and after filling the space between the two dies, the six rods passed together through the shape–giving die to form a thick rectangular bar or plate. Tensile tests of the plate were conducted at room temperature, and the results were compared with those of the un–extruded billet and the extruded plate produced by conventional hot extrusion method, that uses only the shape–giving die. The elongation values of the three different tensile specimens produced from (1) the un–extruded billet, (2) the plate extruded by the conventional method and (3) the plate extruded with the heteromorphic die were 21, 35 and 57%, respectively. Most significant elongation was found in the sample extruded with the heteromorphic die, which is most probably due to the finest grain structure observed in this sample. It is suggested that the recrystallization is induced by a large strain generated in the heteromorphic die due to the friction on the large contact area between the extruded metal and the die orifice wall of the “strain–giving die.”
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  • Effect of Hydrothermal Treatment Coupled with Mechanical Compression on Equilibrium Water Content of Loy Yang Lignite and Mechanism

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    DOI:10.2320/matertrans.M-M2016809

    Measurements of equilibrium water contents (EWCs) in samples obtained from hydrothermal treatment (HT) and HT coupled with mechanical compression (HT–MC) were undertaken across a range of relative humidities (RHs) to investigate the performance of EWC and its mechanism. The changes in the concentrations of carboxyl groups and mesopore volume were measured by an improved barium ion exchange and N2 adsorption–desorption isotherms methods, respectively. The results showed that EWCs decreased with progressively severe HT and HT–MC conditions and EWCs of HT–MC samples were lower than those of HT samples, indicating that HT and HT–MC can upgrade lignite by reducing water loading capacity and HT–MC was better than HT. At low RHs (RH ≤ 10%), the factor that controls EWC is water molecules–active sites interactions and one to two water molecules are associated with each carboxyl group, while at medium RHs (10 < RH ≤ 92%) the amount of monolayer water and mesopore volume gain in significance and ca. two multilayer water molecules are bound to each monolayer water molecule. At high RHs (RH > 92%), EWC is determined by comprehensive factors such as macropores and cracks. Furthermore, EWC can be either higher or lower than residual water content (RWC) based on the RH within a threshold residual water level (ca. 5 to 16%). EWC was generally higher than RWC below a RWC of ca. 5% and the opposite relationship was observed for samples with RWC above ca. 16%. These provide information for the operation of lignite dewatering technique, the control of its water re-adsorption, and storage.
  • Effects of Homogeneous Low Energy Electron Beam Irradiation (HLEBI) on Adhesive Energy of Peeling Resistance of Laminated Sheet with Polyurethane (PU) and Polyethylene Terephthalate (PET)

    pp. 943-948

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    DOI:10.2320/matertrans.M2015478

    2-layer laminated sheets (PU/PET) with Polyurethane (PU) and Polyethylene Terephthalate (PET) were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (≦ 1.72 MGy) homogeneous low energy electron beam irradiation (HLEBI) prior to hot-press under 3 MPa and 348 K. Although the weak hot-press adhesion of the PU/PET was observed without HLEBI, the new adhesion mostly raised the bonding energy as evidenced by the mean adhesive energy of peeling resistance (oEp). Based on the 3-parameter Weibull equation, the lowest oEp value at peeling probability (Pp) of zero (Es) could be estimated. An increasing trend in Es occurred by the double-step treatment applying HLEBI up to 1.29 MGy reaching a maximum at 1.83 kJ·m−1, improving the safety level without radiation damage. When HLEBI cut the chemical bonds in PU and generated terminated atoms with dangling bonds, they probably induced the chemical bonding. Therefore, increasing adhesion energy between the laminated sheets could be explained.
  • Detection and Thickness Estimation of Water Layer in Layered Medium Based on Multi-Reflection of Oblique Incident Ultrasonic Wave

    pp. 949-958

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    DOI:10.2320/matertrans.I-M2016808

    A reinforced concrete (RC) slab of a bridge is sometimes strengthened by attaching a steel plate on the bottom of the slab to enhance the flexural capacity. In this case, epoxy is injected between steel plate and concrete as the adhesive, together with anchor bolts. However, the reinforcement approach has a problem of water invasion into the top surface of a steel plate through an additionally damaged concrete slab, which will lead to a serious corrosion problem of a steel plate. Hence it is of great importance to detect the existence of water layer in the steel-epoxy-concrete layered medium and acquire information on thickness and distribution area of water. In this study, an ultrasonic multi-reflection approach through oblique incidence is developed for thin liquid layer detection. Firstly, reflection and transmission coefficients of multi-layered media including a liquid layer are calculated theoretically. Experiments on multi-layered configurations are conducted with different water layer thicknesses and bottom layer materials. By analyzing the experimental results, the existence of water layer can be clearly distinguished. Through comparison with the theoretical wave travelling time in the water layer, the thickness of the water layer can be estimated from the time interval of reflected wave groups. Different materials as a bottom layer can also affect the reflection notably, which shows good agreement with the calculated water-solid reflection coefficients.
  • Effect of Mn Addition on the Age-Hardening Behavior of an Al-(9–10)%Si-0.3%Mg Die Casting Alloy in T5 and T6 Heat Treatment

    pp. 959-965

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    DOI:10.2320/matertrans.F-M2016810

    This study investigated the effect of Mn adding on the T5 and T6 age-hardening behaviors of Al-(9.0–10.0)%Si-0.3%Mg (equivalent to A360 alloy) and Al-10%Si-2%Cu-0.3%Mg (equivalent to A383 alloy) die casting alloys using a hardness measurement, an electron probe micro analyzer (EPMA) and thermodynamic software. When 0.4%Mn was added, the hardness of the T5 heat-treated Al-Si-Mg die casting alloy increases because the Mn addition suppresses the formation of the π-Al8FeMg3Si6 phase during solidification and distributes Mg into the α solid solution. This mechanism named as π-phase suppression mechanism promotes precipitation strengthening. In the T6 heat treatment, the hardness of the alloys hardly increased when Mn was added. In the Al-Si-Cu-Mg alloys, the hardening by the 0.5%Mn addition was negligible compared to that of the Al-Si-Mg alloys regardless of T5 or T6 treatment. Therefore, the hardening by Mn addition is the characteristic phenomenon in the T5 heat-treated Al-Si-Mg high-pressure die casting alloy.
  • Effect of Shot Peening on Bending Strength of Magnesium Pipe

    pp. 966-972

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    DOI:10.2320/matertrans.P-M2016811

    This paper deals with the effect of shot peening on the bending strength of an AZ31 magnesium alloy pipe. Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. AZ31 alloy is the most widely used commercial magnesium alloy. In our experiment, extruded pipes of 22 mm O.D., 18 mm I.D., and 2 mm wall thickness were used. Shot peening treatments were applied to the surface of the workpiece using an impeller-type or an air-type peening machine. Tensile and compressive tests were carried out under axial load at a crosshead speed of 10 mm/min, and bending strength tests were performed at a crosshead speed of 100 mm/min under lateral load using an Instron-type testing machine. In the bending tests, the peened workpiece could withstand higher bending yield load. The surface layer of the peened workpieces was also observed by electron backscatter diffractometry (EBSD). It was found that multiple deformation twins were formed during shot peening. The results of the present study revealed that the compressive yield stress of shot-peened pipes is strongly related to their bending strength.
  • Joining of Copper Plates by Unusual Wetting with Liquid Tin and Tin–Lead Solder on “Surface Fine Crevice Structure”

    pp. 973-977

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    DOI:10.2320/matertrans.M2015428

    Previously, a “surface fine crevice structure” on a copper plate was created by laser irradiation and was found by the authors to be suitable for “unusual wetting”. Copper plates with “surface fine crevice structure” were joined by an unusual wetting phenomenon using liquid bismuth as joining material. In this study, we examined the viability of using tin and a tin–37 mass% lead solder as joining materials by focusing on intermetallic compound formation with copper. The wettability of the “surface fine crevice structure” on a copper plate by liquid tin and tin–lead solder was investigated and joint experiments were performed using two copper plates. The successful wetting of tin and solder material on the “surface fine crevice structure” of copper and the joining of copper plates was confirmed despite the formation of intermetallic compounds.
  • Effect of Excess Energy on Supersaturated Fe-IIIB Thin Films Formation by Ion Plating

    pp. 978-982

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    DOI:10.2320/matertrans.MBW201508

    Fe-IIIB alloy thin films are widely used in various types of actuators. In this study, Fe–Ga, Fe–Al, Fe–In alloy thin films are deposited on a Si(100) substrate through an ion-plating process using a dual vapor-source. The composition of the thin films was controlled by adjusting the deposition rate of Fe to the IIIB alloys. Deposition rates of Fe and IIIB alloys were measured by using a crystal oscillator. We investigate the effect of introduced excess energy during thin film formation. In particular, the solid solubility limits for each type of Fe-based alloy thin films are estimated and then compared using a Darken–Gurry plot, which was derived by applying the Hume–Rothery rules concerning electronegativity and the atomic radius of elements. The ion kinetic energy and the ionization rate of the evaporated particles were measured using a Langmuir probe and a Faraday cup, respectively. In addition, a multi-grid type electrostatic ion-energy analyzer was added in the plasma to obtain the ion temperature in order to acquire more precise excess energy value. Therefore, we attempt to study and control the excess energy required for Fe-IIIB alloy thin-film formation and the solid solubility limit. These results are expected to contribute significantly to Fe-IIIB alloy thin-film formation through the ion-plating process.
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    DOI:10.2320/matertrans.M2016004

    Mg2Si composite was added to Al-Si filler metal for aluminium alloy vacuum brazing via in situ synthesis. Spreading area method was used to measure the wettability of the brazing alloy on the parent metal in vacuum. The filler metal wetting area increased with increasing Mg2Si content. The compound within the interface was examined with an electron probe and the following results were obtained: Mg2Si content of the brazing interface was lower than that of filler metal, Mg2Si was distributed into both sides of the interface and arranged in block, grain and short rod-like shapes. Si crystal had a primarily needle-like structural arrangement. The elemental distribution on both sides of the interface was analysed using thread scanning method. A solid solution of Mg was formed in the interior parts of the grain in the parent metal. The solid solution content decreased as the distance from the interface increased.
  • A Feasibility Study on the Three-Dimensional Friction Stir Welding of Aluminum 5083-O Thin Plate

    pp. 988-994

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    DOI:10.2320/matertrans.M2015475

    Aluminum ships are increasingly being built these days according to the international marine environment contamination regulations. However, aluminum alloys are associated with many problems such as welding deformation. A basic study was conducted to address the problems using friction stir welding (FSW), a solid-state joining method. The AA 5083-O specimen was 2 mm-thick, and a device that provided five-axis processing control was used for the curvature welding to determine the feasibility of the process. X-ray was used to test the FSW joints quality and to examine inner defects. The characteristics of the FSW joints were evaluated based on the deformation after the welding, tensile strength, and Vickers hardness of each test specimen, according to the welding speed. The welding results were visually satisfactory for the approximate joint length of 200 mm. The joints strength was almost constant regardless of the welding speed. The joint efficiency was about 90% of that of the base material, while the elongation of the joints was about 50% of that of the base material. The hardness distribution of the joints was almost the same as that of the base material regardless of the heat input, which corresponds to the tensile test results.
  • A Novel Method of Antibacterial Evaluation Based on the Inhibition of Hydrogen Sulfide Producing Activities of Salmonella

    pp. 995-1000

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    DOI:10.2320/matertrans.M2016007

    A novel method for detecting antimicrobial activity using an innate property of the Salmonella bacteria, namely, the ability of Salmonella to produce hydrogen sulfide (H2S) was developed in this study. The validity of the method was evaluated by comparing the antibacterial activity of copper to that of aluminum. Salmonella was inoculated over the entire surface of deoxycholate hydrogen sulfide lactose (DHL) agar plates that included Ammonium ferric citrate (C6H8FeN). Approximately 25 μL of cupric chloride (CuCl2, 1% weight ratio) solution or aluminum chloride (AlCl3, 1% weight ratio) solution was added to the center of the medium. The surface of the medium was covered with polyethylene terephthalate (PET) films to induce an anaerobic state. Salmonella was cultured under anaerobic conditions at 310 K (37℃) for 86.4 ksec (24 h). The antibacterial activity of copper was determined by observing the medium surface color change due to iron sulfide (FeS) formation, which was caused by the production of H2S by Salmonella; blackness indicated presence of newly formed FeS. A quantitative evaluation of copper's antimicrobial activity was performed using a gradient of CuCl2 concentrations; results were compared with those of the present standard method, Kirby-Bauer disk diffusion method on the Mueller Hinton medium. Finally, in order to evaluate the antibacterial activity of metals, Salmonella was inoculated on DHL agar plates. Subsequently, Japanese coins (1-yen, 5-yen, 10-yen, 50-yen, 100-yen, and 500-yen coins) were placed on the agar and cultured at 310 K for 86 ksec. Salmonella cultured in the presence of AlCl3 produces black color, while no blackening is observed with CuCl2, suggesting that copper possesses an antibacterial property against Salmonella. CuCl2 suppresses H2S production by Salmonella, as copper ions form a transparent circle or ellipse (new halo) around the point at which CuCl2 had has been plated. The size of the new halo increases in direct proportion to the concentration of CuCl2. The halo is no longer visible at 0.034 mg of CuCl2 in our method, while the halo disappears with 4.34 mg of CuCl2 in the Kirby-Bauer test. Therefore, the present method is 129 times more sensitive than the standard method, suggesting increased usefulness and effectiveness in testing antibacterial activity. No FeS-dependent black circle is formed under any of the coins, with the exception of the 1-yen coin, which contains aluminum and no copper. Therefore, the copper-containing coins have an antibacterial effect.
  • Constituent Element Addition to n-Type Bi2Te2.67Se0.33 Thermoelectric Semiconductor without Harmful Dopants by Mechanical Alloying

    pp. 1001-1005

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    DOI:10.2320/matertrans.M2016031

    N-type Bi2Te2.67Se0.33 thermoelectric materials with added constituent elements were prepared without the addition of harmful dopants using mechanical alloying (MA) followed by hot pressing (HP). All the prepared samples were identified from the Bi2Te3–Bi2Se3 solid-solution diffraction peak. They were all single-phase n-type semiconductors. The maximum dimensionless figures of merit, ZT, of Bi2Te2.67(Se0.33)1+0.06, Bi2(Te2.67)1+0.06Se0.33, and Bi2(Te2.67Se0.33)1+0.03 were 0.93 at 440 K, 0.99 at 441 K, and 0.97 at 442 K, respectively. These results indicate that the figure of merit of Bi2Te2.67Se0.33 doped with constituent elements, prepared using the MA–HP process, is nearly same as the highest value, i.e., 1.0, reported in the literature.
  • A Method for Studying the Nano-Scale Stress-Strain Response of a Material by Nanoindentation

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    DOI:10.2320/matertrans.M2015459

    A method was developed using nanoindentation with a spherical indenter to probe the elastic stress-strain response of a given material quantitatively at the nanoscale. To account for the fact that the realistic indenter tip shape is not strictly spherical down at the nanoscale, this method comprises a procedure to calibrate the indentation strain based on the elastic indentation stress-strain data of a reference sample with known elastic modulus. One of the advantages of the nanoindentation-based approach is that it also enables qualitative assessment of the subsequent elastic-to-plastic transition and post yield behavior of the material. An aluminum alloy tested by the present method was shown capable of exhibiting a significantly greater strength to resist initial plastic deformation than in the case of tensile testing of bulk samples.
  • Measurement of Thermal Expansion Coefficient of 18R-Synchronized Long-Period Stacking Ordered Magnesium Alloy

    pp. 1010-1013

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    DOI:10.2320/matertrans.M2016078

    We measured the thermal expansion coefficients of an 18R-synchronized long-period stacking ordered magnesium alloy (Mg85Zn6Y9) and an α-phase pure magnesium (α-Mg). This was achieved by using a Gandolfi camera, which was attached on a high precision diffractometer at SPring-8 BL40XU beamline. By using this system, fine powder diffraction data could be obtained even from a highly oriented Mg85Zn6Y9 polycrystal at different temperatures between 95 and 440 K. The thermal expansion coefficients along a- and c-axes were determined from the refined cell parameters. The thermal expansion coefficients of the Mg85Zn6Y9 are smaller than those of the α-Mg.
  • Foaming Behavior of Aluminum Foam Precursor Using Only Friction Heat of Rotating Tool

    pp. 1014-1016

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    DOI:10.2320/matertrans.M2016034

    A friction heat foaming process (FHFP) was proposed for the foaming of an aluminum (Al) foam precursor that uses only friction heat. The precursors of the Al foam were also fabricated from Al plates by friction stir welding (FSW). It was shown that the precursor can be foamed using only the generated friction heat in only several tens of seconds. Consequently, Al foam can be fabricated using only friction based processes from the fabrication of the precursor to the foaming of the precursor.

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