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

MATERIALS TRANSACTIONS Vol. 42 (2001), No. 4

  • Recent Advances and Future Research Directions in Bulk Metallic Glasses

    pp. 548-550

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    DOI:10.2320/matertrans.42.548

    These opening remarks will briefly mention recent advances in characterizing the atomic and electronic structure, glass forming ability, thermal stability, and mechanical and magnetic properties of bulk metallic glasses. Future research directions may include the development of first principles models to predict ranges of possible alloy compositions, under-cooling limits, and glass transition temperatures, etc.; the identification of thermodynamic, geometric, electronic, chemical and kinetic parameters for the models; and the correlation of glass nanostructure and chemistry with properties and behavior. The ultimate objective is to predict and control the high mechanical strength and fracture toughness, low sliding-friction coefficient and high wear resistance, corrosion resistance, and low magnetic energy loss corresponding to particular bulk metallic glass compositions and process parameters.
  • Glass Forming Ability of La-rich La-Al-Cu Ternary Alloys

    pp. 551-555

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    DOI:10.2320/matertrans.42.551

    Melting behavior and the reduced glass transition temperature (Trg) in La-rich La–Cu–Al based alloys was systematically investigated. It was found that reduced glass transition temperature increased to the maximum when the liquidus temperature decreased to the minimum for La86−xCuxAl14 (x=10–36) alloys. The best glass formation in La-rich La–Cu–Al ternary system was obtained at La66Cu20Al14 alloy, which is at a eutectic point with the highest reduced glass transition temperature of 0.541 among these alloys. The glass forming ability of these alloys is correlated and discussed with their reduced glass transition temperature.
  • A Relationship between Glass-Forming Ability and Reduced Glass Transition Temperature near Eutectic Composition

    pp. 556-561

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    DOI:10.2320/matertrans.42.556

    Onset temperature (solidus), Tm and offset temperature (liquidus) Tl of melting of a series of bulk glass forming alloys based on Zr, La, Mg, Pd and rare-earth elements have been measured by studying systematically the melting behaviour of these alloys using differential thermal analysis (DTA) or differential scanning calorimetry (DSC). Bulk metallic glass formation has been found to be most effective at or near their eutectic points and less effective for off-eutectic alloys. Reduced glass transition temperature Trg given by TgTl is found to show a stronger correlation with critical cooling rate or critical section thickness for glass formation than Trg given by TgTm.
  • Anomalous Small-Angle X-ray Scattering Studies of Phase Separation in Bulk Amorphous Zr52.5Ti5Cu17.9Ni14.6Al10

    pp. 562-564

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    DOI:10.2320/matertrans.42.562

    We have performed differential anomalous small-angle X-ray scattering (ASAXS) experiments on samples of bulk amorphous Zr52.5Ti5Cu17.9Ni14.6Al10 annealed in the supercooled liquid region. We observe the development of strong small-angle scattering, associated with phase separation on the nanometer scale in the supercooled liquid. Analysis of the Zr-edge ASAXS data reveals that this phase separation is largely due to a redistribution of Zr. Continued annealing results in the nucleation and growth of Zr-rich crystalline intermetallic phases.
  • Thermophysical Properties of Bulk Metallic Glass Forming Alloys in the Stable and Undercooled Liquid — A Microgravity Investigation

    pp. 565-578

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    DOI:10.2320/matertrans.42.565

    The results of an investigation of the thermophysical properties in the stable and undercooled liquid state of the glass forming metallic alloys Zr64Ni36, Zr65Al7.5Cu17.5Ni10 and Zr60Al10Cu18Ni9Co3 is described. In order to make accessible a large range of liquid undercooling and to provide for extended experimentation in the liquid phase the experiments have been performed under the condition of reduced gravity with an electromagnetic levitation device onboard spacelab. Aspects of the experimental method as well as results regarding the thermophysical properties investigated shall be described. Properties investigated included the specific heat and enthalpy of fusion allowing evaluation of the thermodynamic functions, and as such a comparison of the thermodynamic contribution to glass forming ability among different metallic glass forming alloys. Furthermore, transport properties such as the effective thermal conductivity and total hemispherical emissivity as well as the electrical resitivity have been investigated. The temperature dependence of the specific heat capacity and that of the electrical resistivity indicate a temperature dependent chemical short range order.
  • Dependence of High Pressure on Phase Transformation in Zr41.2Ti13.8Cu12.5Ni10Be22.5

    pp. 579-582

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    DOI:10.2320/matertrans.42.579

    The phase transformation of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (BMG), which arises from compression and decompression, has been investigated by using cubic type high-pressure apparatus and Diamond Anvil Cell (DAC). The temperature of phase transformation from the amorphous to the crystalline (Tx) displays a universal decrease under high pressure. Based on the observation of in-situ resistance measurement in a DAC, 24 gigapascals (GPa) was able to lead to the crystallization event of this BMG at room temperature. The dependence of Tx on pressure (P) followed the relation of Tx=714.3−7.97P−0.399P2. Moreover, an unexpected new phenomenon emerged has also been found during decompression. The high pressure induced crystalline phase reverted back to the amorphous state during downloading, which was further confirmed by TEM.
  • Electric-Field-Enhanced Crystallization of Zr41Ti14Cu12.5Ni10Be22.5 Bulk Metallic Glass

    pp. 583-586

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    DOI:10.2320/matertrans.42.583

    Isothermal crystallization studies are performed on Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) with and without applied electric field. The crystallization process of the BMG is markedly affected by the applied electric field. The crystalline phase volume fraction and the growth rate of nucleus are enhanced when annealed in the electric field in the supercooled liquid region. We phenomenologically explain the observations.
  • Formation and Properties of Zr-(Ti, Nb)-Cu-Ni-Al Bulk Metallic Glasses

    pp. 587-591

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    DOI:10.2320/matertrans.42.587

    The effect of composition variations and of B or Si addition on the glass forming ability and thermal stability of Zr–M–Cu–Ni–Al (M=Ti, Nb) bulk metallic glass-forming alloys have been investigated. The structural, acoustic, thermal and elastic properties of the bulk metallic glasses (BMGs) are studied by X-ray diffractmetery (XRD), differential scanning calorimetry (DSC) and ultrasonic method. A small amount of boron and silicon addition can significantly affects the GFA and crystallization behaviors and microstructural nature of the glass-forming alloys. The small changes of the density and acoustic velocities in the BMGs relative to its corrsponding crystallized state indicate a similar electronic state and similar atomic interactions between the glassy and crystalline states.
  • A Study on the Development of Ni-Based Alloys with Wide Supercooled Liquid Region

    pp. 592-596

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    DOI:10.2320/matertrans.42.592

    Ni-based amorphous alloys with wide supercooled liquid region (ΔTx) have been developed through alloy design based upon the empirical rules for high glass forming alloys. The amorphous Ni59Zr20Ti21 alloy shows glass transition temperature of 794 K, onset temperature of the first exotherm (Tx1) of 808 K and supercooled liquid range (ΔTx=Tx1Tg) of 14 K, while the amorphous Ni59Zr20Ti16Si5 alloy shows Tg of 830 K, Tx1 of 876 K and ΔTx of 46 K . The amorphous Ni59Zr20Ti21 and Ni59Zr20Ti16Si5 alloys crystallize through two step reactions. First, primary crystallization of cubic NiTi(Zr) phase occurs from the amorphous matrix and then the NiTi(Zr) and remaining amorphous phases transforms into a mixture of cubic NiTi(Zr) and orthorhombic Ni10(Zr, Ti)7 phase for the ternary alloy and into a mixture of the cubic NiTi(Zr), orthorhombic Ni10(Zr, Ti)7 and an unidentified phase containing Si for the quaternary alloy. Partial replacement of Ti by Si improves glass forming ability. A bulk amorphous Ni59Zr20Ti16Si5 rod with 2 mm in diameter is fabricated by injection casting.
  • A Fictive Stress Model and Nonlinear Viscoelastic Behaviors in Metallic Glasses

    pp. 597-605

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    DOI:10.2320/matertrans.42.597

    Transition behaviors from linear to nonlinear viscoelasticity under constant strain-rate deformation near the glass transition have been investigated for Pd- and Zr-based alloy glasses. The transition occurs at critical strain-rate, and the steady-state viscosity may decrease by many orders of magnitude above the critical strain-rate. Concurrently with the transition, the growth of the stress shows a stress-overshoot; the stress increases initially attaining a maximum, then decreases and attains a steady-state flow. The transition between steady-state Newtonian and non-Newtonian flows can be analyzed by a stretched exponent relaxation function, and both the normalized viscosity and the flow stress can be represented by a master curve in terms of the product of the strain-rate and the Newtonian viscosity. These results imply that the occurrence of the transition from the Newtonian to non-Newtonian is explicitly determined by the flow stress. A model, based on the hypothesis of stress-induced structural relaxation and the concept of fictive stress for the nonlinear viscoelastic behaviors has been proposed. The model calculation has reproduced fairly well the experimental results of the Pd- and Zr-based glasses, in particular, the development of the stress-overshoot behavior. In addition, the model reveals a stress-overshoot and under-shoot oscillation at very high strain-rate. This oscillatory nonlinear behavior has been observed in many polymer solutions, and also the latest study in metallic glasses. The model calculations of other nonlinear viscoelastic behaviors, such as stress relaxation during stress growth after abrupt cessation of steady-state flow, and a stress regrowth after a brief interval of relaxation, are also presented.
  • Pressure Effects on Elastic Properties and Glass Transition of Zr-, Pd-based Bulk Metallic Glasses

    pp. 606-612

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    DOI:10.2320/matertrans.42.606

    The structures and properties of materials are profoundly altered under high pressure due to a large change of atom spacing, chemical bonding and Gibbs free energies. Therefore, materials with novel structures and properties can be created via a process known as pressure-induced phase transition. Here we report the investigations of pressure effects on the elastic properties and the glass transition of Zr-, Pd-based bulk metallic glasses (BMGs). The elastic constants and the Debye temperatures, of a Zr41Ti14Cu12.5Ni10Be22.5C1 and a Pd39Ni10Cu30P21 BMGs are measured by using an ultrasonic technique, and their pressure dependence is exhibited. The equations of state (EOS) of the two BMGs are established. The acoustic attenuation behaviors are also monitored with various pressure in the two BMGs, and a marked difference between the two BMGs is revealed. The effects of pressure-induced structural relaxation on the glass transition of the Pd39Ni10Cu30P21 BMG are investigated by a temperature-modulated differential scanning calorimetry technique. The pressure dependence of the reversible and irreversible glass transition is explained.
  • Extended Plasticity in the Supercooled Liquid Region of Bulk Metallic Glasses

    pp. 613-618

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    DOI:10.2320/matertrans.42.613

    Bulk metallic glasses have good mechanical formability in viscous states. The good formability offers a great advantage of fabricating near-net-shape structural components. Whereas large tensile ductility has been observed in metallic glasses in the supercooled liquid region, the exact deformation mechanism, and particularly whether such alloys deform by Newtonian viscous flow (m=1, where m is the strain rate sensitivity exponent) or not, remains a controversial issue. In this paper, existing data are analyzed and the apparent controversy is discussed. Results obtained from an amorphous alloy (composition: Zr–10Al–5Ti–17.9Cu–14.6Ni in at%) are presented. Dynamic structural evolution is characterized using electron microscopy and focus X-ray. It is demonstrated that, despite the fact that the deformation was carried out in the supercooled liquid range, concurrent crystallization of the amorphous structure occurred. As a result, a non-Newtonian behavior was observed.
  • Flow and Fracture of Bulk Metallic Glass Alloys and Their Composites

    pp. 619-622

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    DOI:10.2320/matertrans.42.619

    The fracture and plastic deformation mechanisms of a Zr–Ti–Ni–Cu–Be bulk metallic glass and a composite utilizing a crystalline reinforcement phase are reviewed. The relationship between stress state, free volume and shear band formation are discussed. Positron annihilation techniques were used to confirm the predicted increase in free volume after plastic straining. Strain localization and failure were examined for a wide range of stress states. Finally, methods for toughening metallic glasses are considered. Significant increases in toughness are demonstrated for a composite bulk metallic glass containing a ductile second phase which stabilizes shear band formation and distributes plastic deformation.
  • Enhancement of Ductility and Plasticity of Zr55Cu30Al10Ni5 Bulk Glassy Alloy by Cold Rolling

    pp. 623-632

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    DOI:10.2320/matertrans.42.623

    With the aim of improving ductility and plasticity of a Zr55Cu30Al10Ni5 bulk glassy alloy, a cold rolling treatment leading to the rolled structure with high-density slip bands was performed. A number of slip bands were introduced along the maximum shear stress plane by cold rolling, and the first slip bands were found to slant significantly with increasing reduction ratio in thickness. At the critical reduction ratios, the second slip bands were introduced at a reduction ratio of 30%, followed by the third slip bands at a reduction ratio of 60%. Mechanical properties of the rolled samples were examined by bending test and Charpy impact test. The maximum bend deflection value before failure increased with an increase of reduction ratio, indicating that the cold rolling improves the plasticity of the bulk glassy alloy. Since the Charpy impact value depends on the rolling direction, we selected an optimum rolling direction in which the maximum Charpy impact value is obtained. The control of the rolling direction causes an increase in the Charpy impact value by 36% as compared with the unrolled alloy. Consequently, the cold rolling process is concluded to be a valuable method for improving the ductility and plasticity of the bulk glassy alloy.
  • Effects of Annealing and Changes in Stress State on Fracture Toughness of Bulk Metallic Glass

    pp. 633-637

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    DOI:10.2320/matertrans.42.633

    The effects of annealing and changes in stress state on the toughness of both 4 mm thick and 7 mm thick plates of a Zr–Ti–Ni–Cu–Be alloy have been determined. In the amorphous state, both notched and fatigue precracked specimens have been tested. The effects of changing the notch root radius from a fatigue precrack to that of a blunt notch on the fracture toughness are dramatic. The toughness increases from approximately 17.9±1.8 MPa\\sqrtm in the fatigue precracked specimens to in excess of 130 MPa\\sqrtm in the notched specimens. These results are compared to similar tests on a range of structural materials, including aluminum alloys, steels, Ti alloys, and metal matrix composites. The increased toughness obtained by increasing the notch root radius in this bulk metallic glass far exceeds that typically observed in other structural materials. Possible reasons for this are presented. In addition, the effects of changes in loading rate and various annealing treatments on the toughness are presented and rationalized via both crack path and fracture surface observations. Annealing of this bulk metallic glass at temperatures below Tg produces increases in strength/hardness, rapid decreases in toughness, and a corresponding change in the fracture morphology. Changes in loading rate did not have a significant effect on the toughness for either notched or fatigue precracked specimens.
  • Effects of Pre-Charged Hydrogen on the Mechanical and Thermal Behavior of Zr-Ti-Ni-Cu-Be Bulk Metallic Glass Alloys

    pp. 638-641

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    DOI:10.2320/matertrans.42.638

    The effects of pre-charged hydrogen on the deformation, fracture and thermal behavior of a Zr–Ti–Ni–Cu–Be bulk metallic glass were investigated. The glass transition and crystallization temperatures were shifted to higher values with increasing hydrogen charging indicating sluggish kinetics. Flow stress was increased and fracture toughness was degraded after hydrogen charging. The atomic jump process which underlies the plastic deformation is believed to be retarded by hydrogen resulting in embrittlement.
  • Deformation Mechanisms of the Zr40Ti14Ni10Cu12Be24 Bulk Metallic Glass

    pp. 642-649

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    DOI:10.2320/matertrans.42.642

    We have studied the mechanical behavior of Zr40Ti14Ni10Cu12Be24 through uniaxial compression and nanoindentation experiments. Quantitative measurements of the serrated plastic flow observed during uniaxial compression are reported. These data are used to predict temperature increases in single shear bands due to local adiabatic heating caused by the work done on the sample as shear propagates progressively across the sample. Since the predicted temperature increases are insufficient to reach the glass transition temperature, it is unlikely that localized heating is the primary cause of flow localization. Instead, localization of shear is more likely caused by changes in viscosity associated with increased free volume in the shear bands. The orientation of the shear bands in compression tests and an indentation size effect for the onset of plastic flow in nanoindentation both point to increased free volume as the cause of localization.
  • Bulk Metallic Glasses and Composites in Multicomponent Systems

    pp. 650-655

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    DOI:10.2320/matertrans.42.650

    Single-phase (Zr/Ti)–Cu–Al–Ni metallic glasses were synthesized by copper mold casting and mechanical alloying of elemental powder mixtures. In addition, nanostructured metallic glass composites were produced by annealing of as-cast specimens and by mechanical alloying of elemental powder mixtures blended with different volume fractions of ZrC particles. For cast specimens, the effect of composition on the thermal stability and the microstructure after partial crystallization was investigated by X-ray diffraction and differential scanning calorimetry. Ti additions lead to a lower overall thermal stability of the material and induce primary crystallization. The grain size of the precipitates after the first crystallization stage becomes progressively finer with increasing Ti content, yielding grain sizes as small as about 2 nm for Zr54.5Ti7.5Cu20Al10Ni8. For mechanically alloyed Zr55Cu30Al10Ni5 powders containing up to 30 vol% nanoscale ZrC particles, stoichiometry variations of the glass due to particle dissolution in the glassy matrix during the mechanical alloying process were observed, which affect the thermal stability of the glassy matrix phase. Nevertheless, the composites maintain an extended supercooled liquid region before crystallization.
  • Corrosion Behavior of Zr65Al7.5Ni10Cu17.5 Amorphous Alloy for Biomedical Use

    pp. 656-659

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    DOI:10.2320/matertrans.42.656

    To evaluate the performance of Zr65Al7.5Ni10Cu17.5 amorphous alloy for the biomedical use, the effects of chloride ion, Cl, pH, and dissolved oxygen, DO, on the anodic polarization behavior of the alloy were examined in phosphate buffered solutions. Polarization resistance, Rp, at open-circuit potential, Eopen, and pitting potential, Epit, were determined from the polarization curve. Compositions of passive film generated in a pH-7.5 solution with various concentrations of DO were characterized with X-ray photoelectron spectroscopy. In the solution with pH 7.5, the Epit decreased with the increase in logarithm of Cl concentration, [Cl], and showed the highest value with the same DO concentration, [DO], as that in vivo. The concentrations of hydroxide group, [OH], and phosphate ions, [HxPO4(3−x)−], in the passive film were changed with various [DO]s, and the Epit decreased with the increase in [OH] and [HxPO4(3−x)−]. In the solution with pH 2.2, the Epit was higher than the Eopen with and without DO. Therefore, this alloy may be resistant to the pitting corrosion in vivo.
  • Bulk Glassy Fe-Ga-P-C-B Alloys with High Saturation Magnetization and Good Soft Magnetic Properties Synthesized by Fluxing Treatment and Copper Mold Casting

    pp. 660-663

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    DOI:10.2320/matertrans.42.660

    The effect of fluxing treatment on the glass-forming ability for the Fe75Ga5P12C4B4 glassy alloy was investigated. The fluxing treatment was found to be effective for the elimination of heterogeneous nucleation sites. The glass transition temperature (Tg), crystallization temperature (Tx), supercooled liquid region (ΔTx) and reduced glass transition temperature (TgTm) are all increased by fluxing treatment. The Tg, Tx, ΔTx and TgTm values for Fe75Ga5P12C4B4 glassy alloy are 731 K, 768 K, 37 K and 0.610 respectively before fluxing treatment, increase to 749 K, 805 K, 56 K and 0.625 respectively after fluxing treatment. Bulk glassy Fe75Ga5P12C4B4 alloy rods with high saturated magnetization (Is) of 1.27 T and good soft magnetic properties of 1.6 A/m for coercive force (Hc) were prepared with diameters range up to 2.5 mm by the copper mold casting method of fluxed alloy melt. The glass synthesis consists of preparing the alloy ingot by induction melting, thermal cycling and purifying the melt in B2O3 flux inside a silica tube and then casting the purified alloy into a copper mold. The size of 2.5 mm in diameter of the rod is not an upper limit.
  • Structure and Magnetic Properties of Chill-cast and Melt-spun Ndx(Fe3Al)100-x and Nd33(FeyAl)67 Alloys

    pp. 664-669

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    DOI:10.2320/matertrans.42.664

    The magnetic properties of chill-cast Nd–Fe–Al rods have been studied as a function of Nd and Al concentrations. High coercivities were obtained in Nd60(Fe3Al)40, Nd50(Fe3Al)50 and Nd33(Fe10Al)67 alloys. The study on the melt-spun ribbons of these alloys has shown that coercivity is dependent on the quenching rate, and high coercivity could only be obtained in alloys prepared after a relatively low quenching rate. Several crystalline Nd–Fe–Al phases have been investigated in this work. A metastable tetragonal phase existed as nearly the single phase in Nd33(FeyAl)67 with y=2–4. The tetragonal phase is antiferromagnetic with a Néel temperature of 260 K . Metamagnetism and magnetoresistivity have been observed. The study on the annealed Nd33(FeAl)67 alloy has shown that a hexagonal phase and an unknown were formed and these two Fe-containing phases, among which one is an antiferromagnetic with a Néel temperature of 280 K and the another is ferromagnetic below 130–140 K.
  • Low Field Magnetic Properties of Nd50Fe40Si10-xAlx Melt-Spun and Bulk Amorphous Alloys

    pp. 670-673

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    DOI:10.2320/matertrans.42.670

    Glass-forming ability and low field magnetic properties of Nd50Fe40Si10−xAlx (x=0–10) melt-spun ribbons and cast rods are investigated in the temperature range 5–600 K . The dependence of the coercive field on the thickness and preparation method is ascribed to the existence in the amorphous matrix of very small Fe–Nd-based ferromagnetic clusters, which can not be detected by XRD measurements, the size of which approaches to a single magnetic domain. Coercivity increases substantially at reduced temperatures even in low fields. The development in Nd–Fe-based bulk amorphous alloys of two different types of magnetic order, i.e. short-range spin-glass-like order and long-range ferromagnetic order is revealed by zero-field-cooled and field-cooled magnetization measurements.
  • Bulk Hard Magnetic Alloys in Nd-Fe-B System Prepared by Casting and Melt Spinning

    pp. 674-677

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    DOI:10.2320/matertrans.42.674

    Cylindrical cast rods and melt-spun ribbons of Nd60Fe30B10 and two Nd67Fe26B7 and Nd10Fe73B17 eutectic alloys were prepared by copper mold casting and melt spinning. Coercivity of the as-cast Nd60Fe30B10 rod was 434 kA/m. Coercivity of the cast rod was increased to 1285.6 kA/m after annealing due to the formation of Nd2Fe14B phase. The as-cast eutectic Nd67Fe26B7 rod, which is partially amorphous, exhibited coercivity value identical to that of the alloy Nd60Fe30B10 (∼430 kA/m). On the other hand, eutectic Nd10Fe73B17 shows better glass forming ability, but lower coercivity (∼100 kA/m).
  • Application of Zr-Based Bulk Glassy Alloys to Golf Clubs

    pp. 678-681

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    DOI:10.2320/matertrans.42.678

    Bulk glassy alloys have high tensile strength, while the Young’s modulus is lower by 20 to 40% than those for the corresponding crystalline alloys. These unique mechanical properties are effective to increase the coefficient of restitution at the impact between a golf club and a golf ball. Bulk glassy alloys have in general been produced by the copper mold casting and die casting methods. We have developed a new manufacturing process for Zr-based bulk glassy alloys. By the use of the new process, we have succeeded in producing a glassy Zr–Al–Ni–Cu alloy in a shell shape with a dimension of about 90×40 mm and a thickness of 3 mm for glassy driver golf clubs. It exhibits excellent mechanical properties such as tensile strength of 1700 MPa, Young’s modulus of 81 GPa, and impact fracture toughness of 130 kJ/m2. These properties are suitable for the material for driver golf club heads. The glassy driver golf club with the shell shape in the impact region was confirmed to have a high coefficient of restitution.
  • Cast Al-V-Fe Alloys with Nanoscale Particles

    pp. 682-685

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    DOI:10.2320/matertrans.42.682

    The sheets or cylinders of Al–V–Fe alloys were prepared by using a water-cooled copper mould. The mixed structure of nanoscale icosahedral particles embedded on the Al matrix was obtained. The precipitation of icosahedral phase is sensitive to the variation of composition. The volume fraction of icosahedral phase increases with increasing the content of V element and Fe element in the composition range of V2–8% and Fe2–6%, respectively. The cooling rate affects significantly the formation of icosahedral phase. With increasing the thickness from ribbon to 1 mm sheet, the particles size of icosahedral phase in Al–V–Fe alloys increases from 20 nm to 50–60 nm. Further increasing the thickness of sheets, Al10V intermetallics may precipitate. Both tensile and compressive yield strength at room temperature were measured. The yield strength of Al–V–Fe alloys is up to 800 MPa. The yield strength of Al–V–Fe alloys improves with increasing the content of V element and Fe element due to the increase of nano-particle of I-phase.
  • The Influence of Strain Rate and Temperature on the Deformation Behaviour of 63Sn/37Pb and 60Sn/40Pb Solder Alloys

    pp. 686-690

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    DOI:10.2320/matertrans.42.686

    The influence of strain rate and temperature on plastic deformation behaviour of 63Sn/37Pb and 60Sn/40Pb solder alloys is investigated by means of a computer controlled servo-hydraulic machine over a temperature range of −40 to 80°C at constant strain rates of 10−3, 10−2 and 10−1 s−1. The fracture characteristics of deformed specimens are analyzed using scanning electron microscopy and correlated with macroscopic behaviour. The results indicate that the flow stress of both alloys is largely dependent on strain rate and temperature. The 63Sn/37Pb alloy, however, is stronger than 60Sn/40Pb over the range of 25 to 300°C. The change in flow behaviour is related to differential strain rates and temperature sensitivities. Over the strain rate and temperature range studied, 60Sn/40Pb exhibits higher strain rate and temperature sensitivities than 63Sn/37Pb. 60Sn/40Pb rupture resistance is found superior to 63Sn/37Pb in light of fracture observations revealing an absence of damage as well as an absence of flow instability. 63Sn/37Pb fracture is catastrophic at a strain rate of 10−3 s−1 and is characterized by shear. With decreasing test temperature, more edge cracks appear due to enhanced brittleness. The use of a deformation constitutive equation in combination with the parameter values obtained through these tests allows for an accurate description of the deformation behaviour of both tin-lead alloys over the range of conditions used in this study.
  • Reactive Diffusion between Ultra High Purity Iron and Silicon Wafer

    pp. 691-696

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    DOI:10.2320/matertrans.42.691

    Reactive diffusion between iron and silicon wafer has been studied by using 99.995% electrolytic iron flakes (4.5N–Fe), a 99.5% iron sheet (3N–Fe) and two kinds of iron plates having different oxygen contents which were made by melting the same 99.9% electrolytic iron flakes under different conditions. The growth rate of the Fe3Si diffusion layers formed in the 4.5N–Fe/Si diffusion couples is faster than that in other couples. The authors have previously reported briefly that Fe3Si formed in bulk Fe/Si diffusion couples consisted of interstitial free iron (IF-steel) and Si wafer grows considerably faster than that in bulk 99.99%Fe (4N–Fe)/Si diffusion couples and proposed a possible explanation that oxygen atoms which initially distribute randomly in the 4N–Fe specimens are enriched in the iron near the Fe/Fe3Si interface and they react with Si atoms and form SiO2 film on the surface of voids formed in the iron near Fe/Fe3Si interface. The SiO2 film acts as a diffusion barrier and slows down the growth rate of iron silicides. Ti and Al atoms in IF-steel remove the effect of oxygen by scavenging oxygen atoms around them. So, Fe3Si in the IF-steel/Si couple can grow faster than that in the 4N–Fe/Si couples. This explanation suggests that the growth rate of Fe3Si is very fast in a Fe/Si diffusion couple, oxygen concentration in the iron is extremely small. The present experimental result that the growth rate of Fe3Si is faster than the IF-steel/Si diffusion couples supports this explanation because the oxygen concentration in 4.5N–Fe is very small.
  • Interface Reaction between Solder and Plated Nickel Film

    pp. 697-701

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    DOI:10.2320/matertrans.42.697

    Ni plating is widely used as the metallization for solder joints in semiconductor devices. However, reliability degradation occurs in the joint interface, because numerous voids are formed during soldering, which leads to heat loss at the solder joints.This paper describes the void formation mechanism and the reaction mechanism between Ni plating and solder. The defective area of an oxide film on plated Ni film can be broken by Sn and H2 before the Ni surface is cleaned. Sn reacts with Ni, resulting in the formation of intermetallic compounds. Voids form in the areas where oxide film is remains. When joining plated Ni film and solder, it is necessary to remove the oxide film from the Ni surface in order to decrease the number of voids.
  • Preparation of Barium Titanate Film by Metal-Organic Chemical Vapor Deposition and its Thermodynamic Analysis

    pp. 702-706

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    DOI:10.2320/matertrans.42.702

    BaTiO3 films were prepared on fused silica substrates by metal-organic chemical vapor deposition (MOCVD). Effect of deposition conditions on the composition, structure and morphology were studied. Thermodynamic calculations well predicted the relationship between deposition conditions and the phases of deposits. BaTiO3 films in a single phase were obtained at 973 K and Ba/Ti ratio in the source gas of 0.25 to 0.35. The grain size of BaTiO3 films increased with decreasing total pressure. BaTiO3 film in thickness of about 1 \\micron had a relative dielectric constant of 480. The dielectric constant of the BaTiO3 film showed the maximum value of 530 at 360 K.
  • The Effect of Oxygen Flow Rate in HVOF Spraying on Oxidation Behavior of Cr3C2 (7 mass%NiCr) Coatings

    pp. 707-711

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    DOI:10.2320/matertrans.42.707

    This study was performed to investigate the influence of the oxygen flow rate in HVOF spraying on the oxidation behavior of Cr3C2 (7 mass%NiCr) coatings. The oxide was formed on the coatings during HVOF spraying regardless of the oxygen flow rate. The oxide observed at the coatings was Cr2O3, but chromium oxides of other forms were not observed. Cr3C2 (7 mass%NiCr) coatings were stable in a temperature range up to 1073 K for 50 h. However, the oxidation behavior of the coatings at 1273 K showed great difference from that at temperature up to 1073 K and the oxygen flow rate had a significant influence on the oxidation behavior of the coatings. The surface of the coatings sprayed with 229 and 243 l/min-oxygen flow rate became porous by the aggressive evaporation of CO, CO2 gases and the oxide clusters were partially formed after isothermal oxidation at 1273 K for 50 h. The oxide clusters were complex oxides consisted of Ni and Cr, whereas the porous surface was composed of only Cr2O3. TG analysis revealed that the mass loss by intensive evaporation of gaseous oxide, in the case of the coatings sprayed with 229 l/min-oxygen flow rate, began after the oxidation time of approximately 42 h at 1273 K . The apparent activation energy (Q) for oxidation varied from 89.04 to 99.96 kJ mol−1 with increasing oxygen flow rate.
  • Improvement of Hydrogen Storage Properties of Mg-Ni Alloys by Rare-Earth Addition

    pp. 712-716

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    DOI:10.2320/matertrans.42.712

    A simple and efficient method has been employed to prepare a Mg-rich Mg–Ni–Nd alloy which exhibits a substantially large hydrogen storage capacity with excellent absorption/desorption kinetics at moderate temperatures. This method consists of fully melting raw materials in a sealed steel crucible filled with Ar and subsequent quenching into cold water. It overcomes the difficulties in the melting process of the materials due to large differences in the melting points, specific weights, oxidizability and evaporativity of the raw materials at high temperatures. Initial activation processes, hydriding/dehydriding rates, and presure-composition isotherm (PCT) characteristics of the alloy have been examined and the results are compared with those of a Mg-rich Mg–Ni alloy prepared with the same technique. The Mg–Ni–Nd ternary alloy can absorb ∼5.0 mass%H (H/M∼1.6) at excellent speeds between 573 and 373 K, and can desorb it at moderate speeds between 573 and 473 K . This attractive property of the alloy can be explained by the catalytic action of Nd as well as the unrelaxed multiphase structure formed in the preparation process.
  • Metallurgical Bonding of Bulk Metallic Glasses

    pp. 717-719

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    DOI:10.2320/matertrans.42.717

    In order to establish metallurgical bonding technology of bulk metallic glasses, we have tried to weld Pd40Ni40P20 and Zr55Al10Ni5Cu30 bulk metallic glasses having a wide supercooled liquid region and high glass forming ability by two welding methods of friction and pulse-current. We have for the first time succeeded in joining bulk metallic glasses by both methods. No crystallization was observed in the interface and heat-affected zones. No visible defect was recognized at the interface, showing an achievement of metallurgical bonding of bulk metallic glasses. The tensile strength of the welded bulk metallic glasses was the same as that of the parent bulk metallic glasses.

Article Access Ranking

16 Jun. (Last 30 Days)

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