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

MATERIALS TRANSACTIONS Vol. 46 (2005), No. 7

  • Isothermal Tetragonal-to-Monoclinic Phase Transformation in a Zirconia–Yttria System

    pp. 1443-1451

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    DOI:10.2320/matertrans.46.1443

    The isothermal tetragonal-to-monoclinic phase transformation in zirconia-0.5–4 mol% yttria ceramics with and without alumina addition is summarized. This transformation proceeds sigmoidally with increasing isothermal aging time. C-shaped T-T-T curves are obtained, and their nose positions shift to shorter times and higher temperatures as the yttria content decreases. The apparent activation energy obtained from the T-T-T curves is almost coincident with that for diffusion of oxygen ions in zirconia–yttria ceramics, irrespective of the environment in water, air or vacuum. The isothermally transformed laths advance from the grain boundaries to the grain interiors and then propagate adjacent grains with increasing aging time. Furthermore, this growth is controlled by the diffusion of oxygen ion vacancies in zirconia. The alumina addition acts to reduce the anisotropy of the transformed monoclinic phase.
  • Preparation and Thermoelectric Properties of NaxCoO2/Co3O4 Layered Nano-Composite

    pp. 1453-1455

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    DOI:10.2320/matertrans.46.1453

    NaxCoO2/Co3O4 layered nano-composite was prepared through the exfoliation, stacking, and sintering processes. Although almost no electrical conduction was observed at low temperatures, a significant increase in conductivity was observed above 750 K, and it reached 1.2×102 Scm−1 at 1200 K, which is comparable to that of Na0.7CoO2. Seebeck coefficient also largely increased above 750 K. This observation might be associated with the electrical behaviors of Co3O4 at high temperature.
  • Effect of the Polymerized Complex Process on Doping Limit of Thermoelectric NaxCo1−yMyO2 (M=Mn, Ni)

    pp. 1456-1461

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    DOI:10.2320/matertrans.46.1456

    The thermoelectric NaxCoO2 ceramics partially substituted by Mn or Ni at the Co site were synthesized by a polymerized complex (PC) process and subsequent pressureless sintering. The effects of the PC process and the partial substitution on the NaxCoO2 phase formation and their thermoelectric properties were investigated. For NaxCo1−yMnyO2, the sintered samples were composed of the single phase of γ-NaxCoO2 without any second phases up to y=0.10. On the other hand, the X-ray diffraction analysis showed that small peaks from the CoNiO2 phase were clearly detected in the pattern of the NaxCo0.90Ni0.10O2. However, the Ni content in the γ phase matrix of the NaxCo1−yNiyO2 synthesized by the PC process was about 1.9 times greater than that of the ceramic sample prepared by the conventional solid state reaction method, indicating that the PC process is effective for expanding the doping level. Both the Seebeck coefficient and the electrical resistivity were increased by the Mn and Ni substitutions over the entire temperature range, and the dimensionless figure of merit was improved by these substitutions, especially by the Ni substitution.
  • Thermoelectric Properties of CuAl1−xMxO2 (M=Zn, Ca)

    pp. 1462-1465

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    DOI:10.2320/matertrans.46.1462

    Substitution was performed with Ca2+ and Zn2+ in the Al3+ site of CuAlO2. We investigated the influence of substitution on thermoelectric properties. Power factors were the highest near 850 K for the samples of CuAl0.999Zn0.001O2 (6.8×10−5 Wm−1K−2), CuAl0.999Ca0.001O2 (7.4×10−5 Wm−1K−2), CuAlO2 (6.6×10−5 Wm−1K−2).
  • Thermoelectric Properties of Lanthanum-Doped Europium Titanate

    pp. 1466-1469

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    DOI:10.2320/matertrans.46.1466

    The thermoelectric properties of lanthanum-doped polycrystalline perovskite-type europium titanate were measured from room temperature to 900 K and compared to those of MTiO3 (M=Ca, Sr, Ba). The differences in the titanates were calculated in terms of the differences of A-site ion and Ti–O distance that determined the covalent bonding strength. The A-site ion appeared to have little influence on the electrical properties. The small Ti–O(Ti) distance results in strong bonding and it causes high thermal conductivity together with high electrical conductivity. Europium titanate showed power factor similar to and thermal conductivity lower than those of the strontium titanate. Eu0.9La0.1TiO3 showed the highest dimensionless figure of merit of 0.25 at 900 K.
  • Thermoelectric Properties of Amorphous Zinc Oxide Thin Films Fabricated by Pulsed Laser Deposition

    pp. 1470-1475

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    DOI:10.2320/matertrans.46.1470

    Thermoelectric properties of non-doped amorphous zinc oxide (ZnO) thin film were studied at between room temperature and around 673 K, where the samples were prepared by pulsed laser deposition at room temperature. The results of X-ray diffraction, transmittance spectroscopy and electron microscope observation indicate that both as-deposited film and heat treated film had amorphous structure with random hexagonal network of ZnO, where the latter included crystallized ZnO grains. The highest absolute value of Seebeck coefficient α was 135 μV/K at 643 K, where the electrical resistivity ρ was 1.01×10−4 Ωm and the power factor P was 1.79×10−4 W/mK2, and the α was almost the same as those of other ZnO compounds such as (ZnO)5In2O3 and (Zn1−xAlx)O. The heat treatment dependence of the ρ and the α indicated the decrease of free electrons originated in amorphous and the transition to the quasi-stable phase of amorphous. It was suggested that the amorphous structure with variable range hopping conduction relates to the thermoelectric properties of a-ZnO thin film.
  • Effect of Yb Filling on Thermoelectric Properties of Ge-Substituted CoSb3 Skutterudites

    pp. 1476-1480

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    DOI:10.2320/matertrans.46.1476

    We report the effect of Yb filling on the thermoelectric properties of polycrystalline Ge-substituted CoSb3 skutterudite compounds. Electrical conductivity, Seebeck coefficient, Hall effect, and thermal conductivity measurements were performed on polycrystalline YbyCo4Ge0.5Sb11.5 (y=0, 0.1, 0.2, 0.3, 0.4 and 0.5). In YbyCo4Ge0.5Sb11.5, the Ge atom acts as an electron acceptor that charge compensates for the Yb ions, resulting in p-type carrier conductivity at low Yb compositions y=0 and 0.1 and n-type one at high y=0.2–0.5. Due to the effect of charge compensation for Yb ions by Ge substitution, the Yb filling fraction limit in YbyCo4Ge0.5Sb11.5 is larger than that in YbyCo4Sb12. The lattice thermal conductivity for YbyCo4Ge0.5Sb11.5 drastically decreases from 8 W/(m·K) (y=0) to 2.4 W/(m·K) (y=0.5) with increasing Yb composition. The marked reduction of the lattice thermal conductivity can be attributed to the increase in the filling fraction of Yb, whose localized thermal vibration, “rattling” motion, substantially contributes to the scattering of phonons. The influence of Ge substitution on the thermoelectric properties in YbyCo4Ge0.5Sb11.5 is also discussed.
  • Thermoelectric Properties of (Ti,Zr,Hf)CoSb Type Half-Heusler Compounds

    pp. 1481-1484

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    DOI:10.2320/matertrans.46.1481

    Half-Heusler compounds have a possibility as a new thermoelectric material due to the large thermoelectric power and low thermal conductivity derived from the band structure and voids in the crystal, respectively. Among these materials, we have paid attention to (Ti,Zr,Hf)CoSb system, and have investigated the improvement of the thermoelectric figure of merit from the measurements of the electrical resistivity, thermoelectric power, and thermal conductivity. We obtained the largest ZT=0.027 on TiCoSb at 921 K. From the analysis by Jonker plot and the difference of the atomic radii between titanium and cobalt on TiCoSb, it is indicated that the dispersion between our data and a few previous data was originated in two effects: one is deviations from the stoichiometric composition by evaporation of antimony on arc melting, and the other is relaxation of the structural disorder by annealing.
  • Effect of Cu Substitution on Thermoelectric Properties of Ge Clathrates

    pp. 1485-1489

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    DOI:10.2320/matertrans.46.1485

    We have prepared polycrystalline n-type Ba8CuxGayGe46−xy (x=0–5, y=16−3x) clathrate compounds by arc melting and spark plasma sintering techniques and investigated the effect of Cu substitution for Ge on their thermoelectric properties. The Hall carrier concentration for Cu-substituted compounds is almost constant at the order of 1020 cm−3, which is comparable to that for Ba8Ga16Ge30 stoichiometric compounds. The Seebeck coefficient for these compounds is comparable to that for n-Ba8GayGe46−y compounds. From the analysis of the properties, the effective mass of the conduction band is estimated to be about 1.4 m0, which is equivalent to or slightly smaller than that of n-Ba8GayGe46−y compounds. The Hall mobility increases as the Cu composition increases. Its temperature dependence obeys approximately T−1⁄2 dependence in the range of 80–300 K, indicating the dominance of the alloy disorder scattering. Two models are discussed to account for the reduction in the alloy disorder scattering by Cu substitution.
  • Solid-State Synthesis of Thermoelectric Materials in Mg–Si–Ge System

    pp. 1490-1496

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    DOI:10.2320/matertrans.46.1490

    Solid solution Mg2Si1−xGex for various concentration of germanium, x, is successfully prepared in single phase by the bulk mechanical alloying (BMA) and the hot pressing (HP). Both BMA and HP process conditions were optimized to yield high dense samples with fine, homogeneous microstructure. The electrical conductivity, the Seebeck coefficient and the thermal conductivity are measured from room temperature up to about 700 K. The Seebeck coefficient is much sensitive to the germanium content, x in Mg2Si1−xGex. The pn-transition takes place at x=0.35 where the Seebeck coefficient drastically changes its sign. The measured band gap of Mg2Si1−xGex decreases with x from 0.71 to 0.54 eV. The figure of merit at 613 K of Mg2Si0.6Ge0.4 reaches 0.34×10−3 K−1 in the case of BMA for N=600 and HP at 773 K by 1 GPa for 3.6 ks.
  • Thermoelectric Properties of p-Type Fe0.9Mn0.1Si2 with Rare-Earth Oxide Addition

    pp. 1497-1501

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    DOI:10.2320/matertrans.46.1497

    The effects of rare earth oxide dispersion on the thermoelectric properties of the Mn-doped p-type β-FeSi2 (Fe0.9Mn0.1Si2) were investigated. The Fe0.9Mn0.1Si2 powders were mechanically alloyed with Y2O3 powder (0.5–4 mass%) and subsequently hot pressed. The added Y2O3 was dispersed in the β phase matrix as a fine particles around 10 nm in size. The thermal conductivity of the sample was significantly reduced by Y2O3 addition, which was caused by enhancing phonon scattering due to fine Y2O3 dispersion. It was also found that the added Y2O3 was partially decomposed in the sample, resulted in solution of elemental Y in the β phase as a p-type dopant. The Seebeck coefficient was slightly improved when a small amount of Y2O3 (0.5 and 1 mass%) was added. The improvement of the Seebeck coefficient could not be explained only by the fine dispersion of Y2O3 and the Y doping as a p-type dopant. The slight increase in the Seebeck coefficient was also observed in the case of the samples with addition of small amounts of La2O3 powder.
  • Thermoelectric Properties of Thallium Compounds with Extremely Low Thermal Conductivity

    pp. 1502-1505

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    DOI:10.2320/matertrans.46.1502

    Polycrystalline samples of thallium compounds, Tl9BiTe6, TlBiTe2, TlSbTe2, and AgTlTe were prepared and the thermoelectric properties such as the electrical resistivity, Seebeck coefficient, and thermal conductivity were measured. The Seebeck coefficients of Tl9BiTe6, TlSbTe2, and AgTlTe are positive, while that of TlBiTe2 is negative. The thermal conductivities of these thallium compounds are very low compared with state-of-the-art thermoelectric materials. Especially, AgTlTe indicates extremely low value, 0.25 Wm−1K−1 at room temperature. The dimensionless figure of merit ZT of thallium compounds are relatively high due to their very low thermal conductivities. The maximum value of ZT is obtained for TlSbTe2 as 0.87 at 715 K.
  • Experimental and Theoretical Evaluation on Thermoelectricity for SPS-Joined p-n Module in Bi–Te System

    pp. 1506-1513

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    DOI:10.2320/matertrans.46.1506

    Thermoelectric p-n modules are prepared by the spark plasma sintering (SPS) solid bonding for experimental and theoretical evaluation on their thermoelectricity. Both p-type (Bi0.4Sb1.6Te3) and n-type (Bi2Te2.85Se0.15) materials are prealloyed from elemental granule mixture via the bulk mechanical alloying, shear-extruded to control their anisotropic texture and joined to fabricate p-n modules. The mutual atomic diffusion layer across the p-n interface is controlled down to 2 μm, 0.04 times narrower than that for hot-pressed p-n interface. Open-circuit voltage and resistance of p-n modules are measured for various interface layer height. They are compared with theoretical estimates via the computer-aided analysis. Analytical expressions are proposed to estimate the thermoelectric characteristics on p-n module. The power generation characteristics of p-n modules is also evaluated for various temperature differences between cold and hot sources.
  • Balancing of Mechanical Properties of Ti–4.5Fe–7.2Cr–3.0Al Using Thermomechanical Processing and Rapid Heat Treatment

    pp. 1515-1524

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    DOI:10.2320/matertrans.46.1515

    Effects of new thermomechanical treatment, which includes consecutive solid solution, cold deformation and rapid recrystallization (SSCDRR), and final aging on microstructure and mechanical properties of the Ti–4.5Fe–7.2Cr–3.0Al alloy was investigated employing optical and electron transmission microscopy, tensile and fatigue testing. Beta grain size fell below 100 μm by hot deformation at a temperature within the two-phase α+β field and subsequent rapid heating up to 1123 K at 20 Ks−1. Further refinement of β grain microstructure up to average grain size of about 7 μm become possible by cold deformation and rapid heating up to 1013–1043 K at 20 Ks−1 or 1023–1063 K at 50 Ks−1. Tensile strength of the fine β-grain specimens increased by aging, up to 1840–1412 MPa while ductility can be varied within rather wide range by changing β-grain size as a result of controlled SSCDRR. Thus, the desired balance between strength and ductility may be achieved by optimizing treatment parameters.
  • Use of a Naphthalene-Based Binder in Injection Molding Net-Shape Titanium Components of Controlled Porosity

    pp. 1525-1531

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    DOI:10.2320/matertrans.46.1525

    We have recently developed a naphthalene-based binder system for use in powder injection molding (PIM) of ceramic and metallic materials. The use of a binder that can be removed via sublimation offers several unique advantages relative to the typical thermoplastic and/or thermoset binders employed in PIM. One of these is that essentially no volume change takes place during debindering. This offers a relatively facile method of introducing porosity into a net-shape part of potentially complex geometry. In the study described in this paper, the effects of powder loading and subsequent isostatic compaction on the size and amount of porosity in the components produced by this technique were investigated. In general, it was found that the amount of porosity is inversely proportional to the initial concentration of metal powder in the PIM feedstock. Likewise, average pore size displays a similar relationship with powder loading.
  • Development of New Ti–Fe–Ta and Ti–Fe–Ta–Zr System Alloys for Biomedical Applications [Retracted]

    pp. 1532-1539

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    DOI:10.2320/matertrans.46.1532

  • Effect of Microstructure on Tensile Properties and Static Fracture Toughness of Dental Gold Alloy

    pp. 1540-1544

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    DOI:10.2320/matertrans.46.1540

    Tensile tests and static fracture toughness tests were conducted on dental type 4 gold alloys subjected to various heat treatments. The effects of microstructures on tensile characteristics and static fracture toughness are discussed.
    The tensile strength of dental type 4 gold alloy increases with the solutionizing temperature. Moreover, the tensile strength of dental type 4 gold alloy increases with aging time at a solutionizing temperature of 1023 K. On the other hand, dental type 4 gold alloy exhibits reduced elongation with an increase in the solutionizing temperature.
    Static fracture toughness of dental type 4 gold alloy increases with an increase in the solutionizing temperature. Static fracture toughness of dental type 4 gold alloy aged for 0.3 ks is the highest, and is the lowest when it is aged for 1.8 ks, with the solutionizing temperature at 1023 K.
  • Mechanical Property, Fatigue Strength and Clinical Trial of Dental Cast Ti–15Zr–4Nb–4Ta Alloy

    pp. 1545-1550

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    DOI:10.2320/matertrans.46.1545

    The mechanical properties and fatigue strength of Ti–15Zr–4Nb–4Ta castings were compared with those of Co–Cr–Mo and Ti–6Al–7Nb castings, which have been clinically used in Japan. The mechanical properties of buffed and chemically polished dental castings were almost the same. The 0.2% proof strength (σ0.2%PS), ultimate tensile strength (σUTS) and total elongation (TE) of the buffed Ti–15Zr–4Nb–4Ta castings were 832±41 MPa, 964±69 MPa and 7±3%, respectively. The σ0.2%PS, σUTS and TE of the buffed Ti–6Al–7Nb castings were 873±30 MPa, 982±27 MPa and 11±4%, respectively. The σ0.2%PS, σUTS and TE of the buffed Co–Cr–Mo castings were 589±23 MPa, 773±19 MPa and 10±2%, respectively. The fatigue strength of the Ti alloy castings at 1×107 cycles was lower than that of the Co–Cr–Mo castings. The fatigue strengths of the Ti–Al–7Nb and Ti–15Zr–4Ta–4Nb castings at 1×107 cycles were approximately 100 and 80 MPa, respectively. Clinical trials were carried out for complete and partial dentures made of the Ti–15Zr–4Nb–4Ta alloy. Clinical observation was conducted over a one year period for patients wearing complete or partial dentures. During the clinical observation, all five patients felt comfortable with the dentures, and fracture of the clasp was not observed.
  • Bending Properties of Co–Ni–Cr–Mo Alloy Wire for Orthodontic Application

    pp. 1551-1554

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    DOI:10.2320/matertrans.46.1551

    In order to evaluate the clinical performance of the Co–Ni–Cr–Mo alloy wire in orthodontic application, bending properties of Co–Ni–Cr–Mo alloy wire was investigated in comparison with the conventional stainless steel wire and Co–Cr alloy wire. Three-point bending test was carried out for the wires with varied drawing rate up to 3.0 mm in deflection and then unloaded with 0.2 mm/s of loading/unloading speed. Bending yield load of the Co–Ni–Cr–Mo alloy wire increased and the residual deflection decreased with increasing wiredrawing rate. The best processing condition was decided as the wiredrawing rate of 78% with the age-hardening treatment. The bending elastic modulus of the Co–Ni–Cr–Mo alloy wire was higher than those of stainless steel wire and Co–Cr alloy wire. The bending strength of the Co–Ni–Cr–Mo alloy wire was lower than that of stainless steel wire and was comparable to that of Co–Cr alloy wire.
  • Fatigue Property of Super-Elastic Ti–Ni Alloy Dental Castings

    pp. 1555-1563

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    DOI:10.2320/matertrans.46.1555

    Ti–Ni alloy is a promising material in the medical and dental fields due to its special mechanical properties, especially super-elasticity. Since dental prostheses are generally used under repetitive stress condition, fatigue properties of Ti–Ni alloy castings were investigated in this study. Ti–50.85Ni (mol%) alloy ingots were used for casting, which exhibited super-elasticity at 310 K in tensile test. Specimens were prepared with a centrifugal casting machine and a magnesia-based mold material. Fatigue test was performed at 310 K under repetitive loading condition with sine-waved load. The minimum stress was set at 0 MPa to evaluate the fatigue properties and change in residual strain. The maximum stress was set in the appropriate range considering the tensile property. Ultimate tensile strength and elongation to fracture of Ti–Ni alloy castings were 732 MPa and 10.6%, respectively, which were between those of CP-Ti and Ti–6Al–4V alloy castings. The fatigue limit of Ti–Ni alloy casting (206 MPa) was equivalent to or higher than that of CP-Ti or Ti–6Al–4V alloy. There was linear correlation between the fatigue ratios to ultimate tensile strength and the elongation to fracture for Ti–Ni alloy, CP-Ti and Ti–6Al–4V alloy castings, while Ti–Ni alloy showed high fatigue ratio to proof stress, which appears to relate to the twin deformation by stress-induced martensitic transformation. The stress-strain properties of Ti–Ni alloy castings were evaluated to be stable, and it is possible to utilize the super-elasticity in cast dental prostheses.
  • Mechanical Properties of Biocompatible Beta-Type Titanium Alloy Coated with Calcium Phosphate Invert Glass-Ceramic Layer

    pp. 1564-1569

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    DOI:10.2320/matertrans.46.1564

    The presence of calcium phosphate invert glass-ceramic (designated as CPIG) layer on the surface of artificial implant products can improve the bonding between these products and bones. In this study, the morphology of the CPIG layer on the surface of a β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), was investigated for biomaterial applications by a dip-coating treatment. Furthermore, the mechanical properties of TNTZ coated with the CPIG layer were also investigated.
    In the CPIG layer, a compositionally gradient zone with a thickness of approximately 2.0 μm exists on the surface of the TNTZ. The titanium concentration in the zone increases with the decreasing distance from the CPIG surface toward the base materials. On the other hand, calcium and phosphorus concentrations in the zone increase with the distance from the TNTZ surface. The tensile bonding strength between TNTZ and the CPIG layer is 25 MPa and that between aged TNTZ and the CPIG layer is 18.6 MPa.
    For easily understanding the change in mechanical properties by a dip-coating treatment, the values of those on TNTZ and TNTZ coated with CPIG layer were shown as follows. The tensile strength increases remarkably by a dip-coating treatment as compared with that of as-solutionized TNTZ while the elongation is a reverse trend. Young’s modulus of TNTZ and aged TNTZ coated with the CPIG increases by 15 to 27 GPa after the dip-coating treatment as compared with that of as-solutionized TNTZ (approximately 60 GPa). The fatigue limit of TNTZ coated with the CPIG layer is nearly equal to that (approximately 300 MPa) of as-solutionized TNTZ. On the other hand, the fatigue limit of aged TNTZ coated with the CPIG layer is a 100 MPa higher than that of as-solutionized TNTZ.
  • Fatigue Characteristics of Low Cost β Titanium Alloys for Healthcare and Medical Applications

    pp. 1570-1577

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    DOI:10.2320/matertrans.46.1570

    Two new low cost β titanium alloys, Ti–4.3Fe–7.1Cr (TFC alloy) and Ti–4.3Fe–7.1Cr–3.0Al (TFCA alloy) for healthcare and medical applications have been recently developed. As for such applications, the alloys are necessary to have high fatigue performance. The aim of this study is, therefore, to investigate fatigue characteristics of the alloys subjected to solution treatment above β transus. Fatigue tests were carried out at a stress ratio, R, of 0.1 and a frequency of 10 Hz.
    Fatigue limit of the solution treated TFC alloy is higher than that of the solution treated TFCA alloy, but both are higher than that of the existing biometallic materials. Fatigue strength of the TFC alloy is almost independent of solution treatment temperature, while, fatigue strength of the TFCA alloy strongly depends on solution treatment temperature, especially, in the low cycle fatigue life (LCF) region. The fatigue ratio and biofunctionality of these new alloys are much higher than those of the existing biometallic materials. In general, a crack initiates from the surface in the LCF region and from subsurface (internal) in the high cycle fatigue life (HCF) region for the TFC alloy, while, in the case of the TFCA alloy, a crack tends to initiate from the subsurface in both LCF and HCF regions. The internal crack initiation sites are found to be the area with low β phase stability in the LCF region and at the area with high stability of β phase in the HCF region. The relatively low fatigue strength of TFCA alloy is associated with the addition of Al that leads to precipitate α phase in which both crack initiation and facet formation are easier to occur.
  • Dry Friction and Wear Behavior of Forged Co–29Cr–6Mo Alloy without Ni and C Additions for Implant Applications

    pp. 1578-1587

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    DOI:10.2320/matertrans.46.1578

    A dry wear behavior of a forged Co–Cr–Mo alloy without Ni and C additions have been investigated using a ball-on-disc type wear testing machine with an alumina ball in ambient air. The wear factor of the Co–Cr–Mo forged alloy without Ni and C additions (hereafter, designated the forged alloy) shows negative contact load dependence. The coefficient of friction decreases with increasing contact load. Worn surfaces are hardened during the wear tests, forming oxide films. This results from significantly high work hardening rate of the forged alloy, caused by the strain-induced martensitic transformation from an fcc-γ phase to an hcp-ε phase, which contributes to the improvement in the dry wear resistance.
    Wear mechanisms of the forged alloy are discussed on the basis of Hertzian contact theory and observations of the wear scars formed on the alloy disc and the alumina ball surfaces. It is considered that the dominant wear mechanism of the forged alloy is the mild adhesive wear, though the extrinsic abrasive wear mediated by the wear debris, i.e., third-body abrasive wear, is exerted as an extrinsic wear mechanism. In addition, it is suggested that a delamination wear resulting from the fatigue fracture likely occurs under the present dry wear condition.
  • Friction-Wear Properties of Nickel-Free Co–Cr–Mo Alloy in a Simulated Body Fluid

    pp. 1588-1592

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    DOI:10.2320/matertrans.46.1588

    Friction-wear properties of a Co–29 mass%Cr–6 mass%Mo alloy (ASTM F799-95) but reducing the amount of nickel were evaluated with friction-wear test using a pin-on-flat type reciprocating friction tester in air and phosphate buffered saline, PBS(−), as a quasi-biological environment under applied stress of 1.0, 3.5 and 5.0 MPa to understand the performance of this alloy for metal-on-metal type artificial hip joints. In addition, metal ions dissolved in PBS(−) after the test was quantified. As a result, wear loss in PBS(−) is much smaller than that in air and increases with the increase of applied stress in both air and PBS(−), while the coefficient of friction in steady state during the test is larger in PBS(−) than in air, according to lubrication behavior of wear debris and PBS(−). Wear damage in PBS(−) is smaller than that in air, however more small scale of irregularity is observed in PBS(−) than that in air. Nickel and molybdenum are preferentially dissolved during the test.
  • Friction-Wear Properties of Nitrogen-Ion-Implanted Nickel-Free Co–Cr–Mo Alloy

    pp. 1593-1596

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    DOI:10.2320/matertrans.46.1593

    Nitrogen ions were implanted in a Co–29 mass%Cr–6 mass%Mo alloy (ASTM F799-95) with reducing the amount of nickel in order to improve the friction-wear properties. The friction-wear properties of unimplanted and nitrogen-ion-implanted Co–Cr–Mo alloys were evaluated using a pin-on-flat-type reciprocating friction tester in air and phosphate-buffered saline, PBS(−), as a quasi-biological environment under applied stress of 3.54 MPa to understand the performance of this alloy for metal-on-metal-type artificial hip joints. As a result, the wear loss in PBS(−) was much smaller than that in air and increased with the increase of applied stress in both air and PBS(−), while the friction coefficient in a steady state during the test was larger in PBS(−) than in air, according to the lubrication behaviors of wear debris and PBS(−). Nitrogen-ion implantation is effective to decrease the friction coefficient in PBS(−) at the sliding interface between mutual Co–Cr–Mo alloys as well as to decrease the wear debris in PBS(−). Both in air and PBS(−), the surface of a N2+-implanted flat specimen was smoother than that of an unimplanted flat specimen. Cobalt phosphate was precipitated as a corrosion product on the pin during the friction-wear test.
  • Anisotropy and Temperature Dependence of Young’s Modulus in Textured TiNbAl Biomedical Shape Memory Alloy

    pp. 1597-1603

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    DOI:10.2320/matertrans.46.1597

    Anisotropy and temperature dependence upon the Young’s Modulus of Ti–24 mol %Nb–3 mol %Al (TiNbAl), a new biomedical shape memory alloy, were characterized in the temperature range from 133 to 413 K by dynamic mechanical analysis in the tensile mode. The material consisted of β-phase (the parent phase, bcc) at room temperature and a well developed {112}⟨110⟩ type recrystallization texture was formed by a severe cold-rolling followed by a recrystallization heat-treatment. Test specimens were prepared from the textured material with the longitudinal direction of specimens being systematically varied within the ND-plane. Young’s modulus was measured as a function of temperature along each loading direction. A large depression in Young’s modulus was observed around β-α″ martensitic transformation temperature, below room temperature. The Young’s moduli of the textured material exhibited anisotropy depending on the loading direction. Compliance anisotropy factor, J, and characteristic modulus S11 of the β-phase were calculated from the obtained results based upon the assumption that the texture was perfectly developed in the material. It was found that the Young’s modulus of the β-phase reaches a minimum value along ⟨001⟩ and a maximum value along ⟨111⟩ in the measured temperature range. A suitable texture to increase the total recovery strain in superelasticity and anisotropy of Young’s modulus were discussed based on the obtained results.
  • The Influence of Aluminum Content on Shape Memory Effect of Ti–7Cr–Al Alloys Fabricated Using Low Grade Sponge Titanium

    pp. 1604-1609

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    DOI:10.2320/matertrans.46.1604

    In this study, the influence of aluminum content on shape memory effect of Ti–7Cr–Al alloys fabricated using low-grade sponge titanium was investigated by measurement of electrical resistivity and Vickers hardness, along with shape-recovery testing. The results obtained are as follows.
    In the STQed state, the phase constitution of non-Al added alloy, Ti–7Cr–0Al alloy, was found to consist of retained β phase and athermal ω, whereas those of Al added alloys, Ti–7Cr–1.5Al, 3.0Al and 4.5Al alloys, were found to consist of orthorhombic martensite, α″, and retained β phase. Resistivity (ρ) at liquid nitrogen (LN) and room temperature (RT) increased monotonously with Al content. Resistivity ratio (ρLN⁄ρRT) increased drastically at 3Al, exceeding unity.
    Shape recovery was exhibited in the 1.5Al, 3.0Al, and 4.5Al alloys having been fabricated using low-grade sponge titanium as raw material. In the 3.0Al and 4.5Al alloys, shape recovery ratio was about 90% at temperatures above 523 K and recovery surface strain was at least 0.03. The resistivity change indicates that stress-induced orthorhombic martensite was produced during bending of the 4.5Al alloy.
  • Osteocompatibility of Stainless Steel, Co–Cr–Mo, Ti–6Al–4V and Ti–15Zr–4Nb–4Ta Alloy Implants in Rat Bone Tissue

    pp. 1610-1617

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    DOI:10.2320/matertrans.46.1610

    To examine the formation of a new bone using various metal implants, 316L stainless steel, Co–Cr–Mo casting alloy, and Ti–6Al–4V and Ti–15Zr–4Nb–4Ta alloys were implanted into the rat femur and tibia for up to 48 weeks. Morphometrical parameters, namely, new bone formation rate, bone contact rate, new bone thickness and osteoid formation rate were investigated. Although a thin osteoid layer in a new bone-metal interface was observed in all the alloy implants, a new bone was well formed around all the alloy implants in the bone marrow of the rat femur and tibia up to 48 weeks. Neither the resorption of bone nor inflammatory reactions such as the presence of foreign-body giant cells and infiltration of inflammatory cells were also evident in the histological examination of these implants. A normal bone remodeling was observed in the new bone-metal implant interface, and osteoblasts capable of differentiating into a new bone tissue were lined on the implant side in the new bone-metal implant interface. Many osteocytes were observed in the lamellar bone tissue. The new bone formed around all the alloy implants developed into a calcified bone consisting of lamellar structure with increasing implantation period. A capsulated fibrous connective tissue was observed in the 316L stainless steel and Co–Cr–Mo alloy implants at 48 weeks after long-term implantation. Many osteoclasts were observed at the interface between the fibrous connective tissue and lamellar bone tissue. The bone formation rates around all the alloy implants were markedly high, approximately more than 90% at 4 weeks after implantation, and thereafter, no marked change was observed. The bone contact rate of Co–Cr–Mo alloy implant was slightly higher than that of 316L stainless steel implant. In the early stage of implantation (4–12 weeks), the bone contact rates of Ti alloy implants were significantly higher than that of Co–Cr–Mo alloy implant. In the late stage of implantation (24–48 weeks), the osteoid formation rates of Co–Cr–Mo and Ti–6Al–4V alloy implants tended to increase, but not significantly. Significant differences in the bone morphometrical parameters, suggesting osteocompatibility, were detected, although histological findings were not evident. Histological examinations of undecalcified sections were essential for confirming the interface between a newly formed bone and a metal implant, and morphometrical parameters, suggested to be good markers of osteocompatibility for the investigation of various metal implants.
  • Biocompatibility Evaluation of Ti–15Al–33Nb(at%) and Ti–21Al–29Nb(at%)

    pp. 1618-1626

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    DOI:10.2320/matertrans.46.1618

    In this work the biocompatibility of two vanadium-free Ti–Al–Nb alloys, Ti–15Al–33Nb and Ti–21Al–29Nb, was evaluated and compared to that for commercially pure titanium (CP Ti) and alumina (Al2O3). Fine particles were milled from sheet-processed material and implanted onto mice calvaria using an established animal model. Various stains, including methylene blue/acid fuchsin, TRAcP, and immunohistochemistry, were used on the particle-treated calvaria to measure the extent of bone deterioration of the calvaria, quantify the amount of osteoclasts, and approximate the presence of T-cells. In addition, reaction with particle-stimulated macrophages was observed and the production of the cytokine TNFα was recorded and quantified. The results indicated that the Ti–Al–Nb alloys statistically outperformed both CP Ti and Al2O3 in terms of their overall biocompatibility with respect to the experiments performed.
  • Surface Characterization and Anodic Polarization of Nitrogen-Ion-Implanted Nickel-Free Co–Cr–Mo Alloy

    pp. 1627-1632

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    DOI:10.2320/matertrans.46.1627

    Nitrogen ions were implanted in a nickel-free Co–Cr–Mo alloy in amounts of 1019, 1020, and 1021 ions m−2 with an acceleration energy of 150 keV and ion-beam current-density of 10−15 mA m−2 to improve the friction-wear properties. Changes in the composition of the surface layer of the alloy with ion implantation, autoclaving, and immersion in Hanks’ solution as a simulated body fluid were characterized using X-ray photoelectron spectroscopy to evaluate the stability of the material and predict the safety and tissue compatibility of the material. The surface oxide layer on the mechanically polished Co–Cr–Mo alloy consisted of oxidic species of cobalt, chromium, and molybdenum, and its thickness was about 2.5 nm. The surface film contained a large amount of OH, that is, the oxide was hydrated or oxyhydroxidized. After N2+ implantation, nitrogen atoms existed as cobalt nitride in the substrate just under the surface oxide and NH3 or NH4 in the surface oxide, and these amounts increased with the increase of the dose. Chromium was concentrated in the surface oxide but depleted in the substrate with ion implantation. Cobalt was preferentially oxidized by autoclaving and depleted in the substrate after autoclaving. Calcium phosphate was formed, and cobalt was preferentially dissolved during immersion in Hanks’ solution. N2+-implanted Co–Cr–Mo alloy with an amount of 1020 ions m−2 showed the highest corrosion resistance.
  • Hydroxyapatite Coatings on a 3D Porous Surface Using Thermal Substrate Method

    pp. 1633-1635

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    DOI:10.2320/matertrans.46.1633

    Hydroxyapatite (HAp) coated films were obtained using a thermal substrate method, whereby an aqueous solution at pH=7 or 8 containing Ca2+ and PO43− ions was used to deposit a coating on porous-surfaces substrates formed by sintering 44–150 μm-sized Ti6Al4V powders on a solid commercially pure titanium (cpTi) base. The HAp coating conditions used were: coating time = ∼900 s and substrate temperature equal to 373 or 393 K. Coatings formed in a pH=7 solution at 373 K for 900 s and in a pH=8 solution at 393 K for 300 s showed that all of the surfaces of the Ti6Al4V sintered particles (both front and back faces) and the base cpTi substrate were covered with HAp, and that they maintained their original open-pored geometry. The precipitated HAp appeared to be denser on porous-surfaced samples compared with plain-surfaced cpTi samples. Use of the thermal substrate method with appropriate pH control, and substrate heating temperature and time was effective for forming HAp coatings on powder-sintered samples with a complex topography.
  • Antibacterial Metals —A Viable Solution for Bacterial Attachment and Microbiologically Influenced Corrosion—

    pp. 1636-1645

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    DOI:10.2320/matertrans.46.1636

    Microbiologically Influenced Corrosion (MIC), otherwise coined as biocorrosion, is the influence of microorganisms on the kinetics of corrosion processes of metals, minerals and synthetic materials caused by their adhesion and growth. A closer observation of the MIC failure case analyses of engineering components showed that MIC occurs at or near welds. Preferential bacterial attack on the austenite phase leaving a skeleton like appearance is commonly reported on welds. The initial step of this phenomenon is the attachment of bacteria, which, over a period of time develop into a biofilm on the material surface. However, the intriguing question that remains to be answered is “Why welds are prone to preferential MIC attack?” Experiments on bacterial attachment on stainless steel surfaces revealed that surface roughness plays a pivotal role. Naturally, welds are with rough surfaces and that explains the preferential attachment of bacteria. Also, it was noticed that shape of the weld beads, determines the extent of bacterial attachment on to their surfaces. Leaving apart the surface roughness as the major contributing factor for the preferential bacterial attachment, studies were carried out to determine whether the underlying microstructure has any influence on it. Results suggested that there is. There was significant difference in percentage area of bacterial attachment between base metal and weld even after nullifying the surface roughness by polishing. Weld metal was preferred for attachment by bacteria more than base metal. Subsequent studies using an image superimposing technique revealed that grain boundary or the austenite/ferrite interface was preferred by bacteria as their initial attachment site. Welds have more such interfaces/or grain boundaries than base metal and thus resulting in more bacterial attachment, quickly leading to the initiation of MIC. The influence of inclusions, energy gradient and alloying elements are also discussed as factors associated with this phenomenon. In order to test the effect of elemental segregation occurring at grain boundaries on bacterial attachment, experiments were carried out using sulfur enriched stainless steel welds as well as high nitrogen stainless steels. Presence of sulfur and nitrogen as alloying elements enhanced bacterial attachment. Sulfur and nitrogen are essential elements for bacterial growth and their presence must have enhanced bacterial attachment. This result led us to the development of antibacterial metals. The hypothesis that worked out was if essential elements enhance attachment, toxic elements should deter it. Controlling bacterial attachment would be beneficial, both for deterring MIC and preventing infection and maintaining hygiene, especially in hospitals and food industries. Silver and copper, the well-known toxic elements were tried as alloying elements in stainless steel. While doing so, the material properties were kept largely in par with the silver/copper free stainless steel. The efficiencies of these antibacterial stainless steels were tested in the laboratory and were found to resist bacterial attachment and MIC. Silver containing stainless steels were tested in a freshwater environment as well. They were found to resist microfouling build up until a period of one month (the maximum duration of the study). Coupon exposure studies for longer duration are being carried out in our laboratory. In order to help in the development of high quality antibacterial metals, a base line data on the antibacterial efficacies of different candidate alloying elements are necessary. For this purpose, various metals were tested for their antibacterial efficacy using a standard method, known as film contact method as well as conventional coupon exposure tests. This chapter also discusses the merits and de-merits of antibacterial metals and their applications.
  • Ultra-Fine Grain Development in an AZ31 Magnesium Alloy during Multi-Directional Forging under Decreasing Temperature Conditions

    pp. 1646-1650

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    DOI:10.2320/matertrans.46.1646

    Grain refinement of a magnesium alloy, AZ31, was studied in multi-directional forging (MDF) with decreasing temperature from 623 to 423 K. The MDF was carried out up to cumulative strains of around 5 with changing the loading direction during decreasing temperature from pass to pass. The structural changes are characterized by the development of many mutually crossing kink bands accompanied by MDF at low strains, followed by full development of very fine grains at high strains. The dynamic changes in grain size evolved can be expressed by two different power law functions of flow stress for the regions of flow stress above or below around 100 MPa. The MDF under decreasing temperature condition can accelerate the uniform development of much finer grains and the improvement in plastic workability, leading to the minimal grain size of 0.36 μm at a final processing temperature of 423 K. The mechanism of grain refinement is discussed in detail.
  • Effect of Pressure Application by HIP on Microstructure Evolution during Diffusion Bonding

    pp. 1651-1655

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    DOI:10.2320/matertrans.46.1651

    The effect of pressure application by hot isostatic press (HIP) during diffusion bonding on microstructure evolution and bonding strength was studied using a couple of an Fe–Al alloy (Fe–Al) and CrMo steel (CrMo). Columnar microstructure evolution from the joint interface to the CrMo side is suppressed and aluminum diffusion from Fe–Al to CrMo is retarded with pressure application. Refined microstructure with fine precipitates is observed in the CrMo side beyond the columnar grains of the couple bonded with pressure. The application of pressure decreases the bonding strength and the strain to failure. It is concluded that the application of pressure provides microstructure refinement and strong hardening in the CrMo side of the couple, although it is not beneficial for bonding strength.
  • Effect of Precipitation of σ-Phase and N Addition on the Mechanical Properties in 25Cr–7Ni–4Mo–2W Super Duplex Stainless Steel

    pp. 1656-1662

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    DOI:10.2320/matertrans.46.1656

    This study was carried out to investigate the effects of precipitation of σ phase and N addition and the change of volume fraction on the mechanical properties in 25Cr–7Ni–4Mo–2W super duplex stainless steel. The results obtained from this study are as follows: With increasing the annealing temperature, the volume fraction of austenite increased while volume fraction of ferrite decreased. Volume fraction of austenite was found to be increased by N addition. Tensile strength decreased and elongation increased due to increasing the volume fraction of austenite by increasing annealing temperature. In the case of specimens with N addition, tensile strength and elongation showed high values. σ phase was formed at ferrite phase and interface of ferrite and austenite. More precipitation of σ phase was stimulated by N addition.
    With increasing volume fraction of precipitated σ phase, tensile strength was increased, while elongation and impact value decreased. In the case of σ phase precipitated specimen (with N addition), tensile strength, elongation, hardness and impact values showed higher values than those without N addition. It was also found that impact value rapidly decreases in early stage of aging.
  • Ductile-to-Brittle Transition Characteristics in W–Cu Composites with Increase of Cu Content

    pp. 1663-1670

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    DOI:10.2320/matertrans.46.1663

    A series of tungsten-copper composites containing copper of 19–80 vol% were subjected to three-point bend tests at temperatures between 77 and 363 K. Temperature dependences of the yield strengths and the maximum strengths were examined for each W–Cu composite. Then the effect of Cu content on the ductile-to-brittle transition behavior of the composite was investigated. The results are summarized as follows. First the composites containing copper of less than 40 vol% demonstrated ductile-to-brittle transition behavior and the transition temperature tended to decrease with the increase of Cu content. The composites containing copper of more than 60 vol%, in contrast, demonstrated no distinctive transition. Secondly production method leading to the microstructure had a significant effect on the maximum strength and consequently on the ductility, though it had almost no effect on the yield strength.
  • Effect of Spray Condition and Heat Treatment on the Structure and Adhesive Wear Properties of WC Cermet Coatings

    pp. 1671-1676

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    DOI:10.2320/matertrans.46.1671

    An improved HVOF spray process called “Gas-shrouded HVOF” (GS-HVOF) has been developed over the past several years. By using an extension nozzle at the exit of a commercial HVOF spray gun, GS-HVOF is capable of controlling the oxidation of sprayed materials during flight as well as achieving higher velocity of sprayed particles. These features result in extremely dense and clean microstructure of the sprayed coatings. The process has been successfully applied to corrosion resistant alloys such as SUS316L, HastelloyC, and alloy 625 as well as cermets such as WC-Cr3C2-Ni. Wear properties of WC cermet coatings were measured by using a pin-on-disk wear tester. The specific wear rates of the coatings prepared by the GS-HVOF with a reducing (fuel rich) flame were close to that of chrome plating. The wear amount of the heat-treated GS-HVOF coatings could not be detected after testing. It is believed that transition to mild wear appeared early because of the increased surface oxidation due to the heat treatment.
  • Compressive Deformation Behavior at Elevated Temperatures in a Closed-Cell Aluminum Foam

    pp. 1677-1680

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    DOI:10.2320/matertrans.46.1677

    Compressive tests at temperatures of 573–773 K with initial strain rates of 8.0×10−4–2.0×10−1 s−1 were carried out on a closed-cell aluminum foam and its bulk reference aluminum (a cell wall material of the aluminum foam). As a result, the stress exponent and the activation energy for elevated temperature deformation of the aluminum foam were in agreement with those of the bulk reference aluminum. In addition, upon compensation by the relative density, the plateau stress of the aluminum foam was comparable to the stress of the bulk reference aluminum. It is concluded that the elevated temperature deformation mechanism in the aluminum foam is essentially the same as that in the bulk reference aluminum.
  • Strengthening of Ti–6Al–4V Alloy by Short-Time Duplex Heat Treatment

    pp. 1681-1686

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    DOI:10.2320/matertrans.46.1681

    The effect of short-time duplex heat treatment on the microstructure and mechanical properties of Ti–6Al–4V alloy was investigated. This heat treatment consisted of solution treatment at 1203 K for 60 s and subsequent water-quenching plus aging at 753, 853 and 953 K for 40 s. The yield strength and tensile strength of the alloy were significantly increased by the above heat treatment and their maximum improvement rates reached about 25%. It was thought that this strengthening was caused by the formation of α′ martensite phase with quenching after the short-time solution treatment and the precipitation of fine α phase in the retained β phase during the short-time aging. In spite of the remarkable improvement in the strength, the ductility of the heat-treated materials remained above the level of the non-treated material, most likely because strain-induced martensite transformation occurred in β phase which was retained even after the short-time aging.
  • Electrical Resistance Change due to Hydrogenation of Pd and Pd–Ni Thin Films Immersed in Hydrogen-Dissolved Water

    pp. 1687-1691

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    DOI:10.2320/matertrans.46.1687

    The Pd and Pd–Ni thin films with an fcc structure were prepared by sputtering. The films were immersed in the pure water and the hydrogen-dissolved water alternatively and the electrical resistance of the films was measured during the immersion. The Pd and Pd–Ni thin films possess good sensitivity to hydrogen dissolved in water. The electrical resistance of the films increases in the hydrogen-dissolved water and decreases in the pure water with excellent reproducibility. The electrical resistance change of the Pd–Ni alloy films is smaller than that of the Pd films. Nickel addition improves the response of increase/decrease of the electrical resistance during the immersion in the pure water and the hydrogen-dissolved water. The detailed electrical behavior of the films is investigated in this study.
  • Glass Formation and Thermal Stability of Bulk Glassy Cu–Zr–Ti–Sn–Si Alloys

    pp. 1692-1694

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    DOI:10.2320/matertrans.46.1692

    The new Cu-based bulk glassy alloys in Cu–Zr–Ti–Sn–Si alloy system were formed by copper mold casting. The critical diameter for glass formation is 5 mm for Cu50Zr42.5Ti7.5, and increases to 6 mm for (Cu0.5Zr0.425Ti0.075)99Sn1 and 7 mm for (Cu0.5Zr0.425Ti0.075)98.8Sn0.6Si0.6. The minor addition of Sn or Sn and Si in Cu50Zr42.5Ti7.5 causes an increase in the supercooled liquid region from about 40 K to about 50 K, and in the reduced glass transition temperature from about 0.59 to about 0.60.
  • Fabrication of Nano-Sized Powders from Waste Solution by Spray Pyrolysis Process

    pp. 1695-1700

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    DOI:10.2320/matertrans.46.1695

    In order to efficiently recycle the Fe–Ni waste acid solution resulting from shadow mask processing, a spray pyrolysis process was used to fabricate the nano-sized Ni–ferrite powder with the average particle size below 100 nm. The properties of the nano-powder were investigated as function of reaction temperature, concentration and injection speed of raw material solution.
    As the reaction temperature increases from 800 to 1100°C, the average particle size of the powder increased accordingly, the microstructure of it gradually became solid which is close to the theoretical density, and the surface area of it decreased significantly. Along with the temperature rise, the formation rate of NiFe2O4 phase also increased.
    As the concentrations of iron and nickel elements in waste solution increased, the average particle size became larger, the particle size distribution became more irregular, the surface area of the powder decreased. Along with the increase of the concentration, the formation rate of NiFe2O4 phase increased significantly.
    As the air pressure increases up to 1 kg/cm2, the average particle size of the powder decreased slightly, yet the ratio of the Ni–ferrite phase kept almost unchanged. As the air pressure increases up to 3 kg/cm2, the average particle size and the ratio of the Ni–ferrite phase decreased significantly, yet the particle distribution size appears much more uniform.
  • Gamma-Radiation Effect on Morphology and Properties of TTCP/DCPA-Derived Calcium Phosphate Cement

    pp. 1701-1705

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    DOI:10.2320/matertrans.46.1701

    The purpose of the present study is to investigate the γ-ray effect on the structure and some critical properties, such as working/setting time and compressive strength, of a TTCP/DCPA-based CPC. Experimental results indicate that working/setting time, compressive strength, TTCP-HA conversion rate and morphology of the present CPC are all related to the dosage of γ-ray sterilization. The best γ-ray dosage appears to be 30 kGy which leads to slightly longer setting/working time, the highest TTCP-HA conversion rate and the highest compressive strength. With increasing γ-ray dosage, the morphology of CPC changed from sharp-edged petal-like morphology (non-sterilized and 10 kGy) to globular-like morphology (20 and 30 kGy) to dull-edged coralline-like morphology (40 and 80 kGy).
  • Development of Glassy Alloy Separators for a Proton Exchange Membrane Fuel Cell (PEMFC)

    pp. 1706-1710

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    DOI:10.2320/matertrans.46.1706

    The Ni60Nb15Ti15Zr10 glassy alloy was developed as a separator material for a proton exchange membrane fuel cell (PEMFC). The corrosion rate of the glassy alloy in sulfuric acid was approximately 3 digits lower than SUS316L. A precise groove forming of the glassy alloy can be achieved by hot-pressing in the supercooled liquid state. The result of the power generation test of the single cell assembled with the groove-formed glassy alloy sheets revealed that sufficient power was generated. Moreover, the deterioration of the morphology of the glassy separator could hardly be recognized even after the durability test for 350 h.
  • Strain Rate Sensitivity of Superplastic Inconel 718

    pp. 1711-1719

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    DOI:10.2320/matertrans.46.1711

    The strain rate sensitivity, m, of a superplastic-quality (SPF) INCONEL 718 alloy has been measured in the temperature and strain rate ranges of 925–1000°C and 10−4–10−2 s−1 using both the classical method of instantaneous strain rate changes and a new method based on the continuous response to a sinusoidal strain rate input. The novel method furnishes continuous information from the whole stress–strain curve on the dependence of m on strain rate transients.
    In agreement with other recent studies, our results show that the maximum m values of the 718 alloy, although interesting enough for industrial superplastic forming, are lower than those shown by other superplastic materials for typical aeronautical application. A texture analysis indicates that crystallographic slip does not merely act here as an accommodation mechanism for grain boundary sliding. It significantly contributes to the total plastic strain, being thus responsible for the relatively low values observed for the strain rate sensitivity m.
  • New Pd-Based Bulk Glassy Alloys with High Glass-Forming Ability and Large Supercooled Liquid Region

    pp. 1720-1724

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    DOI:10.2320/matertrans.46.1720

    With the aim of developing a new bulk glassy alloy which can be applied to biomedical applications, we examined glass-forming ability and mechanical properties of Ni-free glassy alloys in Pd50−xPtxCu30P20 system. As a result, the best glass-forming composition is located at Pd35Pt15Cu30P20, and the alloy can be formed into bulk glassy rods with diameters of up to at least 30 mm by fluxed water quenching. For the bulk glassy alloy, fracture strength, fracture elongation and Young’s modulus were measured to be 1590 MPa, 1.8% and 99.8 GPa, respectively, under a compressive stress and 1410 MPa, 1.7% and 83.0 GPa, respectively, under a tensile stress. These features of high glass-forming ability and good mechanical properties are expected to be used as biomedical materials.
  • Fracture Toughness of Zr55Al10Ni5Cu30 Bulk Metallic Glass by 3-Point Bend Testing

    pp. 1725-1732

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    DOI:10.2320/matertrans.46.1725

    In order to evaluate the fracture toughness of a Zr55Al10Ni5Cu30 bulk metallic glass and to identify possible sources associated with data variability of Zr-based metallic glasses, three-point bending (3PB) precracked and notched specimens with thicknesses of 2.0 to 2.9 mm were prepared. Miniaturized 34 specimens were subjected to plane strain fracture toughness tests at room temperature. The measured fracture toughness values are in a range of 35.9–76.2 MPam1⁄2 and 20 specimens satisfy the KIC criterion, the KIC being in a range of 35.9–50.3 MPam1⁄2 with an average of 43.3 MPam1⁄2. No appreciable difference in fracture toughness is observed between the precracked and notched specimens with root radii of 0.06 and 0.13 mm. Whereas the fracture toughness value varies significantly for each of the precracked and notched specimens. Fracture surfaces show not only a vein pattern typical of fully amorphous alloys but also a flower-like pattern which is less resistant to fracture. All specimens with the entire fracture surface of the vein pattern exhibit very high KQ values of 70.0–76.2 MPam1⁄2. The cause of large variability in the fracture toughness data including literature data is discussed.
  • Mechanical Properties and Electrical Conductivity of Heavily Cold-Rolled Cu100−xZrx Alloys (x=0–8)

    pp. 1733-1736

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    DOI:10.2320/matertrans.46.1733

    The mechanical properties and electrical conductivity of Cu100−xZrx (x=0–8 at%) alloys were examined, whereby the alloys were prepared by casting levitation-melted alloys into a pure copper die and then subsequently cold rolled to a thickness of 200 μm except for the alloys where x=7 and 8. The ultimate tensile strength (σUTS), 0.2% proof strength (σ0.2) and Vickers hardness (HV) of the prepared Cu100−xZrx alloys increase linearly with x, elongation εP is almost independent of x and the electric conductivity (%IACS) decreases when the Zr concentration x increases. The highest values of σUTS, σ0.2, εP and HV for the Cu100−xZrx alloys are 1200 MPa, 800 MPa, 3% and 290, respectively, at x=6 and its electrical conductivity is 35%IACS.
  • Grain Growth Mechanism of Cu Thin Films

    pp. 1737-1740

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    DOI:10.2320/matertrans.46.1737

    Since Cu was found to be attractive as interconnect materials for ultra-large scale integrated (ULSI) Si devices, the electrical properties of Cu films have been extensively studied to prepare low resistance films. It was found in our previous papers that reduction of the electrical resistance of the Cu films was achieved by increasing grain sizes of the Cu films and large-grained Cu films were essential for the low resistance Cu interconnects. The primary factor to increase the grain sizes was also found to be intrinsic and/or extrinsic strain (or stress) introduced into the films. The present paper addresses the driving force of the grain growth of the Cu thin films based on the strain energy criterion model.
  • Manufacture of Aluminum/Carbon Composites Based on Wood Templates

    pp. 1741-1744

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    DOI:10.2320/matertrans.46.1741

    Al/C composites, with microstructures controlled by the natural bio-structures (wood templates), were successfully fabricated by infiltrating the melted Al alloy into the carbon preform, which was pyrolyzed from the wood. The microstructures and the mechanical properties of the obtained composites were researched. The results indicated that the wood templates could have the vital influences on the microstructures of the Al/C composites. Moreover, the Al/C composites exhibited a higher strength than the carbon preform, and their mechanical properties were anisotropic.

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