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

MATERIALS TRANSACTIONS Vol. 56 (2015), No. 3

  • Formation of MgAl2O4 at Al/MgO Interface

    pp. 277-280

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    DOI:10.2320/matertrans.M2014345

    Undercooling and wetting angles of liquid aluminum solidified on single crystal MgO substrates, with specific orientations MgO(100), MgO(110) and MgO(111), are measured. The measured undercooling is observed to be less sensitive even though the lattice misfits provided by the substrates are significantly varied. Transmission electron microscopy analysis reveals formation of MgAl2O4 layer at Al/MgO interface. It has higher potency to act as nucleation substrate for Al and responsible for identical undercooling values for substrates with different lattice mismatch. The higher wetting angle for MgO(110) and MgO(111) surfaces with liquid Al is attributed to surface reaction at higher temperature.
  • On the Periodicity of ⟨001⟩ Symmetrical Tilt Grain Boundaries

    pp. 281-287

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    DOI:10.2320/matertrans.M2014394

    We report an application of the O-lattice theory to systematically analyse the structures of symmetrical tilt grain boundaries with the rotation axis of ⟨001⟩ and demonstrate a theoretical interpretation of the experimentally observed structures of a near Σ5 grain boundary in MgO in terms of the structural-units model and the periodicity of the O-points on the boundary. We further derive generalised decomposition formulae for the symmetrical tilt grain boundaries which are closely related to the distribution of irreducible rational numbers.
  • Improvement of Magnetic and Dielectric Properties of BaFeO3−δ Thin Films by Sn Substitution

    pp. 288-291

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    DOI:10.2320/matertrans.M2014402

    Magnetic and dielectric properties of Ba(Fe1−xSnx)O3−δ (x = 0.5–0.9) epitaxial thin films on (001) SrTiO3 single crystalline substrates have been significantly improved. All of the Ba(Fe1−xSnx)O3−δ (BFSO) thin films were ferromagnetic in nature, even at room temperature, regardless of the amount of Sn-substitution. For the x = 0.7 samples, the saturation magnetization had a maximum value of 0.224 μB/f.u. at 300 K. The ferromagnetic origin of BFSO was considered to be from 180° super-exchange coupling of Fe4+(d4)-O2−-Fe4+(d4). Electrical conduction of the x = 0.9 samples could be determined to be Poole-Frenkel type. In contrast, it was found that several electrical conduction mechanisms coexist for the x = 0.7 and x = 0.8 samples. The leakage current density of the x = 0.7 samples was about 1.04 × 10−4 A/cm2 at the positive bias electric field at 400 kV/cm. The dielectric constant and dielectric loss were 120 and 0.06 even at 1 MHz, respectively.
  • Electric and Magnetic Evolutions in Composite Assemblies of Fe and Si Nano-Particles

    pp. 292-296

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    DOI:10.2320/matertrans.M2014434

    Temperature (T)-dependence of electrical resistivity (ρ) and magnetization curves have been observed for Fe and Si nano-particle (NP) composite assemblies prepared using a double-source-plasma-gas-condensation cluster deposition system. With increasing T, ρ monotonically decreases for the Fe composition, cFe < 0.6, where the Si NP networks are predominant (a semiconductor type conduction), while it monotonically increases for cFe > 0.6, where the Fe NP networks are formed (a metallic conduction). With increasing cFe, saturation magnetization monotonically increases, while magnetic coercivity increases for cFe < 0.4 and gradually decreases for cFe > 0.6. In these Fe and Si NP composite assemblies, magnetic dipole interactions between Fe NPs are reinforced by reductions in inter-particle distances though they are averaged by random configurations of Fe and Si NPs, and random orientations of magnetic moments of Fe NPs. Magnetic exchange interactions are also induced but not much enhanced with cFe due to loose contacts between Fe NPs.
  • Precipitation Behavior and Properties of Cu-Ti Alloys with Added Nitrogen

    pp. 297-302

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    DOI:10.2320/matertrans.M2014216

    The effects of adding nitrogen (N) to age-hardenable Cu-Ti alloys on their microstructure, hardness, and conductivity have been investigated. It was found that the aging of Cu-Ti-(0.06–0.6) mol% N alloys resulted in the continuous formation of finely precipitated needle-shaped α-Cu4Ti grains and the discontinuous formation of coarse cellular components composed of a stable β-Cu4Ti and Cu solid solution at the grain boundaries, in a manner similar to that in the case of conventional Cu-Ti alloys without any N. Furthermore, a small amount of granular TiN particles was also formed in Cu-Ti-N alloys. The hardening behavior of Cu-Ti-N alloys was similar to that of Cu-Ti alloys without N. This similarity was attributed to the finely dispersed precipitation of α-Cu4Ti that was similar between Cu-Ti alloys with and without N. The electrical conductivity of Cu-Ti-N alloys increased more steeply than that of Cu-Ti alloys without N. This is because in the case of Cu-Ti-N alloys, the co-precipitation of α-Cu4Ti, β-Cu4Ti, and TiN efficiently reduced the Ti concentration in the matrix. Thus, the conductivity of peak-hardened Cu-Ti-N alloys can be improved by optimizing the N concentration and aging temperature.
  • Texture Evolution in Aluminum Sheet Subjected to Friction Roll Surface Processing and Subsequent Annealing

    pp. 303-312

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    DOI:10.2320/matertrans.L-M2014847

    Textural evolution in commercial purity aluminum sheet subjected to friction roll surface processing (FRSP) by six combinations of plane/direction and subsequent annealing has been investigated. The characteristic microstructure consisting of fine- and coarse-grained layers in order from the processed surface are formed in the FRSPed and annealed specimens. The shear texture component E {111}⟨110⟩ mainly evolves in the specimen subjected to FRSP and annealing, the fraction of which depends on FRSP plane and direction.
  • Preparation and Characterization of MoSi2/WSi2 Composites from MASHSed Powder

    pp. 313-316

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    DOI:10.2320/matertrans.M2014370

    MoSi2 based materials are considered to have potential for use in high temperature structural part. In this work, MoSi2/WSi2 composites have been successfully prepared by pressureless sintering from mechanically-assisted combustion synthesized powders. The size of green powders shows great impact on the properties of sintered samples. The sample obtained from smaller powders has finer microstructure, and its Vickers hardness, flexural strength and fracture toughness were as high as 10.78 GPa, 327.21 MPa and 7.32 MPa m1/2, respectively. The morphologies of the fractured surface of the composites revealed the mechanism to improve the mechanical properties of MoSi2 matrix. Moreover, this composite exhibits good oxidation resistance at low temperature. A continuous SiO2 layer was formed after exposure to air at 500°C for 120 hours, which could prevent further oxidation of the composite.
  • Differences in Wear Behaviors at Sliding Contacts for β-Type and (α + β)-Type Titanium Alloys in Ringer’s Solution and Air

    pp. 317-326

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    DOI:10.2320/matertrans.M2014365

    The wear behaviors of combinations comprised of a new titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ) and a conventional titanium alloy, Ti–6Al–4V extra-low interstitial (Ti64) were investigated using ball-on-disc type configuration in Ringer’s solution for metal-to-metal contacting biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy combined with energy-dispersive spectroscopy and an electron probe microanalysis. Moreover theses wear characteristics are compared to the results obtained from the wear tests in air. Volume loss of both the disc and ball primarily increases for the TNTZ disc/TNTZ ball combination in Ringer’s solution compared to that in air. This increase can be explained by the ejection of debris from the contact region induced by the presence of Ringer’s solution. Subsequently, this increases the number of areas with asperity junctions between the disc and ball, thereby leading to severe delamination wear. In contrast, the volume loss of both the disc and ball decrease for the Ti64 disc/Ti64 ball combination in Ringer’s solution compared to that in air. It is believed that the predominately abrasive wear associated with Ti64 is effectively suppressed by the use of Ringer’s solution.
  • Estimation of Stress Corrosion Cracking Initiation and Propagation in High-Pressure, High-Temperature Water Environment Utilizing Acoustic Emission

    pp. 327-332

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    DOI:10.2320/matertrans.M2014357

    The stress corrosion cracking (SCC) of type 304 stainless steel during a creviced bent beam (CBB) test in a high-temperature, high-pressure water environment was monitored by an optical fiber acoustic emission (AE) sensor. By examining the number and type of cracks formed by different durations of CBB testing an SCC initiation and propagation behavior model was developed. This model was then used to examine the AE event rate, which was found to agree well with the observed changes in the number and size of the cracks formed. Through analysis of the relationship between crack size and AE, the weaker AE signals were assumed to be produced by the initiation of small cracks, whereas the coalescence of cracks produces moderate and large AE signals. On the basis of these findings, it is concluded that the SCC propagation behavior can be reliably estimated from the event rate and amplitude of AE signals.
  • Carbide Spray Coating Influence on Wear Behavior of Carburized Steel against Two Counter-Rollers

    pp. 333-339

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    DOI:10.2320/matertrans.M2014230

    The wear behavior of carburized SNCM 220 steel subjected to cold treatment and carbide spray coating is investigated. WC/Co coatings in 15 ± 5 µm thickness were deposited on SNCM 220 specimens in a high velocity oxy-fuel (HVOF) process. Specimens were subjected to wear test under normal loads of 95.9 N at 180 rpm on a dry block-on-roller tester and to two different counter-roller materials with hardness values of 42 and 60 HRC. Wear test result after 12 h showed that the cumulative mass loss measurement of carburized SNCM 220 under 188 K subzero treatment was 15 mg, improved from 37 mg mass loss of SNCM 220 steel without cold treatment. In addition, the cumulative mass loss of carburized SNCM 220 specimens with sprayed carbide coating decreased from 37 mg to 4 mg. Moreover, wear tested specimens with HVOF coatings countered with 42 HRC rollers have resulted higher mass losses than those countered with 60 HRC rollers. Analysis of the wear microstructures has revealed the effects of the cold treatment and HVOF coatings. It has shown that 42 HRC counter roller induced plastic deformation on the specimen surface, which is detrimental to the specimen wear resistance. The compatibility of counter-roller and specimen hardness becomes the major factor to improve the wear of SNCM 220 steel.
  • Separation of Nickel and Cobalt Utilizing Selective Reduction of Nickel in Acidic Aqueous Solution

    pp. 340-347

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    DOI:10.2320/matertrans.M-M2014846

    With the aim of separating nickel (Ni) from cobalt (Co) in acidic aqueous solution, selective reduction of Ni was examined. Sodium hypophosphite (NaH2PO2) was selected as a reductant, and reacted with aqueous solution containing 0.1 mol L−1 nickel sulfate (NiSO4·6H2O) and 0∼0.05 mol L−1 cobalt sulfate (CoSO4·7H2O) for 3 hours at 90°C. As a result, Ni was selectively reduced and separated from Co in the acidic region (pH = 4.8). Differences in reduction rate between Ni and Co were discussed, and the influence of impurities on the reduction of Ni was also examined by adding copper (Cu), iron (Fe), and zinc (Zn) ions to the feed solution.
  • Fabrication of Three-Dimensional Titania Building Blocks on Glass Substrate from Mono-Dispersed Titanium Glycolate Spheres and Their Photocatalystic Properties

    pp. 348-352

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    DOI:10.2320/matertrans.M-M2014845

    Mono-dispersed titanium glycolate sphere powders were successfully synthesized through a homogeneous nucleation and growth process. The obtained titanium glycolate sphere powders showed a fine size distribution and shape. On calcination, the titanium glycolate spheres lost chemically bound organic compounds, and changed to anatase (500°C) and rutile (900°C) titania spheres. Titania films fabricated with the synthesized titanium glycolate spheres exhibited marked photocatalytic activity and effective reusability. The fabricated films were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric and differential thermal analyses.
  • H2 Oxidation Activity and Tolerance to CO Poisoning of the Electrochemically Reduced Pt Oxide Catalyst

    pp. 353-360

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    DOI:10.2320/matertrans.MBW201405

    In order to develop a novel anode catalyst for a PEFC, the Pt thin film and the Pt oxide thin film were produced by reactive sputtering, and the catalytic activity of the H2 oxidation in the presence of CO or the tolerance to the CO poisoning was evaluated by the anodic polarization in an H2-saturated H2SO4 solution or a (H2 + CO)-saturated one. The H2 oxidation activity of the Pt thin film remarkably deteriorated due to the CO poisoning. On the other hand, the electrochemical reduction produced a tolerance to the CO poisoning during the H2 oxidation of the Pt oxide thin film. For the Pt oxide thin film electrochemically reduced at −0.3 C, the H2 oxidation current in a (H2 + 100 ppm CO)-saturated solution remained at the same level as in the H2-saturated one. The CO stripping voltammetry also revealed that the CO coverage was only 0.15 for the electrochemically reduced Pt oxide thin film although the CO coverage on the Pt thin film was calculated to be 0.95. Therefore, the electrochemically reduced Pt oxide may be a promising anode catalyst of the PEFC having a tolerance to CO poisoning. Moreover, the XPS analysis showed that there was a distinct difference in the chemical bonding state between the Pt thin film and the electrochemically reduced Pt oxide thin film. That is, a large spectrum due to the Pt-O bond was detected for the electrochemically reduced Pt oxide thin film, while the spectrum scarcely appeared for the Pt thin film. These results suggested that the residual oxygen might improve the tolerance to the CO poisoning during the H2 oxidation of the electrochemically reduced Pt oxide thin film.
  • Sliding Wear Properties of Ti/TiC Surface Composite Layer Formed by Laser Alloying

    pp. 361-366

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    DOI:10.2320/matertrans.M2014330

    Titanium and its alloys have various excellent properties, such as good corrosion resistance and high specific strength. Yet the poor tribological properties of these materials have so far precluded their application to sliding parts under severe wear conditions.
    Laser alloying is an effective process for improving wear resistance. This study was conducted to investigate the wear properties of Ti/TiC surface composite layer formed by laser alloying process of CP-Ti using graphite powder. Wear testing of the composite layer was carried out using a ball-on-flat type reciprocating wear tester.
    A hardened steel ball for bearing use and an Al2O3 ball were used as counterface materials for the wear testing. The tests with the steel ball revealed preferential wearing of the hardened steel, with no observable scarring the Ti/TiC composite. In the tests with the Al2O3 ball, the wear scar on the Ti/TiC composite layer was deeper than the wear scar on a non-laser irradiated substrate.
  • Formation of Inter-Diffusion Layer between NiCrAlY Coating and Nb Substrate during Vacuum Heat-Treatment

    pp. 367-371

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    DOI:10.2320/matertrans.M2014350

    The formation of the inter-diffusion layer between NiCrAlY coating and Nb substrate during vacuum heat treatment was investigated. A NiCrAlY coating was applied on Nb substrate by cathode arc deposition. Vacuum heat treatments were carried out at 800, 900, and 1000°C for 2 h. SEM, EPMA, EDS, and XRD were performed to analyze the microstructure of the inter-diffusion layer and the results were interpreted using the 1002°C isothermal ternary Nb-Ni-Cr phase diagram. It was found that at 800°C the inter-diffusion layer has a single NbNi3 layer; at 900°C the inter-diffusion layer consists of an outer NbNi3 layer, a thin intermediate NbCr2(HT) layer, and an inner Nb7Ni6 layer; at 1000°C the inter-diffusion layer has three well-developed layers of an outer NbNi3 layer, an inner Nb7Ni6 layer, and an intermediate layers comprising NbCr2(HT) and NbNi3. A small amount of Cr exists in both the NbNi3 and the Nb7Ni6 phases as solid solution, and a large amount of Ni in the NbCr2(HT) phase as solid solution.
  • Production of Nanocrystalline (Fe, Co)-Si-B-P-Cu Alloy with Excellent Soft Magnetic Properties for Commercial Applications

    pp. 372-376

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    DOI:10.2320/matertrans.MBW201402

    With the aim of applying to a magnetic core material, the effect of ribbon thickness on the magnetic properties of a (Fe, Co)-Si-B-P-Cu alloy ribbon was investigated. It is found that the Si addition in (Fe, Co)-Si-B-P-Cu nanocrystalline alloy increased the saturation magnetic flux density (Bs), but degraded the coercivity (Hc), suggesting that the Si addition should be suppressed to a little amount. It is also found that the replacement of Fe with Co is quite effective for obtaining better magnetic properties of Fe-Si-B-P-Cu alloy. Even for the thicker ribbons exceeding 30 µm in thickness, the nanocrystalline Fe81.2Co4Si0.5B9.5P4Cu0.8 alloy exhibited low Hc of 7 A/m and high Bs of 1.84 T. Such excellent magnetic properties were successfully reproduced in 50 mm wide ribbons. This regards that the nanocrystallized Co-containing alloy has high applicability to high-efficiency magnetic core material.
  • Photoassisted Electrodeposition of a Copper(I) Oxide Film

    pp. 377-380

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    DOI:10.2320/matertrans.M2014391

    Photoassisted electrodeposition of a cuprous oxide (Cu2O) thin film was studied to find the optimum conditions lowering the deposition temperature. Cu2O films were electrochemically deposited on FTO by cycling the electrode potential between 0.0 V and −0.8 V (Ag|AgCl), in an aqueous solution. A simple deposition cell was designed to allow simultaneous thermostating and polychromic illumination. Under illumination, the Cu2O film deposition occurred, even at a temperature lower than the temperature observed under dark conditions. X-ray diffraction (XRD) analysis confirmed that these films were indexed as cubic symmetric structured pure Cu2O (JCPDS: 05-0667), and UV-visible absorption spectra show an optical band-gap energy of 2.5 eV.
  • Effects of Heterogeneous Cracking of Superconducting Layer on Voltage-Current Curve, Critical Current, and n-Value in High-Temperature Superconducting Layer-Coated Conductor Tape

    pp. 381-388

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    DOI:10.2320/matertrans.MBW201401

    When high-temperature superconducting layer-coated conductors are exposed to high electromagnetic and/or mechanical stress and strain, the superconducting layer is damaged mainly by cracking. As cracking occurs heterogeneously, the critical current and n-value of a test specimen, which is composed of a series circuit of local sections, are dependent on the extent of cracking in local sections. In this work, the correlations of the extent of cracking in local sections with the critical current and n-value of the specimen were studied by modeling analysis. When one section is cracked, the critical current and n-value of the specimen decrease with increasing crack size. When multiple sections are cracked, the properties depend on the difference in crack size among the sections. When the crack size of the sections is similar, the critical current of the specimen decreases and the n-value increases as the number of cracked sections increases. This is caused by the increased voltage and the decreased shunting current at cracks. When there are large differences in the crack sizes of the sections, the section with the largest crack controls the voltage-current behavior of the specimen and determines the reduction in the critical current and n-value. For a given size of the largest crack, the critical current of the specimen is slightly higher and the n-value is lower when there is an intermediate difference in crack size among the sections than when there is a small difference in crack size, and the critical current is lower and the n-value is higher when there is an intermediate difference in crack size than when there is a large difference in crack size.
  • Effect of Hybrid Surface Treatments on Fretting Fatigue Strength of Stainless Steel

    pp. 389-397

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    DOI:10.2320/matertrans.M2014358

    This study was conducted to investigate the effect of hybrid surface treatments on the fretting fatigue strength of austenitic stainless steel JIS SUS316. The hybrid surface treatments were composed of plasma nitriding (hereafter, PN) and fine particle bombarding (FPB) or PN and diamond-like carbon (DLC) coating. Although the combination of PN and FPB slightly increased the friction coefficient, it improved wear resistance through the formation of a hardened layer. The combination of PN and DLC coating markedly improved the friction-wear properties because the thin DLC layer was supported by the hardened layer formed below it. Neither treatment had any influence on mechanical properties. The above hybrid surface treatments greatly improved the fretting fatigue strength. The improvement percentage was 44% in the case of the combination of PN and FPB, and reached 54% with the combination of PN and DLC coating. To examine corrosion resistance, the hybrid-surface-treated materials were fully immersed into 5% salt water held at 363 K (90 degrees C). The results showed that their corrosion resistance was maintained for 2.42 Ms (28 days) without surface damage.
  • Evaluation of Corrosion Critical Variables of 304 Stainless Steel by Delay Time of Acoustic Emission

    pp. 398-403

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    DOI:10.2320/matertrans.M2014389

    In this work, a new experimental setup for acoustic emission (AE) monitoring was designed to study the process of pitting corrosion of 304 stainless steel. Two AE sensors were employed in the present setup to investigate the AE behaviors of the pitting process in the working electrode and the hydrogen bubbles on the counter electrode separately and simultaneously. The AE signals from hydrogen bubbles on the counter electrode started to be detected with a delay time (defined as Δt1) after the pitting potential was reached. Then the AE signals from the pitting process were detected after another delay time (defined as Δt2). The parameters of Δt1 and Δt2 generally decreased with the increase in sodium chloride concentration. Another parameter, Δt3, was defined as the time difference between the first detections of the AE signals from hydrogen bubbles on the counter electrode and the pitting process on the working electrode. The AE signal-derived parameter, Δt3, decreased linearly with the increasing concentration of sodium chloride. Furthermore, the value of Δt3 was directly proportional to open circuit potential (EOC) and pitting potential (EP) of 304 stainless steel, respectively. These correlations imply that the more easily pitting corrosion occurs, the lower the value of Δt3 would be and vice versa. The AE-derived time-delay parameter reflecting the pitting corrosion process can offer an alternative idea for evaluation of the corrosion critical variables and the pitting corrosion resistance.
  • Effect of Annealing Temperature on Microstructure and Superelastic Properties of Ti-Au-Cr-Zr Alloy

    pp. 404-409

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    DOI:10.2320/matertrans.M2014439

    Effect of annealing temperature on microstructure and superelasticity of Ti-4Au-5Cr-8Zr (mol%) was investigated. Only β phase was observed in the specimen annealed at 1173 K, whereas the precipitation of Ti3Au, Zr33Ti40Au27 (Laves phase) and α phase occurred in the specimens annealed below 1073 K. Superelasticity was clearly observed in the specimens annealed at 1073 K and 1173 K, though it was absent in the specimens annealed at 873 K and 973 K. The maximum superelastic recovery strain was increased by the precipitation of Ti3Au in the specimen annealed at 1073 K. This is due to the increase in the critical stress for slip by the precipitation strengthening effect of Ti3Au.
  • Ammonia Synthesis via Non-Equilibrium Reaction of Lithium Nitride in Hydrogen Flow Condition

    pp. 410-414

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    DOI:10.2320/matertrans.M2014382

    Lithium nitride Li3N is hydrogenated below 300°C under 0.5 MPa of H2, and then LiNH2 and LiH are formed as products. Furthermore, the reaction between LiNH2 and H2 proceeds below 250°C under 0.5 MPa of H2 flow condition, which forms NH3 and LiH. In this study, we proposed and investigated another synthesis method of ammonia by combining these two reactions, which proceed in laboratory-scale under more moderate conditions than those of Haber–Bosch process. As a result, it was experimentally clarified that the ammonia synthesis were able to be operated below 300°C with realistic reactions rate by non-equilibrium reaction field under 0.5 MPa H2 flow condition, where a gas circuit system and a larger scale NH3 synthesis system were designed and assembled for the experiments.
  • Site Preference and Stabilization of Antiferromagnetism in M-Substituted Mn2−xMxSb (M = Ti, Cr, Co, or Cu)

    pp. 415-423

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    DOI:10.2320/matertrans.M2014417

    We applied first-principles total-energy calculations to several compounds Mn2−xMxSb (M = Ti, Cr, Co, or Cu) to calculate the total energy. The results indicate that the Ti and Cu (Cr and Co) atoms prefer the Mn(II) site to the Mn(I) site [Mn(I) to Mn(II)]. These results are consistent with experimental observations. The antiferromagnetism (AF) [ferrimagnetism (FR)] is more stable than FR (AF) upon decreasing (increasing) the distance between the Mn(II) and Sb atoms in the z direction in all Mn2−xMxSb systems. This result indicates that the environment around the Mn atom plays a very important role in the stabilization of the AF state, as is the case with Mn2Sb1−xAsx systems. For Mn2−xCoxSb systems, the atomic disorder between the Mn and Co atoms is insensitive to the relative stability of two magnetic phases AF and FR.
  • Application of Diffraction-Amalgamated Grain Boundary Tracking to Fatigue Crack Propagation Behavior in High Strength Aluminum Alloy

    pp. 424-428

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    DOI:10.2320/matertrans.M2014340

    Fatigue crack propagation behavior in a 7075-type Al alloy (Al-5.6%Zn-2.5%Mg-1.6%Cu) was investigated by applying Diffraction-Amalgamated Grain Boundary Tracking (DAGT), which provides grain morphologies and crystallographic orientations in three dimensions (3D). 3D crack morphologies at different propagation stages in the bulk of the sample were successfully obtained using synchrotron radiation X-ray microtomography (SRCT) technique. The apparent crack growth rate, da/dN, which varies significantly along a crack front line, was calculated. There are rapid acceleration and deceleration regions of da/dN due to the interaction with grain boundary (GB) and crack closure segments. Typical crack morphology under the influence of Mode II (in-plane shear) and Mode III (out-of-plane shear), such as crack deflection and twist, is detected by the observation of 2D tomographic slice image. A detailed direct assessment of microstructure-crack interaction behaviors has been achieved by applying the DAGT technique.
  • Effect of Nb Addition on Martensitic Transformation Behavior of AuTi-15Co Based Biomedical Shape Memory Alloys

    pp. 429-434

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    DOI:10.2320/matertrans.M2014418

    The effect of quaternary addition of Nb being from 0 to 2 mol% on the phase constitution, phase transformation behavior and shape memory behavior of Au-50 mol%Ti-15 mol%Co (AuTiCo) alloys is studied. X-ray diffraction analysis shows that, with increasing Nb concentration, the primary phase appeared at room temperature changes from B19 orthorhombic martensite phase to B2 cubic parent phase, and that all the lattice parameters are not largely changed by Nb addition. The maximum transformation strain evaluated in 2 mol%Nb-added AuTiCo is 7.4%. Differential scanning calorimetry revealed that the reverse martensitic transformation finish temperature (Af) decreases from 414 K in Nb-free AuTiCo to 303 K by 2 mol%Nb addition. The ratio of Af change by Nb addition is evaluated to be −55 K/mol%Nb, that is comparably larger than −31 K/mol%Nb in NiTi. These results indicate that Nb addition is effective to stabilize B2 parent phase. AuTiCo alloy containing less than 2 mol%Nb exhibits shape memory effect with 90% shape recovery ratio. Besides, AuTiCo containing 2 mol%Nb exhibits 2.8% superelastic shape recovery at room temperature as well as 7.4% maximum transformation strain. Therefore, Nb addition to AuTiCo is effective to decrease the martensitic transformation temperature and to improve superelasticity, although the transformation temperature hysteresis increases by Nb addition, similar to Nb-added NiTi.
  • Flotation Behavior of Arsenopyrite and Pyrite, and Their Selective Separation

    pp. 435-440

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    DOI:10.2320/matertrans.M2014369

    This study investigated the effect of pH and pulp potential (EH) on the floatability of arsenopyrite and pyrite, which are single minerals, in Hallimond tube, by using xanthate as a collector. On this basis, the study further investigated the selectivity index of arsenopyrite and pyrite, using a mixed sample of arsenopyrite and pyrite. To examine the flotation behavior of each mineral by pH change, flotation was carried out at pH 4 and pH 10. The test results showed arsenopyrite had higher floatability at pH 4, regardless of the potassium ethyl xanthate (PEX) concentration. This is because xanthate ion was oxidized to be stable dixanthogen, which was well adsorbed onto arsenopyrite surface, due to the high EH of pulp. Meanwhile, arsenopyrite had relatively lower floatability at pH 10 than at pH 4, which was because the dixanthogen remained unstable, and was not adsorbed onto the arsenopyrite surface, due to the relatively low EH of pulp. Pyrite had low floatability at both pH 4 and pH 10. Just as for arsenopyrite, the result for pH 10 was caused by the low EH of pulp. Yet, interestingly enough, different from the case of arsenopyrite, pyrite at pH 4 had low floatability, despite its high EH. FTIR analysis was performed, to examine the reason for such contradictory behavior. The analysis result showed that this was caused by poor adsorption with xanthate, due to sulfate ion (SO42−) that was generated by the oxidation of pyrite surface in reaction with oxygen in pulp at pH 4. To further investigate the selectivity index (i.e., the pyrite recovery/arsenopyrite recovery ratio) of arsenopyrite and pyrite, additional flotation tests were carried out on mixed sample of the two minerals. Different from the flotation behavior of single minerals, the results showed that the recovery of arsenopyrite was lower than that of pyrite, and the selectivity index of arsenopyrite and pyrite was the highest when the PEX concentration was the lowest. Such a different trend in flotation behavior of the mixed sample from the flotation behavior of the single minerals was because the surface oxidation reaction of arsenopyrite, which was more affected by EH among the mixed arsenopyrite and pyrite, generated ferric arsenate, a hydrophilic compound, on the surface of arsenopyrite, resulting in poor adsorption with xanthate; in turn, this depressed the floatability of arsenopyrite.
  • Microstructure, Mechanical and High-Temperature Electrical Properties of Cyanide-Free Au-Coated Ag Wire (ACA)

    pp. 441-444

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    DOI:10.2320/matertrans.M2014383

    An efficient and environmental-friendly method, featuring a cyanide-free plating process was established for Au-coated Ag wire (ACA). This new Ag wires can meet the reliability standards of wire bonding. The proposed ACA wire was studied to ensure compatibility with electrical properties; mechanical properties and free air ball characterization. Tensile tests showed that ACA wire was stronger than pure Ag wire. The Au coated layer has excellent an bonded interface with the Ag wire. Electrical properties at high temperature demonstrate that the ACA wire maintains outstanding electrical resistance. Further, the Au layer coating the Ag prevents wire oxidation and corrosion during the packaging process. ACA wire formed by the cyanide-free plating method can be used for IC and LED packaging processes.
  • Feasibility Application of Cu-Contaminated Soil on the Removal of H2S from Hot Coal Gas

    pp. 445-449

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    DOI:10.2320/matertrans.M2014393

    In this study Cu-contaminated soils were chosen as a candidate material for the removal of hydrogen sulfide (H2S) from hot coal gas. Experimental results showed that the H2S was significantly reduced below 10 ppm when the Cu-contaminated soils were reacted with H2S. The optimal removal temperature of H2S was found to be at 923 K in the operating conditions. In addition to Cu species, free Fe oxides in the contaminated soils also performed an active species to react with H2S and enhanced the overall sulfur capacity. Through the XPS analysis, Fe sulfide (FeS) and Cu sulfide (Cu2S) were the major products after removal experiments. Regeneration experimental results also indicated that the Cu-contaminated soils can be regenerated by pass air and thus be reused for many times.
  • Effects of Titanium and Boron Additions with Mechanical Stirring on Mechanical Properties in Al-Si Alloys

    pp. 450-453

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    DOI:10.2320/matertrans.L-M2014848

    Al-Si based alloys are widely used to automobile parts for weight reduction. The mechanical stirring method was performed to achieve the homogeneously dispersed strengthening phases such as AlB2, Al3Ti and TiB2 phases since the specific gravity of strengthening phases is different from the Al matrix. 500 rpm of mechanical stirring results in well dispersion of strengthening phases compared with lower speed (100 rpm) and higher speed (1,000) stirring rate. The higher elastic modulus, hardness and good wear resistance is obtained in the Al-12 mass%Si-2.3 mass%Ti-1 mass%B alloy due to the formation of strengthening phases such as Al3Ti and boride containing (AlTi)B2 compared with Al-12 mass%Si, Al-12 mass%Si-2.3 mass%Ti and Al-12 mass%Si-1 mass%B alloy. Relationship between the microstructure and mechanical properties is discussed based on the solidification phenomena.
  • Removal of Impurity Fe from Mg-3 mass% Al Alloy Melt by CO2 Injection

    pp. 454-456

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    DOI:10.2320/matertrans.MBW201407

    The purification process is required for recycling Mg process. Selective impurity removal has an efficient purification process in the purity level of commercial Mg metal and alloys. Especially, iron impurity deteriorates the corrosion resistance of Mg alloys. Carbon addition to Mg-3 mass% Al alloy melt is an effective method for the removal of iron impurity by the formation of Fe-Al-C compounds. In this study, gas injection of carbon dioxide (CO2) into Mg alloy melt as the method of carbon addition was investigated for the separation of iron compounds. Carbon dioxide was decomposed by Mg melt and carbon substance affected the formation of iron carbide in the melt. Magnesium oxide and Fe-Al-C compound were formed in the melt slag and floated to the top of the solidified Mg-3 mass%Al alloy.
  • Erratum

    pp. 457-457

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    DOI:10.2320/matertrans.ERM201502

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