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

MATERIALS TRANSACTIONS Vol. 56 (2015), No. 10

  • Recent Advances in TASC (Thermal Activation of Semi-Conductors) Technology for Environmental Issues Focused on the Disassembly and Recycling of Solar Panels and Laminated Glass —A New Technology Characterized by Radical Propagation in Giant Molecules—

    pp. 1615-1625

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    DOI:10.2320/matertrans.M2015188

    Thermal activation of semiconductors (TASC) is our novel technology characterized by radical propagation in giant molecules, allowing us to decompose any polymers, in an instant, into H2O and CO2. The present phenomenon has successfully been applied to complete decomposition of VOC (volatile organic compound), or to elimination of polymer matrix in composites in order to recover valuables, for example, decomposition and recovery of FRPs (fiber reinforced plastic), repair of partially damaged FRPs, reclaim of rare-earth powder from resin-bonded magnets, disassembly and recycling of solar panels and laminated glass. The TASC technology dates back to our accidental finding that significant oxidative properties appear in semiconductors when heated at about 350–500°C while quite inactive at room temperature. The oxidative effect (i.e. removal of bonded electrons) has been interpreted as arising from thermally generated defect electrons (“hole”) formed in the valence band of semiconductors. This triggers the decomposition of polymers by creating unstable radicals. Then, the radicals propagate, just like a domino phenomenon, throughout the polymer to make the whole polymer unstable, resulting in the fragmentation of the giant molecule into small pieces such as ethylene and propane. Finally, the fragmented molecules react with oxygen in air to give H2O and CO2 (i.e. complete combustion). This process caused by radical propagation is compared to the reverse reaction of “radical polymerization”. The present overview describes the recent advances in TASC technology with major focus on the disassembly and recycling of solar panels and laminated glass.
  • Effects of Coiling Temperature on the Microstructures, Mechanical Properties and Textures of 08Al Deep Drawing Steel Sheet

    pp. 1626-1632

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    DOI:10.2320/matertrans.M2015150

    Effects of the coiling temperature on the microstructures and mechanical properties of 08Al hot-rolled steel sheet were investigated. Meanwhile, cold rolling and annealing experimental verifications were performed in the laboratory. The results show that when coiling is carried out at 592°C, the hot-rolled steel sheet exhibits good comprehensive mechanical properties. After cold rolling and annealing treatments, the experimental steel sheet also shows the optimal deep-drawability. The volume fraction of {111}⟨UVW⟩ texture component is the highest and the values of {111}⟨UVW⟩/{001}⟨110⟩ and {111}⟨UVW⟩/{001}⟨100⟩ are both the largest. However, the strip-like or massive cementites appear in the steel sheet as the coiling temperature is higher than 620°C, which is harmful to the deep-drawability of the experimental steel. Therefore, the coiling temperature should be controlled to be lower than 620°C in the 08Al deep drawing steel sheet.
  • Effect of Focal Depth of HAADF-STEM Imaging on the Solute Enriched Layers in Mg Alloys

    pp. 1633-1638

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    DOI:10.2320/matertrans.MAW201505

    This study has found that the Z-contrast of aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images of solute enriched layers in Mg-TM-RE (TM:Zn, RE:Y, Gd) alloys is sensitive to the imaging conditions: the defocus and the focal depth. Consequently, the depth position of solute enriched layers in the projected direction shows strong effect on the Z-contrast around each layer. The blurring of the Z-contrast is preferentially observed in both sides region along (0001)Mg basal planes. The boundary position between HCP- and FCC-type stacking sequence at edge regions does not change by defocus. The permissible defocus amount is comparable to the focal depth. The aberration-corrected HAADF-STEM has short focal depth less than 10 nm, so that it is critical for interpreting image contrast that the thin foil thickness and the depth position of the nano-size structure such as the solute enriched layers. In turn, it can be presumed, by the blurring of the Z-contrast, that the depth position of the solute enriched layers in the projected direction. Thus, the focal depth of aberration-corrected HAADF-STEM is quite sensitive to the depth position of solute enriched layers in the thin foil of specimens and the defocus of the electron probe, so that the imaging condition of aberration-corrected HAADF-STEM is critical in order to interpret correctly the Z-contrast of the images.
  • Automatic Reconstruction Approach to Characterization of Prior-Austenite Microstructure in Various Japanese Swords

    pp. 1639-1647

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    DOI:10.2320/matertrans.MAW201509

    Each Japanese sword is unique by its microstructure resulted by the steel composition and heat treatment. In this study, the automatic reconstruction method was applied for characterizing the prior-austenite microstructure at the sharp edge of three Japanese swords made in different time periods. The reconstructed prior-austenite microstructure was compared with that of three carbon steels, in order to clarify the variations of carbon content and heating temperatures of the swords. It was found that in carbon steels, the austenite microstructure is probably affected by initial microstructures, which is predominantly determined by carbon content. The three swords have similar carbon content, but their prior-austenite microstructures are considerably different, probably due to their heating temperatures. The strength at the sharp edge of the modern sword is significantly higher than that of the old sword. It may be due to the fine-grained prior-austenite in the modern sword compared with the abnormally coarse grains observed in the old sword. In order to obtain fine-grained austenite along with high strength and hardness of the cutting edge, it is recommended that the carbon content of Japanese sword is 0.6–0.7 mass%, and the heating temperature is from 750 to 800°C.
  • Frictional and Wear Behavior of Commercially Pure Ti, Ti-6Al-7Nb, and SUS316L Stainless Steel in Artificial Saliva at 310 K

    pp. 1648-1657

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    DOI:10.2320/matertrans.M2015094

    Frictional and wear behavior of SUS 316L stainless steel, commercially pure Ti (Grade 2), and Ti-6Al-7Nb in artificial saliva and in deionized water were investigated at 310 K using a ball-on-disc type frictional test machine with a Ti counterface. The present study aims to obtain information on the in vitro frictional behaviors of Ti-based dental metallic materials, and to investigate the morphological and compositional changes of the surface damages caused by wear and friction. The surface morphology and chemical composition of the wear track was investigated. The results obtained from the frictional test indicates an interpolated dynamic frictional coefficient ranging between 0.3 to 0.5 in both water and artificial saliva, which suggests that solid contact was predominant. The volume loss in water was always higher than that in artificial saliva and the volume loss of Ti-6Al-7Nb and SUS316L decreased with increase in the applied dead load. Microstructural observations suggests adhesive wear to be dominant in specimens tested in artificial saliva, whereas sharper grooves and cracks were frequently observed in the specimens tested in water. The results indicate that surface enbrittlement was caused by oxygen, and the strength of the materials was related to the wear and frictional parameters.
  • Strain Softening Induced by High Pressure Torsion in Copper Alloys

    pp. 1658-1663

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    DOI:10.2320/matertrans.MA201579

    Three kinds of Cu-Al alloys and a pure Cu sample with different stacking fault energies (SFEs) are deformed using room temperature rolling (RR) and high pressure torsion (HPT), respectively. The microstructure is analysed by means of transaction electron microscopy and X-ray diffraction. It is found that HPT is more feasible to obtain nanocrystals and profuse twins. Tailoring the SFE can promote sample strength without sacrificing the ductility of the Cu alloys. The tensile properties of samples processed by HPT and RR are compared. It is discovered that the HPT process leads to the strain softening phenomenon in samples with relatively high SFE. The excellent mechanical properties can be obtained in samples deformed by HPT with a SFE of 6 mJ/m2, in which strain softening was restrained and strain hardening played a dominant role in the deformation process. The relationship between tensile properties and microstructures of the deformed metals is also investigated.
  • Electrodeposition Behavior of Zn–Fe Alloy from Zincate Solution Containing Triethanolamine

    pp. 1664-1669

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    DOI:10.2320/matertrans.M2015230

    The electrodeposition behavior of Zn–Fe alloys has been investigated at 308 K at current densities of 10–500 A·m−2 and a charge of 5 × 104 C·m−2 in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Fe2+ ions. The content of Fe in the deposit changed significantly depending on the current density. At current densities lower than 20 A·m−2, the content of Fe was approximately 90 mass%, that is, the Zn–Fe alloy exhibited normal co-deposition, whereby the electrochemically more noble Fe deposited preferentially. At current densities higher than 100 A·m−2, however, anomalous co-deposition was observed, whereby the less noble Zn deposited preferentially. The current density at which the Fe content in the deposit changed significantly corresponded to that at which the cathode potential in the total polarization curve abruptly shifted to a less noble region than the equilibrium potential for Zn deposition. Iron deposition and H2 evolution were significantly suppressed by the co-existence of Zn2+ ions in the region of anomalous co-deposition at higher current densities, showing the formation of an inhibitor to deposition arising from Zn2+ ions in the cathode layer. The current efficiency for alloy deposition was not close to zero even in the region of normal co-deposition, and the Fe content in the region of anomalous co-deposition was close to the composition reference line, which shows deposition behavior different from that in sulfate solutions. In the region of normal co-deposition at lower current densities, underpotential deposition of Zn occurred with Fe. TEM analysis revealed that Zn–Fe alloys deposited at lower current densities comprised the stable intermetallic compound Fe5Zn21. The activity coefficient of Zn in the deposit appears to remarkably decrease because of this formation of stable Fe5Zn21.
  • Refinement of Thermodynamic Parameters of the Mg24Y5, W and H Phases in the Mg-Zn-Y System

    pp. 1670-1674

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    DOI:10.2320/matertrans.MH201418

    The Mg-Zn-Y alloy shows excellent mechanical properties which can be achieved by combining LPSO phase (known as X phase) and an icosahedral quasicrystal phase (I and Z phases) in Mg solid solution (α phase). Thermodynamic data for the binary/ternary compounds Mg24Y5, X, W and H have to be critically assessed to obtain accurate information of three-phase equilibrium in order to understand equilibria among these phases. In this research, we focused on developing CALPHAD (CALculation of PHAse Diagrams) thermodynamic database to evaluate phase diagrams for the Mg-Zn-Y system. Especially thermodynamic models for the Mg24Y5, W and H phases have been determined based on crystallographic data. Then thermodynamic parameters have been assessed to yield experimental data from EPMA/WDS, SEM, TEM and X-Ray diffraction.
  • Compositional Optimization of Al-Mn-X Alloys and, Their Tensile and Corrosion Properties

    pp. 1675-1682

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    DOI:10.2320/matertrans.F-M2015819

    The ultimate tensile strength of 250 MPa, 0.2% proof stress of 150 MPa, and fracture strain of 10% at the as-cast condition for Al-1.5Mn-X alloys, were objective in this development. As ternary elements, Ca, Mg, Ti and Zn were initially chosen and the values in ΔMk of the s-orbital energy level in alloys were adjusted to be less than 0.017. Their proof stress and fracture strain increased and decreased as ΔMk increased, respectively. The composition of promising alloy was decided to Al-1.5Mn-2.4Mg with ΔMk of 0.029 on the basis of the relation between tensile properties and ΔMk. This as-cast alloy showed the σuts σ0.2 and εf of 270, 135 MPa and 18% showing excellent corrosion resistance in the NaCl solution, which resulted in the approximate satisfaction of the objective. The interaction between the proof stress and dislocation density or hindrance for dislocation migration at the constant strain could be explained by ΔMk, which might lead to the indication of solid solution hardening level using this parameter for Al-1.5Mn-X ternary alloys.
  • Thermal Stress-Based Diffusion Bonding Method: the Case of Oxygen Free Copper to 316L Stainless Steel

    pp. 1683-1687

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    DOI:10.2320/matertrans.M2015197

    Fixture composed of 304 stainless steel (SUS304) and 440C stainless steel (SUS440C) was employed for inducing the thermal stress to 316L stainless steel and oxygen free copper (SUS316L/OFC) cylinders to achieve diffusion bonding. For comparison, the same combination was bonded using the conventional diffusion bonding method, i.e. heating in vacuum under constant pressure. Although the thermal stress-based diffusion bonding is conducted in charcoal-reformed air, the bonding starts from 673 K. This temperature is relatively low as compared with the conventional method (873 K). Furthermore, the joint fabricated using the thermal stress-based method exhibits higher joint efficiency than one prepared using the conventional method. The highest tensile strength is attained at 1073 K and comparable to one of OFC. The bonding deformation of the thermal stress-based method is smaller than with the conventional method, since the fixture does not apply excess pressure to the diffusion couple. Thus the thermal stress-based diffusion bonding method is a promising and may be superior to the conventional method from view points of simplicity and bondability.
  • Alloying Effects on Hydrogen Solubility and Hydrogen Permeability for V-Based Alloy Membranes

    pp. 1688-1692

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    DOI:10.2320/matertrans.MAW201511

    The alloying effects of chromium, molybdenum, tungsten, iron and cobalt on the hydrogen solubility of vanadium have been investigated systematically. The addition of iron or cobalt into vanadium decreases the hydrogen solubility more significantly than chromium, molybdenum and tungsten. Thus, the addition of iron or cobalt into vanadium improves the resistance to hydrogen embrittlement of the vanadium alloy itself effectively. It is also found that, in view of the new description of hydrogen permeation based on hydrogen chemical potential, these alloying elements enhance the hydrogen flux through the vanadium alloy. This is because the PCT factor, fPCT, increases by the addition of iron or cobalt. Thus, alloying these elements into vanadium improves not only the resistance to hydrogen embrittlement, but also the hydrogen permeation ability.
  • Nickel Formation on Graphite Sheet Surface for Improving Wettability with Magnesium Alloy

    pp. 1693-1697

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    DOI:10.2320/matertrans.MAW201506

    Magnesium-calcium alloy-based composites reinforced with vapor grown carbon fibers (VGCFs) are supposed to possess satisfactory high-temperature applications. However, poor wettability of magnesium with carbon fiber is a technical problem encountered in fabrication of the composites. In order to cover the wetting problem, wetting behavior of magnesium alloys on graphite sheet, pure nickel, and nickel coated graphite sheet were investigated using sessile drop method. The graphite was non-wetting by both Mg-5Al alloy and Mg-5Al-3Ca alloy with contact angles about 120°. The droplet of magnesium alloys on nickel plate spread rapidly. Contact angle of Mg-5Al-3Ca alloy decreased from about 94° to 43°. Wettability of magnesium alloys on nickel coated graphite sheet was improved through the dissolution of nickel into the liquid magnesium alloy. Calcium addition showed negative effect on contact angle of nickel substrate, and also slightly hindered the spread of magnesium alloy droplet on nickel coated graphite sheet.
  • Influence of Swaging on the Magnetic Properties of Zn-Bonded Sm-Fe-N Magnets

    pp. 1698-1702

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    DOI:10.2320/matertrans.M2015190

    Swaging was investigated as a fabrication process for high-density Zn-bonded Sm-Fe-N magnets, which mainly consisted of Sm2Fe17Nx, and their magnetic properties were investigated. The demagnetization curves of the annealed specimens with or without swaging suggested that swaging improved the magnetic polarization. The specimen swaged with a reduction ratio (R) of 82%, a high maximum energy product ((BH)max) of 67.8 kJ·m−3 with a high coercivity (HcJ) of 1.89 MA·m−1 was obtained. Sm-Fe-N particles were pulverized and the dispersion of Zn particles was improved during swaging, the density of specimens increased resulting in the increase in HcJ and (BH)max.
  • Evaluation of Adhesion of Hydroxyapatite Films Fabricated on Biomedical β-Type Titanium Alloy after Immersion in Ringer’s Solution

    pp. 1703-1710

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    DOI:10.2320/matertrans.M2015223

    The adhesive strengths between sol-gel fabricated hydroxyapatite (HAp) films and Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) were evaluated before and after immersion in Ringer’s solution at 310 K for 7 d. The effect of the surface morphology of TNTZ on the adhesion of HAp films was also investigated. The fracture surfaces after adhesion tests were observed and fracture areas at the interface between HAp films and TNTZ were also evaluated before and after immersion in Ringer’s solution. No significant differences in the adhesive strengths between HAp films and TNTZ disks with mirror-polished and mechanically polished surfaces were found. The fracture area at the interface between HAp film and mirror-polished TNTZ disk increases after immersion in Ringer’s solution, whereas no fracture occurs at the interface between HAp film and mechanically polished TNTZ disk before and after immersion in Ringer’s solution. It is supposed that Ringer’s solution penetrates along the cracks that are formed in the HAp films during calcination and the regions with weak adhesion between HAp and TNTZ are connected during immersion in Ringer’s solution in the case of HAp films fabricated on mirror-polished TNTZ. From these results, it is found that a relatively rougher surface is effective in improving the adhesion of HAp films fabricated on TNTZ before and after immersion in Ringer’s solution.
  • Contact Resistance Comparison of Flip-Chip Joints Produced with Anisotropic Conductive Adhesive and Nonconductive Adhesive for Smart Textile Applications

    pp. 1711-1718

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    DOI:10.2320/matertrans.M2015106

    For applications in smart textiles, flip-chip bonding was applied with either an anisotropic conductive adhesive (ACA) or a nonconductive adhesive (NCA) to a heat-resistant fabric and a Si substrate as a reference. The average contact resistances of the flip-chip joints produced with each adhesive on each substrate were evaluated with varying the Cu and Sn thicknesses inversely over the range of 0–15 µm to maintain a total thickness of 15 µm of the Cu/Sn bump. The contact resistances of the flip-chip joints produced with ACA on Si, NCA on Si, ACA on fabric, and NCA on fabric were 6.5–12.2 mΩ, 15.6–26.5 mΩ, 5.3–10.2 mΩ, and 5.5–10.1 mΩ, respectively.
  • Thermoelectric Power-Generation Characteristics of a Thin-Film Device Processed by the Flip-Chip Bonding of Bi2Te3 and Sb2Te3 Thin-Film Legs Using an Anisotropic Conductive Adhesive

    pp. 1719-1724

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    DOI:10.2320/matertrans.M2015236

    A thermoelectric thin-film device with a cross-plane configuration was fabricated by the flip-chip process using an anisotropic conductive adhesive. The Cu/Au bumps on the top substrate were flip-chip bonded to the 242 pairs of the n-type Bi2Te3 and p-type Sb2Te3 thin-film legs electrodeposited on the bottom substrate. The internal resistance of the thin-film device was 59 Ω, most of which can be attributed to the interfacial resistance of the 484 flip-chip joints. The thin-film device exhibited an open-circuit voltage of 382 mV and a maximum output power of 652 µW for a temperature difference of 36.8 K applied across its top and bottom substrates.
  • Coral Sand Solidification Test Based on Microbially Induced Carbonate Precipitation Using Ureolytic Bacteria

    pp. 1725-1732

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    DOI:10.2320/matertrans.M-M2015820

    Artificial beachrock, formed by coral sand solidification through microbially induced carbonate precipitation (MICP), could provide coastal protection instead of concrete structures, and would be eco-friendly as well as help minimize costs. The present study was conducted to solidify coral sand through the MICP method by using an ureolytic bacterium (Parahodobacter sp.) isolated from peripheral beachrock. The goal was to obtain a sample with an unconfined compressive strength (UCS) of 20 MPa or more. We also aimed to examine the growth characteristics of this bacterium in the culture medium ZoBell2216E, which is commonly used for marine bacteria. In order to determine the suitability of the MICP test, growth properties of the microbial strain were observed under various culture conditions. A sand solidification test with MICP was carried out in a syringe as well as a PET cylinder. The strength of the resulting specimens was measured with the needle penetration test. The specimen solidified up to 20 MPa of the estimated UCS after 21 days of curing. For optimum growth of the bacterium, 1.0 g of the culture was added to100 mL culture media and incubated with shaking at 160 rpm. The preferred final concentration in solidification promoting solution of both urea and CaCl2 was 0.5 M, with bacterial cell densities of 109 CFU/mL. In order to efficiently induce solidification, the optimum pH was 7.0 or higher, and Ca2+ concentration was maintained at 1.0 g/L. The results were enhanced by re-injecting the culture solution when the pH and Ca2+ concentrations in the specimen were not in the ideal ranges indicated above.
  • Silicate Covering Layer on Pyrite Surface in the Presence of Silicon–Catechol Complex for Acid Mine Drainage Prevention

    pp. 1733-1741

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    DOI:10.2320/matertrans.M-M2015821

    In this paper, prevention of pyrite oxidation by carrier microencapsulation (CME) was investigated. A possible layer structure was suggested following analysis with electrochemical and surface analysis techniques. Electrochemical study of treated pyrite samples showed that treatment with silicon–catechol (Si-Cat) for 6 h at an initial pH of 9.5 gave the best barrier properties and suppression of the samples. Scanning electron microscopy with energy-dispersive X-ray, and Fourier transform infrared (FTIR) analyses confirmed the presence of a silicate layer on the surface of treated pyrite. X-ray photoelectron spectroscopy indicated that the coating layers on the treated pyrite samples consisted of a network of Fe-O-Si and Si-O-Si units bonded to the surface of pyrite. The Si-O-C asymmetric stretching mode was also observed in FTIR spectra. Detailed spectroscopic analyses confirmed the formation of a silicate polymer on a silica–quinone layer, which resulted in the effective suppression effect shown by Si-Cat-treated pyrite at increasing pH.
  • Effects of Pulse Bias Duty Cycle on Composition, Structure and Hardness of Ti–Cu–N Nanocomposite Films Deposited by Pulse Biased Arc Ion Plating

    pp. 1742-1746

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    DOI:10.2320/matertrans.M2015159

    Hard nanocomposite Ti–Cu–N films were deposited on high-speed-steel (HSS) substrates by pulse biased arc ion plating with a single multi-component Ti–Cu (88/12 at%) alloyed target. The effects of pulse bias duty cycle on the elemental content, structure and mechanical properties of the deposited films were investigated. The Cu atom content of the Ti–Cu–N films was analyzed using an electron probe microanalyzer (EPMA). The structure of the films was determined by X-ray diffraction (XRD) and their hardness and elastic modulus were measured using a nanoindenter. Under pulse bias voltages of −300 V and −600 V, the Cu content decreased with an increase in the duty cycle from 10% to 50%. The XPS spectra of Cu 2p for the Ti–Cu–N films showed that only pure metallic Cu was present. With an increase in the pulse duty cycle from 30% to 50%, the diffraction peaks of TiN in the preferred orientations (111) and (220) were observed, for pulse bias voltages of −300 V and −600 V, respectively. Furthermore, no obvious sign of the metallic copper phase was observed in the XRD patterns. Under both pulse bias voltages of −300 V and −600 V, the value of hardness showed first an increase and then a decrease with an increase in the duty cycle from 10% to 50%. The maximum hardness value observed was 31.5 GPa, which was obtained for a 30% duty cycle under a pulse bias voltage of −600 V.
  • Compositional Optimization of β Type Titanium Alloys with Shape Memory Ability and Their Characteristics

    pp. 1747-1755

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    DOI:10.2320/matertrans.M2015233

    The compositions of β type Ti alloys having shape-memory ability above 400 K were proposed by alloying parameters used in the d-electrons concept. They were both Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo which were designed for improvement of thermal stability in shape memory behavior of Ti-6Mo base alloy, preserving the tensile strength of 700 MPa. Their ingots without contamination from the used crucible were produced by cold crucible levitation melting. They consisted of β and α′′ phases after the cold roll and heat treatment, and their amounts were depended on values in the alloying parameters. The shape recovery rate of 40 and 25% was measured after 4 cycles in the loading-unloading tests in Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo, respectively. They showed the As temperature above 490 K and improvement of thermal stability because of a much smaller amount of ω phase than Ti-6Mo. The alloys showed tensile strength of 682 to 718 MPa. These results were caused by exactly prediction of the phase stability, shape memory ability and tensile strength, using alloying parameters.
  • Magnesium Sorting by Vibrating Particulate Bed from Mixed Metal Scrap

    pp. 1756-1758

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    DOI:10.2320/matertrans.M2015226

    As increasing the demand of Mg alloys, recycling of these alloys require for securing a metallic resource and energy conservation. A commercial metal scrap includes other structural materials such as iron, copper and aluminum alloys. These metal elements deteriorate mechanical properties or corrosion properties of Mg alloys. Therefore, these different materials were possibly removed from Mg scrap during recycling process. The separation of Al and Mg materials has difficulty except for the gravity separation. However, there is a limited difference in density between Mg and Al. In this study, Mg recovery from mixed metal scrap was attempted by dry gravity separation using solid particulate vibrating bed. Mg separation with high recovery ratio was achieved by adjusting the density of the particulate bed. It was suggested that the bulk density of the particulate bed affected the behavior of separation materials for the favorable recovery.

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