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

MATERIALS TRANSACTIONS Vol. 47 (2006), No. 7

  • Gasdynamic Simulation of Aerosol Deposition Method

    Hiroshi Katanoda, Kazuyasu Matsuo

    pp. 1620-1625

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    DOI:10.2320/matertrans.47.1620

    Abstract

    The gas flow of aerosol deposition method (ADM) is simulated using the method of computational fluid dynamics (CFD), and the velocity of particles flowing in the gas flow is also calculated by numerically integrating Newton’s second law of motion. The process gas is nitrogen and the particle material is Pb(Zr,Ti)O3 (PZT). The calculated particle velocities are compared with experimental results obtained by using a slit-cell method (SCM), which may disturb the gas-particle jet-flow of ADM during the measurement of particle velocity. The comparison of calculated and measured results reveals that the SCM can cause unexpected measurement error due to disturbing the gas-particle jet-flow caused by the stagnation pressure exceeding a certain value.

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  • Development of Lateral Compression Method of Circular Tube Thin Coating for Mechanical Properties of Plasma Sprayed CoNiCrAlY

    Hiroyuki Waki, Akira Kobayashi

    pp. 1626-1630

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    DOI:10.2320/matertrans.47.1626

    Abstract

    CoNiCrAlY coatings have been developed to protect gas turbine blades from oxidation and corrosion at high temperature. However, the mechanical properties of the thin CoNiCrAlY coatings used in actual turbine system were unknown, because there was not a proper measurement method of thin sprayed coatings. Lateral compression test for the circular tube coatings of plasma-sprayed thin coating was newly developed. In considering the deformation of the tubes, the elastic contact with a flat plate jig and a tube surface was taken into account as well as the bending of the curved beam of the tube. Young’s moduli of well known materials obtained from the lateral compression tests agreed well with the true values. CoNiCrAlY tube specimens independent of substrates were manufactured by dissolving out the substrates by nitric acid. The thickness of coatings were selected from 150 to 700 μm. The effects of spraying particle size, spraying atmosphere and thermal treatment on mechanical properties, such as Young’s modulus and bending strength, of CoNiCrAlY were examined. It was found that Young’s modulus and a fracture stress increased with an increase of the coating thickness. Young’s modulus was sensitive to the spraying powder size and increased with a decrease of the size. It was found that spraying with small spraying powder was the most effective in increasing the Young’s modulus. It was also found that Young’s modulus was governed by the porosity if thickness and process were given. It was found that thermal treatment was the most effective in increasing the bending strength.

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  • In-Situ Densification of Ti Coatings by the Warm Spray (Two-Stage HVOF) Process

    Jin Kawakita, Seiji Kuroda, Sebastian Krebs, Hiroshi Katanoda

    pp. 1631-1637

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    DOI:10.2320/matertrans.47.1631

    Abstract

    Coating of titanium is one of the surface modification techniques attractive for corrosion protection in various industrial and medical applications. In-situ densification of titanium coatings fabricated by the Warm Spray (two-stage high velocity oxy-fuel (HVOF)) process was investigated for the purpose of obtaining impermeability together with minimum oxidation level. Ceramic beads of ZrO2-SiO2 were mixed with titanium feedstock powder. By the peening effect of the ceramic particles the density of the resultant titanium-matrix coatings could be improved and the minimum coating porosity obtained in this study was 0.65 vol%.

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  • Comparison of Microstructure and Oxidation Behavior of CoNiCrAlY Bond Coatings Prepared by Different Thermal Spray Processes

    Mitsuhiro Shibata, Seiji Kuroda, Hideyuki Murakami, Machiko Ode, Makoto Watanabe, Yukihiro Sakamoto

    pp. 1638-1642

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    DOI:10.2320/matertrans.47.1638

    Abstract

    To protect various gas turbine components against high temperature in the hot sections of power generation plants and aircraft engines, thermal barrier coatings (TBCs) have been developed and widely used. Conventional TBCs consist of a MCrAlY bond coating for oxidation resistance and a ceramic top coating for thermal insulation. High quality coatings of MCrAlYs have been produced mostly by low pressure plasma spraying but other more economical processes are also used depending on the operating conditions of the component to be coated. In this study, CoNiCrAlY powders were deposited on Inconel 718 substrate with 3 types spraying system, i.e., low pressure plasma spraying, high velocity oxy-fuel spraying, and atmosphere plasma spraying. The specimens without top ceramic coating were isothermally tested for up to 100 hrs in air at 1373 K and mass gain of the coatings was measured. Microstructure of the coating cross sections and the surface oxides were observed with SEM. Moreover, phase changes during the oxidation test were investigated with calculated phase diagrams for the CoNiCrAlY alloy.

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  • Effect of Spray Distance on the Mechanical Properties of Plasma Sprayed Ni-45Cr Coatings

    Wei-Ze Wang, Chang-Jiu Li, Yu-Yue Wang

    pp. 1643-1648

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    DOI:10.2320/matertrans.47.1643

    Abstract

    Ni-45Cr coating was plasma sprayed at different spray distances in order to clarify the influence of spray distance on the mechanical properties. The mechanical properties of Ni-45Cr coatings include the fracture toughness, elastic modulus and Poisson’s ratio parallel to lamellar plane. The fracture toughness of plasma-sprayed Ni-45Cr coating in terms of critical strain energy release rate (GIc) was investigated using a tapered double cantilever beam approach. The elastic modulus and Poisson’s ratio parallel to lamellar plane were obtained by measuring the relation of stress and strain using strain gauges. It was found that the fracture toughness of plasma sprayed Ni-45Cr coatings was not significantly influenced by spray distance up to 190 mm and further increase in spray distance to 210 mm resulted in an evident decrease in the fracture toughness of the coatings. Moreover, spray distance showed minor effect on the elastic modulus and Poisson’s ratio parallel to lamellar plane of Ni-45Cr coating. The examination of fractured surface revealed that the fracture toughness of plasma-sprayed Ni-45Cr coatings is related with the lamellar bonding.

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  • Corrosion Behavior and Thermal Conductivity of Plasma Sprayed AlN/Al2O3 Coating

    Hongwei Yang, Weiling Luan, Shan-Tung Tu

    pp. 1649-1653

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    DOI:10.2320/matertrans.47.1649

    Abstract

    Plasma sprayed alumina coating has demonstrated great potential in improving the loading capacity and service life of engineering equipments, while the low thermal conductivity limits its application when high heat exchange efficiency is required. In this paper AlN with different proportion was added into the feedstock powder of Al2O3, and a series of AlN/Al2O3 composite coatings was deposited on mild steel substrate by plasma spray. Its mechanical properties were studied and thermal conductivity was measured by Transient Plane Source (TPS) method. XRD and EDS analysis revealed that most of the Al2O3 in composite coating underwent phase transformation from α phase to metastable γ phase during plasma spraying, and the mass fraction of AlN was decreased comparing with the chemical composition of feedstock powders. With the increase of AlN proportion, the microhardness reduced from 847 Hv of pure Al2O3 coating to 685 Hv when the mass fraction of AlN was 0.47, companying with the bond strength decreased from 27.4 to 21.3 MPa, and the corrosion rate decreased by half. The addition of AlN resulted in the increase of thermal conductivity by several times comparing with the original Al2O3 coating.

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  • Characterization of the Microstructure and Electrical Conductivity of Plasma-Sprayed La0.5Sr0.5CoO3 Coating

    Cheng-Xin Li, Min Gao, Chang-Jiu Li, Wei Zhou, Guan-Jun Yang, Yu-Yue Wang

    pp. 1654-1657

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    DOI:10.2320/matertrans.47.1654

    Abstract

    Lanthanum strontium cobalt oxide (LSCO) has been employed as cathode and intercollector materials for solid oxide fuel cells (SOFCs). In the present study, the La0.5Sr0.5CoO3 layer was deposited by atmospheric plasma spray (APS). The effect of heat treatment on microstructure and electrical conductivity of the LSCO deposits was examined. The electrical conductivity of the deposits along the lamellar direction was measured by a four-probe dc approach. The microstructure of the deposit was characterized by scanning electron microscopy and X-ray diffraction analysis. The results showed that the electrical conductivity of plasma-sprayed LSCO coating was lower than that of sintered bulk material with the same composition. The minor metastable phase in the as-sprayed coating reduced the electrical conductivity. The annealing treatment at 1000°C led to the elimination of the metastable phase and improved the electrical conductivity. The lamellar structure features with the limited interface bonding limits the electrical conductivity.

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  • Effect of Heat Treatment Conditions on Micro Structure of Cast Iron Coatings Sprayed by HVOF Spraying

    Takayuki Kuwashima, Hiroshi Horie, Takashi Saitoh, Takahito Takagawa, Takashi Iimura, Tetsuya Sonoda

    pp. 1658-1664

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    DOI:10.2320/matertrans.47.1658

    Abstract

    Steel materials have been replaced with light material for the purpose of reducing weight of products in many industry fields. As for these light metal materials, the wear resistance and heat resistance are inferior to the steel material. The compound with the steel material is given to one of the methods for the solution of this problem.
    In this study cast iron powders were sprayed on the aluminum alloy substrate using HVOF spraying method to produce composite material with excellent wear resistance property. Cast iron powder made by gas atomized method was used as spray materials and Al-Mg alloy (JIS A5083) was used as a substrate.
    In thermal spraying deposition efficiency shows a decreasing trend when spray distance increases. With increasing thermal spray distance, micro Vickers hardness value decreased and mass loss of Suga type abrasive wear test and ball-on-disk wear test increased. In blast erosion test, the mass loss of their coatings increased with increasing blast angle each spray distance and in each blast angle, the mass loss of coating sprayed by distance 200 mm was smaller than other coatings. Spray material and sprayed coatings were heat-treated to examine the influence of heat treatment condition on their micro structure.
    Heat treatment was carried out using electric furnace in the vacuum atmosphere of 1×10−3 Pa. The heating rate was 10 K/min and holding temperature was changed between 673 and 1273 K every 200 K. The graphite phase was observed at the processing temperature of 1073 K or more.
    Powder that had been heat-treated at 1073 K was then sprayed under the same conditions. Cast iron coating included graphite phase was obtained by using the thermal spray material heat-treated by 1073 K.

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  • Microstructural Investigation of CoNiCrAlY Coated Ni-Based Single Crystal Superalloy Prepared by LPPS

    Takashi Sakai, Mitsuhiro Shibata, Hideyuki Murakami, Seiji Kuroda

    pp. 1665-1670

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    DOI:10.2320/matertrans.47.1665

    Abstract

    Recent demand in increasing the efficiency of gas turbines has led the component materials to be exposed at much higher operating temperatures, which accordingly accelerates the microstructural deterioration of the coated materials, mainly caused by the interaction between the coated layer and the substrate. Therefore, controlling the chemistry of interfaces by the coating process is one of the most important keys to minimizing the microstructural changes during service. In this study, effects of surface treatments and coating conditions on microstructure changes of Ni-based superalloy substrates were investigated. CoNiCrAlY (AMDRY 9954) powder was coated on Ni-based single crystal superalloy TMS-82+ by low pressure plasma spraying (LPPS). It was found that grit-blasted treatment drastically distorted the coherent γ⁄γ′ microstructure of substrates, which accordingly promoted the uniform and accelerated precipitation of topologically close-packed (TCP) phases by the post heat treatment at 1273 K for 30 min. On the other hand, specimens without the grit-blast treatment had less amount of TCP precipitates, but showed preferred precipitation orientation along ⟨011⟩{100} direction. Surface preheating and surface sputter cleaning seemed to have less influences on microstructure change compared to the grit-blast treatment.

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  • Influence of Substrate Materials upon Fabrication of Aluminum Nitride Coatings by Reactive RF Plasma Spraying

    Motohiro Yamada, Hajime Nakamura, Toshiaki Yasui, Masahiro Fukumoto, Koyata Takahashi

    pp. 1671-1676

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    DOI:10.2320/matertrans.47.1671

    Abstract

    Influence of the substrate materials upon fabrication of aluminum nitride (AlN) coatings by reactive RF plasma spraying was investigated according to spraying onto various substrate materials. Aluminum particles were injected into Ar/N2 plasma and were deposited onto carbon steel (S45C), aluminum alloy (A6063) and quartz substrates. In the case of using carbon steel substrate, fabrication of thick and dense Al based Al/AlN composite coatings was possible. However, higher concentration of AlN phase in the coatings peeled off the coatings during cool down after spraying due to the difference in thermal expansion coefficient between AlN and carbon steel. Therefore, formation of Al interlayer was attempted between AlN layer and carbon steel substrate in order to decrease the thermal stress. As the result, Al interlayer included Al/AlN composite coating was fabricated onto a carbon steel substrate with control the N2 flow rate in plasma gas during spraying. While fabrication of AlN layer onto Al interlayer was possible, it was concerned that formation of Fe-Al intermetallic compound at the interface between the coating and the substrate formed defects. Then not the Al interlayer but aluminum alloy was used as the substrate. However, the aluminum alloy substrate melted during spraying even the substrate was cooled by water-cooled substrate holder. Therefore, it is demanded to the substrate materials have a melting point that is much higher than aluminum. On the other hand, almost completely AlN coatings were fabricated using quartz substrate, which involves lower thermal expansion coefficient and higher melting point. Therefore, the characteristics of low thermal expansion coefficient and high melting point were required for substrate materials in order to fabricate AlN or AlN based Al/AlN composite coatings by reactive RF plasma spraying. Especially, quartz was useful for the substrate material.

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  • Plasma-Erosion Properties of Ceramic Coating Prepared by Plasma Spraying

    Junya Kitamura, Hiroaki Mizuno, Nobuaki Kato, Isao Aoki

    pp. 1677-1683

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    DOI:10.2320/matertrans.47.1677

    Abstract

    Application of plasma sprayed ceramic coatings with a high purity of more than 99.9% has been sharply increasing in semiconductor and liquid-crystal-display (LCD) production equipments in the last few years. The size of the equipments becomes larger with increasing Si wafer size and the LCD size that promotes the replacement from conventional techniques, such as alumite film and bulk ceramics, to plasma spray coatings, where the high durability against the plasma erosion (anti-plasma erosion resistance) is required. However, as far as we know, no systematic studies on the plasma-erosion properties are reported. In this work, durability of plasma sprayed alumina and yttria coatings against CF4/O2 plasma are investigated by reactive ion etching (RIE) system and are compared to that of the conventional techniques. The erosion mechanism and the effect of the powder properties are discussed through the micro-structural analysis.

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  • Deposition Behaviors of Solid Phases in Liquid-Solid Two-Phase Particles in High Velocity Oxy-Fuel Spraying

    Y.-Y. Wang, C.-J. Li, K. Kusumoto, G.-J. Yang

    pp. 1684-1689

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    DOI:10.2320/matertrans.47.1684

    Abstract

    Three types of composite coatings were deposited by high velocity oxy-fuel (HVOF) spraying using metal-clad WC-18Co and SiC-50Co cermet powders, and sintered-crushed Al2O3-75Ni composite powders. Liquid-solid two-phase state of the sprayed particles with two different structures was achieved prior to their impingement on the substrate. The effects of particle structure and HVOF spraying parameters on volume fraction of the solid phase were investigated. The distribution of ceramic particle size inside coatings was also clarified. Scanning electron microscopy was employed to characterize the microstructure of HVOF sprayed cermet coatings. The volume fraction of solid particles and the distribution of particle size in the three types of coatings were estimated using a quantitatively metallographic approach from the microstructure of the coatings. The volume fraction of the solid phase in the coating made from Al2O3-Ni powders was increased with increase in the fuel gas flow. The maximum volume fraction of the Al2O3 phases reached about 64% of the original powder. On the other hand, the volume fraction of solid phase in the clad cermet coatings was decreased with increasing the fuel gas flow. The volume fraction of the solid phase dropped significantly from 72.2% in the original WC-18Co particle to 8.5% in the coating. The limited retention of the solid phase from spray particle to subsequent coating is due to rebounding off of large solid particle upon impacting.

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  • Phase Formation during Deposition of TiO2 Coatings through High Velocity Oxy-Fuel Spraying

    Chang-Jiu Li, Guan-Jun Yang, Yu-Yue Wang, Cheng-Xin Li, Fu-Xing Ye, Akira Ohmori

    pp. 1690-1696

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    DOI:10.2320/matertrans.47.1690

    Abstract

    The crystalline structure of TiO2 coating is of significant importance for controlling its property and performance, such as photocatalytic activity. The aim of this study is to examine the phase formation mechanisms during high velocity oxy-fuel (HVOF) spraying of TiO2 coating. TiO2 coatings were deposited under different spray conditions using both anatase powder and rutile powder as feedstocks. The results showed that the anatase content in the coatings was increased with the increase of fuel gas flow when using the rutile powder as feedstock. A TiO2 coating of anatase content up to 35% can be obtained by well-melted particles. The high content of anatase phase possibly resulted from rapid solidification and cooling process of the particles. The anatase content in the TiO2 coating deposited with an anatase powder in partially melted state reached 55–65%. The coating deposited by well-melted anatase powder contained the same anatase content as that by rutile powder. A model was proposed to explain the phase formation within the coatings deposited through HVOF spraying.

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  • Simulation of Solid Particle Impact Behavior for Spray Processes

    Kensuke Yokoyama, Makoto Watanabe, Seiji Kuroda, Yoshihiko Gotoh, Tobias Schmidt, Frank Gärtner

    pp. 1697-1702

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    DOI:10.2320/matertrans.47.1697

    Abstract

    Several thermal spray processes developed recently are characterized by relatively low temperature and higher velocity of sprayed particles. They include cold spray, high velocity oxy-fuel spray, and warm spray, in which majority or all the sprayed particles are in solid phase when impinging onto the substrate surface. Therefore, in order to understand the coating formation process of such processes, detailed knowledge concerning impact phenomena of a solid particle is essential. It is generally accepted that there exists a minimum velocity beyond which a particle adheres to the substrate and this velocity is called the “critical velocity”. How the critical velocity depends on various materials and process variables is not fully understood yet. In this study, analysis of a metal particle impacting onto a metal substrate was carried out by using a dynamic finite element code (ABAQUS). Effects of a substrate and a particle temperature on the critical velocity were numerically studied. Also, effects of thermal conduction on the simulation results were discussed. It was found that critical velocity decreases with 1) higher stiffness of the substrate, 2) higher particles temperature, and 3) greater particle size.

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  • Preliminary Study of Performance of Dye-Sensitized Solar Cell of Nano-TiO2 Coating Deposited by Vacuum Cold Spraying

    Sheng-Qiang Fan, Chang-Jiu Li, Cheng-Xin Li, Guang-Jian Liu, Guan-Jun Yang, Ling-Zi Zhang

    pp. 1703-1709

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    DOI:10.2320/matertrans.47.1703

    Abstract

    The control of nanoporous microstructure of TiO2 coating in the dye-sensitized solar cells (DSC) through preparation methods influences significantly the performance of the cells. To investigate the effect of microstructure of TiO2 deposit on the cell’s performance, in present study, vacuum cold spray (VCS) process is employed to deposit nanocrystalline TiO2 coatings on an ITO conductive glass substrate. TiO2 deposits were produced using nanosized particles of 25 nm in the diameter and composite powder composed of polyethylene glycol (PEG) and 25 nm TiO2 particles. The deposition characteristics and the microstructure of the coating are characterized by scanning electron microscopy, x-ray diffraction analysis. The performance of the cell is tested under illumination of a metal halide lamp with a radiation intensity of 600 W·m−2. It was found that a dense TiO2 coating with retention of crystal structure of powder can be deposited by vacuum cold spraying directly using nanosized TiO2 powder. A cell with TiO2 coating of 3.8 μm thick deposited directly by 25 nm powders yielded a short current density of 90.0 A·m−2 and conversion efficiency of 5.1% which was comparable with that of the wet doctor blading TiO2 coating. Using a composite powder of TiO2 with PEG, a porous TiO2 coating with a thickness up to several tens of micrometers can be deposited by vacuum cold spraying. A DSC cell of TiO2 coating deposited using a composite powder containing 41.2% PEG presented a higher short current density of 145.0 A·m−2, and conversion efficiency of 7.1%.

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  • Graphitization Potential of Cast Iron Powder in Atmospheric Plasma Spray Conditions

    I. Ozdemir, Y. Tsunekawa, M. Okumiya, T. Ueno

    pp. 1710-1716

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    DOI:10.2320/matertrans.47.1710

    Abstract

    Graphitization behavior of water-atomized cast iron powder at each thermal spraying step, such as droplet flight, droplet impingement and splat layering, was successively examined. Both as-atomized cast iron powder and coatings sprayed with the powder contain no graphite structure owing to their rapid solidification. A short period of pre-annealing at 1173 K allows the formation of graphite structure in the cast iron powder, in which there exist precipitated graphite of 3.58 mass%. The microstructure observation exhibits that pre-existed pores in the as-atomized powder strongly affect the precipitating sites of graphite, that is, mainly inside the individual powder instead of the surface. However, marked reduction in graphite structure occurs to coatings sprayed with the pre-annealed powder because of in-flight burning and dissolution into molten iron. In-process post-annealing at 773 K for 60 s reveals the formation of graphite structure resulted from the decomposition of iron based metastable carbide in splats and coatings sprayed with the as-atomized powder. Chemical analysis demonstrates that graphitization level of post-annealed cast iron coatings is higher than that of coatings sprayed with the pre-annealed powder. Precipitated intersplat graphite structure of 1.68 mass% appears in cast iron coatings when introducing methane as a powder feeding carrier gas which is liable to decompose in plasma flame. The resultant coatings with graphite structure embedded in hard matrix are anticipated to offer superior wear resistance in comparison to centrifugally cast iron containing flaky graphite of 1.76 mass%.

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  • Preparation and Evaluation of Ordinary Attritor Milled Ti-Al Powders and Corresponding Thermal Sprayed Coatings

    Masahiro Fukumoto, Min Nie, Toshiaki Yasui

    pp. 1717-1722

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    DOI:10.2320/matertrans.47.1717

    Abstract

    Ordinary attritor milling of elemental metallic powders under atmospheric condition was utilized to prepare desirable amount of powders for thermal spraying. The effect of different BPR (Ball to Powder weight Ratio) has been investigated in terms of nitridation during milling. To investigate the effect of heat treatment on the formation of dispersed phases, heat treatment to the powder was performed as well. Titanium aluminide coatings with carbonitride dispersed phases were successfully fabricated by low pressure plasma spraying. The hardness and specific wear of the coatings prepared by the powders with different milling conditions was measured so as to investigate the effect of the content of dispersed titanium based carbonitride phases. Experimental results show that the formation of dispersed carbonitride phases depends strongly on milling condition, irrespective of heat treated powders or thermal sprayed coatings, and directly affects the mechanical properties of the coatings. Compared with the phase composition of heated powders and corresponding thermal sprayed coatings, it seems that the temperature of processing the MA powders is also a decisive factor on the phase formation, especially carbonitride phases and oxide phase.

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  • Critical Velocities for High Speed Particle Deposition in Kinetic Spraying

    Jingwei Wu, Hongyuan Fang, Sanghoon Yoon, Changhee Lee, HyungJun Kim

    pp. 1723-1727

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    DOI:10.2320/matertrans.47.1723

    Abstract

    During kinetic spraying (or cold gas dynamic spraying), small solid particle can be deposited onto the substrate by a supersonic velocity impaction. A critical velocity of flying particle was found for the minimum deposition speed. Generally, it was thought that higher impact velocity caused higher deposition efficiency. However, some different phenomena were observed during spraying processing in laboratory.
    In this study, individual particle impact tests have been carried out to probe the effect of impact velocity. Instead of deposition efficiency (DE) of coatings, ratio of bonds, which was defined as the number fraction of attached particles to total impact particles (Craters + Bonds) in unit area of impact surface, was measured in our test. A maximum velocity for particle deposition was observed, because of which a high fraction of rebounded particles occurred at a high impact velocity. A model considering the adhesion and rebound energy was built up to estimate the particle/substrate interaction. The particle deposition behavior was a result of the competition between adhesion and rebound energies during the impact process. Only when the adhesion energy was higher than the rebound energy, the impacting particles could be attached onto the substrate.

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  • Giant Magnetoimpedance in Fe74.5−xCuxNb1.5V1.5Si13.5B9 As-Quenched Ribbons

    Bo Li, Hongwei Qin, Juan Chen, Jifan Hu

    pp. 1728-1730

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    DOI:10.2320/matertrans.47.1728

    Abstract

    In this work, large values of magnetoimpedance from Fe74.5−xCuxNb1.5V1.5Si13.5B9 as-quenched ribbons is reported. With increasing Cu content, the magnetoimpedance first increases, undergoes a maximum value at x=3.5, and then drops at higher Cu contents. The magnetoimpedance ΔZ⁄Z0 for the Fe71Cu3.5Nb1.5V1.5Si13.5B9 (x=3.5) as-quenched ribbon reaches −31.3% under a field of H=7162 A/m at 1.2 MHz. The grain size of α-Fe(Si) for as-quenched Fe71Cu3.5Nb1.5V1.5Si13.5B9 (x=3.5) ribbon is estimated as 14–16 nm. Results show that nanocrystalline Fe-Cu-(Nb,V)-Si-B ribbons with giant magnetoimpedance can be prepared directly from the melt–spinning technique without annealing.

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  • Removal of Iron from Molten Recycled Aluminum through Intermediate Phase Filtration

    Humberto Lopes de Moraes, José Roberto de Oliveira, Denise Crocce Romano Espinosa, Jorge Alberto Soares Tenório

    pp. 1731-1736

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    DOI:10.2320/matertrans.47.1731

    Abstract

    Aluminum is one of the most versatile materials used in foundry practice; however, iron is one of the most troublesome impurities in aluminum cast materials. During the solidification of aluminum alloys, iron promotes the formation of intermediate phases, which may damage the properties of the final product. In secondary aluminum industries, iron contamination caused by high amounts of iron scrap is always possible. Consequently, the aim of this work was to study the most efficacious method and conditions for the removal of iron from molten aluminum through ceramic filters. The materials studied were based on the AA308 and AA356 aluminum alloys with iron additions. The variables of this work were chemical composition, temperature and the type of filter. The results showed that iron could be efficiently removed through the use of manganese and silicon followed by the decrease of the temperature at which the intermediate phases crystallize.

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  • Candidate Atomic Cluster Configurations in Metallic Glass Structures

    Daniel B. Miracle, Eric A. Lord, Srinivasa Ranganathan

    pp. 1737-1742

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    DOI:10.2320/matertrans.47.1737

    Abstract

    A growing body of evidence supports the importance of solute-centered atomic clusters in the structure and stability of metallic glasses. Beyond a few simple cases, a broad account of these clusters has not been provided elsewhere. Detailed characteristics of a canonical collection of efficiently packed hard sphere clusters are presented here as idealized structural elements in metallic glasses. The nomenclature, topology, geometry and packing efficiency of these clusters are provided and their relevance to the structure of metallic glasses is discussed.

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  • Microstructure and Mechanical Properties of AZ31 Magnesium Alloy Strip Produced by Twin Roll Casting

    Yusuke Nakaura, Akira Watanabe, Koichi Ohori

    pp. 1743-1749

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    DOI:10.2320/matertrans.47.1743

    Abstract

    Twin roll casting has been used to produce AZ31 magnesium alloy strip. The size of the cast strip is 5 mm thick and 250 mm wide. The microstructure of the as-cast AZ31 alloy strip consists of columnar zones from the surface to mid-thickness region and equiaxed zone in the mid-thickness region. The secondary dendrite arm spacing varies from 5.0 to 6.5 μm through the thickness and width of the strip and is much smaller than 34 μm of AZ31 alloy DC ingot used for the comparison. In temperature ranging from room temperature to 400°C, tensile strength and elongation of the as-cast strip are higher and smaller than those of DC ingot, respectively. Elongation is evidently improved by homogenization treatment and becomes more than that of DC ingot. Such an improvement of elongation is though to be caused by homogenization of segregation of Al and Zn atoms in the dendrite cell boundaries.

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  • Effect of Forging Temperature on Microstructure and Mechanical Properties of In Situ (TiB+TiC)/Ti Composites

    Feng-cang Ma, Wei-jie Lu, Ji-ning Qin, Di Zhang

    pp. 1750-1754

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    DOI:10.2320/matertrans.47.1750

    Abstract

    In this paper, 5 vol% (TiB+TiC)/Ti-1100(Ti–6Al–2.75Sn–4Zr–0.4Mo–0.45Si) composite were fabricated using in situ technologies between Ti and B4C powders. Phase identification was carried out by X-ray diffraction. β transus temperature of the composite was measured by metallographic techniques. The composite after ingot breakdown was forged in various temperature ranges. Microstructure of the composite after forging at various temperatures was studied by optical microscopy (OM). Mechanical properties of the composite after forging at various temperatures were evaluated by tensile tests at 873 K. It was found that the β transus temperature of the composites was around 100 K higher than that of monolithic Ti-1100 alloy. Different microstructures were obtained after forging at different temperatures. The composite with different microstructures offered different mechanical properties, which was shown in the tensile tests.

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  • Influence of Si Addition on Microstructure Evolution of Ni3Al0.50V0.50 Alloy

    Makoto Tanimura, Kei-ichi Kondo, Toshihiro Doi, Yasumasa Koyama

    pp. 1755-1761

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    DOI:10.2320/matertrans.47.1755

    Abstract

    The microstructure evolution related to the L12 (supersaturated Ni3Al1−xVx) → L12 (Ni3Al)+D022 (Ni3V) phase separation of the Ni3Al0.50V0.50 alloy, with the addition of a small amount of Si (less than 0.2 mol%), was examined by transmission electron microscopy. The data showed that the L12 single phase was formed via the appearance and subsequent disappearance of the D022 regions under an isothermally holding process, as in the case of the Ni3Al0.50V0.50 alloy without Si. A striking feature of the microstructure evolution of the present alloy was that the formation of the final L12 single phase was accomplished within an extremely brief period of less than 10 min. Such a brief period indicated that the microstructure evolution was not accompanied by atomic diffusion, which was quite different from the case of the Si-free alloy. On this basis, we propose that the Si addition induced a pinning effect on atomic migration (i.e., suppression of long-range atomic diffusion) in the supersaturated L12 matrix and thus accelerated the formation of the final L12 single phase.

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  • Electron Irradiation Induced Phase Transformation in Nd2Fe14B Alloy

    Akihiro Nino, Takeshi Nagase, Yukichi Umakoshi

    pp. 1762-1768

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    DOI:10.2320/matertrans.47.1762

    Abstract

    Transformation and change in the microstructure of Nd2Fe14B compound under electron irradiation were examined. The Nd2Fe14B compound did not maintain its original structure under electron irradiation and was transformed to an amorphous phase through solid-state amorphization. With further electron irradiation, crystallization of the amorphous phase occurred forming a nano-crystalline structure. The phase selection of electron irradiation induced crystallization depended strongly on the irradiation temperature; nanocrystalline α-Fe phase precipitated in the amorphous phase at 104 K, while a nanoduplex structure composed of α-Fe, compounds and residual amorphous phase was formed at 298 K. Electron irradiation induced phase transformation is a very effective method to control the nanocrystalline structure in Fe-Nd-B alloy.

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  • Recrystallization Behavior and Texture Formation of Rapidly Annealed Cold-Rolled Extralow Carbon Steel Sheets

    Takehide Senuma, Kaoru Kawasaki, Yoshito Takemoto

    pp. 1769-1775

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    DOI:10.2320/matertrans.47.1769

    Abstract

    The influence of a heating rate up to 1000°C/s on recrystallization behavior and texture formation of an extralow carbon steel sheet was investigated. To discuss the experimental results of this investigation, a mathematical model for predicting recrystallization behavior was developed. An analysis using the model shows that the heating rate influences the apparent thermal activation energy of recrystallization. At a higher heating rate, C dissolved from cementite and AlN precipitated during heating decreases and as a consequence the apparent thermal activation energy is lower. This can also be a valid explanation for the fact that recrystallization of a steel sheet coiled at low temperature is retarded.
    The main orientations of the recrystallization texture are weakened if the heating rate is increased. This tendency has already been observed at the initial stage of recrystallization. If the specimen is heated slowly up to the initial stage of recrystallization, the decrease in the intensity of the main orientations is reduced even though the heating rate subsequently increases. This result indicates that, concerning formation of the recrystallization texture, the heating rate mainly influences the nucleation process.

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  • Recrystallization Effect and Electric Flame-Off Characteristic of Thin Copper Wire

    Fei-Yi Hung, Yuan-Tin Wang, Li-Hui Chen, Truan-Sheng Lui

    pp. 1776-1781

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    DOI:10.2320/matertrans.47.1776

    Abstract

    Compared with gold wire, copper wire is cheaper and possesses lower cost, greater strength and better electrical conductivity, and therefore is becoming more commonly used. But the lower ductility and oxidation undermine the reliability of copper wire bonding, making the wire susceptible to breaking. In the present study, the annealed effect (at 150–250°C for 1 hour) on the tensile mechanical properties of copper wires with φ=25 μm (1 mil) was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied.
    Experimental results indicate that with annealing temperatures of more than 200°C, the copper wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, the matrix structure transferred from long, thin grains to equiaxed grains and a few annealed twins. The microstructures of the free air ball (FAB) of the variation annealing wires after an EFO process were column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Cu ball, and the preferred orientation was ⟨100⟩. Under the thermal effect of EFO, the necks of the Cu balls underwent recrystallization and the grain growth was induced. Additionally, the decreased hardness and the strength of the HAZ resulted in the breakage sites of the EFO wires being in the HAZ near the Cu balls.

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  • Addition of an Aminic Antioxidant to a Hindered Ester-Based Heat Resisting Oil to Improve Lubrication for Press Forming of Magnesium Alloy Sheets

    Eiji Goto, Takashi Kachi, Haruo Okahara, Yorinobu Takigawa, Kenji Higashi

    pp. 1782-1787

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    DOI:10.2320/matertrans.47.1782

    Abstract

    High heat resistance is required for the lubricant used during the mass production of press formed magnesium parts using a warm press forming process. The heat resistance of a hindered ester has previously been found to be high, but insufficient at temperatures around 573 K. Therefore, further improvement of hindered ester-based heat resisting lubricants is required. This paper describes the influence on lubricity of adding aminic antioxidants to hindered esters. The results showed that excellent heat resistance was obtained by adding 5 to 20% styrenated diphenylamine. While a 5% addition improved heat resistance and inhibited lubricant degradation, addition of 10 or 20% additive resulted in decreased lubricity. Furthermore, the best lubricity was obtained when DLC-coated carbide was used as the die material in combination with the lubricant containing aminic antioxidant.

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  • Copper Leaching Behavior from Waste Printed Circuit Board in Ammoniacal Alkaline Solution

    Kazuya Koyama, Mikiya Tanaka, Jae-chun Lee

    pp. 1788-1792

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    DOI:10.2320/matertrans.47.1788

    Abstract

    A novel energy-saving hydrometallurgical recovery process for copper from electronic scrap employing the Cu(I)-ammine complex has been presented on the basis of a thermodynamic consideration. In order to experimentally explore the feasibility of the leaching stage in this process, the copper leaching behavior from a printed circuit board (PCB) in ammoniacal alkaline solutions has been investigated under a nitrogen atmosphere. Copper in PCB was oxidized by Cu(II) to form Cu(I)-ammine complex ions. The leaching reaction can be expressed as: Cu+Cu(NH3)42+=2Cu(NH3)2+. The Cu(II)-ammine complex significantly enhanced the leaching rate, while the Cu(I)-ammine complex slightly depressed it. Crushing of the PCB effectively enhanced the leaching rate, because the exposed metallic copper area is increased by the crushing. The effect of temperature on the leaching rate was insignificant. Consequently, the feasibility of the leaching stage in the proposed copper recovery process has been experimentally confirmed.

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  • Grain Refinement of Tough Pitch Copper by Electromagnetic Vibrations during Solidification

    Yoshiki Mizutani, Kenji Miwa, Takuya Tamura, Yoshihiro Nakai, Yasuyuki Otsuka

    pp. 1793-1797

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    DOI:10.2320/matertrans.47.1793

    Abstract

    Electromagnetic vibrations, which are generated by simultaneous imposition of a static magnetic field and an alternating electric field, were applied to the refinement of crystal grains of tough pitch copper. The electromagnetic vibrations of the frequency range from 100 Hz to 10 kHz were imposed during solidification of the copper rod. Within this frequency range, the vibration frequency of about 100 Hz was found to be the most effective in refining the copper crystal grains and the average grain size was refined up to 200 μm, which otherwise was around 600 μm in a nonvibrated specimen. It was concluded that by the electromagnetic vibration process tough pitch copper could also be refined as well as Al-Si alloys and AZ91D alloys.

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  • Formation of Fine and Dense Conical Carbides on Tool Steel Surface by Sputter Etching

    Rongguang Wang, Qinglian Zhang, Masahiko Kato, Keijiro Nakasa

    pp. 1798-1804

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    DOI:10.2320/matertrans.47.1798

    Abstract

    Sputter etching of W-Cr-V tool steel specimens containing various amount of residual carbide was carried out by using an RF magnetron sputtering apparatus. For a fully solution-treated specimen having a very small amount of residual carbide, fine and sharp conical carbides with high density and homogeneity are formed on the surface by such treatment. With increasing sputter etching time, the carbides grow to a thick layer but lose their sharpness, part of the layer disappears and a particle-free matrix appears after long time etching. For the quenched and tempered specimen having a large amount of residual carbide, sharp carbides are newly formed among them but the tops of the residual carbides are not sharp. However, the carbide layer formed on the specimen remains even after a long sputter etching time.

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  • The Structure, Phase Composition and Mechanical Properties of Microplasma Electrolytic Coatings Produced on a Ti-6Al-4V Alloy

    O. P. Terleeva, Young-Joo Oh, Myoung-Ryul Ok, A. I. Slonova, I. B. Kireenko, Dong-Heon Lee

    pp. 1805-1809

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    DOI:10.2320/matertrans.47.1805

    Abstract

    The structure and phase composition of microplasma coatings formed on a Ti-6Al-4V alloy using the alternating current mode in solutions with different concentrations of KOH, NaAlO2 and Na6P6O18 were investigated using XRD analysis, microscope analysis and microhardness testing. The thickness and weight gain were measured with electronic thickness gage and correspondingly, with the gravimetric method. The crystal structure of the microplasma electrolytic coatings had amorphous, rutile, α-Al2O3 and Al2TiO5 phase. The coating morphology may be presented as 3 layers—the external amorphous layer, the internal layer, and the barrier layer.

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  • Influence of Electron Beam Irradiation on the Impact Value of Alkali Free Glass

    Yoshitake Nishi, Keisuke Iwata

    pp. 1810-1814

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    DOI:10.2320/matertrans.47.1810

    Abstract

    Influences of electron beam irradiation on impact fracture energy indicated by impact value are studied for alkali free glass. The irradiation, which is able to be one of short-time treatments, reduced the brittleness and increased the impact value of alkali free glass. The impact value enhancement can be explained by stress relaxation induced by increase in density of dangling bonds.

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  • Morphology of Spinels and Al2O3 Particles in an Al2O3/Al-Mg-Si Composite Material Revealed by Scanning Low Energy Electron Microscopy

    K. Matsuda, T. Matsuki, I. Müllerov, L. Frank, S. Ikeno

    pp. 1815-1820

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    DOI:10.2320/matertrans.47.1815

    Abstract

    In metal matrix composite materials consisting of oxide particles and Al alloys, including Mg as a solute atom, MgAl2O4 spinels are formed at the interface between the particles and the matrix. In the present study, the scanning low energy electron microscopy (SLEEM) method has been applied to confirm morphologies of α-Al2O3 particles and MgAl2O4 spinel crystals grown on the alumina particles in the Al2O3/Al–1.0 mass% Mg2Si alloy composite material. The morphology of α-Al2O3 particles before fabrication of the composite material was like a facetted barrel with 2 hexagonal {0001} and 6 trapezoidal {\\bar1101} planes. Spinels were formed on facets of Al2O3 as small particles, and their shape was an octahedron consisting of 8 equiaxial triangles. Spinels and Al2O3 particles keep their orientation relationship which was concluded by our recent TEM study: (111)_MgAl2O4||(0001)_Al2O3, [2\\bar1\\bar1]_MgAl2O4||[2\\bar1\\bar10]_Al2O3, [1\\bar10]_MgAl2O4||[1\\bar100]_Al2O3

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  • Strength of Carbon Fiber Reinforced Cu-25 at%Al Alloy Junction Device

    Yoshitake Nishi, Kazunori Tanaka

    pp. 1821-1825

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    DOI:10.2320/matertrans.47.1821

    Abstract

    By using a duplex-coated carbon fiber felt, copper welding to aluminum is successfully developed. The first step of the welding method is that the felt is contacted and wrapped with molten aluminum, which is solidified under gravity pressure. The second step is that the aluminum-welded felt is contacted and wrapped with a molten copper, which is solidified under gravity pressure. The carbon fiber junction device is a fiber-reinforced alloy and acts as a joining part of copper and aluminum. Tensile strength of the junction device of carbon fiber reinforced Cu-25 at%Al alloy is higher than those of a Cu-25 at%Al alloy and an aluminum rod.

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  • Fatigue Life Prediction of Biomedical Titanium Alloys under Tensile/Torsional Stress

    Equo Kobayashi, Hiroto Mochizuki, Hisashi Doi, Takayuki Yoneyama, Takao Hanawa

    pp. 1826-1831

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    DOI:10.2320/matertrans.47.1826

    Abstract

    In order to contribute for designing the implant devices with appropriate mechanical properties, fatigue properties of biomedical Ti-6Al-7Nb alloy, were evaluated through the tensile/torsional fatigue test. Fatigue properties for the tensile/torsional fatigue, the tensile fatigue, and the torsional fatigue were compared directly using equivalent stress defined by von Mises’ yield condition. In the S-N plots, there were two regions showing different gradients in data and they are corresponded to the boundary of the low cycle fatigue and the high cycle fatigue. By the approximation with Basquin relation of the S-N data, elastic strain, σa, and elastic shear strain, τa, showed good linearity to the fatigue life. Fatigue coefficients and fatigue exponents of Basquin relation obtained by the least square method might be useful to examine fatigue life of these alloys under tensile stress, torsional stress and tensile/torsional stress.

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  • Magnetic Removal of Phosphate from Wastewater Using Schwertmannite

    Akbar Eskandarpour, Kensuke Sassa, Yoshiyuki Bando, Masazumi Okido, Shigeo Asai

    pp. 1832-1837

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    DOI:10.2320/matertrans.47.1832

    Abstract

    A magnetic filtration has firstly been applied to the phosphate removal from wastewater by using schwertmannite, which is ferric oxyhydroxide sulfate with high capacity of phosphate adsorption. High efficiency of phosphate removal without using magnetic seeding was obtained at magnetic intensities of around 1 Tesla, which means no necessity to use a superconducting magnet. The kinetics data of phosphate adsorption have been found to be fitted well with a pseudo-second-order model and adsorption equilibrium data have been explained by the Langmuir isotherm. The effect of pH on the phosphate adsorption in this process was characterized by zeta potential measurement. It is proposed that ligand exchange is a dominant mechanism responsible for phosphate adsorption on schwertmannite.

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  • Nano-Sized Indium Oxide Powder Synthesized by Spray Pyrolysis Process

    Jaekeun Yu, Seonggu Kang, Jinbae Kim, Jwayeon Kim, Joungsu Han, Jaewoon Yoo, Sangwoon Lee, Zousam Ahn

    pp. 1838-1846

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    DOI:10.2320/matertrans.47.1838

    Abstract

    In this study, nano-sized indium oxide powder with average particle size below 50 nm is synthesized from indium chloride solution by a spray pyrolysis process. This study also examines influences of reaction factors on the properties of the synthesized powder. These factors include the reaction temperature, the inflow speed of the raw material solution and the inflow speed of the environmental air.
    As the reaction temperature increases from 850 to 1000°C, the average particle size of the generated powder increases from around 30 nm to 100 nm, the microstructure gradually becomes solid, the XRD peak intensity gradually increases and the specific surface area decreases.
    As the inflow speed of the raw material solution increases from 2 to 5 mL/min, the average particle size of the powder decreases. When the inflow speed is 10 mL/min, the average particle size is larger than that at 5 mL/min. When the inflow speed of solution is 50 mL/min, the average particle size is smaller and the microstructure of the powder is less solid than that at 10 mL/min. The variations of the XRD peak intensity and the specific surface area show the similar tendency to that of the average particle size.
    As the air pressure increases from 0.1 to 0.5 kg/cm2, the average particle size of the powder shows a not significant change from 90 nm to 100 nm. As the air pressure increases up to 1 kg/cm2 and 3 kg/cm2, the average particle size decreases down to 50 nm and the XRD peak intensity decreases.

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  • Correlation between ID⁄IG Ratio from Visible Raman Spectra and sp2/sp3 Ratio from XPS Spectra of Annealed Hydrogenated DLC Film

    F. C. Tai, S. C. Lee, C. H. Wei, S. L. Tyan

    pp. 1847-1852

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    DOI:10.2320/matertrans.47.1847

    Abstract

    The hydrogened diamond like carbon film (DLCH) with 1 μm thickness is made by hydrocarbon gas ion beam deposition method. The relationship between ID⁄IG ratio fitted from visible Raman spectra and sp2/sp3 ratio done from XPS spectra of DLCH film shows a trend. The ID⁄IG ratio of deconvoluted visible Raman spectra shows a correlation with sp2/sp3 ratio from XPS spectra as annealing temperature increases, the graphitization and the disorder increase. The ID⁄IG ratios fitted with two-curve Gaussian functions of Raman spectra tend to be proportional to sp2/sp3 ratio fitted with three-curve with 100% Gaussian function of XPS spectra when post annealed treatment is below 400°C and without severe oxidation.

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  • A Spray Coating and Its Mechanical Properties of Al-Si-Zn Alloy Produced by the Spray Forming Process

    Toru Maruyama, Takeshi Kobayashi, Masatoshi Kano

    pp. 1853-1858

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    DOI:10.2320/matertrans.47.1853

    Abstract

    A 55 mass%Al-1.5 mass%Si-Zn system alloy with good corrosion resistance was sprayed on a plaster substrate. Then, the formation process and some properties of the sprayed coating were investigated. Using the interrupted quenching method, it was found that the sprayed coating structure was not only the layer structure but also a casting structure. Due to large solidification range, the solidification pattern was a mushy type with characteristic of Al-Si-Zn alloys. The maximum temperature and the shrinkage ratio of the sprayed coating decreased as the spray distance increased, due to the decreasing melt particle temperature. Tensile strength and the elongation of the sprayed coating decreased as the spray distance increased, due to an increase in the porosity ratio. In particular, a large amount of oxide was formed in the sprayed coating when air was used as the carrier gas. This oxide formation causes an increase in the shrinkage ratio.

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  • Fume Generation Behaviors in Short Circuit Mode during Gas Metal Arc Welding and Flux Cored Arc Welding

    Hyunbyung Chae, Cheolhee Kim, Jeonghan Kim, Sehun Rhee

    pp. 1859-1863

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    DOI:10.2320/matertrans.47.1859

    Abstract

    Fume generation mechanisms in gas metal arc welding (GMAW) and flux cored arc welding (FCAW) have been widely investigated. The experimental approach using the different contents of chromium and nickel in electrodes and base metal was proposed in this study, in order to quantitatively measure the amount of fume generated from the electrode and the base metal respectively. The experiments were conducted by using a stainless steel electrode and a mild steel electrode, and chromium (Cr) and nickel (Ni) contents of the fume were calibrated by using the different electrodes. The welding fume was generated mainly from the wire electrode. In addition, the relationship between the welding parameters and fume generation rate (FGR) was investigated. FGR increased with welding current; however, weights of fume per unit electrode length showed a reverse trend compared with FGR per unit time.

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  • Copper Enrichment of Iron-Base Alloy Scraps by Phase Separation in Liquid Fe-Cu-P and Fe-Cu-P-C Systems

    Katsunori Yamaguchi, Takuya Ohara, Shigeru Ueda, Yoichi Takeda

    pp. 1864-1868

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    DOI:10.2320/matertrans.47.1864

    Abstract

    A clear phase separation into liquid iron-rich and copper-rich alloys was observed when a mixture of Fe, Cu and P was melted in an alumina or carbon crucible at 1373 K. Since this phase separation is considered to be useful for recovering valuable copper from iron-base alloy scraps, the phase equilibrium in the Fe-Cu-P and Fe-Cu-P-C systems was investigated in this study. The effect of carbon to the phase separation was determined in the concentration range of phosphorous between 7 and 11 mass% at 1373 K. It was found that the addition of carbon enlarged the miscibility gap of the Fe-Cu-P system. Distribution ratios of some minor elements of Au, Ag, Pd, Pt, Rh, Cr, Mn and Ni between the liquid iron-rich and copper rich phases were also measured at 1373 K. It was found that Au, Ag and Pd were enriched in the copper-rich phase, while Pt and Mn were distributed in both phases, and Rh, Cr and Ni preferentially in the iron-rich phase.

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  • Spin-Coating Polyimide Film on Hydrogenated DLC Film Surface Prepared by Ion Beam Deposition Method

    Fong-Cheng Tai, Shih-Chin Lee, Che-Hung Wei

    pp. 1869-1873

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    DOI:10.2320/matertrans.47.1869

    Abstract

    The present work describes the hybrid layers consisting of 1-μm-thick hydrogenated diamond-like carbon (DLCH) film deposited by ion beam deposition (IBD) method as the bottom layer and spin coating polyimide (PI) film at a thickness of 6 μm as the top layer. Optical microscopy shows that all DLCH film, PI film and PI/DLCH film have smooth surface and are free from cracks or wrinkles. Water contact angle measurement shows that the annealed DLCH film has the higher relative adhesive tension and adhesive work than that of PI film. Raman spectra show that the DLCH film can avoid severe graphitization & degradation at 300°C during annealing treatment, and FTIR spectra also exhibit that the PI film will reach 95% imidization during the curing step at 300°C. PI film can act on DLCH film as the stress buffer. This is demonstrate from warpage measurement showing that top PI film with tensile stress can partially reduce the compressive stress over bottom DLCH film with 6.7% warpage reduction. The electrical resistivity of PI/DLCH/Si is similar to that of PI/Si is resulted from the PI passivation effect.

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  • © 2006 The Japan Institute of Metals and Materials

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