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

MATERIALS TRANSACTIONS Vol. 44 (2003), No. 2

  • Optical Properties of Au/SiO2 Nano-Composite Films Prepared by Induction-Coil-Coupled Plasma Sputtering

    pp. 215-219

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    DOI:10.2320/matertrans.44.215

    Au/SiO2 nano-composite thin films with 3 to 65 vol% Au were prepared by induction-coil-coupled plasma sputtering, and the effect of heat-treatment on the nano-structure and optical property of the films were investigated. The mean diameter of the Au particles in the as-deposited films was about 8 nm and increased from 10 to 30 nm after the heat treatments at 900°C. The optical absorption was greatly improved by the heat-treatment due to the increase of Au particle sizes. At the heat-treatment of 900°C, Au/SiO2 films containing 3 to 65 vol% Au showed absorption peaks at the wavelength of 540 to 560 nm, while no absorption peak was observed in the as-deposited films containing more than 12 vol% Au. The intensity of the absorption peak for the Au/SiO2 films heat treated at 900°C increased with increasing Au content, showing a maximum value around the Au content of 37 vol%.
  • The Influence of Titanium and Vanadium on Isothermal Growth Kinetics of Allotriomorphic Ferrite in Medium Carbon Microalloyed Steels

    pp. 220-225

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    DOI:10.2320/matertrans.44.220

    Allotriomorphic ferrite is the morphology of ferrite formed at relatively small undercooling below the Ae3 temperature. Because it is the first transformation in austenite decomposition during cooling, allotriomorphic ferrite affects indirectly the subsequent austenite phase transformations. Although several investigations have been reported in the literature about the nucleation and growth kinetics of allotriomorphic ferrite in medium carbon microalloyed steels, there is a lack of information about the role of titanium and vanadium on this phase transformation. The purpose of the present study is to analyse the influence of both elements on the isothermal growth kinetics of allotriomorphic ferrite by means of microstructural quantitative analysis. A careful comparison of the results showed that vanadium does not affect the ferrite transformation whereas titanium speeds it up.
  • Compressive Deformation of Partially Crystallized Amorphous Si-B-C-N Ceramics at Elevated Temperatures

    pp. 226-231

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    DOI:10.2320/matertrans.44.226

    The deformation behavior of Si–B–C–N ceramics derived from a polymer precursor has been investigated by compression tests at high temperatures. The hot isostatic pressing of pyrolyzed powder compact was conducted at 1450°C and at 900 MPa in order to obtain a dense ceramic monolith. The material consisted of the amorphous matrix and the dispersed Si3N4 particles with the diameter of about 20 nm. While only apparent elastic deformation was observed at the testing temperatures up to 1500°C, significant plastic deformation occurred at temperatures higher than 1650°C. The plastic deformation is considered to be caused by the viscous flow of the amorphous matrix. The flow stress at the testing temperatures in the range of 1650 to 1750°C increased with initial strain rate. The flow stress was not proportional to the strain rate. The shear viscosity at 0.02 strain was about 1011–1013 Pa s and decreased proportionally to about −0.75 power of the strain rate. The decrease in shear viscosity is considered to show a strain localization behavior. Strain hardening was observed during the plastic deformation. As the reason of the strain hardening, the crystallization can be considered, in addition to the decrease in atomic site defects during the deformation.
  • Effect of Sn Addition on the Mechanical and Electrical Properties of Cu-15%Cr In-Situ Composites

    pp. 232-238

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    DOI:10.2320/matertrans.44.232

    Effect of Sn addition on the mechanical and electrical properties of Cu–15%Cr in-situ composites has been studied. The addition of 0.1%Sn is effective for the solid solution hardening. Accumulation of high density of dislocations and development of banding structure by cold drawing give the increment of tensile strength. The precipitation of Cr in cupper matrix was accelerated and distinct secondary hardening occurs after cold rolling and aging treatment. It was found that the tensile strength of 1100 MPa with electrical conductivity of 70%IACS were attained in the Cu–15%Cr–0.1%Sn by the optimization of thermomechanical processing.
  • Change in Vickers Hardness and Substructure during Creep of a Mod.9Cr-1Mo Steel

    pp. 239-246

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    DOI:10.2320/matertrans.44.239

    In order to investigate the structural degradation during creep, interrupted creep tests were conducted of a Mod.9Cr–1Mo steel in the range of stress and temperature from 71 to 167 MPa and 873 to 923 K. The change of hardness and tempered martensitic lath width were measured in grip and gauge parts of interrupted specimens. The lath structure was thermally stable in static conditions, however, it was not stable during creep and the structural change was enhanced by creep strain. The relation between the change in lath width and strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep life consumption ratio. Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep life consumption ratio. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.
  • Influence of the Matrix Microstructure on the Wear Resistance of Alumina Continuous Fiber Reinforced Aluminum Alloy Composites

    pp. 247-252

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    DOI:10.2320/matertrans.44.247

    The solidification microstructure and wear resistant properties were investigated for alumina fiber reinforced Al alloy matrix composites. Alumina continuous fiber of 15 μm diameter was chosen to improve the wear resistance and clarify the wear mechanism. Al–7 to 27 mass%Si alloys, in which the hard Si phase was dispersed in matrix, and Al–4.5 mass%Cu, in which matrix showed age-hardening during heat treatment were used to evaluate the influence of hardness of matrix on wear resistant. Fiber reinforced composites were fabricated via the pressure infiltration process; continuous alumina fibers were placed in a graphite mold, then molten aluminum alloy was infiltrated into the fiber preforms in a vacuum to fabricate the composites specimens with the 55 vol% fiber. The pin on ring type wear resistance test was carried out under the condition of dry and air atmosphere. Wear resistant properties of fiber reinforced composites are improved about 2 to 10 times more than unreinforced alloys. Furthermore, Al–27 mass%Si hypereutectic alloy matrix composites, in which the hard primary Si particles are dispersed in eutectic matrix, shows higher wear resistance than that of hypoeutectic alloy, which consisted of primary dendritic α phase and α + Si eutectic structure. The primary Si hard phase in matrix connects the alumina continuous fibers and prevents the breakaway of fibers from the worn surface. The wear resistances are also increased by the age hardening of matrix for Al–4.5 mass%Cu and Al–7 mass%Si based alloy matrix composites.
  • Corrosion Resistance of HastelloyC Coatings Formed by an Improved HVOF Thermal Spraying Process

    pp. 253-258

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    DOI:10.2320/matertrans.44.253

    The corrosion resistance of coatings obtained by an improved HVOF spraying method was evaluated by various electrochemical techniques. This spraying system could increase the flight velocity of sprayed particles and suppress their oxidation simultaneously by attachment of a gas shroud, employing nitrogen gas at a large flow rate. The process brought about attainment of both smaller porosity and lower oxide content of the resulting coatings. Consequently, the resistance of HVOF sprayed coatings against seawater corrosion was improved considerably.
  • Electro-Deposition of Tantalum on Tungsten and Nickel in LiF-NaF-CaF2 Melt Containing K2TaF7 — Electrochemical Study

    pp. 259-267

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    DOI:10.2320/matertrans.44.259

    Electrochemical study has been carried out on the electro-deposition of tantalum in 55 mol%LiF–35 mol%NaF–10 mol%CaF2 melt containing 1–2 mol%K2TaF7 at 700°C. This has been done for determining the mechanistic features for preparing electrolytic coating of tantalum on nickel and tungsten substrates. Electro-deposition of metallic tantalum occurs primarily by electro-reduction of Ta(V), i.e., TaF72− at a potential of <−0.5 V (vs. nickel used as a quasi reference electrode). At potentials <−0.55 V, TaOF52− also undergoes reduction to form metallic tantalum. The oxide ions generated by reduction of TaOF52− are removed from the surface by an oxide ion getter in the LiF–NaF–CaF2 melt. Pure metallic tantalum without any entrapped salt is successfully deposited on tungsten by galvanostatic polarization at reasonably low current densities. An additional feature on nickel is the formation of an intermetallic compound at potential ∼0.25 V nobler than that of pure tantalum as a result of underpotential deposition of tantalum. This intermetallic compound covers the surface within a short time followed by deposition of pure tantalum, although intermetallic compound keeps growing at the interface of pure tantalum deposit and the substrate as a result of diffusion. Other secondary reactions are (i) a low activity reduction of Ta(V) to Ta(II) at −0.25 V, (ii) a conproportionation reaction at the surface of electrode leading to partial dissolution of tantalum and, (iii) a corresponding disproportionation reaction that forms powdery metallic tantalum at the salt surface.
  • Possibility of Bacteria-Induced Corrosion of Ancient Bronze Mirrors Found in Ground

    pp. 268-276

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    DOI:10.2320/matertrans.44.268

    Excavated bronze objects, depending on how long they have been in the ground and under what conditions, are generally corroded externally as well as having intricately corroded layers inside. To date, our group has performed metallurgical investigations on 18 ancient bronze mirrors and confirmed that pure copper lumps and several varieties of unidentified corrosion products have formed on the surface of the mirrors and in the corroded layers. Accordingly, we performed investigations to identify the corrosion products using an electron probe micro analyzer (EPMA), a scanning electron microscope (SEM) equipped with an energy dispersive spectroscope (EDS), a micro-X-ray diffraction analyzer (μ-XRD), and an X-ray photoelectron spectroscope (XPS), and discussed the possibility that bacteria play a role in inducing corrosion in ancient bronze mirrors. The results are as follows; (1) Amorphous SiO2 had formed in the outermost corroded layer I. (2) Cu2O (cuprite) and Cu(OH)2 had formed in the layers II and III, which comprise the first two internal layers adjacent to layer I. (3) Cu–Sn–Pb-complex oxide had formed in layer IV, the next internal layer. Small amounts of PbSO4 and an Sn-organic compound were also detected. (4) We observed that Cu2S (chalcocite) forms like mold on the polished surface of the corroded layers, especially notable on layer IV, after being mechanically polished and left to stand for about one month. Cu2S is presumed to be the resultant of sulfate reducing bacteria. (5) Numerous pure copper lumps appeared in layers or particles and tended to form in the vicinity of layer IV. (6) The evidence from these analyses suggest that microorganisms could have been the cause of the corrosion found in ancient bronze mirrors excavated from the ground.
  • Synthesis of Ferrite Nanoparticles by Mechanochemical Processing Using a Ball Mill

    pp. 277-284

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    DOI:10.2320/matertrans.44.277

    Ferrites with the spinel structure have a wide field of technological applications. In the present study, various ferrite (Fe3O4, CoFe2O4 and Ni0.5Zn0.5Fe2O4) nanoparticles were synthesized by mechanochemical reaction in aqueous solution of various chlorides (FeCl3, CoCl2 or NiCl2/ZnCl2) and NaOH in a horizontal ball mill. Structures, morphologies, compositions and magnetic properties of the synthesized nanoparticles were investigated using X-ray diffraction (XRD), analytical high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). It was revealed that the particle size of the ferrite nanoparticles can be controlled by milling conditions, such as the milling time and the pH value (R value) of starting solution. The average size of Fe3O4 particles milled for 259.2 ks and 432.0 ks at R=1 were 30 nm and 20 nm, respectively. Also, the particles milled for 259.2 ks at R=0.5 had the size of 100 nm. The formation of Fe3O4 nanoparticles from the aqueous solutions with the different R values proceeded via two different processes. In the case of R=1, α-Fe nanoparticles formed first, and then oxidized to become Fe3O4 nanoparticles. Meanwhile, in the case of R≠1, α-FeOOH phase formed, and changed to Fe3O4 nanoparticles by milling. For magnetic properties, the magnetization at 1.2 MA/m was the value of 72 μWb·m/kg after milling for longer than 86.4 ks with R=1. The coercivity was the maximum of 10.8 kA/m after milling for 259.2 ks with R=0.5. The particle sizes of CoFe2O4 milled for 259.2 ks at R=1 and Ni0.5Zn0.5Fe2O4 milled for 345.6 ks at R=1 were about 30 nm. The magnetization values of CoFe2O4 and Ni0.5Zn0.5Fe2O4 were about 55 μWb·m/kg, with coercivity values of 43.4 kA/m and 5.3 kA/m, respectively.
  • Control of Crystal Orientation in Deposited Films of Bismuth Vaporized in Laser and Resistance Heating Methods under a High Magnetic Field

    pp. 285-289

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    DOI:10.2320/matertrans.44.285

    Bismuth, a non-magnetic material with a crystal magnetic anisotropy was vaporized by laser and resistance heating methods and deposited on a glass plate as a substrate in a high magnetic field of 12 T. The glass plate was set at the position with the maximum magnetic field intensity in perpendicular to the magnetic field direction. In the case of the laser heating method, the tendency of crystalline orientation in a thin film obtained in the presence of the high magnetic field did not agree with the theoretical prediction derived from the viewpoint of magnetization energy, and the particles on the film surface became coarser. On the other hand, in the case of the resistance heating method, the tendency of crystalline orientation appeared as expected from the theoretical prediction and a finer particle size was obtained in the presence of the magnetic field. Furthermore, a new evaluation method for crystalline orientation has been proposed.
  • Effect of Under Bump Metallurgy and Reflows on Shear Strength and Microstructure of Joint between Cu Substrate and Sn-36Pb-2Ag Solder Alloy

    pp. 290-297

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    DOI:10.2320/matertrans.44.290

    The interfacial reaction between Sn–36Pb–2Ag (numbers are all in mass% unless specified otherwise) solder balls and Ni, Ag and Ni/Ag electroplated on a Cu substrate was investigated and the joint bonding strength was measured using a ball shear tester. The intermetallic Ag3Sn was observed at the interface of the Cu/Ag/solder joint and Ni3Sn4 was found at the Cu/Ni/solder joint. In the case of Cu/Ni/Ag substrate, the layer sequence was observed to be Cu/Ni/Ni3Sn4/Ag3Sn/solder. The Ag layer was completely consumed by formation of Ag3Sn but the Ni layer remained. Environmental tests showed that the Cu/Ni/Ag substrate retained better solder joint reliability than either Ni or Ag single plated Cu substrate. Two types of reflow profiles were tested and the specimen reflowed by a higher temperature profile showed a higher solder joint strength. Solder joint strength and microstructural change were observed with several reflow cycles in considering the real board mounting conditions. There was significant evolution of solder and joint microstructures with reflow cycles and it explained well the change of solder joint strength.
  • Fe-Pd Ferromagnetic Shape Memory Alloy Thin Films Made By Dual Source DC Magnetron Sputtering

    pp. 298-304

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    DOI:10.2320/matertrans.44.298

    Fe–Pd films have been deposited onto fused quartz substrates using a dual source dc magnetron sputtering apparatus, equipped with two independent targets of pure Fe and Pd. The Pd content of deposited films can be controlled with an accuracy of 1 at%Pd by varying the power for the Pd target at constant power for the Fe target. Fe–Pd films containing about 29 at%Pd show a fct structure after annealing at 900°C followed by quenching into iced water. These films underwent a thermoelastic fcc-to-fct martensitic transformation and the fct-phase region, where the fct phase is present at room temperature in the annealed films, has a tendency of shifting toward higher Pd content with increasing film thickness. This thickness effect is attributed to the difference in internal stress created during annealing. The martensite start temperature (Ms) of films containing 28.5–30.0 at%Pd was higher than room temperature, and it became lower with increasing Pd content. When Fe–30 at%Pd films were separated from the quartz substrate, they showed shape memory behavior upon heating after deformation.
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  • Chemical Transportation of Heavy Metals in the Constructed Wetland Impacted by Acid Drainage

    pp. 305-312

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    DOI:10.2320/matertrans.44.305

    Chemical transportation of heavy metals in the constructed wetland impacted by acid drainage was investigated seasonally using a combination of the selective sequential extraction of the sediments with elemental analysis of the emergent vegetation in the wetland. Manganese was dissolved from sediments in the constructed wetland by the contact with acid drainage, and then precipitated again as ion-exchangeable forms. It was expected that a part of Mn and Fe bound to oxides were flown out of the wetland as suspended particulate matters. It was observed that there is passive absorption of Mn in leaves of Phragmites austlaris in the upstream of the wetland. The transportation of Cu clearly showed the seasonal variation: there was the decomposition of organic substances with high molecular weights by soil microorganisms in summer. Therefore, Cu was complexed to the humic substances, and dramatically adosorbed onto the roots of Phragmites austlaris in down stream of the wetland. It was also observed that there is active absorption of Fe in roots and leaves of Phragmites austlaris. Most of the zinc was strongly bounded to the sediments, therefore, scarcely uptaken to the vegetation. It was also found that there were heavy metal distributions between plant organs.
  • Use of Kerosene to Improve Toner-Ink Liberation for Office Paper Recycling

    pp. 313-319

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    DOI:10.2320/matertrans.44.313

    A method to disintegrate photocopied or laser printed waste office paper by weak agitation and using kerosene as a toner softening agent was investigated. Under the conventional method using only sodium hydroxide, 3.8% of toner was liberated from paper. This figure increased to 98.1% by using undiluted kerosene, and to 80.1% by using 1% kerosene emulsion. Residual toner particles adhered to only one or a few paper fibers after these kerosene treatments. If residual toner was also included in this figure, toner liberation would reach 100%. The use of surfactants as dispersion agents for kerosene decreased the degree of liberation because it interferes with the softening of toner. It was also confirmed that sodium hydroxide treatment in advance of the kerosene treatment is important to increase toner liberation.
  • Coagulation Using Kerosene for Magnetic Deinking of Waste Office Paper

    pp. 320-326

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    DOI:10.2320/matertrans.44.320

    A method for disintegrating waste office paper using kerosene was reported in our previous paper, which achieved almost a 100% liberation of toner from paper fibers. The liberated toner must be completely separated to realize effective deinking. Recently, a new method for deinking waste officer paper by magnetic separation after hetero-coagulation of magnetic and non-magnetic toner by 1-octadecanol was reported by Augusta et al. Under this method, coagulation was carried out at 72°C. The 1-octadecanol liquid was then cooled to produce strong solid coagulates. As reported in our previous paper, kerosene has the ability to soften toner, and strong coagulates for magnetic separation may be produced by their adhesion when used as a flocculant. The present study investigated the size of toner particles liberated by the kerosene disintegration method, and compared the bonding strength between the toner particles coagulated by the addition of kerosene as a flocculant to those coagulated with 1-octadecanol. After these investigations, the coagulating and deinking properties of kerosene and 1-octadecanol were compared by rejecting toner coagulates with a neodymium-boron magnet. The results showed that nearly perfect deinking can be achieved with little paper loss, even in ambient temperature, due to the large and strong coagulates produced by this method. When kerosene was used in the disintegration and coagulation stages, the average coagulate size was 1114 μm, and a deinking percentage of 98.4% was attained through separation with a neodymium-boron magnet.
  • Diagnosis of Oxide Films by Cavitation Micro-Jet Impact

    pp. 327-335

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    DOI:10.2320/matertrans.44.327

    Oxide films form readily when aluminum alloy castings are melted and/or poured. They could be primary or secondary types of oxide films. The former type is inherited from the ingot and has existed in aluminum alloy casting for a long period of time. During the filling of the mold cavity, the free unstable surface of the molten metal causes a secondary oxide film to exist on the aluminum alloy castings. The oxide films are usually rich in oxygen and are difficult to observe by optical micrographs. This paper presents a simple but powerful method to observe the shape and size of oxide films on the aluminum matrix. During ultrasonic-vibration treatment, cavitation bubbles nucleated, grew and collapsed, generating micro-jets on the surface of sample. The water micro-jets then had an impact on the oxide film initiating micro-cracks. The cracks grew or became linked together which caused fractures in the oxide film. Small or tiny oxide particles detached from the oxide film to erode the surface of the treated sample. This eroded surface would show as a foggy mark via visual or optical observation. A series of photographs were made and are shown to illustrate the cavitation erosion process of oxide film on the surface of an aluminum sample. In addition, the presented method was shown to be useful in the diagnosis of oxide films that formed on aluminum and magnesium alloys, including the ingots, casting or wrought products.

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