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

MATERIALS TRANSACTIONS Vol. 52 (2011), No. 10

  • Using the Low-Cost Waste Materials for Heavy Metals Removal from the Mine Wastewater

    pp. 1849-1852

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    DOI:10.2320/matertrans.M2011191

    The possibility of application of low-cost and easily available materials such as cardboard or sawdust for the heavy metals removal from the acid mine water was investigated. The sawdust was obtained from oak and fir-wood. Those materials were tested on the real acid mine wastewater that contained copper, iron, zinc, nickel, and manganese in the concentrations above the maximal allowed level. The adsorption degrees of those elements were investigated. The results were shown that the iron was mechanically removed. The results of chemical analysis of effluent obtained by the use of sawdust from fir-wood indicate that the values for iron and nickel ions were lower than allowed values by the legislative direction. The highest value for copper adsorption degree of 98.31% was achieved at pH value of 7.94. Content of manganese in the effluent and at the end of process, was near the initial value. Using the sawdust obtained from oak as the adsorption material, zinc and manganese concentration in the effluent was near the start values and copper and iron content was decreased but the values were higher than allowed.
    Using the cardboard, the copper adsorption degree was up to 95 mass%, iron content was under the limit value for the applied chemical detection method. The content of the manganese was not changed and the content of the zinc was decreased but the concentration was over the maximum allowed value.
  • Effect of Aging Treatment on Ultra-Fine Grains and Si-Phase in Al-0.5%Si Alloy Fabricated by ARB Process

    pp. 1853-1859

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    DOI:10.2320/matertrans.L-M2011819

    Using TEM observation and Vickers micro-hardness measurements, this study investigated microstructural changes resulting from aging treatment of ultrafine-grained (UFG) Al-0.5%Si alloy fabricated with a six-cycle accumulative roll-bonding (ARB) process, which includes severe plastic deformation. Results show that the mean grain size of the UFGed Al-0.5%Si alloy produced by the ARB was 253 nm. The hardness of specimens aged at 373 K and 423 K decreased monotonously with increasing aging time in the initial stage of aging. The hardness value of the specimen aged at 373 K then became higher than the value of the specimen aged at 423 K after 10 ks. TEM observation revealed that the mean grain size of the UFG specimen aged at 373 K was less than that of the specimen aged at 423 K. Moreover, results confirmed that Si phase precipitates on the {111} planes on the matrix in the UFG specimen aged at 373 K and 423 K. The mean size of Si-phase in the UFG increased with aging time. The Si phase formation in the UFG specimen aged at 373 K is less than that of 423 K in long-term aging. However, the formation of Si phase on the grain boundaries is more conspicuous than in UFG specimens aged at 373 K and 423 K. These results suggest that restraint of the growth of UFG with aging resulted from Si phase precipitation on the grain boundary and lowering of the aging temperature. Moreover the formation of Si-phase in the UFG suggests precipitation hardening in the ARB-processed Al-Si alloy.
  • The Structures of Precipitates in an Mg-0.5 at%Nd Age-Hardened Alloy Studied by HAADF-STEM Technique

    pp. 1860-1867

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    DOI:10.2320/matertrans.M2011163

    The crystal structures and microstructures of precipitates formed in an Mg-0.5 at%Nd alloy aged at certain temperatures ranging between 170°C and 250°C are studied in detail by high-angle annular detector dark-field scanning transmission electron microscopy. The precipitation sequence can be presented as Mg-solution → GP-zone → β′ (orthorhombic) → β1 (fcc). At the early stage of aging (170°C for 2 h), fine precipitates of planar GP-zones appear in parallel to (100)m planes, with a thickness of sub-nm and a length of 5–15 nm (the subscript letter of m denotes matrix). With an advance of aging, the GP-zones increasingly grow larger and combine with the neighbours, thus making themselves further prolonged along the directions addressed above. When reaching at the top-stage of aging (170°C for 100 h), the alloy additionally allows the β′-phase to coexist, taking the form of lens-shape with a thickness of 2–5 nm and a diameter of 5–15 nm. The β′-phase has an orthorhombic structure (Mg7Nd) with a=0.64 nm, b=1.1 nm, and c=0.52 nm, which is coherently connected to the matrix. At the stage of over-aging, both the GP-zones and the β′-phase disappear and instead coarse precipitates of the stable β1-phase (Mg3Nd; fcc) are formed with particular crystallographic relations of [001]m||[110]p and [110]m||[112]p (the subscript letter of p denotes precipitate).
  • Microstructural Evolution of Nanoindented Ag/Si Thin-Film under Different Annealing Temperatures

    pp. 1868-1875

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    DOI:10.2320/matertrans.M2011160

    The microstructural evolution of Ag/Si thin-film system via nanoindentation and annealing is investigated. Ag films with a thickness of 500 nm are deposited on (100) silicon substrates. Nanoindentation is performed to a maximum depth of 800 nm, and the indented specimens are then annealed at temperatures of 600°C, 700°C and 800°C, respectively. In the as-deposited specimen, the indentation process results in a phase transformation from a diamond cubic structure to amorphous phase within the indented zone. Following annealing at 600°C, the microstructure of the indented zone changes from a fully-amorphous state to a mixed amorphous/nanocrystalline state. The diffusion ability of the Ag atoms into the silicon substrate is enhanced as the annealing temperature is increased. Consequently, the microstructures of the indentation zones in the specimens annealed at 700°C and 800°C, respectively, contain a mixture of amorphous phase, nanocrystalline structures and Ag2Si silicide phase. Overall, the results presented in this study confirm that the annealing temperature has a significant effect on the formation of Ag2Si silicide phase in nanoindented Ag/Si thin-film systems.
  • Behavior of Branch Cracking and the Microstructural Strengthening Mechanism of Polycrystalline Ni-Base Superalloy, IN100 under Creep Condition

    pp. 1876-1884

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    DOI:10.2320/matertrans.M2011074

    Recently, the development of the high-efficiency technology for gas turbine and jet engine is required to minimize carbon dioxide and nitrogen oxide emission. It is effective way to increase the operational temperature to develop the high-efficiency technology for high temperature instruments. To increase the operating temperature, advanced Ni-base superalloys have been developed as a turbine blade material.
    Even though a Ni-base superalloy is used for a structural component, creep damages and creep cracks may be caused due to the external tensile load under high temperature conditions. Therefore, a predictive law of creep crack growth life is necessary to maintain operational safety.
    This study is aimed to clarify the branch cracking behavior due to the microstructural strengthening mechanism of polycrystalline Ni-base superalloy IN100 under the creep condition. The creep crack growth tests were conducted at a temperature of 900°C. The creep crack growth behavior and creep damage formulation were observed by in-situ observational system and FE-SEM/EBSD. Additionally, two-dimensional elastic-plastic creep finite element analyses were conducted for the model which describes the experimental results. The creep crack growth behavior and the creep damage progression were found to be affected by the distribution behaviors of grains and grain boundaries around the notch tip. By comparison of experimental results with mechanical analysis using FEM analyses, mechanisms of the creep crack growth and the creep damage formulation were clarified.
  • Transient Creep in High-Purity Aluminum at Ultra-Low Strain Rate and Room Temperature by Constant Stress and Changing-Stress Experiments

    pp. 1885-1889

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    DOI:10.2320/matertrans.M2011175

    Creep of high-purity aluminum (5N Al) at room temperature and ultra-low strain rate was investigated by a high sensitive helicoid-spring specimen technique under conditions of constant and changing stress. Creep deformation consists of transient creep stages, and no secondary creep stage was observed. Li’s equation showed a good fit to the experimental curves.
    During nominal steady-state creep, the stress exponent is equal to one regardless of initial state of specimens. However, the nominal steady-state creep rate for water quenched 5N Al is one order less than that for the static recovered specimens due to work hardening. With increase in stress, creep strengthening (the creep rate progressively decreasing in subsequent segments) was observed, which is due to different hardening remains because changing-stress creep experiment was conducted in the transient creep stage. Those phenomena of work hardening indicate creep deformation is controlled by recovery and work-hardening mechanism.
    During transient creep, every decrease in stress is associated with the large and long anelastic backflow. The anelastic transient strain for stress reduction is equivalent to elastic deformation corresponding to the applied stress, while transient strain is 2.5 times greater than the equivalent elastic deformation regardless of whether stress increases or is constant. The transient effect was suggested to be due to a mix of anelastic behavior caused by the internal redistribution of stress and inelastic behavior.
  • Creep Mechanisms in a Fine-Grained Al-5356 Alloy at Low Stress and High Temperature

    pp. 1890-1898

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    DOI:10.2320/matertrans.M2011143

    Monotonic creep tests were carried out on fine-grained Al-5356 alloy with grain size dg=5±0.5 μm by the helicoid spring specimen technique at homologous temperatures ranging from 0.63 to 0.74 and applied stresses of 0.13 to 1.42 MPa. At stresses lower than about 0.50 MPa, Bingham-type viscous creep with activation energy Q=80±25 kJ/mol, characterized by a threshold stress which decreases with increasing temperature, was predominant. At a stress above about 0.50 MPa, grain boundary sliding with a stress exponent n=2 and Q=85±25 kJ/mol obviously contributed to the measured creep data. Stress redistribution was evaluated, and it did not greatly influence the stress exponent. The creep mechanisms were elucidated with respect to standard creep models supported by the substructures studied by transmission electron microscopy. Viscous creep (n=1) was identical to be Harper-Dorn creep controlled by dislocation core diffusion. The motion of jogs on edge dislocations dependent on dislocation core diffusion was observed to control the creep. Grain boundary sliding accommodated by slip with n=2 was noted, while hardening and the recovery of dislocations at grain boundaries were suggested to control the creep. Microstructural observations along with a determination of parametric variations in the creep rates were useful for identifying the underlying deformation mechanisms.
  • Ruthenium Solubility and Dissolution Behavior in Molten Slag

    pp. 1899-1904

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    DOI:10.2320/matertrans.M-M2011821

    The solubility and the dissolution mechanism of Ru in the CaO–SiO2, Na2O–SiO2, and Na2O–SiO2–Al2O3 slag systems have been investigated in various conditions in order to understand the Ru dissolution behavior during pyrometallurgical recovery. The Ru solubility increases with an increase in the oxygen partial pressure and content of basic oxides; however it decreases with an increase in temperature. This implies that Ru dissolves in slag as an acidic oxide. The dissolution reaction is found to be Ru+3/4O2+1/2O2−=RuO2 and ΔH°=−130±20 kJ/mol. From the dissolution behavior, Ru loss into the slag during Ru recovery by Cu smelting has been estimated to be about 50 ppmw.
  • Surface Hot Shortness of Copper Containing Steel in a Compact Strip Production Process

    pp. 1905-1911

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    DOI:10.2320/matertrans.H-M2011818

    The compact strip production (CSP) process has received much attention because it is environment friendly and can be used for recycling resources. However, steel scrap, the main material used in the CSP process, causes surface cracks in the hot strip being manufactured as a result of surface hot shortness by Cu and Sn in the steel scrap. This study investigates the influence of heat pattern on the brittleness of Cu-containing steels prior to treatment in a reheating tunnel furnace at 1100°C. The prior austenite grain size of a sample that was reheated from room temperature before being transferred to a tunnel furnace was finer than that obtained by the direct transfer process, and the crack depth was inhibited by 50%. In contrast, the prior austenite grain size of a sample obtained by a process in which austenite is reheated from a cooling stop temperature of 650°C–850°C was almost the same as that obtained by direct transfer to the tunnel furnace. However, the crack depth in the case of reheating from the cooling stop temperature of 650°C–850°C was greater than in the case of direct transfer. This deep cracking was caused by a noninternal oxidation area at the scale/steel interface.
  • Relationship between Foam Stabilization and Physical Properties of Particles on Aluminum Foam Production

    pp. 1912-1919

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    DOI:10.2320/matertrans.F-M2011817

    Experimental investigation of the foam stabilizing factors that influence aluminum foam fabrication is crucial to improve the foaming process. Solid particles contribute to an increase of the viscosity of the liquid phase and overall foam stability. Foam stability depends on the liquid type, wettability and the shape of solid particles. Even though a poor wettable particle contributes effectively to enhance liquid viscosity, the particle leads to the collapse of the foam cell due to the poor energy balance at the interface between the solid and the liquid. In our study, the effect of particles was investigated using both water solutions and an aluminum melts. We show that not only the relative viscosity, but also the physical properties of solid particles need consideration during aluminum foam production.
  • Mechanical Properties of Electron Beam Welded Spheroidal Graphite Cast Iron and Mild Steel Welded Joints

    pp. 1920-1925

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    DOI:10.2320/matertrans.F-M2011820

    Direct welding between spheroidal graphite cast iron (FCD700) and mild steel (SS400) was conducted using electron beam welding to study the microstructure and the mechanical properties of the welds.
    Results showed that one-pass welding yielded an over-hardened fusion zone exhibiting acicular martensite structure (815 HV) with cracks and porosities. Two-pass welding contained fewer porosities. Both one-pass and two-pass welding displayed acicular martensite and ledeburite within the microstructure of spheroidal graphite cast iron in heat-affected zone. The tensile strength of both one-pass and two-pass welded joints was lower than that of mild steel base metals. These joints ruptured at the fusion zone or the mild steel bond. However, two-pass welded joints demonstrated tensile yield stress values greater than or equal to those of mild steel base metals. Hardening of the fusion zone and the heat-affected zone of spheroidal graphite cast iron made the impact strength values of two-pass welded joints conspicuously lower than those of the spheroidal graphite cast iron base metal. The fatigue strength of two-pass welded joints almost equaled that of mild steel base metal, with a fatigue limit of 209 MPa.
  • Effect of B4C Size on Tensile Property of (TiB+TiC) Particulate Reinforced Titanium Matrix Composites by Investment Casting

    pp. 1926-1930

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    DOI:10.2320/matertrans.M2011079

    The aim of this research is to evaluate the microstructure and tensile property of in-situ particulate (TiB+TiC) reinforced titanium matrix composites (TMCs) synthesized by investment casting process. Different size of B4C (1500, 150 and 0.5 μm) were added to the titanium matrix during vacuum induction melting which can provide the in-situ reaction of 5Ti+B4C=4TiB+TiC. The tensile property of TMCs was investigated in accordance with the reinforcement distribution by B4C size. The size and morphology of in-situ reinforcements were quite different according to the B4C size. In-situ synthesized reinforcements by fine B4C were very minute and distributed homogeneously than coarse B4C. Moreover, the improvement of the tensile strength and ductility of TMCs was caused by not only load transfer strengthening but also the matrix grain refinement and homogeneous distribution of the reinforcements.
  • Numerical Simulation of Shrinkage Formation of Pure Sn Casting Using Particle Method

    pp. 1931-1938

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    DOI:10.2320/matertrans.M2011186

    Shrinkage formation often causes fatal defects in castings. Recently, the development of computer technology has provided us with a useful and effective method to predict shrinkage formation. A particle method is a Lagrangian method that uses discrete objects as calculation elements which is referred to as particles, and they can move freely in the space. Therefore, this method can calculate shrinkage formation directly. In this study, solidification simulation and flow simulation programs based on the particle method were combined considering the temperature-dependency of density. The program was applied to the solidification problem of a cylindrical pure Sn casting, and the predicted shrinkage was compared with experimental results. First, the calculation stability for a still fluid was discussed and an improved method was proposed. The flow of a fluid during solidification is quite slow; however, the particle method has a fundamental difficulty in calculating slow flow phenomena. Therefore, creep flow was assumed. When the inertia force was not considered, the calculation stability improved significantly, and introduction of a gravity adjustment coefficient reduced calculation time significantly. Next, the proposed method was applied to shrinkage formation analysis with an influence of air-cooling. As a result, predicted shrinkage shape agreed well with experimental result.
  • Preparation and Photocatalytic Property of TiO2 Columnar Nanostructure Films

    pp. 1939-1942

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    DOI:10.2320/matertrans.MAW201104

    The rutile TiO2 films with columnar nanostructure were prepared by combining the glancing angle deposition (GLAD) technique in magnetron sputtering system with the subsequent two-step annealing treatment. Experimental results showed that all the TiO2 films kept discrete columnar structures as the Ti films deposited by GLAD and accomplished the phase transition from Ti to rutile TiO2. Such TiO2 films performed photocatalytic activity effectively and reusably towards methyl orange under UV light irradiation, which demonstrates the potential applications in wastewater treatment.
  • Effects of Electron Beam Irradiation on Peeling Resistance of Laminated Sheet of High Strength Polypropylene (PP) and Bio-Adaptable Polydimethylsiloxane (PDMS)

    pp. 1943-1948

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    DOI:10.2320/matertrans.M2011129

    The effects of homogeneous low voltage electron beam irradiation (HLEBI) on the adhesive force (maxFp, oFp and minFp) and its energy (oEp) of peeling resistance of laminated sheets of bio-adaptable polydimethylsiloxane (PDMS) with transparency and high strength polypropylene (PP) without glue but with sterilization were investigated. Although both maxFp and oEp were 14 N·m−1 and 0.21 J·m−1 before treatment, HLEBI enhanced the maxFp and oEp up to the maximum values of 34 N·m−1 and 0.89 J·m−1 of the laminated sheets irradiated at 0.30 MGy, respectively. On the other hand, additional HLEBI reduces the maxFp, oFp, minFp and oEp of laminated sheets irradiated at more than 0.22 to 0.65 MGy, although they were apparently larger than those before treatment. In order to investigate the influence of EB irradiation on maxFp, oFp, minFp and oEp, electron spin resonance (ESR) signals related to dangling bonds were observed. When HLEBI generated dangling bonds in PP and PDMS, the dangling bonds probably served as reactive and bonding sites for each polymer at the interface. Consequently, HLEBI from 0.22 to 0.65 MGy reinforced the maxFp, oFp, minFp and oEp of the laminated sheets. Therefore, it was concluded that HLEBI was probably a useful tool for quick lamination of bio-adaptable PDMS and high strength PP.
  • Investigation of Changes in Phases and Properties of a TTCP/DCPA/CSH Cement Immersed in Hanks’ Solution

    pp. 1949-1953

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    DOI:10.2320/matertrans.M2011152

    Investigated in this study are the changes in structure and properties of a tetracalcium phosphate/dicalcium phosphate anhydrous/calcium sulfate hemihydrate (TTCP/DCPA/CSH) cement immersed in Hanks’ solution. Experimental results show that the phase transition involving the hydration of CSH and formation of calcium sulfate dihydrate (CSD) continues up to 7 d of immersion. The phase transition from TTCP/DCPA to hydroxyapatite (HA) is substantially completed after 14 d; after that, both CSH and CSD phase largely diminished, whereas HA becomes and remains to be the only dominant phase throughout 42 d of immersion. A maximum compressive strength is reached; after that, the cement gradually decreases in strength. After 42 d, its CS value is down to 8 MPa. The long-term pH value of the Hanks’ solution wherein the cement is immersed remains in the range between 5.4 and 7.0. The cytotoxicity test reveals that the viability value of the cells incubated with conditioned medium of cement extraction is 85% that of Al2O3 control and 84% that of blank medium for an extraction ratio of 0.2; and 90% that of Al2O3 control and 93% that of blank medium for an extraction ratio of 0.1.
  • An Effective Computational Approach to the Parametric Study of the Cathode Catalyst Layer of PEM Fuel Cells

    pp. 1954-1959

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    DOI:10.2320/matertrans.M2011101

    We propose an integrated modeling, prediction, and analysis framework for the parametric study of the cathode catalyst layer (CCL) of PEM fuel cells. A parametric study is performed on a macro-homogeneous film model of the CCL. An artificial neural network (ANN) is then used in order to model and predict the effect of various structural parameters on the activation overpotential of the CCL. The application of the ANN approach is an asset to deal with the complexity of this problem and leads to considerably save the computational time and cost and to remove undesired computational errors. The proposed computational approach shows that an increase in the platinum mass loading causes a decrease in the activation overpotential or equivalently an increase in the CCL performance. The main effects of increasing the carbon mass loading, gas diffusion layer (GDL) volume fraction in the CCL, and CCL thickness are that the activation overpotential is going up. GDL porosity has almost no effect on the CCL performance while the CCL performance has a quadratic behavior with respect to the membrane volume fraction in the CCL. Further investigation is done in order to quantify these effects as well as the combined effects of these parameters.
  • Multi-Walled Carbon Nanotube-Aluminum Matrix Composites Prepared by Combination of Hetero-Agglomeration Method, Spark Plasma Sintering and Hot Extrusion

    pp. 1960-1965

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    DOI:10.2320/matertrans.M2011146

    Multi-walled carbon nanotubes (MWCNTs) with outstanding mechanical properties are considered as an ultimate reinforcement for conventional metals such as aluminum (Al), though they require uniform dispersion and intimate contacts with the host metal matrix. However, bundled structure of chemically stable, pristine MWCNTs has been the main challenge to achieving the expected structural reinforcement. In addition, the sole contribution of MWCNTs in strengthening the metal matrix has not been recognized yet, due to the concurrent strengthening mechanisms such as metal’s work hardening, grain refinement, etc. Here, we prepared MWCNT-Al matrix composite powders with uniform MWCNT dispersion by using hetero-agglomeration principle, and fabricated fully dense 1.0 vol% MWCNT-Al matrix composite bulk by using spark plasma sintering (SPS) and a subsequent hot extrusion process, with a 40% improved tensile strength and an elongation to failure of 27.3% similar to that of cast pure Al. During the SPS process, the nanoscale surface defects of MWCNTs were infiltrated by momentarily formed liquid Al and an intimate Al4C3-free interface was formed between MWCNTs and bare Al matrix. After the hot extrusion process, straight MWCNTs aligned in the extrusion axis found intimate contacts with the dynamically recovered, crack-free Al matrix. Our study suggests that the tensile improvement realized in our extruded/SPSed composites is directly originated from an effective load transfer at the MWCNT/Al interface, because no evidence of Al work hardening or the formation of interfacial Al4C3 crystals was detected.
  • Improvement in the Frequency Response of Loudspeakers by Using Diamond-Like Carbon Film Coatings

    pp. 1966-1971

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    DOI:10.2320/matertrans.M2011080

    It is well known that a diamond-like carbon (DLC) film has a high mechanical hardness and Young’s modulus. One of the beneficial properties of a DLC film is its ability to change the sound velocity in loudspeakers through its application as a hard coating. In the present study, DLC films were coated onto polyetherimide (PEI) diaphragm substrates at low temperature with radio-frequency (RF) magnetron sputtering. Amorphous DLC films deposited at an RF power of 150 W and with a deposition time of 3 h have a high IDIG ratio and a low surface roughness. The IDIG ratio and surface roughness were 2.27 and l.21 nm (Ra), respectively. From frequency response analysis of the DLC film on the diaphragm, we found that the frequency response increased by 0.2∼1.2 dB on average. This confirmed the excellent adhesion of DLC films onto PEI (or polymer) substrates for future potential applications in acoustic wave devices.
  • CO2 Sequestration via a Surface-Modified Ground Granulated Blast Furnace Slag Using NaOH Solution

    pp. 1972-1976

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    DOI:10.2320/matertrans.M2011110

    This study investigates the improvement of the CO2 sequestration percentage of a ground granulated blast furnace slag (GGBF-slag) with surface modification using a NaOH solution. The amount of CO2 sequestration of the GGBF slag increased via the surface modification with the NaOH solution in the direct carbonation method. The increase of the carbonation percentage of the GGBF slag resulted from the increase in the hydraulic activity of the GGBF-slag. The carbonation percentage on the basis of the total calcium oxide of the GGBF slag was approximately 10 times larger than that of the GGBF-slag without the surface-modification. The carbonation rate depended on the morphology of the calcium carbonates formed on the surface of the GGBF-slag.
  • Preparation and Characterization of Anthocyanin Dye and Counter Electrode Thin Film with Carbon Nanotubes for Dye-Sensitized Solar Cells

    pp. 1977-1982

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    DOI:10.2320/matertrans.M2011063

    This study mainly explores the incorporation of counter electrode thin film and extracted natural anthocyanin dye in dye-sensitized solar cells (DSSCs). We adopt single-walled carbon nanotubes (SCNTs), with diameters of 1–2 nm and lengths of 1–20 μm, as well as multi-walled carbon nanotubes (MCNTs), with diameters of 10–30 nm and lengths of 10–15 μm. This study also uses a doctor bade to coat the purified carbon nanotubes on fluorine-doped tin oxide (FTO) conductive glass, so as to form thin film with single layer thickness of around 100 μm. In addition, for preparation of natural dye, anthocyanin dye is extracted from mulberry fruits. The experimental results show that the DSSCs which are incorporated with purified SCNT counter electrode thin film and anthocyanin dye extracted from mulberry fruit can achieve the photoelectric conversion efficiency of 0.672%.
  • Carbonation of Chrysotile under Subcritical Conditions

    pp. 1983-1988

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    DOI:10.2320/matertrans.M2011155

    The carbonation of chrysotile [Mg3Si4O10(OH)4] under subcritical conditions was experimentally investigated in alkali solution, and the chemical composition as well as the morphological and structural changes were discussed. The starting material was hydrothermally treated by aqueous direct carbonation at a temperature of 100°C and a CO2 partial pressure range of 0.5 MPa∼4 MPa at pH 13. Highly crystalline magnesite was synthesized under a CO2 partial pressure of 3 MPa. The carbonation rate increased at the proportional rate according to the applied CO2 pressure to approximately 57%. The surface morphology of chrysotile changed from the fibrous form to a round or oval shape at the initial stage and subsequently to magnesite with well-faceted rhombohedral planes.
    The dissolution rate of Mg was higher than Si, such that the Mg:Si ratio of chrysotile decreased from 1.56 to 0.4∼0.6 as the reaction time increased. The resultant silica-rich layer of the reaction product ultimately changed through the Mg-depleted skeletal phase to the amorphous silica phase. The experimental results suggest that carbonation in alkali solution under subcritical conditions is of great significance because an excessive amount of acid and alkali reagents can be eliminated in the carbonation process.
  • Influence of Rhenium on the Grain Boundary Strength, Phase Evolution, and High Temperature Mechanical Properties of a Fine-Grain Nickel-Base Superalloy at 982°C

    pp. 1989-1997

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    DOI:10.2320/matertrans.M2011136

    The influence of Re on the grain boundary (GB) strength, phase evolution, and 982°C mechanical properties of fine-grain Mar-M247 superalloy was investigated. Quantitative statistical analysis showed that an increase of Re content in Mar-M247 resulted in a decrease of the size, and an increase in the number of GB carbides. The results of tensile and 982°C/200 MPa creep tests showed that tensile properties and creep life both increase with an increase in Re up to a maximum at 3 mass%. The tensile and GB strength increased with increasing the number of fine GB carbides. The addition of 1∼3 mass% Re reduced steady-state creep rates and postponed the onset of the acceleration stage in three ways: (1) by increasing the amount of primary cuboidal γ′ phase; (2) by increasing the strength of γ matrix; and (3) by increasing the development of γ′ raft. It also prolonged the duration of the accelerating creep stage by refinement and an increase in the number of GB carbides. The above mentioned factors resulted in a prolongation of creep life. It is noted that the GB carbide evolution and GB strengthening effect by addition of Re have not been reported in the nickel-base superalloy before. However, addition of greater amounts of Re, such as 5 mass% Re, causes deterioration of the tensile and creep properties due to the formation of P phases.
  • Dynamic Filling Characteristics of a Capillary Driven Underfill Process in Flip-Chip Packaging

    pp. 1998-2003

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    DOI:10.2320/matertrans.M2011151

    This study investigates the dynamic flow characteristics of capillary-driven underfill flows in a flip chip package. In the present study, we used two different bump arrays using Sn-2.5Ag solder balls with 80 μm and 100 μm diameters on commercially available flip chips, which have different pitches of 150 μm and 180 μm. First, we measured surface tension and viscosity with a rheometer and a tensiometer, respectively, and conducted an experimental visualization of the dynamic filling behavior of the underfill flows. From the captured images, we estimated the filling times, which can be affected by two important factors: bump arrangements and resin viscosities. In addition, we conducted a FVM (finite volume method)-based numerical simulation using commercial CFD code (Fluent v. 6.3.26), and compared its numerical results to both the experimental data and the analytical solutions given by the previous model described by Wan et al. (2005). The numerical predictions and analytical solutions estimating filling time were in good agreement with the experimental data, and the increase in spatial density of solder bumps allowed the flow to fill more slowly due to the increase in flow resistance. We conclude that the non-Newtonian characteristics and bump arrangement are very important factors in the design of flip-chip packaging.
  • Evaluation of Nitrogen Conversion Ratio on Reaction between BN and Aluminum

    pp. 2004-2006

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    DOI:10.2320/matertrans.M2011184

    The fundamental reaction behavior between aluminum powder and boron nitride (BN) powder was investigated, and a quantitative evaluation of aluminum nitride (AlN) formation was carried out. As a result of differential scanning calorimeter (DSC) analysis, an exothermic reaction between BN and aluminum was detected at temperatures between 1073 and 1173 K. The conversion ratio of BN to AlN increased with increasing heating temperature. However, the nitrogen conversion ratio appeared to saturate with a holding time of 3.6 ks at temperatures above 1273 K. The nitrogen conversion ratio increased by using 1 μm BN powder instead of 10 μm BN powder. The effect of using the fine BN powder was significant especially when the heating time was short (<300 s).
  • Rapid Synthesis and Consolidation of Nanostructured Mg2SiO4-MgAl2O4 Composites

    pp. 2007-2010

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    DOI:10.2320/matertrans.M2011188

    Nanopowders of MgO, Al2O3 and SiO2 were made by high energy ball milling. The rapid sintering of nanostructured MgAl2O4-Mg2SiO4 composites was investigated by the pulsed current activated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured MgAl2O4-Mg2SiO4 composites were produced with simultaneous application of 80 MPa pressure and pulsed current of 2800 A within 2 min. The sintering behavior, grain size and mechanical properties of MgAl2O4-Mg2SiO4 composites were investigated.

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