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

MATERIALS TRANSACTIONS Vol. 56 (2015), No. 8

  • Relation between Vickers Hardness and Bragg-Edge Broadening in Quenched Steel Rods Observed by Pulsed Neutron Transmission Imaging

    pp. 1147-1152

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    DOI:10.2320/matertrans.M2015049

    The width of crystal lattice plane spacing (d-spacing) distribution related to microscopic-strain and crystallite size in a martensite phase in a 2 cm thick quenched-ferritic steel sample was quantitatively mapped in real space by a Bragg-edge broadening analysis of spectral data from a pulsed neutron transmission experiment. This analysis was performed under the condition that the instrumental resolution parameters, determined from the data of ferrite in the same sample without microscopic-strain and crystallite size effects, were unchanged over the sample area, and assuming that the d-spacing was distributed according to a Gaussian function in the martensite area. As a result, the full width at half maximum (FWHM) of the Gaussian d-spacing distribution in the martensite was extracted at each position in a sample. Consequently, it was found that the real-space distribution of the FWHM of the d-spacing distribution is closely correlated with a real-space distribution of the Vickers hardness that corresponds to the quantity of martensite. Furthermore, it was indicated that the Vickers hardness was proportional to the FWHM of the d-spacing distribution. The results suggest that it will be possible to measure the Vickers hardness in the martensite non-destructively by using the Bragg-edge neutron transmission method.
  • Titanium Powders via Gas-Solid Direct Reaction Process and Mechanical Properties of Their Extruded Materials

    pp. 1153-1158

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    DOI:10.2320/matertrans.L-M2015816

    In the present study, titanium (Ti) powders containing some nitrogen (N) atoms were prepared by a gas (N2)-solid (Ti starting powder) direct reaction process, and consolidated as an extruded rod with high strength and ductility at ambient temperature. Nitrogen content of the Ti powders via the gas-solid direct reaction process dramatically increased as the treatment time increased while no change in the oxygen content. Ti2N layers were formed at Ti powder surfaces via the above gas-solid reaction, however, no formation of Ti2N compounds was found in the extruded Ti materials. That is, the solid solution of N atoms in α-Ti was complete, and expected to enhance the mechanical strength of Ti materials. 0.2% yield strength (YS) and ultimate tensile strength (UTS) of wrought Ti-N materials were proportional to the additive nitrogen content, and the decrease of elongation was very limited. For example, the extruded Ti powder material with nitrogen content of 0.74 mass% revealed 974 MPa in 0.2%YS, 1120 MPa in UTS and 21.7% in elongation. These tensile properties were superior to those of the conventional Ti-6Al-4V alloy with the standard specification of ASTM B348-00-GR5 (0.2%YS: 918 MPa, UTS: 1047 MPa, elongation: 16.6%).
  • The Deformation Modes of Rock Slopes due to Excavation in Mountain-Type Mines

    pp. 1159-1168

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    DOI:10.2320/matertrans.M-M2015814

    This paper discusses an investigation of mining-induced elastic deformation of a cut rock slope formed in a mountain-type mine using a two-dimensional finite element method. The horizontal elastic deformation mechanism is discussed, including the effects of the Poisson’s ratio, slope angle and progression of the excavation. The results show a clear dependence of the deformation modes characterized by extension, contraction or shear distortion of rock mass, on these three effects, in which the direction of rock movement at the surface due to excavation was opposite. Four effects contribute to the deformation mechanism in mountain-type mines: the Poisson effect (PE), the distributed load effect (DLE), bending effects and shear distortion. Forward surface displacement of the cut rock slope was found to occur during the early stages of excavation due to the release of horizontal compressive stresses due to bending effects around the middle of the mountaintop. As the excavation progresses, forward or backward horizontal surface displacement was found to occur due to PE or DLE, respectively, which depends on the Poisson’s ratio in the subsequent stages of excavation. Asymmetric stress release due to excavation affects the horizontal deformation of the mountain, and induces a moment enhancing the backward displacement due to shear distortion. It should be noted that the direction of the surface displacement of the rock slope could change from forward to backward as the excavation progresses, even though the rock slope may be stable. This is very important in the interpretation of surface displacement monitoring using the Automated Polar System and/or Global Positioning System. In the interpretation of the internal displacement measured using extensometers, we should consider extension during the early stages of excavation, followed by slight contraction during the latter stages, as a sign of a stable cut rock slope in a mountain type mine.
  • Tensile Shear Strength Improvement of 18-8 Stainless Steel/CFRP Joint Irradiated by Electron Beam Prior to Lamination Assembly and Hot-Pressing

    pp. 1169-1173

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    DOI:10.2320/matertrans.M2015105

    Adhesive 2-layer lamination joints of 18 mass%Cr-8 mass%Ni austenite stainless steel and carbon fiber reinforced polymer (18-8/CFRP joint) were prepared using a new adhesion method consisting of applying low dose of 0.13 MGy of homogeneous low energy electron beam irradiation (HLEBI) to connecting surfaces of the 18-8 and CFRP prior to lamination assembly and hot-pressing in vacuum below 1 Pa for 2 h at 401 ± 0.5 K. Although untreated 18-8/CFRP joint exhibited decent adhesion by hot-pressing, application of 0.13 MGy HLEBI dose apparently improved the tensile shear strength, τB of the 18-8/CFRP joint 58% at median accumulative probability (PB = 0.50) from 4.0 to 6.3 MPa. In addition, applying HLEBI from 0.13 and 0.30 MGy was found to enhance the τB at all PB. Based on the 3-parameter Weibull equation, the statistically lowest τB value at PB = 0 (τs) was increased from zero to 4.39 MPa by the 0.13 MGy HLEBI. XPS (X-ray photoelectron spectrometry) measurements detected carbon on the shear-fractured 18-8 interface indicating the residual epoxy adhered well to the 18-8 by the HLEBI. This is probably a result of adhesion force of 18-8/CFRP being made stronger than the cohesive force of epoxy polymer in the CFRP itself. Since HLEBI cuts the chemical bonds and generates active terminated atoms with dangling bonds in epoxy polymer and passive film on 18-8, the increased adhesion force in the 18-8/CFRP joint can be explained by the chemical bonding and coulomb attractive forces thus induced at the interface. Since the experimental data shows the optimum HLEBI dose is about 0.13 MGy, above which at 0.30 MGy the τB begins to drop off, carefulness in optimization is highly recommended when applying in industry to insure safety.
  • Density Dependency of Tempered Martensite Hardness in Sintered Carbon Steel

    pp. 1174-1178

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    DOI:10.2320/matertrans.M2015090

    The density dependence of tempered martensite hardness was studied and we have proposed a new equation to predict the hardness of tempered martensite sintered carbon steel. This was achieved by considering the density-dependent tempering value in the tempering parameter. The existence of porosity influenced both the decrease in tempered martensite hardness and the decrease in the activation energy for tempering, resulting in a lower tempering parameter. The variation of the hardness of tempered martensite predicted by the proposed equation was in good agreement with experimental data obtained under various tempering conditions and relative densities.
  • Optimization of Vacuum Hybrid Welding Process Parameters for YG8 Cemented Carbide and 42CrMo Steel Using Artificial Neural Networks

    pp. 1179-1185

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    DOI:10.2320/matertrans.M2015003

    The mechanical properties of the joint of YG8 cemented carbide and 42CrMo steel were studied by using CuZnNi filler metal in the vacuum hybrid welding. The parameters for optimizing the shear strength of joints were selected by orthogonal experiment, mainly including the brazing temperature, brazing time, diffusion temperature, holding time and diffusion pressure. The artificial neural network technique is a very practical tool for predicting the controllable parameters in the non-linear model. BP (Back Propagation) neural network was established under the environment of MATLAB software to simulate and predict designed process parameters. Thus, the optimal parameters were predicted by BP neural network and validated by experiments. The results show that the proposed BP model can obtain a non-linear relationship between the mechanical properties and process parameters. The predicted values are in good agreement with the experiments with the relative error of −0.2458% and the mean square error of 0.052%. The optimal parameters of BP neural network were obtained at brazing temperature (A) of 1045°C, brazing time (B) of 15 min, diffusion temperature (C) of 750°C, holding time (D) of 40 min and diffusion pressure (E) of 8 MPa, and the prepared joints showed the better mechanical properties like glossy surface, no apparent deformation, uniform brazing region and good adhesive interface, etc.
  • Mechanical and Magnetic Properties of Ni-Mn-Ga-Gd Ferromagnetic Shape Memory Alloys

    pp. 1186-1191

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    DOI:10.2320/matertrans.M2015143

    The effects of rare earth Gd addition on the mechanical and magnetic properties of polycrystalline Ni50Mn29Ga21−xGdx (0 \leqslant x \leqslant 5) ferromagnetic shape memory alloys were investigated in detail. The results show that an appropriate amount of Gd addition significantly improves the mechanical properties of Ni-Mn-Ga alloy. When the Gd content is less than or equal to 1 at%, the compressive strength enhances rapidly as Gd addition increases, and the subsequent increase slows down when the Gd content is in the range of 2 at%-5 at%. However, the compressive strain increases firstly and then decreases obviously. The Ni50Mn29Ga20Gd1 alloy exhibits the best overall mechanical performance among the Ni50Mn29Ga21−xGdx (0 \leqslant x \leqslant 5) alloys. Moreover, Gd doping changes the fracture type of Ni-Mn-Ga alloy. The spontaneous magnetization of Ni50Mn29Ga21−xGdx alloys at 300 K and 4.2 K decreases with the increase of Gd content. The mechanism on the influence of Gd content on the mechanical and magnetic properties is discussed.
  • Activity of Phosphorus Pent-Oxide and Tri-Calcium Phosphate in 2CaO·SiO2-3CaO·P2O5 Solid Solution Saturated with CaO

    pp. 1192-1198

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    DOI:10.2320/matertrans.M-M2015813

    Equilibrium between molten iron and the 2CaO·SiO2-3CaO·P2O5 solid solution saturated with CaO was measured by the chemical equilibrium method with the oxygen partial pressure of 5.22 × 10−12 atm at 1823 K and 1.41 × 10−11 atm at 1873 K. The activity of P2O5 relative to hypothetical pure liquid P2O5 was determined from the analyzed content of P in molten iron and reported thermodynamic data. For the compositions in which the CaO phase was detected by XRD after reaction, the activity of 3CaO·P2O5 was determined by the estimated activity of P2O5 and the activity of CaO which was unity due to its saturation. The activity coefficients of P2O5 and 3CaO·P2O5 in solid solution and the phosphorus partition ratio between molten iron and the mixture of 2CaO·SiO2-3CaO·P2O5 solid solution and CaO were also estimated. Besides, the activity of 2CaO·SiO2 and SiO2 in the solid solution were also estimated by applying the Gibbs-Duhem equation.
  • Effect of Electrolysis Condition on the Lightness and Surface Morphology of Ni Deposit from Chloride Electro-Winning Solutions

    pp. 1199-1206

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    DOI:10.2320/matertrans.M2014432

    To investigate the effects of current density and pH of the solution on the lightness and surface morphology of Ni deposit, Ni electrodeposition was performed at a current density of 100 to 500 A·m−2 and 7.2 × 105 C·m−2 of charge, in an unagitated chloride solution with pH 1 to 3, at 333 K. The composition and structure of the surface of deposits were analyzed by radio frequency glow discharge optical emission spectroscopy and three-dimensional scanning electron microscope (3D-SEM). The lightness of the Ni deposit decreased with increasing pH, and was also related to the current density with the minimum reached at 300 A·m−2. The concentration of the surface oxygen in the deposits increased with pH, with the highest value obtained at 300 A·m−2, which shows that the concentration of surface oxygen possibly affects the lightness. On the other hand, the surface of the Ni deposit was composed of several micrometers of pyramidal microcrystals and the mound formed by the aggregation of pyramidal microcrystals. To separate the two types of structural units, the deposits were cut every 200 nm from the top in the thickness direction using 3D SEM. The number and area of the deposits in the cutting plane were measured and it was found that the lightness of the Ni deposit depended on the surface structure. Therefore, the lightness of the Ni deposit seems to depend on both the surface oxygen content and the microstructure of the deposits.
  • Preparation of Ni-Al-Pt Coating on Ni-6 at%Cr Alloy by Electrodeposition Method and Cyclic-Oxidation Resistance

    pp. 1207-1213

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    DOI:10.2320/matertrans.M2015051

    The formation of a coating layer consisting of Ni, Al and Pt on a Ni-6 at% Cr alloy substrate was attempted by the electrodeposition of Pt and Al. The Pt and Al were deposited by electrolysis in an aqueous solution and molten salt, respectively. The cyclic oxidation resistance of the alloy with this coating was then evaluated in air at 1423 K. Particular attention has been paid to the effects of Pt in the coating and 6 at% Cr in the alloy substrate on the cyclic oxidation resistance. For the sample treated by Pt deposition, followed by the Al deposition, a coating layer comprised of an outer layer consisting of PtAl2 and Ni2Al3 and an inner layer consisting of Ni2Al3 was formed. This coating layer contained about 2 at% Cr. The cyclic oxidation test showed that for the sample with a coating consisting of Ni aluminide without Pt, a mass reduction due to spallation of an oxide scale took place during the oxidation test, whereas for the sample with a coating consisting of Ni aluminide containing Pt, no mass reduction took place. For the sample with a coating consisting of Ni aluminide containing Pt after the oxidation test, the formation of an adhesive Al2O3 scale was observed. The cyclic oxidation test also showed that for the sample with a coating consisting of Ni aluminide containing Pt formed on a pure Ni substrate, a large mass increase took place during the oxidation test, while for the sample with the coating formed on the Ni-6 at% Cr alloy substrate, such a mass increase did not take place. Such effects of Pt in the coating and 6 at% Cr in the alloy substrate on the cyclic oxidation resistance are discussed from the viewpoint of the formation of a protective Al2O3 scale.
  • Effect of Oxygen Evolution on Platinum Dissolution in Acidic Solution

    pp. 1214-1218

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    DOI:10.2320/matertrans.M2015116

    In the present study, we confirmed the enhancement of Pt dissolution during an oxygen evolution reaction (OER). In situ analysis using a channel flow double electrode showed anodic dissolution during the OER and cathodic dissolution from the reduction of Pt oxide. Pt dissolution during the OER showed transient dissolution behavior. Initiation of the OER triggered anodic Pt4+ dissolution; however, the dissolution was strongly inhibited by the development of oxides. Reduction of oxides formed in the OER region required lower potential than those formed below 1.5 V. The lower reduction potential increased the reduction rate of oxides and enhanced the instantaneous dissolution rate of Pt2+.
  • Pitting Corrosion of Stainless Steel 430 in the Presence of Thin MgCl2 Solution Films: Effects of Film Diameter and Thickness

    pp. 1219-1225

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    DOI:10.2320/matertrans.M2015099

    The pitting corrosion of Type 430 stainless steel under thin MgCl2 solution films was investigated under different relative humidities (RHs) to clarify the effect of film dimensions on this property. Thickness and diameter of the solution film were varied within 1–70 µm and 1–13 mm, respectively. No pitting corrosion was detected above 85% RH for all films dimensions. Below 75% RH, the probability of pitting corrosion occurrence decreased with decreasing diameter and thickness. No pit growth occurred when the diameter was approximately 1 mm.
  • Effects of Moisture in the Air on Characteristics of Strength in High Strength Spheroidal Graphite Cast Iron

    pp. 1226-1232

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    DOI:10.2320/matertrans.F-M2015812

    The purpose of this study is to investigate the effects of humidity on the strength characteristics in high strength spheroidal graphite cast iron with two phases, which is ferrite and pearlite. Three spheroidal graphite cast irons (FCD400(FDI), FCD500(FPDI.82) and FCD600(FPDI.55)) were used as specimens. In addition, heat treatment (Normalizing) was conducted in FCD500 (PDI). Tensile test conforming to JIS was carried out using these resultant four materials in air and water. The specimen used was of the 14A type. The relationship between tensile strength and area ratio of brittle fracture was investigated. Fatigue crack propagation test conforming to ASTM was also carried out using these materials. Stress ratio R was 0.1, and the specimen used was of the 1CT type with a thickness of 12.5 mm. The test was carried out at room temperature and three kinds of humidity: 0, 40 and 80%. The relationship between the characteristics of fatigue crack propagation and crack closure generated on the fracture surface was investigated.
    Though tensile strength in FDI and FPDI.82 was not influenced by water brittlement, strength in PDI and FPDI.55, which included pearlite, was decreased by water brittlement. This phenomenon may mainly be caused by the amount of parlite in the matrix. The threshold stress intensity factor range ΔKth of all materials increased with increasing humidity. Crack closure was investigated in all materials. It seemed to become marked with increasing humidity. In the low ΔKeff region of all materials (except FPDI.55, 80%), the fatigue crack propagation rate was almost the same because of oxide-induced crack closure of the ferrite included in the matrix. In the high ΔKeff region of FPDI and PDI, the rate was not the same. The acceleration was investigated because of effect of a phenomenon similar to the water embrittlement of pearlite included in the matrix.
  • Development of an Elasto-Viscoplastic Constitutive Equation for an Al-Mg Alloy Undergoing a Tensile Test during Partial Solidification

    pp. 1233-1241

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    DOI:10.2320/matertrans.L-M2015815

    Predicting hot tearing during direct chill casting using thermal stress analysis requires constitutive equations in both semi-solid state and below the solidus of the alloy. However, numerous difficulties have been hindered constitutive equations used heretofore for hot tearing predictions. (1) Testing methods for obtaining material constants were inappropriate. First, the elastic strain reversibility was unconfirmed. Second, a flat distribution of temperature in the specimen gauge length was not guaranteed. Third, strain was measured not from local strain but from cross-head displacement. Fourth, the melt-back phenomenon was unavoidable in test during partial remelting because of homogenization of the segregation structure. (2) Temperature dependence of the strain-rate sensitivity of stress was not considered. (3) Some material constants were inferred, not obtained experimentally. This study developed elasto-viscoplastic constitutive equations (Hooke’s and viscoplastic Norton-Hoff laws) for partially solidified state and below the solidus. To obtain material constants experimentally, two tensile tests for which issue (1) was addressed were conducted using Al-5 mass%Mg alloy. They were a tensile test after partial solidification and high-temperature tensile test with high-frequency induction coil. After the temperature dependence of elastic and viscoplastic properties was investigated, material constants were obtained and were compared with those obtained using earlier testing methods.
  • Laser-TIG Hybrid Welding of Magnesium Alloy T-Joint with Cold Filler Wire

    pp. 1242-1247

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    DOI:10.2320/matertrans.M2015011

    The weldability of magnesium alloy T-joint using laser-TIG hybrid welding heat source with cold filler wire was studied in this paper. The effects of welding parameters (wire feeding angle α, wire feeding speed VW, welding speed V, shielding gas flow rate acts on either of the connect corner QC, the distance between filler wire and laser beam DLW) on weld appearance and penetration were discussed. Results show that high-quality magnesium alloy T-joint can be achieved by adjusting the parameters. Shearing test result indicates that shear strength of the T-joint welded by laser-TIG heat source can be as high as 92.3% of that of base metal.
  • Effect of the O2/N2 Ratio on the Growth of ZnO Nanostructures on c-Plane Sapphire Substrate via Thermal Evaporation Technique

    pp. 1248-1251

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    DOI:10.2320/matertrans.M2015148

    ZnO nanostructures were grown on c-plane sapphire substrate in an oxygen and nitrogen gas environment at 1000°C by thermal evaporation of Zn powder without using catalyst. The ZnO nanostructures were synthesized at different O2/N2 ratios in order to investigate the effect of O2/N2 ratio in ambient gas on the morphology, crystal structure and cathodoluminescence of ZnO nanostructures. No nanostructures were grown on the substrate in a N2 environment. As the ratio of O2 to N2 increased, ZnO nanostructures with wire shape began to be grown on the substrate. In addition, tilted nanowires, which were grown with tilt angles with respect to the substrate plane, were observed. With further increasing the ratio of O2 to N2, the size of nanostructures increased. The intensity of visible emission in CL spectra increased with the increase in the ratio of O2 to N2.
  • Synthesis with Glucose Reduction Method and Low Temperature Sintering of Ag-Cu Alloy Nanoparticle Pastes for Electronic Packaging

    pp. 1252-1256

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    DOI:10.2320/matertrans.MI201406

    The metallic nanoparticle paste is receiving great interests recently because it is a potential interconnect material which can perform joining at low temperature and serves at high temperature. The nano-Ag paste and nano-Cu paste have been the hot areas of research, whereas the high cost and low resistance of electrochemical migration of the former and the relatively low anti-oxidation property of the latter limit their applications. In this study, Ag-Cu alloy nanoparticles with the size of 20–50 nm were synthesized with glucose as the reducing agent and NaOH as accelerator. The Ag-Cu nanoparticle paste showed no oxidation after sintering up to 350°C in the air, indicating that the antioxidant capacity was superior to that of the mechanically mixed Ag nanoparticles and Cu nanoparticles. In addition, the electrochemical migration resistance of the sintered Ag-Cu alloy pastes was better than that of the Ag nanoparticle paste. This paste can be used to effectively bond silver-plated copper bulks with maximum shear strength of 35 MPa.
  • Evaluation of Torsional Fatigue Behavior of Coronary Stents

    pp. 1257-1261

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    DOI:10.2320/matertrans.M2015075

    The coronary stent treatment, that is one kind of Percutaneous Coronary Intervention (PCI), is a general treatment to the angina pectoris. However, the stent has some problems such as a fracture after implantation and restenosis. One reason of the stent fracture is due to the cyclic load by the heart pulse after implantation. To avoid the stent fracture and restenosis, understanding the mechanical behavior of stents and an appropriate selection of stents are important. Since stent products have quite different design and material, standardizing the quantitative assessment of mechanical property of different stent products is required. In this study, fatigue tests were performed to compare mechanical properties (tensile fatigue and torsional fatigue properties) of four types of stent. Additionally, finite element analysis (FEA) was performed to analyze fatigue behavior of stent in tensile and torsional loading direction. Fatigue Safety Factor (FSF) was used to evaluate fatigue property in the analysis. The results had different tendency of fatigue life between tensile and torsional fatigue tests. The fracture part in fatigue test was consistent with the stress concentration zone analyzed by FEA. Fatigue strength of four types of stents could be estimated by FSF. It is concluded that the fatigue behavior can be evaluated using FEA.
  • Thermal Conductivity Enhancement of Magnetic Fluids under Magnetic Field Based on Percolation Theory

    pp. 1262-1268

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    DOI:10.2320/matertrans.M2015068

    Controversy exists over how the magnetic field (MF) enhances the thermal conductivity (TC) of magnetic fluids. We explain the MF enhancement of the ferrofluid TC using four key parameters based on percolation theory. The percolation of magnetic particles is governed by the particle size distribution, particle volume fraction, magnetic dipole-dipole coupling constant, and Langevin parameter. The magnitudes of the coupling constant and Langevin parameter have been used to indicate the possibility of long chain aggregate formation in MF. Given a fixed magnetization, the coupling constant and Langevin parameter are linearly proportional to the particle volume. Larger particles can more easily form long chain aggregates. In addition, chain aggregates form quickly at a higher volume fraction because the particle-particle collision frequency is quadratically proportional to the number concentration, which is proportional to the volume fraction. However, the particle size and volume fraction should be limited to prevent sedimentation or a significant increase in viscosity.
  • Effect of Various Refinement Methods on the Morphologies of Primary Si in a Hypereutectic Al-18Si Alloy

    pp. 1269-1277

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    DOI:10.2320/matertrans.M2015071

    The present study investigates the effect of different molten metal processing methods on the modification of primary silicon and the microstructure and mechanical properties of hypereutectic Al-18wt%Si alloy. The effects of melt treatment with the addition of electromagnetic vibration, AlCuP, bubbling of argon gas and their combination has been examined and an optimum procedure has been suggested for the treatment of molten Al-Si alloys, which resulted in the finest primary silicon particles with the highest tensile, impact and hardness properties and features of ductile fracture. This optimum procedure includes bubbling of the melt with argon gas for 15 min, the addition of 50 ppm of AlCuP master-alloy and stabilization of the melt for 15 min.
  • Feasibility of Bioleaching in Removing Metals (Al, Ni, V and Mo) from as Received Raw Petroleum Spent Refinery Catalyst: A Comparative Study on Leaching Yields, Risk Assessment Code and Reduced Partition Index

    pp. 1278-1286

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    DOI:10.2320/matertrans.M2015104

    This study investigates the effectiveness of bioleaching in recovery of metals (Al, Ni, V and Mo) from raw petroleum refinery spent catalyst using Acidithiobacillus ferrooxidans (At. ferrooxidans) and Acidithiobacillus thiooxidans (At. thiooxidans). It was found that bioleaching with At. ferrooxidans or At. thiooxidans resulted in higher leaching yields of Ni (55.8–58.6%) and V (33.0–33.4%) as compared to Al (9.3–10%) and Mo (3.9–5.8%). After 168 h of bioleaching with either At. ferrooxidans or At. thiooxidans, the remaining metals in the bioleached spent catalyst samples were present in stable forms (oxidizable and residual fractions). Bioleaching also led to increase in the reduced partition index of all the metals in the bioleached residues (Ni: 0.63–0.65, Al: 0.98, V: 0.90–0.91, Mo: 0.80–0.83) as compared to feed spent catalyst (Ni: 0.14, Mo: 0.63, V: 0.70, Al: 0.94). The low ‘risk assessment code’ (RAC) values of the bioleached residues as compared to feed spent catalyst indicated that bioleached residues posed low or no risk to the environment. The results of the present study suggested that the bioleaching with either At. ferrooxidans or At. thiooxidans is effective in leaching of Ni and V, whereas leaching of Mo and Al requires further treatment.
  • Passivation Behavior of Ce-Containing Hyper Duplex Stainless Steels in Sulfuric Acid Solution

    pp. 1287-1293

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    DOI:10.2320/matertrans.M2015145

    The passivation behavior of Ce containing hyper duplex stainless steels in sulfuric acid solution was investigated by electrochemical testing and X-ray photoelectron spectroscopy surface analysis. The addition of Ce to the alloy increased the corrosion resistance at a passive region of 0.4 VSCE. The Ce addition also improved the stability of the passive film because of the formation of inclusions containing Ce with low Cr content and an enrichment of the Cr oxide and hydroxide in the passive film. Further, Ce addition to the alloy decreased the interface between the inclusion and the metallic matrix functioning as defects in the passive film. The Cr-enriched zones formed around the Ce containing inclusion improved the corrosion resistance of the metallic matrix around the inclusions, which act as corrosion propagation sites.
  • Extraction and Separation of Cadmium from the Chloride Solution of E-Waste Using Cyanex 923 Impregnated Amberlite XAD-7HP Resin

    pp. 1294-1301

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    DOI:10.2320/matertrans.M2015137

    Cadmium(II) is not only hazardous but is also an impurity in the leachate of electronic waste which is processed during the extraction of valuable metals. This research focuses on the removal of cadmium from the leachate of e-waste containing Cu, Ni, Sn, Pb, Cd, Zn and Au using a solvent impregnated resin (SIR). The studies performed for the extraction of cadmium from the high acidity chloride solution showed the effective removal of cadmium forming solvation compound with Cyanex 923 impregnated Amberlite XAD-7HP resin. In the adsorption studies, the kinetics was found to be a second-order rate and followed a Langmuir isotherm. The results also showed that SIR comprising Cyanex 923 is effective for adsorption of zinc and gold from the leachate. The loaded metals on the SIR were separated by using selective eluents, water for Cd and Zn, whereas thiourea eluted Au. The remaining metals in the raffinate could be further processed to recover valuables after removing cadmium and other metals by a suitable hydrometallurgical processes.
  • Transition Metal Oxide (TMO) Thin Film Memristor on Cu Substrate Using Dilute Electrodeposition Method

    pp. 1302-1306

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    DOI:10.2320/matertrans.M2015166

    Instead of titanium dioxide (TiO2), many researches have been done to explore the compatibility of zinc oxide (ZnO) to be used as the active layer of memristor. In this study, an Au/ZnO-Cu2O-CuO/Cu memristor was fabricated using dilute electrodeposition and subsequently thermal oxidation. The XRD result indicates that Zn was oxidized to ZnO and has a wurzite structure while copper (Cu) substrate was also oxidized to copper (I) oxide (Cu2O) and copper (II) oxide (CuO). The surface morphology of ZnO shows the formation of needle-like structure on the surface after the thermal oxidation process. 15 s deposited ZnO-Cu2O-CuO gave the thinnest film of 81 nm with largest value of resistance difference of 14.11 kΩ and resistive switching ratio of 3.76. Empirical study on thermodynamics of metal oxides and diffusivity of Zn2+ and O2− in ZnO shows that the structure is formed due to the difference of diffusivity of each species during the thermal oxidation process. The synthesized Au/ZnO-Cu2O-CuO/Cu memristor shows a potential application in production of a non-complex and low cost memristor.
  • Time Dependent Magnetization of an Al-1.6%Mg2Si Alloy

    pp. 1307-1309

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    DOI:10.2320/matertrans.M2015157

    New observations of time dependent magnetization of an Al-1.6%Mg2Si alloy over a range of constant temperatures between 250 K and 310 K are presented. The post solution heat treatment time variations of magnetization at 300 and 310 K increased with time out to about 1300 minutes, whereas those at 280 and 290 K showed minima around 150 and 50 minutes, respectively. The magnetization at 250 K initially decreased slightly and then became constant with time. The observed time variations of magnetization are explained in terms of clustering reactions of the Mg, Si and vacancies.
  • A Preparation Method for Atomically Clean Sapphire Surfaces and High Resolution Topographic Method for Their Imaging by Non-Contact Atomic Force Microscopy

    pp. 1310-1313

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    DOI:10.2320/matertrans.M2015133

    We sought to establish a method for preparing an atomically clean surface of sapphire (Al2O3(0001)) using non-contact atomic force microscopy (NC-AFM). Repeated iterations of Ar+ sputtering and annealing are generally required to prepare a clean surface of TiO2(110) or other metal oxides. In the case of Al2O3(0001), however, we were able to achieve a periodic pattern of the Al2O3(0001) \sqrt{31} × \sqrt{31} surface using only one iteration of sputtering and annealing. We also succeeded in resolving single atoms of the \sqrt{31} × \sqrt{31} unit cell of the Al2O3(0001) in topographic mode imaging.

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