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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 6

  • Controlling Alternating Current Distribution inside Conductive Material Leads to a Novel Volumetric Examination Method —Experimental Verification

    pp. 1162-1165

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    DOI:10.2320/matertrans.I-MRA2007840

    This paper experimentally demonstrates that controlling alternating current distribution inside conductive material enables one to perform volumetric examinations using electromagnetic phenomena. Several current distributions are superposed to locally realize a unique alternating current distribution having a phase difference of 180 degrees between currents flowing near the surface and those deep inside, while having non-exponential decay in depth direction. Experimental results clearly show that measuring the phase of magnetic field outside the material as a function of the ratio of the superposition provides quantitative information about the depth of defects. In addition, this approach is applicable even though the depth of defects is much deeper than the standard depth of penetration; experimental results show clear differences between signals due to near-side notches of 10, 12, 15, and 20 mm deep, when an exciting frequency of 100 kHz is adopted.
  • Measurement of Potential Drop Distribution by Scanning the Closely Coupled Probes Sensor for Sensitive NDE of Shallow Surface Cracks

    pp. 1166-1172

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    DOI:10.2320/matertrans.I-MRA2007841

    Highly sensitive nondestructive evaluation of shallow surface cracks is realized through the distributions of d-c potential drop obtained by scanning the closely coupled four-point-probes sensor around the crack. A methodology is developed for evaluating the depth and length of a three-dimensional surface crack from the potential drop profiles measured across and along the crack, where the experimental result is compared with the corresponding prediction of finite element analysis. The highly sensitive characteristic of the measured profiles is also extended to the potential drop imaging for identifying the location of cracks in a clear pictorial form. It is verified that the method is a powerful tool for characterizing very small fatigue cracks (sub-millimeter depth) on the surface of metallic structures.
  • Three-Dimensional Fabric Analysis for Anisotropic Material Using Multi-Directional Scanning Line —Application to X-ray CT Image—

    pp. 1173-1178

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    DOI:10.2320/matertrans.I-MRA2007842

    In microscopic analysis, materials are characterized by a three-dimensional (3D) microstructure which is composed of constituent elements such as pores, voids and cracks. A material’s mechanical and hydrological properties are strongly dependent on its microstructure. In order to discuss the mechanics of geomaterials on a microstructural level, detailed information on their 3D microstructure is required. X-ray computed tomography is a powerful non-destructive method for determining the microstructure, however it can be difficult to determine a material’s microstructure from the reconstructed 3D image. We successfully evaluated the 3D microstructural anisotropy of porous and fibrous materials using a multi-directional scanning line method that employs straightforward image analysis, and its results were visualized using stereonet projection.
  • Long Range Inspection of Wall Reduction of Tank Utilizing Zero-th Order Symmetric Mode Lamb Wave —Performance Demonstration of the Method Proposed—

    pp. 1179-1183

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    DOI:10.2320/matertrans.I-MRA2007843

    We developed a new long range inspection method of corrosion-induced wall reduction of storage tanks. The method utilizes the zero-th order symmetric mode (So-mode) Lamb waves excited and monitored by a specially designed rectangular compression type PZT transducer mounted on the edge of the annular plate and side wall. The system can measure both the location and damage depth from the arrival time and amplitude of the So-mode reflected by the defects, respectively. We first measured attenuation of the So-mode wave and then the depth of dish-shaped wall reduction on single carbon steel plate. Amplitude of the So-mode wave reflected by the defects was found to increase proportionally with the defect depth less than 15% of the plate thickness (10 mm). Amplitude of the reflected So-mode Lamb wave from the shallow dish-shaped defects with depth of 0.6 mm or 7.5% to the plate thickness was detected. We also detected the So-mode waves from corrosion-induced dish-shaped wall reduction with 1.45 mm depth in 10 mm plate. Artificial groove of 1 mm depth on the step-weld 8 mm plates could be detected by the proposed method.
  • Corrosion Process in Reinforced Concrete Identified by Acoustic Emission

    pp. 1184-1189

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    DOI:10.2320/matertrans.I-MRA2007844

    Continuous acoustic emission (AE) monitoring in reinforced concrete (RC) was conducted to investigate the corrosion process. In experiments of an accelerated corrosion test and a cyclic wet-dry test, two periods of high AE activities were observed. These AE sources are classified by AE indices of the RA value and the average frequency and the b-value of AE amplitude distribution. At the 1st period, generation of small shear-type cracks is identified. From ingress of chloride ions analyzed, chloride concentration at the cover thickness of the reinforcing steel (rebar) was just over the lower-bound threshold for the initiation of corrosion. Although rebars were removed from the specimen, no corrosion products were observed. The surface of rebar was then examined by the scanning electron micrograph (SEM). The results showed that ferrous ions on the rebar surface disappeared, suggesting that the initiation of corrosion is associated with small AE events of the shear type. Approaching the 2nd period, large-scale tensile cracks were identified by AE. Chloride concentration at the cover-thickness was higher than the threshold level prescribed in the codes. Once rebars were removed, corrosion products were visually observed. This implies that the 2nd AE activities correspond to tensile cracks, which obviously result from concrete cracking due to expansion of corrosive products. These results show that the corrosion process of rebars is identified at the onset of rebar corrosion and at the nucleation of concrete cracking by continuous AE monitoring.
  • Detection of Fatigue Cracks at Weld Toes by Crack Detection Paint and Surface SH Wave

    pp. 1190-1195

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    DOI:10.2320/matertrans.I-MRA2007845

    A crack detection (CD) paint was applied to weld lines of a transverse rib welded joint specimen of a rolled steel for welded structures, and the effects of the paint on visual detection of fatigue cracks were evaluated by performing a fatigue test. Remarkable color development was observed in the CD paint when fatigue cracks propagated along the weld toe lines. At intervals in the fatigue test, surface SH (Secondary Horizontal) wave tests were also carried out in order to confirm the existence of fatigue cracks, and the test results were compared with the color development in the CD paint.
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  • Multiple Scattering Simulation of Ultrasonic Shear Wave in Unidirectional Carbon/Epoxy Composites

    pp. 1196-1201

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    DOI:10.2320/matertrans.I-MRA2007846

    A computational multiple scattering simulation method was applied to analyze the characteristics of the ultrasonic shear wave that propagates in unidirectional carbon-fiber-reinforced epoxy composites with its polarization direction parallel to the fibers. The numerical simulations were carried out for regular as well as random fiber arrangements and for different fiber volume fractions. The results were combined with the one-dimensional theory describing the macroscopic propagation behavior, in order to identify the phase velocity and the attenuation coefficient of the composite. The phase velocity and the attenuation coefficient were found to depend significantly on the fiber volume fraction, but less so on the fiber arrangement in the frequency range examined here. Furthermore, the present analysis showed a good agreement with the experimental data.
  • Backscattered Transverse Wave Imaging of Cracked-Faces with Linear and Nonlinear Ultrasonics

    pp. 1202-1207

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    DOI:10.2320/matertrans.I-MRA2007847

    A new backscattered-wave imaging of a cracked-face itself is proposed. Different from the conventional TOFD and phased array techniques, the wave scattered on a rugged fatigue-cracked face and/or intergranular stress-corrosion-cracking, SCC, face is captured in this technique. By focusing ultrasonic beams at every peak on those faces with a point-focused transducer and a scanner and by mapping the scattered-wave amplitudes on the scanned plane, we make an image of the cracked face itself. For tight cracked faces of nm opening, the second and higher harmonic amplitudes, generated by clapping and/or rubbing such a face with finite amplitude burst waves, are mapped in the similar way. By comparing the linear and nonlinear images of cracked faces, we can classify the extent of the crack opening. Some images of fatigue cracked faces are shown.
  • Michelson-Type Optical Fiber Laser Interferometer for Cylinder Wave Monitoring

    pp. 1208-1214

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    DOI:10.2320/matertrans.I-MRA2007848

    In order to overcome some problems of conventional parallel-type acoustic emission (AE) monitoring system, we developed a new Michelson-type laser interferometer with feedback circuit. We first compared the performance of the developed system with those by the Mach-Zender interferometer previously developed. Average signal to noise ratio (S/N) of the system to the F(1.1) mode cylinder wave is measured as 14.3 dB and comparable to that (14.7 dB) of the Mach-Zender interferometer. Sensitivity of the system to the cylinder waves was found to be significantly improved by multi-winding of the sensing fiber on the pipe. We then measured the attenuation of longitudinal and flexural mode cylinder waves via a pipe wrapped by adhesive tape for corrosion protection. The attenuation of the F(1,1) mode wave by the adhesive tape was measured as 10 dB/m and slightly lower than that (12 dB/m) of the L(0,1)-mode wave. Leakages of water through a hole or medical paper tape were successfully monitored by the highly sensitive system.
  • Evaluation of the Twinning Behavior of Polycrystalline Magnesium at Room Temperature by Acoustic Emission

    pp. 1215-1220

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    DOI:10.2320/matertrans.I-MRA2007849

    In order to study the twinning behavior of polycrystalline magnesium at room temperature, acoustic emission (AE) was measured during the compression process at an intermediate strain rate along the extrusion direction. Microstructure evolution was quantitatively characterized by the twinning area fraction and the strain dependence of twinning size distribution from the observation by optical microscope. Deformation was mainly due to twinning nucleation in the initial stage, and twinning growth and dislocation motions gradually became dominant with the increase of strain. As AE count rate increased greatly in the initial stage of deformation and dropped quickly in the later stage, AE signals in the initial stage were thought to be mainly due to the twinning nucleation. Twinning strain and the fraction of twinning strain rate were calculated by considering the variation of Schmid factor in deformation. A quantitative relation between the twinning strain and the cumulative AE counts was obtained in the initial stage of deformation.
  • Acquisition and Analysis of Continuous Acoustic Emission Waveform for Classification of Damage Sources in Ceramic Fiber Mat

    pp. 1221-1226

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    DOI:10.2320/matertrans.I-MRA2007850

    Waveforms of acoustic emission (AE) events come close and sometimes overlap each other when AE activity is very high. Conventional AE measurement systems which handle discrete AE events are not suitable for this situation because miss-detection of AE event occurs frequently. A new AE measurement system named as Continuous Wave Memory (CWM) was developed to solve this problem by recording the AE waveforms continuously to hard disks for several hours throughout the testing time. This new system enabled multiple analysis of one waveform with different filtering parameters. Short time Fourier transform (STFT) gave the time–frequency–magnitude characteristic of continuous AE waveforms and useful information for evaluation of degradation of materials. In this study, the degradation of ceramic fiber mat during cyclic compression test and the effect of binder-addition were evaluated by this new system. STFT results clearly showed the classification of degradation of the mat; breakage of fibers was the main source in the early compression cycles and sporadic friction between fibers became the main source of AE in the later compression cycles. The effect of organic binder to prevent the degradation of the mat was also estimated. It was observed that the friction signal disappeared and the breakage signal weakened in the binder-added specimens.
  • Ultrasonic Testing Method for Detection of Planar Flaws in Graphite Material

    pp. 1227-1235

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    DOI:10.2320/matertrans.I-MRA2007851

    An ultrasonic inspection method for a graphite ingot was developed to detect internal planar flaws that are oriented in various directions; this method is necessary to perform quality assurance of throat inserts of solid rocket motors. Major problems that are unique to this graphite inspection were solved. An ultrasonic beam in graphite shows uneven propagation behavior both within and among individual ingots. That individual unevenness engenders variation in echo heights of flat-bottomed holes, which can be compensated through two-dimensional scanning accompanying a change in incident angles of two directions. This scanning procedure is therefore necessary to detect internal planar flaws that orient in various directions. The unevenness among ingots can be compensated by measuring the wave velocity and attenuation coefficient in the test block itself before inspection. A test block including artificial internal flaws was fabricated and inspected using the developed method. It was then sliced into several thin disks. The sliced disks were inspected using the conventional ultrasonic testing method using a normal beam technique. The two methods detected identical flaws, thereby validating the developed method. The technique described here has been enacted as JIS Z 2356 under the title, “Method of automatic ultrasonic inspection for graphite ingot”.
  • Reflection of Obliquely Incident Guided Waves by an Edge of a Plate

    pp. 1236-1243

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    DOI:10.2320/matertrans.I-MRA2007852

    This paper analyzes the edge-reflection problem of obliquely incident guided waves in a plate. The generalized guided-wave theories in a plate, including the orthogonality of modes and the mode-decomposition method are summarized. The edge-reflection problem is solved on the basis of the mode-decomposition method. Some numerical results are presented and compared to experimental results.
  • Smart Stress-Memory Patch for Fatigue Damage of Structure

    pp. 1244-1248

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    DOI:10.2320/matertrans.I-MRA2007853

    A new fatigue sensor called “smart stress-memory patch”, which can estimate the cyclic number, the stress amplitude and the maximum stress from the measurement of crack length and acoustic emission (AE), is proposed to evaluate the fatigue damage of such infrastructure as bridges and ships. The fatigue crack growth behavior of thin electrodeposited (ED) Cu specimen for this sensor is investigated. The modified stress intensity factor is proposed to introduce the master curve of fatigue crack growth, because the fatigue crack growth behavior of this patch is affected by the maximum stress and stress ratio. AE signals are also measured to estimate the AE onset stress and examine Kaiser effect of ED Cu specimen. It is expected that the cyclic number, the stress amplitude and the maximum stress in fatigue loading can be estimated by this patch.
  • Enhancement of Impact Mass Estimation Algorithm for a Plate Type Structure

    pp. 1249-1253

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    DOI:10.2320/matertrans.I-MRA2007854

    A new method to more accurately estimate the impact mass when an elastic ball is impacting on a surface of an elastic plate is suggested. Conventionally, frequency ratio (FR) and center frequency techniques have been widely used for a mass estimation. However, these methods do not work when the mounting effect of a sensor is dominant and/or the operating background noise becomes high. Thus a new technique to eliminate these effects by using a time-frequency analysis is attempted and verified through an experiment. It is revealed that the proposed method is valid for estimating the center frequency of an impact response signal easily even in a noisy environment, thus making a mass estimation of an impact source on a plate type structure more successful than the conventional techniques.
  • Evaluation of Rolling Fatigue Damage in Deep Groove Ball Bearings by Divided-Type Focusing Ultrasonic Transducer

    pp. 1254-1259

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    DOI:10.2320/matertrans.I-MRA2007855

    To evaluate quantitatively the damage caused by rolling fatigue in deep groove ball bearings, we used a method in which the wave velocity of a leaky surface acoustic wave (SAW) propagating on the race surface of bearings was measured. The wave velocity was directly measured from the change in the propagation time by defocusing a focusing ultrasonic transducer. A new focusing ultrasonic transducer was developed by molding a piezoelectric copolymer into a concave-shaped film. To fabricate ultrasonic transducers with a lower frequency characteristic, the films were stacked and composite backings made from epoxy resin and tungsten were used. The electrode of the transducer was divided into three areas to receive direct reflection waves and leaky SAW independently without any interference. Two of these electrodes were used for the excitation and reception of leaky SAW, and the shape of the electrodes was designed so that leaky SAW might propagate only on the raceway surface of the inner ring of the bearings. Moreover, in order to suppress the effects caused by edge waves, the shape of the electrodes for leaky SAW was considered. The availability of this method was evaluated by measuring the leaky SAW velocity in the bearings whose worked hours differed. As a result, a small difference in leaky SAW velocity was detected according to the worked hours of the bearings, and it was demonstrated that this method would be useful for non-destructive soundness evaluation of bearings.
  • Alternative Strain Aging Effect for Fatigue of Ductile Bulk Glassy Alloys

    pp. 1261-1265

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    DOI:10.2320/matertrans.MF200614

    The metal fatigue mechanism of bulk glassy alloys (BGAs) resulting from the ductile nature of a glassy alloy differs from that of the conventional crystalline engineering alloys. Extreme hardening of the fatigue crack tip on the fatigue-fractured surface of the Zr- and Pd-based BGAs was usually observed just before the final fracture. Embrittlement around the fatigue crack tip, generated by excessive hardening to stop the fatigue crack propagation, significantly decreases fatigue fracture toughness. Hardening by hydrogen was also considered as an alternative mechanism of the strain aging effect in fatigue of glassy alloys because the second phase cannot be observed on a fatigue fracture surface, and only hydrogen promotes hardening, maintaining a glass structure. Hydrogen analysis of a micro area region was attempted with nuclear reaction analysis which used accelerated ion 15N up to 6.385 MeV to determine the hydrogen concentration of the fatigue-fracture surface. We successfully measured the characteristic enrichment of hydrogen near the fatigue-fracture surface.
  • Origin of the Effect of the Gas Atmosphere during Mold-Casting Zr65Al7.5Ni10Pd17.5 Bulk Glassy or Nano-Quasicrystal-Forming Alloy

    pp. 1266-1271

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    DOI:10.2320/matertrans.MF200619

    We provide a quantitative analysis of the importance of the gas species and pressure during mold-casting process on the apparent glass-forming ability (GFA) of Zr65Al7.5Ni10Pd17.5 alloy, recently reported by Kato et al. (e.g. Scripta Mater. 51 (2004) 13). The cooling characteristics are found to depend in remarkable detail on the gas species and the pressure existing in the cavity between the melt and the mold presumably formed during the cooling process. This understanding has been successfully applied to significantly improve the critical diameter of the glassy rods to 7 mm in an atmosphere of helium environment from 5 mm in that of argon.
  • Transition from Plasticity to Brittleness in Cu-Zr-Based Bulk Metallic Glasses

    pp. 1272-1275

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    DOI:10.2320/matertrans.MF200620

    The effects of addition of Al and Ag on the mechanical properties of the Cu50Zr50 alloy are investigated. It is found that the plasticity of the Cu-Zr-based BMGs decreases as the content of the alloying elements of Al and Ag increases. A clear transition from plasticity to brittleness occurs for the Cu-Zr-based BMGs with increasing the content of Al and Ag. Combining with previous work on the plasticity or brittleness of the Cu-Zr-based BMGs, the role of the atomic binding force between the solute and solvent atoms is suggested to understand the transition from plasticity to brittleness for the Cu-Zr-based BMGs.
  • Drastic Increase in the Toughness of Structural Relaxed Hypoeutectic Zr59Cu31Al10 Bulk Glassy Alloy

    pp. 1276-1281

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    DOI:10.2320/matertrans.MF200623

    In order to improve embrittlement phenomena by structural relaxation, Zr-enriched hypoeutectic Zr-Cu-Al bulk glassy alloys (BGAs) were examined. During annealing for structural relaxation, the density increases significantly with annealing time from 103 s, and apparent saturation is seen at approximately 5.4 ks. Hardness and tensile strength do not change remarkably with annealing temperature. However, the Charpy impact value increases significantly by annealing at 648 K for 5.4 ks. The tendency of distinct increase of the Charpy impact value is maximized at Zr59Cu31Al10 in hypoeutectic Zr-Cu-Al BGAs. A drastic increase in the Charpy impact value is accompanied by an increase in nonlinear density with increasing annealing temperature. Furthermore, the mechanical properties of fully structural relaxed Zr59Cu31Al10 BGAs are characterized by their superior shear band formation and branching ability, which can be estimated by the shear slip width before shear band opening.
  • Compositional Dependence of Thermal and Mechanical Properties of Quaternary Zr-Cu-Ni-Al Bulk Glassy Alloys

    pp. 1282-1287

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    DOI:10.2320/matertrans.MF200622

    To determine the optimized composition of quaternary Zr-Cu-Ni-Al bulk glassy alloy, its thermal and mechanical properties are examined. Zr shows high correlation coefficients with Tg and Vickers hardness, whereas Ni and Al show high correlation coefficients with Tl and Tx, respectively. Only Cu shows no remarkable correlation coefficient with any thermal or mechanical properties. We conclude that a compositional region with a high (over 135 kJ/m2) U-notch Charpy impact (CUE) value is located around the Zr52Cu30Ni8Al10 bulk glassy alloy, which exhibits a maximum CUE of 165 kJ/m2. Moreover, a compositional region with high tensile strength (over 2000 MPa) is also located around the Zr48Cu32Ni8Al12 bulk glassy alloy, which shows a maximum tensile strength of 2100 MPa.
  • Effect of Nanocrystal Distribution on Mechanical Properties of Ti-Based Metallic Glasses

    pp. 1288-1291

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    DOI:10.2320/matertrans.MF200616

    Ti45Zr5Cu45Ni5 metallic glasses in which Ta and Al were substituted for Cu were evaluated in terms of mechanical properties, thermal properties and microstructures in order to determine the factors contributing to an improvement in plasticity. Samples are examined by compression testing, differential scanning calorimetry, X-ray diffractometry and electron microscopy. Mold-cast Ti45Zr5Cu44Ni5Ta1 bulk specimens were confirmed to consist of a metallic glass matrix and nanocrystals homogeneously dispersed at high density within the matrix. The yield stresses of both Ti45Zr5Cu45−xNi5Tax and Ti45Zr5Cu45−xNi5Alx are approximately 1800 MPa, and the maximum plastic strain of 3.1% was obtained for the Ti45Zr5Cu44Ni5Ta1 specimen. The Ti45Zr5Cu45−xNi5Alx bulk specimens exhibited poorer plasticity due to the formation of larger crystalline grains.
  • Electronic Structure and Stability of the Pd-Ni-P Bulk Metallic Glass

    pp. 1292-1298

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    DOI:10.2320/matertrans.MF200617

    In order to investigate the stabilization mechanism of the Pd-Ni-P bulk metallic glass (BMG), electronic structure of the (Ni,Pd)9P trigonal clusters with a phosphorus atom in the center and that of the relevant crystals were investigated by use of first principle calculations; discrete variational Xα potential (DVXα) cluster calculation and full potential linearized augmented planewave (FLAPW) band calculation. Presence of the covalent bonds between phosphorus and nickel/palladium was confirmed in the relevant crystals by observing their density of states, that is characterized by the narrow bandwidth and the eigen values well reproduced by the (Ni,Pd)9P cluster calculation. We found, as a consequence of the theoretical calculations, that the electronic structure and the number of electrons in the trigonal cluster allow the (Ni,Pd) atoms at the vertices and sides of the clusters to be shared by the neighboring ones, and that the connection-direction and connection-angle of the cluster do not significantly alter the cluster levels nor the internal energy of the cluster. Consequently the network of the cluster has large degree of flexibility with keeping the low internal energy. These characteristics lead to the highly-stable Pd-Ni-P BMG.
  • Local Atomic Structure Analysis of Zr-Ni and Zr-Cu Metallic Glasses Using Electron Diffraction

    pp. 1299-1303

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    DOI:10.2320/matertrans.MF200618

    Local atomic structures in Zr66.7Ni33.3 and Zr66.7Cu33.3 metallic glasses were examined by using nanobeam electron diffraction (NBED), energy-filtered selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). Locally ordered regions of atomic medium range order (MRO) were observed in both of the specimens by NBED, although it was difficult to recognize the regions using HREM. Statistical analyses for NBED patterns revealed such a difference in the extended MRO regions between the specimens that the MRO structure in Zr66.7Ni33.3 is more complex with a large dispersion of interplanar spacings than those in Zr66.7Cu33.3. To understand nearest-neighbor atomic coordination, we performed electron intensity analyses using energy-filtered SAED patterns and constructed structure models including about 5000 atoms with the help of reverse Monte Carlo simulation. The nearest-neighbor atomic environments around Ni atoms in Zr66.7Ni33.3 are also different from those around Cu atoms in Zr66.7Cu33.3, consistent with the NBED study. The local structural difference between the two glasses was discussed in relation to their glass-forming abilities.
  • Analysis of Bulk Metallic Glass Formation Using a Tetrahedron Composition Diagram that Consists of Constituent Classes Based on Blocks of Elements in the Periodic Table

    pp. 1304-1312

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    DOI:10.2320/matertrans.MF200604

    The formation of bulk metallic glasses (BMGs) has been analyzed with a tetrahedron composition diagram, which is comprised of constituent classes from blocks of elements in the periodic table. When Al and Ga are involved in the BMG composition environment, they are assumed to correspond to either s- or p-block elements. The analysis under the assumption reveals the presence of a composition band that connects the composition regions over different classes of BMGs. The diagram has a topological simplicity, is applicable to any multi-component alloy system, and can be analyzed from the bonding nature of the atomic pairs. Thus, this diagram is an important tool for analyzing and developing BMGs.
  • Development of Interatomic Potential for Zr-Ni Amorphous Systems

    pp. 1313-1321

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    DOI:10.2320/matertrans.MF200602

    This study develops a way of determining the interatomic potential of Zr-Ni using an embedded atom method for binary systems that can reproduce the material properties of its amorphous states. In order to ensure the robustness of the developed interatomic potential, the potential energies and lattice constants of Zr crystals, Ni crystals, and Zr-Ni binary crystals that involve a wide range of local atomic environments are employed for fitting. The elastic properties of some such crystals are also employed. In addition, in order to reproduce Zr-Ni amorphous properties, the radial distribution function of Zr70Ni30 amorphous structures and the defect formation energies of Zr-Ni structures are employed. By fitting to a portion of the material properties that requires relatively little computation time, optimization using genetic algorithms is carried out as a first step. As a result, several potential parameter sets are generated. The final potential parameter set, which can reproduce all the material properties used for fitting, is selected from them. The developed potential can reproduce the material properties used for fitting which involve the radial distribution function of the Zr70Ni30 amorphous structure.
  • Glass Forming Ability and Mechanical Properties of Quinary Zr-Based Bulk Metallic Glasses

    pp. 1322-1326

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    DOI:10.2320/matertrans.MF200621

    Quinary Zr-based alloy compositions with improved glass forming criteria have been sought and the glass forming ability (GFA), thermal stability and mechanical properties of these alloys have been investigated. Monolithic amorphous structure has been confirmed for all compositions in 5 mm rods prepared by a Cu-mold casting method. They also show large plastic strain maximum of about 12% under uniaxial compression test with yield stress of about 2000 MPa. The compressive plasticity of the cast rods was found to be influenced by the casting temperature to a great extent.
  • Deformation-Induced Nanoscale Dynamic Transformation Studies in Zr-Al-Ni-Pd and Zr-Al-Ni-Cu Bulk Metallic Glasses

    pp. 1327-1335

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    DOI:10.2320/matertrans.MF200615

    Nanoscale dynamic transformations during tensile and compressive deformation of Zr65Al7.5Ni10Cu17.5 and Zr65Al7.5Ni10Pd17.5 bulk metallic glasses have been investigated. Although no apparent differences are observed in the stress-strain curves in the tensile deformation between the two alloys, fine striations and depression zones with viscous flow appear at the fracture surface near the edge in the Zr65Al7.5Ni10Pd17.5 alloy. Unlike the Zr65Al7.5Ni10Cu17.5 alloy and other bulk metallic glasses, the Zr65Al7.5Ni10Pd17.5 bulk metallic glass exhibits a large plastic strain of approximately 7% during compressive deformation. By detailed examination of the microstructure, we provide direct evidence for nanoscale multistep shear band formation in the Zr65Al7.5Ni10Pd17.5 metallic glass. A novel nanoscale structure where fcc Zr2Ni nanocrystalline particles are arranged in “bandlike” areas in the glassy matrix is observed near the compressive fracture tip. The suppression of the propagation of the shear bands due to dynamic nanocrystallization causes this structure. Furthermore, the results are recognized as a novel phenomenon, a nanoscale dynamic structural change by shear band propagation, and provide a new method for improving the mechanical properties of bulk metallic glasses.
  • Molecular Dynamics Study of Glass-Forming Ability of Zr-Based Metallic Glasses

    pp. 1336-1339

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    DOI:10.2320/matertrans.MF200608

    A new method to estimate the stability of supercooled liquid based on the temperature dependence of the free volume fraction, which is obtained by a molecular dynamics simulation with no empirical data was proposed. The molecular dynamics simulations for some Zr-based metallic glasses, Zr55Cu30Ni5Al10, Zr67Ni33 and Zr67Cu33 in Zr-Cu-Ni-Al system were performed. The features of the first peaks in calculated radial density functions well correspond to the experimental results by XRD and EXAFS spectroscope. The free volume fractions at 0 K in the quenched amorphous, Fquenched, and in “fully relaxed” supercooled liquid states, Frelaxed, are evaluated by the fitting of the temperature vs free-volume-fraction curve obtained by a molecular dynamics simulation. The calculated normalized free volume fraction Nfree, defined as FquenchedFrelaxed, shows similar tendency with other experimental Trg. criterion. The temperature dependence of the free volume fraction in a supercooled liquid state governs the quenched free volume in the amorphous phase, which shows that the local structures in supercooled liquid or liquid phases are especially important for the glass formation.
  • Phase Stability of an Amorphous Phase Against Electron Irradiation Induced Crystallization in Fe-Based Metallic Glasses

    pp. 1340-1349

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    DOI:10.2320/matertrans.MF200612

    Electron irradiation induced nano-crystallization of melt-spun amorphous phase in Fe-Zr-B ternary alloys was investigated focusing on the difference in phase stability of amorphous phase during thermal annealing and electron irradiation. Nano-composite structure composed of nano-crystalline α-Fe precipitates with b.c.c.-structure, metallic compounds and a residual amorphous matrix was formed under 2.0 MeV electron irradiation at 298 K, while such nano-structure was hardly realized by thermal annealing. The phase stability of an amorphous phase against electron irradiation was discussed based on the relationship between thermal properties and critical onset total dose of electron irradiation induced crystallization at 298 K.
  • Influence of Silicon Additions on the Microstructure and Mechanical Properties of Cu47Ti34Zr11Ni8 Bulk Metallic Glass Forming Alloys

    pp. 1350-1354

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    DOI:10.2320/matertrans.MF200611

    A group of (Cu47Ti34Zr11Ni8)100−xSix(x=0,1,2,3) bulk metallic glass forming alloys with diameter of 3 mm were prepared by water-cooled copper mould cast. Microstructural investigations reveal that with increasing Si content the precipitated phases exhibit quite different morphologies, which varies from earthworm-like phase for alloys with x=1 to small-sized dendrite phase for alloys with x=2, and finally to developed dendritic phase for alloys with x=3. Room temperature compression tests reveal that a transformation from shear fracture to distensile fracture mechanism occurs for the samples with Si content over a critical value. For the alloys with x=0 and 1, fracture occurs in a shear mode with very high ultimate fracture strength. In contrast, the alloys with x=2 and 3 seem to fracture by a distensile mode with ultimate fracture strength greatly decreased. The fracture behavior of the as-cast alloys were investigated and discussed.
  • Formation of a Ni-Based Glassy Alloy in Centimeter Scale

    pp. 1355-1358

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    DOI:10.2320/matertrans.MF200627

    The effect of B addition on the glass formation in the Ni60Pd20P20 alloy has been investigated. The composition containing 3 at % of B was found to show a drastically improved glass-forming ability. A glassy Ni60Pd20P17B3 alloy rod was prepared with a diameter of 12 mm by a water quenching technique. It is so far the first time to prepare a Ni-based bulk glassy alloy with a diameter over 1 cm. The glassy Ni60Pd20P17B3 alloy also exhibits good mechanical properties, such as high strength of 2060 MPa and a large plastic strain of 0.08 under a compressive load.
  • Dynamic Mechanical Properties in a Zr50Cu40Al10 Bulk Metallic Glass

    pp. 1359-1362

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    DOI:10.2320/matertrans.MF200626

    A large variety of Zr-based bulk metallic glasses has been developed in the last decade. They are attractive due to their high mechanical properties. However, they are faced with a fairly low thermal stability at high temperature. One of the best way to test this stability is to determine the evolution of their mechanical properties versus the temperature. By performing appropriated annealing, either structural relaxation or crystallization (partial or total) can be achieved. The influence of these two structural evolutions have been investigated. It appears that the Zr50Cu40Al10 bulk glassy alloy exhibits very good features concerning the stability criterion.
  • Glassy Solidification Criterion of Zr50Cu40Al10 Alloy

    pp. 1363-1372

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    DOI:10.2320/matertrans.MF200624

    We examined the solidification morphology and structure of arc-melted Zr50Cu40Al10 glass-forming alloys in order to determine the impurity influences using two grades of Zr metals: “sponge Zr” purified somewhat but not highly by the Kroll method, and highly purified “crystal Zr”. When crystal Zr is used, arc-melted Zr50Cu40Al10 alloy exhibits superior glass-forming ability in forming glassy phase, even in a 40-g master alloy. When sponge Zr is used, on the other hand, we can see distinct a chain reaction of exothermic heat due to crystallization after vitrification during solidification. We conclude that the origin of the crystallization in arc-melted Zr50Cu40Al10 alloy with sponge Zr is probably chlorine as an impurity in sponge Zr metals. Furthermore, vitrification in front of the solidification interface of arc-melted Zr50Cu40Al10 alloy with crystal Zr can occur when the crystalline growth phase is an Al-supersaturated B2 (B19’)-type ZrCu phase.
  • Three Stages of Bonding Mode before Nucleation of Metal Crystals

    pp. 1373-1379

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    DOI:10.2320/matertrans.MRA2006635

    Effect of particle size on atomistic structures of vapor deposited Au-atom clusters has been examined by electron microscopy with the following results: (a) Icosahedrons are first formed, and they grow by two types of face sharing of further icosahedrons. (b) The lattice constant decreases more than about 1% in transition from icosahedral structures to cuboctahedral ones, which are a fcc-type structure, when average size of atom clusters becomes larger than about Φ3 nm. (c) Embryo of the final fcc structure is formed when the size of atom clusters increases to about Φ8 nm, and the lattice constant considerably increases more than 2% in spite of the same fcc structure as cuboctahedral ones. After that, the lattice constant scarcely changes even when the particle size increases more than Φ20 nm.
    These facts are considered to be closely related to heterogeneous distribution of electric charge within atom clusters. Based on the results, relationships between electronic structures in the three stages and anomalous behavior of metal-atom clusters, consisting of both fcc-type and bcc-type elements, are discussed.
  • Ellipsometric Characterization on Multi-Layered Thin Film Systems during Hydrogenation

    pp. 1380-1386

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    DOI:10.2320/matertrans.MRA2006193

    Ellipsometric characterization on the basis of multi-layered modeling is proposed to describe the optical and electrical property transients of hydrogenated films. In particular, two-step modeling is developed to make ellipsometric characterization on the yttrium film and the palladium capped yttrium film deposited on the SiO2 glass substrate. In the former, Y2O3 film deposited on SiO2 substrate is prepared to estimate the dielectric response of yttrium oxide layer as the first step. These data are further utilized in the second step to determine optical and electric properties of yttrium-base multi-layers which are composed of metallic yttrium, composite of metallic yttrium and Y2O3, and Y2O3 layer with surface roughness. In the latter, a palladium film deposited on SiO2 substrate is prepared to investigate the dielectric response of palladium hydrides. The estimated dispersion functions are further used in the multi-layered modeling for hydrogenated Pd-capped yttrium films on the SiO2 substrate. Under the ambient hydrogen pressure, palladium coated yttrium films have low resistivity and hydrogenated yttrium is still metallic. This palladium coating works as a top capping layer for yttrium film during hydrogenation and de-hydrogenation.
  • Grain Growth Behaviors in a Friction-Stir-Welded ZK60 Magnesium Alloy

    pp. 1387-1395

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    DOI:10.2320/matertrans.MRA2007040

    Grain growth during annealing of a friction-stir-welded (FSWed) ZK60 magnesium alloy has been investigated. We have found that (1) thermal stability exhibited in different parts of stirred zone (SZ) was very different, (2) grain growth was fairly abnormal, and (3) grain growth was directional and shapes of developed grains resembled flow patterns inherent to FSWed structure. We have shown that all peculiarities of the grain growth behaviors can be explained in terms of heterogeneous distribution of second phase particles resulted from FSW.
  • Growth Manner of Intermetallic Compounds at the Weld Interface of Steel/Aluminum Alloy Lap Joint Fabricated by a Defocused Laser Beam

    pp. 1396-1405

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    DOI:10.2320/matertrans.L-MRA2007838

    An interrupted welding method was performed in order to investigate the formation and growth manner of IMC at the weld interface of steel/aluminum alloy lap joint during defocused laser beam welding. Microstructural transition at the weld interface was precisely investigated by both TEM diffraction pattern analysis and TEM-EDX chemical composition analysis. It was revealed that Al13Fe4 and Al2Fe formed at the early stage of welding process, and the formation of Al5Fe2 subsequently occurred between Al13Fe4 and Al2Fe. Preferential and abrupt growth of Al5Fe2 resulted in the IMC layer which was composed of coarse Al5Fe2 and Al13Fe4. The dominant factor controlling the interfacial microstructure is considered to be the post-welding thermal history. Increase of energy density gave rise to an increment of the IMC layer thickness, and brought about reduced bonding strength. Therefore, lower energy input (higher welding speed when other welding conditions are fixed) is considered to be useful in order to suppress the abrupt grain growth of the IMCs in the layer which possibly occurred during the post-welding thermal history.
  • Superplasticity of Fine-Grained Magnesium Alloy AZ31 Processed by Multi-Directional Forging

    pp. 1406-1411

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    DOI:10.2320/matertrans.L-MRA2007839

    Superplasticity was studied in a fine-grained magnesium alloy AZ31 processed by multidirectional forging (MDF) under decreasing temperature conditions. Tensile tests were carried out at temperatures from 393 K to 473 K and at various strain rates. Superplasticity appears even at a low temperature of 393 K with a stress exponent of around 5.6 and a total elongation of over 370%. The relative large stress exponent can be connected with grain coarsening or refinement taking place during deformation. The initial deformation texture introduced by MDF hardly changes during superplasticity. These suggest that grain boundary sliding can take place during superplasticity, while grain rotation hardly occurs as a whole.
  • Effects of Grain-Boundary Sliding and Plastic Deformation of Grains on the Formation of Grain-Boundary Cracks in a Double Cylindrical Bicrystal of a Cu-SiO2 Alloy

    pp. 1412-1416

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    DOI:10.2320/matertrans.MRA2007027

    A double cylindrical bicrystal is a bicrystal consisting of a cylindrical inside grain with a second grain wrapped around its curved side surface. Using a double cylindrical bicrystal of a Cu-SiO2 alloy, tensile tests were performed at 800 K under 2×10−4 s−1. Three specimens cut from the same bicrystal were deformed to three different strains. Preferential formation of grain-boundary cracks around the cylindrical inside grain was observed after the tensile tests. In addition to the occurrence of grain-boundary sliding, the misfit of slip deformation at the grain boundary affects the formation of the grain-boundary cracks.
  • Effect of Preservative Solution on Fracture Characteristics of Bovine Femoral Cortical Bone

    pp. 1417-1421

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    DOI:10.2320/matertrans.MRA2006368

    Accurate determination of the mechanical properties of bone requires a preservation method that has minimal effects on these properties. It is conceivable that long-term exposure of bone to formalin and/or saline may have some effect on its mechanical properties. We examined the effect of fixation with neutral buffered formalin on the fracture toughness of bovine femoral cortical bone (Haversian or laminar), and we also analyzed the elution of bone minerals in the preservative solution. Formalin-preservation periods were 30 days and 150 days. To test the anisotropy of the bone, two different specimens in which we had introduced an initial crack in a circumferential or radial direction were used as specimens. Fracture toughness testing was performed on three-point bend specimens and with 1 mm/min or 20 mm/min cross-head speed. A 30% maximum decrease in fracture toughness was observed. The rate of decline in fracture toughness was relatively high in the laminar bone specimen under 20 mm/min cross-head speed. Calcium elution into saline was higher than into formalin preservative, confirming that bone minerals elute markedly into aqueous solutions such as saline.
  • Synergetic Effect of Grain Refinement and Spherical Shaped Precipitate Dispersions in Fracture Toughness of a Mg-Zn-Zr Alloy

    pp. 1422-1426

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    DOI:10.2320/matertrans.MRA2006355

    Fracture toughness was examined on a commercial Mg-Zn-Zr alloy, ZK60. The commercial alloy was extruded at a temperature of 493 K to obtain fine grain structures having fine spherical shaped precipitates. The microstructures consisted of equi-axed grains. The average grain size and the precipitate diameter were about 3 μm and 25∼50 nm, respectively. The yield strength and elongation-to-failure were 287 MPa and 26.7%, respectively. The plane-strain fracture toughness, KIC, was estimated to be 34.8 MPam1⁄2 by the stretched zone analysis. These mechanical properties were superior to that of conventional wrought magnesium and magnesium alloys. The deformed microstructure observations showed i) the activation of non-basal dislocations even at room temperature and ii) the pinning of dislocations by the spherical shaped precipitates during the fracture toughness test. Thus, a combination of grain refinement and dispersion of fine spherical shaped precipitates were found to be effective methods for improving the fracture toughness of magnesium alloys.
  • Effect of Helium and Hydrogen Production on Irradiation Hardening of F82H Steel Irradiated by Ion Beams

    pp. 1427-1430

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    DOI:10.2320/matertrans.MBW200611

    Effects of helium and hydrogen production on irradiation hardening of martensitic steel F82H (Fe-8Cr-2W-0.2V-0.04Ta-0.1C) were examined by dual or triple beam experiments. The effects of tempering and cold working were also examined. The irradiations were performed at about 500°C to 50 dpa under simultaneous dual beams of 10.5 MeV Fe3+ and 1.05 MeV He+ or triple beams of those and 380 keV H+ ions. The value of appm-He/dpa for the dual ion beams was about 15, and the values of appm-He/dpa and appm-H/dpa for the triple ion beams were 15 and 15 (or 150), respectively. The hardness of the irradiated specimens measured at room temperature using a micro indentation after the irradiations. Irradiation softening and hardening was observed in F82H-std, F82H+20%CW and a non-tempered F82H steels irradiated at about 500°C to 18 and 50 dpa, respectively, by dual ion beams. The hardness of the specimens irradiated at about 500°C to 18 dpa under triple ion beams was harder than that under dual ion beams.
  • Stress Corrosion Cracking Growth Rates of Candidate Canister Materials for Spent Nuclear Fuel Storage in Chloride-Containing Atmosphere

    pp. 1431-1437

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    DOI:10.2320/matertrans.MRA2006367

    Chloride-induced stress corrosion crack growth rates were measured for candidate canister materials in a simulated marine atmospheric environment. Half-inch compact tension specimens were used to obtain stress corrosion crack growth rates by applying a direct-current potential-drop method to measure crack lengths. The crack growth rates of S31603 and S31260 stainless steels were 3×10−10 m·s−1 and 4×10−13 m·s−1 for an applied stress intensity factor of 30 MPa·m0.5, respectively, at a test temperature of 353 K at a relative humidity of 35%. S31254 specimens did not show stress corrosion cracking susceptibility under the same conditions as above, suggesting their superior resistance to chloride-induced stress corrosion cracking. These data were consistent with the results that S31260 and S31254 stainless steels did not fail after up to 37700 h although S31603 failed after 533 h in constant-load tests under the same environmental conditions. Assuming active-path corrosion to be an anodic subprocess of stress corrosion crack growth, anodic polarization curves of the test materials were obtained in a synthetic seawater solution of pH 1 at 353 K. The maximum anodic current density of the active dissolution of S31603 stainless steel was ten times as large as that of S31260 stainless steel. This result qualitatively explains the difference in the crack growth behavior between S31603 and S31260 stainless steels.
  • Corrosion Behavior of Silicon-Bearing Steel in a Wet/Dry Environment Containing Chloride Ions

    pp. 1438-1443

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    DOI:10.2320/matertrans.MRA2007039

    The rust of Si-bearing steel was analyzed by EPMA, XRF, XPS and TEM, and the electrochemical behavior of the rusted steel was investigated by the electrochemical impedance spectroscopy (EIS) method after wet/dry cyclic corrosion test with chloride ions.
    The 2.0 mass% Si-bearing steel showed high corrosion resistance compared to carbon steel (SM) in the corrosion test. EPMA and XPS showed that Si existed as a intermediate oxidized state such as Si2+ in the inner rust layer for Si-bearing steel. TEM showed that nano-scale complex oxides containing Si were formed in the inner rust of the Si-bearing steel.
    EIS measurement was taken to estimate the rust resistance (Rrust) and corrosion reaction one (Rt) of the rusted steel. It was found that Rrust and Rt of Si-bearing steel were much larger than those of SM after the rust formation. The corrosion of Si-bearing steel could be suppressed by the formation of the nano-scale complex oxide containing Si in inner rust layer to prevent the penetration of Cl ions.
  • Pores and Microbubbles in Al and Al-XSi Alloys

    pp. 1444-1450

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    DOI:10.2320/matertrans.MRA2006351

    Pure aluminum (99.999%) cubes were polished by abrasive papers and then heated in a furnace at 873 K for 25 h in order to grow oxide on the polished surfaces, coded as Al/oxide. These Al/oxide samples were stacked with a pure Al cube and a Al-7 mass%Si cube, respectively, then heated in a furnace at 1023 K for 1200 s in an Ar+H2 atmospheric gas. The sandwiched samples were sectioned and polished after the heated sample was cooled to room temperature. The morphologies of the interface (or junction of the sandwich samples) were recorded photographically. Based on the recorded cavities shown at the interface, we measured both the radii of curvatures and contact angles of the cavities. When the Al/oxide stacking with pure Al sandwich samples was heated in Ar plus H2 gas, cavities were readily shown at the interface; very few cavities have been observed when samples were heated in Ar gas. The cavities were formed when an air-pocket was initiated at the microchannels by hydrogen diffusion, then grew and coalesced at the interface. The air-pockets remained at the interface of the heated Al/oxide stacking with pure Al sandwich sample and were entrapped as cavities after samples solidified. Microbubbles detached from the airpocket forming micropores trapped in a matrix of the Al/oxide stacking with Al-7 mass% Si cube sample.
  • Corrosion Behavior of Pure Iron by Different Droplet Volume of Sulfuric Acid Solution

    pp. 1451-1457

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    DOI:10.2320/matertrans.MRA2006354

    The influence of volume of aqueous sulfuric acid solution on the corrosion behavior of pure iron during the initial 0.6 ks was investigated by potentiostat and atomic force microscope (AFM). Three types of volume of solution, i.e., bulk solution, macro-droplet (millimeter size) and micro-droplet (micrometer size), were used.
    A micro-droplet with diameter of 1∼10 μm can be placed on a pre-assigned target micro-zone of specimen by the cantilever tip of AFM. The corrosion behavior beneath the droplet can be investigated using both the contact mode and the a.c. non-contact mode of AFM. The corrosion rate in bulk solution is much higher than that beneath a micro-droplet of sulfuric acid solution. In the case of a micro-droplet, the corrosion rate is smaller for the smaller droplet. The drying of the micro-droplet to a solid corrosion product in 25–30%RH condition is faster than that in 50–70%RH condition.
  • Activity Coefficient of AgO0.5 in the PbO-SiO2 Melt at 1273 K

    pp. 1458-1462

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    DOI:10.2320/matertrans.MRA2006251

    Activity coefficient of AgO0.5 in PbO-SiO2 melt equilibrated with Ag-Pb alloy in an alumina or a magnesia crucible was investigated at 1273 K. A chemical equilibrium technique was applied to the measurement. The oxygen partial pressure was also measured by an EMF method. The activity coefficient of AgO0.5 in the PbO-SiO2 melt was derived.
    The addition of SiO2 in the PbO melt decreases dissolution of Ag into the oxide phases. However, the activity coefficient of AgO0.5 increases slightly with an increase in the concentration of SiO2 in the PbO melt.
  • Numerical Simulation on Impact Velocity of Ceramic Particles Propelled by Supersonic Nitrogen Gas Flow in Vacuum Chamber

    pp. 1463-1468

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    DOI:10.2320/matertrans.T-MRA2007833

    A low-pressure cold spray, which is conducted in a vacuum chamber, is under development in Japan. In this paper, the gas flow-field as well as the particle velocity of the low-pressure cold spray is numerically solved. A special attention is paid to the effect of the pressure in the vacuum chamber (back pressure) on the particle velocity. The working gas is nitrogen, and its stagnation temperature upstream of the nozzle is set at 573 K. The back pressure is set at constant values ranging from 3×102 to 1×105 Pa. The stagnation pressure upstream of the nozzle is kept constant at 30 times as much as the back pressure. The numerical results show that the decrease in the back pressure causes the decrease in the particle velocity in front of the normal shock wave. On the contrary, the decrease in the back pressure eases the particle deceleration through the normal shock wave. As a whole, due to the balance of the effects of the back pressure and the normal shock wave, the optimum value of the back pressure to obtain the maximum impact velocity varies depending on the particle diameter.
  • In Situ Formation and Refinement of Mg2Si in Fiber-Reinforced AZ91D Magnesium Alloy

    pp. 1469-1475

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    DOI:10.2320/matertrans.F-MRA2007834

    In order to obtain a lightweight material having an excellent high-temperature strength, Mg alloy composites reinforced with short alumina fibers and in situ Mg2Si particles were fabricated. The composites were fabricated by pressureless infiltration of the Mg alloy melt into the preform consisting of the fibers and attached Si particles. The volume fraction of Si particles in the preform, the melting temperature of the Mg alloy, and the cooling rate after the infiltration were varied. P and CaF2 particles were also used as refiners of the Mg2Si. Based on the results, the conditions dispersed the Mg2Si particles finely and homogeneously and the formation and dispersion mechanism of the Mg2Si were clarified. Although the Si content exceeds its equilibrium solubility in the Mg melt when the volume fraction of the Si particles was 9.5 vol%, all of the Si particles reacted with the Mg alloy melt to form Mg2Si particles. The Mg2Si particles were homogeneously dispersed in the matrix, because the segmentation of Mg2Si particles in the infiltration was prevented due to the presence of fibers. As the melting temperature decreased or the cooling rate after the infiltration increased, the Mg2Si particles became finer. The introduction of P or CaF2 further promoted the refinement of the Mg2Si particles.
  • Interfacial Reaction between Ti-Al Binary Alloys and High Carbon Steel

    pp. 1476-1482

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    DOI:10.2320/matertrans.MRA2007012

    Diffusion bonding of Ti-Al binary alloys (Ti-10 to 40 mol% Al) to high carbon steel was carried out between 1073 and 1273 K for 0.9 to 8.1 ks in a vacuum, and the effect of the alloy composition on the interfacial microstructures and the bonding strength was investigated. Three regions, which were composed of reaction products with Ti, Al and Fe, a TiC layer, and ferrite, were formed around the interface, regardless of the alloy composition. The thickness of each region changed with an increase in the Al content in the Ti-Al alloy. In general, the TiC layer formed in Ti/steel joints is known to act as a barrier for diffusion of constituent elements across the interface and to inhibit the formation of other reaction products. In this study, the barrier effect of the TiC layer was overcome by the existence of Al. Although the Ti-Al/steel joints showed a relatively high bonding strength of more than 150 MPa in many cases, the joint with Ti-20 mol% Al alloy separated near the interface promptly after bonding treatment at 1273 K for 3.6 and 8.1 ks. The details and the application of the separation phenomenon are discussed.
  • Novel Electroforming Process for Bulk Nanocrystalline Ni-W Alloys with Minimizing W-Concentration Gradient and Fluctuation

    pp. 1483-1491

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    DOI:10.2320/matertrans.MRA2006346

    An electroforming process for fabricating bulk nanocrystalline Ni-W alloys with minimizing W-concentration gradient and fluctuation is presented. The homogeneities of W-concentration in both micrometer scale and millimeter scale are guaranteed from the W-concentration profiles obtained by the linear analyses of the energy dispersive x-ray spectroscopy (EDS). Mass balance analyses of the metallic ions in the electrolyte are performed by the combination of the experimental results of the inductively coupled plasma mass spectrometry (ICP-MS) and the exact solutions of the simultaneous differential equation. The homogeneous bulk nanocrystalline Ni-W alloy with the thickness above 2 mm is featured for the first time.
  • Heat Transfer Model for Thin Solidified Material in Continuous Casting

    pp. 1492-1500

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    DOI:10.2320/matertrans.MRA2007019

    An asymptotic explicit numerical method was developed for the Stefan problem in which a series of solidification rates and boundary temperatures for the solidified material are given and the boundary heat flux is returned. A spectral method with several basis functions of a specialized shape in the solidification problem was adopted. Combined with multi-dimensional computational fluid dynamics methods for the liquid zone, this method is adequate for resolving the thin solidified material problem for a variety of continuous casting processes e.g. thin slab continuous casting, melt-spinning, twin roll casting, and edge-defined film-fed growth. The method is less expensive than conventional numerical methods and as accurate as a direct numerical approach such as the Finite Difference Method especially in the case of the Stefan number >> 1 or in the case of variable material properties.
  • Estimation of Glass Forming Ability of Amorphous Alloys Based on the Thermal Analysis Data during Cooling

    pp. 1501-1504

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    DOI:10.2320/matertrans.MRA2007026

    Based on the analytic approach, a new parameter ΔTrn (reduced difference of nucleation temperatures) for estimating the glass forming ability (GFA) has been suggested with simple DTA data at two different cooling rates. The new parameter described GFA of amorphous alloys very well. Besides, an equation for estimating the critical cooling rate has also been suggested using the new parameter for GFA. The results of prediction model have been in good agreement with the previous experimental results.
  • Hydroxyapatite Formation on CaTiO3 Film Prepared by Metal-Organic Chemical Vapor Deposition

    pp. 1505-1510

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    DOI:10.2320/matertrans.MRA2007016

    Calcium titanate (CaTiO3) films were prepared on commercially pure titanium (CP-Ti) by metal-organic chemical vapor deposition using Ca(dpm)2 and Ti(O-i-Pr)2(dpm)2 precursors. The formation of hydroxyapatite (HAp, Ca10(PO4)6(OH)2) on CaTiO3 film was investigated in a Hanks’ solution. The formation rate of HAp was significantly affected by deposition conditions of CaTiO3 films, particularly substrate temperature (Tsub). The time for the HAp formation was 3.6 Ms (42 d) on the CaTiO3 film prepared at Tsub=873 K, wheras that was 1.2 (14 d) and 0.3 Ms (3 d) on that prepared at Tsub=973 and 1073 K, respectively. Octacalcium phosphate (OCP, Ca8H2(PO4)6·5H2O) was identified on the CaTiO3 film prepared at Tsub=1073 K by the immersion for 21.6 ks.
  • Effect of Dissolved Oxygen Content on Pin-on-Disc Wear Behavior of Biomedical Co-Cr-Mo Alloys in a Like-on-Like Configuration in Distilled Water

    pp. 1511-1516

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    DOI:10.2320/matertrans.MRA2007601

    The wear behavior of a forged Co-29Cr-6Mo alloy without any Ni and C added has been investigated by using a tribosystem consisting of a pin-on-disc type wear testing machine in distilled water containing different dissolved oxygen content. Dissolved oxygen content in the distilled water was controlled by aerating with oxygen or by deaerating with argon. Wear volume in the distilled water containing high oxygen content is approximately two times larger than in that containing low oxygen content. Accordingly, it is deduced that the overall wear volume is significantly affected by the dissolved oxygen content in the distilled water surrounding the tribosystem. Although abrasive wear, caused by wear debris, is operative as a wear mechanism in the present tribosystem irrespective of oxygen content, the transfer of the wear debris to sliding surfaces, as well as the aggregation of the wear debris on the sliding surfaces, is more prone to occur during the wear process with the lower oxygen content. Therefore, in the present tribosystem with the lower oxygen content, since the transfer of the wear debris to the disc or the pin readily occurs, the generation of the wear debris does not directly contribute to the wear volume, leading to the apparently lower wear volume in the tribosystem with lower oxygen content than in that with higher oxygen content; the transfer of the wear debris is not counted as wear loss because the wear volume is estimated based on the loss in disc and pin weight that occurs during the wear test.
  • Microstructure and Mechanical Properties of Co-29Cr-6Mo Alloy Aged at 1023 K

    pp. 1517-1522

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    DOI:10.2320/matertrans.MRA2007606

    Mechanical properties of Co-29Cr-6Mo alloys consisting of ε phase and σ phase were examined at room temperature. Solution treatment at 1523 K for 7.2 ks was carried out for cast Co-29Cr-6Mo alloy, followed by various aging treatments at 1023 K for up to 21.6 ks. The area fraction of the σ phase in the aged alloys increases with the aging time at 1023 K and reaches 0.6% after aging at 1023 K for 21.6 ks. However, mechanical properties such as 0.2% proof strength, ultimate tensile strength and plastic elongation of the aged alloys do not depend on the aging time. It is found that the σ phase less than 0.6% does not cause the deterioration of mechanical properties of the aged Co-29Cr-6Mo alloy.
  • Effect of Surface Microstructure of Titanium Sheet on the Photocatalytic Activity of Its Oxide Film

    pp. 1523-1528

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    DOI:10.2320/matertrans.MRA2006343

    Titanium oxide film was formed by thermal oxidation directly on titanium sheet. Pretreatments on titanium sheet were carried out using annealing in Argon at 873 K, 973 K and 1073 K for 5 min, 30 min and 100 min, respectively. Photocatalytic performance of titanium oxide film was examined by measuring the degradation of methylene blue. The crystallographic orientation distribution of titanium sheet was analyzed by SEM/EBSP technique whereas the crystalline structure of titanium oxide film was characterized by XRD. Development of recrystallization texture on titanium sheet gained during the annealing, in which stored energy was lowered, was proved to facilitate formation of the preferable oxide film with high photocatalytic property during oxidation. However, grain size of titanium sheet was found to be another important and effective factor since grain boundaries were testified to be the channels for the diffusion of oxygen in the thermal oxidation reaction. Grain coarsening of titanium sheet is probably a detriment to high photocatalytic activity of its oxide film.
  • Preparations of CaRuO3 Body by Plasma Sintering and Its Thermoelectric Properties

    pp. 1529-1533

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    DOI:10.2320/matertrans.MRA2007055

    Dense CaRuO3 body was synthesized by spark plasma sintering (SPS) using CaCO3 and RuO2 powders. The second phases of CaO and RuO2 were identified at the Ru to Ca molar ratio in the source powder (RRu/Ca) of 0.5 to 0.8 and at RRu/Ca=1.1 to 1.4, respectively. A non-stoichiometric solid solution range of bulk CaRuO3 body was first found in the RRu/Ca range between 0.7 and 1.0. The density increased with increasing RRu/Ca and the highest density was 97% at RRu/Ca=1.4. The electrical conductivity (σ) decreased with increasing temperature, showing a metallic conduction behavior. The σ increased from 1×105 to 5×105 Sm−1 with increasing RRu/Ca at room temperature (RT). The Seebeck coefficient (S) was around 25 to 35 μVK−1 from RT to 1023 K independent of composition, exhibiting a p-type conduction. The thermal conductivity (κ) slightly increased with increasing temperature and showed the lowest value at RRu/Ca=1.0. The dimensionless figure of merit (ZT) had the maximum at RRu/Ca=1.1, and the highest ZT value was 0.034 at 1020 K.
  • Life Cycle Assessment of Manufacturing System of Lead-Free Bronze Products

    pp. 1534-1537

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    DOI:10.2320/matertrans.MRA2006349

    Inventory analysis of manufacturing system for both conventional Pb-free bronze made from virgin materials and new Pb-free bronze made by removing Pb from scrap Pb-bronze was assessed from the view point of life cycle assessment (LCA). The result shows that new manufacturing system of Pb-free bronze made by removing Pb from scrap Pb-bronze reduces such environmental impacts as global warming, acidification, energy consumption, resource consumption significantly. Thus, in LCA perspective, the new manufacturing system using a recycling Pb-free bronze is economically superior to the conventional one using virgin materials.
  • Precipitated Phases and Corrosion Behavior in the Dissimilar Alloy 690-SUS 304L Joints Formed by EBW and GTAW

    pp. 1538-1547

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    DOI:10.2320/matertrans.MER2007010

    This study investigates the correlation between the microstructure and the corrosion resistance properties of the fusion zone of Alloy 690-SUS 304L stainless steel dissimilar weldments formed by electron beam welding (EBW). The effects of the EBW process are evaluated by comparing the microstructure and corrosion resistance properties of the EBW weldment with those of Alloy 690-SUS 304L weldment formed by gas tungsten arc welding (GTAW). The experimental results reveal that the interdendritic region of the fusion zone of the EBW weldment contains fine TiN precipitates and Cr-Ni rich phases. The TiN precipitates are originated from the Alloy 690 base metal, while the Cr-Ni rich phases, a new formation of precipitates, is precipitated in the region around TiN during solidification. Microscopic analysis of the samples following a modified Huey test indicates that the matrix around TiN precipitate and the Cr-Ni rich phase precipitate provide the preferred sites for corrosion pit initiation. Due to the rapid cooling in the EBW process, relatively fewer and smaller TiN precipitates and Cr-Ni rich phases are formed in the weldment. Consequently, only limited corrosive pitting is observed which indicates better interdendritic corrosion resistance properties in comparison to joints with GTAW process. Furthermore, rapid solidification in the fusion zone results not only the suppression of chromium carbide precipitation but also the chromium depletion at the grain boundaries. As a result, the intergranular corrosion resistance and interdendritic corrosion resistance of the EBW weldment are significantly higher than that of the GTAW weldment.
  • Determination of Dispersive Properties of Silicas by Inverse Gas Chromatography: Variation with Surface Treatment

    pp. 1548-1553

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    DOI:10.2320/matertrans.MER2007046

    The application of inverse gas chromatography (IGC) to the examination of the surface properties of untreated crystalline and fused silica and surface-treated silicas with silane coupling agents is discussed. The carbon content of the silane coupling agents adsorbed on the surface of the silicas was determined by means of a Carbon Determinator. If the assumption is made that each silane coupling agent molecule occupies an area of 0.5∼1 nm2, the adsorption amounts show that multilayers are generally adsorbed onto the silica surfaces. This paper presents and discusses the dispersive properties expressed by γSD, the dispersive component of the surface free energy, as determined at various temperatures. At the same temperature of IGC measurement, the values of γSD determined by IGC were lower for the crystalline silica than for the fused silica. This means that crystalline silica is more stable than fused silica. The silica surface-treated with γ-methacryloxy propyl trimethoxy silane (MTMS) shows a relatively high γSD value(42.75 mJ·m−2 at 160°C). This means that this sample should be compatible with polyester(27±3 mJ·m−2 at 290°C) at high temperature. The silicas that were surface-treated with γ-glycidoxy propyl trimethoxy silane (GMS) and γ-mercapto propyl trimethoxy silane (MCMS) exhibit γSD values that are in close agreement with those of almost all resins(30 mJ·m−2 at 160°C). The γSD value of the silica surface-treated with γ-amino propyl triethoxy silane (AES) is similar to that of epoxy resin(40 mJ·m−2 at 80°C). This means that this sample is compatible with epoxy resin at relatively low temperatures.
  • ATR-FTIR and Nanoindentation Measurements of PMDA-ODA Polyimide Film under Different Curing Temperature

    pp. 1554-1557

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    DOI:10.2320/matertrans.MER2007045

    ATR-FTIR apparatus is used to measure the curing rate of PMDA-ODA polyimide film in order to avoid sinusoidal interference fringe. From the corrected height method, the curing rate is found to have positive correlative trend with the curing temperature. It was shown that the curing rate under 300 °C is 92.1% than that under 400 °C for one hour. The curing degree related to the mechanical properties was further demonstrated by nanoindentation. The results show that the higher the curing rate the higher the nano-hardness and nano-modulus due to the thermal imidization of polyimide characteristic. The nano-hardness ratio of curing degree at 300 °C over curing degree at 400 °C is 0.89, while the nano-modulus of which is 0.95.
  • Deposition of Nanocrystalline Zinc-Nickel Alloys by D.C. Plating in Additive Free Chloride Bath

    pp. 1558-1565

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    DOI:10.2320/matertrans.MER2007022

    Nanocrystalline zinc-nickel alloy coatings were electro-deposited in chloride bath containing ZnCl2 (50–200 gL−1), NiCl2.6H2O (50-200 gL−1) and H3BO3 (40 gL−1) at 45°C. The initial alloy composition, as investigated by voltammetry, chronopotentiometry or EDX analysis, exhibited a pronounced dependence on the composition of plating bath. However, the alloy composition tended to approach an upper limit of 18 atomic percent when deposits grew thicker, for most of the plating bath compositions. The process was clearly the anomalous codeposition, which was considered to be due to the formation of an adsorbed layer of Zn(OH)2 containing nickel cations, as an intermediate product, whose composition determines the composition of the electro-deposited alloy. The electro-deposited coatings comprised of single-phase structure of γ-phase (Ni5Zn21) for about 12–18 atomic percent nickel and a mixture of γ- and η-phases (hcp) for nickel atom percent below 8. The grain size decreased from about 50 nm to 20 nm with decrease in nickel content away from the stoichiometric composition of Ni5Zn21 along with a decrease in hardness from about 450KHN to 150KHN. The decrease in hardness with a decrease in grain size seems attributable to the grain boundary sliding as predominant deformation mechanism. Anodic dissolution of the alloys involved pronounced dezincification, forming α-phase (fcc) that dissolved at the end.
  • Hydrogen Sorption Property of Zr55V29Fe16 Nanopowder Synthesized by the Plasma Arc Discharge Process

    pp. 1566-1570

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    DOI:10.2320/matertrans.MER2007031

    The present study focused on the synthesis of a Zr-V-Fe-based nanopowder for investigating the possibility of synthesizing zirconium-based alloyed getter nanoparticles by the plasma arc discharge process. The chamber pressure and the mixing ratio of hydrogen:argon in the powder synthesis atmosphere were changed. The chemical composition, phase structure, particle size and hydrogen sorption property of the synthesized powders were analyzed using XRF, XRD, TEM, XPS and the ASTM-F798 method. The synthesized Zr-V-Fe-based powders have a different chemical composition than the raw material, Zr57V36Fe7. The chemical composition of the synthesized Zr-V-Fe-based powders approached that of the raw material with an increasing hydrogen fraction in the powder synthesis atmosphere. The synthesized Zr55V29Fe16 powder has a mixed phase structure of the Zr, ZrH2, FeV and Zr(V1-xFex)2 phases. This powder has an average particle size of about 20 nm. The Zr55V29Fe16 nanopowder synthesized by the plasma arc discharge process showed getter characteristics, even though it had a lower hydrogen sorption speed than the Zr57V36Fe7 getter powder synthesized by the conventional hydride-dehydride method.
  • Coarsening Kinetics of Al3Sc Precipitates in an Al–Mg–Sc Alloy Aged at 573 K

    pp. 1571-1574

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    DOI:10.2320/matertrans.MRP2007048

    The coarsening of Al3Sc precipitates in an Al–1 mass%Mg–0.27 mass%Sc alloy aged at 573 K has been examined using a model developed by Kuehmann and Voorhees. The average size of Al3Sc precipitates was evaluated by transmission electron microscopy and electrical resistivity was employed to measure the Sc concentration in the matrix. Kinetic analyses revealed that before the onset of a coarsening stage, there exist mixed stages of nucleation and growth and of growth and coarsening. The coherent Al/Al3Sc interface energy γ is estimated as 0.23 Jm−2 from data on coarsening alone. The transition from a coherent interface to a semi-coherent interface caused no change in γ.
  • Synthesis of Tungsten Oxide Particles by Chemical Deposition Method

    pp. 1575-1577

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    DOI:10.2320/matertrans.MEP2007057

    Due to the high potential of photoconductive behavior used in electrochromic and sensor devices, tungsten oxide (WO3) is the most promising candidate applied for electrochromic materials, gas sensors, and dye sensitized solar cells. Adsorbing the visible blue light by tungsten oxide nanoparticles would thus be used efficiently to enhance the sun-light harvest efficiency. Recent investigations have been promoted by new methods of ultrafine powder production and their applications. Nanocrystalline tungsten oxide can be prepared by sputtering methods, gas condensation methods, and chemical deposition method. In this study, we would like to prepare of tungsten oxide nanoparticles by chemical deposition method and investigate the experimental parameters of various organic solutions and discuss the relationship between absorbance spectra and which by chemical deposition method. Purged O2 into the various solvent (i.e. DMF and acetylacetone solution), WCl6 was added into the solvent slowly and stirred vigorously. During the filtration process solutions were characterized and analyzed by particles size distribution, UV-visible absorption, and TEM observation. The size of tungsten oxide particles synthesized in DMF is smaller than that in acetylacetone solutions from TEM observation. These results may be related to particle sizes or agglomerated behavior of tungsten oxide. In the photochromic data, it exhibits absorbance result due to valence change of tungsten ion and photochromic effect of tungsten oxide nanoparticles. Since some papers also have been reported that the highest intensity of the solar spectrum is in the blue region, the modification of the oxide semiconductor for blue-light absorption will effectively increase the photon harvest from the incident sunlight and thus generate more electron-hole pairs in addition to those from dyes. It would be appropriately applied in the design of solar cell devices.

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