MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 48 , Issue 6
Showing 1-50 articles out of 67 articles from the selected issue
  • Noritaka Yusa, Ladislav Janousek, Kenzo Miya
    2007 Volume 48 Issue 6 Pages 1162-1165
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Hironori Tohmyoh, Takuma Suzuki, S. Reaz Ahmed, Masumi Saka
    2007 Volume 48 Issue 6 Pages 1166-1172
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Takato Takemura, Manabu Takahashi, Masanobu Oda, Hidekazu Hirai, Atsus ...
    2007 Volume 48 Issue 6 Pages 1173-1178
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Hideo Cho, Takuma Matsuo, Mikio Takemoto
    2007 Volume 48 Issue 6 Pages 1179-1183
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Masayasu Ohtsu, Yuichi Tomoda
    2007 Volume 48 Issue 6 Pages 1184-1189
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Ichihiko Takahashi, Michio Ushijima
    2007 Volume 48 Issue 6 Pages 1190-1195
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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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  • Shiro Biwa, Takushi Kamiya, Nobutada Ohno
    2007 Volume 48 Issue 6 Pages 1196-1201
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Koichiro Kawashima, Morimasa Murase, Keiji Shibata, Toshihiro Ito
    2007 Volume 48 Issue 6 Pages 1202-1207
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Takuma Matsuo, Naoaki Yokoi, Hideo Cho, Mikio Takemoto
    2007 Volume 48 Issue 6 Pages 1208-1214
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Yunping Li, Manabu Enoki
    2007 Volume 48 Issue 6 Pages 1215-1220
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Kaita Ito, Manabu Enoki
    2007 Volume 48 Issue 6 Pages 1221-1226
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Eiichi Sato, Mitsuharu Shiwa, Yoshio Shinagawa, Takashi Ida, Satoshi Y ...
    2007 Volume 48 Issue 6 Pages 1227-1235
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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”.
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  • Arief Gunawan, Sohichi Hirose
    2007 Volume 48 Issue 6 Pages 1236-1243
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Shoichi Nambu, Manabu Enoki
    2007 Volume 48 Issue 6 Pages 1244-1248
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Doo-Byung Yoon, Jin-Ho Park, Young-Chul Choi, Hyu-Sang Kwon, Joon-Hyun ...
    2007 Volume 48 Issue 6 Pages 1249-1253
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Yorinobu Murata, Hiroki Toda, Chiaki Tawa, Masahiro Kiji, Noriyasu Ogu ...
    2007 Volume 48 Issue 6 Pages 1254-1259
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Yoshihiko Yokoyama, Markus Wilde, Katsuyuki Fukutani, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1261-1265
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Albertus Deny Setyawan, Hidemi Kato, Junji Saida, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1266-1271
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Qingsheng Zhang, Wei Zhang, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1272-1275
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Yoshihiko Yokoyama, Tohru Yamasaki, Masahiko Nishijima, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1276-1281
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Yoshihiko Yokoyama, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1282-1287
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Hirofumi Ito, Tokujiro Yamamoto, Masashi Hasegawa, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1288-1291
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Tsunehiro Takeuchi, Daisuke Fukamaki, Hidetoshi Miyazaki, Kazuo Soda, ...
    2007 Volume 48 Issue 6 Pages 1292-1298
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Akihiko Hirata, Takuro Morino, Yoshihiko Hirotsu, Keiji Itoh, Toshihar ...
    2007 Volume 48 Issue 6 Pages 1299-1303
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Akira Takeuchi, Budaraju Srinivasa Murty, Masashi Hasegawa, Srinivasa ...
    2007 Volume 48 Issue 6 Pages 1304-1312
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • T. Kumagai, D. Nikkuni, S. Hara, S. Izumi, S. Sakai
    2007 Volume 48 Issue 6 Pages 1313-1321
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • K. Mondal, T. Ohkubo, T. Mukai, K. Hono
    2007 Volume 48 Issue 6 Pages 1322-1326
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Junji Saida, Hidemi Kato, Albertus Deny Heri Setyawan, Kyosuke Yoshimi ...
    2007 Volume 48 Issue 6 Pages 1327-1335
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Kazuki Sugita, Masataka Mizuno, Hideki Araki, Yasuharu Shirai
    2007 Volume 48 Issue 6 Pages 1336-1339
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Takeshi Nagase, Akihiro Nino, Yukichi Umakoshi
    2007 Volume 48 Issue 6 Pages 1340-1349
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Y. F. Sun, C. H. Shek, S. K. Guan
    2007 Volume 48 Issue 6 Pages 1350-1354
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Zeng Yuqiao, Nobuyuki Nishiyama, Akihisa Inoue
    2007 Volume 48 Issue 6 Pages 1355-1358
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • J. M. Pelletier, Y. Yokoyama, A. Inoue
    2007 Volume 48 Issue 6 Pages 1359-1362
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Yoshihiko Yokoyama, Hasse Fredriksson, Hideyuki Yasuda, Masahiko Nishi ...
    2007 Volume 48 Issue 6 Pages 1363-1372
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Hiroshi Fujita
    2007 Volume 48 Issue 6 Pages 1373-1379
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • D. J. Santjojo, Tatsuhiko Aizawa, S. Muraishi
    2007 Volume 48 Issue 6 Pages 1380-1386
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • S. Mironov, Y. Motohashi, R. Kaibyshev
    2007 Volume 48 Issue 6 Pages 1387-1395
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Kwang-Jin Lee, Shinji Kumai, Naonori Kawamura, Nobuhiro Ishikawa, Kazu ...
    2007 Volume 48 Issue 6 Pages 1396-1405
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Jie Xing, Xuyue Yang, Hiromi Miura, Taku Sakai
    2007 Volume 48 Issue 6 Pages 1406-1411
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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  • Masakazu Seki, Mitsuru Fujimoto, Toshiyuki Fujii, Masaharu Kato, Susum ...
    2007 Volume 48 Issue 6 Pages 1412-1416
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Hisao Kikugawa, Takashi Asaka, Masahito Miyake
    2007 Volume 48 Issue 6 Pages 1417-1421
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Hidetoshi Somekawa, Alok Singh, Toshiji Mukai
    2007 Volume 48 Issue 6 Pages 1422-1426
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Eiichi Wakai, Masami Ando, Tomotsugu Sawai, Somei Ohnuki
    2007 Volume 48 Issue 6 Pages 1427-1430
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Jun-ichi Tani, Masami Mayuzumi, Taku Arai, Nobuyoshi Hara
    2007 Volume 48 Issue 6 Pages 1431-1437
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Toshiyasu Nishimura
    2007 Volume 48 Issue 6 Pages 1438-1443
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Teng-Shih Shih, Chi-Yu Shie, Pai-Sheng Wei
    2007 Volume 48 Issue 6 Pages 1444-1450
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Rongguang Wang, Mitsuo Kido
    2007 Volume 48 Issue 6 Pages 1451-1457
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Shigeru Ueda, Tomomasa Kumagai, Katsunori Yamaguchi
    2007 Volume 48 Issue 6 Pages 1458-1462
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Hiroshi Katanoda, Minoru Fukuhara, Naoko Iino
    2007 Volume 48 Issue 6 Pages 1463-1468
    Published: June 01, 2007
    Released: May 25, 2007
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    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.
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  • Kazunori Asano, Hiroyuki Yoneda
    2007 Volume 48 Issue 6 Pages 1469-1475
    Published: June 01, 2007
    Released: May 25, 2007
    JOURNALS FREE ACCESS
    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.
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