Papers by Author: Goroh Itoh

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Authors: Hideki Iwahashi, Goroh Itoh, Katsuhiro Saitoh, Takahiro Shikagawa
Abstract: An increasing interest has been being taken in hydrogen as a clean energy for solving the global environmental problems. In order to use the hydrogen in safety, investigation on the hydrogen behavior is required. Although hydrogen microprint technique (HMPT) has been known to be effective to investigate the hydrogen behavior, the low detection efficiency for hydrogen was reported. Ion-plating (IP) was reported to increase the detection efficiency in HMPT emitted from the specimen by plastic deformation. On the other hand, no such increase was found for hydrogen permeating through the specimen ion-plated with substrate heating in the previous study by the authors. In the present study, the sheet samples of pure aluminum with 99.99% purity were dehydrogenated and subjected to (a) holding in the IP chamber, (b) bombardment with Ar ions, (c) substrate heating after the bombardment and (d) holding in air. Hydrogen behavior in these samples has been investigated by means of thermal desorption spectroscopy (TDS). The amount of desorbed hydrogen was evidently larger in the conditions of (a) and (b) than in (d). However, the amount of desorbed hydrogen was decreased by the substrate heating (c) to the same level as in (d).
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Authors: Kazuhiro Masuda, Goroh Itoh, Nobuhide Itoh
Abstract: In recent years, reducing carbon dioxide is being demanded in terms of preventing global warming. Lightening autobodies is one of the most practical ways to conduct it, for which converting the body sheets from conventional steel to Al-Mg-Si alloy is effective. Although the Al-Mg-Si alloys have the advantage that they have hardenability during paint baking and do not cause stretcher strain patterns, poor formability is a crucial drawback. Bendability is one of the most important properties related to formability. However, there has been no assessing method having both speediness and quantitative reproducibility. In this study, we have developed a assessing method based on the electric resistance decrease arising from the decrease in conducting section when cracks are formed by bending. Bendability was assessed by electrical resistance change as well as by crack density on the tension surface measured with an SEM. It was found that the new method have far greater speediness with the same quantitative reproducibility than the crack measurement method.
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Authors: T. Izumi, Goroh Itoh
Abstract: High-magnesium Al-Mg alloys are known to be sensitive to stress corrosion cracking involving environmental hydrogen, hydrogen invading from the corrosive environment. In this study, the behavior of the environmental hydrogen in Al-6%Mg and Al-8%Mg binary alloy sheets stretched by 10% during exposure to 3.5%NaCl solution has been investigated by means of hydrogen microprint technique. Microprint image is observed on one surface while the other surface is exposed to the solution. In both alloys, the silver particles corresponding to the sites where hydrogen atoms are emitted from the inside of the sheets are shown on the slip lines. It is shown that the hydrogen atoms are transported with moving dislocations in the alloys.
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Authors: Hidetoshi Umeda, Goroh Itoh, Yoshinori Kato
Abstract: The effect of the annealing atmosphere, the annealing temperature etc. on the hydrogen behavior in several Al-4% Mg alloys during heat treatment, was investigated. The results have shown that the hydrogen content in the as-cast slab is uniform, while the hydrogen content in the slab tends to be higher near the surface than in the interior after annealing. Such a tendency becomes more marked when annealing time is prolonged and Si and Fe content is lowered. The condensation of hydrogen near the surface can be seen only when it is annealed in a wet atmosphere. When annealed in a dry atmosphere, the hydrogen content near the surface becomes lower than in the center of the specimen. The hydrogen in Al-Mg alloys tends to be released to outside intrinsically at temperatures around 400°C and above. It is revealed that oxide film formed on the surface prevents the hydrogen from being released to outside.
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Authors: Tomohiro Tsutsumi, Takahito Watakabe, Goroh Itoh
Abstract: Investigation on the behavior of hydrogen is needed to spread the use of hydrogen fuel cell vehicles. Hydrogen microprint technique (HMPT) has been known as an effective method to investigate the hydrogen behavior by visualizing the microscopic location of hydrogen in relation to the microstructure. In the present study, the behavior of electrolitically charged hydrogen in 6061 and 7075 aluminum alloys with T6-temper has been investigated by means of HMPT. Both in the two alloys, hydrogen was detected on constituent particles and in the matrix. Total amount of detected hydrogen was markedly larger in 7075 than in 6061, although the distribution in depth direction far narrower and the fraction of hydrogen detected in the matrix with respect to that on the constituent was larger. These fact was presumed to be caused by the difference in the fine precipitates between the two alloy formed during final aging treatment.
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Authors: Takahito Watakabe, Goroh Itoh, Yuji Hatano
Abstract: Hydrogen embrittlement has been known to occur by invading hydrogen (environmental hydrogen) in some metallic materials under several certain conditions, although the cause has not been clarified yet. To clarify the cause, investigations on the behavior of environmental hydrogen in metallic materials are needed. It has been reported that environmental hydrogen invades 7075 aluminum alloy through the second-phase particles (Al7Cu2Fe). However it has not been clarified yet whether environmental hydrogen invades aluminum through the interface between the matrix and second-phase or through the bulk of second-phase particles. In this study, tritium autoradiography technique, TARG, has been applied to an aluminum alloy containing a single kind of second-phase particles (Al7Cu2Fe), to elucidate the invasion behavior of hydrogen from two different environments: tritiated water and tritium gas. In TARG, hydrogen (tritium) atoms that stay in the vicinity of the surface can be detected as silver particles. Silver particles (hydrogen atoms) were primarily detected on the interface between the matrix and second-phase. Thus most of the invading hydrogen is concluded to be trapped by the interface.
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Authors: Tsing Zhou, Goroh Itoh, Yohei Iseno, Yoshinobu Motohashi
Abstract: The hot-rolled and extruded AZ31 specimens are subjected to tensile tests at room and elevated temperatures. At room temperature, the yield stress of the hot-rolled specimen is significantly higher than that of the extruded, the reason for which is related to the different textures developed in the two type specimens, as well as the different slip systems activated. At elevated temperatures, the strain rate sensitivity and the activation energy are obtained to characterize the deformation mechanism of the alloy during the temperature range of 423~573K.
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Authors: Sho Ishii, Goroh Itoh, Shingo Mukae, Nobuhide Itoh
Abstract: Lifetime of tungsten electrodes for fusing was investigated in relation to their microstructure. Tungsten electrodes with two types of microstructures (recrystallized equi-axed and unrecrystallized fibrous) were subjected to repeated welding tests where work material was a tough pitch copper. Surface appearance of the electrodes after the test was observed with an SEM. Circumferential edge cracks were observed in the equi-axed electrode, which were presumed to be initiated by plastic flow of the work material. Although cracks were formed in the center of both types of electrodes, the total length of them is longer in the equi-axed electrode. Therefore, the lifetime was expected to be longer in the fibrous electrode than the equi-axed.
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