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Volume 74, Issue 10
Displaying 1-12 of 12 articles from this issue
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Regular Articles
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Kazuhiro Hasezaki, Takashi Hamachiyo, Maki Ashida, Takashi Ueda, Yasut ...Article type: Regular Article
2010 Volume 74 Issue 10 Pages 623-628
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSFine grained samples with a nominal composition of Bi0.5Sb1.5Tex (x=3.0 to 3.4) were prepared by mechanical alloying (MA). Average grain sizes were found to range from 1.0 to 2.1 μm. Tellurium precipitation at x=3.1 was observed by scanning electron microscopy (SEM), X-ray diffraction and differential thermal analysis (DTA). Electrical conductivity as well as Hall and Seebeck coefficients were measured from 300~470 K. Using the relationship between Hall mobility and temperature, carrier scattering factors of the Bi0.5Sb1.5Tex samples were estimated to range from r=−0.9 to −2.0. The thermal conductivities of the samples were found to range from 0.94 to 1.00 Wm−1 K−1 at room temperature. Excess tellurium was recognized to be responsible for the decrease in thermal conductivity. The Lorenz number and the carrier component of thermal conductivity were calculated from the scattering factor and the Fermi integral. The phonon component of thermal conductivity was dominant in the Bi0.5Sb1.5Tex samples. The Seebeck coefficient of the Bi0.5Sb1.5Tex samples was higher than that from the available data which means that the absolute scattering factor of the Bi0.5Sb1.5Tex samples was large. A maximum figure of merit of 7.02×10−3 K−1 was obtained at 310 K for the Bi0.5Sb1.5Te3.1 sample. This high figure of merit results from an enhanced Seebeck coefficient that is due to an increased absolute scattering factor. High thermoelectric performance can, therefore, be established by a reduction in the phonon component of the thermal conductivity and also by an enhanced Seebeck coefficient, which results from an increased absolute scattering factor for finely grained Bi0.5Sb1.5Tex samples that were prepared by MA.
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Shinichiro Haruki, Hirofumi Tokunaga, Sohei Sukenaga, Noritaka Saito, ...Article type: Regular Article
2010 Volume 74 Issue 10 Pages 629-634
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSThe density and the surface tension of the binary tellurite melts, (M2O-TeO2 M=Li, Na and K) were measured. We investigated the thermal and compositional dependences of the properties.
It was found that the density and the surface tension of the binary tellurite melts decreased with increasing temperature and M2O content.
The dependences of the density and the surface tension were attributed to the behavior of added cation and the structural change of melt. It was thought that the added cation intruded into the interspace of the complex tellurite anion, and molar volume decreased, when the radius of added cation was small. TeO4 trigonal bipyramid changes to TeO4 − trigonal bipyramid and TeO3 trigonal pyramid with increasing temperature and M2O content. We explained that the dependences of the density and the surface tension on the behavior of added cation and the structural change of melt.
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Li-Bin Niu, Teruyuki Goto, Takahiro Nakane, Hiroshi Takaku, Yoshihiro ...Article type: Regular Article
2010 Volume 74 Issue 10 Pages 635-642
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSPitting corrosions of 3.5NiCrMoV steel and 13Cr steel, the materials used respectively for rotors and blades of low-pressure steam turbines in power plants, are evaluated by anodic polarization tests in the simulated AVT (All Volatile Treatment) water, and also in the waters added with chloride ions (Cl−) and sulfate ions (SO4 2−), at 308 K. It is clarified that the pitting corrosions of 3.5NiCrMoV steel, in addition to the uniform corrosions, are promoted by adding Cl− and SO4 2− ions into the test waters. As for 13Cr steel, the high pitting corrosion resistance is shown in the test water with only SO4 2− ions due to the stable passive film formed on the specimen while the pitting corrosion is remarkably promoted by adding Cl− ions into the water. It is clear that the coexistence of SO4 2− ions with Cl− ions in the test water exhibits an inhibiting effect on the initiation of corrosion pits but also an accelerating effect on the pit growth, for the high-alloyed 13Cr steel.
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Yoshihisa Sechi, Akio Takezaki, Taihei Matsumoto, Takuya Tsumura, Kazu ...Article type: Regular Article
2010 Volume 74 Issue 10 Pages 643-649
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSDissimilar laser brazing of boron nitride ceramics and cemented carbide has been investigated by using silver-copper-titanium braze alloys with different titanium contents of up to 2.80 mass%; efficient bond strength was achieved using brazes with more than 1.25 mass% of titanium. The contact angle between hexagonal boron nitride ceramics and the molten braze, which was measured by the sessile drop method at 1123 K, decreased to less than 30° when the Ti content was over 0.41 mass%. The difference in the wetting property determined by laser brazing method and that by sessile drop method is attributed to the difference in the heating process of the two methods. Structural analysis of the interface between the boron nitride ceramics and the braze was carried out by electron probe micro-analysis (EPMA).
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Naotaka Fukami, Ryohei Wakamatsu, Nobuya Shinozaki, Kyoko WasaiArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 650-655
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSThe wettability between porous MgAl2O4 substrates and molten iron was investigated by the sessile drop method at 1833 K as a basic study in order to elucidate the interactions between molten iron and a refractory material. For the study, MgAl2O4 substrates with 2, 8, 13, 27, and 39% porosity were prepared. The contact angle increased with the substrate porosity. In substrates with 2, 8, and 13% porosity, the contact angles were independent of time. In contrast, for substrates with 27% and 39% porosity, the contact angle decreased during the first hour and then gradually reached a steady value. The decrease in contact angle with time was attributed to the interfacial free energy. The work of adhesion was 1.27 J•m−2, and it was suggested that the interfacial bond consists of not only a physical bond but also a chemical bond.
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Shinji Koyama, Kentaro KawasumiArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 656-661
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSThe purpose of this study is the development of simultaneous processing of diffusion bonding and surface nitriding. Carbon steel was used as the base material. The surface was nitrided to a 20-μm-thick titanium foil. The sample was arranged in the order of carbon steel, titanium foil, and Al2O3 powder (diameter=1 μm) and placed in N2 gas in a furnace to undergo simultaneous diffusion bonding and surface nitriding. These processes were carried out at a processing temperature T of 1100~1250 K and processing pressure P of 0.5 MPa (processing time=4.8 ks). Because no defect was observed in the bonded interface, it was confirmed that a sufficiently suitable joint can be obtained under these processing conditions. The surface hardness was observed to increase with the increase in processing temperature; it reached approximately HV1600 at 1250 K. The surface of the titanium foil, which had been simultaneously processed at 1250 K, consisted of a single phase of TiN. The results of the ball-on-disc-type wear test revealed that the surface, which had been processed at 1250 K, was hardly worn by the TiN layer.
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Development of New Production Technology for Foam Metal Core Sandwich Panel Using Friction PhenomenaYong-Jai Kwon, Ichinori Shigematsu, Naobumi SaitoArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 662-667
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSThe surface region of electric-discharge-machined aluminum foams was modified by the friction-surface-modifying and rolling (FSMR) process. A new surface was successfully obtained through the FSMR process, which was considerably smoother and denser than that of the unprocessed aluminum foam. In the FSMR process, the amount and morphology of the residual pores are mainly dominated in the surface of metallic foams by the friction surface modification (FSM) process stage. The smoothest surface, however, was formed for the friction-surface-modified and rolled (FSMRed) aluminum foam, which was attributed to the additional rolling process after the FSM process. This result demonstrates that the FSMR process is a very effective technology in controlling the surface morphology of the metallic foams through the cell structure control of the surface region. For the FSMRed aluminum foam, the highest average bonding strength, yield strength and toughness were obtained, which were nearly equivalent to 1.4, 2 and 1.6 times the values of the unprocessed aluminum foam, respectively. This result shows that, in the FSMR process, the additional rolling process after the FSM process is very effective in enhancing the bonding characteristics of the metallic foams by smoothening the surface. In addition, the above-mentioned bonding characteristics were remarkably increased with the decrease in the surface roughness, suggesting the surface morphology is a very important parameter in controlling the bonding characteristics of the metallic foams. The experimental results revealed that the FSMR process is a very effective technology for the improvement of the bonding characteristics of the metallic foams through the control in the surface morphology.
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Tetsuya Akiyama, Tohki Shinohara, Toshio TerasakiArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 668-676
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSIn a previous report, authors conclude that you have to introduce in-plane strain much more than the amount calculated by geodetic analysis when you produce bowl shape thin plate by laser forming. In academic interests, not only to know the best in-plane strain to create the target bowl shape but also to know the mechanism dominantly controlling deformations in laser forming process. To consider what the dominant factor is and how the factor works, we need to study how a numerical model which has a few functions to show major effect on laser forming process could explain experimental results.
In this report, we produce a numerical model which has two functions, accumulation of elastic energy caused by in-plane strain and bending motion. We study how this limited model can explain the experimental results shown in the previous report.
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Yuki Omura, Hidemasa Kawai, Norihiro Murayama, Junji ShibataArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 677-681
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSAnalysis of the chemical composition of spent cylindrical Li-ion batteries for PC, and investigation of the separation of each metal (Li, Co, Ni, Cu) from the Li-ion batteries were carried out by burning under a vacuum, crushing and screening, in order to recover rare metals from the Li-ion batteries.
The cylindrical Li-ion batteries have the structure that the multi-layered electrodes with four−layered foils composed of anode, cathode and two separators are enrolled cylindrically around the core steel bar. Seven kinds of metal such as Li, Co, Ni, Fe, Mn, Al and Cu mainly exist in the Li-ion battery. The whole mass of Li-ion battery used in this study is 39.7 g. The mass of Li, Co, Ni and Cu is 1.38 g, 10.3 g, 0.236 g and 4.62 g, respectively, in one piece of Li-ion battery, while other elements (graphite) are 23.16 g. Three size fractions of 150-125, 125-106 and 106-90 μm obtained by crushing and screening after burning under a vacuum and removing stainless case show almost similar compositions. On the other hand, the size fraction of +425 μm contains a lot of foil-like materials. The separation of Al and Cu with a larger particle size from the crushed product of a burned Li-ion battery is accomplished by using a 425 μm sieve. It is important to separate the foil-like elements such as Al, Cu and Fe from the crushed products of electrode materials by using a sieve with a larger mesh size, for example 5-10 mm.
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Toshiyuki Sawada, Akihiko YanagitaniArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 682-687
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSDistribution of surface residual stress and fatigue property of gas carburized JIS SCM420 with double shot peening were investigated. Developed FeCrB media with 0.1 mm diameter and high hardness of HV 1200 was used as secondary shot peening media, while conventional cast steel media of 0.8 mm diameter was used as primary one. As a reference, the specimen with double shot peening by high speed steel media of 0.1 mm diameter as secondary shot peening media was also examined.
Distribution of surface residual stress of double shot peened specimen had two peaks, which corresponded with the primary and secondary shot peening. The peak value at near-surface region of the specimen shot peened using FeCrB media was 170 MPa higher than that of the specimen using high speed steel media. Fatigue strength was improved by double shot peeing. It was related to integral value of compressive residual stress both of the ranges from the surface to 30 μm and from 30 to 400 μm in depth. Furthermore, the integral value of compressive residual stress in the range from the surface to 30 μm strongly contributed to fatigue strength.
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Toshio Osada, Yuefeng Gu, Yong Yuan, Tadaharu Yokokawa, Hiroshi HaradaArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 688-696
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSGrain growth kinetics was studied in a new Ni-Co base disk superalloy with γ/γ′ two-phase structure (TMW-4M3). The alloy was heat-treated from 1100 to 1160°C for up to 100 h after hot-deformation. The results indicated that the size of un-dissolved γ′-phase increased with increasing of temperature or time because of Ostwald ripening. Meanwhile, the grain size of the alloy showed a good agreement with the Zener's pinning model at all tested conditions, which means that the grain size can be estimated from the size and the volume fraction of the un-dissolved γ′-phase particles. Furthermore, assuming that the coarsening behavior of the pinning γ′ particles follows Lifshitz-Slyozov-Wagner (LSW) theory, we estimate that the activation energy of the γ′ particle growth in TMW-4M3 is 303±28 kJ/mol (within the γ′ sub-solvus temperature range from 1100 to 1150°C), which is close to that of diffusion of Al and Ti atoms in the matrix. Therefore, we suggest that the grain growth in TMW-4M3 follows the diffusion-controlled growth model of γ′ formers in the matrix and the grain growth rate is determined by the coarsening rate of un-dissolved γ′-phase particles.
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Letters to the Editor
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Yoshihiko Hangai, Hiroki Kato, Takao Utsunomiya, Soichiro KitaharaArticle type: Regular Article
2010 Volume 74 Issue 10 Pages 697-699
Published: 2010
Released on J-STAGE: October 01, 2010
JOURNAL FREE ACCESSPorous aluminum was fabricated without the use of a blowing agent by friction stir processing using the gases contained in ADC12 aluminum alloy die-casting plates. The compressive properties of the obtained porous aluminum were investigated. It was shown that a compressive test specimen with a porosity of approximately 70% was obtained that had pores with a relatively small area and high sphericity. Porous aluminum fabricated without the use of a blowing agent exhibited brittle fracture at a relatively high plateau stress and high absorption energy compared with those of ALPORAS.
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