Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
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Volume 71, Issue 9
Displaying 1-27 of 27 articles from this issue
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  • Effect of Heat Treatment Conditions on Microstructures of New Ni-Co Based Superalloys for Turbine Disks
    Tadashi Fukuda, Yuefeng Gu, Chuanyong Cui, Hiroshi Harada
    2007 Volume 71 Issue 9 Pages 667-671
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.667
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      New Ni-Co based superalloys (TMW alloys) for gas turbine disks have been recently developed. These new alloys are designed to have higher temperature capability than that of U720Li disk alloy by 50°C. The concept behind alloy design is to combine two kinds of γ-γ′ structure alloys, U720Li(Ni-Ni3Al) and Co-Ti(Co-Co3Ti) alloys. In this article, we describe the effect of solution heat-treatment conditions on the microstructures of TMW disk alloys (TMW1, 2, 4, and 2+4Co), such as the grain size and volume fraction of the primary γ′ phases and the hardness. Microstructural observation results showed that the average grain size and volume fraction of the primary γ′ phases are strongly influenced by the solution temperatures. For each TMW alloy, we identified the relationship among the solution temperature, volume fraction of the primary γ′ phases, and grain size that is necessary to achieve optimum properties. Vickers hardness testing results showed that the addition of a Co-Ti alloy has a positive effect on alloy strengthening at room and elevated temperatures. These results can help determine the optimum heat-treatment condition.
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  • Atomic Force Microscopic Observation of Microstructural Changes in Fe-Mn-Si-Al Shape Memory Alloy
    Motomichi Koyama, Masato Murakami, Kazuyuki Ogawa, Takehiko Kikuchi, T ...
    2007 Volume 71 Issue 9 Pages 672-677
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.672
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      The surface relief caused by stress-induced fcc/hcp martensitic transformation in an Fe-30Mn-5Si-1Al shape memory alloy, which exhibited a good shape memory effect and an improved ductility due to a small addition of aluminum to a conventional Fe-30Mn-6Si shape memory alloy, was quantitatively analyzed by atomic force microscopy. The orientation of an austenite grain was determined with surface traces of four {111}f planes, which made it possible to determine the surface tilt angles for all 12 variants of hcp martensite and deformation twins. On the basis of these values, the stress-induced martensite and deformation twin, coexisting in a grain, were identified by investigating the surface tilt angles. The surface relief caused by the stress-induced martensite recovered after heating above the reverse transformation temperature, but that due to the deformation twin remained unaltered.
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  • Mechanical Properties and Microstructure of AZ31 Magnesium Alloy during High Temperature Deformation
    Masafumi Noda, Hideharu Shimizu, Kunio Funami, Hisashi Mori, Taro Tsuj ...
    2007 Volume 71 Issue 9 Pages 678-683
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.678
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      In this study, uniaxial and biaxial deformations were applied to a magnesium alloy of AZ31 to reproduce the stresses that occur during product processing and to compare the mechanical properties and microstructure of the alloy after being deformed at each load stress.
       We conducted a high-temperature tensile test on uniaxial and biaxial deformations in the range of initial strain rate of 2.7×10-4 to 2.7×10-1 s-1. The uniaxially deformed alloy achieved a fracture elongation of 230% at an initial strain rate of 2.7×10-4 s-1 and also about 100% at that of 2.7×10-1 s-1. On the other hands, the biaxially deformed alloy indicated higher values of yield stress and tensile strength, 45 MPa and 62 MPa at maximum, respectively, than the uniaxially deformed one, but a fracture elongation of only about 30%. The cross section of the uniaxially deformed alloy was significantly reduced due to the distortion of its sheet thickness and width, while the biaxial deformation was restricted due to the application of a vertical and bi-directional principal stress. For this reason, the biaxial deformed alloy received a higher average stress than the uniaxially deformed one, so it ruptured without huge elongation.
       Although the biaxially deformed alloy suffered less deformation under rupture than the uniaxially deformed alloy, microvoids with a length of about 1 μm that could not be observed after the uniaxial deformation were found in grain boundaries where a fibrous structure could be seen. The formation of this fibrous structure caused local stress and nonuniform strain during deformation, so the grains became corrugated and smaller at a strain rate of 2.7×10-4 s-1 and fine grain of about 2 μm were formed among coarse grains.
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  • Relationship between Deformation-Induced Surface Relief and Double Twinning in AZ31 Magnesium Alloy
    Daisuke Ando, Junichi Koike
    2007 Volume 71 Issue 9 Pages 684-687
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.684
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      In Mg alloys, twins have been known to be an important deformation mechanism. However, their roles on deformation mechanisms have not been well understood. In this work, we performed tensile test of rolled sheets of AZ31 Mg alloys at room temperature. A number of large surface reliefs were observed in a region near a fractured edge. TEM observation showed the formation of twins under the large surface relief. Crystallographic analysis indicated that the basal planes of the twins were tilted by approximately 37° with respect to the basal planes of the matrix, corresponding to the formation of {1011}-{1012} double twins. This is considered to make basal dislocation slip highly active within the twin. The localized deformation within the twins may lead to the formation of crack-like faults.
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  • Evaluation of Porosity Area Distribution in Die Casting by Fractal Dimensions
    Yoshihiko Hangai, Soichiro Kitahara
    2007 Volume 71 Issue 9 Pages 688-692
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.688
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      In high pressure die castings, formation of porosity, which is induced by entrapped gases (gas porosity) or solidification shrinkage (shrinkage porosity), is unavoidable. The porosity has a harmful influence on the mechanical properties and resistance to the air leakage of compressors of car air conditioners. In these days, the discrimination of porosity is not clearly determined, and accurate responses to reduce porosity in the production field are carried out by trial-and-error processes. The accurate discrimination of porosity leads to the accurate discrimination of the direct cause of these porosity. For this purpose, it is necessary to estimate porosity quantitatively, instead of qualitatively. We propose the fractal dimension as the quantitative indicator of the classification of porosity. In an earlier study, the fractal analysis of the shapes of “gas porosity” and “shrinkage porosity” was carried out. However, the porosity extraction bias was inevitable. Also, precision of the shape of porosity was necessary to analyze fractal dimension. In this study, we examined the fractal analysis of the spatial distribution of porosity area. The proposed fractal dimensions are clearly different from inner area (mixing of gas porosity and shrinkage porosity) and surface area (gas porosity only) in the products. The validity of fractal dimension of spatial distribution of porosity area is investigated by examine the fractal analysis of the shapes of corresponding porosity.
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  • Estimation of Metal Temperature at Failed Part of Turbine Blade for Civil Jet Engine
    Tadaharu Yokokawa, Yutaka Koizumi, Hiroshi Harada, Takanobu Suzuki, Ta ...
    2007 Volume 71 Issue 9 Pages 693-698
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.693
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      A failed 2nd stage high-pressure turbine blade taken from one of the P & W 4000 series engines had been examined in order to estimate the metal temperature at the damaged part of the blade during service. By assuming that the equlibrium microstructure had been achieved in the damaged area, this temperature could be determined from correlations between the chemical composition of γ phase measured experimentally and predictions of the NIMS in-house alloy design program. To confirm the validity of this procedure, another experiment was conducted in parallel on a crept specimen of PWA1484 under the condition of 1100°C-137MPa; the results indicated that metal temperature could be deduced by the same method with an accuracy of ±25°C at 1095°C. Analysis for the failed turbine blade revealed that the surface of the inner cooling path had been oxidized, and many cooling holes were blocked by oxide scales. This oxidation process might be induced by sulphidation as a sulfur-enriched region could be detected at the front of oxide layer. In addition, coarsened γ and γ′ microstructures were observed in the area of the damaged part. The estimated metal temperature of the failed region of the blade was above 1100°C; this might be the result of insufficient heat dissipation through cooling channels due to the blockage by oxide scales.
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  • Fatigue Properties of Mg-Zn-Y Alloys with Long Period Orderd Structure
    Shinji Ando, Kazuaki Toda, Masayuki Tsushida, Hiromoto Kitahara, Hidek ...
    2007 Volume 71 Issue 9 Pages 699-703
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.699
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      Recently, Mg-Zn-Y alloys with high strength and good ductility, which have a long period order (LPO) structure, have been developed. Therefore, it is important to understand fundamental fatigue properties in such materials. In this study, the fatigue fracture behavior of Mg96-Zn2-Y2 (two phase) alloy was investigated using a plain fatigue bending testing machine, which was originally developed for thin sheet specimen. One end of the sheet specimen is fixed at a voice coil of the loudspeaker and the other end is set free. A bending mode resonance at a frequency of 250-700 Hz occurs in the specimen due to forced vibration at the fixed end. A S-N curve for Mg96-Zn2-Y2 alloy was obtained and the fatigue limit was estimated as about 180 MPa. The value corresponds to about 45% of 0.2% proof strength of the alloy. Two types of fatigue surface were observed in the alloy. One is striation like pattern and the other is relatively flat surface. For comparison of fatigue behavior, Mg88-Zn4-Y7 (LPO single phase) and Mg99.2-Zn0.2-Y0.6 (α-Mg single phase) alloys were also investigated. Fatigue limit of each alloys were 220 MPa and 140 MPa, respectively. Striation like pattern was also observed in fatigue surface of both alloys. These results show that a fatigue crack in Mg-Zn-Y alloys propagates with activation of basal slip at the crack tip.
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  • Preparation of Cr-Cu-N-O Thin Films by Pulsed Laser Deposition
    Hiroki Asami, Takayuki Kamekawa, Tsuneo Suzuki, Tadatika Nakayama, His ...
    2007 Volume 71 Issue 9 Pages 704-707
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.704
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      Chromium copper oxynitride (Cr-Cu-N-O) thin films have been successfully prepared through the pulsed laser deposition (PLD) method. The copper content in metallic elements (x) ranging from 0.0 to 0.4 were controlled by changing the surface area ratio of Cu target (SR) from 0 to 50%. The X-ray diffraction (XRD) revealed the crystal structure of main phase in all thin films to be NaCl (B1) type. The metallic copper phase exists in the thin films up to x=0.16, whereas diffraction peaks attributed to Cu were not observed in the thin film with x=0.06. From the result of SEM observation, columnar structure were observed in the thin film with x=0.0, 0.6, but the thin films up to x=0.16 shows globular structure. The Cr-Cu-N-O thin film with x=0.06 exhibited the highest Vickers hardness (HV) of 3900.
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  • Fabrication of Porous Copper by Cold Extrusion and Leaching
    Hiroaki Koh, Hiroshi Utsunomiya, Jouji Miyamoto, Tetsuo Sakai
    2007 Volume 71 Issue 9 Pages 708-711
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.708
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      Conventional porous metals show relatively low strength due to softening in high-temperature treatments such as casting or bubbling. In the current study, the authors propose an alternative method to fabricate high-strength porous metals using cold working. A copper pipe filled with Cu and Al wires was deformed by cold extrusion to solid-phase bonding. From the Cu/Al composite, only aluminum is removed chemically by NaOH solution leaching to produce porous copper with one-dimensional pores. The porous copper fabricated shows outstanding compressive yield strength than conventional porous copper.
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  • Long Time Creep Prediction of a Creep Constitutive Equation of Ni-Base Single Crystal Superalloys
    Hitoshi Izuno, Yutaka Koizumi, Tadaharu Yokokawa, Hiroshi Harada
    2007 Volume 71 Issue 9 Pages 712-715
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.712
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      We have proposed and developed a new creep constitutive equation for Ni-base superalloys. In this paper, an application of the creep constitutive equation for long time creep test is discussed. Several creep curves of the test conditions of 1000°C/137 MPa and 900°C/245 MPa are fitted and achieved a good reproducibility. It is also examined to predict the rupture time of a continuing long time creep test from the behavior of the initial stage creep. The initial part of the creep data is fitted by the creep constitutive equation to extract initial creep stage parameters, and parameters belongs to the later creep stage are got by multi regression analysis.
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  • Impact Value Improvement of Aluminum Powders Dispersed Nylon6 by Water Absorption
    Masae Kanda, Keisuke Itou, Yoshitake Nishi
    2007 Volume 71 Issue 9 Pages 716-720
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.716
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      Influences of water absorption on Charpy impact value for composite polymers, which are aluminum powders dispersed nylon6 samples, have been investigated. Although the aluminum dispersion from zero to 40 vol%Al decreases the impact value, the water absorbing treatment for 105 s at boiling point largely increases the impact values of all composite polymers. It is explained that water molecules in nylon6 mainly relax the impact force.
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  • Thermodynamic Analysis of the Ti-H and Zr-H Binary Phase Diagrams
    Shusuke Ukita, Hiroshi Ohtani, Mitsuhiro Hasebe
    2007 Volume 71 Issue 9 Pages 721-729
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.721
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      A thermodynamic analysis of the Ti-H and Zr-H binary system has been performed by combining first-principles calculations with the CALPHAD approach. In order to compensate for the lack of experimental information available, the formation energies of the hydrides and solid solution phases were evaluated in the ground state using the Full-potential Linearized Augmented Plane Wave method. The estimated values were introduced into a CALPHAD-type thermodynamic analysis as well as some experimental information on the phase boundaries and hydrogen isotherms, and optimized parameters for standard Gibbs energies and excess interaction parameters were evaluated. The calculated phase diagrams and hydrogen activities were in good accordance with the previous experimental results. The present calculations revealed the appearance of the metastable miscibility gap in the bcc and hcp solid solutions.
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  • Effect of Zr Composition and Heat-Treatment on Fracture Toughness in Zr-Cu-Al Bulk Metallic Glass
    Nobuyuki Yoshida, Kazutaka Fujita, Yoshihiko Yokoyama, Hisamichi Kimur ...
    2007 Volume 71 Issue 9 Pages 730-735
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.730
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      Fracture toughness tests were carried out using different Zr composition in Zr-Cu-Al based bulk metallic glasses (BMGs) and heat-treated those just under the glass transition temperature (Tg) in order to examine the effects of Zr composition and heat-treatment on the fracture toughness (KQ; fracture toughness including the values under unsatisfying the plane strain condition). Zr50Cu40Al10, Zr55Cu35Al10 and Zr60Cu30Al10 BMGs fabricated by a tilt ark casting method were used. Heat-treatments were done for 90 minutes just under the Tgs of each BMG. Tests were conducted based on ASTM E399. Compact type specimen was used (thickness=2.3, 2.0 mm, thickness : width=1 : 4). Fatigue pre-crack was induced under ΔK less than 6 MPa•m1/2 by a servohydraulic fatigue machine and the fracture toughness test was done by using the same machine. The KQ dominantly increased with increasing the Zr composition. The KQ in heat-treated BMGs decreased in comparison with that in unheat-treated BMGs in all Zr composition. In the BMG of the high Zr composition, however, the decrease was small after heat-treatment, and the KQ showed enough high values. In heat-treated BMGs, the dispersion of KQs did not become small, but fatigue pre-cracks were induced more vertical against the loading axis and less bifurcation than those in unheat-treated BMGs.
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  • Palladium-Rhodium Alloy Membrane Fabricated Using Electroless Plating Technique and Its Hydrogen Permeance
    Shigeyuki Uemiya, Ken-ichiro Yasui, Ryo Yoshiie
    2007 Volume 71 Issue 9 Pages 736-741
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.736
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      The mechanical strength of a Pd-based membrane inevitably lowers with its decreasing thickness for promoting the H2 permeance, resulting in the defect generation and rupture of the membranes. The purpose of this report is to improve the mechanical strength of a Pd composite membrane, which consists of a thin Pd film supported on a porous substrate, by alloying the film with Rh. A Pd-Rh miscible alloy membrane was fabricated by the deposition of Rh/Pd double layer on the porous substrate using an electroless-plating technique followed by heat treatment at 973 K. The resulting Pd-Rh alloy composite membrane gave a higher H2 permeation coefficient as well as higher tensile strength than a pure Pd composite membrane fabricated in the same manner.
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  • Development of Amorphous-Alloy-Film Layering Technique Using the Thermal Spraying Method
    Naoko Nagao, Masahiro Komaki, Ryurou Kurahashi, Yasunori Harihara
    2007 Volume 71 Issue 9 Pages 742-746
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.742
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      Amorphous alloy films with high melting point (about 1200°C) have never been produced by any spraying method. This study showed the possibility that the cooling rate can be increased to the range of 105 to 106 K/s by immediately cooling the spraying flame. Based on this finding, bulk material of amorphous alloy was formed by testing Fe70Cr10P13C7 which is a high corrosion-resistant material. To confirm anticorrosion property, the bulk material was immersed in aqua regia together with a material for comparison, SUS316L. The bulk material of SUS316L completely dissolved in about 6 hours. In contrast, approximately 17% of the balk material of amorphous alloy remained as residue even after 3480 hours, thereby confirming its high anticorrosion property.
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  • Unimorph Device Composed of Pd Coated LaNix Alloy Film Deposited on High Strength CFRP Driven by Hydrogenation: Effect of Palladium Coating
    Tsutomu Oikawa, Haru-Hisa Uchida, Yoshitake Nishi
    2007 Volume 71 Issue 9 Pages 747-750
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.747
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      Hydrogenation operated unimorph device, which is composed of LaNix hydrogen storage alloy film with Pd over-layer, deposited on a carbon fiber reinforced polymer (CFRP) substrate, has been successfully developed. As a result, the bending motion after 100 s, palladium coated LaNix alloy film with the CFRP supporting sheet exhibits the large bending strain of about 250 ppm, which is 6 times larger than that of the Pt coating LaNix film on CFRP.
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  • Abnormal Resistivity Change in Indium-Tin Oxide Films
    Yuta Uenaga, Shinji Takayama
    2007 Volume 71 Issue 9 Pages 751-757
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.751
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      The in-situ resistivity measurement of partial crystalline amorphous ITO films was performed on annealing in various flowing gas atmospheres (air, O2, H2). It was found that an abnormal increase of resistivity showing a sharp peak was observed at 250∼300°C regardless of annealing gas atmospheres. The temperatures at the peak were shifted to higher range in the order of H2, air and O2 gases. The Hall measurement revealed that the carrier density and Hall mobility both sharply decrease at the resistivity peaks. The activation energy of the abnormal resistivity change was measured to be 0.6∼0.9 eV by using the Kissinger's method, whose values are different depending on the annealing atmospheres. The X-ray diffraction profiles and TEM observations revealed that the crystallization took place at ∼150°C on a whole specimen area and their crystal grains continuously grew with further increase of annealing temperature. It was tentatively concluded that the realignment of Sn-O bond to generate a neutral (2SnIn+Oi2-)x complex was most likely responsible for the present abnormal resistivity change observed.
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  • Production of AZ31B Magnesium Alloy Strips by Semisolid Continuous Casting
    Futoshi Kido, Tetsuichi Motegi
    2007 Volume 71 Issue 9 Pages 758-762
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.758
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      Microstructural formation and development of a semisolid casting technique were evaluated for magnesium alloy AZ31B sheet by using an inclined cooling plate to obtain refined and globular primary α crystals. This research investigates the influence of the tundish position and the roll speed on strip processing. It was found that placing the tundish closer to the roll gap increased the strip thickness and smoothness of the sample surface. Increasing the rotating speed of the roll results in an uneven, unstable and oxidized molten surface at the upper side of the sample. 2 mm and 3 mm thick samples were produced by optimizing the solidification conditions.
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  • Metallurgical Validation of Traditional Steelmaking in Southwest Ethiopia
    Eiji Yamasue, Isao Murahashi, Hideyuki Okumura, Keiichi N. Ishihara
    2007 Volume 71 Issue 9 Pages 763-771
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.763
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      An abandoned traditional steelmaking in Southwest Ethiopia (Dime) has been restored, and the technology and knowledge used for the operation have been metallurgically analyzed. The restoration was carried out with local blacksmiths from September to October in 2004, and the steelmaking operation including mining, construction of a furnace and charcoal production, etc was successfully performed. Produced sponge iron contains 0.31∼0.48 mass% carbon without any impurities. The yield ratio of the iron was about 40%. The collected slag contains the elements of Fe, Si, Al, K, P, Ti and Mn, which are typical components of slag. The blacksmiths used three kinds of iron ore, named “Balt”, “Bullo” and “Gachi”. The former two ores mainly consist of goethite (α-FeO(OH)) and kaolinite (Al2O3•2SiO2•2H2O). The latter includes calcium phosphate hydrate (Ca3(PO4)2•xH2O) in its white part, as well as the goethite and kaolinite. The reason why the local blacksmiths specifically selected “Gachi” as the best ore for their steelmaking was discussed from the viewpoint of slag forming ability.
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  • Effect of Specimen Size on Hydrogen Embrittlement Cracking of 2.25Cr-1Mo Heavy Section Steel for Pressure Vessels
    Yoru Wada, Yasuhiko Tanaka, Tadao Iwadate, Toshihito Ohmi, Toshimitsu ...
    2007 Volume 71 Issue 9 Pages 772-780
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.772
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      By means of charging large thick specimens with hydrogen, we investigated the effects of specimen size on hydrogen-embrittlement cracking. Crack extension in a hydrogen-charged 3.5T-CT specimen extended over a longer duration than was the case for a 1.0T-CT specimen. However, the values of the lower-bound threshold stress intensity factor (KIH) for 1.0T-CT and 3.5T-CT specimens were similar to one another when these were determined with a short-term rising load (dK/dt=0.005 MPa•m1/2•s-1). We conducted numerical analysis on the hydrogen diffusion and accumulation around a crack tip, taking into consideration the hydrogen distribution in the specimen. This analysis demonstrated that the maximum hydrogen concentration for cracking can be reached under the conditions present during a short-term rising load test (dK/dt=0.005 MPa•m1/2/s). Thus, the results of the numerical analysis confirm that a minimum value of KIH equivalent to that of a heavy section steel can be obtained with a small fracture mechanics specimen. We also attempted to explain long-term crack extension characteristics, taking into consideration hydrogen dissipation from a specimen. The analysis predicts that when the mean hydrogen concentration falls below a certain level (e.g., about 1.6 ppm under certain assumptions), the value of KIH increases significantly. This increase in KIH occurs because when the necessary stress intensity factor for cracking increases as a result of a decrease in the mean hydrogen concentration, the gradient of the maximum hydrostatic stress distribution becomes moderate, especially when the applied stress intensity factor is more than about 48 MPa•m1/2. Finally, we propose a method for the prediction of the long-term crack extension behavior of a large thick specimen; the method takes into consideration the hydrogen dissipation curve and the effect on KIH of a decrease in the mean hydrogen concentration.
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  • Hydrogen Trapping Behavior of Copper Precipitates in Steel
    Hiroshi Yaguchi, Takuya Kochi, Masahiro Nomura, Takashi Watanabe
    2007 Volume 71 Issue 9 Pages 781-785
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.781
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      The hydrogen trapping behavior at Cu precipitates was investigated in martensitic Fe-0.18%C-1.5%Mn-4.0%Cu steel having various precipitation conditions. A hydrogen desorption peak was observed around 373 K in all samples. Total amount of desorped hydrogen decreased first with aging period but increased later. The initial decrease has been attributed to the recovery of lattice defects, and the increase in the later stage to trapping at Cu precipitates. The amount of desorped hydrogen increased even after peak hardening. The crystal structure of Cu precipitates was observed by SR-XAFS to be basically bcc; however, indication of fcc structure was also observed. The intensity of fcc structure increases with aging time. This suggests that incoherency of matrix-precipitate interface increases with aging time especially after peak strength, and that hydrogen trapping is more pronounced at incoherent interface than coherent one at Cu precipitates. Since misfit strain of coherent Cu precipitate is smaller than other precipitates such as TiC, the ability of hydrogen trapping at coherent Cu precipitates is estimated to be small.
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  • Low-Isostatic-Press Sintering of Iron Alloy Powder
    Hidekazu Sueyoshi, Shigeru Uchida, Takeru Miyanowaki, Keita Kume, Ryo ...
    2007 Volume 71 Issue 9 Pages 786-792
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.786
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      An end-sealed thin stainless-steel pipe in which a high-speed steel compact was inserted was evacuated with a vacuum pump during heating at an elevated temperature using an atmosphere furnace. The sintering behavior of this low isostatic press sintering (LIPS) was examined in detail. The compact is subjected to isostatic compression stress through the deformation of stainless steel owing to atmospheric pressure. As the gas pressure in the stainless-steel pipe is low (about 2×10-2 Pa), as the sintering temperature is high (1573 K), and as the holding time is long (4 h), densification and hardness of the LIPS compact are large (about Hv640). This is because the decomposition of FeO film formed on the surface of the as-received powder is vigorous at low gas pressure in the stainless-steel pipe at high LIPS temperature. Hence, the degree of powder contact increases aided by large plastic flow in the powder particles owing to both the degradation of the strength of high-speed steel powder at a high temperature and the compression stress caused by atmospheric pressure. Higher rates of Fe diffusion is assisted by heating at high temperature. At an early stage of LIPS, pores of the center of the LIPS compacts migrate to the surface, resulting in the reduction of densification near the surface. However, by holding for a long time, the LIPS compact that has high densification from the surface to the center is obtained because of enhanced Fe diffusion. Under optimum LIPS conditions, it is possible to obtain a homogeneous LIPS compact which has porosity and hardness levels equivalent to those of the HIP compact.
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  • Phase Equilibria and Tie-Lined Compositions in a Ternary Ni-Al-Re System at 1423 K
    Shigeru Saito, Kazuya Kurokawa, Shigenari Hayashi, Toshiyuki Takashima ...
    2007 Volume 71 Issue 9 Pages 793-800
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.793
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      Phase equilibria and compositions with tie-lines between the δ-Re, γ, γ′, β, Ni2Al3 as well as Re2Al and ReAl3 phases in a ternary Ni-Al-Re system were investigated at 1423 K by heat-treating of Ar-arc-melted Ni-Al-Re alloys in vacuum for times up to 3600 ks, followed by water-quenching and concentration measurements of Ni, Al and Re across the cross sections by using electron probe micro-analyzer (EPMA). The tie-lined compositions (at%) of each phase are summarized as follows. The δ-Re phase tie-lined with the γ phase (81.9 at%Ni, 15.9 at%Al, and 2.2 at%Re) has 18.8 at%Ni, 0.1 at%Al, and 81.1 at%Re. The δ-Re phase tie-lined with the γ′ phase (77.0 at%Ni, 21.7 at%Al, and 1.3 at%Re) has 16.2 at%Ni, 0.3 at%Al, and 83.5 at%Re. The δ-Re phase tie-lined with the β phase (50.8 at%Ni, 49.1 at%Al, and 0.1 at%Re) has 5.9 at%Ni, 1.8 at%Al, and 92.3 at%Re. The Re2Al phase tie-lined with the β phase (45.8 at%Ni, 53.2 at%Al, and 1.0 at%Re) has 4.4 at%Ni, 33.4 at%Al, and 62.2 at%Re. The ReAl3 phase tie-lined with the Ni2Al3 phase (39.2 at%Ni, 60.7 at%Al, and 0.1 at%Re) has 6.2 at%Ni, 75.9 at%Al, and 17.9 at%Re at 1323 K. There is no ternary intermetallic compound in the Ni-Al-Re system at 1423 K. Solubility limits of Ni and Al in the δ-Re phase in binary alloy systems are 28.0 at%Ni and (0.1∼1.2)at%Al, respectively.
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  • Substance Flow Analysis on Diffused Toxics Contained in End-of-Life Cellular Phone
    Kazuko Nakano, Shuichi Miyabe, Taira Ozaki, Yasuhiko Wada, Kenichi Nak ...
    2007 Volume 71 Issue 9 Pages 801-808
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.801
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      Various low-toxicity substances are contained in the high functional electronic products in recent years. Although there is a little quantity of low-toxicity substances in each electronic product, total amount of them has been increasing by the mass production of electronic products. This means they tends to diffuse into environment and it also results in the loss of valuable metals.
       In this work, a substance flow analysis (SFA) on low-toxicity substances in used cellular phones as a typical example of high functional electronic commodity was carried out based on the actual condition of disposal which was acquired by the questionnaire applied to users and composition of cellular phone analyzed by ICP and EPMA. The amount of some scattered low-toxicity substances has been estimated. It was pointed out that establishment of the recycling system of cellular phones including used ones stored by users is very important in the view point of the avoidance of low-toxicity substance diffusion and recovery of valuable elements.
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  • Heat Treatment for the Stabilization of Hydrogen and Vacancies in Electrodeposited Nickel-Iron Alloy Films
    Nagatsugu Mukaibo, Yasuo Shimizu, Yuh Fukai, Toshiaki Hiroi
    2007 Volume 71 Issue 9 Pages 809-814
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.809
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      In an effort to realize the long-term stability of the magnetism of electrodeposited Ni-Fe alloy films, heat treatments needed for eliminating the possible effect of hydrogen and metal-atom vacancies have been investigated, mainly by use of thermal desorption spectroscopy. While metal-atom vacancies begin to move only above 480 K, hydrogen atoms can undergo slow motion and concomitant changes of states at room temperature, and are therefore believed to be a major cause of the long-term drift of the magnetism. Hydrogen atoms dissolved on regular interstitial sites can be completely removed by high-frequency pulse heating to 668 K, and those trapped by vacancies with relatively low binding energies can be removed by additional heat treatments at 453 K for over 1 h. The effectiveness of using this set of heat treatments to stabilize the performance of magnetostrictive Ni-Fe film sensors has been verified.
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  • Effect of Grain Size on Tensile Properties of TWIP Steel
    Rintaro Ueji, Noriyuki Tsuchida, Hidetoshi Fujii, Daisuke Kondo, Kazut ...
    2007 Volume 71 Issue 9 Pages 815-821
    Published: 2007
    Released on J-STAGE: September 01, 2007
    DOIhttps://doi.org/10.2320/jinstmet.71.815
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      The effect of the grain size of TWIP (twinning induced plasticity) steel on both the strength and ductility in the quasi-static tensile test at room temperature was studied. 31%Mn-3%Al-3%Si steels were cold-rolled to a reduction in thickness of 88% and subsequently annealed at various temperatures ranging from 600°C to 1100°C. The post annealing produced recrystallized grains with mean grain sizes ranging from 0.60 μm (at 600°C) to 62.3 μm (1100°C), while small amounts of the dislocation cell structures and Mn compounds were observed in the specimen annealed at temperatures lower than 620°C. The 0.2% offset stress and tensile strength become higher with decreasing mean grain size as determined by Hall-Petch relationship; whereas the uniform elongation and total elongation become smaller. However, the warm-annealed TWIP steels with ultrafine grained microstructures still keep preferred ductility. The possible reason why the grain refinement of the TWIP steel easily provides the preferable strength ductility balance was discussed.
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