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

MATERIALS TRANSACTIONS Vol. 54 (2013), No. 7

  • Effect of Rapid Thermal Annealing on the Electrical and Structural Properties of Se Schottky Contacts to n-Type Si

    V. Janardhanam, Yeon-Ho Kil, Kyu-Hwan Shim, V. Rajagopal Reddy, Chel-Jong Choi

    pp. 1067-1072

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    DOI:10.2320/matertrans.M2013075

    Abstract

    We have investigated the electrical and microstructural properties of Se Schottky contacts to n-type Si before and after rapid thermal annealing (RTA) at temperatures in the range of 100–200°C for 30 s under N2 ambient. The forward and reverse leakage currents increased with increasing RTA temperature following which the barrier heights decreased from 0.71 to 0.60 eV before and after annealing at 200°C. With increasing RTA temperature, the crystallization of the Se film proceeded and the film was fully crystallized after being annealed at 200°C without the reaction between Se film and Si substrate. The decrease in the barrier height of Se Schottky contacts to n-type Si with increasing RTA temperature could be associated with the decrease in series resistance caused by the phase transformation from high resistance amorphous Se to low resistance crystalline Se. An investigation of the reverse current–voltage characteristics of Se/n-type Si Schottky contacts showed that the Schottky emission mechanism dominates the current transport in the reverse bias at all annealed temperatures in the range of 100–200°C.

  • An Attempt to Image Chemical Ordering in Close-Packed Layer of Mg–Zn–Y 18R Long-Period Stacking-Ordered Structure by Scanning Tunneling Microscopy

    Shu Kurokawa, Akihiro Yamaguchi, Akira Sakai

    pp. 1073-1076

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    DOI:10.2320/matertrans.M2013123

    Abstract

    For the first time, nanostructures of 18R (Mg85Zn6Y9) LPSO (long-period stacking-ordered) were examined using STM (scanning tunneling microscopy), which unambiguously confirmed the proposed model of the atomic structure of the LPSO phase in which the Zn–Y clusters are arranged in a two-dimensional hexagonal lattice in the (0001)hcp plane. The typical domain size of this hexagonal arrangement was estimated to range from several nanometers to a few tens of nanometers. In addition, the structures at the domain boundaries of the hexagonal arrangement were imaged and clarified by STM.

  • Effect of Grain Boundary Structure on Misorientation Change of Pure Copper Bicrystals Pressed by One-Pass Equal-Channel Angular Pressing

    Kentoku Hirayama, Kazuki Nagai, Hiroshi Fujiwara, Hiroyuki Miyamoto

    pp. 1077-1082

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    DOI:10.2320/matertrans.M2013076

    Abstract

    Following a previous paper, (Materials Transactions, Vol. 53 (2012), p. 1858), which reports on the dynamic misorientation change absorbed by the grain boundaries themselves during one-pass equal-channel angular pressing (ECAP), the effect of grain boundary structure on the misorientation change during ECAP was examined as the next step. Two bicrystals with a Σ3{111} grain boundary and a random one were subjected to ECAP for one pass, and compared. Both the bicrystals were designed to have a similar slip pattern where slip activity was concentrated on one slip plane. Direct evidence of misorientation changes absorbed by grain boundary themselves was obtained again, and its marked dependency on grain boundary structure became evident. Namely, in Σ3 grain boundary, misorientation was partially carried by the grain interior in its vicinity, which stems from the dislocation accumulation. On the other hand, in the random grain boundary, most of the misorientation was carried by the boundary itself. These differences are discussed in terms of the capability as a sink of lattice dislocations during severe plastic deformation.

  • In-Situ Neutron Diffraction Study on Tensile Behavior of LPSO Mg–Zn–Y Alloys

    Kazuya Aizawa, Wu Gong, Stefanus Harjo, Jun Abe, Takaaki Iwahashi, Takashi Kamiyama

    pp. 1083-1086

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    DOI:10.2320/matertrans.MI201214

    Abstract

    Tensile behavior of single-phase 18R-Long period stacking ordered structure (LPSO) Mg–Zn–Y alloys and two-phase Mg–Zn–Y alloys which consist of Mg matrix and 18R-LPSO phase were studied by in-situ pulsed-neutron diffraction technique under tensile stress. Anisotropic behavior between the a-axis and c-axis in the 18R-LPSO structure was observed for the single-phase LPSO Mg–Zn–Y casted alloy from the elastic region under tensile stress. On the other hand, two-phase Mg–Zn–Y alloys of low 18R-LPSO phase concentration, which were produced by extrusion, behave isotropic until the yield point under tensile stress, and the 18R-LPSO phase acts as a strengthening phase in the plastic region.

  • Filtering of Acoustic Emission Signals for the Accurate Identification of Fracture Mechanisms in Bending Tests

    Eva Martinez-Gonzalez, Ingrid Picas, Jordi Romeu, Daniel Casellas

    pp. 1087-1094

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    DOI:10.2320/matertrans.M2013089

    Abstract

    In this manuscript, acoustic emission (AE) analysis is used to identify the fracture mechanisms that take place during a three-point bending test of steel specimens. However, an important source of AE was detected and related to the deformation of the supports and the surface of the steel specimen in contact. This source creates AE signals that are very high in number and amplitude, and prevent determining accurately the onset stress for fracture mechanisms in specimens. A signal filtering is proposed based on the properties of the initial part of the recorded AE waveform, combined with a linear localization. The filtering successfully allows the AE signals to be classified according to their source as background noise, damage due to contact of the specimen surface to the supports and fracture mechanisms occurring in the specimen microstructure as a result of the bending test. The aforementioned filter has been successfully applied in case of a cold work tool steel DIN 1.2379 to determine accurately the stress level at which the first damaging mechanisms start to occur in the microstructure in situ during the three-point bending test. Filtered AE signal results indicating damage in the microstructure have been corroborated by inspection of the specimen’s surface in a Confocal Microscope. In default of using the proposed filter, unfiltered signals have been estimated to lead to an overestimation of critical stresses of about 20%, what is undesirable for most applications.

  • In-Situ TEM Observation of Dislocation Interaction with Cavity in Ion-Irradiated Pure Vanadium during Tensile Test

    Kouichi Tougou, Kimihiro Nogiwa, Akihito Shikata, Ken-ichi Fukumoto

    pp. 1095-1101

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    DOI:10.2320/matertrans.M2013012

    Abstract

    To investigate the hardening mechanism due to cavity formation in vanadium, in-situ transmission electron microscopy (TEM) observation was performed for the helium ion-irradiated pure vanadium during tensile test. The obstacle barrier strength α was calculated from the bow-out dislocation based on line tension model and the obstacle barrier strength of cavity in pure vanadium was about 0.5 to 0.7 and slightly increased with increasing the cavity size. Generations of cross-slip and double cross-slip occurred with jog generating after the interaction between dislocations and cavities. The fraction of cross-slip and double cross-slip at dislocation pinning were increased with the increasing cavity size and it is suggested that the cross-slip of dislocation can be formed at cavity due to local climb motion of dislocation on the cavity surface.

  • Distinguishing Stress Concentration or Cracking in Ferromagnetic Material Using Abnormal Magnetic Signals

    Shi Changliang, He Peng, Dong Shiyun, Xu Binshi

    pp. 1102-1104

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    DOI:10.2320/matertrans.M2012393

    Abstract

    In the geomagnetic field, spontaneous magnetic signals in ferromagnetic materials can be induced by stress, which can be potentially applied to estimate the damage degree. In this research, a method of distinguishing stress concentration or cracking in ferromagnetic material was proposed. The normal component of magnetic field, Hp(y), was measured on the surfaces of ferromagnetic specimens with notch. The results indicated that the shapes of Hp(y) curves of stress concentration and cracking were different, there was abnormal magnetic peak in the Hp(y) curve of cracking. Meanwhile, the effect of lift-off on abnormal magnetic peak was studied, and the optimal lift-off value was also presented.

  • Crack and Electrical Resistance Behaviors of Carbon Nanotube-Based Polymer Composites under Mixed-Mode I/II Loading

    Tomo Takeda, Yasuhide Shindo, Fumitsugu Naraoka, Yu Kuronuma, Fumio Narita

    pp. 1105-1109

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    DOI:10.2320/matertrans.M2013080

    Abstract

    This paper studies the crack and electrical resistance behaviors of carbon nanotube (CNT)-based polymer composites under mixed-mode I/II loading by theoretical and experimental approaches. Mixed-mode fracture tests were performed on single-edge cracked plate specimens of the nanocomposites, and the electrical resistance of the specimens was measured. Also, the crack growth direction was predicted by a fracture mechanics approach. In addition, an analytical model based on the electrical conduction mechanism of CNT-based composites was developed to describe the electrical resistance change as a result of inclined crack growth. The predictions on the crack growth direction and the crack induced resistance change were compared with the experimental data, and good agreements were found.

  • Effect of Carbide Size Distribution on the Impact Toughness of Tempered Martensitic Steels with Two Different Prior Austenite Grain Sizes Evaluated by Instrumented Charpy Test

    Shigeto Takebayashi, Kohsaku Ushioda, Naoki Yoshinaga, Shigenobu Ogata

    pp. 1110-1119

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    DOI:10.2320/matertrans.M2013079

    Abstract

    The effect of tempering temperature on the impact toughness of 0.3 mass% carbon martensitic steels with prior austenite grain (PAG) size of about 6 and 60 µm was investigated. Instrumented Charpy impact test (ICIT) was used to evaluate the impact toughness. The tempering temperature of 723 K gives the largest difference in the Charpy impact energy at room temperature between the specimens with two different PAG sizes, where the finer PAG specimen shows higher impact energy at room temperature (RT). The other tempering temperatures do not show a significant difference as compared with that shown among the 723 K tempered specimens. Investigation of the test temperature dependence of Charpy impact energy in the 723 K tempered steels shows a steep transition at around 200 K for the 6 µm PAG specimen, while it shows a continuous slow transition in a wide range of temperatures for the 60 µm PAG specimen. ICIT waveform analysis of these steels shows that the fracture propagation energy mainly controls the temperature dependence of the impact energy, while the fracture initiation energy stays nearly constant against the variation of the test temperature. The carbide size distribution in these two specimens was investigated by secondary electron microscope (SEM) and transmission electron microscope (TEM). The 60 µm PAG specimen shows distribution of coarser carbide than does the 6 µm PAG specimen, which seems to give rise to the observed difference between them in the Charpy impact energy and the other properties of impact fracture.

  • Dealloying Behaviours of an Equiatomic TiCu Alloy

    Zhenhua Dan, Fengxiang Qin, Yu Sugawara, Izumi Muto, Nobuyoshi Hara

    pp. 1120-1125

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    DOI:10.2320/matertrans.M2013033

    Abstract

    The crystalline Ti50Cu50 ribbon was prepared by annealing its amorphous counterpart at 773 K, 84 K higher than its crystallization temperature. An equiatomic TiCu intermetallic phase dominated in the matrix coexisting with trace Ti2Cu phase segregated on the grain boundary. A bi-continuous nanoporous copper from tenths of nanometers to hundredths of nanometers was obtained after dealloying the crystalline Ti50Cu50 ribbons in 0.03 and 0.13 kmol/m3 HF solutions. The TiCu phase stayed inert at the initial immersion and the Ti2Cu zone preferentially dissolved to form trenches. After a prolonged immersion in HF solutions, both TiCu and Ti2Cu phases were fully dealloyed. Final nanoporous Cu had a multiple-channel characteristic in different regions where various intermetallic phases distributed. Finer nanoporous Cu formed in the regions where the TiCu phase with a higher electrochemical stability dominated.

  • Fundamental Characteristics of Work Deformation and Forging Load by High-Speed Large-Reduction Forging — Production Technology for Fine Grained Steel by Large Deformation Forging I —

    Masaru Miyake, Takuro Yazaki, Yasuhiro Sodani

    pp. 1126-1130

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    DOI:10.2320/matertrans.P-M2013805

    Abstract

    A high-speed large-reduction forging technology has been developed to improve the hot strip production process. This technology can be used to produce fine-grained steel by enhancing the dynamic recrystallization caused by high strain. And it has specific features in width deformation caused by intermittent and large deformation. In this paper, laboratory-scale experiments and FE analysis are carried out to clarify the fundamental characteristics of the deformation and stress field. Large reduction results in a large width spread, and intermittent working causes periodic width deviation. The influences of die shape, the amount of feed per pass and the aspect ratio of the width against the thickness of the initial works on width spread and deviation are discussed. Large forging load results in a chevron-like indentation profile of the die surface and produces a thickness profile of the work.

  • Solidification Microstructure and Critical Conditions of Shrinkage Porosity Generation in Die Casting Process of JIS-ADC12 (A383) Alloy

    Masafumi Hamasaki, Hirofumi Miyahara

    pp. 1131-1139

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    DOI:10.2320/matertrans.F-M2013806

    Abstract

    Differential thermal analysis (DTA), analyses of unidirectional solidification process and die casting process, and computational numerical simulations were conducted for JIS-ADC12 (A383) alloy to investigate the generation conditions of shrinkage porosities which occasionally appear in JIS-ADC12 die castings and affect the quality of products. The crystallization temperature of the primary alpha phase and Al–Si binary eutectic phase are estimated to be 856 and 838 K from DTA, respectively. The multi-phase eutectic reaction of JIS-ADC12 alloy starts from 826 K, and finishes at 801 K. The primary alpha dendrites are clearly observed in the unidirectional solidification microstructures, and the relationship between the secondary dendrite arm spacing λ2 and the local solidification time θ f is expressed by the following equation: λ 2 = 6.45θ f0.31. The primary alpha dendrites are also observed in the die cast sample. The average cooling rate estimated from λ2 is approximately 60 K/s at the depth of 0.5 mm from the surface of die castings. The computational numerical simulation reveals that the values of solidification parameter G/√R increases around the surface of the JIS-ADC12 die castings in where the amount of shrinkage porosities decreases. Especially, shrinkage porosities of the size lager than 200 µm is observed when the value of G/√R is less than or equal to 1.4 K0.5s0.5/mm.

  • Controlling Oxygen Content by Varying Oxygen Partial Pressure in Chromium Oxynitride Thin Films Prepared by Pulsed Laser Deposition

    Kazuma Suzuki, Toshiyuki Endo, Teruhisa Fukushima, Aoi Sato, Tsuneo Suzuki, Tadachika Nakayama, Hisayuki Suematsu, Koichi Niihara

    pp. 1140-1144

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    DOI:10.2320/matertrans.M2013047

    Abstract

    Chromium oxynitride Cr(N,O) thin films were prepared by pulsed laser deposition in a highly reactive atmosphere, which consisted of pure oxygen gas and nitrogen plasma from a radio-frequency radical source. In order to control the oxygen content in the thin films, oxygen partial pressure (PO2) in the chamber was varied from 5 to 10 × 10−5 Pa under a fixed total pressure of 1.5 × 10−2 Pa. The thin films were then characterized by X-ray diffraction, infrared spectroscopy, electron energy loss spectroscopy and nano-indentation testing. It was found that the oxygen content of the thin films changed from 0 to 62 mol% with increasing PO2. The thin films with only the NaCl-type (B1) Cr(N,O) phase were prepared under PO2 < 7.5 × 10−5 Pa. The chromium content of the B1 phase decreased from 47 mol%, which was close to the stoichiometric composition of CrN, to 40 mol% when the oxygen content was increased. The hardness increased up to 32 GPa with increasing PO2 up to 7.5 × 10−5 Pa.

  • Synthesis of Silver Nanoparticles with Tunable Morphologies via a Reverse Nano-Emulsion Route

    Anni Feng, Shuang Wu, Senyuan Chen, Huan Zhang, Wenyao Shao, Zongyuan Xiao

    pp. 1145-1148

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    DOI:10.2320/matertrans.M2013005

    Abstract

    In this study, silver nanoparticles with controlled morphologies including spherical-like nanoparticles, and silver nanowires were synthesized in a sodium bis (2-ethylhexyl) sulfosuccinate (AOT) reverse ternary nano-emulsion system. The morphology and structure of the silver nanoparticles are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) spectrum. The result shows that the molar ratio of water to surfactant (w) is crucial for the formation and structure of the nano-emulsion droplets. The controlling of the morphologies of the silver nanoparticles can be achieved through simply adjusting AOT concentration and the formation mechanism of the silver nanoparticles with tunable morphology has been proposed.

  • Controlled Semisolid Forging of Aluminium Alloys Using Mechanical Servo Press to Manufacture Products with Homo- and Heterogeneous Microstructures

    Jun Yanagimoto, Jian-Bo Tan, Sumio Sugiyama, Yi Meng

    pp. 1149-1154

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    DOI:10.2320/matertrans.M2013098

    Abstract

    Controlled forging of aluminium alloys is conducted using a mechanical servo press. Semisolid forging can reduce the number of forging passes and energy consumption to produce a product with suitable microstructure. In the proposed semisolid forging, solid fraction of the aluminium alloys being forged is controlled to enable the manufacture of products with homogeneous and heterogeneous microstructures. Semisolid forging experiments using a predetermined sequence represented by transient changes in stroke were systematically conducted. The relationship between the time-dependent semisolid forging sequence and product quality was discussed to reveal the semisolid forming condition for manufacturing products with homogeneous and heterogeneous microstructures.

  • Effects of Electrical Current on Microstructure and Interface Properties of Sn–Ag–Cu/Ag Photovoltaic Ribbons

    Kuan-Jen Chen, Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen, Dai-Wen Qiu, Ta-Lung Chou

    pp. 1155-1159

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    DOI:10.2320/matertrans.M2013110

    Abstract

    This study presents an electrical current testing that is based on the Sn–xAg–0.5Cu (x = 1, 3 mass%) photovoltaic (PV) ribbon, and investigates the growth mechanism of the intermetallic compounds (IMCs). The microstructure of both alloy solders contains the eutectic region (β-Sn+Cu6Sn5+Ag3Sn) and the base phases (β-Sn). The eutectic phases in the Sn–3Ag–0.5Cu (SAC305) alloy presented a continuous distribution, and its amount was higher. After soldering, the Cu6Sn5 and Ag3Sn IMCs were found at the interfaces, and their morphologies were dominated by Ag contents in the Sn–Ag–Cu (SAC) solder. The whole interfacial characteristics of IMCs were affected after biasing for 40 h. The growth behavior of these IMCs was controlled by the bias-induced thermal diffusion mechanism and the evolution of IMC morphology was dominated by the growth dynamics. The IMCs, formed at the interfaces (SAC/Cu, SAC/Ag), dominated the series resistance of the PV ribbon.

  • Effect of Gamma Radiation on Properties of a Calcium Phosphate-Calcium Sulfate Composite Cement

    Chang-Keng Chen, Chien-Ping Ju, Jing-Wei Lee, Jiin-Huey Chern Lin

    pp. 1160-1165

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    DOI:10.2320/matertrans.M2013007

    Abstract

    The present study investigates γ-radiation effect on structure and selected properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH) cement immersed in Hanks’ solution. The results indicate that, at a dosage of 25 kGy, the working and setting times of the cement paste derived from γ-ray-sterilized TTCP/DCPA/CSH powder did not change significantly. At 50 kGy or higher, however, both significantly decreased. A dose of 25 kGy caused the 1-d compressive strength of the cement to decrease by 15%. Further increases in γ-ray dose did not further change the strength. After immersion for 1 day, the pH values of all non-sterilized and sterilized samples were in the range of 7.6–8.0. The XRD patterns of non-sterilized and sterilized powders were substantially similar. After immersion for 1 day, TTCP phase was still distinguishable, while CSH peaks were largely diminished and apatite phase became dominant. The non-sterilized sample had a significantly higher apatite conversion ratio than those of γ-ray-sterilized samples. The average 1-d porosity values of all sterilized and non-sterilized samples were similar (31–33%). The γ-ray-sterilized cement samples had coralline type morphology with numerous tiny apatite crystals and micropores. Compared to the sterilized samples, the non-sterilized cement showed a smoother and denser morphology.

  • Creation of Adhesive Force between Laminated Sheets of Polyurethane (PU) and Polytetrafluoruethylene (PTFE) by Homogeneous Low Energy Electron Beam Irradiation Prior to Hot-Press for Bio-Adaptable Application

    Yusuke Miyazawa, Masato Uyama, Sho Ishii, Masae Kanda, Yoshitake Nishi

    pp. 1166-1170

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    DOI:10.2320/matertrans.MBW201216

    Abstract

    Bio-adaptable 2-layer polyurethane/polytetrafluoroethylene (PU/PTFE) laminated sheets were prepared by a new adhesion method, a double-step treatment consisting of: (1) applying low dose <0.65 MGy homogeneous low energy electron beam irradiation (HLEBI) to the 2-layer assembly where the HLEBI penetrates through the PU and PTFE layers, respectively, prior to: (2) hot-press under 5 MPa and 403 K. Although the adhesion of the PU/PTFE sheets cannot be observed without the new double-step treatment, bonding forces were created as evidenced by the mean adhesive forces of peeling resistance (oFp). Based on the 3-parameter Weibull equation, the lowest oFp value at Pp of zero (Fs) could be estimated. An increasing trend in Fs occurs by the double-step treatment applying HLEBI up to 0.43 MGy reaching a maximum at 0.38 Nm−1, improving the safety level without radiation damage. When HLEBI cuts the chemical bonds and generates dangling bonds with nonbonding electrons in PU and PTFE, the created adhesion between the laminated sheets can be explained. Based on X-ray photoelectron spectrometer (XPS) surface analysis of the PU/PTFE laminated sheets after the peeling tests, fluorine (F) was detected on the PU peeled surface, indicating the strong chemical bonding generated by the double-step treatment. For these reasons, double-step treatment is a useful method for quick lamination of PU and PTFE with sterilization without the use of glue.

  • Heating Effect of Polycrystalline SiGe/Si Thin Films on Phase Transition of GeSbTe Films

    Seung-Yun Lee

    pp. 1171-1175

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    DOI:10.2320/matertrans.M2013084

    Abstract

    This work reports the detailed manufacturing process of polycrystalline SiGe/Si thin film layers and their heating effect on phase transition of GeSbTe chalcogenide films. The SiGe and Si films were grown successively by chemical vapor deposition, and different methods were applied to dope the SiGe films depending on their semiconducting nature because of phosphorus autodoping. Although the minimum dopant concentration for the n-type SiGe films was much higher than that for the p-type SiGe films, the lowest transition currents were measured almost same with both p- and n-type SiGe films. The transition current decreased further with reducing contact area between the GeSbTe and SiGe films. These results indicate that the contact area scaling and the formation of SiGe/Si films with a dopant concentration smaller than a critical value are both required to induce the phase transition of GeSbTe at a submilliampere level of transition current.

  • Effect of Ion Water Washing of Neutralized Sludge Contaminated by High Concentrations of Chloride

    Chiharu Tokoro, Yuji Oda, Shuji Owada, Hiroshi Hayashi

    pp. 1176-1181

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    DOI:10.2320/matertrans.M2013001

    Abstract

    The effects of NO3− and SO42− ions on chloride ion removal from neutralized sludge were investigated to determine if removal of chloride ions enabled the use of sludge for cement production. An artificial sludge prepared from iron, calcium and chloride that primarily consisted of two-line ferrihydrite was prepared. Chloride ions in the sludge were easily washed out by distilled water, NO3− water or SO42− water to levels below those specified in the standard for Eco-cement production (1,000 mg/kg), but the washed sludges did not meet the standard for ordinary Portland cement (350 mg/kg). Conversely, artificial sludge prepared from aluminum, calcium and chloride mainly consisted of low crystalline boehmite with other minor components. Chloride ions in this sludge were only reduced to below those specified in the standard for the ordinary cement production if SO42− water was used to wash the sludge. The filtration rate during washing using SO42− water was faster than when distilled water or NO3− water was used because SO42− ions were adsorbed onto the sludge particles and the absolute value of the zeta potential of the sludge particles decreased. Overall, sludge washing using SO42− water was the best process for chloride ion removal and efficient filtration.

  • Estimation of Plateau Stress of Porous Aluminum Based on Mean Stress on Maximum-Porosity Cross Section

    Takao Utsunomiya, Ryo Yamaguchi, Yoshihiko Hangai, Osamu Kuwazuru, Nobuhiro Yoshikawa

    pp. 1182-1186

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    DOI:10.2320/matertrans.M2013069

    Abstract

    Porous aluminum with high porosity is very lightweight and has high energy absorptivity. Plateau stress is an important mechanical property that is closely related to the energy absorptivity of porous aluminum. In this study, we attempt to estimate the plateau stress of porous aluminum by simply assuming that when the mean true compressive stress on a maximum-porosity cross section perpendicular to the direction of compressive loading reaches the critical value, a locally deformed layer appears and the nominal compressive stress becomes equal to the plateau stress. Through the comparison of compressive test results with the estimated results obtained according to this assumption, it was shown that the plateau stress can be evaluated approximately when the proof stress is used as the critical value.

  • Thermal Fatigue Behavior of Nitrocarburized and Low Pressure Nitrided Modified JIS SKD61 Hot Work Mold Steel

    Shu-Hung Yeh, Liu-Ho Chiu, Wan-Chung Lo, Chien-Lung Huang

    pp. 1187-1194

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    DOI:10.2320/matertrans.M2013035

    Abstract

    A novel method using induction heating equipment was employed to investigate the thermal fatigue behaviors of two hot-work steels, JIS SKD61 and modified JIS SKD61, vacuum hardened treated to 45 HRC. Selected specimens, austenitized at 1298 K for 25 min, gas quenched to room temperature and tempered at 873 K, were salt bath nitrocarburized at 843 K for 80 min and low pressure nitrided at 813 K for 6 h, respectively. Microstructure, microhardness, X-ray diffraction and thermal fatigue tests were conducted. The results show that the thermal fatigue properties of the 898 K tempered specimen were better than those of other treated specimens. The reason is that the hardened processes would give high tensile strength, which improved the tool material thermal fatigue resistance. The thermal fatigue properties of modified JIS SKD61 specimen, including mean crack length and crack distribution density, were better than those of JIS SKD61 specimen. Low pressure nitriding treatment with a homogeneous nitrided layer could better maintain thermal fatigue resistance than the nitrocarburized steel.

  • Conditions for Osteoblast Arrangement Induced under Long-Term Cyclic Stretching

    Aira Matsugaki, Natsuko Fujiwara, Takayoshi Nakano

    pp. 1195-1199

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    DOI:10.2320/matertrans.M2013091

    Abstract

    Though mechanical stimuli are essential for appropriate tissue morphogenesis, excess stress induces cell death resulting in imperfect development. Bone tissue has a highly ordered structure that is responsible for its mechanical function. Osteoblast mechanosensitivity is considered as one of the regulators for anisotropic morphogenesis of bone tissue, by controlling the balance between cell death and cellular responses, including both morphological and functional changes caused by mechanical stress. The optimal conditions for continuous cyclic stretching required for retaining the osteoblast arrangement in long-term cultivation were determined, which led to the establishment of an ordered architecture of the primary osteoblast monolayer. Long-term cultivation under continuous mechanical stress is quite challenging and has not yet been established, because of the inability to retain cell arrangement without inducing cell death. The present findings are relevant for bone tissue reconstruction with the recovery of the original ordered microstructure of bone tissue because the development of an ordered pattern of osteoblasts is imperative for the following anisotropic bone tissue genesis. To the best of our knowledge, this is the first report on sustaining an ordered cell arrangement under mechanical stress for a long-term period of 168 h.

  • Influence of Silicon on Intergranular Corrosion for Aluminum Alloys

    Yoshiyuki Oya, Yoichi Kojima, Nobuyoshi Hara

    pp. 1200-1208

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    DOI:10.2320/matertrans.M2013048

    Abstract

    In an effort to improve the tensile strength of aluminum–silicon (Al–Si) alloys used in heat exchangers, we investigated the influence of Si concentration and heat-treatment at 453 K on the susceptibility of Al–Si alloys to intergranular corrosion. It was found that the susceptibility to intergranular corrosion increased with an increase in Si concentration. It also initially increased with heat-treatment at 453 K, but then decreased with long-term heat-treatment at 453 K. The addition of Mg and Mn, which affect the precipitation of Si, promoted precipitation and reduced the susceptibility of the Al–Si alloys to intergranular corrosion. With longer heat-treatment at 453 K, large Si precipitates were observed in the grains and at the grain boundaries, which reduced the susceptibility to intergranular corrosion. Short-term heat-treatment at 453 K formed a continuous Si-depleted layer along the grain boundaries, which increased the susceptibility to intergranular corrosion. It is suggested that the susceptibility to intergranular corrosion was dependent on the addition of Mg and Mn.

  • Behavior of Extraction, Stripping, and Separation Possibilities of Rhenium and Molybdenum from Molybdenite Roasting Dust Leaching Solution Using Amine Based Extractant Tri-Otyl-Amine (TOA)

    Jingu Kang, Yung-Uk Kim, Sung-Ho Joo, Ho-Sung Yoon, J. Rajesh Kumar, Kyung-Ho Park, P. K. Parhi, Shun Myung Shin

    pp. 1209-1212

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    DOI:10.2320/matertrans.M2012380

    Abstract

    The main objective of the present study is to separate the rhenium and molybdenum as well as recovery of the targeted metal ion. The behavior of extraction, stripping and separation possibilities of rhenium and molybdenum from molybdenite roasting dust leaching solutions using tri-otyl-amine (TOA) as an extractant has been investigated. From the results, 5 vol% TOA dissolved in kerosene is found to be selective for extraction of rhenium as compared with molybdenum. It extracted, molybdenum with extraction efficiency of less than 30%, whereas rhenium with extraction efficiency of more than ∼99%. The optimum extraction conditions have been determined as: 5 vol% TOA, 900 s of contact time, 298 K temperature, 250 rpm agitation speed, phase ratio (organic/aqueous = O/A) of 0.4 at equilibrium pH 0.0. Stripping (back extraction of loaded metal) of rhenium from loaded organic phase with 5 kmol/m3 HNO3 was proved as efficient and the rhenium stripping efficiencies were obtained about 99% under conditions of O:A ratio of 1, for 900 s time, at 298 K temperature, at the same experimental condition whereas molybdenum stripped ∼31%.

  • Microstructures and Mechanical and Electrical Properties of Hypoeutectic Cu-1, C-3 and Cu-5 at%Zr Alloy Wires Preprocessed by Spark Plasma Sintering

    Naokuni Muramatsu, Takashi Goto

    pp. 1213-1219

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    DOI:10.2320/matertrans.M2013011

    Abstract

    Wires prepared by the solid-phase-compaction followed by heavy wire-drawing of atomized Cu–Zr alloy powders were studied. Microstructures and mechanical and electrical properties of wires drawn from hypoeutectic Cu-1, Cu-3 and Cu–5 at%Zr alloys, preprocessed by spark plasma sintering (SPS), were investigated. The microstructures of specimens formed by SPS of the powders changed into fine dual-phased structures comprising phases of Cu and the intermetallic compound Cu5Zr, which was dispersed in the Cu matrix. The volume fraction of the intermetallic compound Cu5Zr in SPS specimens increased with an increase in the Zr content. The ultimate tensile strength (UTS) values of the specimens increased, while their electrical conductivity (EC) values decreased simultaneously. The alloy wires, preprocessed by SPS, contained dual-phased microstructures in which the intermetallic compound Cu5Zr was dispersed in the shape of small islands in the Cu matrix. Drawn Cu-1, Cu-3 and Cu–5 at%Zr alloy wires exhibited UTS values of 603, 698 and 789 MPa, respectively, and EC values of 87, 70 and 52% IACS (International Annealed Copper Standard), respectively. The UTS values were about 40–56% lower and EC values about 28–60% higher than those previously reported for wires preprocessed by casting. The lamellar structures of the α-Cu and eutectic (Cu+ intermetallic compound Cu9Zr2) phases in the drawn wires preprocessed by casting improved the mechanical properties of the wires. The microstructures of the intermetallic compounds Cu5Zr, which was uniformly dispersed in the Cu matrix in the drawn wires preprocessed by SPS, helped increase the electrical conductivity of the wires.

  • Leaching Behavior of Copper, Zinc and Lead from Contaminated Soil with Citric Acid

    Hongki Park, Kyungbae Jung, Richard Diaz Alorro, Kyoungkeun Yoo

    pp. 1220-1223

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    DOI:10.2320/matertrans.M2013038

    Abstract

    Soil samples contaminated with heavy metals such as lead (Pb), copper (Cu) and zinc (Zn) were leached with citric acid solution. A five step-sequential extraction method involving “exchangeable”, “bound to carbonate”, “bound to Fe–Mn oxide”, “bound to organic matter” and “residue” fractions was also carried out to investigate the leaching behavior of Pb, Cu and Zn with citric acid.
    The leaching efficiencies of Pb, Cu and Zn increased with increasing citric acid concentration. About 86.5, 88.9 and 83.3% leaching efficiencies were obtained for Cu, Zn and Pb, respectively, under the following leaching condition: 2 kmol·m−3 in citric acid concentration, 120 min in leaching time, 10% in pulp density, 50°C in temperature, and 80 rpm in shaking speed. In the sequential extraction test, the heavy metal contaminants were extracted more in “bound to carbonate” and “bound to Fe–Mn oxide” fractions than in “bound to organic matter” and “residue” fractions. When the leaching efficiencies of Pb, Cu and Zn with 2 kmol·m−3 citric acid solution were compared with the results of the sequential extraction, a good agreement with the summation of amount leached in “exchangeable”, “bound to carbonate” and “bound to Fe–Mn oxide” fractions was noted.

  • Anomalous Temperature Dependence of Crystalline-to-Amorphous Transformation Induced by High-Pressure Torsion in Zr50(Cu,Al)50

    Fanqiang Meng, Koichi Tsuchiya, Qingsong Mei, Baozhen Jiang, Yoshihiko Yokoyama

    pp. 1224-1227

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    DOI:10.2320/matertrans.M2013049

    Abstract

    Martensite phases of Zr50Cu50 and Zr50Cu44Al6 were deformed by high-pressure torsion (HPT) at different temperatures ranging from 253 to 473 K. Microstructural observations revealed that the crystalline-to-amorphous transformation induced by HPT showed remarkable temperature dependence: an increase in deformation temperature up to 473 K significantly increased the fraction of the amorphous structure. This result suggests that the lattice instability near martensitic transformation temperature promotes crystalline-to-amorphous transformation, which is coherent to the generalized Lindemann criterion of defect-induced amorphization.

  • Morphology Characterization of Multi-Walled Carbon Nanotubes in Sn–58Bi/CNTs Composites

    Xiaochun Lv, Tiesong Lin, Jun Wang, Jing An, Peng He

    pp. 1228-1231

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    DOI:10.2320/matertrans.M2013117

    Abstract

    0.01 mass% of multi-walled carbon nanotubes (MWCNTs) were ball milled with Sn–58Bi alloy powder and melted at 180°C for 60 s for the preparation of Sn–58Bi/CNTs composites material. During the melting process, a large portion of carbon nanotubes escaped from the mixture. The morphologies of the carbon nanotube in Sn–58Bi/CNTs composites were investigated by field-emission scanning electron microscopy (FE-SEM) which equipped with energy dispersive spectroscopy (EDS). Results showed that CNTs existed in the as-cast composite and the composite after remolten. The bonding between CNTs and the matrix was formed. The CNTs distributed well in the metal matrix and improved the element distribution for more uniform microstructure. The bonding mechanism of the Sn–58Bi alloy with CNTs was discussed.

  • Isothermal Crystallization of Iron-Based Amorphous Alloys in a High Magnetic Field

    Reisho Onodera, Shojiro Kimura, Kazuo Watanabe, Yoshihiko Yokoyama, Akihiro Makino, Keiichi Koyama

    pp. 1232-1235

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    DOI:10.2320/matertrans.M2013136

    Abstract

    Isothermal crystallization of soft magnetic Fe–Si–B amorphous alloys under high magnetic fields was investigated by magnetization measurements. The increase of magnetization due to the precipitation of ferromagnetic α-Fe(Si) from the paramagnetic amorphous matrix was observed as a function of time. The magnetic field dependence of the time evolution of the crystallization was also examined. The relaxation time increases under high applied magnetic fields indicating that the suppression of the precipitated crystal growth rate occurs. Moreover, by normalizing the relaxation time of the crystallization, the time evolutions of the crystallized fraction converge to a universal sigmoidal curve regardless of the applied magnetic field strength. These behaviors indicate that the magnetic field influences the growth rate rather than the elementary processes of crystallization.

  • Microstructure and Magnetic Properties of Mn–Sn–N and Mn–Sn–Co–N Alloys

    Keita Isogai, Keita Shinaji, Tsuyoshi Mase, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto

    pp. 1236-1239

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    DOI:10.2320/matertrans.M2013113

    Abstract

    The microstructure and magnetic properties of Mn–Sn–N and Mn–Sn–Co–N alloys were investigated. All the samples showed low remanences, although high coercivity of 876 kA/m was observed in the Mn–Sn–Co–N alloys. The substitution of Co for Mn increased coercivity. The sample with high coercivity consisted of a fine two-phase microstructure of 0.5–2 µm in size.
  • © 2013 The Japan Institute of Metals and Materials

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