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

MATERIALS TRANSACTIONS Vol. 55 (2014), No. 11

  • Improved Properties of TiC Coating Deposited on Copper Alloy via Friction Stir Processing

    Zhixiong Xie, P. Luo, S. J. Dong, FenFang Tan

    pp. 1639-1642

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    DOI:10.2320/matertrans.M2014203

    Abstract

    In this work, TiC coating on a copper alloy electrode, which is prepared by a special electron-spark deposition process (ESD), was modified by friction stir processing (FSP). The microstructure evolution of the coating was investigated, while the mechanical properties of the coating and interface were measured. The results show that FSP eliminates the cracks within TiC coating and improves the interface bonding between the TiC coating and substrate. The hardness of the FSPed TiC coating is increased about 800 HV by decreasing cracks. The elimination of the cracks within the coating is ascribed to the thermal-mechanical effect on the coating during the FSP. The increase in hardness is attributed to the decreasing number of cracks and the disappearance of columnar Cu grains, which are modified by FSP.

  • Surface Observation of LaNi5 under Deuterium Atmosphere Using Small-Angle Neutron Scattering

    Kazuhiro Mori, Kenji Iwase, Yojiro Oba, Toshiharu Fukunaga, Masaaki Sugiyama

    pp. 1643-1646

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    DOI:10.2320/matertrans.M2014009

    Abstract

    We developed a new sample holder for small-angle neutron scattering (SANS) experiments under controlled atmospheres. Using this new sample holder, SANS profiles of conventional hydrogen-absorbing alloy LaNi5 under a deuterium atmosphere were measured. Changes in the SANS profile of LaNi5 were clearly observed during absorption and desorption. It was found that there is reversibility in the surface morphology of LaNi5; it changed from being markedly rough (fractal dimension of particle surface DS = 2.8, before deuteration) to smoother (DS = 2.5 at 1.05 D/M, i.e., LaNi5D6.3) during absorption (up to 1 MPa), and then reverted to being rough (DS = 2.8) during desorption (under vacuum <5 Pa), where D/M is the deuterium-to-metal ratio.

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  • Influence of Mg/Si Ratio on Nanocluster Formation in Al-Mg-Si Alloys with Constant Mg + Si Concentration

    SeongNyeong Kim, JaeHwang Kim, Equo Kobayashi, Tatsuo Sato

    pp. 1647-1655

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    DOI:10.2320/matertrans.L-M2014832

    Abstract

    Two types of nanoclusters are formed during low temperature aging and play significantly important roles in age-hardening of Al-Mg-Si alloys. The formation behavior of nanoclusters markedly depends on the alloy composition. In this paper, alloy specimens with different Mg/Si ratios in the constant Mg + Si concentration of 1.1, 1.3 and 1.5 mol% were used in order to investigate the influence of the Mg/Si ratio on the nanocluster formation using differential scanning calorimetry (DSC), hardness and electrical resistivity measurements. Two overlapped peaks obtained by the DSC analysis are separated using the Gaussian function method and it is clarified that the volume fraction and formation kinetics of nanoclusters change with the Mg/Si ratio even though in the constant Mg + Si concentration. It is found that the most favorable Mg/Si ratio for the nanocluster formation is almost 1.0 even for the different values of the Mg + Si concentration. The influence of the Mg/Si ratio on the nanocluster formation is discussed in terms of interactions among the solute Mg and Si atoms and vacancies in the matrix.

  • Stability of {4 4 11} ⟨11 11 8⟩ Orientation in a {123} ⟨634⟩ Aluminum Single Crystal Processed by Accumulative Roll Bonding

    Keizo Kashihara, Yoshikazu Komi, Daisuke Terada, Nobuhiro Tsuji

    pp. 1656-1661

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    DOI:10.2320/matertrans.L-M2014833

    Abstract

    A pure aluminum single crystal with a (213) [36\bar{4}] orientation was deformed by accumulative roll bonding (ARB) to an equivalent strain of 7.18 under lubricated conditions. The main orientation of the texture in the center layer was (4 4 11) [11 11 \bar{8}]. Two different kinds of crystal rotations were observed to form (4 4 11) [11 11 \bar{8}]; one was the rotation from (213) [36\bar{4}] to (4 4 11) [11 11 \bar{8}] in the center layer, and the other was the rotation from (116) [33\bar{1}] to (4 4 11) [11 11 \bar{8}] when the area changed its position from the surface to the center. The latter rotation is followed by the cyclic ratcheting mechanism proposed by Heason et al. These crystal rotations lead to the stable existence of the (4 4 11) [11 11 \bar{8}] orientation after many ARB cycles. In the present study using the (213) [36\bar{4}] single crystal, the (\bar{4} \bar{4} 11) [11 11 8] orientation was barely found even after an equivalent strain of 7.18. The lack of (\bar{4} \bar{4} 11) [11 11 8] orientation in the center layer is due to the absence of the (001) [110] orientation in the lower surface layer.

  • On the Elastic Accommodation Between the Structural Units in the LPSO Structures

    Xinfu Gu, Tadashi Furuhara

    pp. 1662-1667

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    DOI:10.2320/matertrans.MAW201420

    Abstract

    Long range periodic stacking ordered (LPSO) structures in magnesium alloy consist of regular arrangements of four layer height fcc structural units separated by several Mg layers paralleling to the base plane. The shear transformation of the structural units from hcp structure involves large transformation strain. This strain can be significantly accommodated by the combination of the structure units with different shears. In addition, the possible lowest elastic energy configuration in both R and H type of LPSO structure is obtained. For H type LPSO structure, the opposite shear directions (or Burgers vectors of the partial dislocations) are operated in nearest structural units, while all three types of shear directions are operated successively in the nearest structural units for R type LPSO structure. This study also intends to discuss the inter spacing between the structural units in terms of the elastic interaction. It is found the elastic interaction alone cannot rationalize the spacing between the structural units.

  • Microstructure and Mechanical Properties of the Extruded and Aged Mg-6Al-2Sn-0.4Mn-xAg Alloys (x = 1, 2 and 3 mass%)

    Hyeon-Taek Son, Yong-Ho Kim

    pp. 1668-1672

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    DOI:10.2320/matertrans.M2014235

    Abstract

    In this study, Mg-6 mass%Al-2 mass%Sn-0.4 mass%Mn with different Ag addition (1, 2 and 3 mass%) were extruded and aged. The effects of Ag additions on microstructure and mechanical properties of the Mg-6Al-2Sn-0.4Mn-based alloys were investigated. In the case of the as-extruded alloys, the strength of Ag-containing alloys was improved approx. 330 MPa as compared with alloy without Ag, due to the solid solution strengthening and weaker basal texture by Ag addition. After ageing treatment, ultimate tensile strength of the 3 mass%Ag containing was remarkably improved to 382 MPa with elongation of 12%. It is probable that fine Mg-Ag precipitates in the α-Mg matrix after ageing treatment, played a significant role in the enhanced strength by Ag addition.

  • Assessment of Temperature and Pressure Dependence of Molar Volume and Phase Diagrams of Binary Al–Si Systems

    Xuantong Liu, Katsunari Oikawa

    pp. 1673-1682

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    DOI:10.2320/matertrans.MAW201407

    Abstract

    This article reports the thermodynamic assessment of the temperature and pressure dependence of the molar volume of Al–Si binary systems, as well as P–T unary and high pressure binary phase diagrams based on the CALPHAD methodology. The molar volumes of stable fcc–Al, diamond–Si, and liquid phases as a function of temperature were directly assessed from the data reported in the literature whereas that of metastable fcc–Si was determined by extrapolating composition dependent volume data for Al–Si and Cu–Si fcc solid solutions through extrapolation to pure Si at atmospheric pressure. The Brosh equation of state, which incorporates the quasi-harmonic model, was implemented to avoid spurious estimations of negative heat capacity and thermal expansion at high pressure; it was subsequently used to predict the corresponding values for these properties. Additionally, the temperature and composition dependence of the molar volume as well as phase diagrams for the binary system at high pressure were calculated. Good agreement was reached between calculated results and experimentally estimated thermodynamic values.

  • Relations between Parameters in Different Sublattice Configurations for CALPHAD-Type Thermodynamic Assessments

    Taichi Abe, Kiyoshi Hashimoto, Ryoji Sahara, Cenk Kocer

    pp. 1683-1688

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    DOI:10.2320/matertrans.M2014252

    Abstract

    For interstitial solid solutions various sublattice configurations have been applied in CALPHAD-type thermodynamic assessments. To construct a thermodynamic database for multi-component systems from the assessed binary and ternary systems, one difficulty is consistency of the thermodynamic models for those phases with sublattices. Previously, to combine parameters of the different sublattice configurations for the same phase, the thermodynamic assessment would need to be repeated. In the present work, we propose a simple method to convert parameters between the different sublattice configurations and demonstrate that the present parameter conversions work well for the Al-B, C-Fe, and O-Ti binary systems. Although it is a simple conversion process utilizing the known parameters, for the case where the valid composition range is limited, the thermodynamic database can be determined for multi-component systems. Furthermore, if a reassessment is required the conversion can be used to estimate initial values for the parameter optimization.

  • Mechanical Properties and Dislocation Substructure of Inconel 690 Alloy Impacted at Cryogenic Temperatures

    Woei-Shyan Lee, Ming-Chia Hsu

    pp. 1689-1697

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    DOI:10.2320/matertrans.M2014165

    Abstract

    The mechanical response and dislocation substructure of Inconel 690 during impact deformation are investigated at strain rates of 2 × 103 ∼ 6 × 103 s−1 and temperatures of −150°C, 0°C and 25°C using a compressive split-Hopkinson pressure bar system. The results show that the flow stress, work hardening rate and strain rate sensitivity all increase with increasing strain rate or decreasing temperature. By contrast, the activation volume reduces as the strain rate increases or the temperature decreases. Moreover, the temperature sensitivity increases with both increasing strain rate and increasing temperature. Optical microscopy observations show that adiabatic shear bands are formed at the highest strain rate of 6 × 103 s−1 in all of the tested specimens. In addition, it is shown that adiabatic shear localisation is the major cause of specimen failure in every case. The dislocation density increases, and the cell size decreases, as the strain rate is increased or the temperature decreased. The change in the dislocation density and cell size is found to have a significant effect on the flow stress and work hardening behaviour of the Inconel 690 specimens; particularly at high strain rates or low temperatures.

  • Structure of Iron-Based Cladding Layer on Al-Mg-Si Alloy Coated by a Resistance Seam Welding Method

    Wenqin Wang, Tomiko Yamaguchi, Kazumasa Nishio

    pp. 1698-1706

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    DOI:10.2320/matertrans.M2014242

    Abstract

    Iron-based cladding layers were successfully fabricated on the 2 mm thick Al-Mg-Si (A6061) alloys to improve the wear resistance of the substrate by a resistance seam welding (RSEW) method. Microstructure showed that the cladding layer consisted of the high carbon iron alloy powders (SHA) reinforcement, A6061 binder and Fe-Al phases. The Fe-Al phases had two kinds of micro-structured morphologies: a needle-like phase in the A6061 identified as FeAl3, and a planer transition phase at the A6061/SHA powders interface identified as Fe2Al5 and FeAl3. A ball-on-disc test was carried out to evaluate the wear resistance of the cladding layers and the wear mechanism was discussed by observing the worn surfaces. Furthermore, the relationship of welding current and the microstructure, as well as the wear resistance of the cladding layer, were also investigated. The results showed that the wear resistance of the cladding layer increased with the increase of the welding current and the best wear performance was found at the welding current of 3.0 kA, where the wear rate was near two orders of magnitude less than the substrate. It was also suggested that the FeAl3 in the cladding layer had a critical role to improve the wear resistance. Moreover, the wear mechanisms of the cladding layer changed from adhesion and delaminate to adhesion with the increase of the welding current.

  • Multiphase Particle Simulation of Gas Bubble Passing Through Liquid/Liquid Interfaces

    Shungo Natsui, Hifumi Takai, Takehiko Kumagai, Tatsuya Kikuchi, Ryosuke O. Suzuki

    pp. 1707-1715

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    DOI:10.2320/matertrans.M2014245

    Abstract

    A newly developed computational fluid dynamics (CFD) model based on a multi-phase particle method is presented for predicting the entrainment behavior of liquid metal into slag due to rising single bubble. By comparing results calculated using this model against experimental data, it was found that the transient behavior of bubbles and the two immiscible liquids can be accurately estimated by this method. The rupturing of the thin water film surrounding the bubble was less reliably predicted, but this 3-dimensional unsteady numerical model still nevertheless provides valuable new information for directly predicting the change in the liquid/liquid interface over time. Such prediction of continuous change in an interface has not been possible by more conventional methods, and thus further improvement in the accuracy of this simulated model may well be the only way to non-empirically predict the metal-slag interface area in actual processes.

  • Quantitative Relation between Mn and S for Mechanical Properties of Flake Graphite Cast Iron

    Toshitake Kanno, Ilgoo Kang

    pp. 1716-1721

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    DOI:10.2320/matertrans.F-M2014831

    Abstract

    We investigated the effects of Mn and S on the mechanical properties of flake graphite cast iron in detail, specifically, hardness, tensile strength, elongation, impact value, deflection, and transverse load. We also investigated the cause. With increasing Mn amount for a constant S content, a transition point appears for each mechanical property. That is, hardness, tensile strength and transverse load become the smallest, and elongation, impact value and deflection become the largest. The mechanical properties of flake graphite are determined by the intervention of four actions; MnS nucleation action, interfacial energy action of soluble S, action of soluble S and soluble Mn to eutectic solidification temperature and pearlitization action of soluble S and soluble Mn. These four actions are thought to be negated by the formation MnS, resulting in the presence of the transition points. In addition, Mn and S amount showing the transition point demonstrate the best type A graphite shape.
    With increasing Mn amount for various S content, many transition points appear. When these points are connected, a new transition point appears near S0.03% and Mn0.32%. Excellent mechanical properties are seen at this new transition point. That is, hardness and tensile strength become the highest, and elongation and impact value which conflict with these properties also become the highest. At this new transition point (0.03%S, 0.32%Mn), MnS just starts to form ([S] × [Mn] = 0.01), and soluble S is the highest. Here, [S] means soluble S and [Mn] soluble Mn.
    Consequently, in flake graphite cast iron, the best excellent properties are obtained at S0.03% and Mn0.32%, which is just before MnS formation.

  • Detection of Fracture in Structural Adhesive Using RFID Tags

    Nariaki Ohashi, Takayuki Shiraiwa, Manabu Enoki

    pp. 1722-1726

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    DOI:10.2320/matertrans.MAW201408

    Abstract

    Although structural adhesives are used in many fields, there are few non-destructive evaluation techniques which are economical and widely applicable. In this study, a new non-destructive evaluation technique of structural adhesives using radio frequency identification (RFID) tags was proposed to keep reliability of structures. This method enables us to detect fracture of structural adhesives by the communication situation of RFID tags. Communication properties of two types of RFID tags, the small tags and in-metal tags, were investigated during bending test, and the effects of tags on mechanical properties were evaluated using finite element method. A fracture of epoxy resin was successfully detected by small tags, and in-metal RFID tag makes it possible to detect internal fracture of epoxy resin covered with SUS304. There is little difference of maximum stress with or without tags in stress field, and it was shown that adhesive strength did not decline with the presence of RFID tags. Therefore, it was shown that this proposed method is effective to find a fracture of structural adhesives.

  • Macro-Segregation Characteristics in Semi-Solid Forging of a High Strength Al-4.8Si-0.7Mg Alloy

    Byoung-Hee Choi, Young-Soo Jang, Byung-Keun Kang, Chun-Pyo Hong

    pp. 1727-1732

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    DOI:10.2320/matertrans.M2014201

    Abstract

    Semi-solid forging of a high strength Al alloy was carried out to investigate the macro-segregation characteristics in regard to the evolution of solidification microstructures. The evolution of segregation was closely affected by the feeding behavior of semi-solid slurries. Two types of macro-segregation were found in semi-solid forging: one is composed of fine dendritic α-Al particles caused by liquid segregation and the other is the residual eutectic segregation. The formation of these segregations was strongly affected by the quality of semi-solid slurries, such as the shape and the size of the primary α-Al particles. In the case of coarse dendritic microstructures, α-Al particles are easily interlocked with each other, resulting in the formation of macro-segregation. In the case of fine and uniform globular microstructures, primary globular α-Al particles can be readily filled into a die cavity during forging, leading to uniform microstructures without the formation of macro-segregation. Optimization of process parameters was carried out both for semi-solid slurry making and for semi-solid forging. The T6 heat treatment was carried out, and hardness distribution on the semi-solid forging specimens was also evaluated to investigate the effect of macro-segregation on mechanical properties.

  • Reverse Current Conduction Mechanism of Transient Voltage Suppression Diode under Electrostatic Discharge Stress

    Daoheung Bouangeune, Ye-Ji Lee, Deok-Ho Cho, Kyu-Hwan Shim, Chel-Jong Choi

    pp. 1733-1737

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    DOI:10.2320/matertrans.M2014214

    Abstract

    A transient voltage suppression (TVS) diode with abrupt junctions was fabricated using low-temperature epitaxy. The effect of electrostatic discharge (ESD) stress on the reverse leakage current conductive mechanism of the TVS diode was investigated using IEC61000-4-2 (IEC) standard analysis, in accordance with temperature-dependent current-voltage (I-V) characteristics. The fabricated TVS diode showed excellent ESD robustness, with negligible degradation up to ±19.5 kV and failure at ±20 kV stress. The ESD stress evidently led to the generation of shallow and deep defect states in the depletion region located 0.52–1.08 eV below the conduction band, and these states served as a main contributor to the resulting reverse leakage current. In devices to which IEC peak voltage stresses of less than ±19.5 kV had been applied, reverse conduction was dominated by generation-recombination current; the application of the ±20 kV failure stress caused reverse conduction to become dominated by a combination of tunneling current via deep defects and Poole-Frenkel barrier lowering. The proposed TVS can serve as a highly stable and reliable ESD protector of electronic components, serving an evolving need in nanoscale technology.

  • Effect of Plastic Deformation on the Proof Strength and Electrical Conductivity of Copper-Magnesium Supersaturated Solid-Solution Alloys

    Yuki Ito, Hirotaka Matsunaga, Hiroyuki Mori, Kazunari Maki

    pp. 1738-1741

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    DOI:10.2320/matertrans.M2014220

    Abstract

    The influences of plastic deformation on the proof strength and electrical conductivity of Copper-Magnesium (Cu-Mg) supersaturated solid-solution alloys are investigated and compared to results obtained for pure copper and conventional binary solid-solution copper alloys. Supersaturated Cu-Mg required cold rolling to only a quarter of the equivalent strain (ε = 0.65) of conventional alloys (ε = 2.66) to obtain the same proof strength and electrical conductivity. Furthermore, when cold-rolled to ε = 2.66, Cu-Mg exhibited an electrical conductivity 2.5 times higher than that of conventional alloys, while retaining comparable proof strength.

  • Adhesive Resistance to Peeling Force of PTFE/PDMS Laminated Sheet Assisted by Homogeneous Low Voltage Electron Beam Irradiation at 77 K

    Chisato Kubo, Takumi Okada, Masato Uyama, Masae Kanda, Yoshitake Nishi

    pp. 1742-1749

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    DOI:10.2320/matertrans.MAW201416

    Abstract

    The effects of homogeneous low voltage electron beam irradiation (HLEBI) under liquid nitrogen on the adhesive force of peeling (oFp) at accumulative probability of peeling (Pp) of laminated PTFE/PDMS sheets of polytetrafluoroethylene (PTFE) and polydimethylsiloxane (PDMS) at 77 K were investigated without glue. oFp values at each Pp of PTFE/PDMS laminated sheets irradiated of 0.04 to 0.43 MGy at both 77 and 298 K exceed the corresponding values of the untreated samples. Although 298 K-HLEBI with 0.04 MGy improves oFp value at low Pp (0.06), 77 K-HLEBI didn’t improve it. On the contrary, the 77 K-HLEBI with 0.22 MGy apparently enhanced the oFp at low-Pp of 0.06. It is higher than that of 298 K-HLEBI with 0.22 MGy. Furthermore, the operation dose range at high oFp value of more than 1.5 N m−1 at low Pp (0.06) at 77 K, indicator of high industrial reliability of production process, was 0.33 MGy, which was more than 3.7 times broader than that at 298 K. Based on the 3-parameter Weibull equation, the lowest oFp value at Pp of zero (Fs) could be estimated. The 0.22 MGy-HLEBI at 77 K apparently improves the Fs, which was higher than that 0.22 MGy-HLEBI at 298 K. Decreasing the irradiation temperature from 298 to 77 K controlled the rapid adhesion and rapid decay of adhesion at low-Pp, which were mainly caused by the low forming ability of dangling bonds induced by strong apparent bonding force, which is related to decreasing atoms vibration energy. Since the 0.22 MGy-HLEBI at 77 K controlled the recovery of dangling bonds and generated the chemical bonds, the strong adhesive force of PTFE/PDMS treated by 0.22 MGy-HLEBI at 77 K could be explained. Therefore, HLEBI under liquid nitrogen was useful tool for quick strong PTFE/PDMS lamination with sterilization for bio-adaptable application.

  • Prediction of Intermetallic Compound Formation Sequences in Pseudo Binary Diffusion Couples: Experimental Examinations for (Sn-xZn)/Cu (x = 2, 5, 10, 15, 20 and 25 mass%) by a Kinetic Model with Thermodynamic Data Using MDR Diagram

    Shinichi Terashima, Tsutomu Sasaki

    pp. 1750-1754

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    DOI:10.2320/matertrans.M2014151

    Abstract

    A kinetic model based on the principle of maximum degradation rate of the total system free energy, MDR law, using thermodynamic data is applied to (Sn-Zn)/Cu diffusion couples to predict intermetallic compound phases and their order to be formed. According to this model, only γ-Cu5Zn8 is predicted to appear when Zn content is less than 10 mass%, while both γ-Cu5Zn8 and ε-CuZn4 can exist with 10 mass%Zn or more, which was in a good agreement with EPMA and TEM observations of Cu plates dipped into Sn-Zn baths. Therefore, it is concluded that the phase prediction based on the MDR law can also be applied to pseudo binary diffusion systems.

  • The Effects of HIP, Solution Heat Treatment and Aging Treatments on the Microstructure and Mechanical Properties of Sintering Cobalt-Based Alloys Strengthened with Tantalum Carbide Additives

    Shih-Hsien Chang, Chien-Chung Chen

    pp. 1755-1761

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    DOI:10.2320/matertrans.M2014066

    Abstract

    This study explored a series of HIP processes, solution heat treatments and aging treatments, in which various amounts of tantalum carbide (TaC) powder are added for sintering cobalt-based composite materials. Experimental results showed that the highest transverse rupture strength (TRS) of 1812.4 MPa was obtained by the 10 mass% TaC added to cobalt-based alloys, which was sintered at 1270°C, and followed by HIP processes, solution heat treatments, and aging treatments for 12 h. The hardness increased to 80.1 HRA. In addition, the added amounts of TaC powder and aging times played important roles in improving the mechanical properties of the cobalt-based alloys. By microstructural observations, it was found that both M6C and M23C6 carbides precipitated in the matrix of the 0% TaC specimens after various aging treatments. However, the more refined and uniform precipitations of M6C, M23C6 and MC carbides were precipitated in the matrix of the TaC powders added to cobalt-based alloys after 12 h of aging treatment at 850°C. This result was effective in improving the mechanical properties of the cobalt-based alloys. Conversely, 15 h of aging treatment at 850°C generated an over-aging phenomenon, which resulted in a decrease in TRS value.

  • Rust Preventive Properties by Using Polarization Curve Measurement on the Metal Coated with the Rust Preventive Oil

    Daisuke Iwashima, Sayaka Hirata, Naoki Nagase, Masahiko Hatakeyama, Satoshi Sunada

    pp. 1762-1764

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    DOI:10.2320/matertrans.MAW201417

    Abstract

    Fe-Cu-C sintered steels are widely used as powder materials, because of its small volumetric shrinkage. However, Cu, which acts as cathode enhance formation of rust (Fe2O3·xH2O) during fabrication. To prevent formation of Fe2O3·xH2O rust preventive oils are genially used. Therefore, it is necessary to develop new rust preventive oils with contradictory properties of low viscosity and superior rust prevention. In this study, we developed technique to quantitatively evaluate rust prevention ability by measuring polarization curve through thin corrosive solution on Fe-Cu-C sintered steels coated with rust preventive oils. Polarization curves were registered after 30 min of exposure to test solution in order to allow corrosion potential (Ecorr) stabilization. From the experimental, it is possible to evaluate the corrosion rate quantitatively in the surface of specimen, which was coated with rust preventive oil through thin corrosive solution. The measurement results suggest the anodic reaction is decreased with oils.

  • Structural and Optical Properties of Smooth Surface TCO Thin Films Deposited on Different-Sized Staked Nanoparticle Layers for Window Electrode of Thin Film Si Solar Cells

    Shuhei Miura, Kazutoshi Suzuki, Shinichi Noda, Masanari Inoue, Kouichi Murakami, Shuichi Nonomura

    pp. 1765-1769

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    DOI:10.2320/matertrans.M2014208

    Abstract

    To improve the light-scattering capacity of transparent conductive oxide (TCO) films without increasing in surface roughness, we formed a stacked nanoparticle layers of ZnO (NP-ZnO) and TiO2 (NP-TiO2), which serve as light-scattering and surface-modifying layers, respectively, between the glass substrate and low-resistive TCO layers. The stacked TCO/NP/glass (NP-TCO) substrate indicated strong light-scattering capacity, with a relatively low surface root mean roughness of approximately 10 nm. In addition, the haze value of NP-TCO substrates increased with an increase in the component particle diameter of the underlying NP-ZnO layers from about 20% (33 nm) to 40% (96 nm) at a wavelength of 550 nm.

  • Numerical Study on Effective Thermal Conductivity of Radial Nanowire Heterostructures with MWCNT Core

    Joo Hyun Moon, Jeongmin Lee, Jooheon Kim, Seong Hyuk Lee

    pp. 1770-1776

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    DOI:10.2320/matertrans.M2014191

    Abstract

    The present study aims to investigate numerically the effective thermal conductivity for different radial nanowire heterostructures (RNWHSs), such as core–shell, tubular–shell, and core–shell–shell types, which are used for resolving thermal dissipation problem. The influence of core radius and shell thickness on the effective thermal conductivity was examined by using the boundary/interfacial scattering (BS) method derived from the Casimir theory. It was found that the effective thermal conductivity of the RNWHSs was smaller than the bulk thermal conductivity of multi-walled carbon nanotubes (MWCNTs) because of the diffusive interfacial scattering effect. When the shell thickness was much thinner than the core radius, the thermal conductivity of the core MWCNT was relatively higher than that of the shell material. Comparing MWCNT/Al2O3 and MWCNT/SiO2 core–shell RNWHSs, the effective thermal conductivities were similar when the core radius was greater than 100 nm or the core porosity was above 0.4, owing to the effect of MWCNT bulk thermal conductivity. Besides, the effective thermal conductivity of the tubular–shell RNWHS with the same cross-sectional area was always lower than that of the core–shell RWNHSs because of additional interfacial scattering at the pores inside the tubular-shell RNWHSs. When the Al2O3 thickness in the core–shell–shell RNWHS of MWCNT/Al2O3/W was less than 135 nm at a fixed MWCNT radius of 100 nm, the effective thermal conductivity increased with core porosity. When the Al2O3 thickness was 1.0 nm, the effective thermal conductivity rapidly decreased with the increase in porosity.

  • Stress Shift to Tensile Side by the Interruption of Deposition during Al and Cr Film Processing

    Junyoung Yu, Youngman Kim

    pp. 1777-1780

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    DOI:10.2320/matertrans.M2014207

    Abstract

    When an average stress in metallic thin film was measured as a function of the film thickness during real time deposition, three distinct stress stages of initial compressive, tensile, and compressive were reported to occur for metals with relatively high mobility. A reversible stress shift to the tensile side was observed due to an abrupt interruption of deposition at the compressive stage. The stress shift occurred rapidly in the beginning and rather slowly later, to reach a saturation value.
    The current study explored the stress shift caused by an abrupt interruption of deposition with focus on the state and magnitude of the thin film stress for the two metals, Al and Cr, with different levels of mobility. For Cr with relatively low mobility, only tensile stress was observed at room temperature deposition, but the three stress stages were observed for Cr deposited at 300°C. It is argued that mobility is a possible factor for the stress evolution mode of the thin film as the diffusivity of Cr at 300°C has a similar order of magnitude as that of Al at the room temperature. No stress shift was observed when deposition interruption occurred at the tensile stress state, but the shift was observed only at the compressive stress state for both Al and Cr. The total amount of stress shift increased as the magnitude of compressive stress at the point of interruption increased for Al.
  • © 2014 The Japan Institute of Metals and Materials

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