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

MATERIALS TRANSACTIONS Vol. 53 (2012), No. 8

  • The Crystalline Structure of O-AlFePd

    Kazumasa Sugiyama, Tatsuo Obata, Kenji Hiraga

    pp. 1357-1362

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    DOI:10.2320/matertrans.M2012130

    Abstract

    The structure of O-AlFePd has been analyzed by single-crystal X-ray diffraction, yielding space group Cmca (No. 64), a = 0.8130(1) nm, b = 1.5474(2) nm, c = 2.3868(4) nm, atoms/cell = 204, F(000) = 3339, Dcalc = 5.621 Mg m−3 and R = 0.0294 for the 2117 observed reflections with Fobs > 4.0σ(Fobs). The structure consists of four Fe sites, one Fe/Pd mixed site, and fifteen Al sites, and the corresponding structural formula is Al13(Fe,Pd)4 (Z = 8). The O-AlFePd phase is a new type of approximant of decagonal quasicrystals with a periodicity of 0.8 nm, and the alternation of flat and puckered layers at an interval of about 0.2 nm is the fundamental structural feature. The structure could be also described by a linkage of pentagonal atom columns similar to that found in monoclinic Al13Fe4. Nevertheless, the columnar linkage for the O-AlFePd phase is unique, and this allows us to advance an idea explaining the fine (001) glide twins frequently found in the Al13Fe4 phase.

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  • Influence of Spinodal Decomposition on the Plastic Behavior of Dynamic Electropulsing Treated ZA22 Alloy

    Y. H. Zhu, S. To, X. M. Liu

    pp. 1363-1370

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    DOI:10.2320/matertrans.M2012024

    Abstract

    Dynamic electropulsing induced phase transformations and their effects on the plastic elongation of a furnace cooled Zn–Al based alloy (ZA22) were studied by using backscattered scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction techniques. Under electropulsing, various transitional phases formed via the spinodal decomposition of α′FC phase. Adequate electropulsing provided favorable identities of both microstructure and dislocation due to pinning dislocation by transitional phases and second phase precipitates. The mechanism of effects of dynamic electropulsing on elongation of the alloy was discussed from the points of view of microstructural evolution and dislocation dynamics.

  • Effect of Ca Addition on Precipitation Behavior of Mg–6.0 mass%Zn–3.0 mass%Al Alloy

    YeLim Kim, Hiroyasu Tezuka, Equo Kobayashi, Tatsuo Sato

    pp. 1371-1378

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    DOI:10.2320/matertrans.L-M2012819

    Abstract

    The effect of 0.5 mass%Ca addition on the precipitation behavior of a Mg–6.0 mass%Zn–3.0 mass%Al (ZA63) alloy was investigated. The as-cast ZA63 and Ca-added alloys were homogenized and solid solution treated at 673 K for 12 and 1 h, respectively, followed by water-quenching. Then, both alloys were aged at 343, 373, 403 and 433 K. The cast ZA63 and Ca-added alloys were mainly composed of the primary α-Mg and Mg32(Al,Zn)49 phases. The Al2Ca phase was detected co-existing in the Ca-added alloy. The Ca addition caused the grain refinement and improved hardness after the solid solution treatment compared with the ZA63 alloy even with the trace amount of 0.5 mass% Ca. The peak hardness of the Ca-added alloy aged at each temperature was higher than that of the ZA63 alloy. The microstructures of the ZA63 and Ca-added alloys produced by peak aging at 433 K consist of rod-like, blocky, plate-like and lath-like precipitates. Moreover, the precipitates in the Ca-added alloy are more finely and densely distributed than those in the ZA63 alloy even though the volume fraction of precipitates in the Ca-added alloy estimated by the electrical conductivity during aging at 433 K for longer than 64 h is smaller than that in the ZA63 alloy. The Cliff-Lorimer plots of the EDS results for the β ’1 phase in the Ca-added alloy aged at 433 K for 1000 h were examined. It was confirmed that the β ’1 phase in the Ca-added alloy contained Ca atoms, indicating that Ca atoms inside the β ’1 phase might change the structure and/or composition of precipitates.

  • Effect of Deformation-Induced ω Phase on the Mechanical Properties of Metastable β-Type Ti–V Alloys

    Xingfeng Zhao, Mitsuo Niinomi, Masaaki Nakai, Junko Hieda

    pp. 1379-1384

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    DOI:10.2320/matertrans.M2012116

    Abstract

    A series of metastable β-type binary Ti–(18–22)V alloys were prepared to investigate the effect of deformation-induced products (deformation-induced ω phase transformation and mechanical twinning) on the mechanical properties of metastable β-type titanium alloys. The microstructures, Young’s moduli, and tensile properties of the alloys were systemically examined.
    Ti–(18–20)V alloys subjected to solution treatment comprise a β phase and a small amount of athermal ω phase, while Ti–22V alloy subjected to solution treatment consists of a single β phase. Ti–(18–20)V alloys subjected to solution treatment exhibit relatively low Young’s moduli and low tensile strengths as compared to cold-rolled specimens. Both deformation-induced ω phase transformation and {332}β< 113 > β mechanical twinning occur in all of the alloys during cold rolling. The occurrences of {332}β< 113 > β mechanical twinning and deformation-induced ω phase transformation are dependent on the β stability of the alloys. After cold rolling, all of the alloys comprise a β phase and an ω phase. The Young’s moduli of Ti–(18–22)V alloys increase because of the formation of a deformation-induced ω phase during cold rolling. The significant increase in tensile strength is attributed to the combined effect of the deformation-induced ω phase transformation and work-hardening during cold rolling.

  • Dislocations in Deformation Microstructure of Extruded Mg97Y2Zn1 Alloy Studied by High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM)

    Kenji Hiraga, Akira Yasuhara, Kaichi Saito

    pp. 1385-1390

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    DOI:10.2320/matertrans.M2012115

    Abstract

    Dislocations in the deformation microstructure of α-Mg and long-period stacking phase (LPS) crystals in an Mg97Y2Zn1 alloy extruded at 350°C are studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Extended a-dislocations in α-Mg crystals are observed as bright line contrasts being parallel to close-packed planes in HAADF-STEM images, showing the segregation of Y and Zn at stacking faults of the extended a-dislocations. On the other hand, a-dislocations in LPS crystals are represented as dark lines in bright fringes of Zn/Y-rich planes periodically arrayed in the LPS structure. Various grain boundaries with slow or sharp bends of close-packed planes are formed by configurations of a series of a-dislocations in the α-Mg and LPS crystals.

  • Machining Heat Induced Phase Transformation on the Surface Hardening Layer of High Strength Ferrous-Based Biomedical Stainless Steel

    Chih-Yeh Chao, Hsi-Jen Chiang, Hsin-Ming Chung, Keng-Liang Ou, Chih-Hua Yu

    pp. 1391-1394

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    DOI:10.2320/matertrans.M2012107

    Abstract

    The present study investigates the drilling characteristics of a high-strength Fe–8Al–30Mn–1C–1Si–3Cr (mass%) biomedical alloy. After machining, a surface-hardening layer with a Vickers hardness number (HV) equal to 600 was observed. In addition, a γ → (γ + κ) phase transition was observed in the matrix and at the stress-induced twin boundaries of the surface-hardening layer. κ-phase carbides ((Fe,Mn)3AlCx) having an L′12 structure with the lattice parameter a = 0.375 nm were precipitated. Furthermore, the heat transfer coefficient of the present alloy was 0.083 cal/(cm2 s °C), which was lower than that of AISI 304 stainless steel, which was 0.098 cal/(cm2 s °C). The instantaneous cutting temperature of the present alloy was approximately 650°C during the machining process. It is believed that the formation of κ-phase carbides not only decreases the machinability of the present alloy, but also reduces the life of the cutting tool. These features could be useful in further understanding the relationship between the machinability and the microstructure of Fe–Al–Mn–C-based alloys, and thus provide information that would be allow these alloys to be used in biomedical and industrial applications.

  • Tensile Plastic Deformation Behavior of Zr70Ni16Cu6Al8 Bulk Metallic Glass at Cryogenic Temperature

    Hitoo Tokunaga, Kazutaka Fujita, Yoshihiko Yokoyama

    pp. 1395-1399

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    DOI:10.2320/matertrans.M2012102

    Abstract

    A hypoeutectic Zr–Ni–Cu–Al bulk metallic glass (BMG) shows a clear tensile plastic deformation under a high strain rate condition at room temperature. In this study, the effect of cryogenic temperature and strain rate on the tensile plastic deformation behavior of the hypoeutectic Zr–Ni–Cu–Al BMG was investigated. Tensile tests were performed for the hypoeutectic Zr–Ni–Cu–Al BMG specimen with gauge part dimensions of 2.3 mm in length and 0.8 mm in diameter at cryogenic temperature (133 K) under different strain rate conditions (10−4 and 10−1 s−1). As the results, the tensile plastic deformation occurs under both strain rate conditions. Especially, in low strain rate condition (10−4 s−1), the amount of plastic deformation is clearly larger than that under the high strain rate condition (10−1 s−1). Furthermore, it was found that there is no positive correlation between the amount of tensile plastic deformation and the number of shear band. In addition, it was inferred that the tensile plastic deformation of the hypoeutectic Zr–Ni–Cu–Al BMG at cryogenic temperature was induced by specimen sliding along only one major shear band.

  • Effects of Pulse Current on Dynamic Recrystallization Behavior of GH4169 Superalloy

    Yang Liu, Lei Wang, Hui-Hong Liu, Xu-Dong Lu, Bei-Jiang Zhang

    pp. 1400-1404

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    DOI:10.2320/matertrans.MBW201102

    Abstract

    The pulse current was applied on the GH4169 alloy during tensile tests at 800°C. The effects of pulse current on the deformation behavior and recrystallization of the alloy were investigated, and the mechanisms were also discussed. The results show that the deformation resistance decreases and the elongation increases significantly by applying the pulse current during tensile tests of the alloy. And the effects of pulse current on the strength and plasticity of the alloy are more remarkable as the pulse current energy increases. It is found that the deformation resistance of the alloy can be decreased since the dislocation motion can be promoted during the tensile testing. The initial temperature of recrystallization can be reduced by the electric effect of the pulse current and the dynamic recrystalllization nucleation is promoted. Therefore, the dynamic recrystallization would occur at lower temperature than that of the alloy without pulse current. That is the main reason for the decreasing of deformation resistance and the increasing of plastic deformation ability of GH4169 alloy under the pulse current.

  • Effects of Chromium and Nitrogen Contents on Microstructural Changes in TiC Particles in (α + β)- and β-Titanium Matrix Composites

    Wataru Sekimoto, Hiroshi Tsuda, Shigeo Mori

    pp. 1405-1411

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    DOI:10.2320/matertrans.M2012127

    Abstract

    New composite materials with high strength and toughness are expected to be obtained from titanium alloys by α-titanium precipitation in ceramic particles dispersed in a matrix. In this study, a series of Ti–Cr–C–N alloys were prepared, and the effects of chromium and nitrogen contents on the microstructural changes in the TiC particles were revealed in (α + β)- or β-titanium alloys. α-Titanium precipitation in the TiC particles was observed when the nitrogen content was more than 2 at% and the chromium content was less than 11 at%. The mechanism of and the conditions for α-titanium precipitation are discussed in terms of the crystallographic relationship between α-titanium and metastable Ti2C.

  • Effects of Electron Beam Irradiation on Charpy Impact Value of Short Glass Fiber (GFRP) Samples with Random Distribution of Solidification Texture Angles from Zero to 90 Degrees

    Michael C. Faudree, Yoshitake Nishi, Michael Gruskiewicz

    pp. 1412-1419

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    DOI:10.2320/matertrans.M2012145

    Abstract

    Compression-molded short-fiber GFRP-BMC panels have random distribution of solidification texture angles from zero to 90 degrees in the center of the mother panels. Hence, there is significantly lower impact strength in the panel center than in the outside. However, experimental results showed homogeneous low voltage electron beam irradiation (HLEBI) applied to the center region apparently enhances the Charpy impact values (auc) 5 to 25%. Fracture mechanism was observed to convert at auc > ∼5.4–6.7 kJ·m−2 from clean to secondary microcrack proliferation and/or bends near the main crack, with increasing fracture surface area as auc increased. SEM observation revealed 0.86 MGy HLEBI treated GFRP had much more polymer adhering to fibers than the untreated. This increased matrix adhesion can be explained by electron spin resonance (ESR) peaks indicating dangling bonds are generated creating repulsive forces between outer shell electrons in the polymer matrix, apparently exhibiting increased compressive stress on the fibers increasing adhesion force. Moreover, the lone pair electrons generated in the matrix may have bonded with the fibers more efficiently. For these reasons, increased fiber-matrix adhesion seen in the 0.86 MGy samples appears to assist for more internal cracking, increasing resilience to impact of the GFRP-BMC, raising the auc.

  • Generation and Characterization of Zirconium Carbide Nanoparticles by Wire Explosion Process

    R. Sugunakar Reddy, M. Kamaraj, U. Kamachi Mudali, S. R. Chakravarthy, R. Sarathi

    pp. 1420-1424

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    DOI:10.2320/matertrans.M2012021

    Abstract

    Zirconium carbide nanoparticles were produced by wire explosion process by exploding zirconium conductor in methane ambiance. X-ray diffraction studies of the particles produced by wire explosion process confirm the formation of cubic zirconium carbide particles. The results of the study indicates that unreacted zirconium content in the zirconium carbide powder could be reduced by exploding the zirconium conductor by depositing energy of three times the sublimation energy in 100 kPa methane pressure. Selected area electron diffraction (SAED) analysis confirms that particles produced are cubic zirconium carbide particles. Transmission electron microscopy analysis indicates that zirconium carbide nanoparticles are spherical in shape and the particle size distribution follows log-normal distribution with the mean particle size of about 20 nm.

  • Experimental Determination and Thermodynamic Assessment of Phase Equilibria in the Co–Mo System

    K. Oikawa, U. R. Kattner, J. Sato, T. Omori, M. Jiang, K. Anzai, K. Ishida

    pp. 1425-1435

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    DOI:10.2320/matertrans.M2012149

    Abstract

    Phase equilibria of the solid phases including the magnetic and martensitic transformation temperatures in the Co–Mo system were investigated using two-phase alloys, the diffusion couple technique, differential scanning calorimetry, and vibrating sample magnetometry. Furthermore, ab initio calculations of D019-Co3Mo and several fcc-base ordered structures, including metastable compounds, were carried out to estimate the formation energy. Based on these results, a thermodynamic assessment using the CALPHAD method was performed. A four-sublattice model was used for the fcc-base phase to describe the order–disorder phase transformation. For the μ phase, both a three and a four-sublattice model were applied. The set of thermodynamic values describing the Gibbs energy of the Co–Mo system reproduces the experimental phase diagram well. The four-sublattice model for the μ phase reproduces the site fractions as well as the phase boundaries better than the three-sublattice model. The calculated metastable fcc-base phase diagram considering chemical and magnetic ordering is also reasonable. This is important for estimating the phase stability of the L12 phase in Co-base γ/γ′ superalloys.

  • Microstructural and Corrosion Characteristics of Alloying Modified Layer on 5083 Al Alloy by Electrical Discharge Alloying Process with Pure Silicon Electrode

    Kuralay Stambekova, Hung-Mao Lin, Jun-Yen Uan

    pp. 1436-1442

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    DOI:10.2320/matertrans.M2012131

    Abstract

    This study examines the surface modification of 5083 Al alloy by electrical discharge alloying (EDA) process, using pure Si as an electrode. Al alloy surface was modified by the EDA process to explore the effect of machining parameters (discharge current, pulse duration and duty factor) on the thickness, hardness and roughness of the alloyed layer. Samples were analyzed by scanning electron microscopy (SEM), electron probe analysis (EPMA) and X-ray diffraction. Since pure Si was used as an electrode, the alloyed layer had high concentration of Si from 2 mass% (the position in the layer at substrate side) to 12 mass% (the position in the layer close to surface side). Experimental results reveal that the thickness of the alloyed layer had a concave downward relationship with the discharge current and pulse duration. High hardness (∼ Hv 250) of the alloyed layer was obtained. The results of X-ray diffraction indicate that the primary phase in the substrate was α-Al, while there were composite phases containing α-Al and Si particles in the alloyed layer. Additionally, the alloyed layer exhibited as good corrosion resistance as 5083 Al alloy in aqueous NaCl.

  • Improving the Erosion and Erosion–Corrosion Properties of Precipitation Hardening Mold Steel by Plasma Nitriding

    Hsiang-Yao Lan, Dong-Cherng Wen

    pp. 1443-1448

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    DOI:10.2320/matertrans.M2012083

    Abstract

    In this study plasma nitriding of precipitation hardening mold steel has been carried out at 470, 500 and 530°C for 12 h in order to achieve good erosion and erosion–corrosion resistance. The microstructure, phase present and microhardness profiles of unnitrided and nitrided layers were examined. The influence of plasma nitriding on the erosion and erosion–corrosion resistance of the tested steel was investigated using a jet solid particle erosion tester and a rotated slurry erosion–corrosion tester.
    The results indicate that the surface properties of the plasma nitrided layers in terms of hardness, erosion wear, and erosion–corrosion resistance are highly dependent on nitriding temperature, and all three plasma surface treatments can significantly improve the surface hardness and effective enhance their erosion resistance under dry erosion. The erosion–corrosion resistance in 20 mass% SiC particles/3.5% NaCl slurry can be effectively improved 48, 65 and 68% by plasma nitrided at 470, 500 and 530°C, respectively. The erosion rate decreases with increasing surface hardness and obeys a power function (\skew4\dotE ∝ H - n) with exponent of 1.047. However, the correlation between erosion–corrosion rate and hardness does not obey any power functions of the exponent in the range of 1–1.5 due to the complexity of the interaction between erosion and corrosion.

  • Effect of Magnesium and Aluminum Oxides on Fluidity of Final Blast Furnace Slag and Its Application

    Jia-Shyan Shiau, Shih-Hsien Liu, Chung-Ken Ho

    pp. 1449-1455

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    DOI:10.2320/matertrans.M2012170

    Abstract

    Generally, decreasing slag volume of blast furnace operation can lead to the lower fuel ratio and higher productivity. For high sinter ratio operation, one of effective ways to obtain a lower slag volume is to reduce the gangue content of sinter. Basically, lowering the amount of serpentine in the sinter mix is a feasible way to produce suitable sinter with the lower gangue content. However, this method may result in lower magnesium oxide content in the final slag that may affect its fluidity. Hence, the objective of this study was to understand the effect of MgO and Al2O3 on the fluidity of final slag. The liquidus temperature and viscosity of semi-synthetic slag were measured using optical softening temperature device and viscometer, respectively, and the data were treated to develop the multiple-regression formula of SiO2–Al2O3–CaO–MgO–TiO2 semi-synthetic slag for liquidus temperature, viscosity equations and iso-fluidity diagrams.
    The experimental results indicated that the lower liquidus temperature and the better viscosity stability lay in the area of MgO = 5.4%, Al2O3 = 10–15%, TiO2 = 0.5% and C/S = 1.2 for the range of composition studied. Several observations in the iso-fluidity diagrams of blast furnace final slag have shown that liquidus temperature decreased with decreasing MgO content and the viscosity of slag could be regarded as being independent of MgO content in the range of MgO = 5–9%, Al2O3 = 15%, C/S = 1.0–1.2. And, slag fluidity became worse with increasing Al2O3 content under the conditions of MgO = 5.4%, C/S = 1.2. This study suggested the MgO contents could be lowered from current 6.5 to 5.4% in the conditions of Al2O3 = 15%, C/S = 1.2 under the stable blast furnace operation with high thermal level. Furthermore, this recipe of lower MgO content (5.4%) had been implemented in CSC’s BF operation to reduce the slag volume, and the formula of fluidity developed in this study had been installed in the process computer of all CSC’s BFs to present slag fluidity in real time.

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  • Surface Hardening of Ferritic Spheroidal Graphite Cast Iron by Friction Stir Processing

    Koichi Imagawa, Hidetoshi Fujii, Yoshiaki Morisada, Yasufumi Yamaguchi, Shoji Kiguchi

    pp. 1456-1460

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    DOI:10.2320/matertrans.F-M2012817

    Abstract

    A ferrite-based spheroidal graphite cast iron (FCD450) is difficult to harden using a conventional surface hardening method, because the carbon content in the matrix is very low. In order to solve this problem, the friction stir processing (FSP) was used in this study as a new hardening method for cast irons. The authors have clarified in a previous study that the pearlite-based cast iron, such as FC300 and FCD700, can be hardened using the friction stir processing and that there are several advantages, such as a higher hardness and no required post surface machining. In this study, it was clarified that a Vickers hardness of about 700 HV is obtained due to the formation of fine martensite even in the ferrite-based spheroidal graphite cast irons, although the optimal process range is much narrower than that of the pearlite-based cast iron due to the requirement of both the heat input for diffusion of the carbon into the matrix and the high cooling rate for the martensitic transformation.

  • Mechanical Properties of Insert-Type Electron Beam Welded Joints of Spheroidal Graphite Cast Iron and Mild Steel

    Shinichi Sekiguchi, Fumio Shibata

    pp. 1461-1467

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    DOI:10.2320/matertrans.F-M2012818

    Abstract

    With the aim of improving the performance of electron beam welded joints between spheroidal graphite cast iron (FCD700) and mild steel (SS490), we applied insert-type electron beam welding that has a insert metal into the I-type butt welding between FCD700 and SS490. By using pure nickel and austenitic stainless steel (SUS304) as the insert metal, the microstructure and mechanical properties of the welded joints were examined.
    Consequently, we found that, with no weld cracks and porosities in the fusion zone, the microstructure of the fusion zone produced by the pure nickel insert-type welding was austenite, while that of the fusion zone produced by the SUS304 insert-type welding was austenite and martensite. The average hardness of the fusion zone produced by the pure nickel insert-type welding and that of the fusion zone produced by the SUS304 insert-type welding were 235 and 393 HV, respectively, showing a decrease in hardening, compared to that of the fusion zone produced by direct welding, 566 HV.
    Concerning the insert-type welded joints, the average tensile strength of the pure nickel welded joint was 425 MPa, while that of the SUS304 welded joint was 443 MPa. The average joint efficiency of the SUS304 welded joint against the mild steel base metal was 84%, showing improvement, compared to that of the directly welded joint, 72%. The impact values of the insert-type welded joints showed almost the same values as those of the directly welded joint. Moreover, concerning the insert-type welded joints (welded joints between FCD700 and SS490), the fatigue limit of the pure Ni welded joint and that of the SUS304 welded joint were 266 and 255 MPa, respectively, showing improvement in fatigue strength, compared to the fatigue limit of the directly welded joint (welded joint between FCD700 and SS400), 209 MPa.

  • Surface Hardening and Microstructural Features of Chromium-Molybdenum Steel via Two-Stage Gas Nitriding with a Short Isothermal Time in Stage One

    Masaki Sumida

    pp. 1468-1474

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    DOI:10.2320/matertrans.M2011397

    Abstract

    In this report, the surface properties and microstructure of chromium-molybdenum steel samples prepared by two-stage gas nitriding with a short isothermal time in stage one are compared with those prepared by one-stage gas nitriding. Two-stage gas nitriding was performed with a short isothermal time in stage one followed by a second stage with lowered NH3 partial pressure, while one-stage gas nitriding was performed under conventional conditions. The variation in microstructure, compound layer thickness (CL), nitrided case depth (d) and surface hardness (HVs) was clarified. In one-stage gas nitriding, the CL, d and HVs increase with increasing isothermal time. In contrast, in two-stage gas nitriding, the CL decreases with isothermal time in the second stage, and surface microstructure observations show partial dissipation of the compound layer. The d and HVs increase at a lower rate of increase than the values observed in one-stage gas nitriding. However, when the second stage temperature was increased in two-stage gas nitriding, the CL decreases and partially dissipates in a shorter time, and d increases at a faster rate than those observed for one-stage gas nitriding. The HVs exhibits a faster rate of increase in the second stage when a higher temperature was used, but the rate is lower than that observed in one-stage gas nitriding. These experimental results are briefly discussed in relation to the microstructure.

  • Effects of Carbon Addition on Microstructures and Mechanical Properties of Binderless Tungsten Carbide

    Akihiro Nino, Kensuke Takahashi, Shigeaki Sugiyama, Hitoshi Taimatsu

    pp. 1475-1480

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    DOI:10.2320/matertrans.M2012148

    Abstract

    Binderless tungsten carbide (WC) with added carbon was sintered at 1800°C using a resistance-heated hot-pressing machine. Dense binderless WCs were obtained in the range from 0.25 to 0.3 mass% C, consisting of only a WC phase. The constituent phase transition with increasing carbon addition was WC + W2C, WC alone, and WC + residual C. Very fine WC grains were formed in the presence of W2C below 0.25 mass% C. When binderless WCs consisted of a WC single phase, larger WC grains were observed. While a high hardness value, more than 23.9 GPa, was measured for binderless WCs below 0.20 mass% C, the hardness decreased markedly in the range from 0.25 to 0.3 mass% C, corresponding to significant WC grain growth. A Hall–Petch-like relationship was confirmed between the hardness value and the grain size for dense binderless WC.

  • Heat Treatment Effects on Electrochemically Grown Bi2Te3 Thin Films for Thermoelectric Applications

    Biswapriya Deb, Yukihiro Isoda, Olga Caballero-Calero, Pablo Díaz-Chao, Marisol S. Martín-González, Yoshikazu Shinohara

    pp. 1481-1485

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    DOI:10.2320/matertrans.ME201106

    Abstract

    Bi2Te3 thin films were grown on a large area of n-Si/Ti/Au substrate by an electrochemical process. The synthesized film sample was cut into four different pieces and each piece underwent different heat treatments for 1 h to optimize their carrier concentration. Heat treatment experiments were performed in an inert atmosphere to prevent oxidation of the films during the treatment. X-ray diffraction showed an increase in the crystallite size with increasing annealing temperatures, which affected the thermoelectric performances of the films. At room temperature, the Seebeck coefficient and electrical resistivity were measured using a custom-built setup. Initially, the measured conductivity appeared to be n-type for all films backed by the metal buffer layer and Si substrate. A simple model that could classify the substrate contribution on the overall transport properties was then developed. The model confirmed that the actual conductivities of the films were p-type, and this was supported by their elemental analysis.

  • High Cycle Fatigue Properties of a Minor Boron-Modified Ti–6Al–4V Alloy

    M. Hagiwara, T. Kitaura, Y. Ono, T. Yuri, T. Ogata, O. Kanou

    pp. 1486-1494

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    DOI:10.2320/matertrans.M2012104

    Abstract

    Ti–6Al–4V alloys modified with minor amounts of boron (B) were prepared, and two types of microstructures, a full lamellar microstructure and an equiaxed microstructure, were generated through combinations of hot-deformation and heat treatments. The beneficial effect of adding a minor amount of B in refining microstructures was confirmed in as-cast ingots and a full lamellar microstructure. For example, a refined prior β grain size of about 100 µm in diameter was obtained for the 0.1 mass percent B-modified alloy with a full lamellar microstructure: accordingly, the size of each colony within the grains was reduced. Contrary to this, equiaxed microstructures with α grain sizes of about 8 µm were obtained for both B-free and B-modified alloys. The room temperature high cycle fatigue (HCF) strength of the B-modified alloys increased compared to the B-free alloy for both microstructures. For example, HCF strength at 107 cycles for the alloy with an equiaxed microstructure increased to 750 MPa by the addition of 0.1% B from 650 MPa for B-free alloy. The fatigue crack was found to originate neither from the TiB/matrix interface nor from the TiB itself but rather from the shear fractures across microstructural units such as colonies or spherical α phases. The reduced colony size and the retarding effect of TiB against the movement of the fatigue initiation area were thought to be responsible for the improved HCF properties of Ti–6Al–4V with lamellar and equiaxed microstructures, respectively.

  • Influence of Hot Pressing Sintering Temperature on β-Sialon-15R Ceramics Synthesized from Aluminum Dross

    Jiajing Li, Jun Wang, Haiyan Chen, Baode Sun

    pp. 1495-1501

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    DOI:10.2320/matertrans.M2012126

    Abstract

    Dense β-sialon-15R ceramics were fabricated by hot pressing sintering method using aluminum dross as a raw material. The effect of hot pressing sintering temperature on densification, microstructure, mechanical properties and impurity were studied. The results indicated that the main phases of the ceramics were β-sialon and 15R AlN polytypoid at 1450, 1550, 1650 and 1750°C, and Fe5Si3 as the main impurity was found. The salts impurities were evaporated from the sample sintered at 1750°C. Most of Mg cations from aluminum dross were incorporated into 15R grains. AlN polytypoids in the multiphase ceramics offer an effective path to reduce the glass phase formed from the oxide impurity in aluminum dross. The aspect ratio of elongated 15R grains increased quickly with the increase of sintering temperature, and a whisker-like microstructure was formed above 1550°C. The β-sialon-15R ceramics obtained the highest density of 3.2 g/cm3 at 1750°C, and the Vickers hardness (Hv10), bending strength and fracture toughness of the material could reach with the value of 12.3 GPa, 432 MPa and 4.31 MPa·m1/2, respectively. Fe5Si3 impurity had a negative effect on the mechanical properties.

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  • Preparation of Conductive Nanoink Using Pulsed-Wire-Evaporated Copper Nanoparticles for Inkjet Printing

    Shinyoung Park, Jaehak Her, Danee Cho, Md. Mominul Haque, Joong Hak Park, Caroline Sunyong Lee

    pp. 1502-1506

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    DOI:10.2320/matertrans.M2012137

    Abstract

    Pulsed-wire evaporation (PWE) was used to synthesize copper nanoparticles having an average diameter of about 100 nm. These were coated with 1-octanethiol (CH3(CH2)7SH) under high vacuum (HV) (5.33 × 10−4 Pa) using vapor self-assembled multilayers (SAMs) to prevent oxidation of the nanoparticles. Conductive nanoink made from the coated nanoparticles was printed on glass. The printed patterns were sintered in hydrogen (99.999 vol%) and mixed gas (Ar 95 vol% + H2 5 vol%) atmospheres; a high copper line density was achieved. Differential scanning calorimetry (DSC) established that the removal temperature of 1-octanethiol was 143°C, well below the 350°C sintering temperature. Complete removal of 1-octanethiol after sintering was confirmed by X-ray photoelectron spectroscopy (XPS). The resistivity of the hydrogen-sintered copper sample was 1.74 × 10−7 Ω·m. This dry powder fabrication and coating method is an alternative approach to inhibit copper oxidation and form inkjet-printed lines.

  • Void Generation Mechanism in Cu Filling Process by Electroplating for Ultra Fine Wire Trenches

    Yasushi Sasajima, Takatoshi Satoh, Kunihiro Tamahashi, Jin Onuki

    pp. 1507-1514

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    DOI:10.2320/matertrans.M2012069

    Abstract

    In the Cu filling process by electroplating for ultra-fine wire trenches in LSIs, voids are generated for narrow wires of less than 80 nm width. We observed the Cu film formation process as a function of time and found that the flow of Cu electrolyte solution is not homogeneous in the trench, resulting in void formation at one side of the trench wall during plating. Numerical analysis of the Cu electrolyte solution flow clarified that Cu ion transportation is lowered substantially by the generation of two vortices in the wire trench when the wire width is less than 50 nm. We proposed a method to enhance transportation of Cu ions by enlarging the open angle at the top edge of the trenches to prevent void formation. The effect of the method for void-free filling was predicted by the numerical analysis of the Cu electrolyte solution flow and confirmed by the actual filling experiment of Cu into the wire trench with 60 nm width.

  • Effects of Porosity and Pore Structure on Compression Properties of Blowing-Agent-Free Aluminum Foams Fabricated from Aluminum Alloy Die Castings

    Yoshihiko Hangai, Hiroki Kato, Takao Utsunomiya, Soichiro Kitahara, Osamu Kuwazuru, Nobuhiro Yoshikawa

    pp. 1515-1520

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    DOI:10.2320/matertrans.M2012125

    Abstract

    Aluminum foam was fabricated without the use of a blowing agent by a friction stir processing route using ADC12 aluminum alloy die castings, which contain a large number of gas pores. In this study, ADC12 foams with a porosity of 50–77% were successfully fabricated, and the pore structures and compression properties of the obtained ADC12 foams were investigated. The ADC12 foams had smaller pores than commercially available aluminum foam. Moreover, the pore size of the ADC12 foams was almost the same regardless of the porosity. According to the results of compression tests, the plateau stress and energy absorption tend to decrease with increasing porosity. Commercially available aluminum foam exhibited higher energy absorption at a low compression stress, whereas the ADC12 foams exhibited higher energy absorption at a high compression stress. Also, the ADC12 foams with higher porosity exhibited higher energy absorption per unit mass, regardless of the compression stress. In contrast, the energy absorption per unit volume was greatest for the low-porosity ADC12 foam at a low compression stress but greatest for the high-porosity foam at a high compression stress.

  • Effect of Mn or Fe Addition on Age-Hardening Behaviour of Al–Mg2Si Alloys

    Shumei Wang, ShanShan Chen, Kenji Matsuda, Tokimasa Kawabata, Junya Nakamura, Susumu Ikeno, Koji Kawakita, Hidetoshi Takagi, Tomokazu Yamashita

    pp. 1521-1528

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    DOI:10.2320/matertrans.MAW201219

    Abstract

    Microstructure and aging hardness variation of Al–Mg–Si alloys with different Mn or Fe content were investigated to reveal the effect of Mn or Fe on the age hardening behavior of Al–Mg–Si alloy using transmission electron microscopy. The peak hardness of the alloys with small content of Mn or Fe is higher than that of the base alloy; the peak hardness of the alloy with 0.2 at%Fe is similar to that of the base alloy but the peak hardness of the alloy with 0.25 at%Mn is lower than that of the base alloy. Si is expensed to form the dispersoid of AlMnSi or AlFeSi in the alloy with 0.25 at%Mn or 0.2 at%Fe. On the other hand, small Mn or Fe addition enhances the formation of β′′ phase which is similar to Co- or Ni-addition alloys because Si is not expensed to form such dispersoid in Co- and Ni-addition alloys. It is thought that this will result in the difference of Si in the matrix for the formation of the precipitate.

  • Effect of 100°C Heating on Further Ductility Improvement of Friction Stir Processed AZ31 Magnesium Alloy

    Hsin-Wei Lee, Truan-Sheng Lui, Li-Hui Chen

    pp. 1529-1535

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    DOI:10.2320/matertrans.M2012081

    Abstract

    Friction stir processed (FSPed) AZ31 Mg alloy with fine grains was deformed in tension at room temperature (RT) and 100°C to be compared with the same alloy in the extruded condition with coarse grains. Results indicate that texture affects the deformation behavior of AZ31 alloy more than grain refinement does. The work hardening rate of the FSPed alloy shows a prolonged ascending stage at RT and a plateau stage at 100°C, while that of the extruded alloy keeps dropping rapidly. The above discrepancy between the tensile properties of the two test materials arises since basal slip and {10\bar{1}2} tension twin of low critical resolved shear stress are favored by the FSPed texture but not by the extruded texture. 100°C heating allows basal slip and {10\bar{1}2} tension twin to contribute significant improvement to tensile ductility in the FSPed alloy, but hastens the instability in plastic strain of the extruded alloy. The work hardening characteristics and deformation properties of the FSPed specimen in tension at RT and 100°C will be compared further in this paper to examine the different tensile behaviors at these two temperatures.

  • Electrochemical Phase Change of Iron Rusts by In-Situ X-ray Diffraction Technique

    Takashi Doi, Takayuki Kamimura, Masugu Sato

    pp. 1536-1538

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    DOI:10.2320/matertrans.M2012159

    Abstract

    In order to investigate the electrochemical cathodic reduction behavior of rusts, we propose the electrochemical cell and the optical conditions for in-situ X-ray diffraction technique. The electrochemical phase change of rust was able to be followed as a function of time. It was observed that β-FeOOH was reduced, and then spinel type iron oxide was formed.

  • Pulsed Current Activated Synthesis and Consolidation of Nanostuctured MgTiO3 Compound

    In-Jin Shon, Hyun-Su Kang, Jung-Mann Doh, Bang-Ju Park, Jin-Kook Yoon

    pp. 1539-1542

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    DOI:10.2320/matertrans.M2012076

    Abstract

    Nanopowders of MgO and TiO2 were made by high energy ball milling. The rapid synthesis and sintering of nanostuctured MgTiO3 compound was investigated by the pulsed current activated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured MgTiO3 compound was produced with simultaneous application of 80 MPa pressure and pulsed current of 2800 A within 2 min. The sintering behavior, gain size and mechanical properties of MgTiO3 compound was investigated.

  • Rapid Consolidation of TiN–Cr2N–(Ti,Cr)N Nanoparticles Using Pulsed Current Activated Sintering and the Mechanical Properties of Sintered Product

    Wonbaek Kim, Chang-Yul Suh, Ki-Min Roh, Jae-Won Lim, Song-Lee Du, In-Jin Shon

    pp. 1543-1546

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    DOI:10.2320/matertrans.M2012153

    Abstract

    We previously reported that the electrical explosion of Cr-plated Ti wires in N2 gas produced nanoparticles composed of cube-shaped TiN, sphere-shaped Cr2N and extremely fine (Ti,Cr)N particles. In this study, the mixture powders were consolidated by pulsed current activated sintering (PCAS). A near-full density compact could be obtained within five minutes at 1600°C. The shrinkage-time profile revealed an abnormally high contraction of the compact at 1500°C after the typical sintering period observed at temperatures between 700 to 1300°C. The sudden shrinkage at 1500°C turned out to be the consequence of the eutectic melting of Cr2N particles which decomposed to Cr and N2. The metallic Cr phase was located mostly at triple points and grain boundaries prohibiting the grain growth of TiN grains. The microhardness of the compact (13.6 GPa) was lower than that of pure TiN compact (16.2 GPa) due to the soft Cr phase. Nevertheless, the fracture toughness of the compact (6.6 MPa·m1/2) was higher than that of the pure TiN compact (6.0 MPa·m1/2) probably because the metallic Cr along grain boundary may deter the crack propagation.

  • Appropriateness of the Hencky Equivalent Strain as the Quantity to Represent the Degree of Severe Plastic Deformation

    Susumu Onaka

    pp. 1547-1548

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    DOI:10.2320/matertrans.M2012077

    Abstract

    The Hencky strain is a logarithmic strain extended to a three-dimensional analysis. Although Onaka has shown that the Hencky equivalent strain is an appropriate measure of large simple-shear deformation (2010), Jonas et al. (2011) have recently presented a paper claiming that the application of the Hencky strain to large simple-shear deformation is in error. In the present paper, it is shown that the claim of Jonas et al. is contrary to recent accepted knowledge on the Hencky strain.
  • © 2012 The Japan Institute of Metals and Materials

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