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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 2

  • Thermodynamic Calculation of Phase Equilibria in the Nb-Ni-Ti-Zr Quaternary System

    Tatsuya Tokunaga, Satoshi Matsumoto, Hiroshi Ohtani, Mitsuhiro Hasebe

    pp. 89-96

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    DOI:10.2320/matertrans.48.89

    Abstract

    The phase equilibria in the Nb-Ni-Ti-Zr quaternary system have been studied using the CALPHAD method. Among the four ternary systems present in the quaternary phase diagram, the Nb-Ti-Zr ternary system was described using a simple ternary extrapolation of the constituent binary systems with no additional ternary parameters. The thermodynamic parameters of the Ni-Ti-Zr ternary system were evaluated using data from first-principles calculations on the ternary NiTi, NiZr, and NiTiZr compound phases as well as available experimental data on the phase boundaries. The calculated isothermal and vertical section diagrams of both the Nb-Ti-Zr and Ni-Ti-Zr ternary systems reproduced the experimental results satisfactorily. The thermodynamic parameters of the Nb-Ni-Ti and Nb-Ni-Zr ternary systems were adopted from previous studies. The liquidus surface in the Nb-Ni-Ti-Zr quaternary system was calculated based on the thermodynamic description of the ternary systems. According to the calculated liquidus surface of Nb40−x−yNi60TixZry alloys, in which a metallic glass was formed over a wide composition range, the liquidus temperature decreased with increasing Zr content up to 20 mol%Zr.

  • Role of Eutectic Intermetallic Phase on Creep Strength in a Die-Cast Mg-Al-Ca Alloy: Evaluation by Internal Stress Measurement

    Yoshihiro Terada, Yukako Mori, Tatsuo Sato

    pp. 97-100

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    DOI:10.2320/matertrans.48.97

    Abstract

    The internal stress during high temperature creep was investigated for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 473 K through the strain-transient dip test technique. The microstructure of the alloy is characterized by the eutectic intermetallic phase covering the primary α-Mg grains. The eutectic intermetallic phase plays dual roles in enhancing the creep strength from the viewpoint of the internal stress. First, the eutectic intermetallic phase sustains the stress-independent component of the internal stress with the magnitude of 15 MPa, resulting in the decrease in the effective stress. And second, it lowers the creep rate by two orders of magnitude at a given effective stress by reducing the mobile dislocation density and/or glide velocity of dislocations.

  • SAXS and XAFS Characterization of Precipitates in a High-Performance Cu–Ni–Si Alloy

    Yohei Takahashi, Takashi Sanada, Shigeo Sato, Toshihiro Okajima, Kozo Shinoda, Shigeru Suzuki

    pp. 101-104

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    DOI:10.2320/matertrans.48.101

    Abstract

    Analyses of small-angle X-ray scattering (SAXS) and X-ray absorption fine structure (XAFS) were performed for characterizing precipitates formed in a Cu-3.1 at %Ni-1.4 at%Si alloy, the strength and electrical conductivity of which were improved by aging. SAXS profiles and XAFS spectra of samples aged at 720 K for different periods of time after a solution treatment were measured. SAXS profiles of samples, which were aged after the solution treatment and subsequently cold rolled, were also measured to investigate the effect of dislocations on precipitation. The results of SAXS measurements showed that nanometer-size precipitates formed in the alloy samples during isothermal aging at 720 K. The precipitates in the samples without cold rolling were coarsened in a single modal size distribution with increasing aging time. In contrast, the precipitates formed in the cold-rolled samples appeared to be coarsened in a multi-modal size distribution with increasing aging time. This aging characteristic of the cold-rolled samples is presumably attributable to their good electrical conductivity. The results of XAFS measurements at the Ni K-edge showed that nickel was substituted for copper in the face-centered cubic (fcc) copper matrix and that the local structure around nickel was changed by isothermal aging. With increasing aging time, extended X-ray absorption fine structure (EXAFS) functions at the Ni K-edge of the samples were found to be changed, which implies that nickel atoms were precipitated as nickel-silicon clusters or intermediate compounds in the fcc copper matrix. In addition, X-ray absorption near edge structure (XANES) spectra at the Ni K-edge indicated that the electronic structure of nickel in the samples was influenced by silicon during aging.

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    3. Electron Irradiation Induced Crystallization of Supercooled Liquid in Zr Based Alloys MATERIALS TRANSACTIONS Vol.48(2007), No.2

  • Calcium-Phosphate Formation on Titanium Modified with Newly Developed Calcium-Hydroxide-Slurry Treatment

    Naofumi Ohtsu, Tetsuya Ashino, Masahito Ishihara, Fuyuki Sakamoto, Takao Hanawa

    pp. 105-110

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    DOI:10.2320/matertrans.48.105

    Abstract

    Authors developed a new surface-modification method with calcium-hydroxide slurry, which make it possible to treat a titanium surface by contacting with an alkaline agent containing high concentration of calcium. The objective of the new surface modification method was to improve a bone conductivity of titanium with simple and low-cost processes. The calcium-hydroxide slurry was prepared by mixture of calcium-hydroxide regent and deionized water. A titanium plate was completely buried in the calcium-hydroxide slurry, and the slurry including the titanium was heated in air at 873 K for 7.2 ks, followed by washing in deionized water, and drying in air. Characterization with X-ray photoelectron spectroscopy revealed that chemical state of the surface-modified-titanium surface was the same as that of calcium titanate. X-ray diffraction pattern showed that the perovskite-type calcium titanate was formed in the surface-modified layer, and depth profile by Auger electron spectroscopy titanium indicated that dioxide layer was formed under the calcium-titanate layer. When the surface-modified titanium was immersed in a Hanks’ balanced saline solution for 9 d, hydroxyapatite was formed on the surface-modified-titanium surface, while was not formed on the unmodified-titanium surface without surface modification. However, after 18-d immersion, hydroxyapatite was also formed on unmodified-titanium surface. X-ray diffraction pattern showed that thickness of the hydroxyapatite layer formed on the surface-modified-titanium surface was thicker than that on the unmodified-titanium surface. These results indicated that the calcium-hydroxide-slurry treatment improves the performance of calcium-phosphate formation of titanium. Therefore, the new treatment technique is one of the promising methods for improvement of bone conductivity of titanium.

  • Degradation Mechanism of Amorphous Silicon Carbide Fiber due to Air-Exposure at High Temperatures

    Kohei Morishita, Tasuku Matsumoto, Shojiro Ochiai, Hiroshi Okuda, Toshihiro Ishikawa, Mitsuhiko Sato

    pp. 111-116

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    DOI:10.2320/matertrans.48.111

    Abstract

    The degradation mechanism of the amorphous silicon carbide fiber, Tyranno-ZMI®, exposed in air at 1173∼1873 K for 20 ks were studied. The average strength of the bare fiber, which was prepared by etching away the oxidation layer on the fiber surface, decreased with increasing exposure temperature, especially when exposed at the temperature higher than 1673 K. The measurement of the crystallite size of β-SiC in the fiber with Sherrer method revealed that coarsening of the crystalline occurred in the fiber exposed at the temperatures higher than 1773 K. The scanning electron microscope observation of the fiber surface showed that the many defects formed on the fiber surface. By introducing an artificial notch directly into the fiber specimens using a focused-ion(Ga+)-beam, the fracture toughness values of the as-supplied fiber and of the fiber exposed at 1673 and 1773 K were determined to be 1.8±0.3, 1.9±0.4 and 1.3±0.4 MPa\sqrtm, respectively. Based on these results, the reason for the degradation of the fiber was attributed to the extension of the surface defect which was enhanced by the reduction in fracture toughness due to coarsening of the β-SiC crystalline.

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    3. Electron Irradiation Induced Crystallization of Supercooled Liquid in Zr Based Alloys MATERIALS TRANSACTIONS Vol.48(2007), No.2

  • Magnetostrictive Properties of Fe-Ga/Ni Bimorph Layers

    Teiko Okazaki, Masamune Tanaka, Norimasa Okanisi, Syun Kojima, Munemi Michigami, Yasubumi Furuya

    pp. 117-120

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    DOI:10.2320/matertrans.48.117

    Abstract

    Giant magnetostrictive Fe-Ga alloys are expected as actuator/sensor materials with high respective velocity and large stress created by the magnetostriction. To develop magnetostrictive material induced by low magnetic fields, we investigated magnetostrictive (positive magnetostriction/negative magnetostriction) bimorph layers, that is, Fe80Ga20 ribbon (146 μm)/Ni (14 μm) film produced by magnetron sputtering. The Fe80Ga20 ribbon was prepared by rapid solidification. The magnetostrictive property of the cantilever-type foil was determined experimentally using the optical lever method. The displacement of the upper part of the foil with a length of 22 mm was 530 μm under a low steady magnetic field of 40 kAm−1 and exhibits little hysteresis. These magnetostrictive properties are also maintained under a low-frequency alternating magnetic field. Moreover, the displacement of the foil at the mechanical resonance frequency exhibits a peak and reaches 2.0 mm at a weak magnetic field of 4 kAm−1. The magnetostrictive bimorph layers are useful for applications in microdevices such as micropumps.

  • Effect of Li Addition on Synthesis of Mg-Ti BCC Alloys by means of Ball Milling

    Kohta Asano, Hirotoshi Enoki, Etsuo Akiba

    pp. 121-126

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    DOI:10.2320/matertrans.48.121

    Abstract

    The effect of Li addition to Mg on synthesis of Mg-Ti BCC alloys by means of ball milling was studied. Mg–x at%Li (x=4,20,46) alloys prepared by the induction melting method consisted of the HCP phase (Mg-type), the HCP phase + the BCC phase (Li-type) and the BCC phase, respectively. Lattice parameters of the HCP phase decreased with the increase in x, whereas those of the BCC phase at x=20 and 46 were smaller than that of Li. Mg–x at%Li (x=4,20,46) alloys and Ti were milled for 50–200 h in an argon atmosphere. Formation of Mg96Li4Ti100 BCC alloy was confirmed by X-ray diffraction (XRD) measurements after 50 h milling. By Li addition to Mg, the synthesis time of the BCC phase was shortened. Li made Mg deformation facile by the activation of the non-basal slips in Mg, and raw materials were efficiently milled. The crystallite size of Ti was readily reduced and formation of the BCC phase was accelerated. The crystallite size and lattice parameter of Mg96Li4Ti100 BCC alloy were similar to those of Mg100Ti100 BCC alloy.

  • Thermal Stability of a Rhenium-Based Diffusion Barrier Coating Layer on a Ni-Based Superalloy

    Yongming Wang, Somei Ohnuki, Shigenari Hayashi, Takayuki Yoshioka, Motoi Hara, Toshio Narita

    pp. 127-132

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    DOI:10.2320/matertrans.48.127

    Abstract

    The thermal stability of coatings containing a Re-based diffusion barrier layer was investigated by surface and cross-sectional analysis methods. A Re-based barrier layer accompanied by an outer Ni-Cr-Al layer was prepared by electrolytic plating onto a Ni-based superalloy, followed by Cr-pack cementation in vacuum at 1523 K. Vacuum annealing was carried out at 1423 K for 25 h. Another type of coating specimen, with an additional Al reservoir layer on the Re-based barrier layer, was oxidized in air for 25 one-hour cycles at 1423 K. EDXRF, XRD, SEM, EDS and EPMA were used for analysis to evaluate the effects of the heat treatments. It was found that the barrier layer decomposed at high temperature when it was coated with a low-Al Ni-Cr-Al phase, but had good stability when it was adjacent to a high-Al Ni-Cr-Al phase.

  • Synthesis of High-Purity Ti3SiC2 through Pulse Discharge Sintering of TiH2/SiC/C Powder Mixture

    Yong Zou, Zheng Ming Sun, Shuji Tada, Hitoshi Hashimoto

    pp. 133-138

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    DOI:10.2320/matertrans.48.133

    Abstract

    Ternary compound Ti3SiC2 was successfully synthesized by pulse discharge sintering the powder mixture of TiH2/SiC/C. When the molar ratio of the starting powder mixture was selected to be TiH2:SiC:C=2.8:1:0.8, single-phase dense Ti3SiC2 was synthesized at 1400°C for 20 min. The grain size of synthesized Ti3SiC2 strongly depends on the sintering temperature. The synthesis mechanism of Ti3SiC2 was revealed to be completed via the reactions among the intermediate phases of Ti5Si3Cx and TiC. It is found that dehydrogenation was accelerated by the synthesis reaction during sintering progress. Compared with Ti/SiC/C powder mixture, the TiH2/SiC/C mixed powder is favorable for synthesizing Ti3SiC2 through PDS technique.

  • Fabrication of Functionally Graded Ti3SiC2–TiC Binary-Phase Material

    Shuji Tada, Kosuke Murase, Hitoshi Hashimoto, Zheng Ming Sun

    pp. 139-142

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    DOI:10.2320/matertrans.48.139

    Abstract

    Ti3SiC2–TiC binary-phase material was investigated with the aim of developing a new hard product. The starting material for the synthesis was prepared by compounding raw powders of Ti, Si and TiC at molar ratios of 1:1:x (x=1.8–7.0). The products were synthesized by sintering and the structures of the samples produced were examined. The product obtained was single-phase Ti3SiC2 when x was 2.0 or less and a Ti3SiC2–TiC binary-phase structure when x was more than 2.0. The mass fraction of TiC in the binary-phase structure increased with increasing x. The optimum sintering temperatures for densification were different for the different synthesized structures: the Ti3SiC2 single-phase structure was well densified at up to 1673 K, whereas higher temperature was required to dinsify the Ti3SiC2–TiC binary-phase structure. These results suggest the possibility of producing Ti3SiC2–TiC functionally graded materials. The traveling-zone sintering method permits integrated sintering of materials at variable temperatures. Powder mixtures with TiC contents from 1.8 to 7.0 mole were layered in the same mold and sintered at variable temperatures from 1643 to 1733 K. The synthesized structure was successfully graded, as in the case of individual synthesis of each of the compounds. The hardness of the produced sample showed a tendency to increase with increasing mass fraction of TiC. These results prove that the traveling-zone sintering method has the potential to fabricate functionally graded materials that require variable sintering temperatures.

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  • Modification of Local Structure and Its Influence on Electrical Activity of Near (310) Σ5 Grain Boundary in Bulk Silicon

    Kentaro Kutsukake, Noritaka Usami, Kozo Fujiwara, Yoshitaro Nose, Takamasa Sugawara, Toetsu Shishido, Kazuo Nakajima

    pp. 143-147

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    DOI:10.2320/matertrans.48.143

    Abstract

    We report on the modification of the local structures of (310) Σ5 grain boundary in bulk silicon as the growth of crystal and its influence on electrical activity. The grain boundary was formed via floating-zone growth method utilizing bicrystal seed. The misalignment of the seed resulted in formation of the grain boundary with small deviations of crystal orientation from the Σ5 singular coincidence orientation. The deviations consist of tilt and twist components and they were found to monotonically decrease with respect to the distance from the seed crystal accompanied by the decrease in density of dislocations on the grain boundary. The change in the grain boundary structure allows a systematic study on the correlation between the structure and the electrical activity at the GB. The density of dislocations was found to control the electrical activity and the (310) Σ5 coincidence grain boundary without any dislocations is expected to show a very low electrical activity.

  • Measurement of Interfacial Thermal Resistance by Periodic Heating and a Thermo-Reflectance Technique

    Yibin Xu, Haitao Wang, Yoshihisa Tanaka, Masato Shimono, Masayoshi Yamazaki

    pp. 148-150

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    DOI:10.2320/matertrans.48.148

    Abstract

    Interfacial thermal resistance is an important factor that has a considerable effect on the thermal conductivity of composites, especially nanocomposites, and must therefore be considered when developing new composites for various structural and nonstructural applications. However, reported data on interfacial thermal resistance are sparse as a result of a lack of efficient measurement methods. We developed a new analytical and measurement method for the determination of the interfacial thermal resistance between a metal and a dielectric material by using a technique involving periodic Joule (ohmic) heating and thermo-reflectance. The principle is based on a one-dimensional model of heat conduction in a two-layered system, taking into account the interfacial thermal resistance. By using this method, the interfacial thermal resistances between Au films and substrates of SiO2 glass or sapphire single crystal were measured. The results were compared with values calculated by the diffusion mismatch model, and the experimental factors that might affect the interfacial thermal resistance are discussed.

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  • Electron Irradiation Induced Crystallization of Supercooled Liquid in Zr Based Alloys

    Takeshi Nagase, Yukichi Umakoshi

    pp. 151-157

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    DOI:10.2320/matertrans.48.151

    Abstract

    Effect of electron irradiation on supercooled liquid in Zr66.7Cu33.3, Zr65Al7.5Cu27.5 and Zr60Al15Ni25 metallic glasses was investigated by in situ TEM observation. The electron irradiation induced crystallization occurred in the supercooled liquid with nucleation and growth mode similar to that by thermal annealing. The electron irradiation accelerated crystallization resulting in different size and morphology of precipitates from those by thermal annealing. There was no significant difference in phase selection and crystallization mode of supercooled liquid between thermal annealing and electron irradiation, while electron irradiation induced crystallization behavior of an amorphous phase was different from that of thermal crystallization.

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  • Fabrication of ZrCuAlNi Metallic Glassy Matrix Composite Containing ZrO2 Particles by Spark Plasma Sintering Process

    Guoqiang Xie, Dmitri V. Louzguine-Luzgin, Hisamichi Kimura, Akihisa Inoue

    pp. 158-162

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    DOI:10.2320/matertrans.48.158

    Abstract

    Using a mixed powder of argon gas-atomized Zr55Cu30Al10Ni5 metallic glassy alloy powder blended with 10 vol% ZrO2 powder, Zr55Cu30Al10Ni5 bulk metallic glassy matrix composite was fabricated by a spark plasma sintering process. The structure, thermal stability and mechanical properties of the sintered bulk metallic glassy matrix composite were investigated. The ZrO2 particles were homogeneously dispersed in the Zr55Cu30Al10Ni5 glassy matrix. No crystallization of the glassy matrix occurred during the spark plasma sintering process. The crystallization behavior of the sintered composite was similar to that of the metallic glassy powder. The sintered composite specimen exhibited larger plastic ductility than that of the as-cast Zr55Cu30Al10Ni5 glassy alloy rod specimen. The increase in the plastic ductility is proposed to originate from the structural inhomogeneity caused by the ZrO2 ceramic particles.

  • Glass-Forming Ability and Thermal Stability of Ti–Zr–Cu–Pd–Si Bulk Glassy Alloys for Biomedical Applications

    Shengli Zhu, Xinmin Wang, Fengxiang Qin, Akihisa Inoue

    pp. 163-166

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    DOI:10.2320/matertrans.48.163

    Abstract

    The thermal properties, glass forming ability (GFA) and mechanical properties of a series of Ti40Zr10Cu40−xPd10Six (x=0, 1, 2) bulk glassy alloys were examined by differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffractometry (XRD) and compression test. The bulk glassy alloys are expected to be used as biomedical materials because of the absence of toxic elements such as Ni, Al and Be. The glass-forming ability and thermal stability of the Ti–Zr–Cu–Pd alloy can be improved by a small amount of Si addition. The critical diameters for glass formation are 5 mm for both Ti40Zr10Cu39Pd10Si1 and Ti40Zr10Cu38Pd10Si2 alloys. A large supercooled liquid region of 65 K was obtained for the Ti40Zr10Cu38Pd10Si2 bulk glassy alloy. The bulk glassy alloys have higher compressive strength of over 1900 MPa and lower Young’s modulus below 85 GPa as compared with conventional biomedical Ti alloys.

  • Microstructure and Corrosion Resistance of Ti–Zr–Cu–Pd–Sn Glassy and Nanocrystalline Alloys

    Fengxiang Qin, Xinmin Wang, Guoqiang Xie, Shengli Zhu, Asahi Kawashima, Katsuhiko Asami, Akihisa Inoue

    pp. 167-170

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    DOI:10.2320/matertrans.48.167

    Abstract

    The microstructure and corrosion behavior of the Ti47.5Zr15Cu30Pd7.5Sn5 as-spun ribbons and as-cast rod have been investigated using HREM and potentiodynamic polarization study in simulated body fluids. The results of HREM reveal that, with decreasing cooling rate, the size and volume of nano-particles dispersed in glassy matrix increase for the Ti47.5Zr15Cu30Pd7.5Sn5 as-prepared samples. The as-spun ribbons with small size nano-particle show high corrosion resistance in PBS(−) and Hanks’ solution, may be due to the formation of CuZr phase, resulting in the enrichment of Ti and Pd in the glassy matrix, which is helpful to form protective passive film. Comparatively, poor corrosion resistance is observed for the as-cast rod sample with larger nano-particles in both solutions.

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  • Effect of Spatial Distribution of SiC Particles on the Tensile Deformation Behavior of Al-10 vol%SiC Composites

    Di Zhang, Kenjiro Sugio, Kazuyuki Sakai, Hiroshi Fukushima, Osamu Yanagisawa

    pp. 171-177

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    DOI:10.2320/matertrans.48.171

    Abstract

    The effect of particle clustering distribution on the damage accumulation and the deformation behavior is investigated in the particle reinforced metal-matrix composites. The clustering tendency of the Al-10 vol%SiC composite is evaluated by the normalized 2-dimensional local number density (LND2D) of the particle. It is found that the uniform material having a spatial distribution close to the random distribution has higher flow stress and larger elongation. The particle/matrix delamination is easy to occur preferentially at the particles of larger size in the more clustered regions in tensile deformation. Composites with lower clustering tendency have larger strain hardening capacity than those with more clustering one.

  • Uniform Equiaxed Grain Structure throughout Thickness of a Hot-Rolled 5083 Al-Mg-Mn Alloy Thick Plate after a Tempering Treatment at 350°C

    Jun-Yen Uan, Hsu-Feng Cheng

    pp. 178-183

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    DOI:10.2320/matertrans.48.178

    Abstract

    In a conventional hot-rolled 5083 Al-alloy thick plate, the crystalline structure at the central part in the thickness direction comprises primarily slender grains. However, the grain structure is always equiaxed near the surface of the rolling plate. In this experiment, the shape of the slab before hot rolling was changed to a trapezoid. The main goal is to increase the amount of plastic strain and increase the dislocation density in the central part of the plate hot-rolled from the trapezoidal aluminum slab. TEM observations indicated that the center of the plate of hot-rolled trapezoidal slab had a higher dislocation density than the center of the rectangular slab. Subsequent heat treatment caused the treated grains to become equiaxed. Therefore, an equiaxed grain structure that was uniform in the thickness direction of a hot-rolled thick plate could be obtained because the hot rolling of the trapezoidal slab caused profound lateral strain, in addition to extensive deformation in the rolling direction. The excess deformation resulted in a high dislocation density in the central region of the as-hot rolled plate, increasing the strain energy that was stored for recrystallization.

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  • Grain Size Dependence of Yield Strength in Randomly Textured Mg-Al-Zn Alloy

    Y. N. Wang, J. C. Huang

    pp. 184-188

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    DOI:10.2320/matertrans.48.184

    Abstract

    The randomly textured Mg-Al-Zn alloy processed by electron beam welding typically exhibits clear grain size dependence of yield strength according to the Hall-Petch relationship: σ0.2=62+202d−1⁄2. The Schmid factor for the basal slip system was deduced to be around 0.031 in the randomly textured Mg alloys. The σ0 in the Hall-Petch equation was theoretically calculated to be ∼65 MPa, which is reasonably consistent with the experimental data of ∼62 MPa.

  • Development and Verification of Accretion Similarity Conversion Method for Gas Bottom-Blowing Process inside Pyrometallurgical Vessels

    Yu Pin Huang, Weng Sing Hwang, Jia Shyan Shiau, Shih Hsien Liu

    pp. 189-194

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    DOI:10.2320/matertrans.48.189

    Abstract

    In this research, a water model with an extra low temperature (−177°C) gas blown-in system was established to simulate the phenomena inside pyrometallurgical vessels for investigating effects of gas bottom blowing conditions on the shape and dimensions of solid accretion sitting on the refractory lining near gas tuyeres.
    In addition, Buckingham Pi theorem was adopted to derive the important dimensionless parameters for correlating conditions of accretion formation in the similar systems. Then, by combining dimensionless parameters with heat transfer equations that describe the heat transfer across the accretion, quantitative relations based on the similarity conversion of the similar systems was established. The method mentioned above is called Accretion Similarity Conversion Method (ASCM).
    Meanwhile, the experimental work of a wax model was conducted to evaluate the accuracy of ASCM. The results indicate that the size of solid accretion inside the wax model under a specific condition can be reasonably estimated by ASCM.

  • Impact and Hot Corrosion Properties of Levitation-Melted NiAl Polycrystals with Different Purity

    Kazuhiro Matsugi, Gen Sasaki, Osamu Yanagisawa

    pp. 195-204

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    DOI:10.2320/matertrans.48.195

    Abstract

    Higher and lower purity NiAl polycrystals with the different levels in impurities were produced by levitation melting, and they had larger or smaller grain. The hardness in grains decreased linearly with increase in temperature up to 900–1100 K, and the lower purity alloys showed its higher value. The impact value increased as the temperature was raised, regardless of the kinds of alloys. The rate of increase in the impact values decreased above the critical temperature depending on the kinds of alloys. The critical temperature meant one showing the maximum value of the maximum load. The fracture mode was predominantly transgranular and intergranular ones below and above the critical temperature, respectively, although there was a mixture of both fracture modes regardless of test temperatures. The impact values decreased as the grain size increased at 293 K, regardless of the purity of alloys. In contrast, at 1373 K, the effect of grain size on the impact values was smaller, but the impact values of the higher purity alloys were 1.3 times-higher than those of lower purity alloys. There was no difference in oxidation behavior at 1373 and 1473 K among experimental alloys. The hot-corrosion weight loss increased in the alloys with the lower purity and smaller grains.

  • Drilling Microholes in Hot Tool Steel by Using Micro-Electro Discharge Machining

    T. Y. Tai, T. Masusawa, H. T. Lee

    pp. 205-210

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    DOI:10.2320/matertrans.48.205

    Abstract

    This study presents an investigation into the drilling of a deep microholes with the depth of 320 μm in tool steel SKD61 by the Micro-EDM process. The electrode with the diameter of 26 μm is machined by the method of wire electrodischarge grinding (WEDG). Optical microscopy, scanning electron microscopy, and confocal laser scanning microscopy techniques are used to determine the influence of the process parameters upon hole enlargement, electrode wear rate, material removal rate, wear ratio, and the observed surface topography. The results of the study reveal the optimum parameter settings for the Micro-EDM machining of a high aspect ratio microhole are as follows: (1) a pulse voltage between 60 and 100 V, (2) a capacitance between 80 pF and 220 pF. Finally when the depth exceeds 200 μm, the shape of the micro hole almost becomes tapered due to the corner wear of the electrode and the secondary discharge along the side of the hole.

  • Effect of Crystallization on the Bonding Strength and Failures of Plasma-Sprayed Hydroxyapatite

    Chung-Wei Yang, Truan-Sheng Lui

    pp. 211-218

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    DOI:10.2320/matertrans.48.211

    Abstract

    Hydroxyapatite coatings were synthesized on Ti-6Al-4V substrates using the plasma spraying process followed by vacuum and atmospheric post-heat treatments at various elevated temperatures. This study provides an evaluation of the bonding strength and crystallization rate of HACs resulting from the variations in crystallinity and thermal induced cracking. Experimental results provide evidence that the atmospheric heat-treated HACs possessed higher crystallization rate than the vacuum-heated specimens. It implies that the presence of an atmosphere with moisture plays an important role in improving the crystallization of HACs. The bonding strength of all samples was improved with increasing HA crystallization, and the optimal heating condition was found to be about 600°C. However, the crystallization-induced defects result in a serious microstructure and bonding strength degradation when the heating temperatures were higher than 600°C for both post-heat methods. On the basis of the fracture morphologies observation and the bonding strength data fluctuation of both heating conditions, the Weibull distribution function provides a powerful statistical analysis for assessing the failure mechanism and the reliability of plasma-sprayed and post heat-treated HACs.

  • Effects of Different Shielding Gases and Power Waveforms on Penetration Characteristics and Porosity Formation in Laser Welding of Inconel 690 Alloy

    Tsung-Yuan Kuo, Yong-Ding Lin

    pp. 219-226

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    DOI:10.2320/matertrans.48.219

    Abstract

    A high power Nd-YAG laser was used to perform bead-on-plate (BOP) welding on high viscosity Inconel 690 alloy plates of 3 mm in thickness with three different shielding gases (Ar, He, and N2). Adopting a rectangular laser power waveform, four different peak-base power differentials (ΔP) were applied with a constant average power of 1.5 kW. A comprehensive investigation was performed into the influences of the shielding gas, the flow rate, and the value of ΔP on the characteristics of the resulting welds, including the weld morphology, the penetration depth, the plume volume, and the porosity formation. The results showed that the weld penetration depth, the depth-to-width ratio, the weld surface roughness and the degree of weld spattering all increased with increasing ΔP. The choice of shielding gas had a significant effect on the porosity ratio (Pr) of the weld. The weld formed under Ar shielding had the highest Pr, while that formed under N2 shielding had the lowest. Under He shielding, the gas flow rate had a significant effect on the porosity ratio. However, under the higher density gases of Ar and N2, the porosity appeared to be insensitive to the flow rate. Finally, an increased ΔP yielded a significant reduction in Pr for the welds with higher porosity.

  • Microstructure and Electrical Conductivity of Epitaxial SrRuO3 Thin Films Prepared on (001), (110) and (111) SrTiO3 Substrates by Laser Ablation

    Akihiko Ito, Hiroshi Masumoto, Takashi Goto

    pp. 227-233

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    DOI:10.2320/matertrans.48.227

    Abstract

    Epitaxial SrRuO3 (SRO) thin films were prepared on SrTiO3 (STO) single-crystal substrates by laser ablation, and their microstructures and anisotropy of electrical conductivity were investigated. (001), (110) and (111) oriented SRO thin films were grown epitaxially on (001), (110) and (111) STO substrates at oxygen pressure of 13 Pa and substrate temperature of 973 K, respectively. Epitaxial (001) and (111) SRO thin films showed flat and smooth surface with a terrace and step structure whereas (110) SRO thin film had a faceted island-like structure. The in-plain orientation relationships of [100] SRO || [100] STO in (001) SRO/(001) STO thin films, [001] SRO || [001] STO in (110) SRO/(110) STO thin films and [112] SRO || [112] STO in (111) SRO/(111) STO thin films were identified. Epitaxial (001) SRO thin films exhibited the highest electrical conductivity of 2.4×105 S·m−1 among the (001), (110) and (111) SRO thin films.

  • The Effect of Frequency of Electromagnetic Vibrations on Vibrational Motion in Fe-Co-B-Si-Nb Bulk Metallic Glasses

    Takuya Tamura, Daisuke Kamikihara, Yuuki Maehara, Naoki Omura, Kenji Miwa

    pp. 234-238

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    DOI:10.2320/matertrans.48.234

    Abstract

    The method for producing Fe-Co-B-Si-Nb bulk metallic glasses using electromagnetic vibrations is effective in forming the metallic glass phase. The purpose of this study was to investigate the effects of the frequency of electromagnetic vibrations on the vibrational motion in Fe-Co-B-Si-Nb bulk metallic glasses. The amplitudes of the electromagnetic vibrations at 5 kHz were calculated to be on the order of micrometers, but those at higher frequencies were on the order of nanometers. It was found that the nanometer-sized amplitudes resulted in the disappearance of the increased cooling rate caused by electromagnetic vibrations observed at lower frequencies. When particles in the sample have lower electric resistance than the molten sample, these particles are considered to vibrate vigorously in the molten sample by Lorentz force because the electric current concentrates in those. It is suggested that this phenomenon is the reason electromagnetic vibrations decrease the number of crystal nuclei.

  • Improved Thermal Stability of Amorphous ZrAlCuNi Alloys with Si and B

    T. H. Hung, J. C. Huang, J. S. C. Jang, S. C. Lu

    pp. 239-243

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    DOI:10.2320/matertrans.48.239

    Abstract

    Both the glass forming ability and thermal stability of the Zr65-x-yAl7.5Cu17.5Ni10 amorphous alloy can be improved by the appropriate addition of Si and B. The metalloid elements would extend the nucleation stage and result in more small crystalline particles. The basic crystallization kinetics for the Si/B containing alloys is still similar to the base alloy, but would proceed at a higher temperature or a more sluggish speed.

  • Development of Metal Recovery Process from Alkaline Manganese Batteries in Sulfuric Acid Solutions

    Shun-Myung Shin, Jin-Gu Kang, Dong-Hyo Yang, Jeong-Soo Sohn

    pp. 244-248

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    DOI:10.2320/matertrans.48.244

    Abstract

    A process for the recovery of Mn from a waste of spent alkaline batteries using sulfuric acid and hydrogen peroxide has been investigated. The proposed procedure consisted of mechanical separation of metal-containing particles and a leaching process. The effects of leaching agent, reaction temperature, time and pulp density for the leaching were also examined. Crushing and sieving of the spent batteries resulted in satisfactory separation of particle size from the waste. 99% Zn and 97% Mn were successfully extracted from the spent battery powder by the leaching at 60°C for 60 min with the addition of hydrogen peroxide as a reducing agent. The hydrogen peroxide addition led to almost doubling Mn extraction compared to without it.

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  • Fabrication of Nano-Sized ITO Powder from Waste ITO Target by Spray Pyrolysis Process

    Jae-Keun Yu, Seong-Gu Kang, Ki-Chang Jung, Joung-Su Han, Dong-Hee Kim

    pp. 249-257

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    DOI:10.2320/matertrans.48.249

    Abstract

    In this study, a nano-sized ITO powder with the average particle size below 50 nm by using waste ITO target is generated by spray pyrolysis proces. This study also examines the influences of reaction parameters such as reaction temperature, concentration and inflow speed of raw material solution on the properties of the generated ITO powder.
    As the reaction temperature increases from 800°C to 1100°C, the average particle size of the generated ITO powder increases from 40 nm to 100 nm, the microstructure gradually becomes compact, the particle size distribution becomes increasingly irregular, the XRD peak intensity gradually increases, and the specific surface area decreases.
    When the concentration of the solution is at 50 g/L, the average particle size of the ITO powder is below 30 nm, and the particle size distribution appears comparatively uniform. As the concentration reaches 400 g/L, which is close to the saturated concentration, the particle size distribution appears extremely irregular, and the particles with the size ranging from 20 nm to 100 nm coexist. Along with the rise of concentration, the XRD peak intensity gradually increases, yet the specific surface area decreases.
    As the inflow speed of the raw material solution increases from 2 mL/min to 100 mL/min, the average particle size of the ITO powder increases from 30 nm to 90 nm, yet the particle size distribution becomes irregular, and individual particles appear in the distinct shape of polygon. Along with the rise of inflow speed, the XRD peak intensity gradually increases, and the specific surface area decreases.

  • Activation Energy of AgInSbTe Film through Isothermal Sheet Resistance Measurements

    Chien-Chih Chou, Fei-Yi Hung, Truan-Sheng Lui

    pp. 258-264

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    DOI:10.2320/matertrans.48.258

    Abstract

    RF sputtering was used to deposit AgInSbTe (AIST) films on silicon substrates. The as-deposited amorphous films were crystallized at temperatures above 413 K and the sheet resistance change was used to characterize the degree of crystallization and the associate activation energy in this study. The sheet resistance of amorphous films quickly decreased when the crystallization was initiated and reached a steady lower value with the IOC index of around 0.7, which means 70% crystallization. The kinetics of sheet resistance change was researched isothermally in an argon atmosphere and compared to the results of DSC measurement with constant heating rates. It was found that activation energy, 0.82 eV, obtained from isothermal sheet resistance measurement was rather close to that, 0.92 eV, obtained from DSC measurement. The Avrami exponent was determined to be 1.1∼1.4 in isothermal sheet resistance measurement. A lower Avrami exponent implied that impingement effects possibly resulted in the sheet resistance decreasing with about 78% crystallization of amorphous films.

  • Creep and Corrosion Properties of the Extruded Magnesium Alloy Containing Rare Earth

    Chao-Chi Jain, Chun-Hao Koo

    pp. 265-272

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    DOI:10.2320/matertrans.48.265

    Abstract

    Effects of microstructures on the creep and corrosion properties were investigated in the Mg-8Al alloys with addition of the rare earth elements (La-rich Mischmetal, RE). The addition of RE to Mg-8Al alloy may form a stable intermetallic phase, Al11RE3 at elevated temperature, and suppress the β phase (Mg17Al12) with poor stability at high temperature. The corrosion rate of the alloy slightly decreases with increasing the added RE contents. The constant-load creep behavior was examined at 423, 448 and 473 K under stresses between 40 and 100 MPa. The RE-containing alloy showed a prolonged period of stead-state creep compared to the Mg-8Al base alloy and slightly reduced minimum creep rates. A stress exponent of 2 estimated suggests that the creep behavior can be controlled by the grain boundary sliding. The apparent activation energy for creep of Mg-8Al and Mg-8Al-2RE alloys are 114 and 104 kJ mol−1, respectively.

  • Supercooled Liquid Bonding of Metallic Glasses by Hot-Pressing

    Shin-ichi Yamaura, Hisamichi Kimura, Akihisa Inoue

    pp. 273-276

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    DOI:10.2320/matertrans.48.273

    Abstract

    In this study, we tried to bond the melt-spun Zr55Al10Ni5Cu30 metallic glassy thin ribbons with the porous metallic substrates by the hot-pressing procedure. As a result, the bonding strength increases with increasing load on the sample during the hot-pressing and also with decreasing pore size of the substrates. This is because both the high pressure and the small pore size can result that the supercooled liquid of the glassy alloy can penetrate down along the pores deeply during the hot-pressing, leading to good anchoring effect. Tensile test results and cross-sectional views of the pressed samples are shown in detail.
  • © 2007 The Japan Institute of Metals and Materials

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