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

MATERIALS TRANSACTIONS Vol. 54 (2013), No. 2

  • Compaction of Commercially Pure Titanium Powder by Friction Powder Compaction Process

    Yoshihiko Hangai, Kousuke Zushida, Hiroaki Yoshida

    pp. 127-129

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    DOI:10.2320/matertrans.MC201208

    Abstract

    A new friction powder compaction (FPC) process is introduced for compacting commercially pure titanium powder. The FPC process is very simple and energy-efficient since it requires only a rotating tool plunged into an aluminum plate with a hole filled with titanium powder, and no external heat source is necessary. The sintering of the powder is mainly achieved by the friction heat and pressing load generated by the rotating tool in the aluminum plate and powder. The microstructure and Vickers hardness of the compacted titanium powder were investigated. It was shown that titanium powder was satisfactorily compacted by the FPC process.

  • Property-Control of Ti Compacts in Spark Sintering Process

    Kazuhiro Matsugi, Akinori Hiraiwa, Yong-Bum Choi, Gen Sasaki, Hideaki Kuramoto

    pp. 130-136

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    DOI:10.2320/matertrans.MC201214

    Abstract

    Neck-seeds among pure titanium powders were homogeneously caused by the pulse discharge as an early stage in spark sintering. Their compacts showed some characteristic microstructures by the adjustment of process parameters such as temperature-history, -amplitude and applied pressure in the following continuous current discharge. Such property-controls might be carried out on the basis of the micro phenomena caused in or between powders. The allotropic transformation of α and β phases was utilized for achievement of full density and microstructure control, as case study of property-controls on Ti compacts. Both nearly full density and characteristic microstructures were achieved by the control of heat and cool cycles in temperature-ranges below and above β transus, due to excellent thermal and load control-ability in the spark sintering equipment. The 0.2% proof and tensile strength were increased, only by rising of relative densities. In contrast, the tensile elongation and reduction of area were affected by both relative densities and microstructures. The relation among mechanical properties, density and microstructures was investigated on obtained compacts, and one method for their property-controls was proposed on the basis of this result.

  • Fabrication of Porous Titanium with Directional Pores for Biomedical Applications

    Ji-Woon Lee, Ji-Sun Lee, Myoung-Gyun Kim, Soong-Keun Hyun

    pp. 137-142

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    DOI:10.2320/matertrans.MC201211

    Abstract

    A new fabrication method was developed for porous Ti with directional pores. Large sized-pores were generated by the evaporation of Mg wires, and small sized-pores were generated by sintering process. The porosity of the material was increased with increasing the number of wires and decreased with increasing sintering temperature and compact pressure. The diameter of large-sized pores was accurately same with that of Mg wire, and the diameter of small-sized pores was varied with the fabrication parameters showing similar trend to the porosity variation. The most advantageous point of the novel fabrication process is that the both porosity of the material and the diameter of the pores can be easily controlled by fabrication parameters, such as the number of wires, the sintering temperature and the compact pressure. The material can be used as possible bone implants possessing not only closer modulus to human bone, but also superior osteogenesis properties.

  • Corrosion Resistance of Titanium–Magnesium Alloy in Weak Acid Solution Containing Fluoride Ions

    Takumi Haruna, Daisuke Motoya, Yuichi Nakagawa, Naoji Yamashita, Toshio Oishi

    pp. 143-148

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    DOI:10.2320/matertrans.MC201210

    Abstract

    We have developed Ti–Mg alloy for dental material corrosion-resistant to aqueous fluoride solutions. Ti plates and granular Mg was put in a sealed vessel and heated at 950°C, so Ti plates were exposed in the liquid and the vapor Mg phases. The conditions made Mg diffuse into the Ti plates to produce Ti–Mg alloy. The Ti–Mg alloy produced in the vapor Mg phase for 430 h achieved homogeneous distribution in Mg concentration of 0.2 at%. A Vickers micro hardness increased almost linearly with an increase in the Mg concentration, and the hardness of the homogeneous Ti–0.2 at%Mg was about 1.2 times larger than that of Ti before alloying. It was confirmed that corrosion resistance of Ti in the fluoride solution was improved by alloying with Mg. The method using the vapor Mg phase contributed much more effective improvement of corrosion resistance than that using the liquid phase. The homogeneous Ti–0.2 at%Mg demonstrated a maximum corrosion resistance of all the specimens, by about 80 times to Ti.

  • Accelerated Calcium Phosphate Formation on Titanium Utilizing Galvanic Current between Titanium and Gold in Hanks’ Solution

    Yusuke Tsutsumi, Equo Kobayashi, Masakimi Ogo, Suyalatu, Satoshi Migita, Hisashi Doi, Naoyuki Nomura, Kazuhiko Noda, Takao Hanawa

    pp. 149-155

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    DOI:10.2320/matertrans.MC201204

    Abstract

    To enhance hard-tissue compatibility of Ti, galvanic current between titanium (Ti) and gold (Au) may be available. Prior to the design of medical devices with the capability to generate a galvanic current, it is necessary to understand the control mechanism. In this study, we first measured galvanic current between Ti and Au with various surface areas in Hanks’ solution. The galvanic current increased immediately after connection of two electrodes, followed by an abrupt decrease and a steady state. The galvanic current varied with the combinations of Ti and Au areas. We, thereafter, evaluated the formation of calcium phosphate on Ti under a condition of applying simulated galvanic current. Surface characterization was revealed in which the calcium phosphate formation was enhanced accompanied by growth of Ti oxide layer under the galvanic current application. A similar result was observed on Ti with patterned Au coating without outer electric power. Therefore, galvanic current is useful to enhance hard-tissue compatibility, and this technique has potential for applications to metallic biomaterials.

  • β-Phase Instability in Binary Ti–xNb Biomaterial Single Crystals

    Wang Pan, Mitsuharu Todai, Takayoshi Nakano

    pp. 156-160

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    DOI:10.2320/matertrans.MC201202

    Abstract

    The ω-phase transformation and β-phase stability in Ti–xNb (28 ≤ x ≤ 40 at%) single crystals were investigated using electrical resistivity measurements, transmission electron microscopy (TEM) observations, and specific heat measurements. The crystal for x = 28 exhibits distinct anomalous negative temperature dependence of the resistivity coefficient and thermal hysteresis accompanied by the presence of the athermal ω-phase and β-phase lattice modulation. Although the crystal for x = 30 appears in the β-phase lattice modulation, it does not exhibit a clear negative temperature dependence of the resistivity coefficient or the athermal ω-phase. The crystal of x = 30 also shows a relatively high absolute value of resistivity at 15 K among the crystals for 28 ≤ x ≤ 40 and a low Debye temperature in a normal conductive state. The crystal for x = 30 that shows the lattice modulation, high resistivity, and low β-phase Debye temperature correspond to the low stability of the β-phase. Moreover, the stability strongly depends on the Nb content of the binary Ti–Nb crystal.

  • β-Grain Refinement of α+β-Type Ti–4.5Al–6Nb–2Fe–2Mo Alloy by Using Rare-Earth-Oxide Precipitates

    Kyosuke Ueda, Shinichiro Nakaoka, Takayuki Narushima

    pp. 161-168

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    DOI:10.2320/matertrans.MC201207

    Abstract

    The effect of the addition of small amounts of rare-earth elements such as La (0.01 mass%), Y (0.1 mass%), Er (0.1 mass%) and Ce (0.1 mass%) on the refinement of β-grains in an α+β-type Ti–4.5Al–6Nb–2Fe–2Mo alloy was investigated in the temperature range 1173–1573 K. The β-grain size and the rare-earth-oxide precipitates obtained after heat treatment were evaluated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Upon heating, alloys exhibited rapid β-grain growth above a threshold temperature, and this temperature depended on the added rare-earth elements. The fine precipitates of rare-earth oxides formed in the alloy suppressed the β-grain growth through pinning. Dissolution of the precipitates in the β-matrix caused rapid β-grain growth. Yttrium was found to be the most effective element for the suppression of β-grain growth at high temperatures such as 1573 K.

  • Tensile and Fatigue Properties of Carbon-Solute-Strengthened (α+β)-Type Titanium Alloy

    Masaaki Nakai, Mitsuo Niinomi, Junko Hieda, Ken Cho, Toshikazu Akahori, Kazuhiro Hayashi, Yoshio Itsumi, Shogo Murakami, Hideto Oyama

    pp. 169-175

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    DOI:10.2320/matertrans.MC201203

    Abstract

    The effects of interstitial carbon solute and titanium carbide on the tensile and fatigue properties of an (α+β)-type titanium alloy, Ti–4.5Al–2.5Cr–1.2Fe–0.1C (KS Ti-531C), with bimodal and Widmanstätten α structures were investigated. In order to control the microstructures, this alloy was subjected to annealing at temperatures just below and just above the β-transus (531C-α+β annealed and 531C-β annealed, respectively). The microstructure of 531C-α+β annealed shows a bimodal structure and any titanium carbide is not observed, whereas that of 531C-β annealed shows a Widmanstätten α structure and some titanium carbides, which are considered to be Ti2C, are observed. The tensile strength and elongation of 531C-α+β annealed and 531C-β annealed are similar, but 0.2% proof stress is higher and further the reduction of area is much larger for 531C-α+β annealed than 531C-β annealed. Their tensile properties depend mainly on the type of microstructure and interstitial element partitioning because the titanium carbide is not observed on the fractured surfaces of both the alloys after tensile tests. Also, the fatigue properties of 531C-α+β annealed are better than those of 531C-β annealed. The titanium carbide is observed on the fractured surface of 531C-β annealed, but not observed on that of 531C-α+β annealed, after fatigue tests. Therefore, titanium carbide is considered to cause deterioration in the fatigue properties of 531C-β annealed compared to those of 531C-α+β annealed.

  • Microstructures and Mechanical Properties of Highly Electrically Conductive Cu–0.5, Cu–1 and Cu–2 at%Zr Alloy Wires

    Naokuni Muramatsu, Hisamichi Kimura, Akihisa Inoue

    pp. 176-183

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    DOI:10.2320/matertrans.M2012264

    Abstract

    Hypoeutectic Cu–Zr binary alloys have originally been studied in order to develop wires with both high strengths and high electrical conductivities. This study aimed to improve the electrical conductivities of Cu–0.5, Cu–1 and Cu–2 at% Zr alloys, which have Zr contents lower than those of high-strength Cu–3, Cu–4 and Cu–5 at% Zr alloys. Cast rod samples, whose lengths and diameters were 180 and 12 mm, respectively, were prepared by copper-mold casting and wire-drawn to diameters in the range of 1–0.031 mm (drawing ratio, η = 4.8–11.1). The microstructures and mechanical properties of the obtained wires were investigated and compared to those of Cu–3, Cu–4 and Cu–5 at%Zr alloy wires that had been investigated in a previous study.
    The eutectic phases found in the cast rods consisted of α-Cu primary phases and phases of the intermetallic compound Cu5Zr. The eutectic phases became isolated, like small islands, in the matrices, and their volume fractions decreased with a decrease in the Zr content. The orientations of the α-Cu and Cu5Zr phases around the boundaries of these eutectic phases were similar. After the wiredrawing process, the intermetallic compound in the eutectic phases transformed into Cu9Zr2 in the case of the Cu–0.5 at%Zr alloy and into Cu8Zr3 in the case of the Cu–1 at%Zr alloy. The electrical conductivity (EC) and ultimate tensile strength (UTS) values of the alloys depended on the volume fractions of their eutectic phases. However, the changes in these properties with the change in the drawing ratio were smaller than those in the case of the high-strength Cu–3, Cu–4 and Cu5 at%Zr alloy wires. The EC and UTS values of the Cu–0.5, Cu–1 and Cu–2 at%Zr alloy wires drawn at values of η greater than 8.0 were 61–83% IACS (International Annealed Copper Standard) and 690–1010 MPa, respectively. When combined together, wires of the resulting hypoeutectic Cu–Zr binary alloy exhibited EC and UTS values of 16–83% IACS and 690–2234 MPa, respectively. These results showed that instead of there being a tradeoff between these properties, the values of both these properties increased at the same time.

  • Influence of High Pressure Treatment on Microstructure Evolution of Cu–Zn Alloy

    Yan Chen, Ya-li Li, Jian-hua Liu, Rui-jun Zhang

    pp. 184-187

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    DOI:10.2320/matertrans.M2012251

    Abstract

    The ordered–disordered phase transformation temperature and time of Cu–Zn alloy before and after 2 GPa pressure treatment were measured by differential scanning calorimeter (DSC). The phase transformation activation energy and Avrami exponent were calculated and the effect of 2 GPa pressure treatment on the microstructure evolution was also discussed based on the kinetic parameters. The results show that 2 GPa pressure treatment on Cu–Zn alloy from ordered (β′) to disordered (β) phase transformation shift to the low temperature region and can shortened the phase transformation time in the subsequent heating process, which is helpful to the formation of the microstructure with a fine grain size in Cu–Zn alloy, but no new phase is generated.

  • Magnetic Field Effects on Crystallization of Iron-Based Amorphous Alloys

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

    pp. 188-191

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    DOI:10.2320/matertrans.M2012242

    Abstract

    The crystallization behavior of iron-based amorphous alloys has been investigated in high magnetic fields by differential thermal analysis (DTA) and magnetization measurements. DTA of Fe–Si–B amorphous alloys showed that the exothermic peaks shift toward higher temperature under high magnetic fields. At 10 T, peak temperatures of the crystallizations increased approximately 3 K, compared with those at a zero magnetic field. Such a variation in the crystallization peak was not observed in the Fe–B–Nb–Y bulk metallic glass (BMG). In the temperature dependence of the saturation magnetization for the Fe–Si–B amorphous alloy, the sudden increase of the magnetization was found at the crystallization temperatures. The magnetization of Fe–Si–B increased 56 and 40 Am2 kg−1 at the first and second crystallization temperatures, respectively. This magnetization behavior indicates the magnetic transition from the paramagnetic to the ferromagnetic state, accompanying the crystallization, whereas there is only a slight increase in magnetization at the crystallization temperature in Fe–B–Nb–Y BMG. The effect of magnetic field on the crystallization peak as observed from DTA is related to the increase in the magnetization at the crystallization temperature.

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  • Deformation Behavior and Texture Formation in AZ80 Magnesium Alloy during Uniaxial Compression Deformation at High Temperatures

    Jinuk Kim, Kazuto Okayasu, Hiroshi Fukutomi

    pp. 192-198

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    DOI:10.2320/matertrans.H-M2012832

    Abstract

    High temperature uniaxial compression deformation is conducted on AZ80 magnesium alloy at 673 and 723 K by varying the strain rates ranging from 1.0 × 10−4 to 5.0 × 10−2 s−1 in order to investigate the behaviors of deformation and texture formation. Particular attention is paid to the development of basal texture. Under the deformation conditions of this study, work softening is observed in all the stress–strain curves without exception. The results of the microstructure observation reveal occurrence of dynamic recrystallization. Formation of fiber texture during the deformation is confirmed. The main component is (0001) when the peak stresses appearing in the stress–strain curves are more than 15–20 MPa, and it develops together with an increase in the peak stress. In contrast, weak fiber textures having a main component at a position 29° away from the basal plane are formed with deformation conditions giving peak stresses of less than 15 MPa. The stress exponent changes at a peak stress near 20 MPa, suggesting that change in the texture corresponds to the change in the deformation mechanism. It is concluded that the formation of basal texture is due to the continuous dynamic recrystallization resulting from the growth of the subgrains formed by the deformation.

  • Formation of Zincate Films on Binary Aluminum Alloys and Adhesion of Electroless Nickel-Phosphorus Plated Films

    Koji Murakami, Makoto Hino, Masashi Ushio, Daichi Yokomizo, Teruto Kanadani

    pp. 199-206

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    DOI:10.2320/matertrans.L-M2012830

    Abstract

    The formation of zincate films and the adhesion of electroless nickel-phosphorus plated films on binary aluminum alloys of Al–2 at%Mn, Al–2 at%Fe, Al–2 at%Cu, Al–2 at%Zn and high-purity aluminum (99.999 mass%) were studied. The precipitation mode of zinc during the zincate treatments significantly varied according to the alloying elements in the substrates. For the first and second zincate treatments of Al–Mn, Al–Fe and high-purity aluminum, the zinc excessively precipitated, then porous films of zinc repeatedly fell off the substrate. The surfaces of the Al–Cu and Al–Zn alloys were immediately coated by uniform zincate films during the first and the second zincate treatments. The precipitation of zinc is considered to be uniform if the oxide film on a substrate uniformly and rapidly dissolves in the zincate solution. When an electroless nickel-phosphorus plating was conducted after the second zincate treatment of the Al–Mn and Al–Fe alloys, the plated films easily peeled off. Those on the Al–Cu and Al–Zn alloys showed excellent adhesion, and dimple patterns of the substrates were observed on the partly peeled areas. The poor adhesion is thought to be caused due to the fact that the excess zinc dissolves at the beginning of the plating and generates hydrogen gas, then gaps are formed between the plated films and the substrates.

  • Synthesis of Cubic Aluminum Nitride Coating from Al2O3 Powder in Reactive Plasma Spray Process

    Mohammed Shahien, Motohiro Yamada, Toshiaki Yasui, Masahiro Fukumoto

    pp. 207-214

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    DOI:10.2320/matertrans.T-M2012831

    Abstract

    Plasma spraying is a versatile technique for producing abradable and protective ceramic coatings. However, it was difficult to fabricate aluminium nitride (AlN) coating by conventional plasma spray processes. It is due to the thermal decomposition of the feedstock AlN powder during spraying without a stable melting phase. Reactive plasma spraying (RPS) has been considered as a promising technology for in-situ formation of AlN thermally sprayed coatings. This study investigated the feasibility of reactive plasma spraying of Al2O3 powder in N2/H2 plasma upon fabrication of AlN coating. It was possible to fabricate a cubic-AlN (c-AlN)/Al2O3 composite coating and the fabricated coating consists of c-AlN, α-Al2O3, Al5O6N and γ-Al2O3. Furthermore, the AlN content was improved with increasing the flight time (spray distance), due to increasing the reaction time between the Al2O3 particles and the surrounding N2/H2 plasma. It was possible to fabricate coating contains about 97% of c-AlN. However, it was difficult to clarify the in-flight reaction during the coating process, due to losing the particles shape and features after colliding and flattening on the substrate surface. The sprayed particles were collected into a water bath to maintain its particle features in order to investigate the in-flight reaction. It was clear from the microstructure and the cross section observation of the collected particles that, the nitriding reaction started from the surface. During the coating process, the sprayed particles were melted, spheroidized and reacted in the high temperature N2/H2 plasma and formed aluminum oxynitride (Al5O6N) which have cubic structure. The particles collided, flattened, and rapidly solidified on a substrate surface. The Al5O6N is easily converted to c-AlN phase via continuous nitriding (both have the same cubic symmetry: cubic and closely packed) during the rapid solidification and plasma irradiation on the substrate. The high quenching rate of the plasma flame prevents the AlN crystal growth to form the hexagonal phase. Therefore, it was possible to fabricate c-AlN/Al2O3 composite coatings through reactive plasma nitriding of Al2O3 powder and the nitriding process of the Al2O3 particle as well as the formation process of c-AlN phase were investigated.

  • Microstructural Evolution and Hardness of Dissimilar Lap Joints of ODS/Stainless Steel by Friction Stir Welding

    Chun-Liang Chen, Asta Richter, Lung-Tien Wu, You-Ming Dong

    pp. 215-221

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    DOI:10.2320/matertrans.M2012281

    Abstract

    Ferritic oxide dispersion strengthened (ODS) alloy and stainless steel are attractive candidates for applications in the high temperature industries. Friction stir welding (FSW) is a very promising technique for the joining of both materials. Severe shear deformation and high heat input during FSW process can significantly change the microstructure and material property of the joints. The joint quality therefore plays a decisive role in material performance, life expectancy and cost. In this study, the different joints between ODS alloy and stainless steel were investigated in three different zones: the thermo-mechanically affected zone, the heat affected zone and the base material. Phase transformations and chemical reactions in the case of dissimilar welds were also studied. Electron backscattering diffraction (EBSD) was used to analyze the grain orientation, the grain boundary geometries and recrystallization behavior. Hardness changes within the welding zones and variation with grain boundary angle are discussed.

  • Characterization of Spinel-Structured Iron Oxide Particles Synthesized by Heating α-Fe2O3 Platelets in Tetra-Ethylene Glycol

    Mikio Kishimoto, Kei Asai, Akari Horiuchi, Hideto Yanagihara, Yukio Nagasaki, Eiji Kita

    pp. 222-224

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    DOI:10.2320/matertrans.M2012353

    Abstract

    Platelet particles of α-Fe2O3 30–50 nm in size were heated in tetra-ethylene glycol to obtain spinel-structured iron oxide particles, which were confirmed by X-ray diffraction. With heating, 100 nm platelets were formed, and the proportion of the 100 nm platelets increased in comparison to 30–50 nm platelets with increasing duration of heating. In all the samples, irrespective of the heating time used during synthesis, the coercive force, which was considered to be dependent on the shape anisotropy of the platelet particles, remained nearly constant at 12.7–13.5 kA/m (160–170 Oe). The saturation magnetization initially increased and then decreased with the heating time and the maximum value observed was 80.5 Am2/kg (80.5 emu/g). The reduction and oxidation were considered to occur simultaneously during the synthesis.

  • Effect of Amount of Gd and Y Contents on Precipitation in Mg–Gd–Y Alloys Aged at 473 K

    Tokimasa Kawabata, Daisuke Nakagawa, Seiji Saikawa, Junya Nakamura, Susumu Ikeno, Kenji Matsuda

    pp. 225-230

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    DOI:10.2320/matertrans.L-M2012829

    Abstract

    Precipitation in Mg–Gd–Y (Gd : Y = 3 : 1) alloys without Zr were investigated by HRTEM and SAED technique, and calculation of HRTEM images and electron density using DV-Xα to understand the relationship between precipitation in these alloys and HRTEM images. The diffuse scattering was obtained in as-quenched samples in each alloy by SAED and the mono-layer zones have been confirmed by HRTEM observation. The β′-phase was confirmed in the 2.9Gd–0.8Y alloy by HRTEM, although the β′′-phase was confirmed in the 2.1Gd–0.6Y alloy before the β′-phase. The β′-phase became predominant after prolonged aging. Zigzag lines were observed at the same time when the β′-phase appeared in the sample. HRTEM images obtained for these precipitates were compared with calculated HRTEM images. The contrast of atomic columns of the matrix in HRTEM image was calculated simplified model of cluster based on the Mg-matrix including one or some atomic columns of RE. This is also corresponded the distribution of electron density of the cluster.

  • Control of Electrical and Thermal Properties on Sn–50Zn Alloy by 8 vol%Al2O3 Addition for Pb-Free AC-Low Voltage Fuse Elements

    Kazuhiro Matsugi, Yoshihiro Saki, Yong-Bum Choi, Gen Sasaki, Ken-ichiro Suetsugu, Koji Fujii

    pp. 231-237

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    DOI:10.2320/matertrans.M2012335

    Abstract

    The addition of 8 vol%Al2O3 particles in the Sn–50Zn was carried out for the control of electrical and thermal properties, for Pb-free fuse elements used in electric power line. The metal matrix composite of the Sn–Zn alloy and Al2O3 particle having the different densities and melting points could be produced by the handling at coexisting range of both liquid and solid phases and showed the homogeneous microstructure of randomly dispersed Al2O3 via ingots. The temperature dependence of specific resistivity, thermal conductivity, specific heat and density was measured to use their values in electrical and thermal calculations in order to obtain the temperature distribution on Pb-free fuse elements. Both the melt and un-melt down performance of main requirements for AC-low voltage fuse elements could be satisfied on the Sn–50Zn–8 vol% Al2O3 element.

  • Preparation of Low-Oxygen Mo Ingot by Optimizing Hydrogen Reduction and Subsequent Melting from MoO3

    Back-Kyu Lee, Jung-Min Oh, Chang-Yul Suh, Hyung-Seok Kim, Jae-Won Lim

    pp. 238-241

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    DOI:10.2320/matertrans.M2012305

    Abstract

    In this study, we prepared low-oxygen molybdenum ingot through optimized hydrogen reduction by preparing the metal powder and repeatedly applying vacuum arc melting. We determined the optimal heat treatment conditions for hydrogen reduction and oxygen content lowering and obtained molybdenum metal powder with 3,000 ppm of oxygen. The obtained molybdenum powder was converted into an ingot with low oxygen contents (<100 ppm) through repeated vacuum arc melting. The molybdenum ingot thus prepared can be used as raw material for sputtering targets.

  • Bi–Mn Binary Phase Diagram in High Magnetic Fields

    Yoshifuru Mitsui, Keiichi Koyama, Kazuo Watanabe

    pp. 242-245

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    DOI:10.2320/matertrans.M2012310

    Abstract

    To examine magnetic field effects on the Bi–Mn equilibrium phase, a high-magnetic fields differential thermal analysis (HF-DTA) was performed for fields up to 18 T and temperatures ranging from 300 to 753 K. For zero field, the peritectic temperatures Tp1 (BiMn1.08 + Bi-rich liquid → BiMn) and Tp2 (αMn + Bi-rich liquid → BiMn1.08), and the eutectic temperature TE (the Bi-rich liquid → Bi solid + BiMn) were determined to be 632, 721 and 538 K, respectively. The Bi–Mn phase diagram at 18 T was obtained, which showed that Tp1 increases with increasing magnetic fields at the rate of 2 K T−1. Furthermore, the liquidus boundary temperature Tliq between BiMn1.08 + liquid and Bi-rich liquid was found to increase nonlinearly with increasing magnetic field.

  • In Situ and Simultaneous Observation of Palladium Redox and Oxygen Storage/Release in Pd/Sr–Fe–O Perovskite Catalysts Using Dispersive XAFS

    Masao Kimura, Yasuhiro Niwa, Kenichi Uemura, Toru Nagai, Yasuhiro Inada, Masaharu Nomura

    pp. 246-254

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    DOI:10.2320/matertrans.M2012297

    Abstract

    We have succeeded in in situ and simultaneously observing the redox reaction of palladium and the oxygen storage/release process in a newly developed palladium-promoted Sr–Fe–O (Pd/Sr–Fe–O) catalyst during redox-gas cycles using dispersive X-ray absorption fine structure (XAFS) analysis at 673 K with a time resolution of less than 20 ms. The Pd/Sr–Fe–O catalyst, which exhibits high performance for automotive emission control, has a unique “multi-phase-domain” structure, where a single grain is composed of nano-sized domains of three phases: SrFeO3−δ, Sr4Fe6O13−δ and SrFe12O19−δ. In situ observation has shown a strong correlation between the redox of the palladium and the oxygen storage/release in the Pd/Sr–Fe–O catalyst, and the correlation factors differ between the reduction and oxidation reactions. The oxide phases exhibit a type of “oxygen buffer” effect in the oxidation cycle and delay the formation of Pd–O, resulting in the high performance of the catalyst.

  • The Influence of Additive-Free Process on the Microstructure of Very Narrow Cu Wires in the Lower Region of a Trench

    Yiqing Ke, Takakshi Namekawa, Kunihiro Tamahashi, Jin Onuki

    pp. 255-259

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    DOI:10.2320/matertrans.M2012331

    Abstract

    Microstructure distribution along the trench depth direction of nano-scale copper interconnects was studied as a function of plating material purity. It was shown that, after annealing in the lower region of the trench, the Cu wire fabricated by the additive-free process has 13% larger grains and 80% lower ratio of small grains (less than 45 nm) than the wire fabricated by the high-purity process, and 25% larger grains and 92% lower ratio of small grains than the wire fabricated by the low-purity process. The grain size distribution in the trench depth direction for the Cu wire plated without additives was much more uniform than that plated with additives.

  • Dynamic Behavior of Non-Newtonian Droplets Impinging on Solid Surfaces

    Joo Hyun Moon, Jae Bong Lee, Seong Hyuk Lee

    pp. 260-265

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    DOI:10.2320/matertrans.M2012215

    Abstract

    This article illustrates the spreading and receding characteristics of non-Newtonian droplets impinging on solid surfaces at different Weber numbers. A xanthan gum solution was used to generate non-Newtonian droplets. From digital images captured using a high speed camera, spreading diameters and dynamic contact angles (DCA) were measured during the impact process. Depending on impact velocity, distinct differences in spreading and receding motions were found between Newtonian and non-Newtonian droplets, which were highly associated with viscous energy dissipation. The maximum spreading diameters for Newtonian and non-Newtonian droplets were nearly the same, but a much slower receding motion was observed for non-Newtonian droplets because of the shear-thinning effect. Moreover, a rapid decrease of DCA in the spreading regime was observed for both non-Newtonian and Newtonian droplets, indicating that the inertial force became dominant. By contrast, measured DCAs for non-Newtonian fluid droplets in the receding regime were larger than those for Newtonian fluid droplets, demonstrating that cohesive surface forces were more dominant than inertial forces in this regime.

  • Estimation of Maximum Solid Solubility in Mg–Hg Alloys by the Lever Rule

    Libo Wang, Peijie Li, Liangju He

    pp. 266-268

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    DOI:10.2320/matertrans.M2012272

    Abstract

    The microstructures of Mg–Hg alloys with 1.1–2.9 mass% Hg were investigated in this paper. Under the non-equilibrium solidification condition, the examined Mg–Hg alloys had a two-phase structure consisting of a solid solution phase and a spheroidal-graphite iron-like divorced eutectic. Eutectic α-Mg and eutectic Mg3Hg formed separately, so the proportion of eutectic Mg3Hg could be accurately measured. A method was proposed to estimate the maximum solid solubility of Hg in Mg under the non-equilibrium solidification condition by measuring the area fraction of Mg3Hg in metallographes. The maximum solid solubility of Mg–2.4 mass% Hg was 0.81 and 0.69 mass%, with cooling rates of 0.67 and 2.0 K/s, respectively. The maximum solid solubility decreased as the cooling rate increased and increased as the Hg content increased.
  • © 2013 The Japan Institute of Metals and Materials

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