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MATERIALS TRANSACTIONS Vol. 52 (2011), No. 7

ISIJ International
belloff
オンライン版ISSN: 1347-5320
冊子版ISSN: 1345-9678
発行機関: The Japan Institute of Metals and Materials

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キーワードランキング

23 Nov. (Last 30 Days)

MATERIALS TRANSACTIONS Vol. 52 (2011), No. 7

Stability and Electronic Structures of Pt-Rh Icosahedral Nanoparticles

Koretaka Yuge

pp. 1339-1343

DOI:

10.2320/matertrans.M2011055

抄録

We investigate the energetic stability and electronic structures of Pt-Rh icosahedral nanoparticles based on first-principles calculations. We find that Pt atom energetically prefers vertex and edge sites at the surface rather than subsurface and core sites, which is a tendency similar to Pt-Rh cuboctahedral nanoparticles. This can be attributed to lower surface energy of Pt compared with Rh. Edges of nanoparticles with second-lowest coordination number are the most favorable sites for Pt atom. This could be attributed to the enhanced interatomic distance at the edge site. 1st order moment of d-state electronic contribution for Pt atom exhibits almost negative dependence in terms of Pt coordination number. This can be qualitatively interpreted by positive dependence of 2nd order moment of the density of states for the Pt atom on the coordination number. Pt surface segregation is expected mainly due to contribution from Pt on-site segregation energy compared with weak ordering tendency of Pt-Rh unlike-atom pairs.

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The Structure of an Al-Ni-Ru Monoclinic Phase Al13(Ru,Ni)4

Reiko Murao, Michiyo Genba, Kazumasa Sugiyama, Wei Sun

pp. 1344-1348

DOI:

10.2320/matertrans.M2011070

抄録

The structure of a Ni-substituted Al13(Ru,Ni)4 phase was analyzed by single crystal X-ray diffraction. The present analysis revealed the distribution of Ni at five heavy metal sites of Ru/Ni(1), Ru/Ni(2), Ru/Ni(3), Ru/Ni(4) and Ru/Ni(5). The anisotropic contraction of the corresponding coordination polyhedra around heavy metal sites was also suggested together with a variation of lattice constants as a function of Ni content.

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Structural Analysis of Pd-Cu-Si Metallic Glassy Alloy Thin Films with Varying Glass Transition Temperature

Susumu Kajita, Shinji Kohara, Yohei Onodera, Toshiharu Fukunaga, Eiichiro Matsubara

pp. 1349-1355

DOI:

10.2320/matertrans.M2011023

抄録

Thin films of Pd-Cu-Si metallic glassy alloys were fabricated by sputtering method, and the effect of the composition on glass transition temperature (Tg) was examined. In order to determine the mechanism of the observed effect, the structural parameters of the thin films based on the short-range order (SRO) were measured, and the correlations between the parameters and the composition were examined. The glass transition temperature (Tg) increased with increasing Si and Cu content. The atomic distances (Pd-Si and Pd-Pd) and the coordination number of Si atoms around a Pd atom (NPdSi) increased with increasing Si content. The Pd-Pd atomic distance increased with increasing Cu content. These results suggest that Si content and Cu content have positive effect on the formation of a trigonal prism that is reported as a structural unit of Pd-based amorphous alloys. From these observed correlations, it can be concluded that Tg increases with an increase in the formation of a trigonal prism. Therefore, an increase in Tg with increasing Si and Cu content is supposed to be caused by the composition-dependent formation of trigonal prisms.

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Effect of Pre-Deformation on Mechanical Response of an Artificially Aged Al-Mg-Si Alloy

Michal Kolar, Ketill Olav Pedersen, Sverre Gulbrandsen-Dahl, Katharina Teichmann, Knut Marthinsen

pp. 1356-1362

DOI:

10.2320/matertrans.L-MZ201127

抄録

In order to investigate the effect of deformation on the artificial aging response of an Al-Mg-Si alloy, a series of tensile tests have been designed and carried out on the aluminium alloy AA6060. Extruded and solution heat treated specimens were pre-deformed 0%, 2%, 5%, and 10% (engineering strain) and subsequently artificially aged at three different aging temperatures (150, 175 and 190°C) for three different times (10, 100 and 300 min). It was observed that the amount of pre-deformation is determining for the final mechanical properties of the short-time artificially aged AA6060 compared to the material aged for longer times when the mechanical properties level out regardless of the introduced pre-deformation. In addition to the hardness measurements and tensile tests, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) have been used to characterize dislocation evolution, microstructure and precipitation state for various combinations of pre-deformation and aging time.

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Effects of T5 Treatment on the Microstructure and Mechanical Properties of Mg-8Al-2Li Alloy

P. C. Wang, H. C. Lin, K. M. Lin, M. C. Lin, M. T. Yeh, C. Y. Lin

pp. 1363-1368

DOI:

10.2320/matertrans.M2011008

抄録

In this study, the effects of T5 treatment on the microstructure and mechanical properties of Mg-8Al-2Li specimens are investigated. The experimental results show the T5-treated Mg-8Al-2Li specimens will produce the β-Mg17Al12 and/or AlLi precipitates depending on the aging temperatures. The T5-treated Mg-8Al-2Li specimens will display an obvious precipitation strengthening, regardless of whether the precipitates are single β-Mg17Al12 phase or dual phases of AlLi and Mg17Al12. Their maximum tensile strengths can reach 355–375 MPa, which are 12–18% increment compared with that of the as-extruded specimen. Meanwhile, the T5-treated Mg-8Al-2Li specimens can still show good ductility with ∼9% elongation for specimens with their maximum strengths.

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First-Principles Study on Enhanced Grain Boundary Embrittlement of Iron by Phosphorus Segregation

Motohiro Yuasa, Mamoru Mabuchi

pp. 1369-1373

DOI:

10.2320/matertrans.MBW201022

抄録

It is known that segregation of P atoms at grain boundaries (GB) enhances the intergranular embrittlement in Fe. In the present work, first-principles tensile tests have been performed on two bcc Fe cell models with a Σ3 (111)⁄[1\\bar10] tilt GB: the cell model without P segregation at the GB (clean GB model) and the cell model with P segregation at the GB (P-segregated GB model). The tensile strength and the strain to failure in the P-segregated GB model were 6% and 13% lower than those in the clean GB model. The first bond breaking occurred at the Fe-P bond due to the covalent-like characteristics, although the charge densities were high at the Fe-P bonds. This premature bond breaking of Fe-P was independent of the location of the P atom.

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Nanoindentation Behaviour and Annealed Microstructural Evolution of Ni/Si Thin Film

Woei-Shyan Lee, Tao-Hsing Chen, Chi-Feng Lin, Jyun-Ming Chen

pp. 1374-1380

DOI:

10.2320/matertrans.M2010323

抄録

The nano-mechanical properties of as-deposited Ni/Si thin films indented to a maximum depth of 800 nm are measured using a nanoindentation technique. The microstructural evolutions of the indented as-deposited specimens and indented specimens annealed at 200°C, 300°C, 500°C and 800°C for 2 min, respectively, are examined via transmission electron microscopy (TEM) and micro-Raman scattering spectroscopy (RSS). The loading curve for the as-deposited Ni/Si thin film is found to be continuous. However, the unloading curve has a prominent pop-out feature. The hardness and Young’s modulus of the Ni/Si thin film are found to vary with the nanoindentation depth, and have values of 13 GPa and 177 GPa, respectively, at the maximum depth of 800 nm. The deformation induced in the nanoindentation process causes the microstructure of the indented zone in the as-deposited thin film to transform from a diamond cubic structure to a mixed structure comprising both amorphous phase and metastable Si III and Si XII phases. However, after annealing at temperatures of 200°C∼500°C and 800°C, the microstructure within the indented zone contains only Si III and Si XII phases and epitaxial NiSi2 phase, respectively. The annealing process prompts the formation of nickel silicides at the Ni/Si interface. The silicides have the form of Ni2Si in the samples annealed at 200°C, but transform to low-resistivity NiSi at annealing temperatures of 300°C or 500°C. At the highest annealing temperature of 800°C, the NiSi phases are replaced by high-resistivity NiSi2 phases.

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Low-Temperature Creep at Ultra-Low Strain Rates in Pure Aluminum Studied by a Helicoid Spring Specimen Technique

Junjie Shen, Shigeto Yamasaki, Ken-ichi Ikeda, Satoshi Hata, Hideharu Nakashima

pp. 1381-1387

DOI:

10.2320/matertrans.M2010405

抄録

The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, \\dotε, lower than 10−10 s−1 and low temperature ranging from 0.32Tm to 0.43Tm. It was found that the creep behavior in this region depends strongly on grain sizes and impurity concentrations. For high-purity aluminum (5 N Al) with an average grain size, dg>1600 μm, nearly the wire diameter of the spring sample, where the role of grain boundary during creep deformation can be negligible, the stress exponent was n∼5 and the activation energy was Qc=32 kJ/mol. Microstructural observation showed the formation of large dislocation cells (∼10 μm) and tangled dislocations at the cell walls. For high-purity aluminum (5 N Al) with dg=24 μm, the stress exponent was n∼1 and the activation energy was Qc=15 kJ/mol. On the other hand, for commercial low-purity aluminum (2 N Al) with dg=25 μm, the stress exponent was n=2 and the activation energy was Qc=25 kJ/mol. Microstructural observations revealed dislocations emitted from grain boundaries, those dislocations interacting with intragranular dislocations and the formation of dislocation cells in the grains. Based on those experimental results, the low-temperature creep mechanisms in pure aluminum at \\dotε<10−10 s−1 have been discussed.

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Investigation of the Resistance to Localized Corrosion Associated with Microstructure of Tube-to-Tube Sheet Welds of UNS S32050 Super Austenitic Stainless Steel for Seawater Cooled Condenser

Seong-Yoon Kim, Soon-Tae Kim, In-Sung Lee, Yong-Soo Park, Min-Chul Shin, Young-Sub Kim

pp. 1388-1395

DOI:

10.2320/matertrans.M2011040

抄録

The behaviors of localized corrosion associated with microstructure of tube-to-tube sheet welds of UNS S32050 super austenitic stainless steel for seawater cooled condenser were investigated in highly concentrated chloride environments. In the interdendritic region, Cr and Mo as α-stabilizers were enriched and N as the γ-stabilizer was depleted whereas in the dendrite core, Cr and Mo were depleted and N was enriched. Based on the PRENIR and PRENDC values, the localized corrosion was selectively initiated at the dendrite core (DC) because the PREN value of the dendrite core was much smaller than that of the interdendritic region (IR). It was found that the resistance to localized corrosion of the UNS S32050 SASS tube-to-tube sheet welds at least as good as that of a UNS S31254 SASS base metal with PREN 47 in highly acidified chloride environments.

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Size-Controlled Hydrothermal Synthesis of Bismuth Sodium and Bismuth Potassium Titanates Fine Particles and Application to Lead-Free Piezoelectric Ceramics

Kiyoshi Kanie, Yoshiki Numamoto, Shintaro Tsukamoto, Takafumi Sasaki, Masafumi Nakaya, Junji Tani, Hirofumi Takahashi, Atsushi Muramatsu

pp. 1396-1401

DOI:

10.2320/matertrans.M2010419

抄録

Cubic-shaped Bi0.5Na0.5TiO3 (BNT) and Bi0.5K0.5TiO3 (BKT) fine particles with narrow size distribution were directly prepared as a single phase from a suspension of TiO2 anatase nanoparticles mixed with Bi(OH)3 in aqueous alkaline metal hydroxides solutions by highly condensed hydrothermal method at 200–250°C for several hours. It was investigated that the effect of particle mean size on the piezoelectric properties of thus obtained BNT and BKT fine particles.

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Dissolved-Oxygen-Induced Intensive Pitting Corrosion of Amorphous ZrCu Alloys in Thin NaCl Solutions

Hisanori Tanimoto, Yosuke Soga, Yoshinobu Takayanagi, Hiroshi Mizubayashi

pp. 1402-1409

DOI:

10.2320/matertrans.M2010437

抄録

Intensive pitting corrosion of amorphous (a-) Zr55Cu45 and a-Zr50Cu50 were observed by immersion in 0.2–200 mM NaCl solutions open to air at room temperature. The decreased corrosion rate in Ar-purged NaCl solution and no corrosion in ultrapure water open to air suggested that dissolved O2 and Cl− played an important role on the corrosion of the ZrCu-base amorphous alloys. The open-circuit potential showed a negative shift with increasing the NaCl concentration from 0.2 to 200 mM like that of pure Cu. These observations suggest that the corrosion of the ZrCu-base amorphous alloys in the NaCl solutions was triggered by Cu dissolution which was induced by the reduction of dissolved O2. The dissolution of Cu and Zr self-catalytically progressed by the local concentration of Cl− and hence the corrosion pits and holes were intensively formed even at the thinner NaCl concentrations.

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Surface Characteristics of Titanium Oxide Films Prepared by Micro-Arc Oxidation: Comparison of Direct Current Electrolysis and Pulse Electrolysis

M. Iwasaki, K. Shimada, K. Kudo, Y. Tamagawa, H. Horikawa

pp. 1410-1417

DOI:

10.2320/matertrans.M2010227

抄録

Oxide layers formed by micro-arc oxidation (MAO) using direct current electrolysis and pulse electrolysis were characterized by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and adhesive strength measurements. Ti oxide films fabricated by pulse electrolysis were found to have a significantly higher adhesive strength than those fabricated by direct current electrolysis. This can be explained by the different interface adhesive strengths between the two Ti oxide layers and the Ti substrate, as revealed by cross-sectional SEM micrographs. In addition, the dependences of the voltage and the current on the electrolysis time were investigated.

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Microstructure and Joint Strength of Friction Stir Spot Welded 6022 Aluminum Alloy Sheets and Plated Steel Sheets

Keyan Feng, Mitsuhiro Watanabe, Shinji Kumai

pp. 1418-1425

DOI:

10.2320/matertrans.L-M2011811

抄録

Friction stir spot welding (FSSW) was performed for joining of an aluminum alloy sheet to a steel sheet. A 6022 aluminum alloy sheet, a non-plated steel and four kinds of plated steel sheets were prepared. They were plated by pure zinc (GI), zinc alloy (ZAM), Al-Si alloy (AS) and zinc alloy including Fe (GA). The melting temperature of each plated layer was 420, 330, 640 and 880°C. The aluminum alloy sheet was overlapped on the steel sheet. A rotating tool was inserted from the aluminum alloy sheet side and the probe tip was kept at the position of 0.2 mm above the lapped interface for 3 s. Temperature change at the welding interface was measured during FSSW by using thermocouples which were located at the joint interface below the rotating tool. The maximum operating temperature was 430°C. It was found that interface morphology, strength and joining area of the joint varied depending on whether melting temperature of the plate layer was higher or lower than the maximum operating temperature. Large joint strength and joining area were obtained for the steel sheet with the low melting temperature of plated layer. In this case, the original plated layer was removed from the interface during FSSW and aluminum/steel interface with a thin intermediate layer was observed.

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Effect of Chromium Precipitation on Machinability of Sintered Brass Alloys Dispersed with Graphite Particles

Hisashi Imai, Shufeng Li, Katsuyoshi Kondoh, Yoshiharu Kosaka, Akimichi Kojima, Haruhiko Atsumi, Junko Umeda

pp. 1426-1430

DOI:

10.2320/matertrans.M2011051

抄録

The machinability of high strength lead-free brass was investigated in this study. Copper-40 mass%zinc (Cu-40Zn) brass powder with chromium was prepared by the water atomization. Chromium was used for strengthening of brass matrix. Graphite particles as machinable element were added to the as-atomized powders by conventional mixing process. Spark plasma sintering process was used to consolidate the above elemental mixed powder (X K SPSed material) at 873 K and 1053 K. The sintered materials at 1053 K were heat-treated for the precipitation of much Cr (HT material) at 1053 K for 12 h in Ar atmosphere. The machinability was evaluated by a drilling test using a drill tool under dry conditions. The matrix hardness of sintered material was higher than that of HT material. On the other hand, the machinability of sintering material was higher than that of HT material. The trade-off relationship between the matrix hardness and machinability of the brass alloys was not established. The solution of chromium content dissolved in the brass matrix of sintered material at 873 K, 1053 K and HT material was 0.55 mass%, 0.42 mass% and 0.19 mass%, respectively in SEM-EDS observation. The chromium carbide increased with decreasing chromium solution in the brass matrix. The generation of hard chromium carbide and decrease in the relative graphite particle caused to inhibit the machinability of HT material.

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Enhanced Mechanical Properties of LaF3 Thin Films by Ion Plating Deposition

Takanobu Hori, Shinji Motokoshi, Hiroshi Kajiyama

pp. 1431-1435

DOI:

10.2320/matertrans.M2010367

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The mechanical properties of lanthanum fluoride (LaF3) films are investigated. The films are deposited by using a resistive heating (RH) boat evaporation method and the advanced ion plating (AIP) method. A severe abrasion resistance test and a laser induced damage threshold (LIDT) test are done on the films. Abrasion resistance is increased by increasing the deposition temperatures for RH films. On the other hand, for AIP films, abrasion resistance is increased by adding direct current (DC) bias voltage. It is confirmed that the AIP films have a superior LIDT characteristics than those of RH films. With an additional DC bias voltage superimposed to a self bias voltage, the abrasion resistance and LIDT value is further improved. Based on the proposed mechanism of LIDT process, the microstructures of LaF3 films are discussed.

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Comparative Study of Microstructures and Material Properties in the Vacuum and Spark Plasma Sintered Ti-Calcium Phosphate Composites

Dibakar Mondal, Swapan Kumar Sarkar, Ik-Hyun Oh, Byong-Taek Lee

pp. 1436-1442

DOI:

10.2320/matertrans.M2011017

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Sintering of Ti-biphasic calcium phosphate (BCP) is difficult because of the chemical instability of the phases at high temperature. When the sintering temperature is above 1273 K, Ti reacts with BCP and forms CaO, TiO2, CaTiO3, TiP etc. Conventional vacuum sintering is common for Ti powder but for Ti-BCP composites, spark plasma sintering in an inert atmosphere is a quick method to overcome the issues associated with a prolonged reaction time. In this study, the effect of two different sintering processes on the sintering reactions and mechanical and biological properties of Ti-30 vol%BCP composites were investigated and compared. Detailed micro-structural and morphological analyses were conducted using scanning electron microscopy (SEM). Mechanical properties were characterized by relative density, Vickers hardness and compressive strength measurement. Phase characteristics were analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Cell viability and biocompatibility were investigated using the MTT assay and by examining cell morphology. In this study, the mechanical properties and biocompatibility for both, spark plasma sintered Ti-Ca-P composites were excellent compare to vacuum sintered composites.

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Formation Process of [B12H12]2− from [BH4]− during the Dehydrogenation Reaction of Mg(BH4)2

Yigang Yan, Hai-Wen Li, Hideki Maekawa, Masakazu Aoki, Tatsuo Noritake, Mitsuru Matsumoto, Kazutoshi Miwa, Shin-ichi Towata, Shin-ichi Orimo

pp. 1443-1446

DOI:

10.2320/matertrans.MA201002

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The existence of Mg(B12H12) as an intermediate compound during the dehydrogenation process of Mg(BH4)2 has been verified. To elucidate the formation process of Mg(B12H12), the dehydrogenation products of Mg(BH4)2 at different temperatures were characterized via X-ray diffraction and 11B magic angle spinning NMR measurements. The experimental results indicate that several new intermediate compounds such as Mg(B2H6) and Mg(B5H9) or Mg(B5H8)2 are expected to be formed prior to the formation of Mg(B12H12). Thus, it is suggested that the formation of [B12H12]2− from [BH4]− occurs via the gradual evolution of the B-H complex anion, i.e., [BH4]−→[B2H6]2−→[B5H9]2− or [B5H8]−→[B12H12]2−.

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Microstructure Development in Neutron Irradiated Tungsten Alloys

Takashi Tanno, Makoto Fukuda, Shuhei Nogami, Akira Hasegawa

pp. 1447-1451

DOI:

10.2320/matertrans.MBW201025

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The aim of this work is to investigate the influence of neutron irradiation condition, especially temperature, on irradiation hardening and microstructure development in irradiated tungsten-rhenium (W-Re) alloys. Neutron irradiations were carried out in JOYO at the range of 400 to 750°C, up to 1.54 dpa. Micro Vickers hardness tests and micro structural observations using a TEM were performed. Irradiation hardening of W-Re alloys irradiated at 538°C were clearly larger than those irradiated at other temperatures. Fine voids and fine needle- or plate-like precipitates were observed in pure W and W-Re alloys irradiated at 538°C, respectively, with high number density. The fine complex microstructure seems to be the cause of the characteristic irradiation hardening.

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A Novel Photoactive Nano-Filtration Module Composed of a TiO2 Loaded PVA Nano-Fibrous Membrane on Sponge Al2O3 Scaffolds and Al2O3-(m-ZrO2)/t-ZrO2 Composites

Nguyen Thuy Ba Linh, Kap-Ho Lee, Byong-Taek Lee

pp. 1452-1456

DOI:

10.2320/matertrans.M2011039

抄録

Novel photoactive nano-filtration modules composed of a nano-particle TiO2 loaded polyvinyl alcohol (PVA) nano-fibrous membrane on sponge Al2O3 scaffolds and concentric multi-layered Al2O3-(m-ZrO2)/t-ZrO2 composites were successfully prepared using the electro-spinning method, which was also used to load TiO2 into the PVA nano-fiber. The diameter of the PVA-TiO2 nano-fibers was approximately 200 nm. Nano-particle TiO2 with a highly crystalline structure at a ratio of 50% were well-dispersed in the PVA nano-fibrous material. In addition, the PVA-TiO2 membrane was found in the crystallize structure. Methyl Orange (MO) was degraded and became discolored after 5 h of oxidation by the nano-filtration membranes under UV irradiation. Sponge Al2O3 scaffolds and Al2O3-(m-ZrO2)/t-ZrO2 composites were successfully coated with PVA-50%TiO2 fibers with the goal of fabricating a novel nano-filtration membrane.

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Fabrication of TiB2–FeAl Cermet by Mechanical Milling and Subsequent Pulsed Current Sintering

Hiroyuki Nakayama, Shuji Tada, Kimihiro Ozaki, Keizo Kobayashi

pp. 1457-1461

DOI:

10.2320/matertrans.M2010434

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A TiB2-FeAl cermet was successfully fabricated by the mechanical milling of TiB2, Fe and Al powders, and subsequent pulsed current sintering. A FeAl phase was formed during the sintering process by the diffusive reaction of Fe and Al. The transverse rupture strength of the sintered sample depends on the milling condition. A suitable condition in this process was the revolution speed of 180 rpm and the milling time for 18 ks. The TiB2-40 mass% FeAl prepared from the powder milled by this condition shows a transverse rupture strength of 1370 MPa and a hardness of 86 HRA.

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Recovery and Concentration of Precious Metals from Strong Acidic Wastewater

Hisayoshi Umeda, Atsushi Sasaki, Kunihiko Takahashi, Kazutoshi Haga, Yasushi Takasaki, Atsushi Shibayama

pp. 1462-1470

DOI:

10.2320/matertrans.M2010432

抄録

Generally, trace precious metals remaining in wastewaters generated from the refining process of precious metals are not recovered, due to a relatively high processing cost as well as various technical problems. Recovery of precious metals from wastewaters is very important for the conservation of resources and the protection of environment. However, wastewaters containing a large amount of ammonium ion (NH4+) cannot be treated by general neutralization operation, due to formation of metal ammine complexes with increasing pH. In this study, the possibility of recovering precious metals and other valuable metals from wastewaters by various traditional metallurgical processes such as cementation, neutralization and reduction, were investigated. A recovery of 99% Copper (Cu), 96% Palladium (Pd), and 85% Gold (Au) by cementation using Iron (Fe) powder, and 99.6% Cu, 99.5% Pd by cementation using Aluminum (Al) powder was achieved. However, complete recovery of all valuable metals by a one-step cementation process was not possible. On the other hand, precious metals and other valuable metals including Copper and Indium, etc., were precipitated by combining neutralization, deammoniation and reduction processes. Results showed that the recovery of Platinum (Pt) in the reduction process was improved by adding deammoniation step. Finally, precious metals are concentrated in the crude copper metal by fusion process. The recovery of Au, Ag, Pd was more than 91%, and that of Pt was about 71%.

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Fundamental Study on Recovery of WC from Hardmetal Sludge by Using Mineral Processing

Jung-Ah Kim, Gjergj Dodbiba, Katsunori Okaya, Seiji Matsuo, Kenji Nishimura, Toyohisa Fujita

pp. 1471-1476

DOI:

10.2320/matertrans.M2011029

抄録

Hardmetals are the composite materials which have carbides and a metal, e.g. Fe, Co, Ni etc., as binder phase. WC-Co is generally called hardmetal, since it has the best mechanical property. In Japan, hardmetal which has finished their cycle, have been recovered and reused or recycled. However, sludge produced from processing of hardmetal tools and its polishing has been discarded because there are difficulties to be treated. In addition, Japan depends on China for tungsten resource, developing recycling method of this sludge is necessary.
In this study, tungsten carbide (WC) was recovered from hardmetal sludge by mineral processing methods such as free-settling and liquid-liquid extraction. Free-settling method, which takes advantage of using the differences in sinking rate of WC and silica (SiO2) after separation by wet tower mill has been used. It was found that WC grade increased with increasing rotation speed of tower mill, but the recovery decreases. Whereas tungsten grade increased with decreasing milling time, the recovery of tungsten decreases. Another finding of this study is that WC grade increases and recovery decreases with increasing sinking time up to 3 h. When rotation speed is adjusted at 1500 rpm, milling time is kept at 1 h and sinking time is kept at 3 h, tungsten grade is increased up to 85.9 mass% from about 66.2 mass% and the recovery of tungsten is about 10 mass%. Moreover silica grade is decreased from 28.5 mass% to 5.9 mass%.
In case using liquid-liquid extraction, ultrasonic, cutter-mill and microwave were used for liberation. Grade and recovery of WC increased with increasing ultrasonic time. It takes more than 20 min for ultrasonication for improving WC grade to more than 90 mass%. By cutter-mill, WC grade decreased with increasing milling time, but the recovery increased. After 1 min WC grade was improved up to 89.9 mass% and the recovery was 23.8 mass%. WC grade was the highest when microwaving time was 5 min. Then, WC grade was 91.3 mass% and the recovery was 16.3 mass%.

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Effects of Ca on Tensile Properties and Stretch Formability at Room Temperature in Mg-Zn and Mg-Al Alloys

Yasumasa Chino, Takamichi Ueda, Yuki Otomatsu, Kensuke Sassa, Xinsheng Huang, Kazutaka Suzuki, Mamoru Mabuchi

pp. 1477-1482

DOI:

10.2320/matertrans.M2011048

抄録

The tensile tests and the Erichsen tests at room temperature have been performed on seven kinds of Mg alloys: Mg-1.5Zn, Mg-1.5Zn-0.1Ca, Mg-3Zn, Mg-3Zn-0.1Ca, Mg-3Al, Mg-3Al-0.1Ca and Mg-1Al-1Zn-0.1Ca-0.5Mn alloys. In the Mg-Zn alloys, the 0.2% proof stress at 90°, which was the angle between the tensile direction and the RD, was decreased by addition of Ca, while the 0.2% proof stress at 0° was increased by addition of Ca. Also, an increase in elongation to failure by addition of Ca at 90° was larger than that at 0°. However, such variations in tensile properties by addition of Ca were not found in the Mg-Al alloy. The stretch formability for the Mg-Zn alloys was significantly enhanced by addition of Ca, while the stretch formability of the Mg-Al alloy was not enhanced by addition of Ca. These results by the mechanical testing are ascribed to the variations in basal texture by addition of Ca.

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Effect of CaO Addition on the Ignition Resistance of Mg-Al Alloys

Jin-Kyu Lee, Shae K. Kim

pp. 1483-1488

DOI:

10.2320/matertrans.M2010397

抄録

The ignition resistance was investigated for CaO added Mg-Al alloys. The ignition resistance was examined by DTA for quantitative data, furnace chip ignition test for the safety of machined chips and torch ignition test for safety of products. The ignition resistances under all conditions greatly increased by CaO addition. AES depth profile was performed to evaluate the ignition resistance in terms of surface oxide stability. In the case of Mg-Al alloy without CaO, there was the thick and porous MgO oxide layer on the surface. The depth profile for CaO added Mg-Al Mg alloys indicated that the surface consisted of the thin and dense oxide layer mixed with MgO and CaO.

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Instantaneous and Complete Decomposition of Formaldehyde by Thermally Activated Oxide Semiconductors

Hideki Shima, Hiroo Takahashi, Hiroyuki Miyauchi, Jin Mizuguchi

pp. 1489-1491

DOI:

10.2320/matertrans.M2011062

抄録

The extensive use of resin-bonded wood in construction as well as the continued expanding application of formaldehyde-based resins has resulted in formaldehyde (FA) becoming a major indoor contaminant. In this investigation, instantaneous and complete decomposition of FA has been studied by thermally activated semiconductors whose system had previously been developed by us. Complete decomposition has been achieved with Cr2O3 at about 500°C for FA concentrations of 100 and 1200 ppm with a residence time of about 20 ms. Our system is simple in structure and compact; nevertheless, quite efficient.

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Thermal Boundary Resistance Effect on Non-Equilibrium Energy Transport in Metal-Dielectric Thin Films Heated by Femtosecond Pulse Lasers

Jae Bin Lee, Seong Hyuk Lee

pp. 1492-1499

DOI:

10.2320/matertrans.M2011021

抄録

The aim of this study is to investigate the effect of interfacial thermal boundary resistance (TBR) at a metal-dielectric interface on non-equilibrium energy transport in Au/SiO2 films heated by femtosecond pulse lasers. In this paper we suggest a combined set of numerical models that include the two-temperature model (TTM) for a metal side and the heat conduction equation for a dielectric layer. In addition, the TBRs between metal and nonmetal layers are calculated using thermal conductance, which is closely associated with the electron-phonon resistance and phonon-phonon resistance. Herein we present the transient and spatial distributions of TBR for a Au/SiO2 film irradiated by a 100-fs pulse laser with a 1053 nm wavelength, which are substantially affected by the phonon temperature and electron-phonon coupling. We also discuss the effect of laser fluence on the TBR and energy transport. The TBR rapidly increases the thermal conductivity at the interface, and becomes dominant at an early stage of laser irradiation over a very short period and then drastically decreases with time. Moreover, the TBR is substantially affected by the electron-phonon coupling and it should be considered for more accurate prediction of the lattice temperature drop at the interface.

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Microstructural Characterizations Following Friction Stir Welding of Dissimilar Alloys of Low- and High-Carbon Steels

Don Hyun Choi, Byung Wook Ahn, Yun Mo Yeon, Seung Hwan C. Park, Yutaka S. Sato, Hiroyuki Kokawa, Seung Boo Jung

pp. 1500-1505

DOI:

10.2320/matertrans.M2010438

抄録

The present study was carried out to evaluate the microstructure and mechanical properties of the friction stir welding (FSW) of dissimilar alloys of low-carbon (SPHC) and high-carbon (SK85) steels. For this work, FSW was performed at two tool rotation speed of 400 rpm and 800 rpm, and traveling speed was fixed at 200 mm/min. Phase transformation of the microstructures in the joints was investigated by scanning electron microscopy imaging. Vickers hardness and tensile test were used to evaluate the mechanical properties of the joints. In the base metal (BM), SPHC and SK85 each has single ferrite phase and globular cementite phase + ferrite phase. After welding, fine ferrite phase and martensite phase were observed in the joint due to phase transformation and dynamic recrystalization. Volume fractions of martensite phase were different according to tool rotation speed. The area fraction of the martensite phase at the higher tool rotation speed was less than that at the lower tool rotation speed. The lower area fraction at the higher tool rotation speed was attributed to the enhanced diffusion of carbon atoms during FSW. Hardness distribution also showed that hardness at higher tool rotation speed was less than that at lower tool rotation speed and it is related to different volume fractions of the martensite phase. After the tensile test, the test specimen was fractured at the SPHC BM region and showed the same yield strength (YS) and ultimate tensile strength (UTS) of SPHC BM.

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Numerical and Experimental Investigation into Effect of Temperature Field on Sensitization of AISI 304 in Butt Welds Fabricated by Gas Tungsten Arc Welding

Hwa Teng Lee, Chun Te Chen

pp. 1506-1514

DOI:

10.2320/matertrans.M2011071

抄録

This study examines the effect of the temperature field on the sensitization tendencies of AISI 304 two-pass butt welds fabricated using the gas tungsten arc welding (GTAW) method. The thermal cycles induced in the two-pass welding process are simulated using ANSYS software based upon a moving heat source model and the function of Element Birth and Death was employed also in the filled metal GTA welding. The validity of the numerical model is confirmed by comparing the simulation results with the corresponding experimental results. The results show that the heat-affected zone (HAZ) in the 2nd pass specimen is susceptible to intergranular corrosion (IGC). However, the HAZ in the 1st pass specimen shows no obvious signs of IGC. The difference in the sensitization tendencies of the two specimens is attributed to a difference in their respective heating and cooling times.

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Flattening Characteristics of Ni20Cr Thermal-Sprayed Coating Layers on Preheated SCM415 Substrates

Dong Hwan Shin, Jae Bin Lee, Jae Lyoung Wi, Seungil Park, Namil Kim, Minhaeng Cho, Jong Min Kim, Seong Hyuk Lee

pp. 1515-1521

DOI:

10.2320/matertrans.M2011068

抄録

The preheating effect of SCM415 steel substrates on the flattening behavior of Ni20Cr flame-sprayed particles was investigated in a temperature range from 278 K to 523 K. In the present study, we calculated the particle temperature and velocity distributions of the continuous and discrete phases before collision with the substrate by using a computational fluid dynamics (CFD) code of Fluent (ver. 6.3.26). Particle velocity and gas temperature decreased rapidly in the radial direction while the particles traveled toward the substrate, suggesting that substrate size and distance from the nozzle should be carefully controlled to improve coating quality. The conventional flame spray gun was used to accelerate molten particles and K-type thermocouples were used to monitor the substrate temperature during a preheating process. Commercially available nickel-based Ni20Cr particles with a mean diameter of 45 μm and 20 μm were used for experiments to examine the particle size effect on the coating characteristics. Herein we present FE-SEM images of coated layers on the substrates. As the substrate preheating temperature increased, the flatter surface morphology was seen at the interface between substrate and coating layer because of better wetting and corresponding higher shear adhesion strength. Moreover, the splat morphology was significantly dependent on the particle size.

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Indium Addition on Intermetallic Compound Evolution in Tin-Silver Solder Bump

Dongliang Wang, Yuan Yuan, Le Luo

pp. 1522-1524

DOI:

10.2320/matertrans.M2011058

抄録

The formation of large Ag3Sn plate in Sn-Ag solder joint has restricted its application in lead-free electronic industry. There is a great interest for finding new approach to suppress the growth of Ag3Sn. In this paper, Sn-2.1Ag and Sn-1.8Ag-9.4In solder bumps are prepared by electroplating of Sn-Ag and indium in sequence. After reflow at 260°C for 30 min with cooling rate 0.33°C/s, the phase composition, microstructure and undercooling of solder alloys are characterized by X-ray diffraction, Scanning electron microscopy and Differential scanning calorimeter, respectively. It is found that after indium addition, large Ag3Sn plate is substituted by Ag9In4 with irregular polygon morphology. It is also found that indium addition can significantly reduce the undercooling of β-Sn, which promotes the solidification of β-Sn and inhibits the growth of Ag9In4 during slow cooling.

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