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MATERIALS TRANSACTIONS Vol. 52 (2011), No. 2

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. 2

Formation of Defect Structure on Ge Surface by Ion Irradiation at Controlled Substrate Temperature

Noriko Nitta, Tokiya Hasegawa, Hidehiro Yasuda, Yoshihiko Hayashi, Toshimasa Yoshiie, Masafumi Taniwaki

pp. 127-129

DOI:

10.2320/matertrans.M2010248

抄録

Ge (001) surface was irradiated by 60 keV Sn ions to a fluence of 8×1018 ions/m2 at a controlled substrate temperature, and the formation of defects was investigated. A damaged layer of about 50 nm thickness was formed on the surface at 150 K. In the case of irradiation at room temperature, a damaged layer was also created, but voids of about 15 nm diameter were created near the top surface. This result is explained by the high mobility of vacancies during irradiation at room temperature, and it is confirmed that the void formation process is dominated by the migration of induced point defects.

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Thermal Desorption Spectroscopy Study on the Hydrogen Trapping States in a Pure Aluminum

Takahiro Izumi, Goroh Itoh

pp. 130-134

DOI:

10.2320/matertrans.L-M2010825

抄録

Hydrogen trapping states in pure aluminum foils with 99.99% purity with different amount of blisters have been investigated by means of thermal desorption spectroscopy. Three peaks are seen in the spectra, where the amount of hydrogen from the third peak at the highest temperature range increases with increasing in the volume fraction of the blisters. Hence, the third peak is revealed to arise from the hydrogen in the blisters. The desorption energy of hydrogen released from the blisters is 76.3 kJ/mol. On the other hand, the first peak is inferred to be due to the hydrogen diffusing with vacancy, considering the diffusion distance of the vacancy as well as untrapped hydrogen atom.

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Microstructure of Ti-Cr Nanoparticles Prepared by Electrical Wire Explosion

Sujeong Lee, Wonbaek Kim, Je-shin Park, Chang-yul Suh, Sung-wook Cho

pp. 135-138

DOI:

10.2320/matertrans.M2010277

抄録

The reaction products of electrical wire explosion with 25 at% Cr-coated Ti wire were identified as β-TiCr2, α-Ti, β(Ti,Cr) and α-TiCr2 based on the selected area electron diffraction patterns. There was a bimodal size distribution where Ti-Cr particles were 40–50 nm in size, and fine particles less than 10 nm were determined to be pure Ti or Cr. The Ti-Cr nanoparticles are not only a mixture of Ti-Cr phases but they are also heterogeneous themselves at a single particle level, due to the non-equilibrium effects of the EWE process. The very rapid collision and subsequent coalescence of Ti and Cr atom clusters are believed to have contributed to the formation of chemically segregated particles.

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Effect of a High Magnetic Field on Carbon Diffusion in γ-Iron

Shou-Jing Wang, Yan Wu, Xiang Zhao, Liang Zuo

pp. 139-141

DOI:

10.2320/matertrans.M2010327

抄録

The effect of 12-Tesla high magnetic field on carbon diffusion in γ-Fe at 1273 K has been investigated using a diffusion couple made by pure Fe and high purity Fe-0.76%C alloy. The results show that the high magnetic field obviously hinders carbon diffusion in the direction perpendicular to the magnetic field direction; while it only slightly enhances the carbon diffusion in the direction parallel/antiparallel to the magnetic field direction.

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Influence of Bath Composition on Tensile Ductility in Electrodeposited Bulk Nanocrystalline Nickel

Isao Matsui, Yorinobu Takigawa, Tokuteru Uesugi, Kenji Higashi

pp. 142-146

DOI:

10.2320/matertrans.M2010279

抄録

We investigated the influence of bath composition on characteristics in an electrodeposited bulk nanocrystalline Ni (nc-Ni). This study was aim to establish the fabrication process of bulk nc-Ni with good tensile property. The bulk nc-Ni was electrpdeposited from a sulfate bath and a sulfamate bath. The nc-Ni was evaluated for microstructure and mechanical properties, such as microhardness, tensile strength. As a result, bulk nc-Ni obtained from a sulfamate bath exhibited enhanced tensile property (ultimate tensile strength of 1006 MPa and ductility of 8.8%) compared to that obtained from a sulfate bath. Dimple pattern was observed in fracture surface of bulk nc-Ni obtained from a sulfamate bath. However, dimple pattern and brittle fracture surface were observed in bulk nc-Ni obtained from a sulfate bath. We consider the ductility of electrodeposited nc-Ni was influenced by internal stress generated from electrodepostion. These experiments and analyses suggest that it is important to control internal stress on fabrication of bulk nc-Ni with high tensile strength and good ductility.

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Two-Dimensional and Three-Dimensional Finite Element Analysis of Finite Contact Width on Fretting Fatigue

Heung Soo Kim, Shankar Mall, Anindya Ghoshal

pp. 147-154

DOI:

10.2320/matertrans.M2010268

抄録

Three-dimensional effects of finite contact width fretting fatigue were investigated using the combination of full three-dimensional finite element model and two-dimensional plane strain finite element model, named as a hybrid layer method. Free edge boundary effect in finite contact width fretting fatigue problem required full three-dimensional finite element analysis to obtain accurate stress state and relative displacement in contact zone. To save the computational cost with sufficient accuracy, traction distributions obtained from coarse three-dimensional finite element analysis was applied to the two-dimensional plane strain finite element model. The key idea of this hybrid layer method was that traction distributions converged faster than the stresses. The proposed hybrid layer method predicted the free edge boundary effects of finite contact width fretting fatigue less than eight percent error bound and reduce the execution time to 5 percent of three-dimensional submodeling technique.

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Mechanical Properties of Titanium Particles Dispersed Magnesium Matrix Composite Produced through Accumulative Diffusion Bonding Process

Koichi Kitazono, Susumu Komatsu, Yuki Kataoka

pp. 155-158

DOI:

10.2320/matertrans.M2010282

抄録

This paper reports improved mechanical properties of AZ91 magnesium alloy at room temperature. Titanium particles dispersed AZ91 magnesium alloy composite is produced through accumulative diffusion bonding (ADB) process. Vickers hardness, ultimate tensile strength and 0.2% proof stress increased with increasing the amount of titanium particles. The composite with 2.0% Ti produced by the ADB process showed significantly high elongation over 30%. Improved ductility would be due to random texture development by severe plastic deformation and stress relaxation by titanium particles.

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Purification of Hafnium by Hydrogen Plasma Arc Melting

Kouji Mimura, Keigo Matsumoto, Minoru Isshiki

pp. 159-165

DOI:

10.2320/matertrans.M2010296

抄録

Purification of two kinds of Hf metal, a high-purity Hf (HP-Hf) with 99.7 mass% and a low-purity Hf (LP-Hf) with 98 mass%, by hydrogen plasma arc melting (HPAM) has been carried out and the removal behavior of various impurity elements has been examined. Many metallic impurities (Fe, Al, Cr, Cu, Mn, Sn, Ti etc.) in the melted Hf, with higher vapor pressures than that of Hf, were removed to the very low levels by vaporization during HPAM and their removal rates increased with the hydrogen content of plasma arc. Then, the purity (except for Zr, O, N and C) of LP-Hf and HP-Hf were improved to nearly 99.998% and above 99.999%, respectively, after 60 min of 20%H2+Ar plasma arc melting. For the removal of Fe, Al, Cu and Ti from Hf, the refining effect of HPAM under atmospheric pressure was found to be superior to that of EBM under high vacuum. Therefore, HPAM has been confirmed to be a very useful method for the purification of Hf and the dissociated and activated hydrogen atoms formed in the high temperature plasma arc must play an important role for the unique refining process of HPAM.

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Prediction Method of Crack Sensitivity during DC Casting of Al-Mn and Al-Mg Alloys

Makoto Morishita, Mitsuhiro Abe, Kenji Tokuda, Makoto Yoshida

pp. 166-172

DOI:

10.2320/matertrans.L-M2010823

抄録

Because it has been difficult to predict crack sensitivity depending on alloy composition during aluminum direct chill casting (DC casting), a new prediction method based on the relationship between the calculated solid fraction and temperature was developed for Al-Mn and Al-Mg series aluminum alloys. In this work, two crack indexes are suggested. The first index is brittle temperature range (BTR). The second index is based on the strain rate difference in the mushy region. These indexes are quantitatively calculated by using thermodynamic software such as Thermo-calc. This method is verified by DC casting of A3000 and A5000 series aluminum alloys. It can be utilized in the alloy design stages to control the crack sensitivity before casting.

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High Strength Bolt Manufacturing of Ultra-Fine Grained Aluminium Alloy 6061

Jun-Seok Choi, Young-Gwan Jin, Hyun-Chul Lee, Yong-Taek Im

pp. 173-178

DOI:

10.2320/matertrans.M2010309

抄録

Bulk nanostructure of commercially available aluminum alloy of AA6061 was made by an equal channel angular extrusion (ECAE). The effect of the ECAE routes of A, Bc and C on change of microstructure was investigated up to four passes by using the split die set-up. Formability of the ultra-fine grained specimens processed by the ECAE was measured by a compression test. In this test, the specimen made of the conventional material did not buckle when the aspect ratio of the height to the diameter (4 mm) of the specimen was 2.1 but the ultra-fine grained specimens with the same aspect ratio buckled. Considering the limiting value of the aspect ratio obtained from the compression test, a bolt forming sequence was developed into three stages. Load requirement and possible defect formation during the forming process were predicted by employing a rigid-viscoplastic finite element analysis. After manufacturing the high strength bolts using the ultra-fine grained specimens, strength increase was confirmed by the tension test and transmission electron microscopy. Homogeneity of strength increase was also examined by measuring local hardness distribution. In addition, the manufactured bolt with the ultra-fine grained AA6061 was compared to the one manufactured with commercially available AA2024 in terms of strength increase and its homogeneity. According to the present investigation, an innovative approach to utilize the ECAE to manufacture the high strength bolt using the conventional material without applying additional alloying elements or heat treatment is demonstrated.

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Criterion for Constitutional Supercooling at Solid-Liquid Interface in Initial Transient Solidification with Varying Solute Content at Interface

Hiroshi Kato, Yukihiko Ando

pp. 179-188

DOI:

10.2320/matertrans.M2010253

抄録

A criterion for appearance of the constitutional supercooling at the solid-liquid interface in the initial transient solidification is discussed theoretically and experimentally. First, a relation between the moving velocity of the interface and the solute content was analyzed to derive a moving velocity of the interface under a simple model of the linear change in the solute content at the interface. And, a criterion for appearance of the constitutional supercooling at the planar interface was analyzed to obtain the distance of the stable growth of the interface with the planar shape. Then, the solidification experiment was carried out with the Al-4 mass% Cu alloy: the aluminum alloy was inserted in the alumina tube of 0.4 to 2 mm in inner diameter and heated for 2.5∼4 h under a temperature gradient to obtain the stationary interface, and then the alumina tube was cooled in the furnace for 0 to 45 s. After furnace cooling, the alumina tube was quenched in water to observe the interface. The interface with the planar shape appeared for 20∼30 s after the start of furnace cooling, and then the columnar structure grew ahead of the interface. Then the solute content in the solid behind the interface was analyzed to show that the solute content in the specimen quenched after furnace cooling was different from that in the specimen quenched without furnace cooling. The experimental results were compared with the theoretical calculations to infer that the interface moved with the planar shape for a short time after the start of furnace cooling, and then the interface became unstable to form the columnar structure.

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Formation Mechanism of Eutectic Cu6Sn5 and Ag3Sn after Growth of Primary β-Sn in Sn-Ag-Cu Alloy

Yoshiko Takamatsu, Hisao Esaka, Kei Shinozuka

pp. 189-195

DOI:

10.2320/matertrans.M2010325

抄録

In Sn-Ag-Cu solder balls, unusual microstructures consisting of both Sn-Ag3Sn and Sn-Cu6Sn5 binary eutectic stratures are sometimes observed. However, the formation mechanism of these unusual microstructures is still unclear. Therefore, in this study, the solidification process has been investigated to clarify the nucleation and growth of binary and ternary eutectic structures in Sn-1.0Ag-0.5Cu alloy by using thermal analysis and interruption tests.
Cu-enriched zone was observed around β-Sn in the liquid before the nucleation of Sn-Cu6Sn5 binary eutectic structure. Sn-Cu6Sn5 binary eutectic structure formed in these regions. Moreover, some Ag-enriched zones were observed around the Sn-Cu6Sn5 binary eutectic structure in the liquid before the initiation of the ternary eutectic solidification. The unusual Sn-Ag3Sn binary eutectic structure formed in these regions just after the temperature reached the ternary eutectic point. The ternary eutectic structures were classified into three types depending upon the fluctuation of the remaining liquid composition at the ternary eutectic temperature.

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The Effect of Jetting Temperature on the Fabrication of Rapidly Solidified Fe-Si-B Systems Alloys Using Single-Roller Melt Spinning

Keiyu Nakagawa, Teruto Kanadani, Yasuyuki Mori, Yuto Ishii

pp. 196-200

DOI:

10.2320/matertrans.M2010321

抄録

Fe-Si-B systems amorphous alloys were rapidly solidified from the melt by the single roller method. In this process the alloys were melted in a crucible and the molten alloy is jetted through a small orifice by gas pressure or gravity. The effects of the jetting temperature of the melting alloy on the ribbon thickness of rapidly solidified Fe75Si10B15 and Fe79.5Si8.5B12 alloys were examined. The rapidly solidified Fe75Si10B15 and Fe79.5Si8.5B12 alloy ribbons’ mean thickness decreased continuously with the increased jetting temperature. However, the temperature dependence of the ribbon thickness in the Fe79.5Si8.5B12 alloy was greater than that of the Fe75Si10B15 alloy.
The results demonstrate that the viscosity of liquid Fe-Si-B systems alloys influences the ribbon thickness. Moreover, when the contact conditions between the rotating roll comes and puddle are good, the ribbon thickness decreases.

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Influence of Rhenium on the Mechanical Behavior and Fracture Mechanism of a Fine-Grain Superalloy at Elevated Temperatures

Jian-Hong Liao, Hui-Yun Bor, Chuen-Guang Chao, Tzeng-Feng Liu

pp. 201-209

DOI:

10.2320/matertrans.M2010299

抄録

This study investigated the influence of rhenium on the mechanical behavior and fracture mechanism of a fine-grain Mar-M247 superalloy at elevated temperatures. Tensile test results showed that the addition of 3 mass% Re significantly improved the ultimate tensile strength and yield strength from room temperature to 760°C. Creep test results showed that steady-state creep behavior dominated creep properties under the test condition of 760°C/724 MPa. The steady-state creep rate and creep life of alloy with 3 mass% Re was reduced by 31% and prolonged by 63%, respectively, compared to alloy without Re. The improvement in tensile and creep properties in 3 mass% Re alloy was associated with a decrease in grain and γ′ size and an increase in strength of γ⁄γ′ matrix. However, adding 4.5 mass% Re resulted in a decrease in the tensile and creep properties due to the formation of needle-like P phase in the grain interior. Fracture analysis demonstrated that during tensile and creep tests, cracks initiated and propagated along grain boundary in alloy without Re and containing 3 mass% Re alloy; however, in the alloy containing 4.5 mass% Re, cracks initiated and propagated along grain boundary and the P phase/matrix interface. Under the current tensile and creep conditions, 3 mass% Re was an optimal addition for casting a fine-grain Mar-M247 superalloy.

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Activation of Ground Granulated Blast Furnace Slag Cement by Calcined Alunite

Hyung-Seok Kim, Joo-Won Park, Yong-Jun An, Jong-Soo Bae, Choon Han

pp. 210-218

DOI:

10.2320/matertrans.M2010350

抄録

To enhance the early strength of grounded granulated blast furnace slag (GGBFS) blended cement, the activation characteristics of GGBFS were examined by a potassium aluminum sulfate (PSA) clinker, consisting of KAl(SO4)2 and amorphous Al2O3 by calcining alunite [K2SO4·Al2(SO4)3·4Al(OH)3] at 650°C for 30 min. The PSA clinker reacted with calcium hydroxide and gypsum to form ettringite (3CaO·Al2O3·3CaSO4·32H2O, AFt) by following reaction: 2KAl(SO4)2+2Al2O3+13Ca(OH)2+5(CaSO4·2H2O)+74H2O→3(3CaO·Al2O3·3CaSO4·32H2O)+2KOH. Mortar was prepared by mixing a blended cement of GGBFS and ordinary Portland cement (OPC) with PSA clinker as activator. The compressive strength of the GGBFS blended cement mortar was compared with that of OPC mortar. When the PSA clinker and gypsum activator was added to the blended cement of GGBFS and OPC, the hydration products investigated by DTA and X-ray diffraction were mainly ettringite and calcium silicate hydrate(C-S-H) gel. The early and long-term strengths of the GGBFS blended cement were higher than those of OPC. Therefore, PSA clinker as activator was shown to improve the early and long-term strengths of GGBFS blended cement.

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Grain Boundary Segregation of Phosphorus and Columnar Grain Growth during Decarburization in Plain Carbon Steels

N. H. Heo, J. K. Lee

pp. 219-223

DOI:

10.2320/matertrans.M2010283

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During decarburization of plain carbon steels, the grain boundary segregation concentration of phosphorus increased with increasing bulk phosphorus content and with decreasing decarburization temperature. The grain growth kinetics decreased with increasing bulk phosphorus content which is due to the grain boundary pinning effect of highly segregated phosphorus. After decarburization at 973 K for 24 h, the columnar grain growth following the abnormal grain growth was observed in the steel containing a low bulk phosphorus content, while the steel containing a high bulk phosphorus content showed only the abnormal grain growth behavior. Such grain growth behaviors can be understood in the light of the abnormal grain growth driven by the grain boundary carbides and the solute drag effect of highly segregated phosphorus on moving grain boundaries. During decarburization at 1173 K, only the normal grain growth was observed due to the absence of grain boundary carbides, regardless of the bulk phosphorus content. The decarburization reaction in the present study can be expressed by the parabolic relationship x = k(Dt)1⁄2 where x is the decarburization depth, k the reaction coefficient, D the diffusivity of carbon and t the decarburization time.

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Adsorption of Cd(II) on Waste Calcite Produced by the Carbonation of Flue Gas Desulfurization (FGD) Gypsum

Kyungsun Song, Wonbaek Kim, Taegong Ryu, Kyung-Won Ryu, Jun-Hwan Bang, Young-Nam Jang

pp. 224-228

DOI:

10.2320/matertrans.M2010344

抄録

The waste calcite, by-product of the carbonation reaction of flue gas desulfurization (FGD) gypsum, was evaluated as low-cost adsorbent for Cd(II) removal from wastewater. Batch experiments were performed in aqueous solution varying contact time, initial pH of Cd(II) solution, adsorbent dose, and Cd(II) concentration. The sorption rate of Cd(II) on the adsorbent was high during initial 1 h and decreased slowly reaching a plateau after about 12 h. The adsorption kinetics of Cd(II) could be best described by the pseudo-second order model while its isotherm was found to fit with the Langmuir model. The maximum adsorption capacity was 7.99 mg g−1. It is believed that waste calcite would be an addition to the list of low-cost adsorbents for Cd(II) removal in wastewater treatment.

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Effect of TM-Addition on the Aging Behaviour of Al-Mg-Si Alloys

Shumei Wang, Kenji Matsuda, Tokimasa Kawabata, Yong Zou, Toshinari Yamazaki, Susumu Ikeno

pp. 229-234

DOI:

10.2320/matertrans.M2010370

抄録

Microstructure and aging hardness variation of Al-Mg-Si-TM alloys (TM = Mn, Cr, Fe, Y, and Gd) were investigated to reveal the effect of TMs on the age-hardening behavior of Al-Mg-Si-TM alloys. The peak hardness of Cr- and Fe-added alloys is similar to the base alloy, while the peak hardness of Mn-, Gd-, and Y-added alloys is much lower than the base alloy. It was found different TMs formed the dispersoids with different ratio of TM/Si calculated from the EDS result of the dispersoid. The Si expensed for the formation of the dispersoid is the most for Y-added alloy and the least for Fe-added alloy among the five TM-added alloys. It is thought that this will result in the difference of Si in the matrix for the formation of the precipitate.

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Effect of Oxalic Acid on Heat Pretreatment for Serpentine Carbonation

Myung Gyu Lee, Kyoung Won Ryu, Young Nam Jang, Wonbaek Kim, Jun-Hwan Bang

pp. 235-238

DOI:

10.2320/matertrans.M2010304

抄録

A novel pretreatment method for the mineral serpentine was proposed to develop an effective carbonation process for CO2 sequestration. Basically, the method involved preheating a mixture of oxalic acid and serpentine and the subsequent aqueous carbonation. The addition of oxalic acid was found to stimulate the decomposition of serpentine during heat treatment. X-ray diffraction analysis revealed that serpentine is transformed into magnesium oxalate and magnesium oxide by heat treatments at 200°C and 500°C, respectively. The addition of oxalic acid was found to enhance the overall carbonation reaction owing to the formation of magnesium oxide during heat treatment. Thermogravimetric analysis showed that approximately 70% of the Mg2+ was transformed into magnesium oxide. Using this method, a carbonation rate as high as 72% could be obtained by aqueous carbonation at 100°C under 4 MPa. This novel method can potentially reduce the high energy cost and unavoidable use of expensive chemicals for pH control.

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Nanoimprinting of Metallic Glass for Periodic Nano-Hole Structures with Dies Fabricated by FIB-CVD and RIE

Yasuyuki Fukuda, Yasunori Saotome, Hisamichi Kimura, Akihisa Inoue

pp. 239-242

DOI:

10.2320/matertrans.M2010241

抄録

Metallic glasses are amorphous structured materials exhibiting perfect Newtonian viscous flow in the supercooled liquid temperature range and superior nanoformability under low stress. These properties make metallic glasses ideal materials for nanoimprinting, which is a promising high-throughput, low-cost method of mass producing micro- and nanodevices. For this study, we fabricated SiO2/Si dies having periodic nanodot structures with dot pitches of 50 nm and 40 nm by focused ion beam (FIB) assisted chemical vapor deposition (CVD), and reactive ion etching (RIE). We successfully nanoimprinted Pt-based metallic glass using these dies. The periodic nanohole structures were accurately imprinted due to the optimization of the loading and unloading thermal cycle conditions in the nanoimprinting process with the flattened and thinned metallic glass specimen. The results demonstrate the excellent capability of metallic glass as a nanoimprintable material for fabricating nanodevices such as patterned media.

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Plastic Working of Metallic Glass Bolts by Cold Thread Rolling

Shigeru Yamanaka, Kenji Amiya, Yasunori Saotome, Akihisa Inoue

pp. 243-249

DOI:

10.2320/matertrans.M2010292

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Bolts are commonly employed machine elements used for joining and fastening, and their performance and reliability influence the overall performance of machines. In this study, we have plastically worked and formed bolts using metallic glass (MG) that exhibits unique mechanical properties such as high tensile strength, low Young’s modulus, and large elastic limit. The large elastic limit increases the permissible elongation range of the bolt and helps avoid bolt loosening, while the low Young’s modulus effectively resists screwed-in bolt loosening by increasing the frictional forces on both bolt-nut contact area and bearing surface. We employed a zirconium-based MG Zr55Al10Cu30Ni5 for our experimental investigations. A pre-form of a hexagon socket head cap screw (bolt) was fabricated by squeeze casting. Cold and warm thread rolling were performed to form a metric screw thread M3×0.5 (class 6g (ISO)) below the glass transition temperature (Tg) using a flat rolling machine. Despite the extremely poor ductility of MG at room temperature, thread rolling was successfully performed. Straining behavior analysis by a three-dimensional finite element method demonstrated that these remarkable results are due to the compressive stress distribution induced during the thread rolling process. In addition, thread rolling is fundamentally an incremental process, and it enhances the deformability of MG by gradually improving ductility in the deformed region. The tensile strength of the thread-rolled bolt was approximately 1600 MPa, which is considerably higher than that of conventional heat-treated high strength steel bolts. MG was thus successfully employed to manufacture improved bolts.

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Characteristics of Fe-Cr-Al Alloy Nanopowders Prepared by Electrical Wire Explosion Process under Liquid Media

Jung-Yeul Yun, Hye-Moon Lee, Si-Young Choi, SangSun Yang, Dong-Won Lee, Young-Jin Kim, Byoung-Kee Kim

pp. 250-253

DOI:

10.2320/matertrans.M2010318

抄録

Fe-Cr-Al alloy nanopowders were successfully prepared by electrical wire explosion method in ethyl alcohol media. The formation of Fe-Cr-Al alloy nanopowder was monitored by X-ray diffraction. The alloy powders have spherical shape and nanometer size. The alloy powders prepared by the electrical wire explosion method have main crystal structures of bcc Fe-Cr alloy. The geometric mean diameter and geometric standard deviation of an alloy powder formed from a wire with diameter of 0.1 mm were 10.2 nm and 1.62, respectively. However, the geometric mean diameter and geometric standard deviation of an alloy powder formed from a wire with diameter of 0.2 mm were 15.4 nm and 1.66, respectively. These values indicate that the particle size of the alloy powders prepared by the EWE method was increased with wire diameter. Fe, Cr, and Al components are uniformly dispersed inside the powder.

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Liquation Cracking of Dissimilar Aluminum Alloys during Friction Stir Welding

Sang-Woo Song, Sang-Hoon Lee, Byung-Chul Kim, Tae-Jin Yoon, Nam-Kyu Kim, In-Bae Kim, Chung-Yun Kang

pp. 254-257

DOI:

10.2320/matertrans.M2010343

抄録

A liquation cracking mechanism of dissimilar Al alloys during the friction stir welding (FSW) is suggested in this study. To identify the mechanism, the precipitates were analyzed and Al-Mg-Cu phase diagrams were calculated. Electron backscattering diffraction (EBSD) analysis and electron probe microanalysis (EPMA) were also conducted. In the same manner as constitutional liquation, at high heating rate, the main liquation-inducing precipitates were not dissolved in the matrix and reacted with Al to form the partially melted zone (PMZ), after which liquation cracking occurred where strain was applied to the PMZ.

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Comparative Analysis of Trends Resulting from the Use of a Multi-Gaussian Curve Fitting Method Applied to the Visible Raman Spectra of Sputtered Amorphous Carbon

Ai-Lin Shen, Tse-Chuan Chou

pp. 258-260

DOI:

10.2320/matertrans.M2010234

抄録

This paper discusses the application of a direct integral area method and a multi-Gaussian curve fitting method to the interpretation of visible Raman spectra. A data analysis study was performed on three amorphous carbon films prepared by magnetron sputtering. Application of XPS, AES and the direct integration of the areas under the curves generated by visible Raman spectra, gave results that represented the diamond-like qualities of three amorphous carbon films in a similar manner, but the representation of data-trends using the multi-Gaussian curve fitting method was irregular. More specifically, we discovered that both the number of Gaussian curves applied, and the analytic regions chosen for analyzing the spectra affected the interpretation of the data obtained; our results indicate that the multi-Gaussian curve fitting method may give rise to inconsistent results when applied to the analysis of the visible Raman spectra of diamond-like (amorphous) carbon films.

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Preparation of Titanium-Chromium Nitride by Gas Nitriding of the Explosion Products of Cr-Coated Ti Wire

Sujeong Lee, Wonbaek Kim, Chang-yul Suh, Sung-wook Cho, Taegong Ryu, Je-shin Park, In-Jin Shon

pp. 261-264

DOI:

10.2320/matertrans.M2010284

抄録

Titanium-chromium nitride nanopowders were prepared by the electrical explosion of the Cr-coated Ti wires in argon and nitrogen gases and subsequent nitriding treatments. The explosion product of the Cr-coated Ti wire in argon gas consisted of α-Ti, TiCr2 and Ti-rich β phases. They transformed into single phase (Ti,Cr)N by the nitriding treatment at 1100°C. On the other hand, the explosion product of Cr-coated Ti wire in nitrogen gas consisted of TiN, Cr2N, and a few nanometer-sized (Ti,Cr)N particles. The particles transformed into the mixture of TiN and (Ti,Cr)N by the nitriding treatment at 1100°C. In this case, the pre-existing TiN in the explosion product was stable during nitriding and remained intact to coexist with newly-formed (Ti,Cr)N. The (Ti,Cr)N particles prepared by nitriding of the explosion product of Cr-coated Ti wire in nitrogen gas had 34.21 at% Ti, which was somewhat lower than 41.27 at% Ti of the (Ti,Cr)N produced by nitriding of the explosion product of Cr-coated Ti wire in argon gas. This is probably because high thermal stability of the pre-existing TiN in the explosion product of Cr-coated Ti wire in nitrogen gas creates a local titanium deficiency in the formation of (Ti,Cr)N particles.

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Some Aspects on the Discoloration and Antimicrobial Property of a Thermally Passivated Copper Surface in a Highly Humid Environment

An-Chou Yeh, Chin-Chuan Huang, Chih-Chen Hsiao, Te-Wei Chu, Yung-Chin Yang, Yi-Wei Feng, Kun-Yi Lin

pp. 265-267

DOI:

10.2320/matertrans.M2010339

抄録

Copper is being considered for touch surfaces applications, such as bathroom accessories, because of their antimicrobial property, which can potentially reduce infection transmission. Since thermal passivation method is widely applied on surface of copper to produce color for decorative purpose, bathroom and toilet interior designers are interested in knowing the property of passivated copper surface in high humidity environment. The present study investigates the discoloration and antimicrobial property of a thermally passivated surface of copper against Escherichia coli (E. coli) bacteria. The spectral colorimeter analysis has been conducted to evaluate the degree of surface discoloration, XRD analysis has been conducted to identify the phases on the surface, a method based on JIS Z 2801: 2000 has been utilized to evaluate the colony forming unit (CFU) of E. coli on sample surface.

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An Effective Anti-Discoloration Coating for Copper

An-Chou Yeh, Chin-Chuan Huang, Chih-Chen Hsiao

pp. 268-270

DOI:

10.2320/matertrans.M2010330

抄録

This article investigated the effectiveness of a newly developed anti-discoloration method for copper (C1100). The procedure involved diffusion of aluminum into the copper substrate and the subsequent formation of Cu-Al oxide spinels on the surface by a heat treatment. Samples of C1100 with and without surface treatment were subjected to ageing at 250°C for various length of time up to 40 min in order to promote surface discoloration due to oxidation. In addition, a commercially available anti-discoloration coating (C-107) was applied on testpieces for comparative studies. Tested samples were subjected to spectral colorimeter studies in order to determine the degree of discoloration occurred on the surface; microstructures and phase identifications were examined by SEM and XRD. In conclusions, the newly developed method exhibited potential to protect the surface of C1100, and its performance surpassed that of C-107.

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