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MATERIALS TRANSACTIONS Vol. 45 (2004), No. 1

ISIJ International
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678
Publisher: The Japan Institute of Metals and Materials

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MATERIALS TRANSACTIONS Vol. 45 (2004), No. 1

Effect of Bonding Character on Electron-Irradiation-Induced Chemical Disordering and Amorphization in III-V Compounds

Hidehiro Yasuda, Hirotaro Mori

pp. 2-4

Abstract

Single crystals of GaSb, GaAs and InAs were irradiated with 2 MeV electrons in the [001] direction in an ultrahigh voltage electron microscope. When electron irradiations were carried out in the semiconductor compounds kept at low temperatures, chemical disordering is first induced and with continued irradiation amorphization sets in. The chemical disordering and the resulting amorphization become more difficult to occur in the sequence of the increasing ionisity (GaSb → GaAs → InAs) at a fixed low temperature.

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Effect of Bonding Character on Electron-Irradiation-Induced Chemical Disordering and Amorphization in III-V Compounds

Giant Fullerene-Like Hollow Spheres Generated from Shock-Compressed C60 Fullerene by an Impact of Metal Flyer

Keisuke Niwase, Tomotaka Homae, Michiko Fujiwara, Kazutaka G. Nakamura, Ken-ichi Kondo

pp. 5-8

Abstract

C60 fullerene powder set into a stainless capsule was shock-compressed by using a powder gun. The capsule was compressed to 57 GPa by a W flyer with a velocity of 1.72 km/s. The recovered sample was investigated by scanning electron microscopy and Raman spectroscopy. We found the generation of fullerene-like carbon hollow spheres up to several μm in diameter on an internal hollow surface of the recovered sample. The spheres are significantly larger than fullerenes reported so far and are revealed to be in a highly graphitized state by Raman spectroscopy. Also we found exfoliation of the internal hollow surface at intervals. The formation mechanism of the carbon hollow spheres through a liquid phase is proposed.

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Giant Fullerene-Like Hollow Spheres Generated from Shock-Compressed C60 Fullerene by an Impact of Metal Flyer

The Recovery of Gas-Vacancy-Complexes in Fe Irradiated with High Energy H or He Ions

Toshitaka Ishizaki, Qiu Xu, Toshimasa Yoshiie, Shinji Nagata

pp. 9-12

Abstract

Isochronal annealing experiments for Fe irradiated with H or He ions were carried out to study interactions between gas atoms and vacancy clusters. The accelerating energy of H and He ions was 1.0 MeV and 3.3 MeV, respectively. The total dose was 1.0 × 1021 H ions/m2 (0.2 dpa) and 9.6 × 1019 He ions/m2 (0.3 dpa), and the irradiation temperature was 300°C. Positron annihilation lifetime and coincidence Doppler broadening (CDB) measurements were carried out after irradiation and annealing for 1 hour up to the complete recovery temperature. Microvoids were detected after H or He ion irradiation. The characteristic difference was mainly shown in the recovery of vacancy type defects. The recovery of vacancy type defects introduced by H ion irradiation finished completely at 450°C, while that by He ion irradiation finished at 1000°C. It suggests that H-vacancy complexes were less stable than He-vacancy complexes. In addition, vacancy clusters formed by He ion irradiation grew after annealing at 600°C. This was caused by the emission of He atoms from small He-vacancy clusters and the coalescence between free vacancies and vacancy clusters, and by the migration and coalescence of He bubbles.

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The Recovery of Gas-Vacancy-Complexes in Fe Irradiated with High Energy H or He Ions

Electron Irradiation Induced Crystallization of the Amorphous Phase in Zr-Cu Based Metallic Glasses with Various Thermal Stability

Takeshi Nagase, Yukichi Umakoshi

pp. 13-23

Abstract

The phase stability of the amorphous phase against electron irradiation and the crystallization behavior under electron irradiation were investigated in Zr-Cu based metallic glasses. The phase stability of the amorphous phase against thermal crystallization, i.e., thermal stability was evaluated by the temperature range of supercooled liquid region (ΔTx). The ΔTx values for Zr66.7Cu33.3, Zr65.0Al7.5Cu27.5 and Zr65.0Al7.5Ni10.0Cu17.5 alloys were 54K, 89K and 119K, respectively. The amorphous phase of Zr-Cu based metallic glasses was not stable under electron irradiation. The crystallization of fcc-Zr2Cu phase was accelerated by electron irradiation instead of bct-Zr2Cu phase which appeared during thermal annealing. The increase in the thermal stability of the amorphous phase is effective for the decrease in the crystallization rate under electron irradiation, but not always effective in suppressing the occurrence of electron irradiation induced crystallization.

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Electron Irradiation Induced Crystallization of the Amorphous Phase in Zr-Cu Based Metallic Glasses with Various Thermal Stability

Metastable Defect Cluster Formation during Radiation-Induced Amorphization in NiTi

Seiichi Watanabe, Takuto Koike, Takanori Suda, Soumei Ohnuki, Heishichirou Takahashi, Nghi Q. Lam

pp. 24-28

Abstract

Chemical and topological disorderings in the NiTi intermetallic compound during electron irradiation were studied using a combination of in situ irradiation inside a high-resolution high-voltage electron microscope and image analyses of molecular-dynamics-simulated atom configurations. It was found that metastable defect clusters formed during the chemical-disordering phase prior to topological disordering leading to amorphization. These planar defect clusters contributed to the characteristic diffuse scattering were also observed in selected-area diffraction patterns.

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Metastable Defect Cluster Formation during Radiation-Induced Amorphization in NiTi

Effect of Fast Neutron Irradiation on the Microstructure in Particle Dispersed Ultra-fine Grained V-Y Alloys

Sengo Kobayashi, Yusuke Tsuruoka, Kiyomichi Nakai, Hiroaki Kurishita

pp. 29-33

Abstract

An alloy having ultra-fine grains with dispersed particles is expected to have the resistance of irradiation embrittlement. We examine the microstructures of V-1.6 and 2.6Y alloys, having ultra-fine grains with dispersed particles, after neutron irradiation at temperatures between 290 and 800°C. The grain size was the level of a few hundreds of nanometers, and the size in diameter of V-2.6Y alloy was much smaller than that of V-1.6Y alloy, where the irradiation did not change the size. The number density of particles in V-2.6Y alloy was higher than that in V-1.6Y alloy. Voids were formed only at 290°C, where the number density of voids in V-2.6Y alloy was smaller than that in V-1.6Y alloy. The void formation was efficiently suppressed due to fine-grains and dispersed particles.

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Effect of Fast Neutron Irradiation on the Microstructure in Particle Dispersed Ultra-fine Grained V-Y Alloys

Bias Mechanism and Its Effects for Fundamental Process of Irradiation Damage

Eiichi Kuramoto, Kazuhito Ohsawa, Junichi Imai, Kiyokazu Obata, Tetsuo Tsutsumi

pp. 34-39

Abstract

In order to obtain the better understanding for bias effects under irradiation computer simulation was made and the basic view for the dislocation bias was presented from the formation energy of radiation induced defects. It was shown that the difference of the formation energy between a self-interstitial atom and a vacancy is the most basic origin for the dislocation bias. On the other hand, for the production bias the detailed information on interstitial clusters is required and it was found in Fe model lattice that the edge dislocation line has a special character, i.e., a periodicity of b/3, but in the case of dislocation loops these stable positions distributed with a periodicity b/3 diffuse out with decreasing loop size and tend to have a periodicity of nearly b in the smaller limit of loop size. This behavior suggests that Peierls potentials which dislocation loops must overcome depend upon the loop size, and smaller Peierls stress can be expected for larger loops and an edge dislocation line probably because of finer periodicity b/3. But at finite temperatures small clusters of crowdions easily tend to have a rather loose coupling structure of composing crowdions, and slip motion as a whole cluster is not well defined, and the diffusion process as a whole might be better to represent the motion of small clusters at high temperatures.

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Bias Mechanism and Its Effects for Fundamental Process of Irradiation Damage

Effects of Grain Boundary Misorientation on Radiation-Induced Solute Segregation in Proton Irradiated 304 Stainless Steels

Ji Jung Kai, Fu Rong Chen, Ting Shien Duh

pp. 40-50

Abstract

This paper describes the effects of the grain boundary misorientation on the radiation induced segregation (RIS) in proton irradiated 304 stainless steels. Experimentally, four test conditions were used for the 304 stainless steel specimens: (1) As-received (AR) with enriched Cr at grain boundary, (2) AR + 1 dpa proton irradiated at 450°C, (3) Thermal sensitized (SEN), and (4) SEN + 1 dpa proton irradiated at 450°C. Compared with no pre-enrichment condition, a delayed Cr depletion was found at grain boundaries in AR + 1 dpa specimens. After irradiation, the Cr concentration profile across grain boundaries became narrower and deeper in SEN + 1 dpa specimens. The degree of grain boundary segregation was observed to be higher at random boundaries than special boundaries. In the case of SEN + 1 dpa specimens, the segregation cusps were observed at grain boundaries of Σ 3, Σ 9 and Σ 15, and the Cr segregation levels at special boundaries were increasing with Σ for value up to Σ = 15. Theoretically, a simple rate equation model with modified boundary conditions, which were related to the grain boundary diffusion of defects and the densities of the grain boundary dislocations, was developed for RIS at boundaries with different Σ and Δθ. The model calculations showed that the RIS model with modified boundary conditions could predict clearly the same trend as that of experiments, in which the Cr depletion levels at special boundaries in irradiated 304 stainless steels were increasing with Σ. The model calculations also showed that the widths of the segregation cusps were decreasing with increasing Σ.

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Effects of Grain Boundary Misorientation on Radiation-Induced Solute Segregation in Proton Irradiated 304 Stainless Steels

Radiation Damage Study by Advanced Dual-Ion Irradiation Methods

Akira Kohyama, Yutai Katoh, Kouichi Jimbo

pp. 51-58

Abstract

For the systematic materials research for advanced energy systems, integrated research facilities are essential. As the part of the SPIRE Center, IAE, Kyoto University, Dual-ion irradiation experimental facility for energy research, DuET, has been established and operated. Its outstanding advantages are its wide flexibilities and excellent controllabilities in radiation damage studies. The design concept and the current features of the DuET facility are introduced followed to the brief introduction of the SPIRE center. Its contribution to the radiation damage studies is presented connecting with the DuET characteristics. As the typical outputs from the DuET, radiation damage effects on SiC/SiC composites, reduced activation ferritic steels, are provided. As the powerful tool to simulate neutron damage as functions of neutron energy, neutron flux, neutron fluence, irradiation environments and their combinations, application methodologies of DuET are presented and the clear insights of the radiation damage processes only obtainable from this facility are indicated.

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Radiation Damage Study by Advanced Dual-Ion Irradiation Methods

Effect of He-Injection on Irradiation Damage in Heat Affected Zone of Welded SUS304 Steel

Dong-Su Bae, Hiroshi Kinoshita, Tamaki Shibayama, Heishichiro Takahashi

pp. 59-64

Abstract

The heat affected zone (HAZ) of welded SUS304 steel has been irradiated using three irradiation modes of electron single irradiation, electron irradiation after He-injection and electron /He ion dual-beam irradiation by 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. Void size in the specimen with pre-injected helium increased considerably and the void size distribution was a bi-modal. Void swelling is the highest in the case of electron irradiation after He-injection. The segregation of solutes of Ni and Cr near grain boundary was suppressed in the cases of electron/He+-ion dual-beam and electron irradiation after He-injection comparing with electron single irradiation.

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Effect of He-Injection on Irradiation Damage in Heat Affected Zone of Welded SUS304 Steel

Plane and Cross-Sectional TEM Observation to Clarify the Effect of Damage Region by Ion Implantation on Induced Phase Transformation in Austenitic 301 Stainless Steel

Dwi Gustiono, Norihito Sakaguchi, Tamaki Shibayama, Hiroshi Kinoshita, Heishichiro Takahashi

pp. 65-68

Abstract

Phase transformation in austenitic 301 stainless steel was studied under 300 keV Fe+ and Ar+ ions implantations to fluence of 1×1021 ions m-2 at room temperature, in order to pursuit the nucleation of martensitic phase transformation in ion-implanted region. Microstructures after ion implantation were observed by transmission electron microscopy (TEM) with plane view and for cross-sectional specimens. The plane view observation of the implanted specimen showed that phase transformation from the γ phase to α phase was induced due to implantation to doses of 5×1020 Fe+ ions m-2 and 1×1020 Ar+ ions m-2. The nucleation of implantation-induced phase increased with increasing of fluence. The orientation relationship between the γ matrix and the induced α phase was identified to be (110)α || (111)γ and [111]α || [011]γ, close to the Kurdjumov-Sachs (K-S) for the Fe+ ion implanted specimen, and (110)α || (111)γ and [001]α || [011]γ close to the Nishiyama-Wasserman (N-W) for the Ar+ ion implanted specimen. The cross-sectional observation after implantation revealed that the phase transformation preferentially nucleated in the region near the surface in metal (Fe+) ion implanted specimen, because the gradient of implanted ion concentration attains maximal near the surface. On the other hand, the behavior of phase transformation in the Ar+ ion implanted specimen was different from that of Fe+ ion implantation and the phase was induced at deeper region from surface than Fe+ ion case.

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Plane and Cross-Sectional TEM Observation to Clarify the Effect of Damage Region by Ion Implantation on Induced Phase Transformation in Austenitic 301 Stainless Steel

Improvement of Mechanical Properties of 7475 Based Aluminum Alloy Sheets by Controlled Warm Rolling

Hiroki Tanaka, Hiroki Esaki, Kenji Yamada, Kazuhisa Shibue, Hideo Yoshida

pp. 69-74

Abstract

An attempt was made to refine the grain structure of 200 mm wide sheets of AA7475 based aluminum alloys containing zirconium by employing a new warm rolling method under the control of both roll temperature and material temperature. The warm rolled sheets as solution heat treated had subgrain structures through the thickness with a high proportion of low angle boundary less than 15°. The average subgrain diameter was approximately 3 μm. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional AA7475 alloy sheets produced by cold rolling. As the most remarkable point in the warm rolled sheets, the high Lankford (r) value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed β-fiber textures, especially with the strong {011} ‹211› Brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.

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Improvement of Mechanical Properties of 7475 Based Aluminum Alloy Sheets by Controlled Warm Rolling

Effects of Ni Addition on the Mechanical and Electrical Properties of Cu-15 mass%Cr In-Situ Composites

Tetsuji Nihei, Hirowo G. Suzuki, Masaharu Kato, Jusheng Ma

pp. 75-80

Abstract

Effects of Ni and Al addition on the mechanical and electrical properties in the Cu-15 mass%Cr in-situ composite are examined. The process consists of melting, hot forging, heavy cold rolling and aging. Ni is partitioned into the Cr phase to make an intermetallic precipitates. The Cr phase in the Cu-15 mass%Cr-10 mass%Ni shows 3.6 times harder compared with the Cu matrix resulting in the poor cold drawability and low strength. The addition of 1 mass% Ni and 0.15 mass%Al is recommended to get good cold drawability and high strength, but it is necessary to make a compound such as Ni3Al to increase the electrical conductivity.

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Effects of Ni Addition on the Mechanical and Electrical Properties of Cu-15 mass%Cr In-Situ Composites

Preparation of Cobalt Ferrite Nanoparticles by Hydrolysis of Cobalt-Iron (III) Carboxylate Dissolved in Organic Solvent

Yasuhiro Konishi, Toshiyuki Nomura, Kazunari Mizoe, Kazutaka Nakata

pp. 81-85

Abstract

Magnetic cobalt ferrite (CoFe2O4) nanoparticles were prepared by hydrolysis of non-aqueous cobalt-iron(III) carboxylate solution with water. When the initial concentrations of cobalt and iron(III) in the starting solution were 0.075kmol/m3 and 0.15kmol/m3, the complete precipitation of cobalt ferrite was achieved within 20 min at 190°C and 1.3 MPa. The resulting cobalt ferrite particles were free from contamination by the organic starting materials. The particle size of cobalt ferrite drastically decreased from 110 nm to 13 nm as the stirring speed of the starting solution increased from 200 to 800 rpm. The magnetic properties of the resulting cobalt ferrite particles were dependent on the particle size, and the magnetization at a magnetic field of 0.8 MA/m and the coercive force were 51.7μWb·m/kg and 4.8kA/m for the ferrite nanoparticles of 13 nm.

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Preparation of Cobalt Ferrite Nanoparticles by Hydrolysis of Cobalt-Iron (III) Carboxylate Dissolved in Organic Solvent

Infrared Absorption Enhancement of Octadecanethiol on Colloidal Silver Particles

Toshimasa Wadayama, Hirochika Yano, Yusuke Sasaki, Jun-ichi Takahashi, Aritada Hatta

pp. 86-91

Abstract

Infrared absorption measurements at normal incidence of radiation have been carried out on octadecanethiol (ODT) deposited from ethanol-water mixed solutions onto colloidal silver particles (ca. 30 nm diameter) on Si(111) substrates. The infrared absorption spectra taken as functions of silver mass thickness and ODT concentration show that the intensities of the CH2 asymmetric and symmetric stretch modes of ODT are twice enhanced in comparison to those observed in the absence of the particles. The spectra also reveal that at any ODT concentration the absorption intensities exhibit a maximum for a particular mass thickness of the particles, indicating that the enhancement is linked to the aggregation of the particles. Contribution of the surface plasmon resonance apparently does not play a major role in the present systems. Approximately the same magnitude of enhancement is obtained for silver hydrosol particles exposed to ODT from the solution followed by depositing on the substrates. Scanning electron morphological inspection has been done on the aggregates in relation to the enhancement.

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Infrared Absorption Enhancement of Octadecanethiol on Colloidal Silver Particles

Evaluation of Microfracture Mode in Ceramic Coating during Thermal Cycle Test using Laser AE Technique

Satoshi Nishinoiri, Manabu Enoki, Koichi Tomita

pp. 92-101

Abstract

We have investigated the technique to detect acoustic emission (AE) signal using a laser interferometer, which can directly detect the surface velocity due to microcracking. Thermal cycle test for Al2O3/NiCrAlY/SUS304 coatings using an infrared image furnace was carried out in order to evaluate the failure process. Laser AE measurement system was improved to increase the sensitivity of AE monitoring for coatings. Microfracture mode during thermal cycle test was analyzed based on the measured AE behavior and a finite element method (FEM) simulation of wave propagation. From the result of waveform analysis, it was found that shear mode microfracture occurred toward the center from one of the edges of the specimen. This result agreed with the propagation direction of delamination determined from AE location results and the observation of the specimen after the thermal cycles were loaded.

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Evaluation of Microfracture Mode in Ceramic Coating during Thermal Cycle Test using Laser AE Technique

Effects of Compressive Stress on Corrosion-Protective Quality and Its Maintenance under a Corrosive Environment for TiN Films Deposited by Reactive HCD Ion Plating

Ken’ichi Miura, Itsuo Ishigami, Tateo Usui

pp. 102-111

Abstract

Titanium nitride films were deposited onto SUS304 substrates under various film thickness, deposition temperatures, and substrate bias voltages. Their protective quality was evaluated by electrochemical testing in accordance with the critical passivation current density (CPCD) method. Two types of tests were employed to evaluate corrosive behavior of coated substrates: a high-temperature and high-pressure corrosion test; and a measurement of the change in anodic current density with immersion time. A scanning electron microscope was used to examine surface morphology and fractured cross-sections of the films. Residual stress in the films was determined by the sin2 ψ method. An increase in film thickness engendered high protective quality. That protective quality was improved with increasing deposition temperature; micrometer-order pores were observed on all parts of films deposited at lower deposition temperatures, whereas few pores existed on films deposited at higher temperatures. This result indicates that these pores are one factor influencing overall protective quality. A film deposited with no substrate bias voltage displayed morphology with a typical columnar-structure; it also demonstrated complete protective quality. As the bias voltage increased, protective quality deteriorated, whereas an excess increase in the bias voltage gave rise to a slightly higher protective quality. Films with lower compressive stress had only a few pores and possessed higher protective quality, suggesting that pore formation originates in compressive stress. Corrosion tests indicated that the coated substrates corroded more rapidly as compressive stress in the film increased. The effect of compressive stress on maintenance of corrosion-protective quality was treated quantitatively. The rate of increase in the exposed area of the substrate was estimated from variation of an anodic current density with immersion time. This evaluation indicates that a decrease in compressive stress contributes greatly to maintenance of protective quality.

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Effects of Compressive Stress on Corrosion-Protective Quality and Its Maintenance under a Corrosive Environment for TiN Films Deposited by Reactive HCD Ion Plating

Torsion and Tensile Properties of Thin Wires of Nickel-Free Stainless Steel with Nitrogen Absorption Treatment

Daisuke Kuroda, Takao Hanawa, Takaaki Hibaru, Syuji Kuroda, Masaki Kobayashi

pp. 112-118

Abstract

A new manufacturing process for nickel-free austenitic stainless steel has been developed by authors. In combination with machining and a nitrogen absorption treatment, this process makes it possible to form small precise devices with a maximum thickness or diameter of 4 mm. The refinement of grains of Fe-24Cr-2Mo in mass% was attempted by thermo-mechanical treatment before nitrogen absorption treatment in order to increase the mechanical properties after nitrogen absorption treatment. Torsion and tensile properties and microstructures of Fe-24Cr-2Mo before and after nitrogen absorption treatment were evaluated to understand the effects of grain refinement on nitrogen absorption. The thin wire of the alloy is completely austenitized with nitrogen absorption at 1473 K for over 7.2 ks. The mean grain size of the alloy with nitrogen absorption decrease with the grain refinement process attempted in this study. The values of ultimate tensile strength and elongation in the alloy with and without nitrogen absorption increase with the grain refinement process. The torsional stress and rotation angle to fracture of the alloy increase with the grain refinement process and nitrogen absorption. According to the results of the torsion and tensile tests, the thin wire of the alloy with nitrogen absorption is expected to have good mechanical properties than conventional austenitic stainless steels.

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Torsion and Tensile Properties of Thin Wires of Nickel-Free Stainless Steel with Nitrogen Absorption Treatment

Elasticity Study of Nanostructured Al and Al-Si(Cu) Films

Yoshio Kabe, Hisanori Tanimoto, Hiroshi Mizubayashi

pp. 119-124

Abstract

In order to get an insight into the elastic property of nanostructured fcc metal films, the Young’s modulus, Ef, and the internal friction, Q-1f, in Al-Si(Cu)sp and Alsp films prepared by rf-sputtering and those in Al-Si(Cu)ve and Alve films by vacuum evaporation were studied for the thickness, d, range of 4 to 300 nm, where the mean grain size was below 40 nm. A decrease in Ef and an increase in Q-1f with decreasing d associated with the grain boundary anelastic process (GBAP) activated above 200 K are commonly observed. GBAP in the nanostructured Al is hardly modified by alloying with Si and Cu, and is very similar to GBAP reported in nanostructured Ag and Au. It is indicated that the elastic property of Al-Si(Cu)sp, Alsp, Al-Si(Cu)ve and Alve nanocrystalline films is governed by GBAP, the internal stress and the surface oxide layer.

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Elasticity Study of Nanostructured Al and Al-Si(Cu) Films

Orientation Rotation Behavior in Aluminum Alloys during Dissimilar Channel Angular Pressing

Jun-Hyun Han, Jin-Yoo Suh, Kyu Hwan Oh, Jae-Chul Lee

pp. 125-130

Abstract

The crystallographic orientation rotation behaviors in aluminum alloys during dissimilar channel angular pressing (DCAP) were investigated. Experiments were conducted to observe the texture evolution due to DCAP. Texture simulation using the full constraint Taylor calculations based on the rate sensitivity model was also carried out both to explain the experimental results and to elucidate the rotation behaviors of the individual orientations due to DCAP.

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Orientation Rotation Behavior in Aluminum Alloys during Dissimilar Channel Angular Pressing

Characterization of Surface of Amorphous Ni-Nb-Ta-P Alloys Passivated in a 12 kmol/m3 HCl Solution

Asahi Kawashima, Takeaki Sato, Naoshi Ohtsu, Katsuhiko Asami

pp. 131-136

Abstract

The melt-spun amorphous (Ni60Nb40-xTax)0.95P5 alloys containing 15 at% or more tantalum are spontaneously passivated in a 12 kmol/m3 HCl solution open to air at 303 K. Their open circuit potentials are nobler than that of pure tantalum metal. The amorphous alloys with 10 at% or less tantalum, however, show the active-passive transition. XPS analysis revealed that the spontaneous passive films are rich in tantalum and niobium cations and deficient in nickel cation. Thickness of the spontaneously passivated film is much thinner than that of less protective film on low tantalum-bearing alloys for prolonged immersion, indicating the passive film is highly dense and stable. Thus the high corrosion resistance of the alloys with high tantalum content is attributed to the formation of highly stable and protective passive film enriched mainly with tantalum cation.

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Characterization of Surface of Amorphous Ni-Nb-Ta-P Alloys Passivated in a 12 kmol/m3 HCl Solution

Effects of Austenite Conditioning on Austenite/Ferrite Phase Transformation of HSLA Steel

Yang H. Bae, Jae Sang Lee, Jong-Kyo Choi, Wung-Yong Choo, Soon H. Hong

pp. 137-142

Abstract

Effects of surface area of prior austenite grain boundaries and deformation bands on austenite/ferrite phase transformation of high strength low alloy (HSLA) steel during hot working were investigated through simulated hot workings using Gleeble 1500. Effective surface areas were controlled by applying different austenite conditionings. It was found that the volume fraction of strain induced dynamic transformation (SIDT) ferrites increased with an increase in the effective surface area. The volume fraction of SIDT ferrite nucleated from the elongated prior austenite grains, however, was higher than that nucleated from equi-axed prior austenite grains at the same effective surface area. From the experiment results and discussions, it was concluded that diffusional austenite/ferrite phase transformation of HSLA steel by the interface nucleation and growth mechanism is accelerated by the deformation bands in the non-recrystallization region.

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Effects of Austenite Conditioning on Austenite/Ferrite Phase Transformation of HSLA Steel

Mechanical Properties of Fine-Grained, Sintered Molybdenum Alloys with Dispersed Particles Developed by Mechanical Alloying

Tomohiro Takida, Hiroaki Kurishita, Mamoru Mabuchi, Tadashi Igarashi, Yoshiharu Doi, Takekazu Nagae

pp. 143-148

Abstract

In order to develop Mo alloys with improved mechanical properties of low-temperature toughness and room- and high-temperature strengths without any plastic working after consolidation, fine-grained, particle-dispersed Mo alloys were fabricated by hot isostatic pressing (HIP) or spark plasma sintering (SPS) of mechanically alloyed powders of Mo and 0.8 mol% ZrC or TaC (designated as ZRC08 and TAC08). The fabricated Mo alloys were subjected to high-temperature annealing for 3.6 ks up to 2470 K, three-point impact bending tests at temperatures from 270 to 470 K at 5 m s-1 and static tensile tests at temperatures from 300 to 1970 K at initial strain rates from 4.2 × 10-5 to 8.3 × 10-2 s-1. The fabricated alloys exhibited no significant grain growth even after annealing at 2470 K for 3.6 ks due to the pinning effect of the particles against grain boundary migration. The ductile-to-brittle transition temperatures (DBTT) assessed by impact bending were lower and the tensile strengths up to 1770 K were higher for the fabricated alloys than for recrystallized pure Mo. In particular, HIPed TAC08 was superior in low-temperature toughness having the DBTT lower by 30-40 K than recrystallized Mo-La2O3 (TEM) with an elongated coarse-grained microstructure. HIP- or SPS-treated ZRC08 was superior in room- and high-temperature strengths, respectively. Furthermore, HIPed ZRC08 showed a large elongation of 551% at 1770 K. These excellent mechanical properties of the fabricated Mo alloys were obtained for the first time in the as-consolidated state without subsequent plastic working, and are attributable to fine-grained microstructure and grain-boundary strengthening by the fine particles.

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Mechanical Properties of Fine-Grained, Sintered Molybdenum Alloys with Dispersed Particles Developed by Mechanical Alloying

Formation of Icosahedral Clusters and Spin Freezing in RE(Fe1-xAlx)13 Amorphous Alloys

Te-Hsuan Chiang, Motoki Ohta, Asaya Fujita, Kazuaki Fukamichi, Eiichiro Mastubara

pp. 149-156

Abstract

The formation of icosahedral clusters in RE(Fe1-xAlx)13 (RE: La, Y, Ce and Lu) amorphous alloys have systematically been investigated. The spin-glass behavior and the magnetic phase diagrams are closely related with the interatomic distance of Fe-Fe pair in the icosahedral clusters formed in the amorphous phases. The existence of icosahedral clusters in the RE(Fe1-xAlx)13 amorphous alloys was confirmed by X-ray diffraction, although the formation in the crystalline state restricts to only RE = La. Mössbauer spectra were also found to be consistent with the X-ray diffraction data. The nearest interatomic distance, 0.255 nm, of Fe-Fe pair in the icosahedral clusters is unchanged in the RE(Fe1-xAlx)13 amorphous alloys and hardly depends on the kind of RE elements. Such a short distance brings about a re-entrant spin-glass state due to the appearance of antiferromagnetic interactions, and the spin freezing temperature is scarcely affected by the variety of RE elements. On the other hand, the Curie temperature depends on the atomic size of REs.

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Formation of Icosahedral Clusters and Spin Freezing in RE(Fe1-xAlx)13 Amorphous Alloys

New Electrically Conductive Adhesives Filled with Low-Melting-Point Alloy Fillers

Jong-Min Kim, Kiyokazu Yasuda, Masahiro Rito, Kozo Fujimoto

pp. 157-160

Abstract

A new class of electrically conductive adhesives (ECAs) has been developed using two different resin materials and a low-melting-point alloy filler powder. The curing or cross-linking behaviors of base resin materials and the melting behavior of filler metal were examined using a differential scanning calorimetry (DSC) instrument. The effects of the reduction capability of base resin material, metal filler volume fraction, and joint height on the coalescence of filler, and morphology of conductive path were examined using a cross-sectional optical laser microscope. The two different types of conductive paths (necking-type and bump-type) were achieved by the coalescence and wetting characteristics of melted fillers into new formulations. The results show a good metallurgical connection and a low contact resistance even at a low filler metal volume fraction of 30%.

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Article Title

New Electrically Conductive Adhesives Filled with Low-Melting-Point Alloy Fillers

Microstructure Control of Fiber-like TiN Particles in Hot Pressed Si3N4-O’SiAlON-TiN Composites

Byong-Taek Lee, In-Cheol Kang, Jae-Kil Han, Ik-Hyun Oh

pp. 161-164

Abstract

The microstructure control of TiN particles in hot pressed Si3N4-O’SiAlON-TiN composites was investigated using waste-Si and sponge Ti powders, dependent upon the ball milling and attrition milling processes. The composites were composed of multi-phases, including β-Si3N4, O’SiAlON and TiN phases regardless milling process used. In the composite using ball milling, TiN particles kept the original shape of sponge Ti powder and included many residual pores. Many microcracks were observed at the interfaces of Si3N4/TiN interfaces due to the difference of their thermal expansion coefficients. However, in the composite using attrition milling, the morphology of TiN particles was changed to a fiber shape, without residual pores and microcracks.

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Article Title

Microstructure Control of Fiber-like TiN Particles in Hot Pressed Si3N4-O’SiAlON-TiN Composites

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