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MATERIALS TRANSACTIONS Vol. 55 (2014), No. 5

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. 55 (2014), No. 5

New Aspects of Ecomaterials from the Viewpoints of the Consumer and Regional Communities

Osamu Umezawa, Yoshikazu Shinohara, Kohmei Halada

pp. 745-749

DOI:

10.2320/matertrans.MB201302

Abstract

The concept and new categorization of environmentally conscious materials, ecomaterials, is proposed. Advanced steps ranging from high eco-efficiency of products, to consumer-oriented and regional community adaptation are introduced. An additional new concept, the robust design of materials, is also proposed as part of a new range of activities in ecomaterials.

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New Aspects of Ecomaterials from the Viewpoints of the Consumer and Regional Communities

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Preparation, Properties and Microstructure of SiC Particle Reinforced Al–Si Matrix Composite

Shiming Hao, Jingpei Xie, Aiqin Wang, Ming Fang

pp. 750-753

DOI:

10.2320/matertrans.M2013473

Abstract

The SiC particles reinforced Al–30Si matrix composite was fabricated by vacuum hot pressing techniques. Mechanical properties of the composite were measured, and the microstructure was observed using SEM, XRD, and TEM. The results show that SiC particles and Si particles were dispersed uniformly in the matrix, the interfaces of the SiC/Si, SiC/Al, and the Si/Al are good and did not find the formation of Al4C3; composites have a low coefficient of thermal expansion (10.4 × 10−6 K−1) and decent tensile strength (192 MPa). The analysis of the fractograph reveals the fracture mechanism of SiC particle reinforced Al–Si matrix composite. The fracture of composite is primarily dominated by the fracture of brittle Si/SiC particles and the subsequent link up of damage through the matrix.

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Preparation, Properties and Microstructure of SiC Particle Reinforced Al–Si Matrix Composite

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Internal Friction of an Ag–In–Yb Icosahedral Quasicrystal

Kenma Handa, Yeong-Gi So, Yasushi Kamimura, Ryuji Tamura, Keiichi Edagawa

pp. 754-757

DOI:

10.2320/matertrans.M2013448

Abstract

Internal friction has been measured for an Ag–In–Yb Tsai-type icosahedral (i-) quasicrystal to investigate an energy-dissipation mechanism by phason relaxation, possibly operating in quasicrystals. A fairly large peak of the magnitude Q−1 ≈ 0.022 was observed, which was shown to be of the thermally-activated relaxation type. The frequency factor and activation enthalpy were evaluated to be 1020 s−1 and 2.6 × 10−19 J (1.6 eV), respectively. The observed peak was analyzed on the assumption that it is of phason-origin. The magnitude of the phonon-phason coupling constant was estimated to be 0.008μ (μ: shear modulus), based on the model of the phonon-phason elastodynamics previously proposed. This value is comparable to those previously reported for Mackay-type i-phases such as i-Al–Pd–Mn and i-Al–Cu–Fe.

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Internal Friction of an Ag–In–Yb Icosahedral Quasicrystal

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Electrical Properties and Carrier Transport Mechanism of Au/n-GaN Schottky Contact Modified Using a Copper Pthalocyanine (CuPc) Interlayer

V. Janardhanam, I. Jyothi, Ji-Hyun Lee, Jae-Yeon Kim, V. Rajagopal Reddy, Chel-Jong Choi

pp. 758-762

DOI:

10.2320/matertrans.M2013449

Abstract

We investigated the electrical characteristics of Au/n-GaN Schottky rectifier incorporating a copper pthalocyanine (CuPc) interlayer using current–voltage (I–V), capacitance–voltage (C–V) and conductance–voltage (G–V) measurements. The barrier height of the Au/CuPc/n-GaN Schottky contact was higher than that of the Au/n-GaN Schottky diode, indicating that the CuPc interlayer influenced the space charge region of the n-GaN layer. The series resistance of Au/CuPc/n-GaN Schottky contact extracted from the C–V and G–V methods was dependent on the frequency. In addition, the series resistance obtained from C–V and G–V characteristics was comparable to that from Cheung’s method at sufficiently high frequencies and in strong accumulation regions. The forward log I–log V plot of Au/CuPc/n-GaN Schottky contact exhibited four distinct regions having different slopes, indicating different conduction mechanisms in each region. In particular, at higher forward bias, the trap-filled space-charge-limited current was the dominant conduction mechanism of Au/CuPc/n-GaN Schottky contact, implying that the most of traps were occupied by injected carriers at high injection level.

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Electrical Properties and Carrier Transport Mechanism of Au/n-GaN Schottky Contact Modified Using a Copper Pthalocyanine (CuPc) Interlayer

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Aging Effect on Microstructure of Cold Groove-Rolled α′-Type Ti–12 mass%V–2 mass%Al Alloys Studied by Transmission Electron Microscopy

Kazuhisa Sato, Hiroaki Matsumoto, Akihiko Chiba, Toyohiko J. Konno

pp. 763-767

DOI:

10.2320/matertrans.M2013463

Abstract

Microstructure and phase decomposition of hexagonal α′ martensite in cold groove rolled (CGR) Ti–12 mass%V–2 mass%Al alloys have been studied by transmission electron microscopy and electron diffraction. Acicular structure of the α′ martensite changes into equiaxed α′ grains by CGR with a cold reduction of 75%. After aging at 573 K for 500 h, local Moiré fringes disappear and diffraction rings become sharp due to recovery. However, Vickers hardness also increased in spite of the recovery. Partitioning of solute atoms and/or formation of fine precipitates can be possible cause for the observed age-hardening. Although a CGR alloy is characterized by a microstructure with polycrystalline equiaxed grains, following orientation relationship is locally observed between β precipitates and α grains after aging at 673 K: (101)β // (01−1−1)α , [010]β // [10−11]α . Electron tomography revealed a heterogeneous nucleation and growth of β precipitates in the deformed α′ matrix.

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Aging Effect on Microstructure of Cold Groove-Rolled α′-Type Ti–12 mass%V–2 mass%Al Alloys Studied by Transmission Electron Microscopy

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Thermal Stability and Transition Behavior of Nanoclusters during Two-Step Aging at 250°C in Al–Mg–Si(–Cu) Alloys

JaeHwang Kim, SeongNyeong Kim, Equo Kobayashi, Tatsuo Sato

pp. 768-773

DOI:

10.2320/matertrans.M2013411

Abstract

Two types of nanoclusters, Cluster (1) and Cluster (2), play an important role in the age-hardening behavior in Al–Mg–Si alloys. Both Cluster (1) formed during natural aging at room temperature and Cluster (2) formed during pre-aging at 100°C cause the higher hardness and higher number density of the β″ phase during the two-step aging at 250°C than those of the single-aged specimen. Both of Cluster (1) and Cluster (2) result in the positive effect of two-step aging even though the mechanism is different. The positive effect of two-step aging for the naturally-aged specimen is caused by the atomic rearrangement from Cluster (1) to the Pre-β″ phase at the early stage of aging at 250°C. On the other hand, Cluster (2) is stable up to 250°C and directly transforms into the β″ phase. The thermal stability of nanoclusters and their transition behavior are discussed based on the age-hardening phenomena.

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Thermal Stability and Transition Behavior of Nanoclusters during Two-Step Aging at 250°C in Al–Mg–Si(–Cu) Alloys

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In Situ and Real-Time Observation of the Solidification Process of Al–20 mass%Cu Alloy by Synchrotron X-ray Radiography

Maodong Kang, Haiyan Gao, Da Shu, Jun Wang, Faguo Li, Yanan Fu, Lishibao Ling, Baode Sun

pp. 774-778

DOI:

10.2320/matertrans.M2014034

Abstract

High brilliance synchrotron X-ray radiography has been used to in situ study the solidification process of Al–20 mass%Cu alloy with nominal spatial and temporal resolutions of 7.4 µm and 300 ms, respectively. The block of favorably oriented dendrites by the unfavorably oriented ones was first observed in metal solidification, which related to solute interaction of neighbor dendrites. Solute interaction can also retard the growth of dendrites at the grain boundary, which makes the unusual overgrowth phenomenon possible. Fragmentation occurred when dendrite branches were detached from mother dendrite by local re-melting during the dendrite ripening. Fragmentations together with nucleated dendrites contributed to the columnar to equiaxed transition (CET) and the gravity played a significant role in the final microstructure due to the density difference between primary aluminum dendrites and the melt. In addition, the microporosity formation was observed in the inter-dendrite at the last stage of solidification.

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In Situ and Real-Time Observation of the Solidification Process of Al–20 mass%Cu Alloy by Synchrotron X-ray Radiography

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Modeling and Simulations of Experimentally-Observed Dislocation Substructures Based on Field Theory of Multiscale Plasticity (FTMP) Combined with TEM and EBSD-Wilkinson Method for FCC and BCC Poly/Single Crystals

T. Hasebe, M. Sugiyama, H. Adachi, S. Fukutani, M. Iida

pp. 779-787

DOI:

10.2320/matertrans.M2013226

Abstract

An attempt is made here to reproduce the experimentally-observed inhomogeneous deformation structures based on FTMP (Field Theory of Multiscale Plasticity), where TEM observations for sheared single crystal samples with four typical crystallographic orientations as well as an EBSD-Wilkinson method-based result for a polycrystal are taken as recent successful examples, ultimately aiming at developing a new technique for in situ/ex situ local-global inhomogeneity evaluation during elasto-plastic deformation combined with these experimental techniques. Crystal plasticity-based finite element simulations utilizing FTMP-based incompatibility model are conducted in connection with a working hypothesis called flow-evolutionary law, whose manifestation is given as a relationship between the incompatibility tensor and the energy-momentum tensor (duality diagram). Demonstrated are not only successful reproductions of the orientation-dependent dislocation substructures and the intra-granularly evolved deformation structures, but also the associated energy flow with the evolved inhomogeneities visualized on the corresponding duality diagram.

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Modeling and Simulations of Experimentally-Observed Dislocation Substructures Based on Field Theory of Multiscale Plasticity (FTMP) Combined with TEM and EBSD-Wilkinson Method for FCC and BCC Poly/Single Crystals

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In Situ Observation of Pseudoelasticity in Fe3Al Single Crystals with D03 Structure

Hiroyuki Y. Yasuda, Yasuhiro Oda, Takenori Maruyama, Mayumi Ojima, Yoshitaka Adachi

pp. 788-795

DOI:

10.2320/matertrans.M2013461

Abstract

In order to clarify the mechanism of pseudoelasticity in Fe–23.0Al (at%) single crystals with the D03 structure, in situ observation of tensile deformation was performed at room temperature using an optical microscope (OM), an electron back-scatter diffraction (EBSD) device and an X-ray Laue back-reflection (XLBR) machine. In the present study, neither martensite nor twin was observed during the pseudoelasticity. In particular, the whole of the tensile specimen could be indexed with respect to the D03 structure by in situ EBSD measurement. (\bar{1}\bar{1}2), (\bar{1}01) and (\bar{2}11) slips were confirmed to occur depending on the loading axis by in situ OM observation. When (\bar{1}01) [111] slip was activated, coarse slip bands parallel to (\bar{101) slip plane were formed during loading. The area fraction of the slip bands increased linearly with increasing plastic strain up to 0.066. During unloading, the slip bands disappeared, resulting in pseudoelasticity. From in situ XLBR tests, the crystal rotation of the loading axis toward [111] slip direction took place during loading. The rotation angle and the plastic strain satisfied the Schmid-Boas relationship at small plastic strains, especially for (\bar{1}\bar{1}2) and (\bar{2}11) slips. These results suggest that the reversible motion of 1/4<111> superpartial dislocation dragging an antiphase boundary (APB) was responsible for the pseudoelasticity in Fe–23.0Al single crystals.

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In Situ Observation of Pseudoelasticity in Fe3Al Single Crystals with D03 Structure

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Refinement of Nanoporous Copper: A Summary of Micro-Alloying of Au-Group and Pt-Group Elements

Zhenhua Dan, Fengxiang Qin, Nobuyoshi Hara

pp. 796-800

DOI:

10.2320/matertrans.M2013445

Abstract

The micro-alloying of 1 at% metals of Au-Group (Ag, Au) and the Pt-Group (Ni, Pd, Pt) with the Ti60Cu40 amorphous alloy resulted in the formation of fine nanoporous copper (NPC) in the order of 6–28 nm. The smallest characteristic pore size of open–cell nanoporous fcc Cu was 7 and 6 nm after dealloying the amorphous Ti60Cu39Pd1 and Ti60Cu39Pt1 precursor alloys for 43.2 ks in 0.03 M HF solution, while NPC had a pore size of 39 nm after dealloying the amorphous Ti60Cu40 precursor alloy. On the basis of TEM micrographs, the refining factor increased approximately from 4 for the Ti60Cu39Ag1 precursor alloy to 1780 for the Ti60Cu39Pt1 precursor alloy. The refinement was attributed to the dramatic decrease in the surface diffusivity during dealloying. The refinement efficiency of the micro-alloying of the Pt-group elements was higher than that of the Au-group elements. The homogeneous distribution of additives in both of the amorphous precursor alloys and the final stabilized NPCs played a key role in refining the NPCs. This strategy may contribute to the fabrication of cost-effective nanoporous metals with a nanoporosity comparable to that of nanoporous Au, Pd and Pt catalysts.

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Refinement of Nanoporous Copper: A Summary of Micro-Alloying of Au-Group and Pt-Group Elements

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Chemical and Structural Properties of Polyethyleneimine Film Coated on a SiO2 Substrate in Different Concentrations

Hyung-Joong Yun, Hyobong Hong, Jouhahn Lee, Chel-Jong Choi

pp. 801-805

DOI:

10.2320/matertrans.M2014013

Abstract

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and atomic force microscopy (AFM) were employed to investigate the detailed surface bonding structure and morphology of polyethyleneimine (PEI) layers coated on a SiO2 substrate in concentrations of 0.5–10.0 mass%. With an increase in the PEI concentration, the C–N bonds corresponding to the imine group (–NH) became dominant in the PEI layers, implying a characteristic feature to verify the immobilization of PEI on the SiO2 surface. The thickness of PEI layer calculated using AR-XPS gradually increased with increasing PEI concentration up to a maximum 5 mass%, above which it became saturated. AFM results showed that an increase in PEI concentration led to a decrease in the root mean square (RMS) roughness of PEI layers. Such a saturation tendency of PEI thickness combined with the strongly dependence of the surface morphology behavior of PEI layers on the PEI concentration indicated that SiO2 surface was fully covered by monolayer PEI with a smooth surface morphology at PEI concentration in excess of 5 mass%.

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Chemical and Structural Properties of Polyethyleneimine Film Coated on a SiO2 Substrate in Different Concentrations

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Solidification Structure of Al–Cu and Sn–Cu–Sb Alloys Obtained by Casting through Induction Stirring Using Permanent Magnet

Fumitaka Otsubo, Satoshi Nishida, Hidenori Era

pp. 806-812

DOI:

10.2320/matertrans.F-M2014804

Abstract

Permanent magnetic stirring is superior in terms of cost and operability compared with electromagnetic stirring. However, it is applied only to melting furnace. In this study, attempts were made to apply permanent magnetic stirring molten metal, and the effects of the stirring on grain refinement, increase in hardness, and suppression of porosity were investigated. We used a stirring device developed by ourselves and two alloys with different solidification morphologies and specific gravities (ρ). Results showed that needlelike crystals were cut off in Sn–Cu–Sb alloy (ρ = 7.4). On the other hand, the growth of columnar crystals was inhibited, and grain refinement and a region growing with equiaxed crystals were observed in Al–Cu alloy (ρ = 2.7) due to the stirring. Furthermore, increased hardness and suppression of porosity were confirmed with the increase in the rotating velocity of magnets in both alloys. Theoretical calculations showed that the molten metal near the mold was directly stirred by Lorentz force, but other regions were indirectly stirred by the flow of force from the directly stirring.

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Solidification Structure of Al–Cu and Sn–Cu–Sb Alloys Obtained by Casting through Induction Stirring Using Permanent Magnet

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Characterization of Spinel-Structured Iron Oxide Nanoparticles Synthesized by Heating of α-FeOOH Platelets in Tetra-Ethylene Glycol

Hawa Latiff, Mikio Kishimoto, Akari Horiuchi, Atsushi Seki, Ryoichi Miyamoto, Hideto Yanagihara, Tatsuya Oda, Nobuhiro Ohkohchi, Eiji Kita

pp. 813-817

DOI:

10.2320/matertrans.Y-M2014805

Abstract

Fe3O4 particles were synthesized from platelet α-FeOOH particles by a liquid-phase reduction process using tetra-ethylene glycol as reduction agent, for their application in hyperthermia or thermoablation therapies that employ hysteresis-loss heating. Fe3O4 particles 60–100 nm in size were finally obtained by heating. The saturation magnetization of the obtained particles increased with the heating time to reach a maximum value of approximately 80 Am2/kg. In contrast, the coercive force of the particles was nearly constant at approximately 12–13 kA/m and was independent of the heating time. Lattice image observation of the synthesized Fe3O4 particles revealed to obtain single crystals. On the basis of experimental results, it was concluded that the single-crystal Fe3O4 particles were formed by recrystallization through the dissolution and precipitation of iron ions from α-Fe2O3 formed by the dehydration of α-FeOOH. The recrystallization of the Fe3O4 particles was promoted with increasing α-FeOOH particle content in tetra-ethylene glycol up to about 0.022 g/mL.

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Characterization of Spinel-Structured Iron Oxide Nanoparticles Synthesized by Heating of α-FeOOH Platelets in Tetra-Ethylene Glycol

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Two-Step Die Motion for Die Quenching of AA2024 Aluminum Alloy Billet on Servo Press

Jae-Yeol Jeon, Ryo Matsumoto, Hiroshi Utsunomiya

pp. 818-826

DOI:

10.2320/matertrans.L-M2014806

Abstract

The authors reported that die quenching of a cylindrical AA2024 aluminum alloy billet less than 9 mm in height was feasible on a servo press. However, it was also found that the reduction in height was limited less than 5% due to partial melting. In order to enhance the deformability in single operation, the two-step die motion is proposed. A cylindrical billet was heated to 823 K and transferred to the press. Then the billet was uniaxially compressed with Δh/h0 = 5%, and further held between the dies for cooling. After sandwiching for 8 s, the billet with a height of h1 = 7.6 mm was further compressed with a reduction in height (Δh/h1) of 2 or 5% at lower temperature. The die quenching process with the two-step die motion leads to increase the total reduction in height to 10%. It is confirmed that super-saturated solid solution successfully formed at the 1st step is maintained in the 2nd step. It is found that the peak hardness of the two-step processed billet is higher than that of the one-step processed billet, and that the precipitation kinetics in artificial aging is accelerated by the two-step motion.

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Two-Step Die Motion for Die Quenching of AA2024 Aluminum Alloy Billet on Servo Press

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Microstructure Observation of Preform for High Performance VGCF/Aluminum Composites

Okyoung Lee, Moonhee Lee, Yongbum Choi, Kenjiro Sugio, Kazuhiro Matsugi, Gen Sasaki

pp. 827-830

DOI:

10.2320/matertrans.MBW201316

Abstract

Although carbon nanofibers show high thermal conductivities and excellent mechanical properties, their composites do not show superior properties because the short nanofibers are discontinuous. Casting vapor-grown-carbon-fiber-reinforced pure-aluminum-matrix (VGCF/Al) composites requires a continuous VGCF preform carbon lattice and bridging between the VGCFs. We investigated how heating affected mesophase pitch (MP) crystallization and how the VGCFs affected the MP-bridging between the VGCFs used to fabricated VGCF preform. The as-received MP and MP heated at 793 K were prepared, and the crystallinities of the two MPs were compared. The (002)-plane lattice spacing of the MP heated at 793 K was remarkably decreased. The heated-MP showed higher crystallinity than the as-received MP, indicating that the heating affected the crystallinity of the MP. The preform was prepared by heating a 1 : 9 mixture of VGCFs and MP particles at 793 K for 1 h under vacuum below 40 Pa, and the crystallinities were compared with the heated MP. The preform (002) plane showed narrow lattice spacing comparable to that of heated MP, the preform showed higher crystallinity than the heated MP, indicating that the VGCFs affected the crystallinity of the MP. The MP enclosed rather than bridged the VGCFs. Moreover, the VGCFs were randomly oriented throughout the MP. The microstructures of the VGCF consisted of linear and wavy carbon structures. The fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) analyses indicated that the wavy structure showed dislocation.

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Microstructure Observation of Preform for High Performance VGCF/Aluminum Composites

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Residual Stresses and Dimensional Changes Related to the Lattice Parameter Changes of Heat-Treated JIS SKD 11 Tool Steels

Yang-Yu Su, Liu-Ho Chiu, Fan-Shiong Chen, Shou-Chi Lin, Yeong-Tsuen Pan

pp. 831-837

DOI:

10.2320/matertrans.M2014031

Abstract

The residual stresses and dimensional changes related to the lattice parameter of the JIS SKD11 tool steel have been investigated for both conventional and cryogenic treatments. As trapped carbon atoms are released from the martensite, the martensite c/a ratios and dimensions of the specimens treated conventionally decreased at tempering temperatures above 673 K. However, these values increased owing to the increase in the c-axis when tempering was conducted at temperatures higher than 673 K. At higher temperatures, the retained austenite is converted into martensite. The martensite c/a ratios and dimension change ratios in the cryogenically treated specimens decreased significantly with the tempering temperature because the amount of retained austenite is reduced by cryogenic treatment. In the conventionally treated specimens, the compressive residual stress decreased with quenching after tempering because of the release of trapped carbon atoms. However, the retained austenite to martensite transformation and the precipitation of alloy carbides leads to increased martensite lattice parameters and dimensional residual stress changes. The residual stress is also changed to generate compressive residual stresses. The dimension change ratio in cryogenically treated and tempered specimens decreased as the tempering temperature increased through a reduction in the amount of trapped carbon. However, the magnitude of the compressive residual stress was reduced to zero.

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Residual Stresses and Dimensional Changes Related to the Lattice Parameter Changes of Heat-Treated JIS SKD 11 Tool Steels

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Molecular Dynamics Simulation of Ga Penetration along Al Grain Boundaries under a Constant Strain Rate Condition

Kayoung Yun, Ho-Seok Nam

pp. 838-841

DOI:

10.2320/matertrans.M2013443

Abstract

While diverse fracture characteristics have been observed in liquid metal embrittlement (LME) depending on the solid–liquid metal pairs, the penetration of nanometer-thick liquid metal films along the grain boundary has been identified as one of the key mechanisms for embrittlement in many classical LME systems, such as Al–Ga, Cu–Bi and Ni–Bi. For example, liquid Ga quickly penetrates deep into grain boundaries in Al, leading to intergranular fracture under very small stresses. We report on a series of molecular dynamics simulations of liquid Ga in contact with an Al bicrystal under a constant strain rate. We identify the grain boundary dislocations that are nucleated at the grain boundary groove tip and climb down along the grain boundary during Ga penetration and characterize their atomic structures based on topological method.

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Molecular Dynamics Simulation of Ga Penetration along Al Grain Boundaries under a Constant Strain Rate Condition

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Low-Stress Creep Deformation in Long-Term Aged Ferritic Heat-Resistant Steel

Shigeto Yamasaki, Masatoshi Mitsuhara, Ken-ichi Ikeda, Satoshi Hata, Hideharu Nakashima

pp. 842-849

DOI:

10.2320/matertrans.M2013427

Abstract

The transition of the creep deformation mechanism in the low-stress region of Grade P92 high Cr ferritic heat-resistant steel was investigated by a helicoid spring creep test. Specifically, the effect of variation in the microstructure of steel on creep deformation behavior was evaluated by subjecting samples to thermal aging for 1000, 3000, 5000, and 10000 h at 700°C over a wide stress range. In addition, stress exponents were determined from the stress dependence of the minimum strain rate in the creep curves up to 270 ks. The transition of the creep mechanism was indicated when the stress exponent decreased from 4 in the high-stress region to 1 in the low-stress region below 40 MPa. A quantitative evaluation of the microstructure of a tempered martensite sample, including the determination of the amount of dissolved Mo and W, dispersion state of the precipitates, and length of the grain boundaries per unit area, was also carried out. Furthermore, the change in the minimum strain rate was evaluated as a function of the microstructural changes that accompanied thermal aging. It was found that the change in the strain rate was the most affected by the fineness of the martensitic lath structure in the high-stress region and by the dispersion density of M23C6 precipitates in the low-stress region. Based on these results, it was concluded that the microstructural parameter that most affects creep deformation behavior differs depending on the stress region due to the difference in the creep mechanism.

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Low-Stress Creep Deformation in Long-Term Aged Ferritic Heat-Resistant Steel

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Effects of Secondary Air Flows on Thermal Characteristics and Particle Behavior in Flame Spray Process

Jae Bin Lee, Dong Hwan Shin, Yeo Hae Lee, Dae Yun Kim, Seong Hyuk Lee

pp. 850-856

DOI:

10.2320/matertrans.M2014007

Abstract

The present study investigates numerically the airflow and thermal characteristics as well as the transient behavior of different particles such as nickel, copper, titanium, and tungsten during the flame spray process by using the computational fluid dynamics (CFD) code (Fluent Ver. 13.0). The combustion model was used in conjunction with the Arrhenius model to describe multi-component turbulent flows occurring during a chemical reaction. It was found that secondary air increased flame temperature and changed the flow direction which can affect the particle behavior. Further, the particle velocity and temperature rapidly changed with the decrease in particle size, causing faster absorption of thermal energy from the hot gas. Moreover, the particle experiences the phase change depending on the temperature and its phase significantly depends on the variation of heat capacity of selected particle. Because the particle phase prior to impact on the sample surface determines the quality of the coating layer, the secondary air pressure should be controlled carefully together with considering the particle type.

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Effects of Secondary Air Flows on Thermal Characteristics and Particle Behavior in Flame Spray Process

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Direct Observation of Pit Initiation Process on Type 304 Stainless Steel

Aya Chiba, Izumi Muto, Yu Sugawara, Nobuyoshi Hara

pp. 857-860

DOI:

10.2320/matertrans.M2014028

Abstract

In situ and real-time optical microscopic observations of pit initiation process on a commercial Type 304 stainless steel with low-sulfur content (0.004 mass%) were performed in 3 M NaCl solution at 298 K. MnS inclusions with diameters of ca. 1 µm were found to act as the initiation sites of pitting, as was the case in a re-sulfurized Type 304 stainless steel (0.027 mass%). The pit was initiated at the boundary between the MnS inclusion and the steel matrix, and grew with time. After a few seconds, no visible change was observed for 1 s, even though the anodic current was measured, suggesting that the steel dissolution proceeded in the depth direction. After that, a small hole suddenly appeared on the steel surface. The hole widened with time, steadily becoming a large stable pit. This pit initiation process in the low-sulfur stainless steel is much like that found in the re-sulfurized stainless steel.

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