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MATERIALS TRANSACTIONS Vol. 50 (2009), 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. 50 (2009), No. 1

Effect of Extrinsic Grain Boundary Dislocations on Mechanical Properties of Ultrafine-Grained Metals by Molecular Dynamics Simulations

Tomotsugu Shimokawa, Tomoyuki Hiramoto, Toshiyasu Kinari, Sukenori Shintaku

pp. 2-10

DOI:

10.2320/matertrans.MD200810

Abstract

The effect of extrinsic grain boundary dislocations (EGBDs) in nonequilibrium grain boundaries on the mechanical properties of ultrafine-grained metals is investigated by molecular dynamics simulations. Aluminum bicrystal models containing cracks and EGBDs impinged from the crack tips are prepared. First, the dependence of the local grain boundary structure on the accommodation mechanism of EGBDs, and on its stress field is studied. Then, the shielding effect of EGBDs on the emissions of dislocations from crack tips is investigated, and the effect of nonequilibrium grain boundaries on the intragranular deformation is discussed. Finally, to investigate the relationship between EGBDs and intergranular deformations, shear loading is applied to the bicrystal models. It is found that extrinsic grain boundaries function as the intergranular deformation source, and the Burgers vector components of the EGBDs lead to anisotropic grain boundary sliding.

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Effect of Extrinsic Grain Boundary Dislocations on Mechanical Properties of Ultrafine-Grained Metals by Molecular Dynamics Simulations

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First-Principles Study of the Stability and Interfacial Bonding of Tilt and Twist Grain Boundaries in Al and Cu

Ru-Zhi Wang, Masanori Kohyama, Shingo Tanaka, Tomoyuki Tamura, Shoji Ishibashi

pp. 11-18

DOI:

10.2320/matertrans.MD200820

Abstract

Nature of grain boundaries (GBs) should affect the micro-structural evolution and mechanical properties of metallic micro-crystalline formed by severe plastic deformation. The stability and interfacial bonding of coincidence tilt and twist GBs in Al and Cu have been examined by using the projector-augmented wave method within the density-functional theory. For the {221} Σ=9 tilt boundary, glide models are more stable than mirror models for Al and Cu, and the {001} Σ=5 twist boundary is more stable than the Σ=9 tilt boundary for Al and Cu, due to smaller structural distortions. There is a tendency that the boundary energies in Al are substantially smaller than those in Cu. This can be explained by the electronic and atomic behavior of bond reconstruction at the interfaces in Al, due to the covalent nature of Al as observed in the charge density distribution, in contrast to rather simple metallic bonding at Cu GBs.

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First-Principles Study of the Stability and Interfacial Bonding of Tilt and Twist Grain Boundaries in Al and Cu

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SPH Analysis of ECAP Process by Using Grain Refinement Model

Ken-ichi Saitoh, Yuuki Ohnishi

pp. 19-26

DOI:

10.2320/matertrans.MD200814

Abstract

Plastic working of metals using severe plastic deformation (SPD) recently attracts interest of researchers, because it is a method that will improve the toughness as well as the strength just by applying enormously large strain on the material. In this study, deformation, stress and strain of aluminum in ECAP (equal channel angular pressing) are analyzed computationally by using smoothed particle hydrodynamics (SPH) method which is one of particle methods. In addition to elastic-plastic constitutive relation, a newly developed theoretical framework in which grain refinement process is involved is proposed here. We try to implement the framework into the SPH computation. The main idea to conduct grain refinement in the material is that applied energy by plastic working causes continuous change in the total area of grain boundaries and averaged diameter in the material becomes smaller and smaller. The reasonable change can be observed by using such simple but theoretical framework. The present paper is focused on implication, formulation and possibility of the grain refinement model.

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SPH Analysis of ECAP Process by Using Grain Refinement Model

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Distributions of Hardness and Strain during Compression in Pure Aluminum Processed with Equal-Channel Angular Pressing and Subsequent Annealing

Tadanobu Inoue, Zenji Horita, Hidetoshi Somekawa, Fuxing Yin

pp. 27-33

DOI:

10.2320/matertrans.MD200819

Abstract

Single compression tests were conducted for two types of pure Al (99.99%): one processed using equal-channel angular pressing (ECAP) through route Bc for 8 passes and the other with the same ECAP but successively annealed at 573 K for 1 h. The distributions of the equivalent strain introduced by the compression were quantitatively examined by finite element analysis (FEA). Comparison was made between the ECAP samples and the ECAP-annealed samples with regard to the inhomogeneity and magnitude of the strain developed during the compression. Hardness variations with the equivalent strain were also compared with those obtained by earlier studies using ECAP and high-pressure torsion. Moreover, the hardness variation throughout the cross section after compression was well predicted using the FEA for both ECAP sample and ECAP-annealed sample. It is shown that the change in the strain path from ECAP to compression affects the hardness variation with respect to the equivalent strain.

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Distributions of Hardness and Strain during Compression in Pure Aluminum Processed with Equal-Channel Angular Pressing and Subsequent Annealing

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Effect of Strain on Microstructural Evolution under Warm Deformation in an Ultra-Low Carbon Steel

Joo-Hee Kang, Tadanobu Inoue, Shiro Torizuka

pp. 34-39

DOI:

10.2320/matertrans.MD200816

Abstract

The microstructural evolution was investigated according to the equivalent strain in uniaxial compression using an ultra-low carbon steel. The equivalent strain was quantitatively calculated by using finite element analysis. The microstructure was rapidly refined up to the equivalent strain of 2.4 with the material flow to rolling direction (RD) with the remarkable development of high angle boundaries. At that time, texture such as (001)[110] and (111)[110] significantly developed. Inhomogeneous deformation behavior according to texture was observed; ⟨100⟩||ND was elongated without the development of subgrain even under large strain, but ⟨111⟩||ND was divided into small grains isolated with high angle boundaries.

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Effect of Strain on Microstructural Evolution under Warm Deformation in an Ultra-Low Carbon Steel

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Coupled Analysis of Heat Transfer and Deformation in Equal Channel Angular Pressing of Al and Steel

Pham Quang, A. Krishnaiah, Sun Ig Hong, Hyoung Seop Kim

pp. 40-43

DOI:

10.2320/matertrans.MD200823

Abstract

In the present paper, the heat transfer and plastic deformation during the equal channel angular pressing of Al alloy and steel were numerically analyzed. The finite element simulations were carried out at various pressing speeds ν=0.18, 1.8, and 18 mm/s, and the temperature and plastic strain distributions were investigated. It is concluded that the pressing speed is the most important processing parameter in rising temperature. Temperature rise in steel is higher than that in Al alloy due to the combined effect of high strength (heat generation effect) and low thermal diffusivity (heat release effect) in steel.

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Coupled Analysis of Heat Transfer and Deformation in Equal Channel Angular Pressing of Al and Steel

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Evolution of Mechanical Properties and Microstructures with Equivalent Strain in Pure Fe Processed by High Pressure Torsion

Kaveh Edalati, Tadayoshi Fujioka, Zenji Horita

pp. 44-50

DOI:

10.2320/matertrans.MD200812

Abstract

Pure Fe (99.96%) was processed by high pressure torsion (HPT) using disc and ring samples. When the microhardness and tensile properties are plotted against the equivalent strain, the individual properties fall well on unique single curves, level off at the equivalent strain of ∼40. At the saturated level, the tensile strength of 1050 MPa and the elongation to failure of 2% are attained. Transmission electron microscopy showed that a subgrain structure containing dislocations develops at an initial stage of straining. More dislocations form within the grains and the subgrain size decreases with further straining. At the saturation stage, the average grain size reaches ∼200 nm, the misorientation angle increases and some grains which are free from dislocations appear. It is suggested that at the saturation stage, a steady state condition should be established through a balance between hardening by dislocation generation and softening by recrystallization.

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Evolution of Mechanical Properties and Microstructures with Equivalent Strain in Pure Fe Processed by High Pressure Torsion

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High Tensile Strength of Low-Carbon Ferritic Steel Subjected to Severe Drawing

Tetsuya Suzuki, Yo Tomota, Atsushi Moriai, Hitoshi Tashiro

pp. 51-55

DOI:

10.2320/matertrans.MD200805

Abstract

Severely drawn low-carbon ferritic steel wire was investigated to make clear the reason of its high tensile strength which is higher than that predicted from the hardness. The microstructure of a specimen subjected to a true strain of 6.6 consists of fine elongated grains and subgrains with high dislocation density. Neutron diffraction showed the existence of (hkl) intergranular residual stress, suggesting a composite strengthening mechanism. The reasons of higher tensile strength achieved by drawing in comparison with other severe deformation processes, like ECAP, ARB and HPT, are estimated to be texture, residual intergranular stress and high dislocation density.

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High Tensile Strength of Low-Carbon Ferritic Steel Subjected to Severe Drawing

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Brittle-Ductile Transition in Low Carbon Steel Deformed by the Accumulative Roll Bonding Process

Masaki Tanaka, Kenji Higashida, Tomotsugu Shimokawa, Tatsuya Morikawa

pp. 56-63

DOI:

10.2320/matertrans.MD200817

Abstract

Brittle-ductile transition (BDT) behaviour was investigated in low carbon steel deformed by an accumulative roll-bonding (ARB) process. The temperature dependence of its fracture toughness was measured by conducting four-point bending tests at various temperatures and strain rates. The fracture toughness increased while the BDT temperature decreased in the specimens deformed by the ARB process. Arrhenius plots between the BDT temperatures and the strain rates indicated that the activation energy for the BDT did not change due to the deformation with the ARB process. It was deduced that the decrease in the BDT temperature by grain refining was not due to the increase in the dislocation mobility controlled by short-range obstacles. Molecular dynamics simulations revealed that moving dislocations were impinged against grain boundaries, creating a shielding field, and were reemitted from there with increasing strain. Grain refining led to an increase in the fracture toughness at low temperatures and a decrease in the BDT temperature. In the present paper, the roles of grain boundaries have been discussed in order to explain the enhancement in the fracture toughness of fine-grained materials at low temperatures, and the decrease in the BDT temperature.

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Brittle-Ductile Transition in Low Carbon Steel Deformed by the Accumulative Roll Bonding Process

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Temperature and Strain Rate Dependence of Flow Stress in Severely Deformed Copper by Accumulative Roll Bonding

Takahiro Kunimine, Naoki Takata, Nobuhiro Tsuji, Toshiyuki Fujii, Masaharu Kato, Susumu Onaka

pp. 64-69

DOI:

10.2320/matertrans.MD200809

Abstract

Tensile tests and strain rate jump tests have been carried out at low temperatures (77 K ∼ room temperature (RT)) using pure Cu specimens that were severely deformed by accumulative roll bonding (ARB). The dependence of the flow stress on the temperature and the strain rate has been investigated and the strain rate sensitivity m and its variation caused by the change in the ARB cycle N are discussed. At RT, the strain rate sensitivity for N≤4 stays at about 0.005. However, for N≥5, m increases with increasing N to become ∼0.018 when N=8. The deformation mechanisms of the ARB processed Cu are discussed with the activation volume V*. The temperature dependence of V* and its variation with increasing N are also discussed.

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Temperature and Strain Rate Dependence of Flow Stress in Severely Deformed Copper by Accumulative Roll Bonding

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Cyclic Deformation Behavior of Ultra-Fine Grained Copper Produced by Equal Channel Angular Pressing

Yoji Furukawa, Toshiyuki Fujii, Susumu Onaka, Masaharu Kato

pp. 70-75

DOI:

10.2320/matertrans.MD200806

Abstract

Cyclic deformation behavior of ultra-fine grained (UFG) Cu of 99.99% purity processed by equal-channel angular pressing was investigated. In tension-compression fatigue tests under strain control, UFG Cu showed cyclic softening. Shear bands were formed along the direction inclined by about 45° from the loading axis. Observations using an electron backscattering diffraction technique and transmission electron microscopy revealed that local grain growth took place in the shear bands and overall grains elongated along the shear direction. Cyclic softening can be understood as a result of dynamic grain coarsening occurred intensively in the strain localized shear bands.

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Cyclic Deformation Behavior of Ultra-Fine Grained Copper Produced by Equal Channel Angular Pressing

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Fabrication and Characterization of Supersaturated Al-Mg Alloys by Severe Plastic Deformation and Their Mechanical Properties

Kenji Kaneko, Tetsuro Hata, Tomoharu Tokunaga, Zenji Horita

pp. 76-81

DOI:

10.2320/matertrans.MD200813

Abstract

Excess amount of Mg was intentionally added to fabricate supersaturated ultra-fine grained Al-Mg alloy by high pressure torsion (HPT). Their microstructures and mechanical properties were examined by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and Vickers microhardness test. It was confirmed that the minimum grain size reached ∼40 nm and maximum microhardness 292 Hv at the Mg content with 30 mass%. Further increase of the amount of Mg resulted the formation of β-Al3Mg2 and decrease of microhardness.

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Fabrication and Characterization of Supersaturated Al-Mg Alloys by Severe Plastic Deformation and Their Mechanical Properties

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The Evolution of Microstructure and Mechanical Properties of a 5052 Aluminium Alloy by the Application of Cryogenic Rolling and Warm Rolling

Ui Gu Gang, Sang Hun Lee, Won Jong Nam

pp. 82-86

DOI:

10.2320/matertrans.MD200801

Abstract

The microstructural evolution and the corresponding mechanical properties of a 5052 Al alloy processed by cryogenic rolling followed by warm rolling were investigated. The application of cryogenic rolling combined with warm rolling at 448 K showed a significant improvement of tensile strength up to 452 MPa. The kinetics and the microstructural evolution occurred during warm rolling were investigated using differential scanning calorimeter and transmission electron microscope. This notable increase of tensile strength was achieved by the formation of fine precipitates during warm rolling. It was found that the cryogenic rolling combined with warm rolling would be effective in improving mechanical properties.

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The Evolution of Microstructure and Mechanical Properties of a 5052 Aluminium Alloy by the Application of Cryogenic Rolling and Warm Rolling

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Grain Refinement and Mechanical Behavior of the Al Alloy, Subjected to the New SPD Technique

Ruslan Z. Valiev, Maxim Yu. Murashkin, Elena V. Bobruk, Georgy I. Raab

pp. 87-91

DOI:

10.2320/matertrans.MD200821

Abstract

The paper focuses on producing of ultrafine-grained (UFG) structure in the Al 6061 alloy by a new severe plastic deformation (SPD) technique, developed recently in our laboratory, namely equal channel angular pressing with parallel channels (ECAP-PC). The evolution of microstructure at ECAP-PC was examined and was proved that the alloy becomes of a homogenous UFG structure after 4 passes. Such a structure increases essentially the alloy’s mechanical properties, specifically strength and ductility. The advantages of this new technique in producing of UFG alloys over conventional ECAP are considered and discussed as well.

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Grain Refinement and Mechanical Behavior of the Al Alloy, Subjected to the New SPD Technique

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Scaling-Up of High Pressure Torsion Using Ring Shape

Kaveh Edalati, Zenji Horita

pp. 92-95

DOI:

10.2320/matertrans.MD200822

Abstract

A 100 mm-diameter ring sample of high purity Al (99.99%) was processed by high-pressure torsion (HPT). It was confirmed that the results of hardness measurements were consistent with those obtained using disk samples and demonstrated that scaling-up the HPT process was feasible using the ring-shaped sample. Evaluating the advantage of using ring sample, the potential for the scaling-up arises from the fact that the ring diameter can be increased by the amount corresponding to the inner central area of disk sample. Furthermore, the applied load is entirely used for the introduction of intense strain and thus for the development of a homogeneous microstrcuture throughout the ring sample.

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Scaling-Up of High Pressure Torsion Using Ring Shape

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Microstructure Evolution in Pure Al Processed with Twist Extrusion

Dmitry Orlov, Yan Beygelzimer, Sergey Synkov, Viktor Varyukhin, Nobuhiro Tsuji, Zenji Horita

pp. 96-100

DOI:

10.2320/matertrans.MD200802

Abstract

High purity Al (99.99%) was subjected to severe plastic deformation through twist extrusion at room temperature. Microstructures were examined for 1 pass and 4 passes on the cross section perpendicular to the longitudinal axis of billets using optical microscopy and electron back scatter diffraction analysis. It was shown that a vortex-like material flow was observed on the cross section and this became more intense with increasing number of the pressing. After one pass, subgrain structures with low angle grain boundaries were developed throughout the section but after 4 passes, the microstructure consisted of grains surrounded by high angle boundaries with fraction of ∼70% in the edge parts. The average grain size at the edge parts is refined to ∼1.6 μm.

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Microstructure Evolution in Pure Al Processed with Twist Extrusion

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Partial Grain Refinement in Al-3%Cu Alloy during ECAP at Elevated Temperatures

Inna Mazurina, Taku Sakai, Hiromi Miura, Oleg Sitdikov, Rustam Kaibyshev

pp. 101-110

DOI:

10.2320/matertrans.MD200807

Abstract

Microstructural changes during equal channel angular pressing (ECAP) in a temperature interval from 523 to 748 K (∼0.6–0.8 Tm) were studied in a coarse-grained binary aluminum alloy Al-3%Cu. Hot ECAP results in grain refinement taking place at all temperatures investigated, leading to a non-uniform development of deformation-induced fine grains and the remnant original grains containing subgrains with low-angle boundaries. Fine-grained structure is developed along microshear bands formed in grain interiors as well as along initial grain boundaries. The number and the average misorientation angle of the boundaries of microshear bands start to increase at above a critical strain of about 2, finally leading to development of new fine-grained structures. The volume fraction and the average misorientation of deformation-induced boundaries are reduced with rising temperature. The thermal stability of the evolved deformation microstructures and several factors controlling grain refinement during hot ECAP are discussed in details.

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Partial Grain Refinement in Al-3%Cu Alloy during ECAP at Elevated Temperatures

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Achieving Microstructural Refinement in Magnesium Alloys through Severe Plastic Deformation

Roberto B. Figueiredo, Terence G. Langdon

pp. 111-116

DOI:

10.2320/matertrans.MD200818

Abstract

Equal-channel angular pressing (ECAP) is an excellent processing tool for achieving exceptional grain refinement, typically to the submicrometer level, in a range of pure metals and metallic alloys. Although processing by ECAP is relatively straight-forward when using soft metals, the processing becomes more difficult when using magnesium-based alloys and other similar difficult-to-work materials. This overview examines the procedures that must be adopted for the successful processing of these materials and then describes some of the advanced properties achieved after the successful processing of two magnesium alloys.

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Achieving Microstructural Refinement in Magnesium Alloys through Severe Plastic Deformation

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Microstructural Evolution of Ti-Mo-Ni-C Powder by Mechanical Alloying

Hiroyuki Hosokawa, Kiyotaka Kato, Koji Shimojima, Akihiro Matsumoto

pp. 117-122

DOI:

10.2320/matertrans.MRA2008280

Abstract

The microstructural evolution of (Ti,Mo)C-Ni powder by mechanical alloying of pure titanium, nickel, carbon and molybdenum as starting powder with the composition of TiC-20 Mo2C-20 Ni in mass% were investigated by X-ray diffraction (XRD) using CuKα radiation, field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) with EDS. The powders were mixed gradually and the size of the mechanically alloyed particles was of sub-micrometer order. The TiC structure, which indicated smaller lattice constant than TiC, clearly appeared after 100 h milling time. The particles consisted of fine grains of about 5 nm size. The nickel was transformed from crystallized phase into an amorphous phase by mechanical alloying. The molybdenum was dissolved into TiC structure and Mo/Ti ratio in (Ti,Mo)C was about 3/7.

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Microstructural Evolution of Ti-Mo-Ni-C Powder by Mechanical Alloying

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Kinetics and Morphology of Isothermal Transformations at Intermediate Temperature in 15CrMnMoV Steel

Mokuang Kang, Ming-Xing Zhang, Feng Liu, Ming Zhu

pp. 123-129

DOI:

10.2320/matertrans.MRA2008194

Abstract

Upper bainite (BU), lower bainite (BL) and granular structure (GS) are three distinguishable microstructures formed through isothermal treatment at temperature range from 350 to 520°C in 15CrMnMoV steel. Although long time isothermal holding leads to the mixed microstructures, single microstructure can be obtained in the initial stage of isothermal transformation when the total transformation fraction is less than 20%. The Arrhenius equations were used to determine the overall activation energies of the transformations in the steel with accuracy of ±8 kJ/mole. To ensure the determined overall activation energy is the true value for single microstructure rather than for a mixture of two or more microstructures, the present determination of the kinetic data of isothermal transformations was carried out in terms of the isothermally transformed fractions of 1 and 5% at various temperatures. Experimental results show that the overall activation energy for single microstructure is significantly different from that for mixed microstructure, which was measured in terms of 50% transformation. Upon the determined kinetic data and the morphology of the microstructures, together with consideration of the reported atom diffusion activation energies, following conclusions are achieved. In steels, the BU transformation is controlled by carbon diffusion in the austenite; while, the formation of BL is only partially governed by carbon diffusion in austenite. As a different microstructure from other two, the GS transformation is controlled by carbon diffusion and has the common features of both equiaxed ferrite and massive ferrite transformations. These results, can be used to further understand the formation mechanism of BU, BL and GS in the 15CrMnMoV steel.

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Kinetics and Morphology of Isothermal Transformations at Intermediate Temperature in 15CrMnMoV Steel

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Solid-State Reactive Diffusion between Sn and Electroless Ni–P at 473 K

Masafumi Yamakami, Masanori Kajihara

pp. 130-137

DOI:

10.2320/matertrans.MRA2008266

Abstract

Nickel–phosphorus alloys are electrolessly deposited onto Cu-base conductors to suppress formation of Cu–Sn compounds during soldering using Sn-base solders. However, a Ni–Sn compound is produced during soldering, and continuously grows during energization heating at solid-state temperatures. To examine influence of P on the growth behavior of the Ni–Sn compound during energization heating, the kinetics of the solid-state reactive diffusion between Sn and electroless Ni–P alloys was experimentally determined at 473 K in the present study. For the experiment, pure Cu sheets were electrolessly deposited with Ni–P alloys containing 4.6 at%, 18.5 at% and 20.4 at% of P, and then sandwiched between pure Sn plates. Such Sn/(Ni–P)/Cu/(Ni–P)/Sn diffusion couples were isothermally annealed at 473 K for various periods up to 1307 h. During annealing, a layer of Ni3Sn4 is formed along the Sn/(Ni–P) interface in the diffusion couple. The annealing time dependence of the mean thickness of the Ni3Sn4 layer is expressed by a parabolic relationship. The parabolic coefficient slightly increases with increasing P concentration in the Ni–P. Thus, P in the Ni–P lightly accelerates the growth of Ni3Sn4 at the interconnection between the Ni–P and the Sn-base solder. Using the experimentally determined values of the parabolic coefficient, the interdiffusion coefficient in Ni3Sn4 was analytically evaluated by a mathematical model. The acceleration effect of P on the growth of Ni3Sn4 is quantitatively explained by the dependence of the interdiffusion coefficient on the P concentration in the Ni–P.

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Solid-State Reactive Diffusion between Sn and Electroless Ni–P at 473 K

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Determination of True Stress–Strain Curves of Sheet Metals in Post-Uniform Elongation Range

Kenichi Hasegawa, Zhong-Chun Chen, Keiou Nishimura, Keisuke Ikeda

pp. 138-144

DOI:

10.2320/matertrans.P-MRA2008838

Abstract

A novel approach to determination of the true stress–strain relation in a post-uniform elongation range by finite element modeling has been proposed, on the basis of the variation of strain-hardening exponent (n) with strain during uniaxial tensile tests. The strain dependence of n-value can be expressed by a linear or simple quadratic function. The proposed method has been applied to several sheet metals with large differences in strain-hardening behavior. The finite element analytical results, obtained by using constitutive equations derived from a variation of n-value with strain, are in good agreement with the measured load–elongation curves. As the number of parameters is sufficient by two at the most, the optimization by an inverse analysis becomes very easy. It has been verified that the proposed method is effective to estimate the stress–strain curves of sheet metals in the post-uniform elongation range.

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Determination of True Stress–Strain Curves of Sheet Metals in Post-Uniform Elongation Range

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Weibull Statistics for Evaluating Failure Behaviors and Joining Reliability of Friction Stir Spot Welded 5052 Aluminum Alloy

Chung-Wei Yang, Fei-Yi Hung, Truan-Sheng Lui, Li-Hui Chen, Jiun-Yu Juo

pp. 145-151

DOI:

10.2320/matertrans.MRA2008341

Abstract

Friction stir spot welding (FSSW) was applied to make lap-joints of 5052 rolled (5052-R) aluminum alloys. The resulting microstructural observation, microhardness, tensile shear failure load and failure morphologies are reported, including a brief look into failure behaviors in the present study. The metallurgical bonded TMAZ region with a plastic metal flow is obviously created around the probe, and the microhardness is significantly increased at the TMAZ region for FSSW-joined 5052 aluminum alloys. The FSSW lap-joints with an obvious metallurgical bonded TMAZ region generally display a higher failure load and ductile failure morphologies with dimples fracture. In addition, the failure load of FSSW lap-joints was increased with increasing the probe penetration depth and the welding time. Based on the data fluctuation of tensile shear failure load, the Weibull model provided a statistical analysis method for assessing the minimum failure, the failure mechanism and the joining reliability for the FSSW lap-joints. Through the statistical analysis of the Weibull distribution function, FSSW-joined aluminum alloys with a wear-out failure model are recognized as reliable lap-joints for further engineering application.

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Weibull Statistics for Evaluating Failure Behaviors and Joining Reliability of Friction Stir Spot Welded 5052 Aluminum Alloy

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Geometry Constrained Plasticity of Bulk Metallic Glass

K. Mondal, K. Hono

pp. 152-157

DOI:

10.2320/matertrans.MRA2008342

Abstract

Distinction between the geometry constrained plasticity and the unconstrained plasticity in compression stress-strain behaviors of bulk metallic glasses (BMG) has been attempted. Unusually large plasticity of BMG exceeding 20% is possible due to the geometry constrained effect in compression tests even if sample aspect ratios of 1.5–2 are used. Care must be taken because apparent large plasticity can arise if the unconstrained plastic deformation by the uniform formation of fine shear bands allows the deformed parts to touch the crosshead.

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Geometry Constrained Plasticity of Bulk Metallic Glass

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Residual Stress Relaxation in Shot Peened Surface Layer on TiB2/Al Composite under Applied Loading

Weizhi Luan, Chuanhai Jiang, Vincent Ji

pp. 158-160

DOI:

10.2320/matertrans.MRA2008272

Abstract

The residual stress relaxations in the shot peened surface layer on the TiB2/6351Al composite under static and cyclic loading were investigated. The results show that the compressive residual stresses were relaxed under applied tensile stresses. The relaxation of the residual stresses in the longitudinal direction is more important than the one in the transverse direction. Under cyclic loading, the fast relaxation of residual stresses occurred in the first few circles. The main reason of the residual stresses relaxations is the inhomogeneous local plastic deformation caused by the large number of the reinforcement particles in the matrix during applied loadings.

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Residual Stress Relaxation in Shot Peened Surface Layer on TiB2/Al Composite under Applied Loading

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Finite Element Simulation with Coupled Thermo-Mechanical Analysis of Superplastic Dieless Tube Drawing Considering Strain Rate Sensitivity

Tsuyoshi Furushima, Ken-ichi Manabe

pp. 161-166

DOI:

10.2320/matertrans.P-MRA2008837

Abstract

The deformation behavior in superplastic dieless tube drawing is studied numerically by the finite element method (FEM). The FEM with coupled thermo-mechanical analysis is conducted considering strain rate sensitivity to clarify the effect of dieless tube drawing conditions such as tensile speed and material properties on the deformation behavior of the tube. In the calculation, the material properties were dealt with as a function of temperature in a special subroutine, whose constitutive equation considering strain rate sensitivity and strain hardening was used, and was linked to the solver. FEM results for both heat transfer and the deformation profile are in good agreement with experimental results. Therefore, the validity of FE modeling of superplastic dieless drawing is demonstrated. In addition, the effect of material properties m and n values on the deformation profile is demonstrated numerically. As a result, a higher m value constrains the local instability deformation. In cases where the m value is high, the n value has little effect on the deformation profile. Consequently, it is found that analysis considering strain rate sensitivity is important for the prediction of the deformation profile in the dieless drawing process.

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Finite Element Simulation with Coupled Thermo-Mechanical Analysis of Superplastic Dieless Tube Drawing Considering Strain Rate Sensitivity

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Retraction:Fine Measurement of Thermal Conductivity for (Bi0.5Sb1.5)Te3 Compounds

Takashi Hamachiyo, Maki Ashida, Kazuhiro Hasezaki

pp. 167-170

DOI:

10.2320/matertrans.MRA2008241

Abstract

This article was retracted. See the Notification.

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Retraction:Fine Measurement of Thermal Conductivity for (Bi0.5Sb1.5)Te3 Compounds

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Removal of Trace Impurity from Limestone Using Flotation Techniques

Masami Tsunekawa, Yugo Honma, Kyoungkeun Yoo, Naoki Hiroyoshi, Mayumi Ito

pp. 171-176

DOI:

10.2320/matertrans.M-MRA2008839

Abstract

High grade limestone was obtained by removing trace impurities through reverse and carrier flotation techniques. A simple method for measuring the impurity content of limestone was developed by correlating the amount of impurities and the turbidity of suspensions of residue from limestone dissolved in 20% acetic acid.
Impurity removal more than 50% with limestone recovery better than 85% was obtained under suitable conditions by both reverse flotation and carrier flotation using sodium oleate (NaOl) and dodecylammonium acetate (DAA) as collectors. Limestone containing more than 0.15 mass% impurity was used as the carrier. These results suggest that limestone treated by flotation can be used as high quality limestone in paper manufacturing.

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Removal of Trace Impurity from Limestone Using Flotation Techniques

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Effects of Water Absorption on Impact Value of Aluminum Dispersed Composite Nylon6

Masae Kanda, Yoshitake Nishi

pp. 177-181

DOI:

10.2320/matertrans.MRA2008170

Abstract

Composite polymers, which are nylon6 materials with aluminum powders dispersed homogeneously, are prepared. Influences of water absorption on Charpy impact value of composite polymers have been investigated. Although the aluminum dispersion from zero to 40 vol%Al decreases the impact value, the water absorbing treatment for 105 s at boiling point largely increases the impact values of all composite polymers. It is explained that water molecules in nylon6 mainly relaxes the impact force. If the water absorption also enhances the interfacial energy to form the crack in nylon6 and its composites, the high impact value with smooth undulating surface can be explained.

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Effects of Water Absorption on Impact Value of Aluminum Dispersed Composite Nylon6

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Direct Dry Syntheses and Thermal Analyses of a Series of Aluminum Complex Hydrides

T. Sato, K. Ikeda, H.-W. Li, H. Yukawa, M. Morinaga, S. Orimo

pp. 182-186

DOI:

10.2320/matertrans.MER2008251

Abstract

Synthesis of a series of aluminum complex hydrides, namely, LiAlH4, Li3AlH6, NaAlH4, Na3AlH6, Mg(AlH4)2, MgAlH5, Ca(AlH4)2, and CaAlH5, was attempted by the mechanochemical milling of AlH3 and the other elemental hydrides. Aluminum complex hydrides, except MgAlH5, were synthesized, and their dehydriding (decomposition) properties were systematically investigated by thermogravimetry. The dehydridng temperatures possibly showed a correlation with the geometrical distances in space between M′ (M″) and H in the crystal structures of the aluminum complex hydrides.

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Direct Dry Syntheses and Thermal Analyses of a Series of Aluminum Complex Hydrides

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Synthesis of Ultra Fine Titanium-Tungsten Carbide Powder from Titanium Dioxide and Ammonium Metatungstate

Gil-Geun Lee, Gook-Hyun Ha

pp. 187-191

DOI:

10.2320/matertrans.MER2008271

Abstract

In the present study, the focus is on the synthesis of ultra fine titanium-tungsten carbide powder by the carbothermal reduction process. The starting powder was prepared by the combination of drying and calcination methods using titanium dioxide powder and an aqueous solution of ammonium metatungstate to obtain a target composition of 60 mass%TiC-40 mass%WC, i.e., (Ti0.83W0.17)C. The synthesized oxide powder was mixed with carbon black, and this mixture was then heat-treated under a flowing argon atmosphere. The changes in the phase structure, thermal gravity and particle size of the mixture during heat treatment were analyzed using XRD, TG-DTA and SEM. The synthesized oxide powder has a mixed phase structure of anatase-TiO2 and WO3 phases. This composite oxide powder was carbothermally reduced to titanium-tungsten carbide by solid carbon through three steps with increasing temperature; the reduction of WO3, the reduction of TiO2 and formation of tungsten carbides, and the formation of titanium-tungsten carbide. The synthesized (Ti1−xWx)Cy powder at 1673 K for 10.8 ks has an average particle size of about 200 nm.

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Synthesis of Ultra Fine Titanium-Tungsten Carbide Powder from Titanium Dioxide and Ammonium Metatungstate

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Surface Modification of Porous Metals Using Friction Phenomena

Yong-Jai Kwon, Ichinori Shigematsu, Naobumi Saito

pp. 192-196

DOI:

10.2320/matertrans.MER2008288

Abstract

The surface region of the aluminum foams (trade name ALPORAS) was modified through the friction stir processing (FSP) which was performed by using friction phenomena with a high-speed rotating tool. The tool was rotated at speeds ranging from 820 to 2400 rpm, and plunged from the top surface of the aluminum foam, and then traversed at speeds ranging from 50 to 300 mm/min. The surface-modified zone (SMZ) had considerably smoother surface in comparison to the unprocessed zone (UZ). Especially for 1390 rpm and 150 mm/min, the smoothest surface was obtained, which was attributed to the smaller amount of pores in the SMZ. In addition, a very dense layer was formed near the surface of the SMZ through the localized collapse and densification of the cell structure near the surface region, which was attributed to the friction phenomena with the high-speed rotating tool. The mechanical properties of the aluminum foams were significantly improved through the FSP. Especially for 1390 rpm and 150 mm/min, the SMZ exhibited the highest average maximum indentation strength and energy absorption ability, which were equivalent to about 2.2 times the values of the UZ. The tool rotation speed and the tool traverse speed were very important parameters not only in controlling the surface morphology, but also in improving the mechanical properties of the aluminum foams. The FSP was a very effective technology for the remarkable improvement in the mechanical properties through the cell structure control of the surface region of the aluminum foams, without any dense skin materials.

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Surface Modification of Porous Metals Using Friction Phenomena

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Dissimilar Friction Stir Welding for Tailor-Welded Blanks of Aluminum and Magnesium Alloys

Ichinori Shigematsu, Yong-Jai Kwon, Naobumi Saito

pp. 197-203

DOI:

10.2320/matertrans.MER2008326

Abstract

In this study, tailor-welded blanks (TWBs) composed of A5052P-O aluminum and AZ31B-O magnesium alloys were produced by the friction stir welding process. The sound surfaces without large defects were successfully obtained at the tool rotation speeds ranging from 1000 to 1400 rpm under the constant tool traverse speed of 300 mm/min, and the surface roughness was decreased in the friction-stir-welded zone (SZ) with the increase in the tool rotation speed. Also for 100, 300 and 500 mm/min, the sound surfaces without large defects were obtained under the constant tool rotation speed of 1400 rpm. The increase of the tool traverse speed led to the decrease in the surface roughness of the SZ. In the SZ, the bonded interface was clearly evident with plastic flow pattern between the aluminum and magnesium alloys, although an onion ring pattern was not formed. During tensile testing, the TWBs were fractured in the SZ at the early stage of the plastic deformation, i.e. strain hardening region, without remarkable area reduction near the fracture region. The TWBs exhibited the similar average tensile strength, showing that there were not noteworthy changes in the tensile strength as a function of the tool rotation speed. The average tensile strength, however, was slightly decreased with the increase in the tool traverse speed. It is noticeable that, in all cases, the joint efficiency of the TWBs exceeded 62%, and the maximum average tensile strength of about 143 MPa was obtained at 1400 rpm under the tool traverse speed of 100 mm/min, which was nearly equivalent to the joint efficiency of about 72%. The average total elongation of the TWBs was about 2% or less considerably lower than those of the base metals, without significant changes as functions of the tool traverse speed and the tool traverse speed.

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Dissimilar Friction Stir Welding for Tailor-Welded Blanks of Aluminum and Magnesium Alloys

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FeSiBPCu Nanocrystalline Soft Magnetic Alloys with High Bs of 1.9 Tesla Produced by Crystallizing Hetero-Amorphous Phase

Akihiro Makino, He Men, Takeshi Kubota, Kunio Yubuta, Akihisa Inoue

pp. 204-209

DOI:

10.2320/matertrans.MER2008306

Abstract

Technically important nanocrystalline soft magnetic alloys and their derivatives always include metal elements such as Nb, Zr, Mo, etc. and/or Cu to realize the nanostructure, which results in a remarkable decrease of saturation magnetic flux density (Bs) and a significant increase in material cost. With the aim to solve the serious problem, we successfully developed new FeSiBPCu nanocrystalline soft magnetic alloys. The melt-spun Fe83.3–84.3Si4B8P3–4Cu0.7 (at%) alloys have heterogeneous amorphous structures including a large amount of α-Fe clusters, 2–3 nm in size, due to the unusual effect of the simultaneous addition of the proper amounts of P and Cu. The hetero-amorphous alloys exhibit higher Bs of about 1.67 T than the representative amorphous and the nanocrystalline alloys, and the low coercivity (Hc) of 5–10 Am−1. A homogeneous nanocrystalline structure composed of small α-Fe grains with a size of about 10 nm can be realized by crystallizing the hetero-amorphous alloys. The nanocrystalline alloys show extremely high Bs of 1.88–1.94 T almost comparable to the commercial Fe-3.5 mass%Si crystalline soft magnetic alloys, and low Hc of 7–10 Am−1 due to the simultaneous realization of the homogeneous nanocrystalline structure and small magnetostriction of 2–3×10−6. In addition, the alloys have a large economical advantage of lower material cost and better productivity than the ordinary soft magnetic nanocrystalline alloys now in practical use.

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FeSiBPCu Nanocrystalline Soft Magnetic Alloys with High Bs of 1.9 Tesla Produced by Crystallizing Hetero-Amorphous Phase

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Microstructure Refinement and Texture Evolution of Titanium by Friction Roll Surface Processing

Meiqin Shi, Yoshimasa Takayama, Tomohiro Umetsu, Hajime Kato, Hideo Watanabe, Hirofumi Inoue

pp. 210-214

DOI:

10.2320/matertrans.MER2008294

Abstract

Friction roll surface processing (FRSP), as a novel severe plastic deformation technique, has been put forward and experimentally investigated. Commercial pure titanium sheets were subjected to FRSP and subsequent annealing. An extremely large strain was imposed on the surface layer of the sheet. Consequently, a uniform ultrafine-grained microstructure with a grain size of approximately 80 nm and a deformation texture were obtained in the surface layer. The FRSP texture was found to be strongly related to the processing direction. The evolution of texture during annealing was also investigated. The texture analysis revealed that new preferred orientations could be developed during FRSP.

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Microstructure Refinement and Texture Evolution of Titanium by Friction Roll Surface Processing

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Deoxidation Thermodynamics of β-Titanium by Ca-CaCl2 and Ca-CaF2 Fluxes

Seung-Min Han, Young-Seok Lee, Joo-Hyun Park, Good-Sun Choi, Dong-Joon Min

pp. 215-218

DOI:

10.2320/matertrans.MRP2008284

Abstract

Deoxidation of β-titanium was investigated by Ca-CaCl2 and Ca-CaF2 fluxes at 900 to 1400°C. The content of oxygen in Ti was strongly dependent not only on the Ca potential but on the stability of CaO in the fluxes. The present experimental results indicate that deoxidation of Ti by Ca-calcium halide fluxes could be controlled by the activity ratio of CaO to Ca. The ratio of aCaO⁄aCa=0.06∼0.1 was strongly recommended for obtaining oxygen content of 40∼160 ppm.

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Deoxidation Thermodynamics of β-Titanium by Ca-CaCl2 and Ca-CaF2 Fluxes

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The Synthesis of Graded Thermal Barrier Coatings on Nickel Substrates by Laser Induced Thermite Reactions

T. M. Yue, H. O. Yang, T. Li, K. J. Huang

pp. 219-221

DOI:

10.2320/matertrans.MRP2008304

Abstract

Al2O3 and ZrO2-Al2O3 bearing coatings were synthesized onto nickel substrates by laser induced thermite reactions. The oxide coatings were produced via thermite reactions between NiO and Al powders with and without the addition of Y2O3-stabilised ZrO2 (YSZ), respectively. In the case where no YSZ was added, a graded coating with a top layer of Al2O3 was produced. Whereas, when YSZ was added, the coating essentially comprised ZrO2 dendrites with the interdendritic regions filled with the ZrO2-Al2O3 eutectic phase. The formation process of the coatings is described.

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The Synthesis of Graded Thermal Barrier Coatings on Nickel Substrates by Laser Induced Thermite Reactions

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Stabilization of Stacking Faults and a Long Period Stacking Phase Dispersed in α-Mg Crystalline Grains of Mg-0.7 at%Zn-1.4 at%Y Alloy

Jongbeom Lee, Kazuhisa Sato, Toyohiko J. Konno, Kenji Hiraga

pp. 222-225

DOI:

10.2320/matertrans.MRP2008335

Abstract

Mg-0.7 at%Zn-1.4 at%Y alloys annealed at low temperatures after quenching in water from 520°C were studied by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Stacking faults, thin bands of a 14H-type long period stacking (LPS) phase and relatively thick bands of LPS were precipitated in α-Mg crystalline grains by annealing at 300°C, 400°C and 500°C, respectively. The precipitation of stacking faults, LPS phase and a supersaturated solid solution without any precipitates were reversibly transformed by annealing at low temperatures. It can be concluded that the stacking faults and LPS phase are stabilized by the segregation of Zn and Y from a supersaturated solid solution.

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Stabilization of Stacking Faults and a Long Period Stacking Phase Dispersed in α-Mg Crystalline Grains of Mg-0.7 at%Zn-1.4 at%Y Alloy

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Direct Bonding to Aluminum with Silver-Oxide Microparticles

Toshiaki Morita, Yusuke Yasuda, Eiichi Ide, Akio Hirose

pp. 226-228

DOI:

10.2320/matertrans.MRP2008277

Abstract

This study demonstrated that direct bonding between electrode and aluminum by using silver oxide particles which added acetic acid silver, followed by heating in air at 350°C under a pressure of 2.5 MPa. Direct bonding with aluminum by using solder materials containing tin, lead, or the like has been impossible in the past. We think this technique creates strong bonding between silver and the natural oxide film formed on an aluminum surface by the combustion heat generated during oxidation of acetic acid (which is generated by decomposition of the silver acetate as it is heated).

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Direct Bonding to Aluminum with Silver-Oxide Microparticles

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