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Volume 66, Issue 2
Displaying 1-11 of 11 articles from this issue
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Naoki Torazawa, Shigeo Arai, Koji Shimoyama, Yoshihisa Takase, Hiroyas ...2002 Volume 66 Issue 2 Pages 47-52
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMicrostructure of Pb-free Sn-Ag solder and joints between the Pb-free solders and electroless Ni-P was examined by means of transmission electron microscopy. Microstructures of the solders consist of β-Sn matrix dispersed with Ag3Sn particles. Analysis of the diffraction patterns shows that there are more than one orientation relationships between β-Sn and Ag3Sn. The solder joint of the Pb-free solders is essentially similar to the joint of Pb-Sn eutectic solders. Analysis of distribution of the elements by EDX analysis shows that Ag does not diffuse into Ni-P. Both of the as-deposited Ni-P and P-enriched Ni, the latter being formed as a result of reaction with Sn-Ag solder, have FCC structures based on pure Ni. In other words, P is dissolved in Ni to form a solid solution.View full abstractDownload PDF (1318K) -
Koichi Kitazono, Eiichi Sato, Kazuhiko Kuribayashi2002 Volume 66 Issue 2 Pages 53-59
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSElastic modulus, coefficient of thermal expansion and thermal conductivity of an anisotropic closed-cell metal foam were derived based on continuum micromechanics. Eshelby’s equivalent inclusion method and Mori-Tanaka’s mean-field approximation were used for the calculation. Assuming the eigenstrain in the cell phase, the effect of the gas pressure was incorporated into the calculation. Anisotropic cell structure was modeled by the cell of spheroidal shape. The analytical results were compared with previous Ashby’s unit-cell model which has been widely applied to many cellular materials. It was revealed that the present micromechanics model has high advantage for high-density and anisotropic closed-cell metal foams. The analytical results agreed well with the experimental result of lotus-structured porous copper with anisotropic cell structure.View full abstractDownload PDF (449K) -
Ryuta Onodera2002 Volume 66 Issue 2 Pages 60-66
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSConstitutive equation was proposed for high-temperature deformation of pure aluminum based on the supposition that 1. there exists effective stress, 2. work-hardening rate is almost identical to that of room temperature, 3. work-hardening rate is uniquely determined by internal stress and recovery rate are determined by internal stress and temperature. The constitutive equation was applied to stress change test, strain rate change test and stress relaxation test in order to obtain strain (or stress)-time curve in these tests. It was supposed that there is a transition time of 0.02 s when stress or strain rate is abruptly changed in these tests. The strain (or stress)-time curve obtained by computer simulation agreed very well with experimental results in literature, which suggests that the current theory is doubtful that effective stress does not exist in high-temperature deformation of pure aluminum.View full abstractDownload PDF (577K) -
Yoritoshi Minamino, Yuichiro Koizumi, Nobuhiro Tsuji, Toru Yamada2002 Volume 66 Issue 2 Pages 67-74
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCo diffusion in a B2-type ordered NiAl compound was investigated at seven compositions between 40.9 at%Al and 52.6 at%Al at five temperatures from 1423 K to 1623 K, using a diffusion couple method. The Co diffusion coefficients at each temperature have a minimum value at the stoichiometric composition, while their activation energies and pre-exponential factors reveal maximum values at this composition. The activation energies decrease gently with the Ni content in the Ni-rich side, but decrease steeply with the Al content in the Al-rich side. The interpretation of this behavior is discussed in terms of the diffusion mechanisms; the triple defect mechanism at stoichiometric composition, the antisite bridge mechanism in the Ni-rich side, and the next nearest neighbor jump mechanism with the structural Ni vacancies.View full abstractDownload PDF (635K) -
Koji Tanoue, Ryo Ijichi2002 Volume 66 Issue 2 Pages 75-80
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt is investigated how sliding and cavitation at grain boundaries have an effect on the measurement of threshold stress σT. The effect of the potassium concentration on σT is then clarified under the condition that such effects resulting from grain boundaries are almost negligible. The flow stresses and the hardness of grain interiors, which are obtained at high and room temperatures, respectively, using tungsten fine wires of secondary recrystallized grains arranged in a simple morphology, increase with increasing potassium concentration. It is shown that if grain morphology is arranged in a way that makes it free from grain boundary sliding and cavitation, the threshold stress can be measured by abrupt stress change tests during creep and increases with potassium concentration. However, it is also noted that the effect of σT on the creep rate is much less than that caused by the change of grain morphology.View full abstractDownload PDF (707K) -
Toshimitsu Tetsui2002 Volume 66 Issue 2 Pages 81-86
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA precision cast Ti-46Al-8Nb-1Cr-0.3Si-0.3Ni (at%) TiAl turbine wheel containing β phase was investigated to determine the effects of HIP condition on elimination behavior of cast defects, as well as changes in microstructure and mechanical properties. Microstructural change such as the formation of lamellar structure from the surface occurred during HIP treatment, and the microstructure of blades (i. e., the thinner portion of the turbine wheel) were completely changed to a fully lamellar structure by HIPing at temperatures above 1300°C. The stabilization of the α2 phase and disappearance of the β phase induced by the invasion of oxygen during HIPing are considered to be responsible for this behavior. In contrast, although the difference of microstructures by HIP condition was small, the lamellar spacing of the HIPed material increased at the inner portion of the turbine wheel compared with the as-cast material. Given these microstructural changes, the strength of the blades and the inner portion of the HIPed turbine wheel declined in comparison with the as-cast material.View full abstractDownload PDF (1211K) -
Makoto Nanko, Taku Oyaidu, Toshio Maruyama2002 Volume 66 Issue 2 Pages 87-93
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSUsing pulse current pressure sintering, the densification behavior of Ni-20Cr alloy powder, 70 μm average particle diameter, was investigated via microstructural observations and by kinetic analysis of the densification rate. Observation of the microstructures revealed that the neck radii were very small. Recrystallization and melting at the grain interface did not occur. Densification rates calculated by a model that assumed steady-state creep were consistent with the experimental results. Creep rates obtained from the model calculation agreed with previously reported values. Densification of Ni-20Cr alloy powder by pulse current pressure sintering was rate-controlled by steady state creep. The pulse current affected the densification by increasing the macroscopic temperature of the sample.View full abstractDownload PDF (1320K) -
Makoto Nanko, Taku Oyaidu, Toshio Maruyama2002 Volume 66 Issue 2 Pages 94-100
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSNi-20Cr alloy powder, 70 μm average particle diameter, was oxidized to have a Cr2O3 scale, which was 1 μm in thickness. The oxidized powder sintered by a pulse current pressure sintering technique at sample temperatures from 1205 to 1377 K under 13 MPa of applied pressure. The densification was compared with the as-received powder. Observations of the microstructure revealed that the neck radii were very small. Recrystallization and melting at the grain interface did not occur, even though an oxide scale existed. The oxide scale decreased the sample temperatures at the same die temperatures. At the same sample temperatures, densities of the sintered bodies with oxide scales were similar to those without oxide scales.View full abstractDownload PDF (1927K) -
Masafumi Noda, Mitsuji Hirohashi, Kunio Funami, Yutaka Suwahara, Masar ...2002 Volume 66 Issue 2 Pages 101-108
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGrain refinement of aluminum alloy can be achieved by introducing a large amount of lattice dislocations during an intense heavy plastic deformation. In this paper, the effect of the strain loading process on the grain refinement and mechanical properties in aluminum alloy was investigated, in terms of mechanical properties, grain boundary misorientations and microstructures. Uniaxial or biaxial forging was performed at 473 K for the grain refinement of the 1100 aluminum. In biaxial forging, the work pieces were rotated by 90° on the longitudinal axis in each forging process.
As the result, the bulk materials with biaxial forging at 473 K showed a significant development in grain refinement; to the grain sizes less than 1 μm. On the other hand, these fine grains of sub-micron size were never obtained through a uniaxial forging even at the same temperature. In the biaxial forged materials, it was shown by using high resolution EBSP and TEM that most of fine grains were surrounded by high-angle and random boundaries whose misorientations are larger than 15°. The formation of these fine grains during the forging and reheating process was deeply associated with the development of the sub-grain boundaries within the larger grains surrounded by high angle boundaries. Tensile test at room temperature showed that strength increases with an increase of strain in biaxial forging and also larger total elongation is obtained in comparison with a uniaxial forging material. The yield stress and tensile strength in the biaxial forged materials are higher than that in the uniaxial forging process, when they are compared under the same amount of pre-deformation.
As described above, multi-axial forging technique is one of the most effective methods to produce fine grained structure and enhance strength without a decrease of ductility.View full abstractDownload PDF (1343K) -
Shigeru Asano, Yushi Amaki2002 Volume 66 Issue 2 Pages 109-116
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA data treatment procedure is formulated for quantitative evaluation of the amplitude dependence of the damping capacity and applied to the decaying process of elastic resonant vibration for aluminum and its alloys. Pure aluminum exhibits a very high damping capacity with characteristic amplitude dependence, which is almost equivalent to that of pure magnesium, a well-known high-damping metal. Work hardening of pure aluminum suppresses the damping capacity in general, although a slight initial strain appears temporarily to enhance it.
Upon the addition of 0.8 at%Mg to aluminum, solid-solution hardening considerably suppresses the damping capacity, and work hardening of this dilute alloy reduces it further. Meanwhile, upon the addition of 0.7 at%Fe or 0.7 at%Ni to aluminum, precipitation hardening moderately suppresses the damping capacity, but work hardening of these alloys enhances it. These phenomena can be explained in terms of short-range dislocation motion that synchronizes with the elastic resonant vibration of specimens. High-damping alloys with sufficient strength and ductility can, in principle, be designed by work hardening of the precipitation-hardened alloys with no solid-solution-hardened matrix.View full abstractDownload PDF (387K) -
Fumie Seki2002 Volume 66 Issue 2 Pages 117-121
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFor the production of thin high-purity aluminum foils for capacitor, it is essential to develop cube texture in the foils. The foils are produced in the following way: hot-rolled plates are cold-rolled by high reduction, intermediately annealed at a relatively lower temperature to cause primary recrystallization, then cold-rolled by a small amount and finally annealed at a higher temperature to develop cube texture. In this work, a crystallographic orientation distribution of a cold-rolled sheet with high reduction was examined in comparison with that of a primarily recrystallized sheet to study the mechanism of cube texture development in the foils. The orientation on a transverse section of these sheets of 500 μm in thickness were studied by electron back-scatter diffraction pattern measurements. The results are summarized as follows: (1) The cold-rolled sheet showed an elongated layered structure, nearly parallel to the rolling direction. Although there were large misorientation angles between layers, every layer contained many fine regions with small misorientation angles. (2) In the inhomogeneous cold-rolled sheets, fine cube-oriented regions were already present at certain position: 15 μm, 80 μm from the surface and in the central part. They were most frequently observed at about 80 μm. (3) In the primary recrystallization texture, cube grains were frequently observed 80 μm to 200 μm in the depth from the surface. It is considered that fine cube-oriented regions are closely related to the development of cube texture in the annealed sheets for capacitor.View full abstractDownload PDF (591K)
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