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Volume 61, Issue 4
Displaying 1-16 of 16 articles from this issue
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Koji Morita, Masato Uehara, Sadahiro Tsurekawa, Hideharu Nakashima1997 Volume 61 Issue 4 Pages 251-260
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to clarify the grain-boundary structure of molybdenum and influence of impurities on the microstructures, bicrystals with symmetric tilt boundary (⟨001⟩(1\bar30)Σ5, ⟨001⟩(1\bar20)Σ5, ⟨001⟩(1\bar40)Σ17, ⟨001⟩(1\bar50)Σ13 and ⟨110⟩(33\bar2)Σ11 coincidence boundaries) were prepared, and the boundary structures were observed by transmission electron microscopy.
For the purified specimens, periodic structures were observed along the boundary, and well explained by geometric models (coincidence site lattice and O-lattice theories) for the periodicity and by molecular dynamics calculation for microstructures. It was found that the grain boundary structures consist of the combination of structure units of stable boundaries ((0\bar10) and (1\bar10) Σ1 single crystals, and (1\bar30) Σ5 coincidence boundary).
On the other hand, in the not-purified specimens, precipitates and lattice bendings, which were probably caused by impurities, were observed at the boundaries. From these findings, it is concluded that impurities are one of the most important factors affecting the boundary structures in molybdenum. However, the effect was very different from each boundary.View full abstractDownload PDF (1635K) -
Souichirou Tanimori, Shuji Shimamura1997 Volume 61 Issue 4 Pages 261-266
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectronic structure calculations in deformed lattices of Pd have been carried out in order to explore the role of electrons in deformation and fracture in fcc transition metals. Deformed lattices with periodically cleaved or slipped {111} planes have been used for the calculations; the slip direction is ⟨110⟩. Variations in the density of states, the electron energy and the electron density distribution have been calculated by means of the tight binding method which reproduces ab initio band structures in the fcc lattice. The d band width narrows in the cleaved lattice and broadens in the slipped lattice. In consequence, the electron energy increases with cleavage and decreases with slip. Variations in the electron density distribution with lattice deformation are shown for cleavage-sensitive and slip-sensitive states. Cleavage-sensitive states cause the movement of electrons to the cleavage plane. Slip-sensitive states cause the rearrangement of the interatomic bonding near the slip plane.View full abstractDownload PDF (524K) -
Toshiyuki Fujii, Toru Ono, Masaharu Kato1997 Volume 61 Issue 4 Pages 267-273
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of magnetic field on the growth of ferromagnetic Co precipitate particles in Cu-2.7 mass%Co alloy single crystals have been examined by the magnetic anisotropy measurement. The (110) disk specimens of the solution-treated Cu-Co alloy were aged at 973 K for 1∼24 h under the magnetic field of 1.25 MA/m parallel to the [001] direction. The magnetic anisotropy was examined by measuring magnetic torque around the (110) plane. Considering the crystal and shape magnetic anisotropies, the torque curves were analyzed theoretically. It is found that the Co particles which precipitate under the magnetic field slightly elongate to the [001] direction parallel to the magnetic field. Furthermore, the torque curves were also sensitive to the coherent→incoherent shape change of the Co particles. The results can be explained by considering the minimization of the magnetostatic energy of the Co particles.View full abstractDownload PDF (1294K) -
Hideki Hagi1997 Volume 61 Issue 4 Pages 274-281
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIntroduction of a large amount of hydrogen into specimens of a low carbon steel by cathodic polarization produces hydrogen damages such as blisters, microcracks, and dislocations. Hydrogen in the specimen exists as hydrogen atoms dissolved in iron lattice, atoms trapped at lattice defects such as dislocations, and gas precipitated in void-type defects such as blisters and microcracks. Hydrogen in the annealed specimens detected by the electrochemical permeation method was the lattice dissolved hydrogen, and the majority of hydrogen detected by the glycerol displacement method was the precipitated molecular hydrogen. In the case of the annealed specimens, one peak was observed in the thermal spectrum of hydrogen evolution rate. This peak originated in evolution of the precipitated hydrogen, and the peak temperature depended on specimen thickness, hydrogen concentration, and heating rate. In the case of cold-rolled specimens, two peaks were observed. The lower and higher temperature peaks originated in evolution of the precipitated hydrogen and the trapped hydrogen, respectively.View full abstractDownload PDF (1080K) -
Keiichiro Oh-ishi, Minoru Nemoto1997 Volume 61 Issue 4 Pages 282-290
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMicrostructural variations and correlated hardness changes in a β-NiAl containing different amounts of Hf have been investigated in terms of transmission electron microscopy and hardness tests. The alloys harden appreciably by aging after quenching from higher temperatures. At the beginning of aging, fine plate-like L21-type Ni2AlHf precipitates are formed on the {111} planes of the NiAl matrix keeping the lattice coherency with the NiAl matrix. The orientation relationship between the Ni2AlHf precipitate and the NiAl matrix is ⟨100⟩Ni2AlHf\varparallel⟨100⟩NiAl, {001}Ni2AlHf\varparallel{001}NiAl. By prolonged aging Ni2AlHf precipitates lose their coherency and change their morphology to the spherical ones surrounded by misfit dislocations. The orientation relationship between the NiAl matrix and the Ni2AlHf precipitates, however, is kept even after prolonged aging. The lattice misfit between the Ni2AlHf precipitate and the NiAl matrix is estimated from the electron diffraction patterns and the spacings of misfit dislocations to be approximately 4.5% at 1173 K, which is about four times as large as that of the NiAl-Ni2AlTi system. It is suggested that the interfacial energy and the magnitude of lattice misfit strongly affect the age hardening behavior and the morphology of precipitates in this alloy.View full abstractDownload PDF (1389K) -
Kensuke Kageyama, Hiroshi Kato1997 Volume 61 Issue 4 Pages 291-297
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA numerical simulations of crack bowing and deflections was performed on glass matrix-alumina particulate composite to evaluate relationship between the aspect ratio of the ellipsoidal particle and the toughening by crack bowing and crack deflections. Three models of the crack extension process were set up. First, only crack bowing occurs (bowing model); secondly, only crack deflection occurs (deflection model); and thirdly, both of them occur (mixture model). The numerical simulation revealed that in the case of the bowing model, the fracture toughness of composites increased monotonously with the fracture toughness of the particle but in the case of sphere particle dispersed glass and the deflection mixture models, it increased by 30% at most.
Then, the fracture toughness of the composites whose aspect ratios were changed from 0.2 to 5 was calculated. The fracture toughness of the composites in the bowing model was almost unchanged from that of the sphere particle dispersed composites. Meanwhile, when the major axis of ellipsoidal particles was normal to the crack plain, the toughening of the composites in the deflection and mixture models became higher than those of the sphere particles dispersed composites as the particle is inhomogenized. Nevertheless, when the major axis of ellipsoidal particles was parallel to the crack plain, the fracture toughness of the composites was lower than that of the sphere particle dispersed composites and thus the fracture toughness of the composites was also inhomogenized as the particle was inhomogenized.View full abstractDownload PDF (701K) -
Toshinori Shibusawa, Yasuo Kobayashi, Keisuke Ishikawa1997 Volume 61 Issue 4 Pages 298-302
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSWe studied the effects of heat treatments and environmental and experimental conditions on the fatigue crack propagation behavior of AZ91D magnesium alloy. Fatigue crack propagation rate (FCPR) is reduced by solution treatment but accelerated by aging. FCPR is higher in air than in argon. FCPR increases with decreasing test stress frequency. The minimum stress intensity factor range increases with decreasing load ratio (Pmin⁄Pmax). FCPR of this magnesium alloy is sensitive to oxygen, because of the formation of brittle oxide films on the fresh fatigued surface.View full abstractDownload PDF (413K) -
Kenji Matsuki, Masato Kamigaito, Mitsugu Tokizawa, Norio Takatsuji, Ta ...1997 Volume 61 Issue 4 Pages 303-310
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of Cr and Zr contents on the mechanical properties of the extrusions from the Al-3Fe-3Ni-x mass%Cr (x=0, 3.0, 4.5) and Al-3Fe-3Ni-3Cr-x mass%Zr (x=0, 0.7, 1.5) alloy powders have been investigated at the temperatures from ambient temperature to 573 K. The microstructures of these alloy powders and extrusions were analyzed by using an X-ray diffractometer, a differential scanning calorimeter, a scanning electron microscope and a transmission electron microscope. The addition of Cr increased the tensile strength of the extrusions and decreased the ductility at all testing temperatures. The low ductility is recovered by the addition of up to 0.7 mass%Zr which increases the strength at the same time. In the alloy containing Cr, the quasicrystalline Al80Cr13.5Fe6.5 phase particles were observed in the rapidly solidified fine powders. The EDX analysis revealed that the quasicrystalline phase contains the Ni element. After the extrusion at 623 K, the quasicrystalline phase as well as equilibrium Al13Cr2 were finely dispersed in a matrix of the Cr containing alloy, which improved the tensile strength at elevated temperatures. In addition, Zr addition to the alloy caused the finer microstructure and the higher ductility even though it remained in the solid solution.View full abstractDownload PDF (1396K) -
Keijiro Nakasa, Masahiko Kato, Hiroki Matsuyoshi1997 Volume 61 Issue 4 Pages 311-318
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMixtures of Ti and TiB2 powder with various molecular ratio were spark- and resistance-sintered at various temperatures ranging from 1073 to 1773 K to obtain TiB particles-dispersed Ti composites (mono-layer specimens), and the layers of TiB 80%, TiB 40% and Ti were laminated and sintered to fabricate a TiB-Ti functionally graded material. The ralative density and the bending strength of mono-layer specimen decrease with increase in TiB ratio. The hardness increases to reach a maximum with increase in TiB ratio. The bending strength of TiB-Ti functionally graded specimen is almost the same as that of TiB 80% mono-layer specimen when the TiB 80% layer is thin, but it is low when the thickness of the TiB 80% layer is almost the same as that of the Ti layer. The change of bending strength with relative thickness of TiB 80% layer agrees qualitatively with the tendency of calculated residual stress which seems to be generated during cooling after sintering. No delamination is observed along the interface of each layer after bending test.View full abstractDownload PDF (1370K) -
Toru Kuzumaki, Takuya Hayashi, Hideki Ichinose, Kun-ichi Miyazawa, Kun ...1997 Volume 61 Issue 4 Pages 319-325
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSCarbon nanotube reinforced nanocrystalline C60 was prepared at room temperature by drawing the composite sheathed in silver tube. Fine structures of the composite were examined by high resolution electron microscopy (HREM) and the mechanical properties by conventional tensile tests.
HREM observation shows that carbon nanotubes in the composite are defect free and aligned well in the direction of the wire. The stress-strain curve of the composite wire de-sheathed by evaporation of silver through heat treatment gives approximately 20 times increase in the fracture stress over that of polycrystalline C60 with higher fracture strain (over 10%). The fracture surface of the wire shows that nanotubes were pulled out but not fractured.
TEM observation of interface structure of C60 vapor deposited nanotubes as well as pull-out tests were performed of C60 single crystals vapor-deposited on single high elasticity carbon fibers which have similar surface structure as nanotube to examine the origin of the large elongation of the composite. It has been inferred that shear deformation takes place in the carbon fiber/C60 single crystal interface with little deformation of matrix but without fracture of the fiber and that the pull out was mainly caused by the shear deformation, which was probably made possible by a weak interaction between graphitic basal plane and C60.
The experiments lead us to a new concept of a ductile C/C composite.View full abstractDownload PDF (1339K) -
Muneo Oka, Shinji Imai, Taichi Matsuura, Hisaki Okamoto1997 Volume 61 Issue 4 Pages 326-333
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of the additional amount of Y2O3 into ZrO2 on the superplastic characteristics of Al2O3-20 and 30 mass%ZrO2 composites containing 0, 2, 4 and 6 mol%Y2O3 respectively were considered from experimental results carried out by tensile tests at 1400, 1450 and 1500°C and at initial strain rates from 3.33×10−5 to 1.11×10−3 s−1. The obtained main results were as follows.
(1) The values in elongation of most of the Al2O3-30 mass%ZrO2 composites were generally larger than those of the Al2O3-20 mass%ZrO2 composites. A maximum elongation of 164 and 158% was obtained for each Al2O3-30 mass%ZrO2 (4 mol%Y2O3) and Al2O3-20 mass%ZrO2 (4 mol%Y2O3) composite respectively.
(2) The microstructural observation revealed that both Al2O3-20 and 30 mass%ZrO2 composites containing 4 mol%Y2O3 indicated the largest elongation resulting from the finer grain size, more uniform distribution between Al2O3 and ZrO2 phases and less microstructural defects such as voids or cracks.
(3) As a reason why the grain size of the composites containing 4 mol%Y2O3 was so small and stable during hot deformation, it is pointed out that their microstructures consisting of the dual phases of t and c were smaller than those of a single t phase in the composites containing 2 mol%Y2O3. Also these smaller ZrO2 grains were dispersed among Al2O3 grains by a pinning effect, then the composites containing 4 mol%Y2O3 were considered to exhibit larger elongations.View full abstractDownload PDF (1003K) -
Seiichi Toriyama, Takehiko Mae, Koichi Arai1997 Volume 61 Issue 4 Pages 334-341
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of Ga content and aging treatment on local corrosion characteristics of Al-9 mass%Mg alloys containing a small amount of Ga content were investigated by the measurements of the polarization curves and potentiostatic corrosion and immersed corrosion tests. The scanning electron microscopic observation of precipitates of the secondary phase with aging treatment and surfaces of the specimens corroded in NaCl containing 1×10−2 kmol/m3 H2SO4 solution at 303 K were also performed. The main results obtained are summed up as follows:
(1) The Al3Mg2 compounds of secondary phase of Al-9 mass%Mg alloys aged at 453 K for 6.0 ks precipitate along the grain boundary irrespective of the specimens used. However, the rodlet precipitates are observed even within the grain, and the precipitate free zones are formed along the grain boundary of the specimens aged at 453 K for 307.2 ks.
(2) The pitting potential Epit of Al-9 mass%Mg alloys is shifted to a more basic potential with increasing NaCl concentration, Ga content in the alloys and aging time intervals, and thus the degradation of local corrosion resistance is observed.
(3) The apparent anodic dissolution rates of the specimens under the potentiostatic condition are enhanced with increasing Ga content in the alloys and aging time irrespective of the specimens used. The rates are increased in the order of super-saturated solid solution<the specimens aged at 453 K for 6.0 ks<the specimens aged at 453 K for 307.2 ks.
(4) The corrosion of super-saturated Al-9 mass%Mg alloys in a H2SO4-NaCl solution is mainly pitting attack. However, the corrosion form of the aged specimens is observed both intergranular and pitting attacks.View full abstractDownload PDF (1142K) -
Hirokazu Yoshida, Itsuo Ohnaka1997 Volume 61 Issue 4 Pages 342-349
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn algorithm has been developed for simulating the solidification in copper billet continuous casting based on the direct finite difference method by assuming a flow field in the melt. The simulation model considers the temperature dependent thermo-physical properties, convection heat transfer due to the movement of liquid and solid phases, latent heat of solidification and heat transfer among carbon and copper molds, billet and cooling water. The simulation results were compared with a measured sump shape, cooling curves and dendrite-arm-spacing (DAS). The sump shape was estimated from the solidification structure obtained by adding molten Sn during casting. An experimentally determined relationship between DAS and cooling rate was used in the estimation of the DAS distribution in the billet. The comparison between calculated and measured results showed a good agreement and it was found that neglecting the heat transfer into the casting direction results in a maximum error of 16.4%. It was also found that a more accurate estimation of the thickness of the solidified layer and temperature near meniscus requires more accurate information on the velocity field.View full abstractDownload PDF (957K) -
Hiromichi Ohta, Hiroyuki Shibata, Toshihiko Emi, Yoshio Waseda1997 Volume 61 Issue 4 Pages 350-357
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA new approach by applying the Monte Carlo method has been developed to estimate the radiative component of heat transfer of a mold flux film in the continuous steel casting process. The variation of total heat flux in the mold flux film for continuous casting of steel is calculated as a function of scattering albedo for cases with and without contact resistance between the mold flux and the mold. The scattering albedo of the crystallized mold flux was also determined from the measurement of the ratio of transmitted laser beam intensities through two samples of different thicknesses. Eight to thirty% of the total heat flux in the mold flux film is induced by crystallization, due mainly to the change in absorption of the radiative component.View full abstractDownload PDF (876K) -
Fumiyoshi Kirino, Shigekazu Ohotomo, Nagatsugu Koiso1997 Volume 61 Issue 4 Pages 358-365
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe magnetic properties, the thermal stability, and the corrosion resistance of Fe-Ta-C thin films prepared in an atomsphere containing N2 were studied. As the N2 content in the sputtering gas is increased, Bs and μ decrease, while Hc and λs increase. A film prepared in Ar+N2 (1.5 vol%) has Bs of about 1.4 T, and μ (at 1 MHz) higher than 2000. A film prepared in Ar+N2 (2 vol%) has Hc of 80 A/m, and λs of 1.4×10−6. Fe-Ta-C thin films produced in an atomsphere containing N2 have a high thermal reliability. After thermal treatment at 873 K, the soft magnetic properties of Fe-Ta-C thin film produced in the atomsphere containing N2 did not change, while that of Fe-Ta-C thin film produced in pure Ar atomsphere changed, namely, Hc increased and μ decreased.
The corrosion resistance was measured by change of Bs. The value of Bs of the Fe-Ta-C thin film prepared in an atomsphere containning N2 did not change after being immersed in pure water for 3.96×105 s. Furthermore, this film has a high corrosion resistance in pure water with Ar bubbling for 1800 s. However, Bs of Fe-Ta-C thin film prepared in pure Ar atomsphere decreased to 65% of the initial value. After immersing the Fe-Ta-C thin film prepared in Ar+N2 (0.5 vol%) in 0.01 N NaClaq for 3.96×105 s, Bs decreased to 75% of the initial value, while in the case of Fe-Ta-C thin film prepared in Ar+N2 (5 vol%), Bs decreased to 95% of the initial Bs.View full abstractDownload PDF (1108K) -
Katsumi Koyama, Goroh Itoh, Motohiro Kanno1997 Volume 61 Issue 4 Pages 366-367
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (383K)
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