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Volume 62, Issue 2
Displaying 1-12 of 12 articles from this issue
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Toru Ujihara, Kozo Osamura, Yoshiyuki Amemiya1998 Volume 62 Issue 2 Pages 117-124
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe structural anisotropy of GP zone in an Al-Zn binary alloy has been investigated using in situ small angle X-ray scattering measurement with a synchrotron radiation source. As a result, 2-dimensional images of scattering intensity showed the orientation dependence. The maxima of scattering intensities were observed along the ⟨001⟩ directions. In the high scattering vector range, the contour of scattering intensities also showed anisotropy and the form for the early stage of aging was different from that for the late stage. The difference among each Guinier radii determined from one dimensional profile along the ⟨001⟩, ⟨110⟩ and ⟨111⟩ directions predicted a facetting for the {111} interface of GP zone. Assuming the form of GP zone is faceted sphere, we calculated the structure factors. The result agreed with the experiments in the range, where the scattering intensity gives information on the shape of small precipitates like GP zone.View full abstractDownload PDF (753K) -
Byung-Nam Kim, Teruo Kishi1998 Volume 62 Issue 2 Pages 125-132
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe axi-symmetric finite element method is developed in order to simulate 3-dimensional migration behavior of grain boundary around a spherical paticle. At first, the method is applied to the simulation of shrinkage behavior of a spherical grain boundary. The spherical grain boundary shrinks in keeping its original shape, and the velocity is consistent well with the theoretical prediction, indicating a validity of the present method. In the simulation of the interaction between curved grain boundary and spherical particle, the velocity of the grain boundary varies during the interaction process depending on the location from the particle. Since the velocity of the grain boundary near the particle is higher than that distant from the particle, the shape of the grain boundary is considerably deformed during the interaction. A minimum migrating velocity occurs at different time depending on the location of the boundary, and on the ratio between the diameter of the particle and the radius of curvature of the grain boundary. The decrease of the velocity and the time loss due to the particle-induced pinning increases with increasing particle radius.View full abstractDownload PDF (657K) -
Kenji Matsuda, Tomoo Yoshida, Hiroshi Gamada, Kaname Fujii, Yasuhiro U ...1998 Volume 62 Issue 2 Pages 133-139
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh resolution transmission electron microscopy (HRTEM) was performed on the micro-structure analyses of a two-step aged Al-1.6 mass%Mg2Si alloy in order to elucidate the characteristic two-step aging behavior of Al-Mg-Si alloys. The optimum conditions for the HRTEM observation of fine precipitates were determined, including accelerating voltage, defocus and crystallographic orientations. The alloy aged at 343∼423 K for 60 ks was found to produce fine G.P. zones with mono layer or multi layer structures. When the specimens containing such G.P. zones are finally aged at 473 K up to their maximum hardness conditions, a number of random-type precipitates, which are assumed to contain high concentration vacancies, are homogeneously formed. These precipitates result in the increased hardness, exhibiting so-called positive effect of the two-step aging. On the contrary, the alloy aged at 293 K for 60 ks, the primary G.P. zones with the diameter of ∼1 nm are formed with high number density. When this alloy is finally aged at 473 K up to a maximum hardness parallelogram-type precipitates are preferentially formed. These parallelogram-type precipitates result in the decreased hardness, exhibiting negative effect of the two-step aging. Based on the microstructure analyses it is concluded that both the primary and mono layer G.P. zones almost dissolve into the matrix at the beginning of 473 K aging, while multi layer G.P. zones continuously transform into random-type precipitate or act as effective nucleation sites for the random-type precipitates.View full abstractDownload PDF (2477K) -
Toshikazu Akahori, Mitsuo Niinomi, Atsushi Ozeki1998 Volume 62 Issue 2 Pages 140-149
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMechanical properties of biomedical Ti-6Al-4V ELI with equiaxed and Widmanstätten α structures at various fatigued steps were investigated. Fatigue crack initiation characteristics of the same alloy were also investigated in this study.
The fatigue crack initiates mainly at the interface between primary α grains in equiaxed α structure while that initiates in the colony along about 45° direction versus stress axis in Widmanstätten α structure. The specimen with Widmanstätten α structure fractures before adequate fatigue hardening because a lot of micro-cracks are easily formed while the specimen with equiaxed α structure fractures after adequate fatigue hardening. The mechanical properties, that is, tensile strength and hardness tend to increase clearly according to the fatigue steps in particular in the low cycle fatigue (LCF) region, while impact toughness and elongation show the reverse trend. The hardness far from the specimen surface is greater than that near the specimen surface at the early stage of LCF. Both hardness is however nearly equal each other at the latter stage of fatigue. It can be understood therefore that the dislocation multiplies near the specimen surface at the early stage of fatigue while at the latter stage of fatigue, the dislocation multiplies also near the center of the specimen. The dislocation multiplication will finally saturates in the whole specimen.View full abstractDownload PDF (2210K) -
Yoji Mine, Taro Moriya, Shinji Ando, Kazuki Takashima, Hideki Tonda1998 Volume 62 Issue 2 Pages 150-158
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe fatigue crack growth behavior of Fe-3 mass%Si single crystals has been investigated in the laboratory air at room temperature. Three types of SEN specimens A, B and C with different notch orientations were prepared. The notch plane and direction in the A-specimen were (110) and [001], and those in the B-specimen and in the C-specimen were (110) and [1\bar10], and (001) and [100], respectively. A definite dependence of crystallographic orientation on the fatigue crack growth behavior is obtained. The crack in the A-specimen deflects approximately 30° from the notch plane and subsequently changes its growth direction into (110)[001]. Striations aligned parallel to [1\bar10], [1\bar11] and [131] are observed on the fatigue surface. These results indicate that the crack extends by alternating shear on two intersecting slip systems {11\bar2}⟨111⟩ and {01\bar1}⟨111⟩, and that the crack planes are to be {110} which is a bisector of the activated slip planes. The crack in the B-specimen grows parallel to the [1\bar10] notch direction. Cleavage-like features with lines parallel to the [1\bar1\bar3] direction which is the direction of the intersection between (\bar12\bar1) and (2\bar11) are observed on the fatigue surface. If two sets of slips ((\bar12\bar1)[111] and (2\bar11)[\bar1\bar11]) are activated at the crack tip and the dislocation reaction occurs to form sessile dislocations, cracking may occur on the (110) which is the maximum tensile stress plane due to stress concentration of dislocation pile-up during cyclic loading. The fatigue crack propagates along (100)[001] in the C-specimen. Cross-hatch patterns composed by two intersecting ⟨011⟩ furrows are observed on the fatigue surface.View full abstractDownload PDF (2496K) -
Jianguo Hu, Keisuke Ikeda, Tadasu Murakami1998 Volume 62 Issue 2 Pages 159-166
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSOn the basis of the Continuum Mechanics of Textured Polycrystals (CMTP), yield loci of several ideal textures appearing in pure aluminum and its alloy sheets were calculated. The shape variations of yield loci in the rolling plane and influence of the orientation scatter width on them were all analyzed. Then, forming limit diagrams (FLDs) of the ideal textures were predicted by means of an incorporation of the anisotropic CMTP yield function into Marciniak and Kuczynski’s (M-K) model. Anisotropy of forming limit diagrams for different textures was analyzed. The distinct corresponding relationship between yield loci and FLDs for textured aluminum sheets is indicated. Reasonable agreement is observed between the predicted and measured FLDs for pure aluminum and A5083 alloy sheets. An optimum combination of different texture components that lead to reducing in-plane plastic anisotropy and improving the formability of aluminum sheets was also discussed.View full abstractDownload PDF (660K) -
Osami Seri1998 Volume 62 Issue 2 Pages 167-172
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt is well-known that the more FeAl3 intermetallic compound particles exhibited on aluminum are more detrimental to corrosion. The effective surface treatment, by which preferential removal of FeAl3 particles from the aluminum surface can proceed, has been investigated. The proposed treatment is the electrochemical treatment that the specimen is kept in the potential of −2.0 V vs. Ag/AgCl for 1000 s and quickly then held at the potential of 0.0 V vs. Ag/AgCl for more over 1000 s in 0.1 kmol·m−3 Al(NO3)3 solution. Appreciable FeAl3-particle-free surface was obtained by this treatment.View full abstractDownload PDF (759K) -
Hiroyuki Masuda1998 Volume 62 Issue 2 Pages 173-180
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe small water droplets which adhere to the material surface cause corrosion and photo catalytic reaction. It is important to study the behavior of these small water droplets to understand the mechanism of these reactions. Recently the author has succeeded in observing the droplet of pure water on graphite by a non-contacting AC AFM mode. In this paper, the behavior of water droplets was studied by combining the contact and non-contact scanning modes on graphite, mica and SUS304 stainless steel. The behavior of water droplets was dependent on the material and the solution and the water droplets were easily moved by contact mode scanning. Small water droplets were generated at the step site on the graphite surface, while only water films evolved on the mica surface at the humidity of 90%.View full abstractDownload PDF (1803K) -
Yoshinori Sakamoto, Chiaki Shibuta, Sumiko Sanuki, Takehiko Mae, Hisak ...1998 Volume 62 Issue 2 Pages 181-188
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe changes in mechanical properties and corrosion resistance of Al-Mg alloys with the addition of Cu by the electron beam welding process were investigated by the measurements of tensile tests, anodic polarization curves and immersed corrosion tests of the specimens with or without improved treatment in a dilute HClO4 solution at 303 K.
The X-ray diffraction or EDAX analysis of the precipitates and the observations of scanning electron micrographs of the specimens and the surface of the corroded specimens were also performed.
The main results obtained are summarized as follows:
\ oindent(1) The grain size of Al(α) phase of the improved Al-Mg alloys decreased in comparison with the untreated specimens, and the size was below ca. 10 μm in diameter. The Al(α)+Al2Cu(θ) eutectic structure precipitates around the grain boundary of Al(α) phase, and the surface area ratios of eutectic structure increased with increasing Cu content in the improved Al-Mg alloys. However, in the improved 5154 alloy, in addition to the Al2Cu compound, Al2CuMg compound is also detected. (2) The mechanical properties such as 0.2% proof stress, U.T.S. and Vickers hardness of Al-Mg alloys are increased by the improved treatment. On the contrary, the elongation of the improved specimens was reduced below ca. 5% regardless of the specimens. (3) The corrosion resistance of improved specimens decreased greatly with increasing Cu content in the alloys. The deterioration of the corrosion resistance was caused by an electrochemical interaction of galvanic coupling produced between the grain of Al(α) phase and the eutectic structure.View full abstractDownload PDF (1045K) -
Kyu-Sang Cho, Hiroshi Takamatsu, Hiroshi Honda1998 Volume 62 Issue 2 Pages 189-196
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMetal wires of Pb, Zn and Fe77.5Si7.5B15 were produced by the In-Rotating-Water Spinning Method. The effects of drum velocity (5.2∼8.5 m/s), jet ejection velocity (3.8∼11.4 m/s), incidence angle (30° and 60°) and nozzle diameter (0.1 and 0.2 mm) as well as the kind of metals on the formation of a wire were examined. Pb showed the best spinnability among the tested metals, although the cross section was relatively flat and marked ripples were formed on the wire surface when the incidence angle and the jet velocity were relatively large. A long, straight Fe77.5Si7.5B15 wire was produced when the jet velocity was a little higher than the drum velocity. A higher jet velocity was required for a smaller nozzle diameter dn. The produced Fe77.5Si7.5B15 wire had a smooth surface and a round cross-section. However, the wire showed a shape like a string of beads for dn=0.1 mm.View full abstractDownload PDF (1227K) -
Yasuo Kogo, Hiroshi Hatta, Akimitsu Okura, Yasuhiro Goto, Yutaka Sawad ...1998 Volume 62 Issue 2 Pages 197-206
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSiC coatings for oxidation protection of Carbon-Carbon (C/C) composites were produced by the Si/Polymer (S/P) process and the SiC/C/Polymer (S/C/P) process; these processes are much simpler than the conventional CVD process. Oxidation tests were also carried out to evaluate effectiveness of the coatings.
In the S/P process, C/C composites were coated with slurry of Si particle-polymer mixtures. The slurry coated composites were then heat treated to carbonize the polymer and form SiC by the liquid silicon-carbon reaction. Porous and dense two-layer SiC coatings were observed. As for the S/C/P process, a carbon layer containing SiC particle was first formed on C/C composite; this layer was then reacted with impregnated liquid silicon. A dense SiC layer was therefore formed through the S/C/P process.
Although the oxidation rates of C/C composites were reduced in all the testing temperatures (900∼2000 K), the SiC coatings by the S/P process were less effective than those by the CVD process. This was explained by small and nonuniform thicknesses of the dense SiC layer in the coatings by the S/P process. On the other hand, C/C composites coated by the S/C/P process showed almost the same oxidation rates as those by the CVD process.View full abstractDownload PDF (1594K) -
Yoshimitsu Okazaki, Kenji Kyo, Yoshimasa Ito, Tetsuya Tateishi1998 Volume 62 Issue 2 Pages 207-214
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe combined effect of O and N additions on the fatigue properties with Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.2%O-0.05%N and Ti-15%Sn-4%Nb-2%Ta-0.2%Pd-0.2%O alloys were investigated by fatigue testing in a physiological saline solution at 310 K. The fatigue test was carried out under the condition of a tension to tension mode with a sine wave at a stress ratio of 0.1 and at a frequency of 2 Hz and 10 Hz in Eagle’s medium solution using an environment cell with 90%N2+5%CO2+5%O2 gas bubbling. Further the effect of human hip joint load profile estimated by analysis of forces and actions for human hip joint on the corrosion fatigue strength were examined.
The effect of heat treatment on the mechanical strength of the new Ti alloys were investigated. As the solution treatment temperature increased the ductility of Ti-Zr and Ti-Sn alloys decreased. After solution treatment, the mechanical strength of Ti-Zr and Ti-Sn alloys did not change much as the aging time and the aging temperature increased. The additions of O and N to the new Ti alloys and heat treatment substantially increased the ultimate tensile strength to 1000 MPa. Also, the total elongation was more than 10%. The fatigue strength of Ti-Sn alloy added 0.2%O, 0.005%N and Ti-Zr alloy added 0.2%O, 0.05%N at 108 cycles was 1050 MPa and 950 MPa, respectively. The effect of frequency on the fatigue strength at 2 Hz and 10 Hz was almost similar. Moreover, the fatigue strengths ware almost the same for sine wave and human hip joint load profile in both Ti-Zr and Ti-Sn alloys.View full abstractDownload PDF (1185K)
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