All issues
Volume 66, Issue 1
Displaying 1-7 of 7 articles from this issue
- |<
- <
- 1
- >
- >|
-
Yukiko Oyama, Atsushi Nishikata, Tooru Tsuru2002 Volume 66 Issue 1 Pages 1-8
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSResponse current to strain for iron electrode polarized at a potential of about 200 mV less than the pitting potential was measured in a sodium borate and boric acid buffer solution of pH 8.39 containing 5 mol/m3 chloride ions. The different types of strain waveforms (triangular, trapezoidal and negative saw teeth) were employed to clarify the current decay behaviors in the unloading cycle. Rapid current decay during the unloading cycle was observed for sinusoidal and triangular strains. For the response current induced by the trapezoidal strain, it was observed that current decay came to an end during the holding period at the maximum strain. Current flow was not observed during the unloading cycle after the current decay finished. It was detected from the negative saw teeth strain waveforms that current decay came to an end during the unloading cycle was under way. It suggested that there was an existence of certain strain value where the current decay stopped during the unloading cycle. The response current in the negative saw teeth waveform was calculated, assuming that the current decay was caused by not only the repassivation process at the crack tip but also the reduction of active fresh surface area which was introduced in the preceding loading cycle. The calculated results agreed well with the experimental results. Moreover, response current in the two cyclic strain waveforms was calculated. One was a triangular strain waveform with strain rate kept constant, the other was a sinusoidal strain waveform with strain rate changing continuously. It was confirmed that the changing in the fresh surface area influenced to the current response induced by the cyclic strain.View full abstractDownload PDF (543K) -
Yoshiki Mizutani, Hideyuki Yasuda, Itsuo Ohnaka, Nobuhiro Maeda, Yoshi ...2002 Volume 66 Issue 1 Pages 9-15
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCoupled growth in the undercooled solidification of the Al2O3-YAG eutectic system was investigated for specimens in a composition range of 17.0 to 20.0 mol%Y2O3 by using an optical DTA apparatus. Growth rate of the eutectic interface was estimated from solidification time and specimen size and the possible growth rate was from 10−5 to 10−4 m/s. The relationship between the eutectic spacing and growth rate obeys λ2V=const in the experimental condition. Specimens with compositions of 1 mol% less or more than the eutectic composition always exhibited primary Al2O3 or YAG phases. In contrast, the specimens with the eutectic composition were completely covered with the eutectic structure. The coupled growth was confirmed in the Al2O3-YAG system, but the composition range of coupled growth was 1 mol% at most. The growth rate from 10−5 to 10−4 m/s did not affect the coupled growth zone.View full abstractDownload PDF (874K) -
Goroh Itoh, Yohei Iseno, Yoshinobu Motohashi2002 Volume 66 Issue 1 Pages 16-21
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGrain refinement is known to be an effective method to improve the poor ductility at room temperature, as well as to achieve an excellent formability caused by superplasticity at high temperatures, in magnesium alloys. In the present study, as an attempt to develop a convenient grain refinement method, wrought products of a commercial magnesium alloy AZ31 have been subjected to further cold rolling and subsequent annealing. The influence of the angle between the original working direction and the cold-rolling direction on the grain size has also been investigated. A hot-rolled sheet and an extruded bar were cold-rolled by 15% directly and after annealing at 250°C for 1 h, respectively, subsequently annealed at 250°C for 1 h, and then subjected to optical microscopy. The present process consisting of cold rolling and subsequent annealing was found to be effective to refine the grain size. Grain refinement became more marked when the angle between the original working direction and the cold-rolling direction increased. Yield strength and hardness were confirmed to increase with decreasing grain size. The minimum grain size obtained in the present study was 6.4 μm, which seemed to be sufficiently fine for the occurrence of superplasticity.View full abstractDownload PDF (1119K) -
Takashi Kanamori, Toshitsugu Maruta, Yoshihisa Matsumoto, Yasunori Har ...2002 Volume 66 Issue 1 Pages 22-27
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSExperiments were performed with high purity chromium to make a search for some method for improving the ductility at room temperature. The ductile-to-brittle transition temperature (DBTT) was about 555 K for as-sintered specimens. However, it was lowered by about 200 K using proper thermomechanical treatment. For example, the rolling at 973 K to reduce the specimen thickness by 15% per pass, and the subsequent annealing at 1273-1373 K were repeated until the total reduction of specimen thickness reached 85%, followed by the final annealing at 1473 K. When such thermomechanically treated specimens were then pre-strained by 2-5%, polycrystalline chromium exhibited a fracture elongation exceeding 20% even at room temperature.View full abstractDownload PDF (757K) -
Yasubumi Furuya, Nesbitt W. Hagood, Sizuka Tamoto, Takesi Kubota, Teik ...2002 Volume 66 Issue 1 Pages 28-33
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSRapid-solidified Fe-29.6 at%Pd alloy is a ferromagnetic shape memory alloy, in which giant magnetostriction is caused by the re-arrangements of the activated martensitic twin variants due to applying magnetic field. We have tried to evaluate the transformation phenomena from fct martensite twin phase to fcc austenite stable one in this alloy by use of a magnetic Barkhausen noise (MBHN) technique. The envelope of BHN voltage vs time in Fe-29.6 at%Pd alloy shows two peaks, where secondary peak on intermediate state of magnetic process decreases with increasing temperature, while the BHN envelope in iron and nickel does not change. The power voltage of high frequency part (8∼10 kHz) in BHN spectrum increases with increasing temperature and it shows a maximum value at As (∼370 K) and then, decreases. From the analysis of BHN, it can be concluded that the variation of BHN due to the phase transformation is apt to arise at the higher frequency part of the BHN spectrum during intermediate stage of magnetization process, and BHN seems to be a useful technique for the non-destructive evaluation of the martensite phase transformation in ferromagnetic shape memory alloy with activated twins.View full abstractDownload PDF (538K) -
Yoshikazu Todaka, Masahide Nakamura, Satoshi Hattori, Koichi Tsuchiya, ...2002 Volume 66 Issue 1 Pages 34-39
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFerrites with the spinel structure have a wide field of technological applications. In the present study, various ferrite (Fe, Co and Ni-Zn) nanoparticles were synthesized by mechanochemical reaction in aqueous solution of various chlorides (FeCl3, CoCl2 and NiCl2/ZnCl2) and NaOH in a horizontal ball mill. Structures, morphologies, compositions and magnetic properties of the synthesized nanoparticles were investigated using X-ray diffraction (XRD), analytical high-resolution transmission electron microscope (HRTEM) and vibrating sample magnetometer (VSM). It was revealed that the size and morphology of ferrite nanoparticles can be controlled by milling conditions, such as, milling time and pH value (R value) of starting solution. The particle sizes of Fe3O4/γ-Fe2O3 milled for 72 h and 120 h at R=1 were 30 nm and 20 nm in diameter, respectively. Meanwhile the particles milled for 72 h at R=0.5 had a particle size of 100 nm and a coercivity of 10.8 kA/m. The particle sizes of CoFe2O4 milled for 72 h at R=1 and Ni0.5Zn0.5Fe2O4 milled for 96 h at R=1 were about 30 nm. The magnetization values of CoFe2O4 and Ni0.5Zn0.5Fe2O4 were about 55 μWb·m/kg, with coercivity values of 43 kA/m and 5.3 kA/m, respectively.View full abstractDownload PDF (1863K) -
Makoto Hasegawa, Hiroshi Fukutomi2002 Volume 66 Issue 1 Pages 40-45
Published: 2002
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe difference of formation mechanisms of microstructure between dynamic and static recrystallization in pure nickel was studied on the basis of texture and EBSP analysis. Uniaxial compression was conducted at room temperature, followed by annealing at 905 K from 10 s to 28.8 ks. The process of static restoration was traced by optical microscopy and the measurement of micro Vickers hardness.
Fraction of statically recrystallized region was 30% and 80% at annealing for 10 s and 60 s, respectively. Annealing longer than 60 s results in a 100% recrystallized state. The value of maximum pole density of texture was 4.6 after the uniaxial compression up to the true strain of −0.66. During static recrystallization, the texture became weak and finally the maximum pole density fell off in 2.0. The position of maximum pole density, however, did not change from (011). At the initial stage of static recrystallization, new grains nucleated with random orientation in the vicinity of grain boundaries; inhomogeneously deformed regions. On the other hand, at the final stage of static recrystallization, new grains formed from the regions suffered from relatively homogeneous deformation. At this stage, the main component of the texture was (011) although it was the weak texture. In dynamic recrystallization, new grains always nucleated with random orientation at the deformation giving high values of Z. The reason is given as follows. During dynamic recrystallization, the deformation simultaneously proceeded and hence regions of inhomogeneous deformation continuously formed at the vicinity of grain boundaries. New grains nucleate preferentially from these regions.View full abstractDownload PDF (956K)
- |<
- <
- 1
- >
- >|