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Volume 65, Issue 2
Displaying 1-9 of 9 articles from this issue
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Hiroshi Fukutomi, Makoto Hasegawa, Mitsuhiro Yamamoto2001 Volume 65 Issue 2 Pages 71-77
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe behavior of dynamic recrystallization of pure nickel is investigated by uniaxial compression tests at temperatures and strain rates ranging from 873 K to 1573 K and from 2.5×10−5 s−1 to 1.0×10−3 s−1, respectively. The textures formed during dynamic recrystallization are investigated by calculating orientation distribution function. Orientation measurements of individual grains also carried out by EBSP technique. It was found that the texture varies depending on the value of Zener-Hollomon parameter (hereafter abbreviated as Z). At high Z conditions, area of high pole density is distributed from (011) to 10 degrees away from (011) to (001). No sharp textures were observed at low Z conditions. It was concluded that new grains were formed by strain-induced grain boundary migration at low Z conditions. During the migration, many twins are formed, resulting in no texture formation. The fraction of twin boundary varied depending on the value of Z, suggesting that dynamic recrystallization is available for grain boundary character distribution control.View full abstractDownload PDF (957K) -
Yukio Inokuti, Kazuhiro Suzuki2001 Volume 65 Issue 2 Pages 78-84
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe textures of TiN, TiCN and TiC films made on (011)[100] single crystals of silicon steel by ion plating have been studied. For examining the influence of deposition techniques on texture formation, the ceramics films were coated on the polished single crystal surfaces by three different ion plating methods: hollow cathode discharge(HCD), electron beam(EB)+radio frequency(RF) and electron beam(EB)+hollow cathode discharge(HCD). Pole figures of the textures of the ceramics thin films and the steel matrix were measured simultaneously using an auto pole figure apparatus equipped with a solid-state detector(SSD). The {111}TiN pole figure of the TiN films deposited by the HCD method showed a dominant {111}⟨110⟩ oriented texture. The corresponding pole figures of the TiCN and TiC films deposited by the same method showed a weaker texture than that of the TiN films. The intensity of {111} pole figures of the ceramics films depended on the deposition methods. From these results, it is concluded that the {111}-texture formation in TiN, TiCN and TiC films is affected by the crystallographic coherency between the films and the single crystal matrix of silicon steel, and also by the degree of ionization of Ti in the deposition process.View full abstractDownload PDF (753K) -
Masakazu Kobayashi, Yoshimasa Takayama, Hajime Kato, Hideo Nakajima2001 Volume 65 Issue 2 Pages 85-92
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to express temperature dependence of grain growth practically, the Monte Carlo simulation using the Potts model has been performed in consideration of reorientation accompanied with activation state. Grain growth is reproduced appropriately at different temperatures by an algorithm used in this study. While little evolution of microstructure is observed at low temperatures, grains grow remarkably at higher temperatures. A lot of 1-site grains are found in a simulated microstructure at high temperatures in the neighborhood of boundaries of comparatively-large grains. This is considered to be formed by large thermal fluctuations at high temperatures. The microstructures obtained from the present simulation are compared with those in previous work. Similar rates of grain growth are observed with and without consideration of a temperature factor of T=0.55Tm, though differences in the grain boundary shapes and grain area distributions are found.View full abstractDownload PDF (601K) -
Yoshinobu Motohashi, Youji Murata, Tetsuya Suzuki, Tokuzou Tsujimoto2001 Volume 65 Issue 2 Pages 93-99
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn a previous paper, we have reported that room temperature ductility of a Ti-48 at%Al alloy deteriorates as the degree of work-hardening, caused by mechanical processings and mechanical polishings to shape the alloy into specimens, is increased. In the present paper, effects of stress relief annealings for the specimens having work-hardened surface regions on room temperature mechanical properties are studied. The microstructure of the alloy is made up of mixed bands of granular γ single-phase and granular (α2+γ) dual-phase structures, both of them being lying parallel to the longitudinal axis of the specimens. The annealing treatments for the as-surface-processed specimens were carried out at 973 to 1173 K for 7.2 ks in a vacuum or in a high-purity argon gas atmosphere. The room temperature mechanical properties were evaluated by four-point bending tests in a laboratory air.
All of the annealed specimens including electrolytic polished one showed very low room temperature deuctility. The formation of thin, but hard and brittle Ti-rich layers was observed at the surface of the annealed specimens. It was found that if these brittle surface layers of the annealed specimens are removed by mechanical and subsequent electrolytic polishings, then the room temperature ductility is completely revived. The Ti-rich layers are, therefore, thought to be one of the causes of the deterioration of the room temperature ductility. It seems that the existence of the γ⁄γ grain- and γ⁄α2 phase-boundaries of which cohesive strengths would be weakened by invasion of oxygen during the annealings are also responsible for the deterioration of the ductility.View full abstractDownload PDF (467K) -
Satoru Yamamoto, Yoshihito Isshiki, Hisayoshi Kobayashi2001 Volume 65 Issue 2 Pages 100-108
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn the present work, the cohesive energy, energy fluctuation and Mulliken’s population of metal cluster have been calculated by the extended Hückel method. The behaviors of alloying elements and the stability of Mg alloys at high temperatures have been discussed by comparing the calculated results with the actual experimental results. The main results of the present works are as follows:
(1) The cohesive energy and Mulliken’s population are quantities suitable for the discussion of the behaviors of alloying elements in Mg alloys.
(2) The additional elements to increase the strength of Mg alloys can be classified into two types, age-hardening type and heat-resistant type by the effects on the energy fluctuation of the corresponding metal cluster at high temperatures.
(3) In the age-hardening type, the energy fluctuation is small at room temperature but is large at high temperatures, therefore the strength of corresponding Mg alloys is high at room temperature but low at high temperatures. In the heat-resistant type, on the other hand, the energy fluctuation is small both at room and high temperatures and the strength is remarkably large even at high temperatures.
(4) The elements such as Al, Zn, Zr and Mn belong to the age-hardening type and the rare earth elements like Y, Ce, Pr, Nd, Pm and Sm etc., belong to the heat-resistant type.View full abstractDownload PDF (696K) -
Norito Nishiyama, Shigeru Asano2001 Volume 65 Issue 2 Pages 109-114
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSInternal friction was measured as a function of strain amplitude in high-damping metals, whose damping mechanism is based on dislocation motion. The amplitude of resonant transverse vibration was continuously recorded during the free-decay process and its logarithm was differentiated with time in a computer for the evaluation of logarithmic decrement.
For annealed magnesium, the logarithmic decrement in the steady-state vibration, evaluated from the initial stage of free decay, increases monotonously with the maximum strain amplitude in the steady-state vibration. Such an amplitude dependence of internal friction occurs in an increasing run of amplitude of the steady-state vibration and also in a decreasing run of it, but the values of internal friction are always higher in the decreasing run than in the increasing run. This hysteretic behavior can be reasonably interpreted in terms of the density of moving dislocations.
In contrast, the logarithmic decrement in the free-decay process, evaluated from the continuous change in amplitude during free decay, differs remarkably from that in the steady-state vibration, and thus reflects much sensitively the dislocation motion. The logarithmic decrement for annealed magnesium shows a peak shape when plotted against the maximum strain amplitude in the high-strain range. Slight cold work below 1% increases internal friction and enhances the peak, but heavy cold work over 5% decreases internal friction and suppresses the peak, so that its amplitude dependence becomes the same as the one in the steady-state vibration. This characteristic behavior can be explained on the basis of the mobility of active dislocations.View full abstractDownload PDF (310K) -
Michihisa Fukumoto, Shigenari Hayashi, Shigeru Maeda, Toshio Narita2001 Volume 65 Issue 2 Pages 115-121
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSOxidation properties of sintered Fe-3 mass%SiO2 (Fe-3SiO2) as well as Fe-1.5 mass%Si alloy (Fe-1.5Si) and Fe, for comparison, were investigated at 1273 K for up to 7.2 ks in air and air containing 10.5 vol%H2O (air-10.5H2O). In air-10.5H2O, the Fe-3SiO2 was oxidized faster than in air and also than the Fe-1.5Si in air-10.5H2O. The scale was composed of a duplex structure, an inner FeO+Fe2SiO4 and an outer Fe-oxides layers, where many voids existed in both layers. The similar scale structure containing voids was observed for the Fe-3SiO2 in air. Marker experiment with a small Pt wire was carried out for the Fe-3SiO2 oxidized in air-10.5 vol%H2O and the Pt-marker located between the inner and outer layers, suggesting that the inner layer grows due to inward migration of oxygen and the outer layer due to outward iron diffusion. In both air and air-10.5H2O Fe showed a parabolic oxidation, forming exclusively an outer Fe-oxides scale. It was suggested that SiO2, which changed to FeO+Fe2SiO4, acts as an obstacle for the outer layer recession, leading a formation of voids in the inner layer. Oxygen used to form the inner FeO+Fe2SiO4 layer was supplied by the dissociation of outer Fe-oxides, leaving voids, probably by a perforating dissociation mechanism. Both oxygen and water molecules could be diffusing species through the void.View full abstractDownload PDF (1380K) -
Katsuhiko Takahashi, Mitsuru Shimizu, Masahiro Kawakami2001 Volume 65 Issue 2 Pages 122-127
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt is known that metal powders containing dispersed oxide particles are difficult to sinter by the conventional process. Spark Plasma Sintering (SPS) method was tried for making the dense sinter tablets from Ni powders containing MgO. The high-temperature hardness of the sinter tablets were examined from room temperature to 1173 K. The results were summarized as the follows.
The relative density of the tablets increased with an increase in sintering temperature. The relative density of more than 97% was obtained at higher temperature than 1273 K with MgO contents of 0, 2.5, 5 and 10%. The Vickers hardness of the sinter tablets increased with an increase in MgO contents and an increase in sintering temperature. The maximum hardness of about 270 Hv, which corresponded to more than 2.5 times of pure Ni, was obtained with 10%MgO at 1273 K sintering. These high relative density and hardness can be obtained by SPS method but not by the conventional sintering.
The high-temperature hardness decreased with an increase in the temperature. Plotting the logarithm of hardness against the temperature, two straight lines were obtained. The reflection point which showed the change in deformation mode was shifted to high-temperature side by the dispersion of MgO particles. The high-temperature hardness straightly increased against a reciprocal of a space between MgO particles.View full abstractDownload PDF (707K) -
Takumi Haruna, Kozo Onishi, Toshio Shibata2001 Volume 65 Issue 2 Pages 128-133
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of irradiation of ultra-violet(UV) light on stress corrosion cracking(SCC) behavior for sensitized SUS304 stainless steel in a deaerated 10−3 kmol·m−3 NaCl solution at 368 K has been investigated by using a slow strain rate testing(SSRT) apparatus with a dynamic observation system. The UV light, whose range of wavelength was from 250 to 400 nm, was emitted by a mercury lamp, and was irradiated to the specimen through the test solution. In order to change an intensity of the UV light, some neutral density filters were set in front of the quartz glass window on the cell. A potential of −200 mVAg⁄AgCl was applied to the specimen before and during SSRT, and the UV light was irradiated up to the strain showing almost the yield stress. It was obvious that the SCC initiation was inhibited by the UV light irradiation to the specimen during SSRT. Crack initiation frequency varied with the light intensity, and an optimum intensity range existed for inhibiting crack initiation completely. On the other hand, the crack propagation rate showed almost no dependence on the irradiation conditions. In the case that the UV light was irradiated to the shielding material mounted in front of the specimen, a lot of cracks were initiated on the specimen, similar to the case without irradiation. This fact indicates that the SCC is not influenced by the solution chemistry altered by the UV light irradiation.View full abstractDownload PDF (578K)
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