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Volume 65, Issue 1
Displaying 1-10 of 10 articles from this issue
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Yoshihiro Nakayama2001 Volume 65 Issue 1 Pages 1-5
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAl-10%Mg alloy was isothermally annealed and tensile tested in order to investigate the effect of microstructure changes on the serration of the stress-strain curve. The effects of the formation of precipitates and decrease in concentration of solute Mg atoms with aging time on the serration were discussed in detail. The following results were obtained. The critical strain for onset of the A-type serration increased with the lapse of aging time, while that of the B-type decreased. Since it has been reported that the development of a cell structure is greatly accelerated by the formation of precipitates, it is reasonable to speculate that an increasing rate of a mobile dislocation density with increasing plastic deformation may be depressed by the formation of stable or metastable precipitates in Al-Mg based alloys. This suppression of the multiplication of the mobile dislocation may be responsible for the variation in the critical strains of the A- and the B-type serrations with the aging treatment.View full abstractDownload PDF (597K) -
Yuzuru Ogura, Masayuki Kondo, Tatsuo Morimoto, Akira Notomi, Takahiro ...2001 Volume 65 Issue 1 Pages 6-12
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe evaporation rates of plasma sprayed Y2SiO5 coatings were measured in a low pressure air; pair=4.6 Pa and 110 Pa, over a temperature range of 1943 to 2173 K. A xenon image furnace was used for heating specimens in a pressure-controlled chamber. The evaporation rate of the Y2SiO5 coating in pair=4.6 Pa at 1973 K was 3×10−7 kg/(m2·s), which is about 10−3 times of the evaporation rate of SiO2 calculated from the equilibrium pressure of SiO(g) and about 102 times of that of Y2O3 calculated from the equilibrium pressure of YO(g). The recession rate of the Y2SiO5 coating converted from the evaporation rate is 10−4 μm/s. A duplex coating consisting of an outer 100 μm-thick Y2SiO5 layer for erosion protection and an inner SiC layer, which we proposed for oxidation protection coating for C/C composites, is considered to be sufficiently resistant against recession due to evaporation during re-entry of the H-II orbiting plane-experimental (HOPE-X).View full abstractDownload PDF (448K) -
Yuzuru Ogura, Masayuki Kondo, Tatsuo Morimoto, Akira Notomi, Takahiro ...2001 Volume 65 Issue 1 Pages 13-20
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe oxidation resistance of a Y2SiO5/SiC coating was evaluated by oxidation tests under thermal cycles between room temperature and 1973 K in pO2=440 Pa, which simulates the re-entry of the HOPE-X (H-II Orbiting Plane-Experimental) space shuttle. The Y2SiO5 layer was produced by atmospheric plasma spraying on a CVD-SiC precoated graphite. Addition of the Y2SiO5 layer to the SiC coating improved oxidation resistance of the coating remarkably at the initial stage up to 7 thermal cycles and a spallation of the Y2SiO5 layer accelerated the oxidation of the SiC layer. An in situ observation of the behavior of opening and closing of cracks in the Y2SiO5 layer, and EPMA analysis on the cross section of the coating revealed that the cracks close at high temperature and hardly accelerate oxidation of the SiC layer. High temperature mass spectrometric analysis of the oxidation behavior in pO2=3.2 Pa revealed that suppression of pO2 at the Y2SiO5/SiC interface by the Y2SiO5 layer prevents active oxidation of the SiC layer and causes an interfacial reaction between Y2SiO5 and SiC.View full abstractDownload PDF (2289K) -
Zhangfu Yuan, Kusuhiro Mukai, Katsuhiko Takagi, Masahiko Ohtaka2001 Volume 65 Issue 1 Pages 21-28
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the range of oxygen partial pressure, PO2, from 2.85×10−19 to 8.56×10−6 MPa.
At PO2=2.85×10−19 and 1.06×10−15 MPa, the surface tension of molten tin decreases linearly with increasing temperature and the temperature coefficients were (∂σ⁄∂T)PO2=−0.151, −0.094 mN·m−1·K−1, respectively. At higher oxygen partial pressure (PO2=3.17×10−10, 8.56×10−6 MPa), the surface tension increases with increasing temperature near the melting point (505 K). However, at temperatures ranging from 723 to 1033 K, the surface tension decreases with increasing temperature. Consequently, dependence of the surface tension decrease with PO2 in the vicinity of the melting point is pretty large in comparison with that at temperatures ranging from 823 to 1023 K. The observed results were explained qualitatively based on a model proposed by Passerone et al.21) which incorporates both thermodynamic and kinetic considerations.View full abstractDownload PDF (601K) -
Hiroyuki Toda, Toshiro Kobayashi, Akihiro Takahashi, Ataru Hoshiyama2001 Volume 65 Issue 1 Pages 29-37
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCoarse inclusion materials have shown evidence of inclusion cracking ahead of a crack-tip by in-situ SEM observations, which degrades the fracture toughness. In-situ strengths of various inclusions have also been estimated in the preliminary analysis. The present work is aimed at numerical analyses of toughness degradation due to the existence of damaged inclusions with an A2091 alloy as its model material. Especially, microstructural control for toughness enhancement is discussed in the lights of the results.
The investigation employs a combination of HRR singularity and an Eshelby model, which considers both elastic mismatches between a matrix and inclusions and back stresses due to rigidity of the inclusions, to conduct an estimation of internal stresses in the inclusions. The essential feature of the model is to predict crack initiation toughness and crack path morphologies using a mixed-mode fracture criterion. An appropriate criterion for the damage initiation, effects of a deflected crack-tip and shielding/antishielding effects due to the damaged inclusions are taken into consideration.
The toughness is found to be degraded in the case of large matrix grains, high volume fraction of inclusions, and low fracture strength of the inclusions. When the spatial distribution of the inclusions is homogeneous, these effects are predicted less than 10%. However, the effect is remarkably pronounced when the inclusions are agglomerated. Some of these results are consistent with those by in-situ SEM observations reported elsewhere. The estimated lower boundary values of the fracture strengths are 2520 and 2440 MPa respectively for Al3Zr and Al3Ti particles. These values are of particular interests, because they are several times larger than the measured in-situ strengths of CuAl2 and Al2CuMg particles. Aligned weak inclusions on grain boundaries act to deflect the crack along the grain boundaries even when inferior crack propagation resistance within grain boundary PFZs is not considered.View full abstractDownload PDF (619K) -
Masami Taguchi, Maki Watanabe2001 Volume 65 Issue 1 Pages 38-44
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThere are many cases when atmospheric corrosion produces serious problems-for example, in electronic equipment. In this report, Au and Ni were vacuum-evaporated to produce a thin film on a quartz oscillator and the mass changes of the fresh surfaces during introduction/evacuation of N2 and artificial air were measured by the QCM technique in order to investigate the initial oxidation details of a fresh nickel surface near room temperature. The monolayer adsorption could be achieved on a fresh Au surface when the N2 pressure reached 1.01×105 Pa, but the adsorbed layer was completely desorbed by evacuation of the gas. For the fresh Ni surface, the monolayer adsorption, which was formed within 10 seconds of the N2 introduction, did not disappear even if the N2 was evacuated. The mass change of the fresh Au surface during the introduction/evacuation of artificial air was substantially the same as that of N2. However, the XPS analysis revealed that a nickel compound, NiO, was formed on the fresh Ni surface very early during the introduction of artificial air. A contaminant, SO2, had a tendency to accelerate the rate of mass gain during the gas introduction, while H2O only increased the mass of the initial adsorption layer.View full abstractDownload PDF (540K) -
Hyeoung-Ho Park, Min-Ho Lee, Shoji Goto, Setsuo Aso, Yoshinari Komatsu2001 Volume 65 Issue 1 Pages 45-52
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to evaluate the corrosion resistance of a cathode-side separator for a molten carbonate fuel cell (MCFC), SUS316 and SACC-SUS316, in which chromium and aluminum were simultaneously deposited by diffusion into a SUS316 austenitic stainless-steel substrate by a pack-cementation process, were used as separator materials. In the case of SUS316, corrosion proceeds via three steps: formation of a corrosion product until the corrosion product becomes stable, protection against corrosion until breakaway occurs and the advance of corrosion after breakaway. Because SUS316 exhibited a rapid corrosion rate in the cathode environment, it would be impossible to use this separator without suitable surface modification due to the occurrence of a severe problem involving the stability of the cell during long-time operation. In contrast, SACC-SUS316 was demonstrated to exhibit more effective corrosion resistance than the present separator, SUS316. In particular, there was no corrosion behavior exhibited by SACC-SUS316 after 480 h at 923 K. Moreover, it is considered that this will be very useful as an alternative separator at the cathode side in MCFCs in the future.View full abstractDownload PDF (1550K) -
Shinji Itoh, Hitoshi Yamaguchi, Toshiyuki Hobo, Takeshi Kobayashi2001 Volume 65 Issue 1 Pages 53-59
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGlow discharge mass spectrometric (GDMS) analysis of zirconium-based alloys has been studied by using a VG 9000 instrument. Disk samples were dry-polished with 120-grit zirconium oxide endless-paper and preliminary exposed to glow discharge for 1.8 ks in the discharge cell. Optimum glow discharge conditions and the most suitable size of tantalum front mask were examined take the advance of analytical precision into consideration. The relative sensitivity factor (RSF) of each analyzing element was evaluated from the analytical values of thirteen standard reference materials: JAERI CRMs Z1∼Z16. As an example, the average RSF obtained were 1.612 for iron and 1.332 for hafnium. For the analysis of the zirconium-based alloys NIST SRMs 1234∼1239, relative standard deviation (RSD) of repetitive five measurements for each analyzing element was compared with those of obtained by the X-ray fluorescence spectrometry using theoretical alpha coefficients. RSD of GDMS analytical value change a little against the varying of analyzing element concentration, and it was within 10% for each trace impurity at mass ppm level. The GDMS analytical value of hafnium in those SRMs was in good agreement with the certified value and RSD of that was within 5%.View full abstractDownload PDF (358K) -
Tatsuhiko Tanaka, Naoki Yorimoto, Takashi Ishiyama2001 Volume 65 Issue 1 Pages 60-63
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA simple and rapid method is described for the determination of molybdenum(VI) at μg·L−1 level based on differential pulse anodic stripping voltammetry at a glassy carbon disk electrode without adding any complexing agents. Octamolybdate formed in a 0.05 mol·L−1 hydrochloric acid −0.05 mol·L−1 nitric acid mixture solution (4 mL) at pH 3 in the presence of 10 vol% acetone was electrodeposited on the working electrode at −1.2 V vs. SCE for 10 min, and the deposits were then stripped in another solution (the acid mixture solution in the absence of acetone) at a scan rate of 50 mV·s−1 to 0.2 V vs. SCE. A quantitative and reproducible peak was obtained, although the peak was split into two signals. The calibration (peak area vs. molybdenum(VI) concentration) curve was linear over the concentration range of 1.0×10−7 to 1.0×10−6 mol·L−1 and passed through the origin, with a relative standard deviation of ca. 4% for 50 μg·L−1 (n=5). The sensitivity was 8.9×10−2 μA·V·(μg·L−1)−1. The detection limit (3σ) was 2.5×10−8 mol·L−1 using a deposition time of 10 min. Tantalum(V), tungsten(VI), vanadium(V) and phosphate interfered with the molybdenum(VI) determination severely. The addition of hydrogen peroxide served to prevent interferences of titanium(IV) and zirconium(IV). The proposed method was applied to the determination of 4.47 mass% of molybdenum in the high-temperature alloy standard sample (JAERI-R4, Ni71.9 mass%) and was achieved with fairly good precision and accuracy within 60 min without any preliminary separation of the matrix. The method could be applied to the determination of molybdenum of down to 20 mass ppm in nickel metal provided the deposition potential was changed into −0.9 V vs. SCE.View full abstractDownload PDF (274K) -
Kazuhisa Kita, Takayuki Kita, Kazuo Yamana, Kazuo Kitagawa, Ryoichi Mo ...2001 Volume 65 Issue 1 Pages 64-69
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effects of alloying elements (Sb, Sn, Ti, P and Be) in the range of addition up to 0.1 mass% on the recrystallization behavior of a Cu-2.0 mass%Fe alloy have been investigated by means of micro-hardness measurement and metallographic observation. The incubation time for recrystallization and the grain growth rate during recrystallization depend strongly on the content of each element. The grain formation and growth are accelerated by the addition of P and are suppressed by the addition of Sb, Sn, Ti and Be. A 0.05 mass%Be-added alloy recrystallizes least easily. Most recrystallization nuclei in Ti- and P-added alloys form at Fe2Ti and Fe3P particles larger than about 1.0 μm. For the alloys with Sb, Sn and Be, the nucleation of recrystallization takes place predominantly at α-Fe particles, larger than 0.3 μm, on grain boundaries. A good correlation is found between the time for recrystallization and the size of the Fe2Ti particles, Fe3P particles and α-Fe boundary particles. The larger the particle size, the more easily the nucleation of recrystallization occurs. Adding the solute elements affects the dispersion of α-Fe in-grain particles which retards grain-boundary migration and thus may control the grain growth.View full abstractDownload PDF (610K)
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