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Volume 67, Issue 2
Displaying 1-6 of 6 articles from this issue
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Masayuki Sagara, Yasuyuki Katada, Toshiaki Kodama, Tooru Tsuru2003 Volume 67 Issue 2 Pages 67-73
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSurface of high nitrogen-bearing austenitic stainless steel was analyzed by using X-ray photoelectron spectroscopy (XPS). Test specimen was 23 mass%Cr-4 mass%Ni-Mo-free-1 mass%N stainless steels produced by nitrogen gas pressurized electroslag remelting (P-ESR) equipment. The specimens were polarized electrochemically in artificial seawater to passive region potential before the analysis. Pitting or crevice corrosion did not occur during the polarization. In XPS measurement, takeoff angles were changed to obtain information of depth distribution. It could be supposed that metal hydroxide exists at outer layer and oxide exists at inner layer in passive film. Passive film involved chromium and iron oxides are formed at the surface of stainless steel, and metallic chromium and iron exist at the inner layer. Spectra of N1s had mainly 2 peaks. The lower binding energy peak indicates nitrogen atoms or nitrides existed at inner layer of the passive film. The effect of polarization condition on the state of surface was determined. The degree of nitrogen concentration at inner layer increased with polarization potential.View full abstractDownload PDF (525K) -
Yongjia Zheng, Tohru Yamasaki, Tohru Mitamura, Mititaka Terasawa, Take ...2003 Volume 67 Issue 2 Pages 74-78
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to overcome the irradiation embrittlement in austenitic stainless steels, ultra-fine grained SUS316L steels with very fine TiC particles have been developed. The SUS316-TiC nanocomposite powders having 1.0 to 2.0 mass%TiC were prepared by ball-milling SUS316-TiC powder mixtures for 125 h in an argon gas atmosphere. The milled powders were consolidated by hot isostatic pressing (HIP) under a pressure of 200 MPa at temperatures between 700∼1000°C, and the bulk materials with crystallite size ranging between 100∼400 nm have been produced. The possibility of using fine-grained TiC particles for pinning grain boundaries and thereby to maintain the ultra-fine grained structures has been discussed.View full abstractDownload PDF (861K) -
Kazutaka Fujita, Tetsuo Takayama, Akihisa Inoue, Tao Zhang, Hisamichi ...2003 Volume 67 Issue 2 Pages 79-84
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA nano-scale crystal (NC) dispersed bulk metallic glass has both high tensile strength and high ductility. The new alloy is therefore expected as a candidate of high-strength structural materials in machines and structures. However, fatigue life properties in the NC bulk glass has not been examined. In this report, effects of the nanocrystalline dispersion on fatigue was studied in a NC glassy alloy Zr55Al10Cu30Ni5 (at%). Fatigue ratio, fatigue limit σw⁄tensile strength σB, in the NC bulk glass was estimated to be about 0.13. The value was 3 times larger than that of single phase bulk metallic glasses with the same composition reported in the literature. It is considered that the inhibition of the slip initiation and growth was induced by the nanocrystal dispersion and it increased the σw.View full abstractDownload PDF (949K) -
Tsutomu Ito, Junya Saeki, Masahisa Otsuka2003 Volume 67 Issue 2 Pages 85-92
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe high temperature ductility of coarse grained Mg-2.7 mol%Al and Mg-4.5 mol%Al alloys has been investigated. Both alloys showed superplastic-like elongation over 250% at 723 K. The superplastic-like deformation is rate controlled by solute drag of dislocations which often governs the creep of what is called Class I solid solution alloys. As for the ductility in solute drag creep, the number of slip systems is essential. The number of slip systems in magnesium alloy is only three at room temperature. However, superplastic-like behavior appears at high temperature, since non-basal slip is activated. Superplastic-like elongation observed in Mg-Al alloys is thus comparable to that observed in both Al-Mg and Al-Cu alloys.View full abstractDownload PDF (741K) -
Takafumi Niwa, Yoichi Ikematsu, Akira Taniyama, Daisuke Shindo2003 Volume 67 Issue 2 Pages 93-97
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTo evaluate the accuracy of measurements using stereoscopic observation employing a transmission electron microscope (TEM), the thickness (∼0.6 μm) of platelet-type α-Fe2O3 particles was investigated by stereoscopic observation using TEMs and imaging plates. The accuracy of these measurements was evaluated by comparing ts with tg, where ts and tg were the thicknesses determined by stereoscopic observation and geometric calculation taking the particle’s shape into account, respectively. The standard deviation of the difference between ts and tg decreases with increased tilt angle up to 20°. The minimum standard deviation of the difference was evaluated to be 4.8% at a tilt angle of 20°. From the present study, it was found that a particle’s shape, such as thickness on a sub-micrometer scale, can be evaluated by stereoscopic observation using a TEM set at the highest accuracy at a tilt angle of about 20°.View full abstractDownload PDF (1014K) -
Masafumi Noda, Mitsuji Hirohashi, Kunio Funami2003 Volume 67 Issue 2 Pages 98-105
Published: 2003
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn practical application, an appearance of low temperature superplasticity is one of necessaries conditions. In this paper, to estimate an appearance and deformation mechanisms of this superplasticity, the role of grain boundary sliding, intragranular deformation and the change of microstructure during superplastic deformation have been investigated for ultrafine-grained Al-Mg alloy with a grain size of less than 1 μm using Multi-Axial Alternative Forging (MAF) technique. In these materials, it shows that the elongation and strain rate sensitivity (m-value) were 340% and 0.39, respectively, at 473 K under a strain rate of 2.8×10−3 s−1. These result shows that superplastic appearance is possible at 473 K. The void formed at 473 K elongated in parallel to the tensile direction, with a length of 15 μm and a width of 5 μm. The intragranular deformation contribution was estimated from the aspect ratio of the grains after deformation and its contribution ratio was about 43%. Therefore, for the appearance of lower temperature superplasticity with large elongation and m-value, the role of intragranular deformation was the most important factor together with grain boundary sliding under these conditions. As described above, the MAF technique is one of the most effective methods to produce ultrafine-grained material and appearance of lower temperature superplasticity.View full abstractDownload PDF (2006K)
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