Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
Volume 66 , Issue 10
Showing 1-13 articles out of 13 articles from the selected issue
  • Kenzaburo Marukawa, Masayuki Tabuchi
    2002 Volume 66 Issue 10 Pages 973-981
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    In the discussion of the mechanism of the bainitic transformation, it is indispensable to clarify the precise nature of the transformation strain associated with bainites. In the present study, a new technique utilizing interference fringes in transmission electron micrographs was applied to observe and analyze the transformation strain. Based on the theoretical consideration of image formation, the appearance of these fringes along the interface of a bainitic precipitate was taken to be evidence of the existence of a shear-type transformation strain. From the analysis on the spacing of interference fringes, the direction and magnitude of the shear strain were obtained. It was found that the shear strain associated with bainites has almost the same crystallographic direction and magnitude as the one associated with martensites in the same alloy. On the basis of these findings, a new model on the mechanism of the bainitic transformation has been presented, in which the dislocation motion bringing about the lattice transformation is controlled by the atomic diffusion through a local concentration change. This model consistently explains both of existence of the transformation strain and the diffusion-control nature of the transformation. The model was compared with previous models.
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  • Shingo Iwamura, Masaru Nakayama, Yasuhiro Miura
    2002 Volume 66 Issue 10 Pages 982-988
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    Coherency of the Al3Sc precipitates in Al-0.2Sc, Al-3.0Mg-0.2Sc and Al-2.5Cu-0.23Sc was investigated by quantitative analysis of spherically symmetrical strain contrasts around the precipitates in the TEM images. Measurement of coherency strain was made utilizing the equations developed by Ashby and Brown and assuming negligible solutions of Mg and Cu in the Al3Sc phase.
    Elastic strain at the Al/Al3Sc interface in the binary alloy is almost independent of particle size. The strain in the ternary Al-Mg-Sc alloy tends to be smaller than that in the binary alloy, and shows negligible dependence on particle size. The critical radius for coherency-semicoherency transition as defined to be the critical radius where misfit dislocations appear, ranges from 20 nm to 40 nm in the binary alloy, while that in the Al-Mg-Sc ternary alloy ranges from 40 nm to 80 nm. For the Al-Cu-Sc alloy, coherency strain becomes slightly smaller with the growth of the Al3Sc precipitates, and the critical radius falls on the same range as that for the binary alloy. The results above show that the addition of Mg or Cu enhances stability of the Al3Sc precipitates.
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  • Toshiyuki Fujii, Masashi Ogawa, Susumu Onaka, Masaharu Kato
    2002 Volume 66 Issue 10 Pages 989-996
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    Upon precipitation of a second phase from a solid matrix crystal, dislocations frequently act as preferential nucleation sites. It is well known that internal and external stresses promote the formation of preferential variants of precipitates. It is therefore reasonable to consider that stress fields around a dislocation play an essential role on the variant selection of precipitates. The present research is aimed to quantitatively evaluate the role of the stress fields around a dislocation on the preferential formation of specific precipitate variants. Solution-treated Cu-0.32 mass%Cr alloys were deformed in tension by 5%. To form Cr precipitate particles, the deformed specimens were aged at 773 K for 1.8 ks and successively aged at 973 K for 1.8 ks. To characterize variants of Cr particles and dislocations, thin foils sliced from the aged specimens were observed by using a transmission electron microscope. From analysis of selected-area diffraction patterns, it is revealed that only a certain Kurdjumov-Sachs variant of Cr particles among the 24 crystallographically equivalent ones is formed on given dislocations. By considering the interaction between transformation strains upon precipitation and stress fields around dislocations, it is successfully explained that the specific Cr variants are formed preferentially on the given dislocations.
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  • Hiroyuki Kutsumi, Seiichi Muneki, Takehiko Itagaki, Fujio Abe
    2002 Volume 66 Issue 10 Pages 997-1003
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    The effect of alloying elements on the steam oxidation behavior of carbon-free Fe-12Ni-9Co base martensitic alloys has been investigated in steam at temperatures between 873 and 1023 K for up to 3.6 Ms. The alloys tested are twelve new alloys developed for ultra-super critical power plants and three commercial 9-12Cr ferritic steels. Mo and W affected steam oxidation resistance of Carbon Free Martensitic Alloys, and Fe-12Ni-9Co-5Mo alloy showed the best steam oxidation resistance among three alloys (Fe-12Ni-9Co-5W, Fe-12Ni-9Co-10W and Fe-12Ni-9Co-5Mo). The steam oxidation resistance is improved by an increase of Ni content at temperatures higher than 973 K, while remarkable effect is not observed by varying Si, Cr and Pd content. The mass gain due to steam oxidation of alloy with 18Ni at 973 K is approximately the same as that of three commercial 9-12Cr ferritic steels at 873 K. An austenitic layer with lower Fe and higher Ni than the base metal forms at the interface between Fe3O4 oxide scale and the base metal in the carbon-free martensitic alloys, which is responsible for the improvement of steam oxidation resistance in these alloys.
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  • Prasert Chalermkarnnon, Itsurou Shishido, Masao Yuga, Hideki Araki, Ya ...
    2002 Volume 66 Issue 10 Pages 1004-1008
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    A β+-γ coincidence positron lifetime spectrometer equipped with two electromagnetic lenses was constructed. The electromagnetic lens was used to have energy-selected positron beam. It accomplished a time resolution of 385 ps (FWHM) for the total system with a Pilot U plastic scintillator. By using a silicon avalanche diode instead of Pilot U plastic scintillator to initiate start timing signals, the time resolution was improved to 345 ps (FWHM). With this method, in-situ positron lifetime measurements at high temperatures or under high stresses can be attained easily.
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  • Yoshihiro Takahara, Shin-ichi Towata, Nobutaka Narita
    2002 Volume 66 Issue 10 Pages 1009-1013
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    The chemical interaction (chemical bond) of constituent atoms in Zr65Cu35 and Zr65Ni35 metallic glasses has been investigated. The relationship between the stability of supercooled liquid state and the chemical bond is discussed. The feature of chemical bonds in those glasses was evaluated from the local electronic structures of hcp-like clusters which were calculated using the discrete-variational (DV)-Xα molecular orbital method. The hcp-like cluster models used here were constructed on the basis of local structure parameters determined by EXAFS (extended X-ray absorption fine structure) analysis. The strength of the Zr-Ni bond is larger than that of Zr-Cu bond, while the Cu-Cu bond strength is nearly equal to the Ni-Ni bond. Moreover, the strength of the Zr-Zr bond is larger in Zr65Cu35 glass than in Zr65Ni35 glass. This indicates that the formation of primary crystalline phase is more difficult in Zr65Cu35 glass than in Zr65Ni35 glass. The difficulty contributes to the relative stabilization of supercooled liquid state in Zr65Cu35 glass compared with that in Zr65Ni35 glass.
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  • Yoshikuni Kadoya, Ryotaro Magoshi, Hisataka Kawai, Tomohiro Tsuchiyama
    2002 Volume 66 Issue 10 Pages 1014-1021
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    Effect of the compositional balance of Mo and W on long-term creep strength of 10%Cr-3%Co steels was investigated at temperature of 600 and 650°C under stress of 200 and 120 MPa respectively. The creep rupture strength in both conditions took a maximum point in the parameter of 0.5W/(Mo+0.5W). This phenomenon may occur through different solid solution hardening of Mo and W due to differing behaviour of the Laves phase precipitation, suggesting that it depends on the compositional balance of Mo and W. It is also found that dispersion hardening and dislocation hardening after long-term creep are unaffected by the difference between the compositional balance of Mo and W. In spite of the difference between the compositional balance of Mo and W, the long-term creep strength of the steels can be described as a function of the solute mole fraction, C, times the second power of the size-misfit parameter, εb2. This is suggested that the long-term creep strength of the steels is controlled principally by solid solution hardening, in addition to dispersion hardening and dislocation hardening.
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  • Yoshikazu Mantani, Yoshito Takemoto, Moritaka Hida, Akira Sakakibara
    2002 Volume 66 Issue 10 Pages 1022-1029
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    The α″ martensite phase in the quenched Ti-40 mass%Nb alloy transforms reversely to the β phase upon short-time aging at 623 K for 0.9 ks, resulting in the β+ω microstructure in the aged specimen. The relationship between the tensile property and the microstructure of this specimen was investigated by the observation of the structural changes in the quenched and aged specimen during tensile deformation. Products of the β phase, which were similar to {332} twins, surrounded by the matrix of α″ martensite were formed in the quenched specimen upon tensile deformation. In the aged specimen, on the other hand, α″ martensites and {332} twins were formed upon tensile deformation. The amount of α″ martensite in the two specimens was larger in the nonuniformly deformed area near the fracture. In particular, concentrated slip occurred in the nonuniformly deformed area of the aged specimen accompanied by the extinction of ω phases. The results indicate that the α″ transformation and then the reverse α″→β transformation were involved in the formation of 332 twins. It is suggested that the formation of {332} twins was due to lattice instability, and that besides the role of deformation resistance, ω phases played a part in nonuniform deformation.
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  • Masaru Yokota, Fuminori Sugaya, Haruhisa Mifune, Yoshiyuki Kobori, Kat ...
    2002 Volume 66 Issue 10 Pages 1030-1038
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    Excavated bronze objects are, depending on how long they were in the ground and under what conditions, generally corroded externally as well as having intricately corroded layers inside. To date, our group has performed metallurgical investigations on 18 ancient bronze mirrors and confirmed that pure copper lumps and several varieties of unidentified corrosion products are formed in and on the corroded layers of the mirrors. Accordingly, we investigated the corrosion products by using EPMA, SEM, μ-XRD and XPS, and discussed the possible causes of corrosion. The results are as follows;
    (1) Amorphous SiO2 had formed in the outermost corroded layer I. (2) Cu2O (cuprite) and Cu (OH)2 had formed in the layers II and III, which comprise the first two internal layers adjacent to layer I. (3) Cu-Sn-Pb- complex oxide had formed in layer IV, the next internal layer. Small amounts of PbSO4 and an Sn-organic compound were also detected. (4) We observed that Cu2S (chalcocite) forms like mold on the polished surface of the corroded layers, especially notable on layer IV, after being mechanically polished and left to stand for about one month. Cu2S is presumed to be the resultant of sulfate reducing bacteria. (5) Numerous pure copper lumps appeared in layers or particles and tended to form in the vicinity of layer IV. (6) The evidence from these analyses suggest that microorganisms could have been the cause of the corrosion found in ancient bronze mirrors excavated from clay.
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  • Yukinobu Takada, Masayuki Kudoh
    2002 Volume 66 Issue 10 Pages 1039-1047
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    A new experimental setup was constructed to make one suspending droplet. This method was named as “the suspended droplet method”. Some fundamental findings on the droplet solidification of pure Al and Al alloys were obtained by the method.
    In this study, solidification behavior of a suspending droplet in Ga-50 at%Sb, Ga-40 at%Sb and Ga-60 at%Sb alloys is investigated. A droplet with approximately 1 mm and 2 mm in diameters is solidified with naturally or forcedly cooled conditions. Also it is forcedly cooled under micro-gravity atmosphere. In the naturally cooled solidification, all specimens with 1 mm and 2 mm in diameters have indefinite shape with a projection except for the specimen with 2 mm in diameter of a Ga-60 at%Sb alloy. The solidified microstructure of a Ga-50 at%Sb alloy might be composed of one dendrite. On the other hand, forcedly cooled specimens have a shape like sphere and their grain sizes become large when the specimen is 1 mm in diameter or solidifies under micro-gravity even though it is 2 mm in diameter.
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  • Ryuta Onodera, Zhu Gui He
    2002 Volume 66 Issue 10 Pages 1048-1054
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    We examined the strain-aging phenomena in annealed low carbon steels with grain size of 13 and 40 μm. The specimens were pre-strained to prescribed strain (1.9%∼7.3%), followed by aging at various temperatures (293 K∼493 K) during a fixed time interval (0.2 h∼27 d) and then re-strained. Experimental results are as follows: 1. The extrapolation of smooth part of re-straining s-s curve passed through the ending point of pre-straining s-s curve, 2. Aging not only restored the yield point phenomena (i.e. increased the yield stress), but also enhanced the work hardening rate, 3. The aging time necessary for restoration of yield stress was shorter than that for the enhancement of work hardening rate, 4. Effects of grain size and pre-strain on the restoration were different from those on the enhancement. If we accept the following hypothesis, the experimental results mentioned above are easily understandable; 1. the internal stress of low carbon steel consists of two part; the one, Yint is ordinary stress which is work-hardened, and other, Yir which is work-softened is the cause of the yield point phenomena, 2. Yir is age-hardened, on the other hand, Yint is not age-hardened, but its work hardening rate is enhanced by aging.
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  • Takuo Shoji, Yoshihito Kawamura, Yasuhide Ohno
    2002 Volume 66 Issue 10 Pages 1055-1062
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    In order to establish metallurgical bonding technology of bulk metallic glasses, welding of Zr41Be23Ti14Cu12Ni10 bulk metallic glasses with a wide supercooled liquid region and high glass forming ability has been tried by friction welding. The Zr41Be23Ti14Cu12Ni10 bulk metallic glasses have successfully welded to the same bulk metallic glasses together. Under a wide range of conditions, no crystallization and no visible defects were observed in the interface. The tensile strength of the welded bulk metallic glasses was the same as that of the parent ones. Moreover, the effects of friction-welding conditions such as friction time, rotational speed and upsetting pressure have been investigated.
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  • Daisuke Kusano, Yasuhiko Hori
    2002 Volume 66 Issue 10 Pages 1063-1065
    Published: 2002
    Released: April 24, 2008
    JOURNALS FREE ACCESS
    We have investigated thermoelectric properties of p-type Bi-Te thermoelectric material doped with PbTe. The samples (Bi2Te3)0.2(Sb2Te3)0.8+xmass%PbTe(x=0, 0.05, 0.1, 0.3, 0.5) were fabricated by mechanical alloying and spark plasma sintering(SPS) method. The Seebeck coefficient(α), the electric conductivity(σ) and the thermal conductivity(κ) were measured in the temperature range 323-523 K. The α decreased and the σ increased with increasing PbTe content. The dimensionless figure of merit(ZT) were calculated. The maximum point of the ZT shifted toward higher temperature with increasing PbTe content. The maximum ZT of 1.12 was obtained for x=0.3 sample at 373 K.
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