Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
Volume 53 , Issue 5
Showing 1-11 articles out of 11 articles from the selected issue
  • Kazuhisa Azumi, Toshiaki Ohtsuka, Norio Sato
    1989 Volume 53 Issue 5 Pages 479-486
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    The electronic properties of the passive films formed on iron in pH6.5 borate solution were investigated by measuring the transient photocurrent. An anodic spike-like photocurrent followed by a small steady one was observed after switching on the illumination onto the passive electrode. Another spike-like current was also observed in the reverse direction after switching off the illumination. The charges and time constants of decay of the spike-like current and the steady state photocurrent were measured as a function of film formation potential and measurement potential. A simulation was made to explain the transient behaviour of the photocurrent by assuming an equivalent circuit with the generation of a photo-induced free carrier pair in the n-type passive film. From the simulation the transient photocurrent behaviour can be explained from the relations among the thickness of the passive film, the recombination rate of the photo-induced free carrier in the film, the density of surface states, and the redox system in the solution which can energetically exchange the hole or electron with the electrode.
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  • Yasutoshi Noda, Nobuyuki Otsuka, Katashi Masumoto, Isao Nishida
    1989 Volume 53 Issue 5 Pages 487-493
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    The Mg2Si1−xGex solid-solution semiconductors were prepared in the composition range 0≤x≤0.45. The Ham effect, thermoelectric power and electrical conductivity were measured and the maximum figure-of-merit (Z) was estimated for the undoped sample at the composition x=0.45. The carrier concentrations at 300 K were controlled at this compositon to 1.4×1025 m−3 electrons and 1.8×1025 m−3 holes by doping the nominal amount of 1600 ppm Sb and 20000 ppm Ag at this composition, resulting in the figure-of-merits of 6.8×10−4 K−1 and 3.8×10−4 K−1, respectively. The measurement of thermoelectric power showed that these doped samples behaved as extrinsic semiconductors up to 850 K. The maximum figure-of-merits at 700 K were estimated to be 1.5×10−4 K−1 for the n-type sample and 3.4×10−4 K−1 for the p-type one. From the fact that the value of the n-type sample was larger than those of the traditional materials, the Mg2Si1−xGex solid-solution semiconductors can be expected as a new candidate material for thermoelectric energy conversion in the middle-temperature range.
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  • Yutaka Takahashi, Minoru Mori, Yoichi Ishida
    1989 Volume 53 Issue 5 Pages 494-501
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    Dislocations in oxide superconductors YBa2Cu3O7−x and Bi(Pb)-Sr-Ca-Cu-O have been studied by high voltage electron microscopy. In the analysis, it was assumed that c-axis component of the Burgers vector is zero, because both materials have a layered structure. In YBCO, only one type of dislocation (b=a⟨1,0,0⟩) was observed. The population of the defect, however, is low in a sintered specimen. Twin boundary may act as a pinning center of the superconducting fluxoid. In BSCCO, two types of dislocations (b=a⁄2⟨110⟩ and a⟨100⟩) were found. Dislocation network can be formed by the combination of them. Most of high density of dislocation are grown-in defects and, therefore, they must be related to a critical current property. In order to explain the existence of dislocations with large Burgers vector b=a⟨100⟩, a model with ‘decomposition of partial dislocation in Bi2O2 layer’ is proposed.
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  • Yoshimitsu Okazaki, Kazuya Miyahara, Noboru Wade, Yuzo Hosoi
    1989 Volume 53 Issue 5 Pages 502-511
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    This study is aimed at making clear the effect of Mn and Cr on the microstructure and toughness of an Fe-Cr-Mn alloy which is considered as one of the candidate alloys for reduced activation materials for the first wall application of the fusion reactor.
    The microstructures of Fe-12%Cr-(5∼30)%Mn(mass%) alloys after solution treatment at 1373 K for 3.6 ks are markedly varied with Mn contents; α′(martensite)+δ(ferrite) in 5%Mn alloy, α′+δ+ε(martensite)+γ(austenite) in the 10%Mn alloy, α′+ε+γ in 15%Mn alloy, ε+γ in the 20%Mn alloy, and ε+γ+δ in the 25%Mn alloy, and γ+δ in the 30%Mn alloy. It is to be noted that the δ phase increases with increasing Mn content when the Fe-12%Cr alloy contains more than 25%Mn, which suggests that Mn plays the role of a ferrite former.
    In Fe-15%Mn-Cr alloy, the δ phase is not observed in the range of Cr contents up to 12%, whereas it is markedly increased with the addition of 16%Cr. C, N and Ni are very helpful in forming the γ phase in these alloys as generally known in Fe-Cr-Ni alloys.
    The toughness evaluated by the Charpy impact test at 273 K and room temperature is very low in the 5%Mn alloy which consists of the α′ and δ phases. It is, however, significantly improved by a small amount of the γ phase and increases with increase of γ phase stability.
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  • Yoshimitsu Okazaki, Kazuya Miyahara, Yuzo Hosoi, Mitsuru Tanino, Hazim ...
    1989 Volume 53 Issue 5 Pages 512-521
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    Allays of Fe-(8∼12%)Cr-(5∼30%)Mn were solution-treated at 1373 K for 3.6 ks, followed by cold-working of 50% reduction. Both solution-treated and 50% cold-worked materials were aged in the temperature range from 773 to 973 K for 3.6×103 ks.
    The identification of σ phase formation was made by using X-ray diffraction from the electrolytically extracted residues of the aged specimens. The region of σ phase formation determined by the present work is wider than that on the phase diagram already reported. It is to be noted that Mn promotes markedly the σ phase formation, and that three different types of σ phase formation are observed depending on Mn content: α→γ+α→γ+α+σ in 10%Mn, α→γ+σ a in 15 to 20%Mn alloys, α→χ(Chi)→χ+σ+γ in 25 to 30%Mn alloys. An average electron concentration (ea) in the σ phase was estimated by quantitative analysis of alloying elements using EPMA.
    The ea value in the σ phase formed in Fe-(12∼16%)Cr-Mn alloys aged at 873 K for 3.6×103 ks is about 7.3, which is independent of Mn content. In order to prevent σ phase formation in Fe-12%Cr-15%Mn alloy, the value of Ni*eq of 11 (Ni*eq=Ni+30(C)+25(N)) is required.
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  • Yoshimitsu Okazaki, Noboru Wade, Kazuya Miyahara, Yuzo Hosoi
    1989 Volume 53 Issue 5 Pages 522-528
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    Tensile properties of Fe-12%Cr-Mn(mass%) alloys have been studied in the temperature range between room-temperature and 1073 K. Mn contents of the alloys are ranged from 5 to 30%. The tensile properties of Fe-12%Cr-Mn alloy is markedly affected by Mn content. Relatively high strength and low ductility are obtained in 5 and 10%Mn alloys which consist of mainly α′-martensite structure at temperatures below 673 K. The transformation from α′-martensite to austenite results in a large drop of tensile strength and an increase of ductility. The tensile strength of the 15%Mn alloy decreases linearly with increasing test temperature. In the case of the 20%Mn alloy. The tensile strength decreases rapidly at temperatures up to 473 K where ε-martensite transforms to austenite, and it decreases gradually with increasing temperature. In the austenite range, the tensile properties scarcely depend on Mn content.
    C and N additions improve the tensile properties of the Fe-12%Cr-15%Mn alloy markedly. Combined alloying of 0.2%C and 0.2%N with the alloy makes the strength as high as that of JPCA (0.05%C-15%Cr-16%Ni-2.5%Mo-0.2%Ti steel), increases the creep strength pronouncedly and decrease the steady state creep rate.
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  • Ken-ichi Ohasi, Hiroshi Fukutomi, Takao Endo
    1989 Volume 53 Issue 5 Pages 529-535
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    Observations were conducted on the specimen surface after high temperature fatigue of aluminum by means of optical and interference microscopy. The surface markings produced during high temperature fatigue were convex or concave under the action of tension-compression stress cycles, whereas they were like stairs under the action of tension-tension stress cycles. Based on the metallographic observations, a model for the formation process of surface markings was proposed. It was confirmed experimentally that the first faint groove, which appeared in a specimen subjected to a process of annealing-mechanical polishing-electrolytic polishing prior to a fatigue test, corresponds to the position of grain boundary just after annealing. However, the grain boundary position just before the fatigue test was different from that after electrical polishing. This is because the grain boundaries which intersect free surface are liable to move during the heating-up process prior to high temperature fatigue in order to decrease their interfacial energy. This explains the first large displacement of grain boundary migration. A tentative model was proposed to account for the reason why the displacement of grain boundary migration during high temperature fatigue is large notwithstanding the small unidirectional deformation.
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  • Kazuaki Sato, Hirokazu Miyazaki, Yuichi Ikuhara, Hiroaki Kurishita, Hi ...
    1989 Volume 53 Issue 5 Pages 536-542
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    In order to determine the relationship between structure and strength of grain boundaries in Si, bicrystals with ⟨111⟩ twist boundaries were prepared from 6 N high-purity Si single crystals by press-joining, and their fracture strength was measured by 3-point bending test and the structure was observed by TEM. The results obtained are as follows. (1) The fracture strength depends on the twist angle in a similar manner as predicted theoretically by Inomata et al. without any consideration of the relaxation of boundary structure. However, the observed misorientation-dependence is much weaker than the prediction. (2) The measured grain-boundary energy depends on the twist angle in the same way as the fracture strength. (3) The boundary extension is too small to be observed. These results are compared with those of covalent-bonded SiC and refractory metal Mo, and the cause of the boundary extension observed in SiC and Si3N4 is discussed.
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  • Masahiro Susa, Kazuhiro Nagata, Kazuhiro S. Goto
    1989 Volume 53 Issue 5 Pages 543-549
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    The spot heating method has been developed as a new method for measuring the thermal conductivity (λ) and the thermal diffusivity (κ) of thin materials.
    The principle of this measurement is based on three relations between the temperature increase of the sample surface heated by the laser beam and the thermophysical properties of the sample. These relations are obtained by solving the Fourier’s equation under different ranges of time. The temperature increase measured in a short time range is proportional to the square root of time. The slope of this straight line gives the value of λ⁄κ1⁄2. On the other hand, the temperature increase of a long time range is inversely proportional to the square root of time. The slope of this line offers the value of λκ1⁄2 and the intercept at 1⁄t1⁄2=0 gives λ. Therefore, the thermal conductivity and the thermal diffusivity can be determined by using two of the above three relations.
    With the use of this method, first, the thermal conductivity and the thermal diffusivity of thick materials with a thickness of about 10 mm have been measured at room temperature. Fused-SiO2, PbO-SiO2, glass plates, micas and silicone rubbers are employed. The results are in good agreement with the literature values.
    Second, this method has been successfully applied to thin materials of 200 μm-1 mm in thicknesses, such as fused-SiO2 plates, glass plates and photoresist films without the influence of substrates. The obtained values are also in good agreement with the values of the thick materials.
    Finally, errors and the potentiality of its application to thin films have been discussed in detail.
    The spot heating method may be of great promise for the measurements of the thermal conductivity and thermal diffusivity of various materials, especially thin materials.
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  • Kazuo Yamanaka, Junichiro Murayama
    1989 Volume 53 Issue 5 Pages 550-557
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    In high temperature NaOH solution, the initial repassivation processes of anodic reaction on newly created surfaces of nickel-base alloys containing 0∼30 mass% chromium were investigated by a rapid straining electrode technique. And also the corrosion films of these alloys were mainly analyzed by ion micro mass analyzer (IMMA). The results obtained are as follows:
    (1) The repassivation rate of nickel base alloys increased with increasing chromium content.
    (2) The corrosion film had a double layer structure, that is, nickel hydroxide or oxide in outer layer and chromium hydroxide of oxide in inner layer. The chromium concentration in the inner layer increased with increasing chromium content.
    (3) The caustic corrosion resistance seems to be influenced by the repassivation rate and the inner chromium oxide layer, and be important of the existence of the outer nickel hydroxide and/or the oxide layer.
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  • Toshiharu Fujisawa, Tadaaki Kuno, Hiroyuki Fukuyama, Shoji Takai, Chik ...
    1989 Volume 53 Issue 5 Pages 558-564
    Published: 1989
    Released: April 04, 2008
    JOURNALS FREE ACCESS
    Activities of NaO0.5 and Na(CO3)0.5 in Na2O-CO2-Sb2O5 melts were determined at 1423-1523 K by the EMF method, using beta″-alumina as a solid electrolyte, over the composition range N≥0.7{=nNa2O⁄(nNa2O+nSb2O5), n: the number of moles} under various partial pressures of CO2. The activity of SbO2.5 was calculated from the activity of NaO0.5 by integrating the Gibbs-Duhem relation. The partial pressure of CO2 has great influence on the activities of the components in the system. The existence of a liquid state miscibility gap was suggested in the Na2CO3-rich composition range. The solubility of CO2 in the melts was also measured at 1523 K. The results of the solubility measurements of CO2 imply that Na2CO3 is decomposed according to the stoichiometric reaction corresponding to the formation of Na3SbO4 species in the melts, and, therefore, the activity of Na3SbO4 was also discussed.
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