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Volume 60, Issue 2
Displaying 1-17 of 17 articles from this issue
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BingShe Xu, Hideki Ichinose, Shun-ichiro Tanaka, Yoichi Ishida1996 Volume 60 Issue 2 Pages 121-127
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSJosephson junctions both direct (S/S) and indirect (S/Ag/S) with a thin silver layer were fabricated by solid state joining of (001) surfaces of two flaky Bi2Sr2CaCu2Ox single crystals. A small area junction of 100∼200 μm in diameter was fabricated by Ar+ ion selective etching of one of the two thin single crystalline superconducting Bi2Sr2CaCu2Ox flakes. A silver layer with a thickness of 2∼100 nm was deposited on the (001) planes by a sputtering method just prior to joining to produce S/Ag/S junctions. The critical current Ic of S/Ag/S junction was the function temperature with Ic=IOH(1−T⁄Tc)2 for T≥0.6Tc, and Ic=IOLexp(−GT1⁄2) for T≤0.5Tc. High Ic values were obtained when the [001] twist angle θ was 23°, 28° and 37°. It was indicated that the Josephson effect is strongly influenced by both the temperature T and the [001] twist angle θ in the S/S and S/Ag/S junctions.View full abstractDownload PDF (1300K) -
Xingguo Li, Katsuhisa Ohsaki, Masahiro Uda, Akihiko Chiba1996 Volume 60 Issue 2 Pages 128-134
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSUltrafine powder AlN/Al with an average size of 300 nm was synthesized by an arc-plasma method. This powder was added up to 20 mass% into two kinds of commercial AlN powders prepared by direct nitridation of Al and carbothermal reaction of Al2O3. The samples were sintered at a temperature range from 1973 to 2123 K in a flow of N2 gas with the help of sintering aid Y2O3 and their density and thermal conductivity were measured at 300 K. The ultrafine powder AlN/Al has a noticeable effect to reduce the sintering temperature and enhance the thermal diffusivity of the two kinds of AlN powders. This effect is more significant in the direct nitrided powder than that in the reduced powder. The sintered AlN compact with high density and high thermal diffusivity can be obtained at temperature lower than 2123 K with the aid of the ultrafine powder AlN/Al. Mechanism of this effect can be elucidated by the fact that the ultrafine powder AlN/Al has a large specific surface area and react easily with Y2O3 at low temperature where the commercial AlN powders can not. The effect of the ultrafine powder AlN/Al changes with the sintering temperature and Y2O3 content and the good effect of the ultrafine powder AlN/Al is observed when the sintering temperature is lower than 2123 K and Y2O3 is less than 8 mass%.View full abstractDownload PDF (1207K) -
Dazhou Jin, Yoshihiro Nakayama, Tetsuya Takaai, Yuuji Yamada1996 Volume 60 Issue 2 Pages 135-140
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA commercial 5083 aluminum alloy was aged at 453 K for an extended time in order to study the changes in the microstructures. In this alloy, the mechanical properties generally deteriorate with the variation in the microstructure; e.g. the precipitation of β-phase and/or decrease in solute Mg concentration in the matrix. This paper dealt with the changes in the microstructure during aging treatment at 453 K for times up to about 107 s. Variation in the solute Mg concentration was estimated by electrical resistivity measurement, X-ray diffraction and electron probe microanalysis. Precipitation of the β- and/or β′-phase was also investigated by means of microscopic strain measurement, differential scanning calorimetry and microstructural image analysis. The specimens aged for times longer than 106 s show decreases in electrical resistivity and lattice constant in relation to the formation of precipitates. Microscopic strain, which is induced by the formation of precipitate having a partially coherent interface with the matrix, shows a peak value for the aging time of about 106 s and then decreases.View full abstractDownload PDF (1356K) -
Hideshi Nakatsu, Setsuo Takaki1996 Volume 60 Issue 2 Pages 141-148
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of austenite (γ) grain size on the transformation to ε martensite (ε) and mechanical properties have been investigated in high manganese steels by means of calorimetric analysis, optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Austenite grain size of steels was controlled to be 100 μm or 10 μm in the mean grain size by the recrystallization method. With grain refining, the starting temperature of γ→ε transformation tends to be lowered and the formation of ε is suppressed in all of high manganese steels which undergo γ→ε transformation. For 15∼31 mass%Mn steels, both of elongation and tensile strength are markedly enlarged by grain refining. Fracture modes of these high manganese steels are largely dependent on microstructures and deformation behavior. Effect of γ grain size on the fracture modes was discussed in detail for 22 mass%Mn and 27 mass%Mn steels. When the size of γ grains is as large as 100 μm, a significant stress concentration takes place at the intersections of ε plates in a 22 mass%Mn steel, while does at grain boundaries on which deformation induced ε plates impinge in a 27 mass%Mn steel. Such a stress concentration at ε plates or grain boundaries causes the formation of microcracks and this leads to the onset of quasi-cleavage fractures. When the size of γ grains is refined to 10 μm, however, quasi-cleavage fractures are suppressed in the both steels. Refining of γ grains produces favorable effects; 1) change in the morphology of athermal ε, 2) decrease in the stress concentration at grain boundaries, 3) uniform dispersion of strain. For the suppression of quasi-cleavage fractures by γ grain refining, the effect 1) is most contributive in a 22 mass%Mn steel, while in a 27 mass%Mn steel, only the effects of 2) and 3) are workable.View full abstractDownload PDF (1670K) -
In Seong Chang, Tatsumi Tozawa, Hajime Kato, Yoshimasa Takayama1996 Volume 60 Issue 2 Pages 149-154
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe evaluation of the uniformity on microstructure of materials by subjective sense inspection of an expert generally includes fuzziness or ambiguity. Although our final purpose would develop an automatic evaluation system of the uniformity on microstructure of materials, this paper aims to get fundamental knowledge on how to objectively evaluate the uniformity on grain structure as a first stage. We investigate the expert’s judgements of the uniformity on grain structure in order to identify subjective evaluation process for grain structure, based on sensory engineering. Sensory engineering (or Kansei engineering) is a technology for translating human feelings or mental images into physical design components. First, the categories (adjective words) that can quantitatively characterize the human feeling of the uniformity are selected. Next, the sensory tests by questionnaire using these categories are carried out to acquire physical parameters that relate both the sensory evaluation and the characteristic of the microstructure. Finally, the quantitative evaluation of the uniformity on grain structure using linear regression analysis is carried out based on the two kinds of physical indices such as Usp and Usize.View full abstractDownload PDF (676K) -
Shinichi Takagi, Chiaki Ouchi1996 Volume 60 Issue 2 Pages 155-162
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of Zr on tensile strength and ductility of cast-HIP’ed γ-TiAl were investigated. A Ti-48 at%Al alloy was chosen as the base alloy and Zr was added to the base alloy up to 4 at% with Al/(Ti+Al) of 0.48 atomic ratio. In the tensile test of the HIP’ed alloys at room temperature, as the Zr content increased, the yield strength rose rapidly and the elongation decreased. However, the alloys containing 1 at% to 2 at%Zr showed a marked strength improvement with little decreasing elongation, which indicated the excellent strength-ductility balance that was not observed in other ternary alloys we investigated previously. All microstructures of the HIP’ed alloys studied consisted of grains in lamellar form and equiaxed γ grains. The volume fraction of grains in lamellar form increased as the Zr content increased. The yield strength of all the HIP’ed alloys showed a linear relationship with the volume fraction of grains in lamellar form. Thus the yield strength of the HIP’ed alloys could be analyzed on the basis of the rule of mixture in which these alloys were assumed to be composed of grains in lamellar form and equiaxed γ grains. The equiaxed γ region had the Zr segregated zone that enclosed lamellar colonies forming like a network. It was considered that superior strength-ductility balance of HIP’ed Zr-containing alloys was caused by strength improvement resulted from increasing volume fraction of grains in lamellar form and by ductility improvement of equiaxed γ grains due to the Zr segregated zone and of its network-like morphology. The annealing of the HIP’ed alloys at 1603 K resulted in a disappearance of the superior strength-ductility balance and the Zr segregated zone. The relationship between microstructure and tensile property of Zr-containing γ-TiAl was studied in detail.View full abstractDownload PDF (1697K) -
Kunimasa Takeshita, Hiromitsu Naya1996 Volume 60 Issue 2 Pages 163-168
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSFour alloys of Al-3.8 mol%Mn-0.9 mol%Cr-Xmol%Si (X=0, 1, 2, 4) were rapidly solidified to foils with 60∼70 μm thicknesses and 6 mm width by the planar flow casting method. The effects of silicon addition amount to an Al-3.8 mol%Mn-0.9 mol%Cr alloy have been investigated by examining the microstructures and mechanical properties of the as-solidified and subsequently annealed foils.
As for the alloys of Al-3.8 mol%Mn-0.9 mol%Cr-Xmol%Si (X=0, 1), the precipitation of Al12 (Cr, Mn) occurs on annealing, accompanying the decomposition of supersaturated solid solutions resulting in the increase in hardness. These alloys annealed at 800 K for 7.2 ks, which contain largely grown Al12 (Cr, Mn), have a poor ductility of 0.4% in fracture strain.
In the alloys of Al-3.8 mol%Mn-0.9 mol%Cr-Xmol%Si (X=2, 4), the precipitation of Al12 (Cr, Mn) does not occur on annealing and the gradual decrease in hardness takes place with the increase in annealing temperature. These alloys annealed at 800 K for 7.2 ks, which contain relatively fine particles of Al15Mn3Si2 and Al7Cr, have an improved ductility of more than 1.2% in fracture strain. It is found that regardless of annealing temperature, the alloy containing 2 mol% silicon has good ductilities as well as relatively high 0.2% proof stresses and tensile strengths.View full abstractDownload PDF (764K) -
Hisashi Ito, Yuji Yamasaki, Satoru Matsuo, Ken-ichi Takagi, Kazuhiro M ...1996 Volume 60 Issue 2 Pages 169-176
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMullite ceramics containing zirconia were rapidly solidified (RS) to obtain amorphous ceramic powder using plasma centrifugal atomization (PCA). The RS powder was hot-pressed into disk specimens at various temperatures ranging from 1623 to 1823 K. For comparison, non-RS mullite-zirconia disk specimens were also produced. Test pieces were machined from the disks. Transverse rupture strength (TRS), Vickers hardness and fracture toughness (KIC) of RS and non-RS hot-pressed samples were measured at room temperture. The TRS of the RS samples increased with increasing hot-pressing temperature from 1623 to 1723 K. A maximum TRS of 550 MPa was recorded at 1723 K. A similar trend of TRS was observed for the non-RS samples; the maximum TRS also obtained at 1723 K, was lower than that of the RS compacts. SEM observations revealed that the mullite-zirconia samples produced from the RS powder had a much finer microstructure than the non-RS samples. The higher TRS of the RS samples compared to the non-RS samples was attributed to the finer microstructure of the RS samples. The fracture toughness, obtained using the indentation fracture (IF) method, was approximately 3 MPa·m1⁄2 for both materials. Although the RS samples exhibited higher TRS values than the non-RS samples, there was no appreciable difference in fracture toughness.View full abstractDownload PDF (1309K) -
Satoshi Itoh, Takeshi Azakami1996 Volume 60 Issue 2 Pages 177-183
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to elucidate the kinetics and mechanism of synthetic ilmenite reduction with carbon monoxide, reduction experiments were carried out using thermogravimetric technique in the temperature range between 1173 and 1373 K. The reduction rate was analyzed in terms of the mixed-control kinetics by applying the isothermal shrinking unreacted-core model, on the basis of the observation of cross section of the partially reduced ilmenite and reduction reaction path in the Ti-Fe-O ternary phase diagram. Reaction rate constant kc and effective diffusivity De determined are expressed by the following equations:
(This article is not displayable. Please see full text pdf.)
\ oindentwhere R: gas constant (J·mol−1·K−1), T: temperature (K). The activation energy of the reaction was 130 kJ·mol−1. The calculated reduction curves using the rate parameters finely reproduced the experimental data. The reduction rate increases as the reduction temperature increases. In the initial stage of reduction, the overall rate is controlled by a mass transfer step through the gas film and a chemical reaction step, while in the final stage both the diffusion step of carbon monoxide through pores of the product layer (Fe+TiO2) and the chemical reaction step determine the overall reaction rate.View full abstractDownload PDF (790K) -
Yutaka Shiraishi, Seizo Nagasaki, Michiyasu Yamashiro1996 Volume 60 Issue 2 Pages 184-191
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn ultra-wide range viscometer which can be applied to a viscosity range from 1012 to 101 Pa·s was developed. The viscometer consists of a combination of indentation, parallel plate and rotational plate method and can be used to measure a viscosity change from the glassy to molten states in an ascending temperature process. Since the principle of this viscometer is rather simple, it seems to give the right orders of magnituder of viscosity without use of calibration curves based on a standard reference material.
Reproducibility of the viscometer was demonstrated by the measurements of polymer glasses, acrylic resin and polystyrene, up to 570 K in their molten states.View full abstractDownload PDF (988K) -
Yoshiyuki Sato, Motoi Hara, Yutaka Shinata1996 Volume 60 Issue 2 Pages 192-197
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSHigh temperature oxidation behavior of Ni in an 1%HCl-50%O2-N2 atmosphere was examined at 973-1273 K by thermogravimetric technique, XRD and EPMA analyses. Mass loss was observed at all the temperatures and increased with time and with temperature. The consumptions of Ni in 1%HCl were larger than those in 100%O2. This fact suggests that Ni is acceleratedly corroded in 1%HCl. After the oxidation test, a NiO scale was found on the specimen. Furthermore, it was found that the NiO scale is constructed of some layers and Cl exists around the metal/scale interface in the scale. Evaporation of NiCl2 was identified by analysis of deposits inside the experimental reaction tube. The formation of NiCl2 was also recognized from the fact that total consumption of Ni was larger than consumption of Ni for NiO formation. Namely, the difference of the two consumptions represents Ni consumption for NiCl2 formation. From these results and thermodynamical discussion, it was suggested that the oxidation of Ni in an 1%HCl atmosphere proceeds by alternate reactions of oxidation and chlorination.View full abstractDownload PDF (957K) -
Manabu Noguchi, Toshio Narita1996 Volume 60 Issue 2 Pages 198-204
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSulfidation behavior of Fe-Cr alloys containing up to 25 at%Cr was investigated under the sulfur pressures above a dissociation pressure of ferrous sulfide at temperatures of 1023, 1073 and 1123 K using a thrmo-gravimetry and an electron micro-probe analysis.
The surface sulfide scale was composed of (Fe, Cr)1−δS and its growth kinetics was parabolic. The parabolic rate constants (kp) increased with increasing Cr content and sulfur partial pressure, while they showed an abnormal temperature dependence at a 10−3 Pa sulfur pressure. These could be due to a competitive effect of a dynamic factor (cation diffusivities) and a driving force factor (sulfur activity difference across the scale).
It was found that Cr in the scale enriched near an alloy/scale interface and then decreased gradually toward a scale/gas interface, and these cation profiles became steeper with increasing sulfur pressure. Diffusional analyses of cation distributions showed that Cr is a slower-diffusant in the (Fe, Cr)1−δS sulfide, with the DCr⁄DFe ratios ranging from 0.1 to 0.5. Scale structures and cation distributions could be elucidated by paths of change in composition on the Fe-Cr-S phase diagram.View full abstractDownload PDF (740K) -
Masayuki Nishifuji, Akihiro Ono, Yasuhiro Hayakawa, Tatsuhiko Tanaka, ...1996 Volume 60 Issue 2 Pages 205-211
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA new method for the determination of trace amounts of carbon in highly purified iron has been developed. The method is based on the gasification of carbon by the heat of a sample in hydrogen, and the detection of extracted gases, such as methane and carbon monoxide, by the use of flame ionization detector-gas chromatography. Highly purified iron was prepared in the size of φ0.1 mm × 10 mm, and set in a quartz tube. The sample is pre-heated at 673 K in a nitrogen and oxygen (20.1 vol.%) gas mixture so as to eliminate adsorbed carbon on the surface of the sample (surface carbon). Subsequently, the sample is heated at 1373 K for 10 min in hydrogen gas. Carbon in the sample (bulk carbon) diffuses thermally, and is extracted as methane and carbon monoxide.
Bulk and surface carbon of the sample can be determined separately by the proposed method. Carbon content about 4 μg/g in highly purified iron can be determined with a relative standard deviation (RSD) of about 10%. The determination limit (10 σ of blank values) of this method is 1 μg/g carbon in a 1 g sample. The time required to analyze one sample is about 50 min.
The determined values of carbon by proposed method agree well with the reference values obtained by an infrared absorptiometric method after combustion.View full abstractDownload PDF (706K) -
Yukio Inokuti, Kazuhiro Suzuki, Yasuhiro Kobayashi1996 Volume 60 Issue 2 Pages 212-217
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to clarify the influence of bombardment on the magnetic properties of TiN-coated silicon steel sheet, various bombardment treatments were applied to polished silicon steel sheets prior to TiN coating by the HCD method. The following results were obtained.
(1) With no bombardment or bombardment for a short time prior to TiN coating, the iron loss W17⁄50 (W/kg) of TiN-coated silicon steel sheets was dramatically improved by 0.12-0.14 W/kg. In contrast, bombardment for a long time reduced the rate of improvement as the bombardment time inceased.
(2) The decrease in the rate of improvement of iron loss with increasing bombardment time was attributed to a decreased rate of improvement in hysteresis loss.
(3) In the analysis of elements and three-dimensional analysis of the surface roughness of the polished silicon steel sheet after bombardment, the oxygen content increased with increasing bombardment time, and the roughness of the sheet also increased. The increase in oxygen caused deterioration of the adhesion of the TiN-coating to the silicon steel sheet.
(4) Thin-film X-ray diffraction inspection indicated that a strong peak of (111) of TiN was weakened with increasing bombardment time.View full abstractDownload PDF (521K) -
Sung-Kil Hong, Hiroyasu Tezuka, Akihiko Kamio, Byong-Sun Chun, Seong-S ...1996 Volume 60 Issue 2 Pages 218-224
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMechanism of macro-segregation formation in SiC whisker/pureAl, Al-Mg and Al-Li alloys composites formed during squeeze casting was investigated by using micro-Vickers hardness, X-ray diffraction, EPMA, SEM and TEM observations. The macro-segregated area is formed along the infiltration routes of molten metal from side walls and top surface of the SiCw preform at the center-low zone in the SiCw/aluminum alloys composites. It is the main reason for the formation of macro-segregation that the melt reduced active solute element (Mg or Li) due to the interface reaction between SiO2 contained in the preform and the matrix alloys squeezes toward the center-low zone which solidifies finally in the composite and solidifies as it is. The following compounds were detected as interface reaction products; Al2O3 in the SiCw/pureAl, spinel type of MgAl2O4 and Mg2Si in the SiCw/Al-Mg, and LiAlSi, lithium oxides in the SiCw/Al-Li alloy composites. Finally the sound composites without the macro-segregation can be obtained by using the specially designed fabrication method for this study.View full abstractDownload PDF (1117K) -
Masahiro Okumiya, Yoshiki Tsunekawa, Itaru Niimi, Toshiyuki Matsumoto, ...1996 Volume 60 Issue 2 Pages 225-230
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn the plasma carburizing process, the influence of electron temperature and electron density measured by a langmuir probe on carbon content was studied on low carbon steel foils of 0.25 mm in thickness. The increases in plasma current and plasma voltage cause the decreases in electron temperature. The carbon content decreases curvilinearly as the electron temperature increases. Generally the carbon content approximately 0.8 mass% is targeted to obtain an effective mechanical property. But the decreasing rate of carbon content to electron temperature at around 0.8 mass%C is large, so a highly accurate control with electron temperature is difficult. The increase in plasma current and plasma voltage cause the increases in electron density. The carbon content increases linearly as electron density increases. Negative charges balance with positive charges in plasma, so the density of positively charged carbon ions increases as the electron density increases, hence the carbon content increases. Even if the electron temperature or electron density is constant, the carbon content increases as the premixed methane ratio increases. Because the increase in premixed methane ratio causes the increased retained methane ratio and the increased carbon potential. Even if the plasma current or plasma voltage changes in plasma carburizing, the carbon content can be predicted and controlled by the electron density.View full abstractDownload PDF (645K) -
Seungkyun Ryu, Junichi Kaneko, Makoto Sugamata1996 Volume 60 Issue 2 Pages 231-237
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to prepare SiCw/SiCp/Al duplex composites, SiCp was dispersed in Al by mechanical alloying and subsequently reinforced with SiCw by powder metallurgy. Mechanical alloying was carried out for 10 h by using an Attritor ball mill with addition of methanol. Mechanically alloyed powder which was mixed with SiCw was used for hot press and hot extrusion. The microstructures and mechanical properties were examined on the extruded composites. Uniform distribution of SiCp and SiCw was obtained in both composites with 100% relative density. SiCp/Al composites show a drastic increase of tensile strength by dispersion strengthening, while their elastic modulus remained nearly the same. Tensile strength and elastic modulus of SiCw/SiCp/Al composites increased with increasing SiCw volume fraction. Dispersion strengthening attained by mechanical alloying was higher than strengthening by SiC whiskers in composites. SiC whiskers of smaller diameter (0.45 μm) show higher strengthening effect than those of larger diameter (1.2 μm). The highest tensile properties were obtained in the SiCw/SiCp/Al duplex composites; tensile strength 565 MPa and elastic modulus 105 GPa at room temperature, and tensile strength 233 MPa at 573 K.View full abstractDownload PDF (767K)
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