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Volume 55, Issue 2
Displaying 1-20 of 20 articles from this issue
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Yuji Asada, Etuo Nakada, Akimitu Miyazaki, Tadaharu Yokokawa1991 Volume 55 Issue 2 Pages 105-109
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe data on lattice constants L(a,b,c), Tc and oxygen content z in YBa2Cu3Oz are retrieved from the factual database of superconducting materials, which is now being constructed in NRIM. The linear relations between L(a,b,c) and z are statistically obtained with high values of correlation coefficient. Especially, the lattice constant c is highly correlated with z. These relation can be used to estimate z-values which are not described in the paper referred. The orthorhombic distortion p(=b−a) is introduced to investigate the structural transformation and variation of Tc. The values of z, where phase transitions take place, are discussed. Tc drastically changes at z1=6.75 and z2∼6.5 which are related to the structural change. We propose that Tc should be related to p rather than z.View full abstractDownload PDF (585K) -
Chen Lu, Hiroshi Fujita, Eiji Taguchi1991 Volume 55 Issue 2 Pages 110-117
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDetails of the θ′→θ phase transformation in an Al-1.6 at%Cu alloy have been investigated by high resolution electron microscopy including in-situ experiments. The results obtained are summarized as follows.
(1) Growth of θ′-phase occurs by movement of both the incoherent interfaces and ledges of the stepped structure on θ-phase coherent interfaces, and a large coherent strain is induced at the growth front so that the interfacial dislocations are formed.
(2) θ-phase crystals are frequently formed at the intersection between two θ′-phase structures.
(3) θ-phase crystals of rod-shape grow to platelets with a large aspect ratio by absorbing the θ′-phase nearby, but the interfaces of both structures are separated from each other in general.
(4) The interface of θ-phase crystals has also a stepped structure whose main component is one of the {110}θ planes of the θ-phase, and its average orientation is inclined at about 13° against one of the {100}α planes of the matrix aluminum in this alloy. The average orientation widely changes in the foil specimens by in-situ aging in general.
These results are discussed from a viewpoint of the interfacial energy based on the orientation relationships among the matrix, θ′-and θ-phase structures.View full abstractDownload PDF (2848K) -
Hiroshi Fujita, Chen Lu1991 Volume 55 Issue 2 Pages 118-124
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMicrostructure of the interface of θ-phase crystals has been investigated in an Al-1.6 at%Cu alloy by high resolution electron microscopy with the following results.
(1) Rod-shape θ-phase crystals are formed along a fixed direction inclined (about 13° in this alloy) to one of the {100}α plane of aluminium matrix.
(2) θ-phase crystals have interfaces consisting of one each of the {110} and {100} planes of θ-phase at the initial stage, and then each of them grows to a platelet with a large aspect ratio.
(3) A group of diffraction spots like superlattice ones appears at each diffraction spot of both θ-phase and the matrix along the perpendicular direction to ledges of the stepped structure which is parallel to the axial direction of θ-phase. The spacing of these spots corresponds to the width of terraces.
The results obtained are discussed from a viewpoint of the surface energy of interfaces.View full abstractDownload PDF (2463K) -
Woo-Yeong Lim, Moritaka Hida, Akira Sakakibara, Eiichi Sukedai, Yosuke ...1991 Volume 55 Issue 2 Pages 125-131
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe mechanical alloying (MA) behavior for β type solid solutions in Ti-14 mass%Mo and Ti-20 mass%Mo systems was examined by means of X-ray diffractometry (XD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and chemical analysis. The phase transformation and thermal stability of mechanically alloyed solid solutions were also compared with those of the cold-worked powders of the Ti-Mo ingots prepared by melting.
β phase solid solution was formed by MA and the formation time decreases with increasing Mo content. The further MA causes the appearance of the α phase without the formation of the ω phase. On heating the solid solution at temperatures above 823 K, the β phase was stabilized through the precipitation of the α phase. It was also noticed that a great deal of impurity, Fe was dissolved into the powder from the balls and the vessel during the MA process.View full abstractDownload PDF (1287K) -
Yoshinobu Motohashi, Keiichi Ohsawa, Taiji Hoshiya, Yoshizo Okamoto, M ...1991 Volume 55 Issue 2 Pages 132-140
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA method has been developed to produce fine grain sizes in Ti-50.7 at%Ni alloy by means of thermo-mechanical treatment (TMT). The TMT process involved sequential stages of intermediate annealing and cold rolling followed by recrystallization. The intermediate annealing was carried out for precipitating fine Ni-rich phase particles as well as for recovering internal strains. The relations of the cold rolling, recovery and recrystallization to transition behavior and the grain size dependence of transition temperatures have been studied.
In order to obtain uniform and equi-axed fine-grained recrystalllized structure, the recrystallizing heat treatment should be done at somewhat high temperatures at which all precipitates can be re-occluded in the matrix crystal. It was found that the martensitic transformation temperature (Ms) increased with a decrease in grain size. This may be caused by the facts that the grain boundaries can act as nucleation sites for the martensitic transformation and the insufficient recovery of Ni concentration in the matrix caused by undissolved precipitates. The TMT process used in the present study would not lower the properties of the alloy.View full abstractDownload PDF (1985K) -
Ryuji Uemori, Mitsuru Tanino1991 Volume 55 Issue 2 Pages 141-150
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMorphology and chemical compositions of the precipitates formed at the peak stage of secondary hardening in an Fe-Mo-C alloy were examined by atom probe field ion microscopy (AP-FIM). The present AP-FIM analysis has confirmed the existence of not only needle-like Mo2C precipitates along the ⟨100⟩α−Fe directions but also plate-like precipitates lying parallel to the {100}α−Fe planes at the peak stage of secondary hardening. The latter were deduced to be clusters of Mo and a small fraction of Fe atoms that contain neither C nor N. These Mo-rich clusters are finer and more densely distributed than Mo2C. Thus, its presence may significantly contribute to the secondary hardening of Mo steels.View full abstractDownload PDF (2574K) -
Eiichi Sato, Kazuhiko Kuribayashi, Ryo Horiuchi1991 Volume 55 Issue 2 Pages 151-157
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSuperplastic deformation mechanisms have been investigated, based on experimental results of Al-33%Cu and Al-33%Cu-0.3%Cr alloys.
Though Cr bearing had little effect both on the flow stress in the regions II and III and on the deformation induced grain growth in the regions I and II, it increased the flow stress in the region I. These results were explained by the following superplastic deformation model: while the main mechanism is grain boundary sliding in the regions I and II, its rate controlling process is diffusional accommodation in the region II and threshold process in the region I, respectively, and in the region III the ordinary dislocation creep also contributes.
The diffusional accommodation of grain boundary sliding divided experimentally was considered to be the grain boundary diffusion for grain switching because of its grain size dependence and its absolute flow stress.View full abstractDownload PDF (918K) -
Seiichi Muneki, Yoshikuni Kawabe, Toshio Kainuma, Junji Takahashi1991 Volume 55 Issue 2 Pages 158-165
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSEffects of beta grain size and aged microstructure on mechanical properties have been investigated for a Ti-15V-3Cr-3Sn-3Al based alloy.
The beta grain size linearly increases with increasing solution treatment temperature. With increasing solution treatment temperature from 1023 to 1173 K, the 0.2% yield strength in the solution treated condition decreases in accordance with Hall-Petch relationship. The 0.2% yield strength of the specimens aged at 773 K for 28.8 ks indicates an approximately constant value of 1100 MPa, independently of the grain size. The elongation and reduction in area are strongly dependent on grain size and decrease with increasing grain size. The notched tensile strength is independent of the grain size, while, KIC slightly increases with increasing grain size. Unusual age-hardening behavior exhibiting two hardness peaks at 623 and 723 K for 28.8 ks can be observed. These two peaks indicate the same values of hadness and tensile strength. However, the specimen aged at 623 K shows both poor ductility and notched tensile strength, compared to the higher temperature aged structure, due to fine and coherent α precipitation in beta matrix.View full abstractDownload PDF (3235K) -
Shinji Hirai, Hideaki Murakami, Hiroshi G. Katayama1991 Volume 55 Issue 2 Pages 166-171
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe mixture of Al2O3 and MgO at a mole ratio of 1: 1, was fired between 1173 and 1623 K in air, to investigate the effects of the particle size and type of Al2O3, and the kind of additives on the formation rate of MgAl2O4 and, at the same time, to elucidate the mechanism of the reaction. The results are shown as follows. (1) MgAl2O4 was formed more rapidly from Al2O3 than from Al2O3. (2) The addition of CaB4O7, B2O3 and NaF accelerated the formation of MgAl2O4, but the addition of CaF2, CaCl2 and CaCO3 in an amount of 1 mass% or below had little effect on this reaction. (3) With the progress of the reaction, the Al2O3-MgAl2O4 interface moved from the outside to the inside of Al2O3 particle, whereas the MgAl2O4-MgO interface moved to the outside of the particle. On the basis of this finding, the reaction rate was analyzed using the solid-diffusion controlled equation which includes a correction factor for the change of molecular volume. As a result, the apparent activation energy value was estimated to be 316 kJ/mol for the addition of 1 mass%CaB4O7 and 270 kJ/mol for no addition. These values were approximated by the activation energy value of the interdiffusion of Mg2+ and Al3+ within the defective MgO-Al2O3 spinel.View full abstractDownload PDF (877K) -
Yasuhiro Kojima, Kenji Matsuo, Kunihiko Nakashima, Kenji Morinaga1991 Volume 55 Issue 2 Pages 172-179
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSOn the basis of a TTT diagram during solidification of a melt in the system SiO2-Al2O3-MgO-MgF2-K2O-B2O3, the effect of heat-treatment conditions on grain size, morphology and crystallization degree of fluor-phlogopite crystallized was discussed. By isothermal heat-treatment in the temperature range of 1253 to 1473 K, fluor-phlogopite as spherical grains was crystallized directly from a super cooled liquid. On the other hand, below 1253 K spinodal decomposition type phase separation occurred as a prelude to the crystallization sequence. Energy dispersive X-ray analysis suggested that the growth rate of fluor-phlogopite crystals was controlled by diffusion of Mg ions. A linear relationship between the spinodal wave length and the plate diameter of fluor-phlogopite platelets was obtained as a result of the crystallization occurred in a Mg-rich phase.View full abstractDownload PDF (1530K) -
Naosuke Takiuchi, Takayuki Taniguchi, Yasukuni Tanaka, Nobuya Shinozak ...1991 Volume 55 Issue 2 Pages 180-185
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe surface tension and the contact angle of liquid iron on the alumina substrate were measured at 1873 K, 1923 K, 1973 K and 2023 K by the sessile drop method.
The surface tension of liquid iron decreases with increasing oxygen concentration in the iron over the temperature range from 1873 K to 2023 K.
The temperature coefficient of surface tension is negative for the lower oxygen concentration than 0.007 mass%, but it is positive for the higher oxygen level.
The standard free energy change for the adsorption reaction of oxygen at the liquid iron surface is given by the following equation:
(This article is not displayable. Please see full text pdf.)
The contact angle of liquid iron on the alumina substrate decreases and the work of adhesion increases with increasing oxygen concentration in the iron. However, the contact angle is not affected by the temperature.View full abstractDownload PDF (626K) -
Toshio Shimoo, Hideya Inagaki1991 Volume 55 Issue 2 Pages 186-193
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe mechanism of the carbothermic reduction of SiO2 containing Al2O3 has been investigated. The reduction rate has been measured by means of thermogravimetry under an argon atmosphere at temperatures from 1773 K to 1973 K.
The addition of small amounts of Al2O3 to SiO2 increases the reduction rate of SiO2 and the yield of SiC. The formation of SiC is retarded by the excess addition of Al2O3. In particular, most of SiO2 is evaporated as SiO at the low temperature.
At the early stage of the reaction, the reduction rate is controlled by the chemical process on the surface of the graphite particles at the lower content of Al2O3 and by that on the surface of the SiO2-Al2O3 particles at the higher content of Al2O3, respectively. At the low temperature, the rate-determining step is the chemical reaction on the SiO2-Al2O3 particles independently of Al2O3 content. The rate is strongly dependent on the phase present in SiO2-Al2O3.
At the late stage of the reaction, the reduction rate is determined by the gaseous diffusion through the porous layer of Al2O3 left on the SiO2-Al2O3 particles.View full abstractDownload PDF (1137K) -
Futao Li, Masahiro Susa, Kazuhiro Nagata1991 Volume 55 Issue 2 Pages 194-203
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThermal conductivity, thermal diffusivity and specific heat of the PbO-SiO2 glass system were determined with the hot strip method over the temperature range of 300 to 1200 K. The results led to the elucidation of their dependences on temperature and composition.
The thermal conductivity of PbO-SiO2 and fused-SiO2 monotonously increased with increasing temperature but that of crystalline PbO decreased. The temperature dependence of the thermal diffusivity for PbO-SiO2 and PbO were the same with that of the thermal conductivity for the respective substances but the thermal diffusivity of fused-SiO2 was little varied by change of temperature. The specific heat of all the samples increased with temperature increase.
The thermal conductivity and thermal diffusivity of PbO-SiO2 were determined to be smaller than those of fused-SiO2 but not distinctly dependent on the PbO content.
The dependences of the thermal conductivity and the thermal diffusivity on temperature and composition were discussed based on the Debye’s theory.
The specific heat of PbO-SiO2 was larger than the estimated one, which was calculated assuming that the specific heat of PbO-SiO2 was linearly proportional to the respective contents of PbO and SiO2. The difference between the two values was considered to be excess specific heat.View full abstractDownload PDF (1314K) -
Masami Taguchi, Jiro Kurihara1991 Volume 55 Issue 2 Pages 204-210
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe nitriding behavior of chromium in nitrogen gas at 773-1473 K and the corrosion resistance of the nitriding products in sulfuric acid solution have been investigated. The main results obtained are summarized as follows.
(1) Nitriding of chromium starts at about 873 K and the surface product was the mixture of α-Cr and Cr2N. The product changed to the mixture of Cr2N and CrN at 973-1273 K. It transformed into the single phase, Cr2N by the dissociation reaction of CrN above 1323 K.
(2) Chromium loses the ability of self-passivation by nitriding. However, surface products at 973-1273 K showed good corrosion resistance which was comparable with passivation films. The products also dissolved as Cr2O72− ions at potential higher than 1.0 V vs. Ag/AgCl.
(3) The mixture of α-Cr and Cr2N, and the single phase of Cr2N were rapidly attacked in 1 kmol·m−3 H2SO4 at 373 K. On the other hand, the mixture of Cr2N and CrN, which contained 33 at% nitrogen or more, showed improved corrosion resistance. This means that the single phase of CrN should have high corrosion resistance.
(4) Cyclic voltammetry showed chromium nitride dissolved mostly as Cr2+ ions. It was presumed that Cr2+ ions were then oxidized to Cr3+ ions on the catalytic platinum surface.View full abstractDownload PDF (1917K) -
Kunimasa Takeshita1991 Volume 55 Issue 2 Pages 211-218
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMicrostructure and mechanical properties of melt spun Al-8 mass%Fe alloy ribbons have been investigated. The solidification structure is composed of two zones. Zone A found on the substrate side of ribbon has a limited etching response and the Vickers hardness of 2.1 GPa while zone B found on the air side and darkened by etching has the Vickers hardness of 1.1-1.3 GPa. The increase in roller surface velocity from 17 to 27 m/s results in the decrease in ribbon thickness from 63 to 42 μm associated with the increase in area fraction of zone A from 0.2 to 0.7. The ribbon hardness consequently increases with decrease in ribbon thickness, though the hardness of zone A and B is independent of ribbon thickness. As for the ribbons whose area fractions of zone A are not less than 0.34, the 0.2% proof stress σy0.2 and ultimate tensile strength σTS at room temperature are related to the ribbon hardness Hvr as; σy0.2=0.31 Hvr and σTS=0.34 Hvr respectively.
In order to calculate the area fraction of zone A, a solidification model considering the kinetics of α-Al dendrite growth in the undercooled alloy melt is also presented.View full abstractDownload PDF (1786K) -
Yoshio Sakka, Tetsuo Uchikoshi1991 Volume 55 Issue 2 Pages 219-226
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSurface conditions of three kinds of iron ultrafine powders (UFPs) were estimated by thermal desorption measurements. The iron UFPs exposed to air contain mixtures of Fe3O4 and γ-Fe2O3 phases and in some case additional α-Fe2O3 phase. Moreover, iron oxyhydroxide or its precursor compounds are produced by the reaction of surface oxides of UFPs with moisture in air.
Reduction experiments were carried out with thermogravimetry in a stream of hydrogen. The reduction is rate-controlled by the interface reaction and the reduction rate of the iron UFPs depends on the oxidation level, where the higher oxidized UFPs tend to lower the reduction rate. Activation energies of the reduction rate constants of two kinds of iron UFPs are 54 and 59 kJ/mol.View full abstractDownload PDF (1188K) -
Tokushi Kizuka, Hideki Ichinose, Yoichi Ishida1991 Volume 55 Issue 2 Pages 227-228
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (656K) -
Norikatsu Yokota1991 Volume 55 Issue 2 Pages 229-230
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (428K) -
1991 Volume 55 Issue 2 Pages 231a
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSPlease see pdf. Wrong:*Unknown Right:*—: UnknownView full abstractDownload PDF (54K) -
1991 Volume 55 Issue 2 Pages 231b
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSPlease see pdf. Wrong:Fig. 7 Right:[Please see PDF]View full abstractDownload PDF (54K)
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