All issues
Volume 60, Issue 1
Displaying 1-17 of 17 articles from this issue
- |<
- <
- 1
- >
- >|
-
Toshiaki Yoneoka, Takayuki Terai, Yoichi Takahashi1996 Volume 60 Issue 1 Pages 1-8
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSYttrium sesquioxide (yttria) is considered to be one of the most hopeful candidate materials for a collector electrode of the separated uranium atom in a laser uranium enrichment system. In order to confirm a required property for the electrode, the conductivity measurement of yttria was performed under a simulated condition in the presence of molten uranium. Because of the extremely low oxygen pressure in the U-UO2 system, such a condition was locally realized by placing yttria specimens between plates of titanium or vanadium at high temperature. The specimens were reduced in advance to hypostoichiometry with titanium or vanadium plates under the condition of 1600 K and 2.5 Ms in vacuo. The electrical conductivity measurement was performed by the AC four-probe method in the temperature range of about 900∼1600 K and the frequency range of 60 Hz∼30 kHz.
The electrical conductivity of hypostoichiometric yttria reduced by titanium was higher than that of intrinsic germanium at room temperature (2.1 S/m). This specimen showed the characteristic behavior in the temperature dependence of conductivity; the conductivity showed semiconductor-like behavior in the range of 1400∼1600 K, while it had a minimum at about 1250 K and again increased below this temperature. That of hypostoichiometric yttria reduced by vanadium was much lower than that of the specimen reduced with titanium and followed a straight line in the Arrhenius plot above 1000 K. The conductivities of both hypostoichiometric specimens were independent of frequency, which means the conduction carrier was the electron or electron hole. From the oxygen concentration of the metals which were used for the reduction, the oxygen pressures equilibrated with the yttria specimens were estimated to discuss the relation to the measured conductivities.View full abstractDownload PDF (793K) -
Toru Kuzumaki, Takuya Hayashi, Hideki Ichinose, Kun-ichi Miyazawa, Kun ...1996 Volume 60 Issue 1 Pages 9-15
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe mechanical properties and the fine structure of plastically deformed carbon nanotube were examined by transmission electron microscopy (TEM). The carbon nanotube discovered by Iijima in 1991 is like a whisker crystal so that an extremely high tensile strength and the lack of plasticity are generally predicted. The in-situ observation performed in TEM, however, proved that the carbon nanotube is not brittle but bends plastically at room temperature. High resolution electron microscopy of the fine structure showed that the deformation is a series of bucklings in the compressive side of the cylindrical network of carbons. The fine structure is simulated by both the network models of carbon atoms and molecular mechanics calculation. The deformed structures lead us to a new concept of fiber material with ideal mechanical properties. The process, however, assumes that the buckling may be reversibly eliminated.View full abstractDownload PDF (1676K) -
Shohei Yoshioka, Shin-ichi Orimo, Hironobu Fujii1996 Volume 60 Issue 1 Pages 16-21
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to investigate the processes of amorphization and phase separation in the YNi2-H system, we studied the feature of structural changes in the YNi2-H system by X-ray diffraction method and thermal analysis as a function of hydriding temperature and time under a hydrogen pressure of 1 MPa. From the X-ray diffraction and differential thermal analysis, it was demonstrated that the amorphization reaction for hydriding at 473 K is much delayed in comparison with those at 573 and 273 K. This temperature dependence of the formation rate of the amorphous phase can be qualitatively explained by considering two promoting factors for Ni-diffusion, the lattice expansion by hydrogen absorption and thermal activation. We could also clarify that yttrium-rich tetrahedral sites (3Y+1Ni) increase with increasing hydriding temperature and time by analyzing the differential thermogravimetric data. In particular, when the hydriding temperature is high enough, the yttrium-rich sites in the amorphous phase drastically increase. This suggests that the growth of yttrium-rich and nickel-rich clusters occurs in the amorphous structure, which may be recognized as a pre-phenomenon of the phase separation into YHx and YNi3+δ phases.View full abstractDownload PDF (500K) -
Sengo Kobayashi, Takeshi Sumi, Toshiyuki Koyama, Toru Miyazaki1996 Volume 60 Issue 1 Pages 22-28
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe composition gradient method recently proposed is applied to determine the coherent phase boundaries of the Ni-V and Ni-Mo alloy systems by utilizing the alloys having the macroscopic composition gradient. The result, obtained are as follows:
(1) The coherent phase boundaries of Ni/(Ni+Ni3V) were experimentally determined to be a line connecting 15.5 at%V at 873 K and 18.0 at%V at 1173 K, which was consistent with Moreen’s empirical results obtained from the metallographic examinations.
(2) The phase boundaries of Ni/(Ni+Ni4Mo) and (Ni+Ni4Mo)/Ni4Mo were also obtained, which were almost coincident with those in the equilibrium phase diagram of Ni-Mo proposed by Massalski. The new method is recognized to be very powerful for a metallographic determination of the coherent phase boundary.View full abstractDownload PDF (667K) -
Toshitada Shimozaki, Kenjirou Chikumaru, Yoshinori Wakamatsu, Masami O ...1996 Volume 60 Issue 1 Pages 29-36
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSReactive diffusion of the Ti-Si binary system has been studied by using bulk diffusion couples consisted of a 99.5%Ti plate and a ⟨111⟩ oriented Si wafer as well as a un-recrystallized 99.99%Ti plate and the Si wafer in the temperature range from 723 K to 1123 K. In these diffusion couples, 2∼4 kinds of Ti silicides were formed in the range. TiSi2 occupies a 80∼90% portion of the diffusion layer. The growth of the TiSi2 phase formed in the 99.5%Ti/Si diffusion couples was slower than that in the 99.99%Ti/Si diffusion couples. The square of the growth rate constant k2 has been written as
(This article is not displayable. Please see full text pdf.)
\ oindentfor the 99.5%Ti/Si diffusion couples and
(This article is not displayable. Please see full text pdf.)
\ oindentfor the 99.99%Ti/Si diffusion couples.
The growth rate of TiSi2 formed in some diffusion couples consisted of the Si wafer and a recrystallized 99.99%Ti, however, was smaller than that for the un-recrystallized 99.99%Ti/Si diffusion couples. The differences of the growth rate and the activation energy for layer growth between these diffusion couples have been discussed by in terms of the oxygen content in the Ti specimens.View full abstractDownload PDF (1028K) -
Masaki Hanai, Masafumi Houkyou, Naoki Utiyama, Akio Fuwa1996 Volume 60 Issue 1 Pages 37-43
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe behavior of phase layer growth in the diffusion couple of aluminum thin films and gold bulks at the temperatures from 523 K to 773 K was studied by means of SEM, EPMA and optical microscopy. The effect of calcium addition on phase layer growth was also studied. The experimental results show: before the disappearance of aluminum thin films, five intermetallic phases in its equilibrium phase diagram form in the couple and after the aluminum disappearance, the phases with a lesser gold content disappear in sequences. After the disappearance of the AuAl2, AuAl and Au2Al phases, the Au4Al phase grows in the Au5Al2. Kirkendall voids are found to form in the Au5Al2, adjacent to Au4Al. The addition of a small amount of calcium to the Au bulks affects the morpohology, making void sizes smaller and diffusion easier, thus promoting the growth of the Au4Al phase.View full abstractDownload PDF (1743K) -
Yoshimasa Takayama, Tatsumi Tozawa, Hajime Kato, Yuichi Akaneya, In Se ...1996 Volume 60 Issue 1 Pages 44-49
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSConcept of uniformity on microstructure of materials has been clarified. On this basis, uniformity on grain structure has been understood as size uniformity, representing the distribution of grain size, and spatial uniformity, expressing the degree of clustering of similar-sized grains. Indices of uniformity, Usize and Usp have been proposed: Size uniformity, Usize is designated by the inverse of the geometric standard deviation for grain intersect area, a, σga. Spatial uniformity, Usp for the square object area of side length, L is expressed by the deviation of a microstructural center of gravity from a simple center as follows.
(This article is not displayable. Please see full text pdf.)
\ oindentwhere, the simple center G(xG, yG) is the center of gravity for the whole object structure, and the microstructural center GS(xS, yS) is the center weighted by the intersect area of each grain. Usp depends on setting a standard length, L; the ways of setting are one corresponding to mean grain size and another of representing an absolute value. Further, it has confirmed that the evaluation of uniformity is useful to the actural microstructures of pure iron samples.View full abstractDownload PDF (700K) -
Wan Jiang, Ryuzo Watanabe, Yoko Yamada, Akira Kawasaki1996 Volume 60 Issue 1 Pages 50-55
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe anisotropy of the thermal expansion coefficient in hot pressed particulate composites of molybdenum/partially stabilized zirconia was measured over a whole composition range by the laser speckle photography that had been specifically designed for the determination of regional thermal displacement in a sintered compact. On the presumption that the anisotropy is closely related to the microstructural orientation resulted from the uniaxial loading of hot pressing, the flattening and preferred orientation of the dispersed particles were quantified using the concept of equivalent ellipsoids and also with an anisotropic parameter, i.e. the deviation angle distribution. The definite anisotropy in the thermal expansion coefficients has been found; the thermal expansion coefficient parallel to the hot pressing direction is larger than that in the normal direction. It has been found that the difference in the thermal expansion coefficient is dependent on the composition with the largest difference at around 60 vol%PSZ. The anisotropy (difference in the thermal expansion coefficient between the two directions) is linearly related to the anisotropic parameter that represents the particle orientation. The dependence of thermal expansion coefficient on the oriented particle distribution has been discussed by the Eshelby’s theory. The experimental trend has been well explained by the present prediction.View full abstractDownload PDF (746K) -
Takahisa Ohnuki, Yo Tomota, Masayoshi Ono1996 Volume 60 Issue 1 Pages 56-64
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe residual elastic strains in 22 vol.%SiC whisker/A2014 metal matrix composites made by squeeze-casting were examined using a neutron crystal diffractometer with a one-dimensional position sensitive detector (PSD) and a neutron time-of-flight diffractometer with two-point detectors (TOF). The ingot of the sample was hot-extruded, then hot-swaged and finally hot-rolled to sheets of 2 mm in thickness. The hot-rolling was performed either parallel (specimen P) or vertical (specimen V) to the direction of extrusion. The whiskers are aligned with a little scattering against the extrusion direction in the specimen P, while their orientation distribution is nearly two-dimensionally random in specimen V. The residual stresses were introduced by rapid quenching from 448 K (T6 heat treatment) or 773 K (solution treatment). SiC whisker and A2014 alloy were used as the reference materials. It is found that the residual elastic strains in the samples depend upon the orientation distribution of the whiskers. The ratio of residual elastic strains in the T6 treated specimen to those in the solution treated one is about 3.0, which is consistent with the ratio of their temperature gaps upon quenching. The results by PSD and TOF are found almost identical. The residual elastic strains have been calculated on the basis of Eshelby’s equivalent inclusion and Mori-Tanaka’s mean field theories. In the calculation, the 3-dimensional orientation distributions of whiskers obtained from the SEM observations on the two mutually orthogonal planes of the specimens were taken into consideration. The calculated results were in good agreement with the measurements.View full abstractDownload PDF (1159K) -
Hiroyasu Fujiwara, Liang Jin Yuan, Kenshirou Miyata, Eiji Ichise, Ryot ...1996 Volume 60 Issue 1 Pages 65-71
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSFlux treatment is one of the effective methods in the refining of metallurgical grade silicon to the soller grade. However, if the process is carried out under a low oxygen potential, the components in the flux will be reduced to the metallic phase. In this study, the distribution of the metallic elements and boron between Si-based liquid alloys and CaO-Al2O3-SiO2 fluxes satulated with alumina or calcium-aluminates are investigated at 1873 K.
Aluminum and calcium concentrations in the silicon alloys can be related to the flux composition. When the XSiO2⁄(XSiO2+XCaO) ratio in flux varies from 0.25 to 0.87, [mass%Al] and [mass%Ca] increase from 0.4 and 0.02 to 10 and 8 mass%, respectively. The equilibrium distribution ratio of boron: (mass%B)/[mass%B] is about unity in the composition range investigated, and shows a peak value at XSiO2⁄(XSiO2+XCaO)=0.67.View full abstractDownload PDF (565K) -
Toshio Shimoo, Takuya Yamazaki, Kiyohito Okamura1996 Volume 60 Issue 1 Pages 72-78
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe kinetics and the mechanism of the reaction between Si3N4 and Fe-Ni alloy have been investigated in N2 or Ar atmospheres at temperatures from 1123 to 1573 K. Using a Si3N4/Fe-46.9 mass%Ni alloy powder mixture, the reaction rates were determined with a thermobalance.
A characteristic feature of TG curves was the incubation period that preceded the mass loss. The incubation period was decreased with increasing temperature. The mass loss was larger in Ar atmosphere than in N2 atmosphere. A prolonged heating resulted in establishment of equilibrium in N2 atmosphere. The reaction continued for 72 ks in Ar atmosphere.
The initial rate followed a linear rate law. Below 1323 K, the rate constant was less in N2 atmosphere than in Ar atmosphere. The activation energies were 348 kJ·mol−1 in N2 atmosphere and 304 kJ·mol−1 in Ar atmosphere. The reaction rate was controlled by the interfacial reaction. At 1373 K and above the rate constant in N2 atmosphere was identical to that in Ar atmosphere and the activation energy was 98 kJ·mol−1. The rate-determining step was considered to be the gaseous diffusion through the interparticle pores.
When the alloy particles were covered with the reaction layer, the kinetics was described by the parabolic rate law. The rate constant was independent of the atmosphere. The activation energy was 337 kJ·mol−1. The rate-controlling step was the solid-state diffusion through the reaction layer.View full abstractDownload PDF (691K) -
Junji Saida, Eiji Akiyama, Koji Hashimoto, Akihisa Inoue, Tsuyoshi Mas ...1996 Volume 60 Issue 1 Pages 79-83
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSNi-Mo-B amorphous ultra-fine particles were prepared by a chemical reduction method using KBH4 as a reducing agent. The concentration of molybdenum contained in the ultra-fine particles is about 10 at% when 30∼40 mol% of metal ions in the solution are molybdenum. The molybdenum concentration in the particles becomes the maximum value of about 30 at% in the aqueous solution where 90 mol% of metal ions are molybdenum. The structure is amorphous for all samples and the particles diameter is 20∼50 nm. The XPS Mo3d spectrum consists of Mo0, Mo4+, Mo5+ and Mo6+ as-precipitated sample. The simultaneous determination of the composition of the surface film and underlying alloy indicates the enrichment of molybdenum in the surface oxide film. Nickel and boron are also composed of the metallic and oxidized states, the latter of which is associated with the surface oxide film. The XPS analysis clearly reveals that molybdenum can be reduced to the metallic state by reductive co-precipitation with nickel and boron.View full abstractDownload PDF (683K) -
Toshio Yamauchi, Yoshinori Nishida1996 Volume 60 Issue 1 Pages 84-91
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe permeability defined by D’Arcy’s law is one of the important properties of fibrous preforms used for the fabrication of composites by squeeze casting when the infiltration of molten metal into the preforms is analyzed theoretically. Then, an apparatus was constructed to measure the permeability using compressed air as a fluid instead of a molten metal to make easy the measurement of the permeability. The major factors influencing the permeability are the fiber diameter, volume fraction of fibers and alignment of fibers. The effects of those factors were examined on SiC whisker, 9Al2O3·2B2O3 whisker and Al2O3 short fiber preforms. First, the apparent permeabilities were obtained from the experimental data. Then the true permeabilities were calculated from the apparent ones using approximate equations which describe the flow of air in the preforms. The apparatus developed was proved to be useful for the measurement of permeability comparing with the theoretical values.View full abstractDownload PDF (966K) -
Hironori Fujita, Fumio Nonoyama, Tosikazu Satou, Atsushi Danno1996 Volume 60 Issue 1 Pages 92-99
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAl-5, 10, 20, 25 and 30 at%Ti mixed powders were repeatedly forged by our developed bi-axial compression in the Ar atomosphere at 200∼300°C.
This new processing enables us to synthesize and consolidate the bulk metals with non-equilibrium phases and little amounts of inpurities such as O, N and Fe.
In case of 120 shots repeated forging of Al-Ti mixed powders, non-equilibrium phase of L12 type crystal structure Al3Ti compound was formed and only of L12 phase was observed in the composition of Al-20 and 25 at%Ti.
L12 phase, heated for 1 h at 400∼500°C, is transformed into non-equilibrium DO23 type Al3Ti and further to equilibrium phase, DO22 type Al3Ti by heating at above 600°C.
Lattice parameter of L12 phase was 0.398-0.399 nm and L12 and DO23 phases have very fine particles in size of 5∼20 nm.
A forged Al-20 at%Ti specimen shows a remarkable age-hardening property; hardness chaneged to Hv450 in the sample heated at 350∼450°C from Hv200 before heating.View full abstractDownload PDF (872K) -
Kazutoshi Yamada, Teruo Takahashi, Muneyuki Motoyama1996 Volume 60 Issue 1 Pages 100-105
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTo prepare a TiC-dispersed magnesium, the mixtures of elemental Mg, Ti and graphite powder were mechanically alloyed up to 288 ks in Ar. The obtained fine grain mixture of the Mg-Ti-C system was heat-treated up to 773 K for 3.6 ks in vacuum.
CKα X-ray spectra of TiC, graphite, micro crystalline graphite and mechanically alloyed products were measured by an electron-probe microanalyzer (EPMA) with the second-order reflection of a Johann-type lead stearate multilayer pseudocrystal.
The progress of the mechanical alloying (MA) reaction was monitored with the CKα X-ray spectral change which quantitatively reflects the amount of TiC in the reaction mixtures. The early stage of the MA reaction is solely a refinement of graphite; graphite did not react on Ti. The next stage is the formation of TiC from refined graphite and Ti. Heat-treatment accelerates the formation of TiC, but graphite is not completely converted into TiC with the MA reaction and heat-treatment because a small amount of refined graphite has been subsequently detected in the reaction mixtures even after a prolonged MA time and heat-treatment at 773 K.View full abstractDownload PDF (677K) -
Yukitaka Mizuno, Akira Kawasaki, Ryuzo Watanabe1996 Volume 60 Issue 1 Pages 106-112
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe authors have developed an “in-situ monitoring system of sintering shrinkage” using digital image processing, and have applied it to the measurements of the nonuniform and anisotropic sintering shrinkage of powder compacts prepared by metal injection molding (MIM) on a non-contact and real time basis. In the present study, the regional distribution of nonuniform shrinkages in two kinds of stainless steel (SUS304) powder compacts prepared by MIM were determined. The nonuniform shirinkages caused by the density inhomogeneities due to local temperature differences within the sample, by gravity effect of the sample, and by frictional restraint against free dilatation were confirmed. The nonuniform shrinkage caused by the density inhomogeneities due to local temperature differences has been found to take place in the early stage of sintering, where the thermal conductivity of compact is small because of large porosity and the shrinkage rate increases sharply with time, but it attenuates reversely in the final stage. The rate of the nonuniform deformation by constant load, i.e. by the gravitational loading, is proportional to the shrinkage rate during sintering. These effects will concurrently operate in the nonuniform sintering of complex-shaped MIM compacts.View full abstractDownload PDF (1112K) -
Akiko Hanazaki, Toru Takayama, Hiroyuki Anada, Sigeharu Hinotani1996 Volume 60 Issue 1 Pages 113-120
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe role of precipitates in the corrosion of Zircaloy-4(Zr-1.5 mass%Sn-0.22%Fe-0.11%Cr) has been studied by high resolution transmission electron microscopy/energy dispersive X-ray spectroscopy (HRTEM/EDS) with electron microbeam and field emission scanning electron microscopy (FE-SEM/EDS). In Zircaloy-4, the solubility of Fe and Cr is low, and Fe and Cr precipitate as an intermetallic compound Zr(Fe, Cr)2. The size of the precipitate changed with temperature in the intermediate annealing process. The size of precipitates in the specimen annealed at 780°C are significantly larger than that in the specimen annealed at 630°C. The corrosion rate in pressurized steam at 400°C was higher in Zircaloy-4 with finer Ze(Fe, Cr)2 particles precipitated by the intermediate annealing at 630°C.
The observation of the corroded layers by HRTEM/EDS showed that the surfaces of precipitates oxidized together with the matrix and decomposed to dissolve into ZrO2 during the corrosion. As the precipitates oxidize, the atomic ratio of Fe/Cr in the precipitates changes from 2 in the metal to 0.5 in the oxide. This phenomenon suggests that Fe component predominantly diffused into the matrix.
The cations of Fe and Cr generated by oxidation and diffused into the matrix ZrO2, were thought to replace Zr4+ sites. The higher corrosion rate in Zircaloy-4 with finer precipitates was attributed to larger amounts of Fe and Cr cations that are made available during the early stage of corrosion.View full abstractDownload PDF (1509K)
- |<
- <
- 1
- >
- >|