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Volume 60, Issue 12
Displaying 1-16 of 16 articles from this issue
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Mitsuharu Yonemura, Naoki Hara, Kazuhito Kamei, Takahiro Takada1996 Volume 60 Issue 12 Pages 1143-1148
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSHigh resolution electron microscopy (HREM) observation with the multislice simulation was performed in order to analyze the structure of Ca-Nd-Ti-O microwave dielectrics which have recently been synthesized.
The detailed structure that was predicted by X-ray diffractmetry and Rietvelt analysis was the structure in which the lattice vacancies exist selectively in the (002) plane of perovskitelike unit cells.
We confirmed the predicted structure by comparing the HREM images with simulated images. We also revealed the antiphase boundary (APB) caused by the displacement of the (002) defective planes.View full abstractDownload PDF (632K) -
Susumu Arai, Tohru Watanabe1996 Volume 60 Issue 12 Pages 1149-1154
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSn-Ag alloys, which are considered to be suitable for use as Pb-free solders, were formed by an electrodeposition method. In the alloys formed by an electrodeposition method, un-equilibrium phases, which do not exist in the phase diagram occasionally appear. Therefore the composition, morphology, produced phases and microstructure of the elecrtodeposited Sn-Ag alloys were studied. The results are summarized as follows.
(1) A good relationship was observed between the morphologies of the electrodeposited Sn-Ag alloys and their compositions.
(2) The electrodeposited Sn-Ag alloys had two phases (β-Sn and an intermetallic compound) in the range of 5 to 75 atomic percent Ag content, and were composed of grains of submicron-order diameter.
(3) The phases which exist in the electrodeposited Sn-Ag alloys were those reported in the Sn-Ag alloy phase diagram.View full abstractDownload PDF (1675K) -
Kenichi Takai, Yoshikazu Homma, Kaori Izutsu, Michihiko Nagumo1996 Volume 60 Issue 12 Pages 1155-1162
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe trapping sites of hydrogen detected by Thermal Desorption Spectrometry (TDS) have been identified by Secondary Ion Mass Spectrometry (SIMS). High-strength steel specimens were given applied loads in D2O and 20% NH4SCN solution at 323 K. In SIMS analysis, deuterium ions can be detected with greater sensitivity than hydrogen ions and measurement can be started in a matter of minutes. TDS analysis shows that hydrogen thermal desorption rate has two peaks, corresponding to trap activation energies of 20.7∼22.5 kJ/mol and 82.2∼87.4 kJ/mol for the lower and higher temperature peaks, respectively. These values are close to 26.8 kJ/mol reported in the literature as the trap activation energy for desorption from dislocations and ≥72.3 kJ/mol from the interfaces of inclusions and precipitates. By applying SIMS image-analysis to specimens cooled after the respective peak temperatures, we could identify the trapping sites corresponding to the lower temperature peak as sites within the matrix such as defects including dislocations, and those corresponding to the higher temperature peaks as inclusion interfaces, precipitate interfaces, and segregation bands of phosphorus. These SIMS results confirm the location of the trapping sites to be the same as those estimated from trap activation energy by TDS.View full abstractDownload PDF (696K) -
Yasubumi Furuya, Minoru Taya1996 Volume 60 Issue 12 Pages 1163-1172
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThis paper describes the shape memory effects of TiNi fiber Al matrix (TiNi/Al) composites on enhancement of its mechanical properties: tensile and fatigue resistance. A TiNi/Al composite was processed by a powder metallurgical route. The yield stress and fatigue resistance showed that they would increase with prestrain at temperature above the austenitic finish temperature of TiNi fiber (Af). The increases in tensile properties (yield stress) and fatigue resistance were attributed to the compressive stress field in the matrix which was induced when prestrained TiNi fibers shrank to its initial length upon heating above Af. The predictions based on the analytical model agreed reasonably well with the experiment.View full abstractDownload PDF (937K) -
Yonosuke Murayama, Shuji Hanada1996 Volume 60 Issue 12 Pages 1173-1180
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of concentration ratio of niobium to aluminium on stress-strain curves and deformation microstructures of Nb3Al at high temperatures was examined. Specimens prepared by hot isostatically pressing (HIP) Nb-Al alloy powders under 200 mesh size contain Nb3Al over 95% in volume. The samples with four compositions which were from the phase boundary between Nb3Al and Nb solid solution to that between Nb3Al and Nb2Al were prepared. Compression tests were carried out above 1273 K at 1.67×10−4 s−1.
Yield stress increases with increasing concentration of aluminium at 1473 K. This composition dependence becomes indistinct with increasing compression temperature. The width of dissociated a/2 ⟨100⟩{001} dislocations in Nb3Al show a composition dependence. The dissociated width increases with increasing concentration of aluminium at 1473 K. Fine dynamically recrystallized grains constituting the so-called ‘necklace structure’ and a large deformation softening in the stress-strain curve were observed in the sample with widely dissociated dislocations. However, the composition dependence becomes indistinct with increasing compression temperature, because the size of grains resulting from dynamical recrystallization is large and then an amount of deformation softening decreases suddenly.View full abstractDownload PDF (2754K) -
Katsunori Yamaguchi, Yoshiyuki Chiba, Masahito Yoshizawa, Kazuo Kameda1996 Volume 60 Issue 12 Pages 1181-1186
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSLow temperature specific heats of the GaP, InP, GaAs and InAs compounds were measured over the temperature range 4.5 to 298.15 K using an adiabatic calorimeter. The Debye temperatures were derived from the obtained specific heat data. The curves of Debye temperature as a function of temperature for the GaP, InP, GaAs and InAs compounds exhibit a minimum in the temperature range of 15∼30 K and a maximum at somewhat higher temparatures (approximately 130∼180 K). The standard entropies of the GaP, InP, GaAs and InAs compounds determined from the specific heat data were 50.5, 62.1, 64.1 and 75.5 J/(mol·K), respectively. A relation was found between the standard entropy and the cohesive energy. The standard entropies of the III-V compounds decreased linearly with increasing cohesive energy per bond.View full abstractDownload PDF (510K) -
Shigenori Yamamoto, Masahiro Kawakami, Toshihide Takenaka1996 Volume 60 Issue 12 Pages 1187-1191
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSExfoliation corrosion proceeds laterally along planes parallel to the surface of high strength aluminum alloys. The ASTM G34(EXCO) test is widely used to predict exfoliation corrosion susceptibility. The susceptibility is determined by visual examination in which the surface profile is compared with the reference standard photograph. This method is ambiguous, so that it is difficult to distinguish general corrosion (overall corrosion, pitting) from exfoliation.
In this study, a quantitative estimation method of exfoliation corrosion susceptibility based on ASTM G34 was developed, and the effect of composition and heat treatment of the alloys on exfoliation corrosion susceptibility were examined by this method.
The specimens used were of 7XXX, Al-Li series alloys treated in T6, T7 and T4 modes. The normal procedure of ASTM G34 was carried out. Moreover, as quantitative measurements, the mass losses and quantity of exfoliation were evaluated by the following procedure. The specimens were soaked in nitric acid for 2 min and rinsed in water after being rated. After drying for about 30 min, the mass losses were measured. One week later, piles on the specimens were removed from the surface by a tooth brush. The piles and residues in solution were treated with hydrochloric acid, so that the weight of the metallic component was estimated by the amount of evolved hydrogen gases. The quantity of exfoliation was defined by the weight.
The results obtained in this study were as follows;
(1) The quantity of exfoliation was slightly correlated with ASTM G34 rating. The exfoliation corrosion could be distigushed from the overall corrosion and pitting.
(2) Exfoliation susceptibility was especially high in the alloys containing from 0.7 to 1.0%Cu. The alloy containing 0.37%Cu was the lowest.
(3) The heat treatment in T7 gave high susceptibility of exfoliation corrosion, while that in T4 gave high susceptibility of overall corrosion and pitting.View full abstractDownload PDF (628K) -
Seiichi Iwata, Yuzuru Ohji, Akitoshi Ishizaka1996 Volume 60 Issue 12 Pages 1192-1199
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn the study of X-ray-induced surface potential changes of ultrathin SiO2 films on Si caused by X-ray irradiation, we investigated why the time constant for the X-ray-irradiation time dependence decreases with increasing oxide thickness and saturates at about 10 nm thickness. We conclude that the above changes are caused by the hole trapping at traps close to the SiO2/Si interface and that the time constant is greater at small thicknesses because the hole concentration is effectively smaller at thicknesses close to the hole mean free path, which could be estimated to be about 1.8 nm.View full abstractDownload PDF (921K) -
Junji Saida, Kenjiro Izutani, Yasuji Tanaka1996 Volume 60 Issue 12 Pages 1200-1206
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAmorphous Co66Fe4Ni1Si14B15 alloy powders were consolidated by high-voltage discharging at various initial packing factors, specimen resistances and input energies. Compressed amorphous alloy powders with initial packing factor of 75% are consolidated retaining their amorphous structure below in input energy of 0.53 kJ/g. The relative density of the amorphous alloy compacts has a maximum value of approximately 95% when prepared with an initial packing factor of 85% and the input energy of 0.53 kJ/g. The densification increases on starting with a lower initial packing factor. The maximum increase in densification with the retaining amorphous structure is about 12%. The amorphous alloy compacts have no distinct pores and defects. The Vickers hardness of the compacts is nearly equal to that of melt-spun ribbons with the same composition. The coercive force does not change with their relative densities. However, magnetization increases with increasing relative density and it is saturated at 0.55 T above a relative density of 90%. The change of maximum permeability with their relative densities can be fitted to an equation with a parameter β which depends on the properties of the powders and the conditions for consolidation. The value of β has been found to be 0.007 in the present case.View full abstractDownload PDF (1022K) -
Hiroyuki Higuchi, Makoto Sugamata, Junichi Kaneko1996 Volume 60 Issue 12 Pages 1207-1214
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSWith a purpose of attesting selective oxidation of solute Li and Mg in solid Al, mechanical alloying was carried out for Al-Li and Al-Li-Mg alloys with or without addition of various metal oxides, and subsequently P/M materials were prepared. Constituent phases were determined by XRD for the mechanically alloyed powders and the as-extruded and heat-treated P/M materials. Hardnesses and microstructures were examined for the P/M materials.
It has been confirmed that Li is selectively oxidized and LiAlO2 is generally formed in the Al-Li alloys. In the Al-Li-Mg alloys, Mg is oxidized in preference to Li. After hot extrusion, hardness increases were not observed with progressing preferential oxidation and reduction of the added metal oxide. Coarsening of LiAlO2 particles was observed in the P/M materials after heating at 873 K. As-extruded P/M materials showed relatively high hardness and hence dispersion hardened materials of high mechanical strength can be expected by applying preferential oxidation of the solute in aluminum.View full abstractDownload PDF (887K) -
Yahui Huang, Motoyoshi Ohwatari, Masahiro Fukumoto1996 Volume 60 Issue 12 Pages 1215-1221
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of substrate material on the flattening behavior of the plasma sprayed Ni particle was investigated. The results obtained are summarized as follows:
(1) From the study of the splat behavior of Zr and Fe particles, it was clear that the splashing tendency of the plasma sprayed metallic particles can be evaluated by the relationship between surface tension and initial solidification rate of the powder material.
(2) It was observed that the transition temperature varied with substrate materials as evidenced by the splatting behavior of Ni particles. It was found that the flattening of the particle was influenced by the substrate material.
(3) Under the same wetting conditions between particles and substrate, it was found that the larger the thermal conductivity of the substrate material, the higher the transition temperature. Therefore, it was clarified that the particle’s splashing was influenced considerably by the initial solidification of the particle.
(4) Under the same solidification coditions, it was observed that the higher the substrate material’s activity, the higher the transition temperature. This seems to depend on the wetting of the Ni particle on the oxide surface. The effect of wettability on the flattening of the particle cannot be neglected.View full abstractDownload PDF (1135K) -
Michinari Asano, Toshiro Kobayashi, Masahiro Nawa, Koichi Niihara1996 Volume 60 Issue 12 Pages 1222-1228
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSStatic and dynamic fracture toughnesses in precracked Y-TZP/Mo composites fabricated by hot-pressing through a nanocomposite approach are investigated. Fracture toughnesses in these composites are virtually unaffected by loading velocity. The composite containing 70 vol%Mo, whose microstructure exhibits a continuous Mo phase, shows the highest fracture toughness. X-ray diffraction analysis on fracture surface indicates no transformation from tetragonal to monoclinic phase in ZrO2in the fracture process. Therefore, the improvement of fracture toughness in these composites is considered to be attributed to the incorporation of second phase and the change in the morphology of the microstructure. Moreover, a toughening mechanism of these nanocomposites is discussed from a microstructural point of view.View full abstractDownload PDF (1070K) -
Ken-ichiro Igashira, Koji Nishio, Haruki Hino, Shozo Okazaki1996 Volume 60 Issue 12 Pages 1229-1235
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe elevated temperature capability of the Si-Ti-C-OF/SiC composite was evaluated in association with the study on the degradation mechanisms, the life prediction techniques, and the improvement of the durability of the material. Test samples were fabricated by polymer-impregnation pyrolysis (PIP) combined with chemical vapor infiltration (CVI) techniques. These materials were exposed to the temperatures ranging 1173-1673 K either in the oxidation atmosphere or in vacuum for the maximum duration of 500 h, then the weight, flexure strength and fracture toughness were measured at room temperature. The Larson-Miller parameter (LMP) was used to evaluate the durability of the composites so that the effects of both the exposure temperature and time may be taken into account, by which the relationships among the weight change, remaining strength and fracture toughness of the samples were simply described. The magnitude of the strength reduction of all the samples, as well as the weight loss of the samples exposed to the high temperatures in vacuum, showed a drastic change at around the LMP of 17. The samples exposed to the high temperatures in the oxidation atmosphere, on the other hand, showed a gradual weight gain and fracture toughness reduction as the LMP increased. TEM micrographs showed that the weight gain of the samples was due to the crystallization of the amorphous Si-Ti-C-O at the fiber/CVIed-SiC matrix interface. The results of these evaluations indicated that the decreases in strength and fracture toughness of the composite are largely dependent on the thermal decomposition of the fibers and the oxidation at the fiber/CVIed-SiC matrix interface, respectively. Thus it was concluded that using the matrix material which is capable of producing the anti-oxidation sealant to prevent the fibers from the oxidation, as well as using the high temperature resistant reinforcement fibers, is crucial in order to improve the elevated temparature durability of the composite material.View full abstractDownload PDF (1626K) -
Kenji Matsunaga, Toshihiro Ishikawa, Shinji Kajii, Toshihiko Hogami, Y ...1996 Volume 60 Issue 12 Pages 1236-1242
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe present study deals with the relationship between the mechanical properties up to high temperature and the fiber’s volume fraction (Vf) of the Si-Ti-C-O fiber-bonded ceramics (FBC) which was produced by hot-pressing the laminated material of the sheets of pre-oxidized Si-Ti-C-O fiber with a surface oxide layer. As the Vf became higher, the compressive and flexural strengths at high temperatures became much larger. On the basis of the detailed investigation of the differences in the fracture appearance, it was concluded that the excellent mechanical properties of FBC with high Vf at high temperatures could be caused by the less influence of the softening of the SiO2, which existed in the interstices between the fibers, because the higher the Vf, the smaller the amount of the interstices becomes. The observed Close-packed structure of the Si-Ti-C-O fiber-bonded ceramics (Vf=90%) was very effective in retaining good mechanical properties up to high temperatures.View full abstractDownload PDF (1375K) -
Fumiyoshi Kirino, Shigekazu Ohotomo, Nagatsugu Koiso1996 Volume 60 Issue 12 Pages 1243-1250
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDependences of corrosion resistance of an Al-doped Fe-Ta-C magnetic thin film on Al, Ta, and C contents were examined. The higher the concentration of the doped Al in Fe-Ta-C alloy, the higher became the pitting potential and the oxidation potential. The resistance against corrosion such as pitting corrosion and wet corrosion increases with increasing Al concentraition. When the Al content in the Fe-Ta-C film is incresed to 9.8 at%, a passive film is formed on the alloy film surface where the pitting potential is 0.5 V (vs. Ag/AgCl electrode), and oxidation of the metal such as Fe does not occur. This film is thus highly resistant to corrosion when it is immersed in 0.5N-NaCl solution. The corrosion resistance depends on [Ta]/[C] ratio. When the [Ta]/[C] ratio is greater than 0.72, the film with 9.8 at%Al corrodes in 0.5N-NaCl solution. When the [Ta]/[C] ratio is between 0.52 and 0.68, the highest corrosion resistance is realized. The crystal structure analysis using X-ray diffraction indicates that the grain size of TaC precipitates is very small in these films. Magnetic properties of the 9.8 at%Al-doped Fe-Ta-C film (Bs=1.3 T, Hc=20 A/m, μ=3000, and λs=2×10−6) are suitable for magnetic head applications.View full abstractDownload PDF (849K) -
Fumiyoshi Kirino, Shigekazu Ohotomo, Nagatsugu Koiso, Fumiko Yano1996 Volume 60 Issue 12 Pages 1251-1258
Published: 1996
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSEffect of additional elements such as Al or Cr, Ru on the corrosion resistance of Fe-Ta-C magnetic thin films was studied. The electrochemical characteristics of Al, Cr, or Ru doped Fe-Ta-C magnetic thin films were measured. For the Fe-Ta-C thin film doped with Cr or Ru, a passive layer is formed on the surface of the film. However, the protection current of the passive layer is so high that the magnetic film has a rather low corrosion resistance. The Al doped Fe-Ta-C magnetic thin film (Al concentration is about 10 at%) is covered with a passive film, which has a high corrosion resistance. To study the difference of corrosion resistance among the films with different additional elements such as Al, Cr, or Ru the following model samples were prepared. In the model samples, as Al layer or a Cr layer was formed on the Fe layer. The depth profiles were studied by AES method after annealing these samples. In the Al/Fe sample, Al diffuses into the Fe layer after annealing at 773 K. But, on the Cr/Fe sample, Cr does not diffuse into the Fe layer by annealing at 973 K, it was also found that carbon exists at the Fe/Cr interface. This result implies that the carbon at the Fe/Cr interface supresses the diffuse of Cr into the Fe layer. As a results, a solid solution is formed at the Fe/Al interface, but there is no solid solution at the Cr/Fe interface. The bonding energies in these samples were measured by the ESCA method.
The bonding state of Cr in the Fe-Ta-Cr-Ru-C film is metallic, and there exists another state of Cr which could not be identified as a result of a broad peak width. Some of the Al atoms in the Al-doped Fe-Ta-C film are in the metallic bonding state and some others are in the oxide state. Al is the most easily oxidized element among these elements. Thus, Al doped Fe-Ta-C alloy film has a high corrosion resistance. We have demonstrated that the effective additional elements for improving the corrosion resistance of the magnetic film are those which have a high diffusivity into Fe, without forming carbides, and which form a passive film on the surface of the magnetic thin film easily.View full abstractDownload PDF (903K)
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