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Volume 58, Issue 7
Displaying 1-18 of 18 articles from this issue
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Shigeo Sugawara, Jirô Watanabé1994 Volume 58 Issue 7 Pages 715-719
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe dissolution at screw dislocation sites and dislocation-free sites of the Cu (111) surface was studied as a function of concentration of HBr in Marukawa’s etchant (FeCl3·6H2O-HCl-HBr). Etching was carried out for 10 s at 280 K, and the dissolved quantities along lateral and longitudinal directions at dislocation, H and D, and the dissolved thickness of the matrix surface, S, were determined from measurement of size of dislocation etch pits and the step height at the boundary between the masked surface and the etched surface, respectively. An increase of the concentration of HBr in the etchant caused a decrease in H and an increase in D, but it produced no change in S. The role of inhibitor HBr was discussed on the basis of the spiral theory of crystal dissolution at screw dislocation and the two-dimensional nucleation theory at dislocation-free surface.View full abstractDownload PDF (814K) -
Eiichi Asayama, Hiromichi Takebe, Kenji Morinaga1994 Volume 58 Issue 7 Pages 720-727
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSPhase transformations of cordierite (2MgO·2Al2O3·5SiO2) glasses have been studied by X-ray diffraction, differential thermal analysis (DTA), optical microscopy (OM), and transmission electron microscopy (TEM). Continuous-Heating-Transformation (CHT) diagram and Time-Temperature-Transformation (TTT) diagrams are proposed. Continuous heating of bulk and powder glasses at 0.005∼0.33 K/s leads to the initial crystallization of μ-cordierite and subsequent μ→α transformation. There are two transformation processes in isothermal treatments of bulk glasses at 1123∼1473 K: One is the transformation from μ-cordierite to α-cordierite and the other is the direct crystallization from glass to α-cordierite. The microstructures of α-cordierite are affected by the transformation processes. The α-cordierite crystals transformed from μ-cordierite crystals contain microcracks, dislocations, and planar faults. The α-cordierite crystals formed directly from the glass show needle-like segments extending three dimensionally from the center. For powder glasses, isothermal treatments at 1123∼1473 K lead only to the μ→α transformation. This is due to the predominant nucleation of μ-cordierite on the surface of the glasses.View full abstractDownload PDF (1308K) -
Byung-Nam Kim, Teruo Kishi1994 Volume 58 Issue 7 Pages 728-733
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn analysis is conducted on the toughening mechanisms in composite materials reinforced with spherical particles in terms of pinning and deflection. The requisite for a crack to be deflected at particle/matrix interface depends both on the fracture toughness of the interface and on the impinging angle. According to the cracking behavior at the interface, dispersed particles are classified into two types of particles for crack-pinning and for crack-deflection. The respective toughening mechanisms are analyzed by introducing the equivalent crack closure stresses.
The crack deflection has a little effect on the enhancement of the fracture toughness compared with that of the crack pinning, and can be neglected in the case of the higher interface toughness. The apparent fracture toughness of the composites increases with both the interface toughness and the volume fraction of particles. Various dependencies of the apparent fracture toughness on the volume fraction are derived by varying the interface toughness, which substantiate well experimental results. The value of the interface toughness is also estimated indirectly from the comparison of the theoretical prediction with the experimental results.View full abstractDownload PDF (788K) -
Satoru Yoshimura, Yutaka Hiraoka, Katsushi Takebe1994 Volume 58 Issue 7 Pages 734-739
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSBy adding TiC (target content of Ti: 0.1-1.0 mass%), molybdenum-titanium alloys having titanium in solution up to 1 mass% and a certain content of oxygen were produced by powder-metallurgy technique. For these materials, tensile tests were performed at temperatures from 173 to 363 K. Yield and fracture (or tensile) strengths and total elongations were calculated from the load-displacement curves obtained at each temperature.
Then the critical stress and temperature that were parameters representing the low-temperature fracture strength and the ductility of the material, respectively, were evaluated after correcting for the grain size effect. Finally the effect of titanium in solution on the ductile-brittle transition characteristics was discussed in terms of apparent intergranular and transgranular fracture strengths and yield strength.
The results are summarized as follows.
(1) TiC additions induced a relative reduction of oxygen content and a slight decrease of grain size compared to titanium additions.
(2) The critical stress increased with increasing content of titanium in solution. Both the intergranular and transgranular fracture strengths increased with increasing content of titanium in solution up to 0.3 mass%. With a further increase of titanium in solution up to 1 mass%, the apparent transgranular fracture strength tended to decrease, whilst the apparent intergranular fracture strength was almost constant.
(3) Corresponding to the increase of critical stress, the critical temperature was decreased with increasing the titanium in solution up to 0.3-0.5 mass%. However, the critical temperature began to increase at 1 mass% of titanium in solution, notwithstanding the critical stress was almost constant. The latter result is due to the relative increase of yield strength with the increase of the content of titanium in solution.
(4)The fracture mode was mainly intergranular fracture, though the proportion of transgranular fracture tended to increase slightly for the alloy having 1 mass% of titanium in solution.View full abstractDownload PDF (932K) -
Akira Nozue, Masahisa Otsuka, Hiroshi Suzuki, Masayuki Takayama, Hidey ...1994 Volume 58 Issue 7 Pages 740-745
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAmorphous Ni60Mo30B10 powders have been hot-pressed, crystallized and heat-treated to control microstructures for excellent mechanical properties.
In materials (HP) hot-pressed at 1373 K, borides such as Mo2NiB2 are dispersed in Ni solutions saturated with alloy elements. These boride precipitates are quite fine and homogeneous. Materials of HP are solution-treated at 1373 K and aged to precipitate within its Ni solutions (973STA, 1073STA, 1273STA). Symbols of 973, 1073 and 1273 signify aging temperatures. In materials of 973STA and 1073STA, the borides, and Ni3Mo and NiMo compounds are dispersed, but little Ni solution exists. On the other hand, materials of 1273STA are formed of the borides and the NiMo compounds within the Ni solutions.
Materials of 1073STA give higher hardness in the temperature range between 300 and 800 K compared with HP materials. Its high hardness is about 8.3 GPa and compressive strength at room temperature is about 3.0 GPa. On the other hand, 1273STA materials of relatively high hardness exhibit large ductility because of the existence of the Ni solutions.
It is found that these composites maintain an excellent hardness and a moderate ductility up to about 800 K due to the thermal stability of its microstructures.View full abstractDownload PDF (875K) -
Hiroyuki Anada, Yoshiaki Shida1994 Volume 58 Issue 7 Pages 746-753
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSOxidation behavior of Mo modified Ti-34.5 mass%Al intermetallic compounds in air at 1073, 1173 and 1273 K was investigated by comparing with that of a binary Ti-34.5 mass%Al. Oxidation mass gain of the Mo-modified TiAl isothermally oxidized below 1273 K decreased with increasing Mo content. At 1273 K, however, a minimum in a mass gain-Mo content curve was observed at 2 mass%Mo content. A parabolic oxidation curve for the Mo modified TiAl was obtained under the cyclic oxidation condition at 1173 K, in contrast to a linear curve for the binary TiAl. As a result of SEM-EPMA observation, the scale of the Mo modified TiAl was found to have a layered structure in the following order from out side; TiO2/Al2O3/TiO2+Al2O3/Ti3Al (Mo enriched phase)/TiAl (matrix). Al2O3 was observed to form along the Mo enriched phase. The second Al2O3 layer from outer and the Al2O3 in the inner layer were much more continuous and must have acted as protective layers. The oxygen solid solubility decreased in the Mo modified TiAl and further in the Mo enriched phase region, which must be the cause for the external Al2O3 formation.View full abstractDownload PDF (2579K) -
Yoshiaki Shida, Hiroyuki Anada1994 Volume 58 Issue 7 Pages 754-762
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe influences of beneficial additional elements (W, Mo, Nb and Si) on the oxidation behavior of Ti-34.5%Al alloy have been compared and the roles of those elements were studied. Relative effectiveness was in the order W≥Mo=Nb≥Si at 1173 K. After the analyses of rate law and comparison in the Arrhenius plots of parabolic rate constant, it was clarified that the oxidation resistant temperature was raised by 100 and 200 K for the Mo (Nb) and W added alloys respectively in comparison with the binary alloy for which the temperature was somewhere around 973 and 1023 K. The Mo, Nb and W added alloys did not show internal oxidation nor breakaway oxidation behavior which were observed in the binary alloy. The reason for the non-occurrence of internal oxidation in these ternary alloys was verified by the result that those elements cause reduction of oxygen solubility in the TiAl alloys very significantly. Owing to this effect, the 2nd from outer Al2O3 layer may be stabilized and the morphology of the Al2O3 in the inner layer may become more impermeable.View full abstractDownload PDF (2360K) -
Ryoji Okada, Masayuki Yamada1994 Volume 58 Issue 7 Pages 763-767
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of heat treatment on hardness and wear resistance of WC-27%NiCr sprayed coating on SUS403 made by High Velocity Oxygen Fuel Spraying (HVOF) has been studied to improve abrasive wear resistance.
Specimens were heated to either 573, 673 and 773 K and held at those temperature for various times, up to 45 h. The change in micro-vickers hardness (load 2.94 N) after heat treatment was measured after the samples coold to room temperature. The wear rate of the specimens against α-SiC with the plane-on-plane contact pressure of 0.196 MPa, in water suspending 9 mass% silica powder were measured by a sliding velocity of 0.5 m/s.
The results obtained are as follows:
(1) Heat treatment increased the hardness of WC-27%NiCr sprayed coatings.
(2) The increase of the hardness due to heat treatment was dependent on the void decreasing of the sprayed coatings.
(3) The wear rate of the heated WC-27%NiCr sprayed coatings in water suspending silica powder became triple increment against that of the coating before heating.View full abstractDownload PDF (654K) -
Michiko Yoshitake, Kazuhiro Yoshihara1994 Volume 58 Issue 7 Pages 768-774
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe present study was done on the Ti concentrated surface of the Nb film which was formed by the rapid diffusion of the substrate element Ti through the Nb film. It was observed that \ding”C0 the surface concentration of Ti saturated, \ding”C1 the depth profile of the Ti concentration did not change in spite of the increase of the heating time, \ding”C2 the saturation concentration was constant between 770 and 880 K, \ding”C3 The Ti concentrated layers were quickly reformed by re-heating after they are sputtered away. These experimental results show that the Ti concentrated surface has a stable structure.
From the results of angle-resolved XPS, it was suggested that the concentration of Ti decreased from the surface to the inside of the Nb film (up to 5 nm), and that the multi-layered segregation seemed to occur. By the statistical thermodynamics, the multi-layered segragation can be explained with the assumption of the different atomic interactions between the layers.View full abstractDownload PDF (566K) -
Hisashi Amaya, Hideaki Miyuki1994 Volume 58 Issue 7 Pages 775-781
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSStainless steels, such as types 316L and 304 have high susceptibilities to pitting and crevice corrosion in natural seawater even though they have low susceptibilities in synthetic seawater. Recently, this type of corrosion has been recognized as a kind of Microbially Influenced Corrosion (MIC) in aerobic aqueous environments. The mechanism of MIC on stainless steels in natural seawater is studied by the electrochemical and biological techniques. Measurements of cathodic polarization curves of stainless steels were carried out in natural and synthetic seawater. The corrosion potential of stainless steels was measured in seawater and culture medium of the bacteria isolated from natural seawater. The corrosion potential of stainless steels became noble in natural seawater compared with synthetic seawater, and the cathodic polarization behavior indicates that some substances exist, which have higher redox potential than that of oxygen. It has become clear that the susceptibility to corrosion of stainless steels in natural seawater is effected by bacteria in the mature biofilm. As a result of the experiment using isolated bacteria, the corrosion potential became noble in the logarithmic phase of bacterial growth. These results suggest that the aerobic metabolism of the bacteria causes the ennoblement of stainless steels. Hydrogen peroxide, which could be generated due to the reduction of oxygen in the presence of enzyme (oxidase), was detected in the mature biofilm. Hydrogen peroxide has a higher redox potential than that of oxygen. Therefore, this result supports the fact that the hydrogen peroxide, as an intermediate substance in the aerobic metabolism of bacteria in the biofilm, causes the ennoblement of stainless steels in natural seawater. The potential ennoblement and the occurrence of crevice corrosion of stainless steels were successfully reproduced in the laboratory by using the synthetic seawater with the addition of oxidase and substrate.View full abstractDownload PDF (1314K) -
Noriaki Kurita, Norihiko Fukatsu, Teruo Ohashi1994 Volume 58 Issue 7 Pages 782-788
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSEmploying the same method of Otsuka’s oxygen analyzer (Trans. JIM, 25 (1984) 639), we developed a new type hydrogen analyzer based on coulometric titration using a proton conductive solid electrolyte. The following electrochemical cell was constructed by utilizing indium doped calcium zirconate as the electrolyte and utilizing sintered porous platinum as the electrodes.
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\ oindentThe cell was operated at 973 K. The left electrode chamber was exposed to the flowing Ar+1%H2 gas, while the right electrode chamber was closed and Ar gas was circulated. On imposing the positive constant voltage to the cell, the right electrode worked non-reversible and the hydrogen potential of the right electrode chamber was decreased to the very small value specified by the Hebb-Wagner’s polarization condition state. In the polarization state, the hydrogen to be analyzed was injected to the right electrode chamber by a micro-syringe and the excess current due to proton transport from the right to the left electrode was measured in the external circuit. The quantity of electricity calculated by the integration of the decay curve of the excess current was in good agreement with theoretical value evaluated from the amount of injected hydrogen by Faraday’s law. The hydrogen in a commercial palladium plate was analyzed successfully by dropping the specimens in the combustion furnace locate in the circulating path of the right electrode chamber. The performance and the best analyzing condition were discussed theoretically in terms of the electrochemical properties of the electrolyte. This type of hydrogen analyzer doesn’t need a standard sample and any calibration for the blank conditions and has high ability to detect a small amount of hydrogen as little as 10−8 mol(H).View full abstractDownload PDF (890K) -
Takeshi Kobayashi, Shin-ichi H asegawa, Takayuki Yoshioka, Ryosuke Has ...1994 Volume 58 Issue 7 Pages 789-795
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn analytical method has been established for the direct determination of trace amounts of each analyte in iron and steels solution by graphite furnace atomic absorption spectrometry (GF-AAS). The iron and steel were dissolved in nitric acid. After the solution (20 mm3) was pipetted into a L’vov platform or pyrolytically coated graphite tube furnace, it was ashed (773 K-60 s, hydrogen 5 cm3/s) and then atomized by using argon as a purge gas, and atomic absorption of each analyte was measured. The effect of diverse elements was suppressed by the use of peak area measurement. Synthetic calibration solutions were prepared by addtion of standard solution of each analyte to iron matrix solution (2 kg/m3). For cadmium, zinc, magnesium, thallium, bismuth, lead, manganese, copper, nickel, vanadium, cobalt, palladium and molybdenum, the limits of detection (3σ of blank values) were 0.003, 0.002, 0.004, 0.030, 0.042, 0.035, 0.021, 0.038, 0.045, 0.21, 0.040, 0.044 and 0.12 ppm, respectively, when one gram of the specimen was used. The proposed method is able to be applied to other analyte in iron and steels.View full abstractDownload PDF (998K) -
Toshio Shimoo, Shin-ichiro Adachi, Kiyohito Okamura1994 Volume 58 Issue 7 Pages 796-802
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe kinetics and the mechanism of the reaction between Si3N4 and Nb have been investigated under a N2 or an Ar atmosphere at temperatures from 1373 to 1673 K. Using a Si3N4-Nb powder mixture, the reaction rates were determined with a thermobalance, and the reaction products were examined by X-ray diffraction.
Under the N2 atmosphere, the mass gain was caused by the production of the niobium nitrides. With increasing temperature, the nitrides changed in the following order: Nb4.62N2.14, Nb2N, Nb4N3, NbN0.95, and NbN. It is considered that Nb is not reacted with Si3N4 but with N2.
Under the Ar atmosphere, the reaction products were both the nitrides (Nb4.62N2.144, Nb2N and NbN) and the silicides (Nb5Si3 and NbSi2). At higher temperatures and on prolonged heating, the niobium nitrides disappeared as a result of the interaction with Si3N4. Above 1523 K, the production of niobium silicides resulted in the mass loss. The initial rate followed a linear rate law, and the activation energy was 320 kJ/mol. An interfacial reaction may be considered as the rate-determining step. At a late stage of the reaction, the kinetics followed a parabolic rate law, and the activation energy was 507 kJ/mol. The reaction rate is probably controlled by a solid state diffusion through the reaction layer.View full abstractDownload PDF (732K) -
Hiromichi Nakata, Takao Choh, Naoyuki Kanetake1994 Volume 58 Issue 7 Pages 803-809
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe spontaneous infiltration of liquid pure aluminum into the mixture of raw materials is used to synthesize particulate reinforced aluminum composites with the in situ process. The addition of powder of a column IVa element (Ti, Zr) or a column Va element (Nb, Ta) into the raw carbide particles of Al4C3, SiC or B4C allows liquid pure aluminum to infiltrate into the mixture spontaneously and subsequently in situ formation of the carbide particles of column IVa and Va elements occurs in the melt. It is revealed from macroscopic and SEM observations that liquid aluminum completely infiltrates into the mixture independently of the kind of atmosphere used in the experiment, nitrogen or argon. However, processing under nitrogen gas, which can react with the aluminum melt, is effective in prohibiting pores from remaining in the composite. The rate of in situ reaction of the (Ti+B4C) system is somewhat high compared to those of (Ti+SiC) and (Ti+Al4C3) systems. Very fine TiC and TiB2 particles simultaneously synthesized through the decomposing reaction of B4C are dispersed in the aluminum matrix. As soon as liquid aluminum begins to infiltrate, the melt temperature increases drastically not only in (Ti+raw carbide) systems but also in a (Ti+Al2O3) system. Hence, it seems that the spontaneous infiltration of liquid aluminum is attributed to the exothermic formation of Al3Ti.View full abstractDownload PDF (2308K) -
Kazuyoshi Saida, Yunhong Zhou, Thomas H. North1994 Volume 58 Issue 7 Pages 810-818
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of base metal grain size and quenching method form the brazing temperature on isothermal solidification during TLP-brazing with Ni-11 mass%P filler metal were investigated. Single crystal, coarse-grained and fine-grained nickel base metals were brazed at 1423 K for various holding times, and the test specimens were then air-cooled, oil-quenched or water-quenched. Scanning electron microscopy and element analysis revealed that the eutectic width produced in air-cooled and in oil-quenched samples were smaller than that in the water-quenched specimens. This difference in eutectic width was due to different solidification modes occurring during cooling from the brazing temperature.
The eutectic width decreased linearly with the square-root of the brazing time in single crystal, coarse-grained and fine-grained nickel base metals. The completion time for isothermal solidification decreased in the order of single crystal, coarse-grained and fine-grained base metals. The difference in isothermal solidification rates produced when brazing the different base metals could be explained qualitatively by the influence of base metal grain boundaries on the apparent mean diffusion coefficient of phosphorus in solid nickel.View full abstractDownload PDF (2098K) -
Mok-Soon Kim1994 Volume 58 Issue 7 Pages 819-825
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA fully lamellar structure with the average grain size between 28 and 270 μm was achieved by reactive sintering in Ti-43.4Al-1.6Mn (mol%) alloy with TiB2 particulates. Using the alloy with a fully lamellar structure, the effect of grain size on the strength, ductility and fracture was investigated at both room temperature and 1073 K.
At room temperature, the yield strength obeys the Hall-Petch relation, and the Hall-Petch parameter, ky, is found to be larger than that of the single phase γ alloys reported previously. When TiB2 content is lower than 5 vol%, the fracture strength also obeys the Hall-Petch type relation and the elongation increases with a decrease in grain size, suggesting that the critical stage of fracture is associated with the nucleation of the crack based upon a pile-up model.
At 1073 K, when the grain size is smaller than 90 μm, the yield strength decreases with a decrease in grain size, and the elongation exhibits a higher value than that at room temperature. The maximum peak of the tensile strength appears at the grain size of about 60 μm.
All these results indicate that the suitable grain sizes are in the range from 40 to 90 μm in considering the balance of ambient and elevated tensile properties.View full abstractDownload PDF (2124K) -
Satoshi Inoue, Masahito Kato, Shigeki Kano, Yasushi Isshiki, Jun-ichi ...1994 Volume 58 Issue 7 Pages 826-834
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSNb-based alloys are ones of the promising materials for structural applications in advanced nuclear power systems. A systematic estimation for high-temperature tensile strength, high-temperature creep strength, corrosion resistance to liquid sodium and alloy density was performed in order to get useful information for the design of the Nb-based alloys, as was similarily done for Mo-based alloys.
The high-temperature micro-hardness and the high-temperature tensile strength were found to be predictable using the same calculation method employed in the Mo-based alloys. The differences in the atomic radius and in the Young’s modulus between the Nb atom and alloying elements were taken into account in the prediction. The melting temperature was calculated readily by taking the compositional average of melting temperatures for constituent metals, and used as an indication for the creep strength of alloys. The corrosion resistance to liquid Na was also found to be significantly lower in the Nb-based alloys than in the Mo-based alloys. In addition, the corrosion resistance of Nb-based alloys were largely varied with alloying elements. From a series of corrosion tests with various Nb-M binary alloys, alloying elements which are effective in improving the corrosion resistance were selected. Furthermore, alloy densities were estimated by taking the compositional average of the densities for constituent metals in alloy.
Based on these results, a Nb-W-V-Zr system was selected as the most promising alloy for nuclear power plants. The specific properties were estimated with varying alloy compositions, even though extensive investigation is further needed to draw a conclusion on the corrosion resistance of these alloys. Finally, it was concluded that the present predicting method could provide an useful indication for the efficient design of Nb-based alloys.View full abstractDownload PDF (1270K) -
Wan Jiang, Akira Kawasaki, Kazuhiro Date, Ryuzo Watanabe1994 Volume 58 Issue 7 Pages 835-841
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA non-contact measurement system for the coefficient of thermal expansion (CTE), as well as the displacement of a rigid body, using laser speckle photography has been constructed which enables to determine precisely a regional CTE variation in a specimen at temperatures as high as 1473 K. Mo/PSZ sintered composites was used for the measurement of the dependence of CTE on temperature and Mo/PSZ mixing ratio.
A double photographic exposure of laser speckle patterns before and after thermal displacement and a re-irradiation of laser beam to the photographic film yield a Young’s fringe corresponding to the displacement involved. A stepwise temperature increment method has been employed to get better speckle patterns and for the determination of CTE at high temperature. It has been found that, Au coating is needed to avoid the fading of speckle patterns and thus of the Young’s fringes due to laser beam transparency through PSZ. The temperature and composition dependences of CTE of Mo/PSZ composites have been found to be determined with sufficient accuracy. It has been suggested the present method will be applied for the determination of regional CTE variation in functionally gradient materials having graded compositional distributions in themselves.View full abstractDownload PDF (1017K)
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