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Volume 65, Issue 4
Displaying 1-15 of 15 articles from this issue
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Kazuhisa Kita, Ryoichi Monzen2001 Volume 65 Issue 4 Pages 223-228
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTransmission electron microscopy has been used to measure the average sizes during coarsening of spherical α-Fe and γ-Fe precipitates in Cu-1.0 mass%Fe and Cu-2.0 mass%Fe alloys aged at 873, 923 and 973 K, and electric resistivity has been used to measure the depletion of Fe concentration in the Cu matrix with aging time t. The growth kinetics of α-Fe and γ-Fe precipitates obeys t1⁄3 kinetics, as predicted by the Lifshitz-Slyozov-Wagner theory. The kinetics of the reduction of Fe concentration for α-Fe and γ-Fe precipitates is consistent with the predicted t−1⁄3 time law. The equilibrium solubilities of Fe in the matrix at the α-Fe/Cu interface are smaller than those at the γ-Fe/Cu interface. The former and latter values are in good agreement with those previously reported by Tammann and Oelsen, and Andersen and Kingsbury, respectively. The values of the Fe/Cu interface energy Γ and volume diffusion coefficient D have been independently derived from the data on coarsening. The value of Γ for the incoherent α-Fe/Cu interface is estimated to be 0.52 J/m2, and two times as large as the coherent γ-Fe/Cu interface energy, 0.25 J/m2, which is nearly consistent with values previously reported. The pre-exponential factor and activation energy for diffusion of Fe in Cu are determined to be 1.05×10−4 m2/s and 213 kJ/mol, respectively.View full abstractDownload PDF (369K) -
Koichiro Inoue, Takeshi Nakata, Tohru Watanabe2001 Volume 65 Issue 4 Pages 229-235
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe crystallographic structure and surface morphology of Fe films electrodeposited in three kinds of baths were studied in detail by SEM and XRD. Fe deposits were prepared in a sulfate bath, chloride bath and sulfamate bath. The surface morphology of Fe deposits on Ni-P amorphous substrate were found to vary according to the electrodeposition bath composition. The (211) plane appeared to be the dominant orientation of deposited films for all baths examined in this study.View full abstractDownload PDF (2106K) -
Ryuta Onodera, Tatsuya Morikawa2001 Volume 65 Issue 4 Pages 236-243
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe critical (onset) strain εc of a serrated flow was predicted by phenomenological theory based on the strain-softening model. The critical strain predicted by the theory agreed quantitatively with experimental data. In particular, the theory could explain the relation between εc and strain rate \dotε:3lnεc=C+ln\dotε+E⁄RT without using the concept of a Cottrell atmosphere. Moreover, the increase in the critical strain for very small strain rates (the so-called type C serration) could also be simply explained by the theory.View full abstractDownload PDF (635K) -
Ryuta Onodera, Tatsuya Morikawa2001 Volume 65 Issue 4 Pages 244-252
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA strain aging test was conducted at room temperature in aged Al-4.5Cu alloy. The stress-strain curve during restraining exhibited a peculiar shape (the stress plateau). Both the strain rate and the aging time strongly affected the aging phenomena. Two characteristics, the stress increase (the difference in the stress between before and after aging) and the transition strain (the strain during the stress plateau) were measured. The shape of the s-s curve and the two characteristics were successfully explained by phenomenological theory based on the strain-softening model constructed to explain the Portevin-Le Chatelier effect.View full abstractDownload PDF (738K) -
Han-Cheol Choe, Yeong-Mu Ko, Keum-Yeon Hwang2001 Volume 65 Issue 4 Pages 253-261
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTo increase the corrosion resistance of magnetic materials, surfaces of Sm-Co and Nd-Fe-B based magnets were plated with Ti/TiN multi-layer and then electrochemical corrosion tests were performed in 4 kinds of electrolyte solutions (0.9 vol%NaCl, 1 vol% lactic acid, 0.05 vol%HCl and modified Fusayama’s artificial saliva). Ti/TiN layer coated on magnet grows into preferred direction with lamellar structure and its thickness is 3.0 μm. Sm-Co base magnets coated with Ti/TiN multi-layer have good corrosion resistance in 1% lactic acid. Nd-Fe-B base magnets coated with Ti/TiN multi-layer showed good tendency of corrosion resistance in 0.05 vol%HCl solution. The amount of elements released from both Sm-Co and Nd-Fe-B base magnets coated with Ti/TiN multi-layer were more significantly decreased than that of uncoated one. The mean surface roughness values of both Sm-Co and Nd-Fe-B base magnets coated with Ti/TiN multi-layer were smaller than that of uncoated one after corrosion test. The decreasing rate of micro-hardness of both Sm-Co and Nd-Fe-B base magnets coated with Ti/TiN multi-layer were lower than that of uncoated one after corrosion test. Magnets coated with Ti/TiN multi-layer produced corrosion product such as TiO2 on the surface and resulted in better corrosion resistance than uncoated one.View full abstractDownload PDF (1943K) -
Yuji Kurata, Katsumi Tachibana, Tomio Suzuki2001 Volume 65 Issue 4 Pages 262-265
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCorrosion tests using plate and U-bend specimens of Alloy 800H, Hastelloy XR and Inconel 600 were conducted in sulfuric acid decomposition environment of thermochemical hydrogen production process. Then tensile tests using bar specimens after corrosion were carried out to evaluate the effect of the corrosion on high-temperature tensile properties. Corrosion in sulfuric acid decomposition environment proceeds through formation of surface corrosion film and grain boundary penetration consisting of internal oxidation and sulfidation. Corrosion cracking and acceleration of corrosion under stress were not observed in the corrosion tests at 850°C in this environment. The values of 0.2% proof stress after corrosion are above 80% compared with those of solution-treated alloys and values of ultimate tensile strength after corrosion are above 90%. In addition, little decrease in high-temperature ductility by corrosion is observed.View full abstractDownload PDF (480K) -
Yasuhiro Maeda, Yasuo Yamada, Takashi Hanai, Hiroyuki Nomura2001 Volume 65 Issue 4 Pages 266-272
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to obtain sound green compacts, which are necessary for producing quality sintered products by metal injection molding (MIM), it is important to control the filling behavior of the slurry in the mold cavity. Pressurized air, which exists near the final filled-up area, exerts a large effect on both the flow dynamics of the slurry and the properties of the green compact. A permeable die has a lot of microscopic pore channels in the mold cavity. Use of a permeable die is a useful technique to enhance the slurry flowability. In this study, the flow behavior and the properties of green and sintered compacts of stainless steel were investigated in several injection experiments using both ordinary and permeable dies. A numerical simulation was also conducted. The results showed that the molding speed and the quality of the green and sintered compacts are better when the permeable die is employed rather than the ordinary die. Furthermore, the backpressure of the air and the volume of the exhausted air were calculated by the FAN method combined with backpressure analysis. The results of these analyses will serve as useful information for designing compacts of uniform quality with no defects.View full abstractDownload PDF (675K) -
Yong-Jai Kwon, Makoto Kobashi, Takao Choh, Naoyuki Kanetake2001 Volume 65 Issue 4 Pages 273-278
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCopper matrix composites reinforced with TiC particles which were formed in situ by a combustion reaction between titanium and carbon were fabricated from a powder mixture of Cu, Ti and C. The effects of igniting method, preheating, and composition on the combustion reaction for the Cu-Ti-C system were investigated. The copper matrix composites including 20 to 80 vol%TiC could be fabricated by heating directly using the heater. The use of an ignitor is not useful for self-propagating combustion reaction, but preheating can help the self-propagation. When the mole ratio of Ti to C was 1:1, residual graphite was observed in the synthesized composites as well as copper matrix and TiC reinforcements. However, hardly any graphite remained in the composite in which the mole ratio was 1:0.75. The combustion reaction between Ti and C in the Cu-Ti-C system initiated near the melting point of pure copper, suggesting that the reaction is initiated by the formation of liquid copper.View full abstractDownload PDF (1429K) -
Guofeng Zhang, Masao Morishita, Koichiro Koyama2001 Volume 65 Issue 4 Pages 279-287
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe oxidation property of a Ni-NiMo2B2 alloy which is expected to be a new heat resistant-material was investigated. The phase relationship of the Ni-Mo-B-O system at 973 K was determined to clarify the oxidation path of the alloy from the point of view of thermodynamics. The phase relationship suggested that Ni3B2O6, NiMoO4, MoO3, MoO2, NiO and B2O3 are formed in the atmosphere on the oxidation path of the alloy. Oxidation tests of the alloy were carried out at 773, 973 and 1173 K. The oxide film formed on the surface of the alloy was composed of Ni3B2O6, NiMoO4, MoO3, MoO2, NiO and B2O3 as expected from the phase relationship. The oxide film was very dense and appeared to be protective for the alloy, and as a result, the oxidation resistance of the alloy was very excellent.View full abstractDownload PDF (1270K) -
Kazutoshi Nishimoto, Kazuyoshi Saida, Ryoichi Tsuduki2001 Volume 65 Issue 4 Pages 288-297
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe in-situ sintering bonding of Fe-base and Ni base ODS alloys was carried out using pulsed electric current sintering (PECS) technique. The mechanical alloying powders with the same composition as base alloys were inserted between bonding specimens as an insert layer for PECS bonding. Bonding conditions were varied between 1023-1323 K for 0-5.4 ks applying the bonding pressure of 30-70 MPa. The relative density in bonded interlayer was increased with bonding temperature and holding time, finally attained to perfectly densificated. The densification of bonded interlayer was remarkably accelerated by the bonding pressure while the densification is slightly accelerated when the particle size insert powder decreases. The aspect ratio of prior particles in bonded interlayer increased with the lapse of holding time whereas the average size of it did not change so much through the bonding process. The kinetics of densification of bonded interlayer during PECS bonding process could be expressed by two kinds of kinetic equation. It was elucidated that the densification behavior of bonded interlayer during PECS bonding process was controlled by two sequential mechanisms of grain boundary diffusion creep and diffusion.View full abstractDownload PDF (1192K) -
Hideki Katayama, Kazuhiko Noda, Masahiro Yamamoto, Toshiaki Kodama2001 Volume 65 Issue 4 Pages 298-302
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAC impedance method has been applied to atmospheric corrosion monitoring under thin film of artificial seawater. An atmospheric corrosion sensor, which consists of a pair of identical electrodes embedded concentrically in epoxy resin, was used for measuring the corrosion rates. The instaneous corrosion rates of carbon steel in the atmosphere of 60% to 95% Relative Humidity (RH) have been monitored by the continuous measurements of the impedance at 10 mHz and 10 kHz. The carbon steel under a thin water film including 0.1 kg/m2 salt showed the highest corrosion rate at 60%RH. Above 70%RH, however, the carbon steel under a liquid thin film including 0.01 kg/m2 salt gave the largest corrosion rate. The average thickness of a water film formed on the corrosion sensor was thermodynamically calculated by analyzing the drying and absorption processes of the artificial sea salt. The average thickness of water film formed on the corrosion sensor under film including 0.01 kg/m2 salt was 10∼100 μm above 70%RH. The corrosion rate of carbon steel showed a maximum at the average water film thickness of several 10 s of micrometers.View full abstractDownload PDF (348K) -
Tomoyuki Nishida, Hidekazu Sueyoshi2001 Volume 65 Issue 4 Pages 303-309
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGraphite was bonded to Inconel 718 in a vacuum using an RF-induction furnace. The influence of joining conditions on the bending strength of the graphite/Inconel 718 joint, and changes in the microstructure and hardness of Inconel 718 near the joining interface, were investigated. Thermal stress induced in the joint was estimated using the finite element method. Good solid-state bonding becomes feasible by annealing at temperatures higher than 1173 K under compressive stress of 35 MPa. The adequate joining temperature and joining compressive stress in graphite/Inconel 718 bonding are higher than those in graphite/nickel bonding. This is because fracture of passive-oxide film on the surface due to plastic deformation of Inconel 718 and the resulting direct contact of graphite with matrix of Inconel 718 are required on solid-state bonding. The bending strength of the joints is nearly equal to or greater than that of graphite. This is because the compressive stress induced on the surface of graphite by the plastic deformation of Inconel 718 after bonding and the resulting elastic deformation of graphite in the radial direction relaxes the tensile thermal stress induced on the surface of graphite during cooling or the compressive stress remains. Heat treatment is required to recover the strength of Inconel 718 since intermetallic compounds precipitated in Inconel 718 dissolve in matrix during annealing and age hardening disappears.View full abstractDownload PDF (937K) -
Sukeharu Nomoto, Teruo Izumi, Yuh Shiohara, Takateru Umeda2001 Volume 65 Issue 4 Pages 310-316
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIt is well known that the columnar grains incline toward the upstream direction of the melt flow during the solidification of metallic alloys. Understanding of this phenomenon is important for estimation and analysis of the material characteristics. In this study, numerical analyses of the isothermal and two-dimensional columnar growth of a binary alloy in the melt flow are performed by solving the phase field model equation simultaneously with the convective diffusion equation and the non-compressive Navier-Stokes equation. Consequently, it is shown that the interface growth on the upstream side in the neighborhood of the cell tip is faster than that on the opposite side due to larger absolute values of the normal gradient of solute concentration on the upstream side than that on the opposite side. Furthermore, the effectiveness of this numerical method to understand the phenomenon is clarified by the calculation of multiple grains and multiple crystalline orientations, in which the faster growing grains are strongly influenced by this effect of the solute concentration gradient on upstream side and these inclined grains grow toward the upstream direction than the slower growing grains.View full abstractDownload PDF (566K) -
Hideto Yamada, Seiji Kuroda, Takeshi Fukushima, Hisami Yumoto2001 Volume 65 Issue 4 Pages 317-322
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA new method for capturing and evaluating the condition of thermal sprayed particles has been developed by using an agar gel target. HVOF sprayed Hastelloy C particles were collected by a gel target placed 380 mm downstream from the spray nozzle exit. A large number of fine particles were observed in the surface layer of the target; whereas globular particles were trapped at greater depth. The ratio of the number of particles in the surface layer to that embedded in the gel varied with respect to process parameters.
An additional technique involved separating the particles from the gel by dissolving it in hot water and then performing SEM morphological analysis. Particles collected from the target’s surface layer were smaller than 10 μm and consisted of fine spherical particles and fragments of dendritic crystals. Since the original powder rarely contains particles under 10 μm, it was concluded that these were formed by disintegration of molten particles upon impact onto the gel. Particles collected from the deeper part of the gel were mostly unmelted particles; some of which exposed dendrites.
Results obtained by other techniques such as splat observation and in-flight diagnostics are compared with these results. It was concluded that this unique and simple method of capturing thermal sprayed particles with a gel target allowed visualization and quantification of the melting conditions for the HVOF sprayed particles.View full abstractDownload PDF (1578K) -
Fumihiko Kamiya, Hiroyuki Toda, Toshiro Kobayashi, Masanobu Takasu, Na ...2001 Volume 65 Issue 4 Pages 323-330
Published: 2001
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAl2O3/TiC composites having various fraction ratio between Al2O3 and TiC phases are prepared through the hot-press process. Static and dynamic fracture toughness values are measured experimentally. Crack deflection angle and areal fraction of each fracture path (intergranular and transgranular fractures both through the Al2O3 and TiC phases and Al2O3/TiC interface) are measured on lateral surface of specimens and fracture surfaces, respectively. Local fracture toughness in each fracture path is analyzed using the above data.
Measured fracture toughness increases with the increase in the mass percent TiC phase. Local fracture toughness is higher for the passes through the TiC phase than those through the Al2O3 phase, whether it is transgranular or intergranular. The weakest path is the Al2O3/TiC interface in all of the samples.
Microstructural configuration for improved fracture toughness in Al2O3/TiC composites is discussed in light of local fracture toughness at both grain interior and boundaries.View full abstractDownload PDF (1682K)
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