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Volume 58, Issue 9
Displaying 1-19 of 19 articles from this issue
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Isao Ohsugi, Tsutomu Kojima, Makoto Sakata, Isao Nishida1994 Volume 58 Issue 9 Pages 985-988
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSChromium disilicide is known as a degenerate semiconductor useful for thermoelectric applications in a high-temperature atmosphere. For sintered CrSi2, thermoelectric properties had been consistently analyzed by a detailed calculation based on the Fermi-Dirac distribution of carriers. The crystal structure of CrSi2 belongs to the hexagonal symmetry group D6h4, which suggests uniaxially anisotropic properties. Strong anisotropies about the c-axis were observed in resistivity and thermoelectric power of a CrSi2 single crystal. The anisotropy in resistivity may be deduced from that in mobility, which originates from anisotropic scattering of carriers. The anisotropy in thermoelectric power was numerically analyzed by calculating some transport parameters expressed in terms of the Fermi-Dirac integral. The analysis revealed that the acoustic phonon scattering (s⊥=0) is dominant in a direction perpendicular to the c-axis, while in the c-direction, dominant is a mixed scattering (s\varparallel=0.7) by acoustic phonons and ionic impurities. The theoretical curves deduced from the anisotropic scattering were in good agreement with the observed data. The results of this analysis were also consistent with those of a magnetic analysis previously performed for the single crystal.View full abstractDownload PDF (348K) -
Kenichi Yoshida, Kenzo Asaoka, Masafumi Yamanaka, Kiyoshi Sakamaki1994 Volume 58 Issue 9 Pages 989-993
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe acoustic emission (AE) method was applied to the determination of the transformation temperature and the level of dispersed elastic energy during isothermal aging of the alloy. The binary alloys of Pd-30, 45 and 50 mass%Cu were prepared as the specimens and were heat-treated in the following procedures; that is, the first group was homogenized at 1000°C after alloying and cooled slowly in a furnace. The other group of the alloys was heated up to 950°C after the same homogenization annealing as the first group and quenched into ice-water (solid solution heat treated). AE signals from the alloy which was placed in an electric furnace were passed through the wave guides (SUS304 rod) to the outside of the furnace, and were detected by the AE sensor. The signals were converted to electrical pulses by the AE sensor and amplified. Detected data showed that AE events were high at the temperatures where the order-disorder transformation and the precipitation of the β phase into the solution treated alloy structure took place. These results were confirmed by differential thermal analysis and the change in hardness. Activation energy for the precipitation of the β phase in the disordered matrix of the solid solution-treated alloy was estimated to be 140 kJ/mol from the Arrhenius plots on the detected time of AE events versus isothermal aging temperature of Pd-45 mass%Cu alloys. This is consistent with the values reported previously on the measurements of electrical resistance and hardness changes for similar compositional alloys. It is suggested that the AE method is a helpful technique to investigate the mechanisms of phase transformation of the alloy because the AE signals can be picked up in a dynamic temperature field.View full abstractDownload PDF (354K) -
Sadahiro Tsurekawa, Masafumi Nakashima, Hideo Yoshinaga1994 Volume 58 Issue 9 Pages 994-1000
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to clarify the effect of Nb or Mo addition on ductile-brittle transition behaviour of titanium carbide, sintered TiC, TiC-10 mol%Nb and TiC-10 mol%Mo have been studied using a three-point bending test at temperatures from room temperature to 2020 K, and the fracture surface has been observed by scanning electron microscopy (SEM). It is found that the Nb addition decreases the ductile-brittle transition temperature (DBTT) of TiC by 400 K and increases the ductility, whereas little change of the behaviour was observed when Mo was added. The effect of Nb addition is discussed from the viewpoint of ability for plastic deformation.View full abstractDownload PDF (1536K) -
Shinichi Takagi, Chiaki Ouchi1994 Volume 58 Issue 9 Pages 1001-1007
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effects of alloying elements and post annealing on the strength and ductility in cast-Hipped TiAl were investigated. The aluminum content was varied from 46 to 49 at% in Ti-Al system, and various alloying elements were added by around 2 at% in TiAl with Al/(Ti+Al) of 0.48 atomic ratio. Tensile properties of all alloys showed a linear relationship between 0.2% offset yield strength and elongation. Cr and Mn addition results in ductility improvement accompanied with a reduction of strength, and the other alloying elements reduced ductility with an increase of strength. The Al content or alloying elements in TiAl varied widely the volume fraction of grains in lamellar form and the lamellar spacing in the lamellar structure, which markedly affected the overall strength of alloys and the hardness of lamellar grains, respectively. The yield strengths of various alloys with a two phase structure consisting of equiaxed γ and lamellar grains were analyzed based on the rule of mixture. Addition of Mo or Cr tended to form the β phase. The post annealing at 1603 K resulted in a significant improvement of strength-ductility balance although the strength was markedly decreased. The microstructural factors controlling the strength and ductility of TiAl were discussed in detail.View full abstractDownload PDF (2091K) -
Yuji Ieki, Shigeru Asano1994 Volume 58 Issue 9 Pages 1008-1014
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSHardening and embrittlement caused by cathodically charged hydrogen were measured at room temperature in Fe50Ni50−xMnx alloys, with special attention to the subsidiary effect of hydrogen-induced phase transformation. There are two types of hydrogen-induced phase transformation in most FCC iron alloys; γH and εH. After cathodic hydrogen charging, the γH phase is formed in the nickel-rich composition of Fe50Ni50−xMnx alloys and εH phase in the manganese-rich composition, but there occurs no transformation in the intermediate composition such as Fe50Ni20Mn30. The effect of dissolved hydrogen on their mechanical properties can therefore be distinguished from the influence of two types of phase transformation by testing these alloys.
Hydrogen-induced hardening and embrittlement were found in all the compositions of Fe50Ni50−xMnx alloys, apparently being a complex effect of dissolved hydrogen and hydrogen-induced phase transformation. The hardening was restored almost completely to the original state after outgassing of hydrogen. In addition, the embrittlement seemed to be more remarkable in the transformation-free Fe50Ni20Mn30 alloy than in other alloys. This means that the hardening and embrittlement are mainly caused by dissolved hydrogen in the FCC matrix, where the hydrogen-induced phase transformation does not play a very important role. The conclusion may apply to any FCC iron alloys including austenitic stainless steel.View full abstractDownload PDF (975K) -
Akira Nozue, Takashi Kubo, Hideo Okada, Tadatsune Okubo1994 Volume 58 Issue 9 Pages 1015-1020
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA new solution treatment has been developed to increase the crack growth resistance R. Its solution treatment was carried out at β and α+β regions to precipitate many quasi-circular platelike α phases. When a crack exists nearly perpendicularly to the quasi-circular platelike α, the crack stops, blunts and then deflects in front of its α phase. Eventually, the R value is increased. This crack growth behavior has been confirmed in the present alloy with in-situ observation. Three-dimensional shapes of acicular and plate α have been also identified, and these α shapes are found to be almost similar to the quasi-circular platelike α. It is concluded that the high R values are attributed to a crack deflection and the local bluntness of the crack at the quasi-circular platelike α.View full abstractDownload PDF (1783K) -
Hirotsugu Ogi, Masahiko Hirao, Takasi Honda, Hidekazu Fukuoka1994 Volume 58 Issue 9 Pages 1021-1028
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSElectromagnetic acoustic resonance (EMAR) is applied for determining the frequency dependence of the ultrasonic attenuation and the average grain size of carbon steels. Use of a noncontacting electromagnetic acoustic transducer (EMAT) makes it possible to isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT to the specimen surfaces and then eliminates the uncorrectable losses, which otherwise occur with the piezoelectric transducers. The measurement is independent of the EMAT used, the specimen thickness, the surface condition, the liftoff, etc., and is stable because of the noncontacting aspect. A measurement has two steps. First, we measure the resonance frequencies, to the accuracy in the 10 Hz order, by sweeping the operating frequency and obtaining its amplitude spectrum. The ringing signals are excited and received by an EMAT and then processed with a superheterodyne phase sensitive detector. The frequency is swept through a band in the 0.5∼20 MHz range. Second, we determine the attenuation coefficient as a function of the resonance frequency. At each resonance frequency, the output signal from the detector rings down exponentially with time and the coefficient is obtained by fitting to an exponential decay. After being corrected for the diffraction effect, the average grain size is obtained from the fourth power term in the frequency dependence. The final results are favorably compared with the average of the 3D distribution of grain sizes calculated from the photomicrographs of the exposed cross sections.View full abstractDownload PDF (933K) -
Isao Tsuchitori, Hideharu Fukunaga1994 Volume 58 Issue 9 Pages 1029-1035
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn the composite system of rutile type TiO2 powder and Al, non-reacted composites have been fabricated depending on the temperature conditions of the squeeze casting process. The non-reacted composites have hardened by isothermal heat treatment. The hardening behaviour at various temperatures, the structure change and the reaction products of the composites have been investigated because this phenomenon is useful in hardening and strengthening the structural aluminum practically.
The rutile type TiO2/Al composites produce α-Al2O3 and Al-Ti intermetallic compound, which consists mainly of Al3Ti, during isothermal heat treatment. These reaction products increase as the reaction proceeds and the hardness of the composites increase gradually from Hv215 to 765. The mixture of the rutile type TiO2 and Al change to the Al-Ti intermetallic compound matrix composites with fine α-Al2O3 dispersion with decreasing Al phase. In this process, the layer of the reaction products was not found on the interface between the TiO2 particle and the matrix alloy. In the hardening reaction, the apparent activiation energy is 257.0∼262.3 kJ/mol. The hardness of the composites after heat treatment keeps Hv240 at 973 K and Hv150 even at 1273 K, and the coefficient of thermal expansion is attained to one-half to one-third of aluminum.View full abstractDownload PDF (1452K) -
Hiroyuki Anada, Yoshiaki Shida1994 Volume 58 Issue 9 Pages 1036-1043
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIsothermal and cyclic oxidation behavior and scale structures of the W modified Ti-34.5 mass%Al alloys at 1073, 1173 and 1273 K in air were investigated comparing with those of a binary Ti-34.5 mass%Al. Isothermal oxidation resistance of TiAl was extremely improved by the W addition at temperatures from 1123 to 1273 K. Mass gains of the W-modified TiAls, which were isothermally oxidized below 1173 K, significantly decreased with increasing W content. However, at 1273 K, minimum appeared in the mass gain vs. W content curve at 4 mass%W. W was a beneficial element under the cyclic oxidation condition. Scale spallation did not occur. A multi-layered scale structure of the W-modified TiAl was observed to be in the following order from the outside: TiO2/Al2O3/TiO2+Al2O3/Ti3Al/TiAl (matrix). The Al2O3 internal oxidation was suppressed by the reduction of the oxygen solid solubility caused by the W addition, which resulted in the external Al2O3 formation at the interface. The second Al2O3 layer and the inner Al2O3 layer which was observed to be interconnected were observed to be moe continuous than those of the binary TiAl, and must act as protective layers.View full abstractDownload PDF (2794K) -
Takashi Yamada, Mitsunori Tsutsui, Keishi Itani, Shigeo Asai1994 Volume 58 Issue 9 Pages 1044-1049
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of a direct magnetic field on the solid phase deposition of aluminum has been studied by using the molten salt of 2AlCl3-NaCl with addition of 5 mass% MnCl2. In the weak magnetic field range natural convection predominates the mass transfer rate of deposition and in the strong magnetic field range electromagnetic force controls the mass transfer rate and increases the critical current density to keep the deposition surface bright and smooth. Based on the boundary layer theory taking account of the electromagnetic force the analytical expression of the mass transfer rate has been derived. The theoretical result predicts the critical current density is proportional to one third power of the magnetic flux density and is confirmed by the experimental results.View full abstractDownload PDF (537K) -
Hiroyuki Umehara, Takakazu Suzuki, Ryuichi Hayashi1994 Volume 58 Issue 9 Pages 1050-1054
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTitanium aluminides tend to have very attractive properties of a low density and an excellent oxidation resistance at around 1000 K. They, however, suffer from lack of adequate creep strength and, in most cases, from inadequate ductility and toughness. The intermetallic matrix composites reinforced with heat resistive fibers are expected to improve the ductility and the toughness of intermetallic compounds. Vapor phase processings are hopeful methods for near-net-shaped and continuous fiber reinforced composites or lamellar matrix composites. The synthesis of TiAl from laminated Ti/Al films by a radio-frequency magnetron sputtering method has been studied. The Ti-Al synthesized films were evaluated by Auger electron spectroscopy, an X-ray diffraction analysis and a differential thermal analysis. The Ti-Al phases to be synthesized depend on the atomic ratios of Ti and Al, temperatures of a substrate and of subsequent heat treatment. It is clarified that TiAl3, Ti3Al, and TiAl are synthesized respectively from Ti/Al laminated films with temperatures of 773 K, 873 K, and 973 K.View full abstractDownload PDF (464K) -
Yasunori Miyata, Kiyoshi Sugawara, Atushi Takano, Takahiro Kakiuti1994 Volume 58 Issue 9 Pages 1055-1060
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe flow in the melt will affect the morphology of solidification but has rarely been studied quantitatively, because of difficulties in controlling melt flow near the tip of a dendrite. The supercooled melt in circular loop is partially heated to drive the melt and to cause the melt flow by buoyancy. The dendritic growth in this forced melt flow is studied for the supercooled pure succinonitrile. The growth rate of the dendrite tip increases with the increase of forced melt flow when the flow is coming to the tip. The flow affects more significantly the growth rate of dendrite in lower supercooling than in higher supercooling in the melt.View full abstractDownload PDF (710K) -
Hiroyuki Yamazaki, Atsumi Ohno, Toru Shimizu1994 Volume 58 Issue 9 Pages 1061-1066
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSStellite alloy rods produced by the heated mold continuous casting (Ohno Continuous Casting) method exhibit a unidirectional structure. The mechanical and physical properties of these products have been examined. It was found that the OCC stellite materials have superior wear, corrosion and shock resistance properties compared with those of weld-deposited stellite materials. Thus, it was proposed in this work that OCC rods with different cross-sectional shapes can be simply welded onto the objects which require wear resistance by using the existing joining techniques.View full abstractDownload PDF (840K) -
Biing Hwa Yan, Sung Long Chen1994 Volume 58 Issue 9 Pages 1067-1072
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn this paper, the effect of dielectric suspended with electrically non-conductive powder, such as alumina, on electrical discharge machining characteristics of SKD11 is investigated. The main results indicate that the alumina powder has no effect on the gap distance, but it is verified that the dielectric suspended with alumina powder has a significant influence on the electric discharge machining characteristics of SKD11. It was found also that the improvement mechanism of work surface finish due to the improved effect of the electrode surface and the recasting rise was restrained by the alumina particles. It was found also that it is an effective method for promoting the material removal rate of SKD11 when rotating the electrode and machining in the dielectric suspended with alumina powder under optimun conditions. The experimental results also indicate that the best performance from the viewpoint of surface finish is achieved using the conditions of the particles diameter of 1 μm, concentration of 4 g/L, and the electrode rotation speed of 60 rpm.View full abstractDownload PDF (1406K) -
In situ SEM Observation on Microscopic Deformation of Particle Reinforced Aluminum Matrix CompositesNaoyuki Kanetake, Masahiro Nomura, Takao Choh1994 Volume 58 Issue 9 Pages 1073-1079
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to directly observe microscopic behavior of particles, matrix and their interfaces of particle reinforced metal matrix composites during static loading, the in situ tensile test in the scanning electron microscope equipped with a deformation stage was examined for the Al2O3 particle reinforced aluminum matrix composite produced with the melt stirring method. Two types of sheet tensile specimens were investigated, the one has a small hole in the center of the general tensile specimen and the another is reduced in width with a round radius. The stress and strain distributions in their specimens were analyzed by an FEM calculation and compared with observed microcracks distribution. It is possible to observe only microstructural degradation owing to structural defects without the influence of stress localization by using the latter specimen, because the stress distribution in the center part is almost homogeneous in the specimen. Some microcracks owing to the interface debonding and the particle fracture are found at early loading point before maximum loading. The microcracks do not propagate in the matrix because of its ductility, but a number of new microcracks are initiated during increasing load.View full abstractDownload PDF (1420K) -
Sakae Saito, Yukio Abe, Hiromi Tokuno, Shuji Hanada1994 Volume 58 Issue 9 Pages 1080-1085
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA new process developed for fabrication of superconducting Nb3Al wires, called clad-chip extrusion (CCE), was applied for fabrication of bulk Nb3Al rods. This method is characterized by chipping and extruding the clad-sheets of niobium and aluminum. The chemical composition is controlled by the layer thickness ratio at cladding. The extruded Nb/Al composite bar is then converted into Nb3Al by heat treatment.
The CCE method can produce the single phase Nb3Al bulk material without Nb solid solution, micro-cracks and oxide particles such as alumina. Tantalum added Nb3Al is also fabricated successfully by this method.
The compression tests on the CCE-processed Nb3Al were carried out at elevated temperatures. The results show that the yield stress increases with tantalum addition.View full abstractDownload PDF (2533K) -
Hiroyuki Toda, Toshiro Kobayashi, Mitsuo Niinomi1994 Volume 58 Issue 9 Pages 1086-1094
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSTEM-EDX analysis has been carried out to study segregation in the SiCw/6061 Al composite, and Mg was found to be segregated at reinforcement-matrix interfaces. It is shown that the segregation of Mg to the interface is consistent with the hypothesis of non-equilibrium segregation based on the vacancy-drag mechanism.
A method is described of thermally treating the MMC to improve and tailor its precipitation structure according to these informations. The method comprises subjecting the MMC for a short period of time above a solvus temperature of the GP(II) zone or β′ transition phase, and a subsequent aging treatment. Partial dissolution of the GP zone or the transition phase is caused by dependence of the solvus temperatures on the solute concentration, and produces a more homogeneous distribution of the precipitates after the re-aging treatment. The beneficial effects on the mechanical properties of the MMC became clear, and its mechanism has been investigated.View full abstractDownload PDF (1674K) -
Yukichi Umakoshi, Wataru Fujitani1994 Volume 58 Issue 9 Pages 1095-1100
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSFormation of intermetallic phases in Al/Au and Al/Cu thin film couples annealed at temperatures between 100°C and 250°C has been investigated using X-ray diffraction and optical reflectivity techniques. Several intermetallic compounds which exist in a binary equilibrium phase diagram were produced in the couples after annealing. The formation and growth of Al2Cu, AlCu and Al2Au phases could be observed by the variation of optical reflectivity with wavelength. The interdiffusion of metals in Al/Au thin film occurred faster than that in Al/Cu during annealing. For example, the growth rate constants (k) of Al2Au and Al2Cu layers in the thin film couples annealed at 200°C were 3.4×10−8 and 2.4×10−9 m/s1⁄2, respsctively. The growth rate of these intermetallic layers was faster in thin films than in diffusion couples of bulk metals.View full abstractDownload PDF (615K) -
Hiroshi Suzuki, Hiroshi Araki, Tetsuji Noda1994 Volume 58 Issue 9 Pages 1101-1102
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (246K)
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