All issues
Volume 59, Issue 7
Displaying 1-12 of 12 articles from this issue
- |<
- <
- 1
- >
- >|
-
Hidehiro Yasuda, Hirotaro Mori1995 Volume 59 Issue 7 Pages 681-685
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAlloying behavior of gold atoms into nanometer-sized amorphous antimony (a-Sb) clusters has been studied by transmission electron microscopy (TEM). Gold atoms which came in contact with a-Sb clusters quickly dissolved into the clusters, and clusters of either an a-(Sb-Au) alloy or the compound AuSb2 were formed, depending on the gold concentration in clusters. The ease with which such rapid spontaneous alloying takes place decreased with increasing size of original a-Sb clusters. It is suggested that the origin and mechanism of rapid spontaneous alloying are common to both amorphous and crystalline atom clusters.View full abstractDownload PDF (1650K) -
Hiroshi Fujimura, Hiromitsu Ino1995 Volume 59 Issue 7 Pages 686-693
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSNonequilibrium phases in melt-quenched Fe-Al-C alloys, austenite(γ), ordered austenite(γ′) and perovskite Fe3AlC(κ) were examined by X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy and computer simulation. As the result, it is confirmed that the second nearest local interaction of Al-C atomic pairs in austenite is strongly attractive(∼30 kJ/mol) and the interaction is in favor of the formation of the κ phase.
The κ phase is paramagnetic in the stoichiometric composition (Fe3AlC), in contrast to the ferromagnetic behavior(TC∼210°C) in the non-stoichiometric alloy(Fe3AlC0.64). It is concluded that the magnetic moment of iron atoms in the κ phase is mainly determined by the number(0, 1 or 2) of the nearest neighboring carbon atoms. It is also found that the equilibrium composition region of the κ phase at high temperatures(800∼1200°C) is much extended compared with that shown in the previously reported phase diagram.View full abstractDownload PDF (709K) -
Hideyuki Ikeda, Hidehiko Matsuda1995 Volume 59 Issue 7 Pages 694-702
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe Monte Carlo method combined with the static variational method is applied to a computer simulation on the phase decomposition process when the elastic constant of precipitates in a bcc binary alloy is harder than that of the matrix. The present study is compared with our previous results that were obtained for the case of the same elastic constant of the precipitates as that of the matrix in our previous report. We have adopted the Jonson-type potentials as the interaction between the constituent elements, and have used three kinds of interaction potentials between solute atoms.
We find an anisotropic structure in the alloy whose elastic constant of the precipitates is equivalent to the constant of the matrix. The alloy that has harder precipitates than the matrix shows an isotropic structure or a little anisotropic structure depending on the value of elastic constant of the precipitates.
We presume that the isotropic structure is yielded because of the larger contribution of the interfacial energy than the elastic strain energy. Evidently the total energy of the alloy with isotropic clusters is lower than that with anisotropic clusters for every potential used in the present simulation. Therefore we conclude that the formation of anisotropic clusters is not due to the shape of precipitates with the minimum elastic energy but due to the dynamical process of phase decomposition concerned with nonlinear many body effect.View full abstractDownload PDF (887K) -
Makoto Usui, Kiyohito Ishikawa, Shigeru Asano1995 Volume 59 Issue 7 Pages 703-707
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSYoung’s moduli of two kinds of high manganese austenitic steels, 18Mn-4Cr and 15Mn-17Cr steels, were measured by the resonance method of free-free transverse vibration. In both engineering steels, the temperature dependence of Young’s modulus showed a remarkable anomaly, that is, an abrupt drop near the Néel temperature TN and a successive lowering below TN, as has been reported in some antiferromagnetic alloys. Such elastic softening may be considered to originate from the generation of magnetostriction in the antiferromagnetic range below TN. In particular, the abrupt drop of Young’s modulus of the 18Mn-4Cr steel was extremely large compared to those reported in the literature. Hydrogen charging did not affect the anomaly but caused a slight increase in Young’s modulus over the entire temperature range examined.View full abstractDownload PDF (406K) -
Mitsuo Niinomi, Toshiro Kobayashi, Masahiko Iwai, Tomoaki Hirota, J. C ...1995 Volume 59 Issue 7 Pages 708-716
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSFracture characteristics of Ti-24Al-11Nb (at%) were related to microstructures based on the results of tensile tests and fracture toughness tests. Fracture mechanisms were also investigated.
Fracture toughness, JIc, increased when microcracks were formed at the interfaces of colonies or acicular α2 in β solutionized and furnace cooled materials. The microcracks were formed by the coarse and big slip bands which were activated widely near the crack tip as a result of the formation of colonies. The crack propagation resistance, Tmat, increased with increasing crack deflection and shear ligaments in addition to microcracks.
JIc and Tmat decreased with increasing precipitations of fine α2 in β during air cooling in α2+β solutionized and air cooled materials. The blunting of the crack tip was inhibited because the deformability of β was inhibited by the finely precipitated α2.
The microstructure of equiaxed α2 which is obtained by the solutionizing at 1313 K for 7.2 ks followed by water quenching gave the best balance among strength, elongation and fracture toughness.View full abstractDownload PDF (1713K) -
Atsushi Hibino1995 Volume 59 Issue 7 Pages 717-725
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe propagating behavior of combustion wave is mathematically analyzed in the synthesizing process of an intermetallic compound from a Ni/Al green mixed powder compact by the heat of reaction. The exothermic reaction rate in the heat balance equation is usually expressed by an Arrhenieus style as an empirical formula. However, the basis for this expression is not clear and this assumption seems to treat a powder compact as a continuum. A preliminary experiment disclosed the combustion process was fairly well simulated with a spherical shell model based on the reaction between particles. The expression of the exothermic reaction rate using this model is applied to this analysis. The characteristics of propagation of combustion wave are affected by preheating condition of compact, heat of ignition, power particle size etc.View full abstractDownload PDF (860K) -
Shinji Tsuji1995 Volume 59 Issue 7 Pages 726-732
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe surface hardening of 5Cr-1\frac14Mo-1V Die Steel was studied by a complex process consisting of initially physical vapor deposition of an Al thin film about 3 μm thick (step 1), next diffusional dilution of the film under conditions of zero surface flux (step 2), and finally ion nitrizing (step 3). The diffusion anneals of step 2 were done at temperatures from 1123 to 1323 K for 3.6 ks, and Al concentration-distance curves were obtained from EPMA measurement, ZAF correction, and another by considering conservation of mass for an Al thin film. A numerical model where a finite/semi-infinite type of binary diffusion couple under the initial condition is a composite of a thin layer at the maximum soluble concentration of Al in the α phase throughout and a parent metal at the uniform concentration of Al has been presented to describe the Al concentration profiles. Interdiffusion coefficients for the α phase in the Fe-Cr-Al system were determined by best fitting a numerically calculated Al concentration-distance curve to the measured one. The Al rich layers of the steel nitrided at 923 K for 7.2 ks for step 3 show the hardness of about from HV 1300 to 1400.View full abstractDownload PDF (589K) -
Joon-Pyou Park, Kensuke Sassa, Shigeo Asai1995 Volume 59 Issue 7 Pages 733-739
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThough the aluminum alloy containing silicon exhibits high wear-resistance, primary silicon deteriorates mechanical properties such as elongation and tensile strength due to its brittleness.
In this paper a new solidification processing of the aluminum alloy which enable to improve wear resistance without deterioration of the mechanical properties, is proposed, The principle of the processing is to make use of the EMF (electromagnetic force) induced by imposing direct electric current and static magnetic field in the alloy. When EMF is imposed in the molten hyper-eutectic Al-Si alloy in which the primary silicon has been crystallized, EMF scarcely acts on primary silicon particles due to its lower electric conductivity in comparison with the molten alloy. Thus, the primary silicon particles are moved to the surface of a product opposite to the direction of the imposed EMF.
The validity of the processing was confirmed by the solidified structures obtained with and without EMF. The high wear-resistance and excellent hardness were demonstrated by using the test pieces treated in the new processing.View full abstractDownload PDF (1269K) -
Kazuhiro Matsugi, Tomei Hatayama, Osamu Yanagisawa1995 Volume 59 Issue 7 Pages 740-745
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe relationship between the number of pulses and the specific resistivity for the copper and iron powder compacts has been investigated to reveal the phenomena which are caused between powder particles in the early stage of the spark sintering process. The results are summarized as follows: The values of specific resistivity of the both powder compacts decrease with increasing the number of pulses, and the rates of decrease of specific resistivity increase with decreasing the applied punch pressures. The limited changes of the relative densities of compacts are observed in this continuously pulse discharge process. Therefore, it is considered that the specific resistivity of compacts are decreased, not because their relative densities are changed but because the properties of the contact area between powder particles are changed by the pulse discharge. Where, this change of the properties is caused by the dielectric breakdown of the oxide film between the powder particle surfaces in the pulse discharge process. The metallic contact parts are created between powder particles after this dielectric breakdown. It is cosidered that the spark can not be caused in these metallic contact parts.
It is suggested on the basis of the simple model of electric resistance of a compact that the fraction of the metallic contact area created by the dielectric breakdown of the oxide film is extremely small.
It is assumed on the basis of the first order equation of the chemical reaction that the rate of decrease of the area fraction of the oxide film between powder particles per one pulse discharge is proportional to this retained area. The relationship between the number of pulses and the specific resistivity of compacts can be explained quantitatively by this assumption.View full abstractDownload PDF (488K) -
Takashi Oki, Kazuhiro Matsugi, Tomei Hatayama, Osamu Yanagisawa1995 Volume 59 Issue 7 Pages 746-753
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe relationship between the microstructures and tensile properties was investigated for vacuum sintered and vacuum sintered+HIP’ed titanium.
For the pure titanium sintered in vacuum at the temperatures below and above the critical temperature, 1400 K, their microstructures consisted of equiaxed and irregularly shaped grains, respectively. The tensile ductility, measured as the reduction of area and as the elongation, increased with increasing sintering temperature in the temperature range below this critical temperature. However, the ductility decreased significantly until reaching a constant level with increasing sintering temperature above this temperature.
HIP of vacuum sintered titanium was carried out at the temperatures above 1400 K to get the fully densified materials. The equiaxed grain was obtained, when HIP was carried out below the α↔β transformation temperature. The irregularly shaped grain was observed in titanium HIP’ed above the transformation temperature. Furthermore, the substructures which aligned in one direction was observed in the large equiaxed grain in the HIP’ed materials at a high temperature of 1373 K. Higher proof stress, higher ultimate tensile stress and better tensile ductility were obtained with an equiaxed grain structure compared with the other type of microstructures. Particularly, a large reduction of area was observed in the specimens HIP’ed below the transformation temperature. It is concluded that the HIP process at low temperatures is effective for improvement of strength and ductility of vacuum sintered titanium.View full abstractDownload PDF (1281K) -
Yuji Muramatsu, Tsuneo Ohkoshi, Hiroo Suga1995 Volume 59 Issue 7 Pages 754-760
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTiAl intermetallic compounds of 48 at%Al were prepared by conventional sintering of mixed powder compacts of TiH2 and TiAl3. They were further densified by HIPing at 1470 K and 202 MPa for 3.6 ks without canning. In this study, the densification due to HIPing was examined. The hardness and oxidation behavior of HIPed TiAl were also examined.
The results were as follows: (1) The density of HIPed TiAl increased with an increase of sintered density, and became saturated when the relative density exceeded 94%. The saturated density was nearly equal to the theoretical density. (2) The room temperature hardness of HIPed TiAl varied with sintering temperature, and increased with increased sintering temperature. The temperature dependence of hardness was similar to that of wrought TiAl, and homogeneous lamellar structural TiAl showed higher high temperature hardness than duplex structural TiAl. (3) The oxidation behavior was dependent on microstructure, and homogeneous lamellar structural TiAl showed an excellent oxidation resistance as compared with duplex structural TiAl. In comparison with wrought TiAl, HIPed TiAl exhibited a better oxidation resistance.View full abstractDownload PDF (1036K) -
Yutaka Ishiwata, Yoshiyasu Itoh, Ryuzo Watanabe1995 Volume 59 Issue 7 Pages 761-768
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSYttrium oxide dispersed tungsten (Y2O3/W) composite has been developed as a crucible material for melting of reactive metals. In this study, the corrosion behavior and its mechanism of the Y2O3/W composite in molten metal were investigated in comparison with that of pure W. The 20 vol%-Y2O3/W and pure W crucibles whose relative densities became over 99% by HIPing were used for melting experiments descrived below. Yttrium (Y, melting point: 1775 K), which was one of the reactive metals, was melted with 20 vol%-Y2O3/W and pure W crucibles at 1923 K for 3.6 ks in Ar atmosphere.
The contamination of W in the molten Y in the case of using the 20 vol%-Y2O3/W crucible was found to decrease less than that for the pure W crucible. This observation shows that the Y2O3 dispersed crucible has excellent corrosion resistance in molten Y. On the contrary, a remarkable penetration of molten Y into grain boundaries was observed in the case of the pure W crucible. It is considered that the difference of W contamination in molten Y for both cases depends on the difference in the corrosion resistances of the grain boundaries.
From an auger electron spectroscopy analysis, a large amount of phosphorus (P) was detected at the grain boundaries of the pure W, which shows that the attack of grain boundaries observed in the pure W crucible was caused by the reaction between the segregated P and the molten Y. For the Y2O3/W composite, the P contents at the W grain boundaries were lower than that in the pure W, because P or P oxide (PO4) was partly taken into the Y2O3 particles during sintering. The growth of Y2O3 particles in the Y2O3/W composite, which contained a small amount of Y2(WO4)3 complex oxide, occurred in the surface region after heating above 1573 K, and the W grain boundaries were covered with Y2O3, which was considered to be a main reason for the excellent corrosion resistance of this composite.View full abstractDownload PDF (1350K)
- |<
- <
- 1
- >
- >|