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Volume 55, Issue 1
Displaying 1-15 of 15 articles from this issue
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Chen Lu, Hiroshi Fujita, Eiji Taguchi1991 Volume 55 Issue 1 Pages 1-8
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe G.P.zone→θ′-phase transition in an Al-1.6 at%Cu alloy has been investigated by in situ experiment of electron irradiation induced diffusion with a 300 kV high resolution electron microscope and the following results were obtained: (1) Two kinds of G.P.-2 zones whose Cu-rich layers are separated with two, G.P.-2(2), and three Al {100} planes, G.P.-2(3), respectively, are formed by aging. The former is mainly formed at relatively high temperatures around 423 K and the latter at low temperatures around 373 K. In these zones, only the former, G.P.-2(2) zones, can transform to the θ′-phase. (2) Formation of θ′-phase occurs at the center of a multi-layered G.P.-2(2) structure, and G.P.-2(2)-like structures, i.e., buffer layers, are formed in the vicinity of θ′-phase interfaces. (3) G.P.-2(3) zones can also change to the θ′-phase when they change to G.P.-2(2) zones.
Based on the results, the mechanism of G.P. zone→θ′-phase transition is discussed.View full abstractDownload PDF (3840K) -
Chen Lu, Hiroshi Fujita, Eiji Taguchi1991 Volume 55 Issue 1 Pages 9-16
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe growth process of θ′-phase in an Al-1.6 at%Cu alloy has been investigated by in situ experiment with electron microscopes, and the following results were obtained.
(1) Buffer layers are frequently formed in the vicinity of the {001}θ′ coherent interfaces of θ′-phase structures. They change to stepped structures so often, and growth of θ′-phase occurs by movement of their ledges.
(2) Incoherent interfaces with a number of interfacial dislocations are formed at edges of θ′-phase platelets.
(3) Interfacial dislocations are also induced at ledges of the stepped structure with large steps.
(4) Growth of θ′-phase proceeds rapidly by coalescence between two adjacent θ′-phase structures, and slowly in the Ostwald type growth.
Based on the results, the formation process of the buffer layers and the growth process of θ′-phase structures are discussed.View full abstractDownload PDF (3846K) -
Yuh Fukai1991 Volume 55 Issue 1 Pages 17-21
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSOur knowledge on the phase diagram of metal-hydrogen systems has been limited to easily accessible ranges of composition and temperature, and therefore remained very incomplete.
In this paper, it is attempted, by extending the range of equilibrium partial pressure of hydrogen to a few GPa, to delineate the general features of the phase diagrams over the whole composition up to temperatures including the melting point (Tm) of all constituent phases.
Examination of existing data on the distribution coefficient of hydrogen in several metals and pressure-composition-temperature relation of the Ti-H system led to the conclusion that Tm of host metals is lowered drastically by dissolution of hydrogen. This lowering of Tm is explained as being the consequence of interstitial dissolution of hydrogen both in solid and liquid phases.
The general form of the phase diagram is found to be characterized by the following two factors; (1) a peritectic or eutectic reaction between solid solution and hydride (e. g. MH2) phases, (2) the immiscibilitY of metallic and molecular (hydrogen) phases. Tentative phase diagrams are constructed accordingly for fcc and bcc (hcp) host metals.View full abstractDownload PDF (784K) -
Yasunari Yoshitomi, Kuniteru Ohta, Yozo Suga, Tadashi Nakayama, Nobuyu ...1991 Volume 55 Issue 1 Pages 22-28
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA method for strain measurement by Electron Channelling Pattern (ECP) Image analysis has been newly developed. The sharpness of ECP, which is defined by the ratio of sharp pseudo-Kikuchi lines in ECP image, is used as a parameter describing the remaining strain. Fe-3.25%Si alloy single crystal and polycrystal were used as test specimens. Strain changes during deformation and recrystallization were measured by this method and compared with the hardness and line broadening of X-rays. The main results obtained are as follows.
(1) The sharpness of ECP decreased as strain was increased. This method is useful for measuring the strains of less than 15% cold reduction and less than 20% tensile elongation. And its strain sensitivity is larger for the smaller strains than that of line broadening of X-rays.
(2) The sharpness of ECP was influenced by the initial crystal orientation before deformation. This phenomenon was specially recognized in the case of the smaller strains, indicating that the accumulated strain is mainly influenced by the initial crystal orientation before deformation.
(3) The sharpness of ECP was increased during recrystallization. The fraction of a change of the sharpness of ECP during recrystallization was more significant than those of hardness and line broadening of X-rays.
(4) It is believed that this method is useful for analyzing the crystal orientation dependence of the accumulated strain and a decrease of strain during recovery and recrystallization, as well as the inhomogeneity of strain in the grain interior and near the grain boundary.View full abstractDownload PDF (1386K) -
Takashi Ebata, Reimon Hanada, Hiroshi Kimura1991 Volume 55 Issue 1 Pages 29-35
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSLow frequency (∼1 Hz) internal friction measurement was performed in tantalum-nitrogen (∼1 at% ) alloys loaded with hydrogen (H) or deuterium (D). A well defined internal friction peak was observed at 50 K for H and at 65 K for D. Magnitude of the peak was measured as a function of H (D) concentration and found to saturate to a constant value when H (D) concentration becomes comparable with that of nitrogen. This indicates that a simple N-H or N-D pair is formed in Ta and the jump of H (D) around N gives rise to the peak. The activation energy of the peak was measured by a peak shift method giving E=65±10 for H and 95±15 meV for D.
Debye function was calculated assuming two different temperature dependence of T7 or exp(−E⁄kT) for hydrogen jump (a short range diffusion).
Comparison with the experimental result reveals that the latter one is valid around 50 K for hyrogen jump in Ta.
Referring experimental results on Nb-N-H single crystals where δs′=0 has been found, the site where H (D) atom is trapped to N atom is seeked. The 2T state which consists of two t-sites located at the 3rd or 4th neighbor distance from N atom is found to be the most likely candidate.
Also the anelastic strain due to hydrogen trapped to nitrogen atom was estimated with assuming the trigonometric symmetry for the N-H pair and no significant difference was found between H and D.View full abstractDownload PDF (1045K) -
Kusuhiro Mukai, Mikio Watanabe, Tatsuhiro Yamada, Naosuke Takiuchi, No ...1991 Volume 55 Issue 1 Pages 36-43
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe presence of certain impurities in the base metal has been known to affect the molten pool geometry of an arc weld. Some views concerning dominant factors governing the weld pool geometry have been proposed, but those have not been unified as yet. So, in order to clarify the formation mechanism of molten pool, the effects of the various factors on the molten pool geometry of binary Fe-O and Fe-S test specimens were examined by use of a plasma heating equipment with a gas shielded chamber.
The depth of the molten pool increased and the width decreased with the increase of the oxygen or sulfur content in the base metal.
The shape changes of metal wire markers in solidified pool indicated that the outward flow occurred at the surface of the molten pool for the case using the base metal of low oxygen content and the inward flow did for the high oxygen content. The relation between the temperature coefficient of surface tension and the oxygen content could explain these flow behaviors.
The width of the arc frame was kept constant in the region of the oxygen content below 0.08 mass% or the sulfur content below 0.07 mass%.
Conclusively, it could be deduced that the surface tension driven flow was a dominant factor in determining the molten pool geometry.View full abstractDownload PDF (1116K) -
Naosuke Takiuchi, Takayuki Taniguchi, Nobuya Shinozaki, Kusuhiro Mukai1991 Volume 55 Issue 1 Pages 44-49
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe surface tension and the contact angle of liquid iron on the alumina substrate were measured at 1823 K over a wide range of oxygen concentration in the iron by the sessile drop method under the condition of oxygen transfer from the gas phase to liquid iron (3.8×10−6 mol/m2s).
It was presumed from the considerations of time-dependence of surface tension and the increasing rate of oxygen in liquid iron that the adsorption reaction at the liquid iron surface should be nearly in equilibrium with oxygen in liquid iron under the rate of oxygen transfer in the present study.
From the Gibbs adsorption isotherm, the excess quantities for oxygen at the liquid iron surface and the interface between liquid iron and alumina substrate were calculated as 2.1×10−5 mol/m2 and 2.4×10−5 mol/m2, respectively. The excess quantity for oxygen at the liquid iron surface is in good agreement with those obtained by previous investigators under the assumption of adsorption equilibrium of oxygen at the surface.
The relation between the surface tension, γlg (N/m), and the oxygen activity in the liquid iron is given by the following equation:
(This article is not displayable. Please see full text pdf.)
\ oindentThe contact angle of liquid iron on the alumina substrates decreases with increasing oxygen content in the iron. The work of adhesion increases with increasing oxygen content up to 0.03 mass%, while above 0.03 mass%, it increases very gradually with increasing oxygen content. FeO·Al2O3 was detected at the interface for the high oxygen level.View full abstractDownload PDF (917K) -
Toshio Shimoo1991 Volume 55 Issue 1 Pages 50-57
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe reduction rate of (FexMg1−x)Cr2O4 melted in a graphite crucible with the silicate slag was measured by means of thermogravimetry under an argon atmosphere at 1873 K. The dissolution of (FexMg1−x)Cr2O4 into the slag was examined by microscopic observation and chemical analysis.
The reduction of the FeCr2O4 component precedes that of the MgCr2O4 component, and the FeO component is preferentially reduced during the reduction of the former. The reduction of chromite in CaO-SiO2 binary slag is sluggish, because of poor contact of the slag with the graphite and less dissolution of chromite into the slag. In the silicate slag containing Al2O3 or/and MgO, the reduction rate is significantly increased by both the good wettability of the slag to the graphite and the refinement of chromite particles in the slag.
It is considered that the rate of the smelting reduction of (FexMg1−x)Cr2O4 is controlled by the dissolution of the chromite particles into the flux.View full abstractDownload PDF (2022K) -
Choonho An, Katsuhisa Sugimoto1991 Volume 55 Issue 1 Pages 58-66
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe formation process of Ta2O5 films in MOCVD using Pentaethoxy tantalum (PET) as the metal organic source and O2 as the reactant gas has been analyzed by in-situ ellipsometry at deposition temperatures of 473-773 K. According to the change in the growth rate of the films, the formation process can be devided into three stages, that is, the initial stage, the transition stage and the final stage. The growth rate and the optical constant of the films were found to depend on the type of substrate, the deposition temperature, and the deposition time. The corrosion resistance of the films also depends on substrate temperatures. The films formed at 673 K had the highest corrosion resistance in HCl and HF solutions. These films also showed a very high value of resistivity such as 1.5×1011 Ω·m at 10 mHz. All films obtained at temperatures of 473-773 K had amorphous structures.View full abstractDownload PDF (2082K) -
Toshio Narita, Tatsuo Ishikawa1991 Volume 55 Issue 1 Pages 67-71
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSUsing a reflection-type acoustic microscope, surface acoustic wave (SAW) velocities were measured with a frequency of 500 MHz on the partially stabilized zirconia (PSZ) ceramics itself as well as those joined to nickel-Kovar alloy, with and without external stresses.
The relationship between SAW velocities (VR, m/s) and tension stresses (σ, MPa) was given by the equation; VR=−0.21σ+3270. With this relationship, SAW velocities measured on the ceramic surface of the joint were transformed into stress and its distribution.
For the joint as-bonded, the largest tension stress of ca. 1 GPa was observed at the metal/ceramic interface and then it decreased rapidly far from the interface. With applying external load, the stress at the interface was unchanged, whereas the stress gradient tended to be steeper. After broken down the joint, a flat distribution was observed for the ceramic surface detached from the metal, showing residual stress free.
It was proposed that an acoustic microscope equipped with a minute loading unit shows considerable promise for non-destructive and localized evaluation of stress and its distribution on the ceramic surface, with and without external stresses.View full abstractDownload PDF (757K) -
Toshiro Kobayashi, Hiroyoshi Iwanari, Shinji Hakamata, Mitsuo Niinomi, ...1991 Volume 55 Issue 1 Pages 72-78
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSResearches and developments concerning aluminum matrix composites which are excellent in specific strength and specific modulus have been reported and applications of aluminum matrix components are expected as the structural materials of composites of automobiles and aircraft. However, there are few reports on the fatigue crack propagation characteristics which are very important for the design of structural materials. Since composites fracture in a complicated manner such as exfoliation between matrix and reinforcement or failure of reinforcements. Therefore, such properties as well as tensile strength should be evaluated for the applications of aluminum matrix composites as structural materials especially from the viewpoint of the guarantee of higher security.
The effect of volume fraction of SiC particles on the fatigue crack propagation characteristics of 6061 aluminum alloys reinforced with SiC particles (SiCp/6061-T6 composites) manufactured by powder metallurgy process were investigated. The following results were obtained. In a higher stress intensity range, unstable fatigue crack propagation was found as the threshold stress intensity range ΔKth and ΔKeff.th increased with increasing content of SiC particles. However, ΔKeff.th was suggested to be solely a function of the mean SiC particle size and to be independent of the volume fraction. This implies that for near-threshold crack extension, the maximum plastic zone size at the crack tip must exceed the mean SiC particle size.View full abstractDownload PDF (1897K) -
Makoto Kobashi, Takao Choh1991 Volume 55 Issue 1 Pages 79-84
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe process of particulate incorporation into liquid aluminum and the uniformity of particulate distribution in the matrix were investigated. During the melt-stirring period, particles take three different states as follows: (a) as powders, (b) particulate agglomerates combined with metal, and (c) particles incorporated in the matrix.
During the early stage of stirring, particulate incorporation does not start, although agglomerates are formed. However, particulate incorporation begins rapidly after a definite time of stirring (τ). Comparing the incorporation process of SiC particles with the wetting process of SiC plate to liquid aluminum, the wettability is found to be a dominant factor for the particulate incorporation process. The particulate distribution was not uniform just after particulate incorporation has finished, because particles were incorporated into melt as agglomerates. However, a sufficient stirring time makes the uniformity of particulate dispersion better. On the other hand, by adding surface active elements such as Pb or Bi, which decreases the surface energy of liquid aluminum, the uniformity of particulate dispersion in Al-Li and Al-Mg liquid aluminum alloys was improved in a shorter stirring time.View full abstractDownload PDF (1246K) -
Yuji Tsukita, Sakae Saito, Shuji Hanada, Akihiko Nagata, Keisuke Ikeda1991 Volume 55 Issue 1 Pages 85-91
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSNb/Al-X (X=Mg, Ti, Ta, Ge, Si) composite wires were fabricated by the Clad-Chip Extrusion (CCE) method to study the effects of alloying elements on workability of wires, the diffusion process to produce the Nb3Al-based A-15 phase and its superconducting properties. Nb/Al-2∼4 at%Mg and Nb/Al-1 at%Ti composite wires had good workability. However, other alloying elements deteriorated workability of wires more or less. Addition of Mg and Ti so enhanced the diffusion reaction that the optimum reaction temperature and time were largely reduced in comparison with binary Nb/Al. Moreover, Mg and Ti were effective elements for decreasing Kirkendall voids. Although all of Nb/Al, Nb/Al-3 at%Mg and Nb/Al-1 at%Ti gave JC above 108 A/m2 at 18 T, BC2 of the Ti-added wire was the highest among them. Ge and Si enhanced JC at high magnetic fields only by heat treatment at high temperatures more than ∼1800 K.View full abstractDownload PDF (1322K) -
Hiroshi Sato, Takateru Umeda1991 Volume 55 Issue 1 Pages 92-97
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAmorphous phases were prepared by the melt spinning method from oxide samples having compositions (S) 41.3 mol%SrO-41.3 mol%Fe2O3-17.4 mol%B2O3 and (T) 63.1 mol%SrO-19.4 mol%Fe2O3-17.5 mol%B2O3. When the amorphous phases were crystallized by heat treatment, SrO·6Fe2O3 crystal particles precipitated in matrices of unknown phases. The SrO·6Fe2O3 particles were extracted by acid-leaching the matrix, and the coercive force of the particles was discussed in terms of the composition of the starting oxide sample and the particle size. The coercive force is strongly dependent on the average particle size. The coercive force reaches 400-560 kA/m at the average particle sizes of 0.05-0.8 and 0.1-0.8 μm in diameter for the SrO·6Fe2O3 particles obtained from the samples of compositions S and T, respectively. When the average particle sizes reduce to less than 0.05 μm and 0.1 μm for the particles from samples of compositions S and T, respectively, the coercive forces begin to decrease due to the thermal activation of spins. Also, when the average particle sizes exceed 0.8 μm in both the cases of compositions, the coercive forces begin to decrease. The activation energies (n=7) of the grain growth of the SrO·6Fe2O3 particles are 812 and 854 kJ/mol when they precipitate in the amorphous ribbons prepared from samples of compositions S and T, respectively.View full abstractDownload PDF (1728K) -
Hideo Tanabe, Masahiro Kitada1991 Volume 55 Issue 1 Pages 98-104
Published: 1991
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of film thickness on the magnetic and electrical properties of permalloy magnetoresistive sensors is investigated. The thicknesses of permalloy thin films used are between 15 and 200 nm. The films are deposited on glass substrates by electron beam deposition and then formed into 10 μm × 50 μm patterns by photolithography.
The coercivity and the magnetic anisotropy field of the films are increased by patterning. The coercivity of patterned film increases with increasing film thickness in the range of 15 to 45 nm and decreases above 80 nm. This is because the magnetization reversal process in thinner films is caused by rotation magnetization with the buckling magnetic domain structure. While, in thicker films it is caused by the magnetic domain wall displacement. On the other hand, the magnetic anisotropy field of patterned film increases linearly with thickness, due to an increase of the demagnetizing field.
The half width of the magnetoresistive response curve and the output voltage of the magnetoresistive sensor decrease with increasing film thickness, because of the increasing demagnetizing field. Moreover, the discontinuity of output voltage due to the Barkhausen effect decreases with increasing film thickness. The Barkhausen noise is related to the occurrence and sudden extinction of buckling magnetic domains in thinner films and to the sudden movement of magnetic domain walls in thicker films.View full abstractDownload PDF (1430K)
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