Materials Transactions, JIM
Online ISSN : 2432-471X
Print ISSN : 0916-1821
ISSN-L : 0916-1821
Volume 38 , Issue 3
Showing 1-13 articles out of 13 articles from the selected issue
  • Akihisa Inoue, Tadahiro Negishi, Hisamichi Kimura, Takahiro Aoki
    1997 Volume 38 Issue 3 Pages 185-188
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    The replacement of Al by B for Zr65Cu27.5Al7.5−xBx amorphous alloys was found to cause an extension of the supercooled liquid region before crystallization. The largest value of the supercooled liquid region (ΔTx) defined by the difference between crystallization temperature (Tx) and glass transition temperature (Tg) is 100 K for Zr65Cu27.5B4Al3.5. The ΔTx value is much larger than that (72 K) for the Zr65Cu27.5Al7.5 alloy. The increase is due to the significant increase in Tx by the addition of B exceeding the degree of the increase in Tg. The crystallization from the supercooled liquid takes place through a single exothermic reaction in the B concentration range less than 4 at%. The crystallized structure consists of Zr2Cu, Zr2Al and Zr5Al3 for the Zr–Cu–Al alloy and changes into more multiple phases of Zr2Cu, Zr2Al, Zr3Al, Zr5Al3 and ZrB2 for the Zr65Cu27.5B4Al3.5 alloy. Besides, the temperature dependence of the storage and loss moduli (E′ and E″) in the supercooled liquid also changes from the single stage for the Zr–Cu–Al alloy to the two stages for the Zr–Cu–Al–B alloy. The first-stage changes in the E′(T) and E″(T) fit between both alloys and the second-stage change for the B-containing alloy takes place in the temperature range above Tx of the Zr–Cu–Al ternary alloy. It is therefore concluded that the generation of Zr–B atomic pair with stronger bonding nature and longer relaxation time by the addition of B causes the increase in the thermal stability of supercooled liquid region through the retardation of the crystallization reaction. Furthermore, this is the first evidence on the synthesis of the amorphous alloy with the large ΔTx above 100 K for the Zr–Cu–B–Al alloy containing higher B content as compared with Al content.
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  • Akihisa Inoue, Akira Murakami, Tao Zhang, Akira Takeuchi
    1997 Volume 38 Issue 3 Pages 189-196
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    The effect of Si additions on the thermal stability of the supercooled liquid before crystallization, glass-forming ability (GFA) and soft magnetic properties was examined for amorphous alloy series Fe72−xAl5Ga2P11C6B4Six, Fe72Al5−xGa2P11C6B4Six, Fe72Al5Ga2P11−xC6B4Six and Fe72Al5Ga2P11C6−xB4Six. The increases in the thermal stability and GFA and the improvement of soft magnetic properties were recognized in the replacements of P by 1 to 2 at%Si and of C by 1 at%Si. The supercooled liquid region (ΔTx) defined by the difference between crystallization temperature (Tx) and glass transition temperature (Tg) increases from 53 K for Fe72Al5Ga2P11C6B4 to 58 K for Fe72Al5Ga2P11C5B4Si1. The maximum thickness for glass formation (tmax) by copper mold casting increases from 1 mm for the Fe–Al–Ga–P–C–B alloy to 2 mm for the Fe72Al5Ga2P10C6B4Si1 alloy. The increases in ΔTx and tmax are presumably because of the increase in the degree of the satisfaction of the three empirical rules for the achievement of large glass-forming ability, i.e., (1) multicomponent alloy systems consisting of more than three elements, (2) significantly different atomic size ratios above about 12% and (3) negative heats of mixing. The soft magnetic properties are also improved by the replacement of 1 at%Si for P or C through the increase in the squareness ratio of B-H loop (BrBs) and the decrease in coercive force (Hc). The best soft magnetic properties for the bulk amorphous alloys are obtained for the Fe72Al5Ga2P10C6B4Si1 alloy and the saturation magnetization (Bs), Hc, BrBs, and Curie temperature are 1.14 T, 1.5 A/m, 0.45 and 594 K, respectively. The success of forming the Fe-based bulk amorphous alloys of 2 mm in thickness exhibiting the good soft magnetic properties is promising for future development as a new type of soft magnetic material.
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  • B. K. Prasad, A. K. Patwardhan, A. H. Yegneswaran
    1997 Volume 38 Issue 3 Pages 197-204
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    An attempt has been made in this investigation to characterize the sliding wear response of a modified zinc-based alloy at the sliding speed of 2.68 m/s over a range of applied pressures. A conventional zinc-based alloy (conforming to ZA 27) and a leaded-tin bronze (conforming to SAE 660) were also subjected to identical test conditions in order to assess the (wear) performance of the modified (zinc-based) alloy. A correlation has been established between the nature of the various microconstituents and the wear response of the alloys. Wear mechanisms have also been studied through the examination of wear surfaces, subsurfaces and debris.
    The study clearly indicates that the presence of nickel and silicon comprising microconstituents led to a considerably increased wear and seizure resistance of the modified zinc-based alloy over its conventional counterpart. Further, zinc-based alloys attained better wear resistance (prior to seizure) but inferior seizure pressure when compared with those of the bronze. As far as the extent of frictional heating is concerned, the conventional zinc-based alloy suffered from a maximum extent of heating while the bronze experienced the minimum. The response of the modified zinc-based alloy was intermediate between the two in this context. The modified alloy also attained improved thermal stability than the conventional (zinc-based) alloy.
    In general, (microcracking assisted) adhesion was the predominant mechanism of material removal. However, abrasion was also observed to contribute to material loss. The zinc-based alloys experienced considerable wear induced subsurface deformation and formation of a stable transfer layer while such observations were weakly made in the case of the bronze due to the cracking tendency of the latter.
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  • Norio Matsuda, Keisuke Matsuura
    1997 Volume 38 Issue 3 Pages 205-214
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    Deformation and fracture behaviours were investigated in a continuous alumina fiber reinforced aluminum composite by tensile tests of specimens with different tensile axis orientations to the fiber axis at various temperatures from room temperature to 773 K. The orientation dependence of the tensile strength is well described by the maximum stress theory as well as by the Tsai-Hill’s theory.
    Temperature dependences of strength σc of composite in the direction of fiber axis, shear strength τu of the matrix along the fiber axis and tensile strength σu of the matrix in the direction normal to the fiber axis were determined. It is concluded that the decrease in the tensile strength of the composite with the rise of temperature is mainly due to the decrease in the τu and σu. It is suggested from the observation of fracture surfaces that the decrease in τu and σu at high temperatures is not only due to the decrease in strength of the matrix, but partly to the lowered shear and tensile strength of the matrix-fiber interface.
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  • Shojiro Ochiai, Masaki Hojo
    1997 Volume 38 Issue 3 Pages 215-219
    Published: 1997
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    To describe the feature that the tensile strength of unidirectional discontinuous fiber (whisker)-reinforced aluminum matrix composites decreases with increasing temperature more than that of continuous fiber-reinforced ones, a calculation of the critical length and stress concentration factor affected by the temperature-dependence of mechanical property of matrix, and a Monte Carlo simulation, were carried out. The reduction in strength of both continuous and discontinuous fiber-composites at high temperatures could be attributed to the predominancy of the effect of the matrix-softening-induced increase in critical length over the effect of the decrease in stress concentration arising from the existence of fiber-ends and fiber-breakages. The larger reduction in strength of discontinuous fiber-composites at high temperatures than that of the continuous ones could be explained from the view-point of the larger reduction in the stress carrying capacity of fibers and easier fiber-pull-out.
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  • Masashi Ookawa, Toru Sakurai, Sayuri Mogi, Toshio Yokokawa
    1997 Volume 38 Issue 3 Pages 220-225
    Published: 1997
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Optical absorption was investigated as for lead silicate glasses containing Fe3O4 up to 10 mol%, which have been melted under air or argon atmosphere. The absorption coefficient over the whole optical range increased with increase of iron content. The variations of the spectrum profiles were also observed with Fe2+ content; the tail from UV region shifted to low energy side and another absorption band (near 14500 cm−1) beside d-d transitions was observed. These were considered to be caused by the interaction including the charge transfer between Fe2+ and Fe3+ ions.
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  • J. Qiu, T. Shibata, C. Rock, K. Okazaki
    1997 Volume 38 Issue 3 Pages 226-231
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    Electro-discharge consolidation (EDC) was carried out for atomized Al-based alloy powders produced at YKK. Input energies of 2.5 to 3.8 kJ/g produced compacts of 88 to 99% in theoretical density. The densification can be described by a simple relation of Δρ=11.8[ERs⁄(Rs+2)]0.36 in % where Rs is the specimen resistance, and it predominantly depends on input energy, E. A comparison of XRD spectra before and after EDC with respect to the peaks’ position and intensity indicates that no microstructural change occurred. Oxide film removal by EDC was confirmed by TEM observations. Compression tests of EDC compacts at room temperature produced under the present conditions (specimen resistance Rs=9.4–15.8 mΩ) yielded 800 MPa and 24% elongation for true ultimate compressive stress and true compressive strain, respectively. The annealing treatment at 573 K for 1.2 ks raiseds compressive strength by at expense of ductility due to precipitation of solute atoms, indicating that a super-saturated solid solution is maintained in the EDC state.
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  • Yoshikazu Genma, Yoshiki Tsunekawa, Masahiro Okumiya, Naotake Mohri
    1997 Volume 38 Issue 3 Pages 232-239
    Published: 1997
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    This paper presents the influence of particle shapes and sizes on the incorporation of Al2O3 particles into molten Al-5 mass%Mg alloy by melt stirring with ultrasonic vibration. A new theoretical model of particle transfer into molten metal dealing with different shapes is proposed to estimate the difficulty in incorporation of spherical and massive particles. In the model, the particles are assumed to be spheroids with different major and minor axes. The difficulty depends on the maximum acceleration which originates from the interfacial tension: the incorporation of Al2O3 particles into molten Al–Mg alloy becomes more difficult with the negative maximum acceleration increased. Four kinds of preheated Al2O3 particles were added to a molten Al-5 mass%Mg alloy surface and stirred with ultrasonic vibration at 1023 K in a nitrogen atmosphere. The volume fraction of incorporated particles is related to the calculated maximum acceleration; that is, it is experimentally found to decrease as the negative maximum acceleration increased. According to the proposed model, the ultrasonic vibration makes the apparent contact angle of the Al2O3 particle and the molten Al–Mg alloy improve from 1.78 to 0.87 rad. Gas defects, which are known to be a serious problem in metal matrix composites (MMC) produced by melt stirring, disappear in MMC samples formed with ultrasonic vibration. Moreover, the rotating torque for melt stirring decreases by applying ultrasonic vibration, because of the decomposition of agglomerate particles. Hence, the application of ultrasonic vibration to melt stirring is a novel candidate method of MMC production.
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  • Osamu Yanagisawa, Kazuhiro Matsugi, Tomei Hatayama
    1997 Volume 38 Issue 3 Pages 240-246
    Published: 1997
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The 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 in the spark sintering process. 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 applied punch pressures. The limited variations of the relative densities of compacts are observed in the 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 the powder particles after this dielectric breakdown. 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. Furthermore, it is assumed on the basis of the first order equation of the chemical reaction that the rate of the creation of the metallic contact area between powder particles per pulse discharge is proportional to the fraction of the contact area consisting of an oxide film between particles. The relationship between the number of pulses and the specific resistivity of compacts can be explained quantitatively by this assumption.
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  • Hideki Araki, Shigeoki Saji, Tsuyoshi Okabe, Yoritoshi Minamino, Toshi ...
    1997 Volume 38 Issue 3 Pages 247-254
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    The powder of a single phase of the Al-10.7 at%Ti-0.6 at%Fe supersaturated solid solution with an average crystallite size of 11 nm has been obtained from a pure Al and Ti mixed powder by means of a high energy planetary ball mill. The mechanically alloyed (MA) powder was consolidated into cylinders 4 mm in diameter and 2.5 mm in height at temperatures of 473∼773 K under hydrostatic pressures of 0.1 MPa ∼ 3 GPa. The consolidation at high temperatures causes the decomposition of the supersaturated solid solution obtained by MA, whereas the compacts consolidated at low temperatures retain the supersaturated solid solution and nanostructure. The upper limiting temperature where the compact can retain the supersaturated solid solution becomes higher with increasing consolidation pressure, and the application of high pressure consequently permits consolidating the MA powder at higher temperature without decomposing the supersaturated solid solution. On the other hand, the higher consolidation pressure and temperature can give higher density and hardness to the compact. Thus the application of high pressure is effective for the consolidation of MA powder with the retention of the supersaturation and nanostructure.
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  • N. Q. Wu, J. M. Wu, Z. Z. Li, G.-X. Wang
    1997 Volume 38 Issue 3 Pages 255-259
    Published: 1997
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    Ball milling has been performed on the Al–Ti and Al–Ti–C powder mixtures in a planetary ball mill. The structural changes of the as-milled powder samples have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). The results obtained show that an amorphous phase is formed at an early milling stage, and transits later to a nanocrystalline f.c.c. metastable phases. In addition, crystallization of the amorphous phase upon heating results in the equilibrium phases instead of the f.c.c. phase. This indicates that the crystallization induced by ball milling is different from that by annealing. The contamination of nitrogen and oxygen has a significant influence on the crystallization during ball milling.
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  • Makoto Kobashi, Norihisa Okayama, Takao Choh
    1997 Volume 38 Issue 3 Pages 260-265
    Published: 1997
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Aiming at producing AlN/Al composite materials with the help of an exothermic reaction, spontaneous infiltration of molten aluminum into magnesium nitride (Mg3N2) powders was investigated. In an alumina crucible, a pure aluminum ingot was placed on Mg3N2 powders (either loose or compacted powders). In a nitrogen atmosphere, specimens were heated up to 1473 K and held for 3600 s in order to induce the spontaneous infiltration and the subsequent in situ reaction. During the high-temperature holding, molten aluminum infiltrated into Mg3N2 powders spontaneously, as expected. Neither large pores nor non-infiltrated regions were visible in the cross-section. The cross section of the specimen after the high-temperature holding was analyzed by an X-ray diffraction method. The result revealed a formation of aluminum nitride (AlN) in an aluminum alloy. The sizes and the volume fraction of AlN particles produced from loose Mg3N2 powders were in a range of 5∼50 μm and 21%, respectively. The volume fraction of AlN increased from 21 to 57.4% by using an Mg3N2 powder compact instead of using loose powders. The morphology of synthesized AlN also changed from discrete to continuous by using the powder compact. Differential-thermal-analysis data revealed a sharp exothermic peak caused by the reaction between Mg3N2 and aluminum. During the fabrication process, a sharp increase in the temperature was also observed by a thermocouple embedded in the powder layer. The peak temperature (1840 K) showed a good agreement with a thermodynamically calculated adiabatic temperature (1900 K).
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  • Yukio Inokuti
    1997 Volume 38 Issue 3 Pages 266-274
    Published: 1997
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The mechanism responsible for ultra-low iron loss in TiN-coated silicon steel sheet was clarified by electron microscope observation of the magnetic domain and the structure at the interface of the TiN film and single crystal of silicon steel, and by X-ray pole figure measurement. Marked domain refinement due to thin TiN film coating was accomplished, satisfying the coherency relationship of (1\bar11)TiN//(011)Si-steel, [110]TiN//[100]Si-steel between the TiN film and single crystal matrix, by applying a strong surface tension to the [100]Si-steel direction (elastic strain along only one axis). Fine transverse fringes were observed at the interface using a transmission electron microscope, and the elliptical shape of the {200}Si-steel pole peaks was detected by measuring the dual textures of X-ray pole figures.
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