Materials Transactions, JIM
Online ISSN : 2432-471X
Print ISSN : 0916-1821
ISSN-L : 0916-1821
Volume 31 , Issue 11
Showing 1-12 articles out of 12 articles from the selected issue
  • Sung Gyoo Kim, Akihisa Inoue, Tsuyoshi Masumoto
    1990 Volume 31 Issue 11 Pages 929-934
    Published: 1990
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    Mg–Ni–Y and Mg–Cu–Y alloys were found to form an amorphous solid in wide compositional ranges of 0 to 40 at%Ni or Cu and 0 to 40%Y by the melt spinning technique. These amorphous alloys exhibit a wide supercooled liquid region before crystallization and the glass transition temperature (Tg) increases from 398 to 568 K with increasing Y content, while a minimum at about 15%Ni or Cu is seen in the change of Tg with Ni or Cu content. The temperature span ΔTx (=TxTg) shows a maximum around the central composition in the range where the glass transition is observed and the largest ΔTx is 41 K for Mg50Ni30Y20 and 61 K for Mg65Cu25Y10. Furthermore, the Mg-based amorphous alloys containing above about 70%Mg have a good bending ductility and the tensile fracture strength (σf) reaches 830 MPa for Mg80Ni15Y5 and 800 MPa for Mg85Cu5Y10. The specific strength defined by the ratio of σf to density is 3.5×105 N·m/kg for both alloys which is about 2.0 times as high as the highest value for conventional Mg-based crystalline alloys. The Mg-based amorphous alloys are attractive as a new type of high-strength material with light weight.
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  • Tsugio Tadaki, Hiroshi Okazaki, Yoshiyuki Nakata, Ken’ichi Shimi ...
    1990 Volume 31 Issue 11 Pages 935-940
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The atomic configuration in a β phase Cu-21Au-45Zn (at%) shape memory alloy with the L21 structure has been investigated by means of electron channelling enhanced microanalysis (ALCHEMI) utilizing an analytical electron microscope, and powder X-ray diffractometry. ALCHEMI has been successfully applied for determination of site occupancies of the constituent atoms, especially, of Cu and Zn atoms, which is difficult to be determined by conventional X-ray diffraction method, and thus had remained unclear to date. ALCHEMI showed that Zn atoms were located at the body-center sites, while Cu atoms were at the corner sites, referring to the fundamental bcc lattice. The crystal structure thus identified was in agreement with that formerly proposed by Duggin and Rachinger. On the other hand, X-ray diffraction revealed that the L21 ordering was completed in the present alloy during quenching even when rapidly quenched. This is consistent with the fact that Ms temperature of the present alloy is almost the same between specimens quenched into iced water and into boiling water, and with the fact that the transformation temperature is almost unchanged during aging at room temperature.
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  • Tsugio Tadaki, Hiroshi Okazaki, Yoshiyuki Nakata, Ken’ichi Shimi ...
    1990 Volume 31 Issue 11 Pages 941-947
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Site occupancies of the constituent atoms in a M18R martensite of a Cu-26Au-45Zn (at%) alloy, well-aged at room temperature, have been examined by electron channelling enhanced microanalysis (ALCHEMI) and powder X-ray diffraction techniques. As a result, the sites preferentially occupied by Cu and Zn atoms were uniquely distinguished by ALCHEMI, which were previously unclear: The atomic configuration in the basal plane of the M18R martensite reduced by ALCHEMI was consistent with that directly derived from a {220} plane of the L21 parent phase proposed by Duggin and Rachinger, following the lattice correspondence between the two lattices. Appreciable disordering (by about 20%) was found between Cu and Au atoms by X-ray diffraction. Since the degree of order in the L21 parent phase was previously shown to be complete, the observed disordering should have occurred during martensite aging at room temperature. The stabilization of martensite, i.e., rises of the reverse transformation temperature for the L21 to M18R martensitic transformation, is thus considered to be due to the interchange between Cu and Au atoms. The occurrence of the rubber-like behavior upon martensite aging of this alloy system is discussed in terms of the disordering observed.
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  • Aruna Bahadur, O. N. Mohanty
    1990 Volume 31 Issue 11 Pages 948-953
    Published: 1990
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    Aluminium diffusion coatings are known to protect steel from corrosion at elevated temperatures (950°C) and in sulphurous atmospheres. The literature however, is not clear with regard to the underlying mechanism. The properties of calorized material have been attributed to aluminium oxide and to different intermetallic compounds.
    Calorized mild steel pipes, produced at NML by pack-cementation, have shown good corrosion properties at 600°C in a sulphurous atmosphere comparable with those of imported calorized steels. The micro-hardness profile across coating thickness shows in general values between 450–650 compared to matrix hardness of 220 (pearlite) and 140 (ferrite). A high hardness phase with 850–1000 hardness has been detected at some places, within 30 μm of the outer edge of the coating.
    X-ray diffraction has established the general presence of FeAl and Fe3Al phases in the diffusion zone. It is of importance to note that these compounds satisfy the Pilling Bedworth condition of continuity for protective oxide coating, extended here to cover calorized coatings, i.e.,
    (Remark: Graphics omitted.)
    where VMAlx=Volume of metal aluminide and VM=Volume of metal used to form aluminide.
    On this basis, the presence of other phases such as FeAl3, FeAl2, Fe2Al5 is considered undesirable as the compatibility with the matrix would be poor. The calorizing parameters need to be standardized so as to obtain beneficial phases only for superior performance of coatings.
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  • Hideki Hagi
    1990 Volume 31 Issue 11 Pages 954-958
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Diffusion coefficients of hydrogen in the palladium films of α-phase have been measured between 278 and 323 K by an electrochemical stripping method. Palladium films were deposited on iron by RF sputtering. The values of the diffusion coefficient of hydrogen obtained for the film specimens 0.68 μm and 1.36 μm in thickness were about 2 orders of magnitude lower than those reported for the bulk specimens in the literature, and the temperature dependence of the diffusion coefficients of hydrogen was given by DH(m2⁄s)=4.16×10−9exp(−25.7(kJ/mol)⁄RT).
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  • Tae Hyun Nam, Toshio Saburi, Ken’ichi Shimizu
    1990 Volume 31 Issue 11 Pages 959-967
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Cu-content dependence of the shape memory characteristics in Ti–Ni–Cu alloys has been investigated by means of electrical resistivity measurements, differential scanning calorimetry and constant load thermal cycling tests. Transformation start temperature for the B19′ martensite, Ms, decreased largely, whereas that for the B19 martensite, Ms′, increased slightly with increasing Cu-content. Thus, the temperature range over which the B19 martensite was stable became wide. The maximum recoverable elongation associated with the B2→B19 transformation decreased from 3.2 to 2.7%, and the hysteresis associated with the transformation decreased from 11 to 4 K with increasing Cu-content from 10 to 20 at%. The temperature dependence of stress required to induce the B2→B19 transformation was nearly constant (about 8 MPa/K) without regard to the Cu content for the alloys with above 10 at%Cu. The residual elongation decreased with increasing Cu content.
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  • Masamichi Miki, Yoshikiyo Ogino
    1990 Volume 31 Issue 11 Pages 968-974
    Published: 1990
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    The effects of Si addition on the nucleation and growth of the grain boundary cell in a Cu-10%Ni-8%Sn alloy on aging at 723 K after quenching from 1123 K were investigated by means of hardness measurements, optical and electron microscopic observations, and X-ray analysis. The addition of Si retarded the precipitation of the γ′ phase in the matrix and suppressed the nucleation and growth of the grain boundary cell. In the alloy containing more than 0.4% of Si, the cell was scarcely observed even after the long time aging. Very fine particles of Ni31Si12 phase were observed in the grain boundaries and matrices of the as-quenched specimens containing more than 0.4% of Si. Therefore, these fine particles in the grain boundaries must have occupied the nucleation sites of a γ((Cu·Ni)3Sn) phase and resulted in the suppression of nucleation of the cells which consisted of lamellar mixtures of the γ and α phases.
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  • Haruo Doi, Kenki Hashimoto, Kazuo Kasahara, Tokuzou Tsujimoto
    1990 Volume 31 Issue 11 Pages 975-982
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    The X-ray diffraction method to determine the long range order parameter in binary alloys has been extended to examine the site occupancy of third elements (V, Mn, Zr and Nb) and the amount of mutually exchanged Ti and Al atoms in TiAl-phase for ternary TiAl–X alloys.
    In the present analysis, unknown parameters βAl and βX were determined by solving simultaneous equations βAl=P+Q×βX with respect to different P and Q values, where βAl or βX represents the amounts of Al or X occupied in the Al site in TiAl-phase, and P and Q are experimentally determined; the former depends predominantly on the ratio of integrated intensity whereas the latter only depends on the atomic scattering factors in superlattice reflections.
    It turned out that V and Mn atoms occupy predominantly the Al site whereas Zr and Nb atoms occupy the Ti site; the amount of mutually exchanged Al and Ti atoms decreases with increasing concentration of V and Mn, whereas it decreases at first and then increases for the concentration above 5 at% of Zr and Nb.
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  • Kaneaki Tsuzaki, Hirohisa Matsuyama, Mamoru Nagao, Tadashi Maki
    1990 Volume 31 Issue 11 Pages 983-994
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Superplasticity of a 25Cr–7Ni–3Mo ferrite/austenite duplex stainless steel has been studied with particular emphasis on the microstructural change during deformation, in order to clarify roles of dynamic recrystallization in the superplastic deformation. A microduplex structure consisting of fine ferritic subgrains and austenite particles (grain size: 1 μm) is obtained by annealing at 1273 K after 90% cold rolling of a fully ferrite structure. The steel with this fine-grained structure exhibits high-strain rate superplasticity at 1273 K in the ferrite/austenite two-phase region. A maximum elongation over 1700% is obtained at a strain rate of 1.7×10−2/s. Even at a higher strain rate of 1.7×10−1/s the elongation is near 1000%. Ferrite/ferrite boundaries are low-angle boundaries before the superplastic deformation. These low-angle boundaries are changed to high-angle ones by dynamic recrystallization of the ferrite matrix in the early stage of deformation. During the deformation after the recrystallization of the ferrite matrix, dislocations are scarcely observed in the whole of specimens. It is concluded that grain-boundary sliding is the dominant mode of the superplastic deformation, and that the role of the dynamic recrystallization is to make the fine structure suitable for the grain-boundary sliding in the early stage of deformation. A mechanism of the dynamic recrystailization is briefly discussed.
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  • S. Asano, Y. Nishino, K. Fujiyoshi
    1990 Volume 31 Issue 11 Pages 995-998
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    In FCC Fe–Ni–Mn alloys charged cathodically with hydrogen, internal friction was measured from 170 to 370 K at about 600 Hz in the fundamental mode of free-free transverse vibration. The hydrogen peak was found in these alloys, as has been observed in austenitic stainless steel, 36%Ni Invar, Fe–Ni and Fe–Cr–Mn alloys. As a result of cathodic hydrogen charging, there occurred either of two types of hydrogen-induced phase transformation for the most composition range of Fe–Ni–Mn alloys; hydride formation or martensitic transformation. However, for some intermediate composition of the alloys such as Fe65Ni15Mn20, Fe50Ni20Mn30, Fe40Ni30Mn30 and Fe30Ni40Mn30, cathodic hydrogen charging did not induce any phase transformation and yet produced a well-defined hydrogen peak of internal friction. This means that the hydrogen peak originates from dissolved hydrogen in the FCC alloy matrix, independent of hydrogen-induced phase transformation. The activation energy of the hydrogen peak was estimated to be 37 kJ/mol for the Fe50Ni20Mn30 alloy, which is considered as that of hydrogen diffusion.
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  • Shinya Yao, Hidetoshi Uchida, Zensaku Kozuka
    1990 Volume 31 Issue 11 Pages 999-1004
    Published: 1990
    Released: May 23, 2007
    JOURNALS FREE ACCESS
    An oxygen analyzer with a closed system was set up to investigate the thermal stability of praseodymium oxides. It was composed of a circulation pump, specimen, and an electrochemical oxygen pump: Pt, air/ZrO2(+CaO)/Ar+O2 gas, Pt. Praseodymium oxide was heated up and successively cooled down at a constant rate in circulating Ar gas, in which the oxygen chemical potential was maintained at a constant value by a potentiostatic operation. The phase transition was monitored using the change in an electrical current passing through the oxygen pump. Pr5O9⇔Pr9O16 and Pr9O16⇔Pr7O12 occured gradually at first and then rapidly with time, which are consistent with the isothermal chemical hysteresis reported in the literature. The temperature of the phase transition: PrOx(σ)→Pr2O3(A), i.e., CaF2-related structure→A type sesquioxide, was very dependent on the heating run numbers, implying that at least two factors affect the relative stability of the two phases. The closed-system potentiostatic technique permits measurements with such a high sensitivity that 10−8∼10−9 g of oxygen is detectable, and therefore, it may be applicable for the investigation of micro-reactions.
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  • M. Oguchi, A. Inoue, H. Yamaguchi, T. Masumoto
    1990 Volume 31 Issue 11 Pages 1005-1010
    Published: 1990
    Released: June 01, 2007
    JOURNALS FREE ACCESS
    Al84Ni10Mm6 (Mm=mischmetal) amorphous sheets with a maximum thickness of 7.0 mm were produced by the two-stage quenching technique consisting of high-pressure argon atomization and the subsequent incremental impact deposition on a rotator. The amorphous sheets had a thickness of 0.1 to 7.0 mm and an average width and length of 40 and 100 mm, respectively, and the thickness was controlled by changing the amount of the molten alloy in one ejection. The formation of an amorphous sheet with a large thickness up to 7.0 mm is quite different from the result by melt spinning that the amorphous ribbon is formed in the thickness range below about 0.13 mm and is thought to result from an incremental deposition at an interval of the order 10−3 s of the supercooled liquid droplets with high kinetic energies produced by high-pressure gas atomization. The glass transition and crystallization behavior remained unchanged over the entire thickness range of 0.1 to 7.0 mm and were the same as that of the melt-spun ribbon, but the density and hardness of the sheets were slightly lower than those of the ribbon probably because of the inclusion of pores. The thermal stability allows us to conclude that there is no distinct difference in amorphicity between the sheet with a thickness of 7.0 mm and the ribbon with a thickness of 0.02 mm. It is concluded therefore, that the present two-stage quenching technique provides an appropriate cooling condition for the formation of an amorphous thick sheet.
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