MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 47 , Issue 2
Showing 1-40 articles out of 40 articles from the selected issue
  • Katsuya Inoue, Sang-Koo Kwon, Shigeru Suzuki, Masatoshi Saito, Yoshio ...
    2006 Volume 47 Issue 2 Pages 243-246
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Quantitative X-ray structural analysis using an in-house X-ray diffraction apparatus has been used for characterizing the atomic-scale structure of the γ-FeOOH (lepidocrocite) particles prepared by dipping a pure iron and an iron-silicon alloy into aqueous solutions containing sodium chloride. The morphology of the γ-FeOOH particles was observed by transmission electron microscopy (TEM), and their bonding structure were analyzed using Fourier transform infrared spectroscopy (FT-IR). The realistic atomic-scale structures in the γ-FeOOH particles were estimated by fitting the interference functions with the help of the reverse Monte Carlo (RMC) simulation technique. The results showed that the linkages of fundamental FeO6 octahedral units in the particles were deviated from the ideal crystal structure. The structural deviation is considered to be due to the incorporation of foreign ions during the formation of these particles in the aqueous solutions.
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  • Tomonobu Owa, Takeshi Shinoda
    2006 Volume 47 Issue 2 Pages 247-250
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    In order to improve high-temperature oxidation resistance of titanium, fabrication of TiAl intermetallic compounds as a surface layer by plasma transferred arc surfacing (PTA surfacing) was investigated. Powder of unalloyed aluminum was fed into the plasma during the PTA surfacing and TiAl-based intermetallic layers were successfully synthesized. The surface layers had no cracks and porosities with optimized conditions of the PTA surfacing. The surface layers that largely consist of TiAl and Ti3Al phase could be achieved, while the microstructures of them were significantly influenced by the conditions such as the arc current. The TiAl-based layers exhibited high resistance to oxidation under isothermal conditions at 1073 K or less and had practically the same resistance as SUS310S had.
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  • Kiyoshi Nozaki, Toshio Itami
    2006 Volume 47 Issue 2 Pages 251-254
    Published: 2006
    Released: February 17, 2006
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    The dc electrical conductivity, σdc, was measured for liquid (AgI)x–(Ag2O)y–(B2O3)1−(x+y) (x=0.7–0.9; y=0.05–0.2) by using an ac impedance method in particular concern with the precipitation mechanism in the α-AgI precipitated glass, which was prepared by a rapid quenching technique due to a twin-roller apparatus. The temperature dependence of σdc exhibits two inflexion points. The existence of two liquid phase separation was confirmed by the electrical conductivity measurements with the use of specially designed cell. In addition, the X-ray diffraction and the SEM (Scanning Electron Microscope) experiments were performed for the rapidly quenched samples. The α-AgI precipitated glass was obtained by adopting the higher holding temperature even for the composition for which the β-AgI precipitated glass was prepared in the case of a lower holding one. These results indicate the role of two liquid phase separation on the preparation process of nano α-AgI crystallites in the glass matrix.
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  • Yi Zhang, Jian Lu, Tsuyoshi Ikehara, Ryutaro Maeda, Chikashi Nishimura
    2006 Volume 47 Issue 2 Pages 255-258
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Single-layer Pd membrane with the thickness of about 2.5 μm was successfully prepared by microfabrication technology. Hydrogen permeation of the as-prepared Pd membrane was investigated in the temperature range of 473–673 K under hydrogen transmembrane pressure of ∼40 kPa. Hydrogen permeation of Pd membrane with the thickness of 0.70 mm was also carried out for comparisons. It was found that the hydrogen permeability of the 2.5 μm-thick Pd membrane was about half of that of the 0.7 mm-thick Pd membrane. Surface resistance was less significant in hydrogen permeation through the thin microfabricated Pd membrane than thin Pd membranes supported by porous materials. Grain growth was observed in the thin microfabricated Pd membrane upon hydrogen permeation.
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  • Zheng-cao Li, Hiroaki Abe, Naoto Sekimura
    2006 Volume 47 Issue 2 Pages 259-262
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Transmission electron microscopy observation of cross-sectional specimens prepared by focused ion beam milling method have been applied to study the deep radiation damage and depth profile of point defects generated during ion irradiation in Cu–1 mass%Co alloy specimens by means of coherent precipitates. The specimens were irradiated at a temperature range of 250 to 500°C by 4 and 0.6 MeV self Cu ions to a dose of 0.3 dpa. The damage range has been observed at depths well beyond that expected from ion damage range calculations.
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  • Hiroaki Yamamoto, Kenji Shinzaki, Koichiro Koyama
    2006 Volume 47 Issue 2 Pages 263-266
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The preparation process of white heart malleable cast iron in Na2O–SiO2 oxide molten salts was studied. We investigated the effect of the molten salt composition on the decarburization of white cast iron. A specimen of white cast iron (φ8mm×8mm) containing 3.34 mass% carbon was immersed in a Na2O–SiO2 molten salt at 1323 K for 24–72 h. After the heat treatment of white cast iron in Na2O–SiO2 (64–36 mol%) at 1323 K for 48 h, low-carbon surface layer had a thickness of about 100 μm and contained 0.53 mass% carbon. This surface layer was formed as a result of the reaction of carbon in white cast iron with free oxygen in the oxide molten salt. However, no decarburized layer was observed on the specimen surface after the heat treatment in the Na2O–SiO2 (38–62 mol%) molten salt. As the Na2O composition increased within the limit of 41 < Na2O (mol%) ≤ 65, the thickness of the decarburized layer also increased. It was found that white heart malleable cast iron could be prepared from white cast iron in Na2O–SiO2 oxide molten salts, and the degree of decarburization depended on the composition of the molten salts.
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  • Naoyuki Ohnishi, Shinji Yoshida, Yoshiharu Namba
    2006 Volume 47 Issue 2 Pages 267-270
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The microstructure of a mechanically finished calcium fluoride (CaF2) was studied by transmission electron microscopy (TEM). The (111) oriented surfaces of high-purity CaF2 single crystals were finished to a flat surface by ultra-precision mechanical polishing. A float polishing method—with 7-nm-diameter silicon dioxide powder, pure water, and a tin lap—was employed for the finishing. Prior to the float polishing, ultraprecision grinding was performed as the preliminary treatment. A cross-sectional TEM study indicated that the thickness of the subsurface damage introduced by ultraprecision grinding was relatively small when compared with that by the conventional optical polishing process. Further, the float polishing process did not introduce any mechanical damages in the CaF2 crystals. The TEM images showed that the float-polished surface had a faceted structure consisting of (111) terrace planes and nanometer-sized steps. The size of a single terrace depends on the mismatch angle between the sample surface and the (111) plane. The high-resolution TEM observation suggested that an atomically smooth (111) surface with a bulk fluorite structure was obtained over a relatively wide area on the large terrace planes.
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  • Kenji Iwase, Takashi Kamiyama, Yumiko Nakamura, Kazuhiro Mori, Masao Y ...
    2006 Volume 47 Issue 2 Pages 271-274
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The average and local structures in the (Ti0.45Cr0.35Mo0.20)–D system have been investigated by neutron powder diffraction and total neutron scattering. From the result of neutron powder diffraction, the crystal structure of the system was found to change from CaF2-type structure to bcc structure in the hydrogen desorption process, and the D atoms occupy the tetrahedral (T) sites in both CaF2-type and bcc phases. The D–Ti, D–Cr, D–Mo and D–D correlation lengths and the nearest neighbor coordination number around a D atom have been obtained by the RDF analysis of total neutron scattering data. The D atoms occupy the T sites surrounded mainly by the Ti atoms in both CaF2-type and bcc phases.
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  • Keizo Kobayashi, Kimihiro Ozaki
    2006 Volume 47 Issue 2 Pages 275-278
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Mechanical alloying and pulsed-current sintering were used to synthesize TiB2–Fe–Al cermet alloys consisting of titanium boride and iron aluminide intermetallic compound. A mixture was obtained to which Fe was minutely distributed by mechanically alloying TiB2 powder and Fe powder for 180 ks. Mixture powders of TiB2–20 mass%Fe3Al and of TiB2–24 mass%FeAl were prepared by mixing an Al powder with this mechanically alloyed powder using a mortar. The added Al reacted with Fe after it had melted when these mixtures were heated. These powders were sintered for a short time and at low temperature using pulsed-current sintering process, but these sintered compacts had pores.
    Several iron aluminide intermetallic compounds were generated in the TiB2–20 mass%Fe3Al. Therefore, the TiB2–20 mass%Fe3Al compact was hard and brittle. However, the TiB2–24 mass%FeAl sintered body was composed only of TiB2 and FeAl, and had better ductility. A slight weight increase resulted from oxidation even though it was heated to 800 K or more in the air, but both sintered compacts retained their pores.
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  • Joon Woo Bae, Jae-Won Lim, Kouji Mimura, Minoru Isshiki
    2006 Volume 47 Issue 2 Pages 279-282
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Hf films have been deposited on Si(100) substrate with or without a substrate bias voltage using a non-mass separated ion beam deposition (IBD) method. Secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GDMS) have been used to determine impurity concentrations of Hf films and a Hf target. By the SIMS results with Cs+ and O2+ ion beams, the Hf film deposited at Vs=0 V contains more impurities than the Hf film deposited at Vs=−50 V. In addition, from GDMS results for the Hf target and the Hf films deposited at Vs=0 and −50 V, almost all the impurities have reduced by applying a negative substrate bias voltage. It means that applying a negative bias voltage to the substrate can decrease the impurity concentrations in Hf films.
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  • Naoyuki Nomura, Mariko Abe, Atsushi Kawamura, Shigeo Fujinuma, Akihiko ...
    2006 Volume 47 Issue 2 Pages 283-286
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Porous Co–29Cr–6Mo (mass%) compacts without Ni were fabricated by hot pressing and their microstructure and mechanical properties were investigated. PREPed Co–29Mo–6Mo powder with a diameter range (300–500 μm) was hot-pressed under the uniaxial pressure of 40 MPa at 1223 K for 7.2 ks. Hot-pressed compacts were annealed at 1473 K for 7.2 ks for further sintering. X-ray diffraction analysis revealed that γ and ε phases appeared dominantly in the PREPed powder, while ε and σ phases coexisted in the compact which was hot-pressed at 1223 K. After annealing at 1473 K, only the ε phase was detected although the γ phase was stable at this temperature. Therefore, the ε phase formed during furnace cooling.
    Tensile behavior of porous Co–29Cr–6Mo compacts was characterized by the stress–strain curves. The as-hot pressed compact showed linear deformation followed by sudden fracture. The annealed compact showed higher ultimate tensile strength (UTS) and lower yield strength than the as-hot pressed compact. Young’s modulus of the annealed compact was difficult to determine from the stress–strain curve. However, the annealed compact possessed a tensile strength of 116 MPa, which is comparable to that of human cortical bone.
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  • Sang-Hak Lee, Eiji Takahashi, Naoyuki Nomura, Akihiko Chiba
    2006 Volume 47 Issue 2 Pages 287-290
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The wrought Co–Cr–Mo alloys with C contents of 0.02, 0.09 and 0.18% (mass%) were fabricated by hot-forging process to study the influence of carbon contents on the microstructures and mechanical properties. The microstructures of Co–29Cr–6Mo–0.02C and Co–29Cr–6Mo–0.09C consist of equiaxed uniform grains which contain stacking faults, twins and ε martensite bands. No carbide found at inter- and intra-granular region. Co–29Cr–6Mo–0.18C consists of irregular grain sizes and carbide found at inter- and intra-granular region. The carbide in Co–29Cr–6Mo–0.18C was identified as M23C6 type carbide from the XRD pattern analysis. It is found that the amount of stacking fault and ε martensite are strongly dependent upon the C content. The density of stacking faults and ε martensites observed in Co–29Cr–6Mo–0.09C decrease as compared with those observed in Co–29Cr–6Mo–0.02C. Moreover, the volume fraction of the γ phase slightly increased with C content. Within an extent of C addition that no carbide precipitation occurs, the carbon addition reduces the amounts of crystal defects such as stacking faults and twins, and ε martensites. In addition, tensile strength slightly increases with C content and ductility reaches a maximum at C content of 0.09%, though 0.2% proof strength shows no noticeable differences.
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  • Jestine Ang, Akihiro Sato, Kyoko Kawagishi, Hiroshi Harada
    2006 Volume 47 Issue 2 Pages 291-294
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    A novel family of bond coats designed to be in EQuilibrium with their nickel-base superalloy substrates has been developed. These coatings have hence been termed ‘EQ coatings’. The first step taken for EQ coating development was to examine the γ–γ′ tie-lines of several superalloys. In these superalloys, γ and γ′ are in equilibrium with each other, and elemental activities are thus equal in these two phases. With equal activities, there will be no chemical potential differences between the two phases, and there is thus no driving force for diffusion. Applying γ,γ′, or a combination of both as bond coat candidates will ensure that no inter-diffusion zone (IDZ) will form. This is desirable, as IDZ causes gross local mechanical property degradation.
    In this paper, the γ′ volume fraction was varied from 0 to 100% at 25% intervals along the γ–γ′ tie-line of a nickel-base single-crystal alloy, TMS-82+. Cyclic and isothermal oxidation tests were conducted at 1100°C in ambient atmosphere. The resultant oxide structures, and the element concentration profiles from around the oxide/substrate interface, through the depletion zone, into the sound substrate, were analyzed by SEM/EDX.
    All samples started with the same element activities; hence, at the onset of oxidation, all samples were expected to form the same oxide structure. However, experiments showed that the specimens formed vastly different oxide structures, and that γ′ had the best resistance against high temperature oxidation.
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  • Masatomo Yashima, Kazuhiko Maeda, Kentaro Teramura, Tsuyoshi Takata, K ...
    2006 Volume 47 Issue 2 Pages 295-297
    Published: 2006
    Released: February 17, 2006
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    Gallium zinc oxynitride (Ga0.93Zn0.07)(N0.90O0.10) is a new type of photocatalyst that is capable of overall water splitting under visible light. The crystal structure of the (Ga0.93Zn0.07)(N0.90O0.10) was refined by Rietveld analyses of neutron powder diffraction data. The (Ga0.93Zn0.07)(N0.90O0.10) was confirmed to have a wurtzite-type structure (space group: P63mc). The present work demonstrates that oxygen substitutes for nitrogen in the crystal structure, and may be responsible for the desirable optical properties of (Ga0.93Zn0.07)(N0.90O0.10) as a photocatalyst for visible light-driven overall water splitting. The neutron scattering amplitude distribution through the maximum-entropy method (MEM) and MEM-based pattern fitting revealed that the crystal structure of the (Ga0.93Zn0.07)(N0.90O0.10) is free of interstitial sites and large disorder.
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  • Satoshi Kojima, Hidetoshi Fujii
    2006 Volume 47 Issue 2 Pages 298-301
    Published: 2006
    Released: February 17, 2006
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    At the fractured tip of thin foil metals, heavy deformation takes place. At this heavily deformed region, vacancies play an important role. In Al–Pb alloy, lead precipitates are separated into small particles which are considered to be a result of enhanced diffusion by excess vacancies. The production source for these vacancies is considered to be internal nanocracks. In order to test this hypothesis, voids were searched in thin foil aluminum and gold, and void formation was confirmed in gold. It is considered that nanocracks not only become nuclei of voids but also contribute to the growth of voids by glide motion. The “Nanocrack fragment” model was proposed in order to account for the slide motion of nanocracks.
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  • Shuji Tada, Kenji Aoki, Zheng Ming Sun, Hitoshi Hashimoto
    2006 Volume 47 Issue 2 Pages 302-305
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    A Concurrent process for the synthesis and fabrication into rods of the machinable ceramic Ti3SiC2 by using a traveling-zone sintering method was investigated. Two different powder mixtures were prepared for the synthesis of Ti3SiC2. The first (TSC1) had the stoichiometric composition of Ti/Si/C = 3:1:2. In the second (TSC2), TiC was used instead of C to give a molar composition Ti/Si/TiC = 2:2:3. In the production of Ti3SiC2 rod from TSC1, there was a tendency for the cylindrical mold to become cracked during the sintering, because the synthesis of Ti3SiC2 from the simple mixture of Ti, Si and C occured by a tandem process and the primary exothermic reaction of Ti with C to form TiC caused a large thermal expansion of the material compact. On the other hand, Ti3SiC2 rod was successfully produced from the TSC2 mixture. Their density was elevated as increasing the sintering temperature and reducing the rate of movement of the stage, but employing too high temperature caused a reaction between the material powder and the mold, resulting in the product having unsatisfactory properties. The Ti3SiC2 rod produced contained varying amounts of TiC phase, the percentage of which showed a tendency to decrease under the same sintering conditions required to obtain a high density. We concluded that a well-densified, homogeneous Ti3SiC2 rod with high purity can be produced by the traveling-zone sintering method under the sintering conditions of a high temperature and a prolonged sintering time, if attention is paid to preventing reaction between the material compact and the mold.
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  • Hongbo Guo, Hideyuki Murakami, Seiji Kuroda
    2006 Volume 47 Issue 2 Pages 306-309
    Published: 2006
    Released: February 17, 2006
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    Thermal barrier coatings (TBCs) with different levels of segmentation crack densities (Ds) were sprayed at different substrate temperatures (Ts). Thermal cycling resistance of the TBC specimen was examined. The segmented coating significantly improved the thermal cycling resistance as compared to the traditional non-segmented coating. Maximum thermal cycling lifetimes were achieved in the coating with a crack density level of 2.2 mm−1. New segmentation cracks were hardly generated during thermal cycling testing. Spallation of segments within the segmented coating occurred, which is different from spallation of the whole coating from substrate in the case of traditional coating. Oxidation of bond coat and limited phase decomposition of YSZ topcoat were considered as not responsible for the failure of TBCs.
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  • Mitsuharu Yonemura, Takahiro Osuki, Hidenori Terasaki, Yuichi Komizo, ...
    2006 Volume 47 Issue 2 Pages 310-316
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Characterizing of directional solidification mode of Fe–Cr–Ni alloys during welding was performed using intense synchrotron radiation probe. Consequently, the crystal growth in the rapid solidification process was revealed in detail and the peak profile was systematically analyzed in order to acquire the essential information for controlling the weld microstructure. Then, the crystallization timing of the primary and secondary phases was discussed. Furthermore, the possibility of the lattice rotation to commensurate (i) each dendrite and (ii) crystallites in the dendrites is suggested.
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  • Jin Liang, Nader Dariavach, Paul Callahan, Dongkai Shangguan
    2006 Volume 47 Issue 2 Pages 317-325
    Published: 2006
    Released: February 17, 2006
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    The wetting of a molten solder on metallic surfaces is a rather complex phenomenon. In addition to physical spreading due to surface tension reduction, there are interfacial metallurgical and flux chemical reactions with the metallic substrate surface. Substrate dissolution and intermetallic formation take place rapidly during soldering. Since lead-free soldering requires substantially higher soldering temperatures (around 250°C), the rates of intermetallic growth and substrate dissolution for lead-free solders are expected to be significantly greater than those for the current Sn–Pb eutectic solder. This study systematically investigates the metallurgy of the solid–liquid interface reactions and intermetallic growth kinetics for three lead-free solders: Sn–Ag eutectic (96.5%Sn–3.5%Ag), Sn–Cu eutectic (99.3%Sn–0.7%Cu) and Sn–Ag–Cu eutectic (Sn–3.8Ag–0.7Cu, SAC 387) with three metallic substrates: Cu, Ni, and Alloy 42 (42%Ni–52%Fe) over temperatures ranging from 225 to 280°C for reaction time from 10 s to 16 h. Wetting behavior of these three alloys on PCBs with OSP, immersion Sn, and Ni/Au finishes, was also examined from 220°C up to 260°C. A thorough understanding of lead-free solder/substrate interfacial reactions should give guidance to the optimum lead-free soldering processes and to the optimum lead-free coating thicknesses for component and PCB terminal finishes, as well as for under-chip metallurgical coatings for flip-chip and BGA applications.
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  • Nguyen Van Duc, Takuya Ohba
    2006 Volume 47 Issue 2 Pages 326-330
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Precursor phenomenon on the martensitic transformation was studied in Au50.5Cd49.5. For the precursor study, single variant of ζ2′ martensite was produced and the reverse transformation process was utilized to avoid a superposition of several variants in diffraction experiments through the martensitic transformation, i.e. from parent to martensite phase. Atomic parameters in martensite state were refined with use of single crystal structure determination procedure by X-ray at various temperatures approaching the reverse transformation temperature. Atomic positional parameters of some atoms which are expected to have relatively large displacements from parent phase showed first-order feature.
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  • Masataka Hattori, Nobuhiro Goto, Yoshinori Murata, Toshiyuki Koyama, M ...
    2006 Volume 47 Issue 2 Pages 331-334
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Interdiffusion coefficients of the refractory elements in Ni–X–Y (X, Y=W, Re, Ru, Al) ternary systems, which are the fundamental systems of Ni-based superalloys, were estimated by a series of experiments using diffusion couples. The modified ternary Boltzmann–Matano method was employed for analyzing the experimental data. The cross interdiffusion coefficients were smaller than the main interdiffusion coefficients in all systems. Especially, the cross interdiffusion coefficient \\ ildeDReRuNi is much smaller by an order of magnitude than the main interdiffusion coefficient \\ ildeDReReNi in Ni–Ru–Re system. This result indicates that the thermodynamical interaction parameter (Wagner’s interaction parameter) between Ru and Re is negligible, and implies that Ru does not affect the distribution behaviour of Re into γ and γ′ phases.
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  • Akihiro Nino, Takeshi Nagase, Yukichi Umakoshi
    2006 Volume 47 Issue 2 Pages 335-340
    Published: 2006
    Released: February 17, 2006
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    Change in nanocomposite structure in rapidly solidified Fe86Nd9B5 alloy during electron irradiation was investigated. Nanocrystalline structure composed of α-Fe, Fe3B, Nd2Fe14B and Nd2Fe23B3 crystalline phases was formed by rapid solidification. Electron irradiation can introduce amorphization of intermetallic compounds and crystallization of an amorphous phase, resulting in the formation of a novel nanocomposite structure in which α-Fe and Nd2Fe14B nanocrystals are embedded in the amorphous matrix. The mechanism of nanocomposite structure formation was discussed based on the phase stability of amorphous and crystalline phases under electron irradiation.
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  • Naoki Miyano, Takahiro Norimura, Teruhiko Inaba, Kei Ameyama
    2006 Volume 47 Issue 2 Pages 341-347
    Published: 2006
    Released: February 17, 2006
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    The triangular phase in Ti–15V–3Cr–3Sn–3Al is observed after two-step aging. The three-dimensional shape of the phase is a triangular pyramid that is composed of three precipitates. The reason for the formation of the triangular shape is investigated by means of crystallographic analysis and high-resolution TEM observations. According to the HR-TEM observations, it is possible that the triangular phase has Potters OR with the matrix despite the existence of Burgers OR in an intragranular precipitate, as reported in previous studies. This suggests that in the alloy under consideration, the OR between the precipitate and the matrix is selectable in terms of lattice correspondence. As for the growth direction of the precipitate, an invariant line is investigated. Although the three precipitates have a common direction, which is [2\\bar1\\bar10]α⁄[111]β, their invariant lines are not parallel with each other, i.e., [\\bar447]α1, [\\bar744]α2, and [4\\bar74]α3. Therefore, the precipitates expand along each direction while growing and form a triangular shape.
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  • Kyong-Ho Chang, Chin-Hyung Lee
    2006 Volume 47 Issue 2 Pages 348-354
    Published: 2006
    Released: February 17, 2006
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    In this study, high temperature tensile properties of high strength steels, POSTEN60 and POSTEN80, whose tensile strengths were 600 and 800 MPa respectively, were investigated through the elevated temperature tensile test. Residual stress measurements were also carried out to estimate the residual stress relaxation due to phase transformation (martensite transformation) in the process of cooling after welding. A finite element (FE) model which was able to include the volumetric changes due to the austenite → martensite phase transformation was developed on the basis of the experimental results. The three-dimensional thermal elastic-plastic FE analyses using the FE model were conducted to determine residual stresses in weldments of the high strength steels.
    The results show that the extents of residual stress relaxation due to the austenite → martensite phase transformation in the process of cooling after welding are approximately 0.85 σx⁄σY0 and 0.75 σx⁄σY0 in the FZ and HAZ of POSTEN60 and POSTEN80, respectively. And residual stresses of weld line direction in the base metal (BM) which is adjacent to HAZ, therefore, do not undergo martensitic transformation increase (655MPa<870MPa) with increasing tensile strength of the high strength steels (POSTEN60 < POSTEN80).
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  • Woei-Shyan Lee, Tao-Hsing Chen
    2006 Volume 47 Issue 2 Pages 355-363
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The dynamic mechanical properties of high strength aluminum–scandium (Al–Sc) alloy are investigated using a compression split Hopkinson bar. Dynamic impact testing is carried out at nominal strain rates (abbreviated to strain rate hereafter) ranging from 1.2×103 to 5.8×103 s−1 at room temperature. The effects of strain rate on the mechanical properties, microstructural evolution and fracture characteristics are investigated and the relationship between the mechanical properties of the alloy and its microstructure is explored. The measured strain–stress curves reveal that the dynamic mechanical behaviour of Al–Sc alloy is highly dependent on the strain rate. The flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but the fracture strain and activation volume decrease. The Zerilli–Armstrong fcc constitutive law is used to model the shear flow response of the Al–Sc alloy. A good agreement is found between the predicted and measured shear flow responses. The Al–Sc alloy specimens fracture as a result of shear band formation and crack propagation within the shear band. SEM observations indicate that the fracture features are dominated by a transgranular dimple-like structure. The density and depth of the dimples decrease with increasing strain rate. TEM microstructural observations reveal that the presence of Al3Sc precipitated particles in the matrix and at the grain boundaries prevents dislocation motion and leads to a significant strengthening effect. An analysis of the dislocation substructure indicates that a higher strain rate increases the dislocation density, thereby reducing the size of the dislocation cells. The variations of the dislocation cell structure reflect different degrees of strain rate sensitivity and activation volume, and correlate well with the impact flow stress–strain response.
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  • Satoshi Sunada, Masanori Kariba, Kazuhiko Majima, Katsuhisa Sugimoto
    2006 Volume 47 Issue 2 Pages 364-370
    Published: 2006
    Released: February 17, 2006
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    A stress corrosion cracking (SCC) test was carried out at room temperature in aqueous solutions containing both H2SO4 (0–5.5 kmol·m−3) and NaCl (0–4.5 kmol·m−3), in order to study the influences of both solutes on the corrosion type of SUS304 steel. The two solutes have synergistic influence on the corrosion type, that is, SCC and general corrosion occur within a specific concentration range and elsewhere, respectively. For a constant H2SO4 concentration the mass loss of corrosion shows a V-shape when it is plotted against NaCl concentration. On the other hand, maximum crack length of the SCC increases with increasing NaCl concentration up to a certain value, and then decreases. This gives a nearly inverse V-shape curve. In addition, the NaCl concentration ranges for the minimum mass loss and for the maximum crack length are almost the same. It was also confirmed that NaCl concentrations showing the minimum mass loss and the maximum crack length are inversely proportional to H2SO4 concentrations.
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  • Huey-Jiuan Lin
    2006 Volume 47 Issue 2 Pages 371-374
    Published: 2006
    Released: February 17, 2006
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    A green process has been successfully developed to mass-produce carbon nano-tubes (CNTs) using electric-arc-furnace (EAF) dusts as the catalyst. The CNTs were prepared by a thermal CVD process with the gas mixture acetylene and nitrogen flown directly on the EAF dust that was firstly treated by a reduction period. Preliminary experimental results illustrated that CNTs were easily synthesized in large quantity and in curly shapes. The characteristics of as-grown CNTs were evaluated by transmission electron microscopy and Raman spectrometry to be of good graphitic structure. This production method is extremely meaningful both environmentally and industry-wise.
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  • Huey-Jiuan Lin, Hsuan-Chung Wu, Tzu-Ray Shan, Weng-Sing Hwang
    2006 Volume 47 Issue 2 Pages 375-382
    Published: 2006
    Released: February 17, 2006
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    The formation and ejection behavior of droplets created by a squeeze mode piezoelectric inkjet printing device using a double pulse voltage pattern are investigated in this study. Two types of fluid, de-ionized (DI) water and ethylene glycol, are used. The effects of operating frequency, positive voltage keeping time and pulse voltage magnitude on the volume and velocity of the droplets are discussed. The experimental results are consistent with the propagation theory of acoustic waves. The maximum allowable pulse frequencies in DI water and ethylene glycol are 2,000 and 22,700 Hz respectively. If the positive voltage keeping time equals the time required for the acoustic waves to propagate through the printhead, optimal ejection behavior is achieved. As the pulse voltage increases, both the velocity and volume of each droplet become larger.
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  • Kazuhiro Hasezaki, Yoshinori Morisaki, Hiroshi Araki, Hiroyuki Kitagaw ...
    2006 Volume 47 Issue 2 Pages 383-387
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    A plastic deformation process and ratio study of p-type Bi0.5Sb1.5Te3 was performed. The ingots were grown by the Bridgman method. Disks were cut from the ingots and deformed by either cold-pressing or by hot-pressing under pulse current heating. The plastic deformation ratio was controlled from 55 to 90%. The crystal structures of the deformed samples were identified by X-ray diffraction and pole figure analyses. The diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Thermoelectric properties change depending on not the plastic deformation ratio but the kind of plastic deformation process. The power factor for hot-press deformed samples exceeded those for the original ingots and cold-press deformed samples. The results suggest that the process of hot-press deformation enhances the thermoelectric properties of p-type Bi0.5Sb1.5Te3.
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  • Yifang Ouyang, Xiaping Zhong, Hongwei Shi, Yong Du, Yuehui He
    2006 Volume 47 Issue 2 Pages 388-391
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Amorphous Al2FeZr6 alloy was prepared from elemental powders by mechanical alloying. The microstructure evolution was identified by X-ray diffraction. The thermal stability of amorphous Al2FeZr6 was determined by DTA. There are two overlapped exothermic peaks observed in curves of DTA. This indicates that two exothermic reactions in the procedure of crystallization of amorphous Al2FeZr6 alloy. The effective activation energies of crystallization were evaluated using Kissinger’s plot. The evaluated values of effective activation energy corresponding to the first and the second exothermic reactions are 266 and 299 kJ/mole respectively. The products of crystallization of amorphous Al2FeZr6 alloy are binary intermetallic compounds AlZr2 and FeZr2 instead of intermetallic compounds Al2FeZr6. It was explained by comparing their relative stabilities based on enthalpies of formation of intermetallic compounds.
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  • Shijie Guo, Qichi Le, Yi Han, Zhihao Zhao, Jianzhong Cui
    2006 Volume 47 Issue 2 Pages 392-398
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The effects of electromagnetic vibration on macrosegregation in AZ80 magnesium alloy billets have been investigated experimentally. Comparing to conventional direct-chill casting, the enrichment for the alloying elements close to the billet surface is significantly reduced by the electromagnetic vibration. Increasing the stationary magnetic field, i.e., increasing the intensity of the electromagnetic vibration results in uniform distributions of the metallic elements in the billet. The distribution of impurity iron has the same tendency with alloying element manganese with and without the electromagnetic vibration. The uniformity in the concentration profile of iron is higher than that for the alloying elements in the billet and increases with increasing the stationary magnetic field of the system used for generation of electromagnetic vibration.
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  • Tomoyuki Nishida, Hidekazu Sueyoshi
    2006 Volume 47 Issue 2 Pages 399-404
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Five carbons with different graphitization degrees, which were heat-treated at temperatures of 1273 to 3273 K, were prepared. These carbons were bonded to nickel in a vacuum, using an RF-induction furnace, with joining temperatures of 1073 to 1273 K. On the basis of the results of these experiments, the effects of the graphitization degree on the solid-state bonding of carbon to nickel were examined. Carbon heat-treated at 1273 K remains amorphous, whereas most of the carbons heat-treated at 3273 K change into graphite because the graphitization degree increases with increasing heat treatment temperature. Strong bonding of amorphous carbon to nickel is not accomplished. The bending strength or joinability of carbon (with a graphitization degree lower than 0.28)/nickel joints depends on the joining temperature. Good bonding of carbon with a graphitization degree higher than 0.28 to nickel is achieved regardless of the joining temperature. The graphitization degree and thermal stress affect the joinability and bending strength of the joints.
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  • Hiroyuki T. Takeshita, Yasuhiro Kamada, Akihiro Taniguchi, Tetsu Kiyob ...
    2006 Volume 47 Issue 2 Pages 405-408
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The effect of melting of LiAlH4 on its dehydrogenation properties was examined using Differential Scanning Calorimetry (DSC). LiAlH4 samples purified in advance were examined on their hydrogen desorption behaviors in the various heating conditions in which some of them were melted and the others not. Some of the as-received samples were mechanically ground in an Ar atmosphere for a short time of period using a ball milling machine and then supplied to DSC measurements. The color of the sample after milling changes from gray-beige to grey, probably due to contamination of metal elements such as iron and chromium from hardened steel vessel and balls during grinding. The rapid hydrogen desorption was observed for the samples melted by heating, whereas the insignificant hydrogen desorption was observed for the ones which were not melted by heating, in spite that heating and cooling were repeated three times. The time from melting to decomposition of LiAlH4 accompanied by hydrogen desorption was 90±30 s, independent of hydrogen desorption temperature. The samples milled in hardened steel vessel using a planetary-type ball milling machine exhibited about 2 K lower melting temperature and 15 K lower hydrogen desorption temperature than the as-purified samples. These changes can be considered to happen because contamination metal elements contributed to lowering a melting temperature and worked as a catalyst to decrease the activation energy for decomposition of liquefied LiAlH4. These results indicate that metal elements such as iron and chromium certainly contribute to improve hydrogen desorption temperatures of alanates, as reported in many papers, but it is more important to lower their melting temperatures in order to improve their hydrogen desorption kinetics.
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  • Jiunn-Yuan Huang, Ji-Jung Yeh, Sheng-Long Jeng, Charn-Ying Chen, Roang ...
    2006 Volume 47 Issue 2 Pages 409-417
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    High-cycle fatigue tests were conducted to investigate the effects of temperature, stress ratio (R), specimen orientation, welding and specimen size on the fatigue behavior of type 316L stainless steel. The high-cycle fatigue test results indicated that the fatigue limits significantly decreased when the stress ratio (R) decreased. The corresponding fatigue limits were reduced to lower values when tests were conducted at 300°C, compared to those obtained at room temperature. The fatigue behavior and fatigue limits of standard and subsize specimens were observed to be consistent at both room temperature and 300°C. The constant life diagram was established from the S–N curves acquired. The fatigue limit strongly depended on the materials strength, which was a function of specimen orientation, test temperature, and welding processes. The dimension of the fatigue damaged area on a fracture surface increased as the stress ratio decreased. In the case of R=−1.0, the fatigue damaged region extended over the whole fracture surface. The subgrain boundaries after high-cycle fatigue tests were clearly demonstrated by their diffraction patterns, which were related to the dynamic recovery of multiple dislocations.
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  • Kazuhiro Yoshida, Hiroshi Mishina, Shinya Sasaki, Masafumi Morita, Kiy ...
    2006 Volume 47 Issue 2 Pages 418-425
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    TiC/Ti and TiC/Ti–15Mo cermets were fabricated for the bearings of joint prostheses and were then evaluated in terms of their mechanical properties, such as density, hardness, bending strength and fracture toughness, as well as biocompatibility. The cermets were fabricated by spark plasma sintering. When the volume fraction of the metal phase was increased, the fracture toughness and the bending strength of the TiC/Ti and TiC/Ti–15Mo increased. The TiC/Ti and the TiC/Ti–15Mo cermets show high biocompatibility and corrosion resistance. These results indicate that TiC/Ti–15Mo cermets are suitable for use in the bearings of joint prostheses.
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  • Shih-Hsien Chang, Shih-Chin Lee, Tzu-Piao Tang, Hsin-Hung Ho
    2006 Volume 47 Issue 2 Pages 426-432
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Hot Isostatic Pressing (HIP) is widely used in the casting industry to remove the internal porosity generated during the casting process. It combines higher pressure and temperature to produce materials and parts with substantially better properties than those by other methods. This results in improved strength, ductility and fatigue life of castings. The aim of this paper is to discuss the methods and to find a suitable soaking time of HIP for Inconel 718 superalloy castings. In this study, the HIP temperature was maintained at 1453 K, pressure was kept 175 MPa and three different soaking time are 2, 3 and 4 h. The experiment results show that HIP treatment at 1453 K under the pressure of 175 MPa for 4 h for Inconel 718 superalloy is the optimum condition. It can decrease the porosity of Inconel 718 superalloy castings. In this study, it can reduce porosity about 86% after HIP treatment. For the tension test at a fast strain rate (0.001 s−1) that it increased the tensile strength by 31% at room temperature, 27% at 813 K, and 24% at 923 K. While at a very slow strain rate (0.0001 s−1), it increased the tensile strength by 24% at room temperature and 20% at 813 K. For a 3-point bending test, it showed that the optimum soaking time of HIP procedure could enhance the bending strength by 38% at room temperature and 26% at 813 K.
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  • Chao-Chi Jain, Chun-Hao Koo
    2006 Volume 47 Issue 2 Pages 433-439
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    In this study, the effect of RE content on the microstructure and creep properties of Mg–8Al–xRE (x=0, 1, 2 or 3 mass%) alloys were investigated. The microstructural analysis and phase characterizations of Mg–8Al alloy with 1–3 mass% RE (La-rich Mischmetal) additions were conducted. (i) The as-extruded Mg–8Al–xRE alloys consisted of an α-Mg matrix, β (Mg17Al12) and Al11RE3 compounds. (ii) Raising the extent of RE in the alloy also increases the amount and coarsening of the Al11RE3 compounds, but the amount of β phase diminishes and turns into the fine particles. The creep rupture life increment measured at 423 K is around 40–100 MPa, and the creep rupture life over 423 K is also prolonged. The marked improvement in high-temperature tensile creep properties is attributed to the fine rod-like Al11RE3 compound having high thermal stability in the alloys.
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  • Chau-Jie Zhan, Chun-Hao Koo
    2006 Volume 47 Issue 2 Pages 440-445
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The creep behavior of the Ti–40Al–16Nb alloy and the effect of the minor addition of Sc are investigated by creep tests at 1073 K under constant load from 200 to 280 MPa. The creep curve of the alloy with high Nb contents does not exhibit a steady-state region, and the minor addition of Sc added to the alloy has no effect on minimum creep rate. The creep responses of the alloys with high Nb contents are strongly correlated with tertiary creep behavior. The effects of Sc addition are apparent on the properties of tertiary creep rate and rupture life. The tertiary creep rate of the Sc containing alloy is reduced and the creep fracture life is increased. Subgrain structures of dislocations are absent in the alloys with high Nb contents during secondary creep, and the deformation of creep converges mainly at the B2 phase. A stress exponent of 4.5 estimated indicates that the mechanism of controlling creep behavior is dislocation climb. The creep fracture of the alloys is dominated by cleavage fracture over the entire fracture surface. Sc2O3 particles are an effective obstacle to the propagation of cracks and the motion of dislocations.
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  • Liming Liu, Zhaodong Zhang, Gang Song, Yong Shen
    2006 Volume 47 Issue 2 Pages 446-449
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    The Cadmium Chloride flux increases the weld penetration evidently in the Alternating Current Tungsten inert gas (AC TIG) welding of magnesium alloy. In the present study, in order to investigate the effect of the CdCl2 active flux on the weld shape and arc voltage, bead-on-plate specimens are made on AZ31B magnesium alloy pre-placed with CdCl2 active flux by the AC TIG process. Weld pool cross-sections and the arc voltage are analyzed under different welding parameters, welding speed, weld current and arc length. The results showed that compared to the conventional AC-TIG, welding penetration and the weld depth/width with CdCl2 flux are both two times greater than that of without flux under optimal parameters. The voltage decreases with decreasing of travel speeds and arc length decreasing. Besides, the phenomenon of arc trailing in the EN period and arc contraction in the EP period were observed in AC TIG welding of magnesium alloy with CdCl2 flux. It found that the arc voltage increases with the increases of welding current, more energies are supplied for welding, resulting in the increases of arc voltage and weld penetration.
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  • Jun Luo, Huiping Duan, Chaoli Ma, Shujie Pang, Tao Zhang
    2006 Volume 47 Issue 2 Pages 450-453
    Published: 2006
    Released: February 17, 2006
    JOURNALS FREE ACCESS
    Effects of yttrium and erbium additions on glass-forming ability (GFA), thermal stability and mechanical properties of glassy Zr55Al10Ni5Cu30 alloy were studied. (Zr0.55Al0.10Ni0.05Cu0.30)100−xREx (RE = Y, Er and x=0,0.5,1,2,3,5 at%) metallic glasses were formed by melt-spinning and copper mold casting. It was found that the addition of Y or Er greatly enhanced the glass-forming ability, thermal stability and mechanical properties of Zr55Al10Ni5Cu30 alloy. The alloys containing 1–3 at% Er can be cast into glassy rods with a diameter of 15 mm, which is larger than the critical diameter (10 mm) of the base alloy in the present work. With the addition of 1 at% Y, supercooled liquid region ΔTx of the base alloy was extended from 89 to 102 K, compressive strength was increased from 1650 to 1800 MPa and plastic strain reached a value as high as 3.5%.
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