MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 51 , Issue 2
Showing 1-41 articles out of 41 articles from the selected issue
  • Frantisek Schauer, Petr Schauer, Ivo Ku\\v{r}itka, Hua Bao
    2010 Volume 51 Issue 2 Pages 197-201
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: November 26, 2009
    JOURNALS FREE ACCESS
    The comparison of the susceptibility of aryl-substituted polysilanes to the photodegradation by electron beam (EB) and UV radiation is examined on the prototypical material, poly[methyl(phenyl)silylene] (PMPSi). The main purpose of this paper is to compare the photoluminescence (PL) and cathodoluminescence (CL) after major degradation, predominantly in the long wavelength range of 400–600 nm, studying the disorder due to dangling bonds, conformational transformations and weak bonds created by the degradation process. The UV degradation was a completely reversible process, whereas the EB degradation process was only reversible, provided certain material specific level of degradation was not exceeded. This observation supports different paths and final states in both UV and EB degradations. The results serve for the optimization of polysilane nanoresists.
    Download PDF (140K)
  • Ji\\v{r}ina Mat\\v{e}jková-Plšková, Dalibor Janci ...
    2010 Volume 51 Issue 2 Pages 202-208
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: November 18, 2009
    JOURNALS FREE ACCESS
    The hindwings of the male Sasakia charonda charonda butterflies comprise iridescent purple-blue areas, iridescent white-pearl areas, yellow spots and red spots as well as brown background. We have examined the microstructure of their scales by scanning electron microscopy, for applying their photonic crystal structures to fine light manipulators such as reflection elements in laser diodes. The scales in the yellow spots, red spots and brown background have almost the same structure, which is an optical diffraction grating made of ridges with two cuticle layers. Their difference comes from the contained pigments. The scales in the iridescent purple-blue and white-pearl are also the same in structure. They have seven tilted cuticle layers lapped on the ridges, which also constitute a grating. The widths of the ridge and groove in the grating are different between scales of the two kinds. It is shown that the vivid iridescence is mainly attributed to multiple interferences caused between rays reflected from the seven cuticle layers with air gaps.
    Download PDF (4090K)
  • Ond\\v{r}ej Man, Libor Pant\\v{e}lejev, Ludvík Kunz
    2010 Volume 51 Issue 2 Pages 209-213
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Thermal stability of ultrafine-grained (UFG) structure of 99.9% pure copper produced by eight equal channel angular pressing (ECAP) passes was studied. The annealing experiments were conducted at 180°C in a tube furnace under argon as a covering gas. The dwell times were in the range of 10 min to 120 min. The electron backscattering diffraction (EBSD) analyses were performed before and after annealing at exactly the same area in order to quantify the degree of decomposition of the UFG structure. Definition of grain boundaries was based on the misorientation angle of 1°. More advanced analysis of the EBSD results based on a kernel average misorientation (KAM) parameter was performed. Inverse pole figure maps with included grain networks did not reveal any substantial changes of UFG microstructure due to annealing. Some shift in the KAM modus in comparison with the initial state was observed but its magnitude was found negligible. Also changes in texture were found to be minor. On the other hand the microhardness increases with increasing time of annealing.
    Download PDF (3362K)
  • Zuzana Pokorná, Lud\\v{e}k Frank
    2010 Volume 51 Issue 2 Pages 214-218
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 02, 2009
    JOURNALS FREE ACCESS
    Reflection of very slow electrons from solid surfaces has been reported to be inversely proportional to the local density of electronic states coupled to the incident electron wave. The reflected electron flux at units of eV used as the image signal in a scanning electron microscope allows mapping of the local density of states at high spatial resolution. Good performance of the microscope at very low energies is enabled by introducing the beam-retarding immersion lens (the cathode lens) with a biased specimen serving as the cathode. Results of demonstration experiments on aluminum are provided.
    Download PDF (1257K)
  • Miran \\v{C}eh, Hsing-Chao Chen, Miin-Jang Chen, Jer-Ren Yang, Makoto ...
    2010 Volume 51 Issue 2 Pages 219-226
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 02, 2009
    JOURNALS FREE ACCESS
    Al-doped ZnO thin films were prepared on the (0001) sapphire (c-Al2O3) substrates by atomic layer deposition (ALD) using alternating pulses of Zn(C2H5)2, Al(CH3)3 and H2O precursors and post-deposition high-temperature annealing. Photoluminescence (PL) spectroscopy showed that the threshold of stimulated emission decreases with increasing Al concentration, from 49.2 kW/cm2 of the ZnO film to 12.2 kW/cm2 of the ZnO film nominally containing 4% Al. This reduction is attributable to the increase in the optical scattering resulting from segregation of excess Al in heavily Al-doped ZnO films. The structure of these films was investigated by analytical scanning-transmission electron microscopy (STEM) as well as X-ray diffraction (XRD). It was revealed that a single crystal ZnO layer containing a small amount of Al is formed with the orientation relation with respect to the c-Al2O3: [0001]ZnO || [0001]Al2O3 and [01\\bar10]ZnO || [2\\bar1\\bar10]Al2O3, and that a polycrystalline ZnAl2O4 layer is formed between the ZnO layer and the c-Al2O3 substrate. The electron microscopy observation accounts for the results of the electro-optical experiments. The growth mechanism of the observed two layers is discussed.
    Download PDF (4095K)
  • Lingwei Li, Eitaro Sakada, Katsuhiko Nishimura
    2010 Volume 51 Issue 2 Pages 227-230
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 02, 2009
    JOURNALS FREE ACCESS
    A series of single-phased La(Pt1−xAux)4Ge12 compounds were prepared by an arc-melting method. The crystal structure and basic superconductivity parameters have been systematically investigated by X-ray diffraction and by examining the temperature and field dependences of electrical resistivity, magnetization and heat capacity. The lattice parameter a increases and the superconducting transition temperature Tc decreases gradually with increasing Au content x. The low critical field Hc1(T) and the upper critical field Hc2(T) were estimated from the isothermal magnetization (M-H-T) and electrical transport (ρ-H-T) measurements, respectively. The evaluated Hc1(0) and Hc2(0) indicate a decrease tendency with increasing x, and enable us to deduce the coherence length ξ(0), penetration depth λ(0), Ginzburg-Landau parameter κ(0) and thermodynamic critical field Hc(0). The present results are compared with those of the related systems.
    Download PDF (793K)
  • Hiroshi Saijo, Makoto Shiojiri
    2010 Volume 51 Issue 2 Pages 231-236
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 09, 2009
    JOURNALS FREE ACCESS
    We have constructed a cathodoluminescence (CL) detection system that records the CL spectra emitted from each point raster-scanned by the incident electron probe in a conventional scanning electron microscope. The CL spectrum is detected by a 32 channel high-speed high-sensitive photoelectron multiplier array set behind the spectrometer. The shortest signal sampling time is 8 s for a frame of 512×512 pixels and all the imaging and spectroscopic signals are stored in two 8-megabyte files. Maximum image size is 2048×2048 pixels. The microscope displays a spectral accurate full color (whole spectrum) CL image, twenty-nine monochromic images and the spectrum of each pixel point in the corresponding secondary electron image. The spatial resolution of CL image reaches 25 nm by reducing the quantum noise and the phosphorescent delay effect using a slow signal sampling time of 40 s with a 6-keV incident electron probe. Some examples are demonstrated using SnO2-doped ZnO-Ba2O3 ceramics and photosensitive cyanine dyes.
    Download PDF (7606K)
  • Miloš Hovorka, Filip Mika, Petr Mikulík, Lud\\v{e}k Fran ...
    2010 Volume 51 Issue 2 Pages 237-242
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 09, 2009
    JOURNALS FREE ACCESS
    Variously doped n-type structures (dopant concentration between 1.5*1016 cm−3 and 1.5*1019 cm−3) on a lightly doped p-type silicon substrate (doped to 1.9*1015 cm−3) have been examined by a photoemission electron microscope equipped with a high-pass energy filter and by an ultra-high vacuum scanning low energy electron microscope. High contrast have been observed between the n-type areas and the p-type substrate and its monotone dependency on the doping level of structures has been manifested. The relation between the energy spectra of photoelectrons and the doping level has been studied, too. The scanning electron microscope images obtained with the landing energy of the primary beam in the low keV range exhibit contrasts similar to those appearing in the full threshold photoemission micrographs.
    Download PDF (1026K)
  • Wen Zeng, Tianmo Liu, Zhongchang Wang
    2010 Volume 51 Issue 2 Pages 243-245
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 16, 2009
    JOURNALS FREE ACCESS
    TiO2-doped SnO2 nanopowder is synthesized via a sol-gel method and characterized by atomic force microscopy and X-ray diffraction. Using this nanopowder, we have fabricated a novel semiconductor gas sensor that is sensitive to UV light illumination. We find that gas-sensing properties of TiO2-doped SnO2 sensor can be enhanced significantly under the exposure of UV light. The sensor exhibits a high sensitivity of 25 and rapid response-recovery times of 8 s and 24 s, respectively, under an ethanol gas of up to 100 ppm at room temperature (323 K). This suggests the possibility of development of a gas sensor for detecting ethanol at room temperature.
    Download PDF (362K)
  • Prasonk Sricharoenchai, Nurot Panich, Patama Visuttipitukul, Panyawat ...
    2010 Volume 51 Issue 2 Pages 246-252
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 07, 2010
    JOURNALS FREE ACCESS
    Fabrication and development of TiB2-based nanostructured coatings was investigated in the present work. By varying the sputter-target power density, substrate temperature, deposition time, substrate-to-target distance, substrate biasing and substrate sputter cleaning, the relationship between the sputtered structure, properties and sputtering conditions were established. The experimental results showed that the target-to-substrate distance played a major role in the coating structure and properties. Sputter cleaning of substrate helped to improve TiB2 coating hardness and adhesion. The deposition process could be controlled to produce a TiB2 coating with both high hardness and good adhesion strength. This was achieved by introducing substrate sputter-cleaning and then biasing for the early stage of deposition, followed by deposition without biasing.
    Download PDF (2631K)
  • Mong-Kai Wu, Miin-Jang Chen, Feng-Yu Tsai, Jer-Ren Yang, Makoto Shioji ...
    2010 Volume 51 Issue 2 Pages 253-255
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 16, 2009
    JOURNALS FREE ACCESS
    A new method was developed to fabricate high-quality ZnO nanopillars with good uniformity using atomic layer deposition (ALD). The ZnO island seeds were prepared on the (0001) sapphire by the initial 5∼20 ALD cycles at 180°C and then heat-treated at 900°C for 1 h. Afterwards, the ALD growth of ZnO at a temperature as high as 300°C proceeded preferentially on the ZnO island seeds over the sapphire substrate, leading to the formation of ZnO nanopillars. The average diameter and height of the nanopillars are about 60 nm and 50 nm, which can be effectively controlled by the numbers of initial ALD cycles and the following high-temperature ALD cycles, respectively. The ZnO nanopillars have high crystallinity with the [0001] orientation, and exhibit a significant ultraviolet luminescence at room temperature.
    Download PDF (1085K)
  • M. A. Abdel Rahim, A. El-Korashy, S. Al-Ariki
    2010 Volume 51 Issue 2 Pages 256-260
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The thermal crystallization behavior of bulk Se90−xTe10Cdx (x=0, 3, 9, and 15 at%) glasses was studied by differential thermal analysis, (DTA), under non-isothermal conditions. The glass transition temperature, (Tg), the onset crystallization temperature, (Tc), and the peak temperature of crystallization, (Tp), were found to be dependent on both the composition and the heating rates. From the dependence on the heating rates (α) of (Tg) and (Tp), the activation energy for the glass transition, (Et), and the activation energy for crystallization, (Ec), were calculated and their composition dependence is discussed. The crystalline phases resulting from DTA and scanning electron microscopy (SEM) have been identified using X-ray diffraction. The results indicate one dimensional growth from the surface to the inside for all the studied compositions. The kinetic parameters determined have made it possible to discuss the glass forming ability.
    Download PDF (1262K)
  • T. Hashizume, A. Saiki, K. Terayama
    2010 Volume 51 Issue 2 Pages 261-264
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Potassium tantalate with perovskite structure (KTaO3) is an incipient ferroelectric material that has promising functions in electromechanical and sensing sectors. Potassium tantalate with pyrochlore structure (K2Ta2O6) appears promising in a photocatalystic field. Potassium tantalate powders and bulks were fabricated at high temperature such as over 400°C from Ta2O5 and KOH. A sheet of tantalum was hard to react with potassium hydroxide in the mild hydrothermal condition at 100–150°C and low alkaline concentrations (0–2 M). Pyrochlore potassium tantalate film was synthesized with a mild hydrothermal method (100–150°C) at short reaction time by using a sputtered tantalum substrate on ITO glass. Synthesis of this film employed significantly low concentrations of KOH solution (0.1–1 M). The potassium tantalate film fabricated by the hydrothermal condition of 0.5 M-KOH solution, 100°C and 3 h reaction time was a smooth surface and became transparent. The particle size of this film was 150 nm.
    Download PDF (1703K)
  • Ilona Müllerová, Miloš Hovorka, Renáta Hanzl ...
    2010 Volume 51 Issue 2 Pages 265-270
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Instrument and methodology is presented for very low energy scanning transmission electron microscopy. The detector system provides simultaneous acquisitions of total reflected and transmitted electron fluxes. Introductory experiments incorporated examination of ultrathin foils of gold, carbon and graphene flakes. Extremely sensitive thickness contrast obtained at units of eV is demonstrated. The phenomenon of electron transmissivity apparently exceeding 100% owing to the contribution of secondary electrons released near to the exit surface is described and discussed.
    Download PDF (2557K)
  • S. Khamseh, M. Nose, T. Kawabata, K. Matsuda, S. Ikeno
    2010 Volume 51 Issue 2 Pages 271-276
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 23, 2009
    JOURNALS FREE ACCESS
    CrAlN films were prepared using a pulsed DC balanced reactive sputtering system under different N2/Ar ratios and pulse widths. We investigated the oxidation resistance of two CrAlN films with different microstructures; i) with a fcc-CrN structure, lower internal stress and moderate hardness, and ii) with a mixed structure of hcp-AlN and hcp-Cr2N phases, higher internal stress and super high hardness of 41 GPa. The CrAlN film (i) having the single fcc-CrN structure showed good oxidation resistance up to 900°C. The plastic hardness of this film increased to a maximum of 38.5 GPa at 900°C. In contrast, the CrAlN film (ii) with the mixed structure of hcp-AlN and hcp-Cr2N phases was stable up to 800°C. The plastic hardness of this film decreased gradually with annealing.
    Download PDF (2810K)
  • Yong Zou, YanHai Cheng, Lin Cheng, Wen Liu
    2010 Volume 51 Issue 2 Pages 277-281
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    In this study, the ternary Ni-P-Sn alloy coatings were prepared using electroless plating, and the effect of tin element on amorphous formation and anticorrosive properties of deposits in different corrosion medium were investigated. The different tin contents in deposits could be obtained by adjusting the amount of NaSnO3·3H2O in plating bath. The X-ray results indicate that the small amount of tin addition can improve the formability of the amorphous phase. At the same time, the hardness of deposit decreases and the crystalline temperature shifts to lower temperature with increasing amount of Sn. The electrochemical corrosive experiments of deposits resulted that the addition tin improves the anticorrosion property in 3.5 mass% NaCl solution, but reduces the anticorrosion ability in sulfuric acid solution.
    Download PDF (923K)
  • Masateru Nose, Tokimasa Kawabata, Sara Khamseh, Kenji Matsuda, K. Fuji ...
    2010 Volume 51 Issue 2 Pages 282-287
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 07, 2010
    JOURNALS FREE ACCESS
    TiAlN/a-C nano-composite coatings were synthesized by a reactive co-sputtering process to investigate the effects of sputtering conditions on the microstructure and mechanical properties. Coating films were deposited on square plates of Si and high speed steel (ANSI M2) by the co-sputtering of TiAl (pulsed-d.c. sputtering) and C (d.c. sputtering) targets using a “Facing Target-type Sputtering” system at an atmosphere with a mixture of Ar and N2 but without hydrocarbon gas. The structure of the coatings was investigated by means of XRD, XPS and HRTEM with GIF (Gatan Imaging Filter). Mechanical properties of coating films were measured by a submicron indentation system.
    Though TiAlN and a-C coatings showed hardness of about 32 and about 10 GPa, respectively, TiAlN/a-C coatings containing 4.6 at% of C showed higher hardness of 43 GPa. The energy filter images depicted that a change of contrast in the zero-loss image corresponded to nanometer-size of Ti agglomerates in Ti map. C1s spectrum in XPS analysis revealed that carbon in the coatings was bounded as C-C and C-N without bonding of Ti-C or Al-C. These results indicated that the TiAlN/a-C nano-composite coatings consisted of complicated mixture of nanocrystalline Ti-Al-N phase and a-C phase (including C-N bonding).
    Download PDF (4655K)
  • Weijun Luo, Meijun Yang, Fei Chen, Qiang Shen, Hongyi Jiang, Lianmeng ...
    2010 Volume 51 Issue 2 Pages 288-291
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 14, 2010
    JOURNALS FREE ACCESS
    The Bi-doped Mg2Si0.8Sn0.2 single phase compound is prepared by a solid state reaction (SSR)-spark plasma sintering (SPS) method. The effect of the Bi content on the thermoelectric properties of the Bi-doped Mg2Si0.8Sn0.2 compound is mainly investigated. The results show that the thermoelectric properties of the obtained samples are sensitive to the Bi content. With the increase in Bi content, the electrical conductivity (σ) and Seebeck coefficient (α) of the samples are increased, while the thermal conductivity (κ) is decreased slightly between 300 K and 850 K. When the Bi content is greater than 3.0 at%, the sample shows a maximum figure of merit (ZT) value (1.17±0.05) at 850 K.
    Download PDF (791K)
  • Šárka Mikmeková, Miloš Hovorka, Ilona M&uu ...
    2010 Volume 51 Issue 2 Pages 292-296
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Study of the grain structure in the equal channel angular pressing processed copper by means of the cathode lens equipped ultrahigh vacuum scanning low energy electron microscope is reported. The grain contrast was found achieving its maximum at electron energies below about 30 eV where it alternated its sign and exhibited dependence on electron energy specific for the grain orientation. The energy dependence of the electron reflectance seemed to be capable of serving as a fingerprint enabling determination of the crystalline orientation. In the cathode lens mode at hundreds of eV fine details of the microstructure are also observable including twins and low angle grain boundaries. This is explained by acquisition of high-angle backscattered slow electrons, normally not acquired in standard scanning electron microscopes. The very low energy electron reflectance is promising as an alternative to the EBSD method owing to its high resolution and fast data acquisition.
    Download PDF (5415K)
  • Atsushi Saiki, Takashi Hashizume, Kiyoshi Terayama
    2010 Volume 51 Issue 2 Pages 297-300
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 14, 2010
    JOURNALS FREE ACCESS
    In this study we investigated YSZ thin film deposition from an aqueous solution by applying constant electrical field and the effect of a pulsed electrical field upon the growth condition of films. The precursor was an aqueous solution of Zr(NO2)3-2H2O, Y(NO3)3-6H2O, and 0.5 vol% NH3(aq). The thin film was deposited on the minus electrode side of the glass substrate, which was placed above the minus electrode with a gap distance of 48–530 μm. By applying the electrical field, the thin film was effectively deposited on glass substrates under an applied voltage of 2.5 V for 300 s at room temperature. The as-deposited film was amorphous, and a crystalline phase with a transparent and smooth surface can be obtained after annealing at 773 K for 3 h in air. When a pulse bias is applied to the electrical field, the film thickness, surface defects, and roughness were changed with the frequency. At 2 Hz, the film was fabricated effectively, and a thick film was obtained, but films with smoother and fewer defect surfaces were obtained in a range of about 10–100 Hz.
    Download PDF (879K)
  • Tokimasa Kawabata, Kenji Matsuda, Susumu Ikeno
    2010 Volume 51 Issue 2 Pages 301-304
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The aging behavior of a ternary Mg–15%Gd–6.4%Sc (mass%) alloy was examined by high-resolution transmission electron microscopy. During the first stage of age hardening of the alloy, a contrast corresponding to a precursor of the β″ phase was observed predominantly. The β″ and β′ phases coexist in the second stage of hardening, up to the point of maximum hardness. In the over-aging stage, the spheroidal contrast of the β′ phase became longer along the ⟨1\\bar100⟩Mg direction. The addition of Sc to the Mg-Gd alloys is useful to clarify the precipitation behavior and contribution of the β″ and β′ phases to age hardening, as indicated by the two stage in the early stage of aging.
    Download PDF (713K)
  • Xin-mei Li, Yong Zou, Zhong-wen Zhang, Zeng-da Zou
    2010 Volume 51 Issue 2 Pages 305-309
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The microstructure evolution of a novel Super304H stainless steel aged at different temperatures was investigated using various analysis methods. The results reveal that the microstructure of the Super304H steel after aging at 973–1623 K consists of the primary γ matrix and a small amount of precipitated phases. Grain size of γ-matrix shows a slow increase when the aging temperature is lower than 1373 K and it increases quickly when the aging temperature is beyond 1423 K. The lattice parameter of γ-matrix varies at different aging temperatures, and this variation corresponds to the phases precipitated or redissolved. The variation of grain size and precipitated phases can affect the performance of the steel when exposing to steam oxidation and be subject to creep at high temperatures.
    Download PDF (2548K)
  • J. Nakamura, K. Matsuda, T. Kawabata, T. Sato, Y. Nakamura, S. Ikeno
    2010 Volume 51 Issue 2 Pages 310-316
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The metastable β′-phase that forms in an alloy with composition Al-1.0 mass% Mg2Si-0.5 mass% Ag, over aged at 523 K, has been investigated by transmission electron microscopy (TEM) in order to understand the effect of Ag-addition on the crystal structure of this phase. According to the results of analyses of selected area diffraction pattern, high resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDS), the elemental maps by energy-filtered TEM (EFTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), this precipitate consists of Mg, Si and Ag, and has a hexagonal unit cell which is similar to that of β′ phase in Al-Mg-Si alloys without Ag. However, the unit cell a-axis of β′ with Ag was 0.69 nm, which is slightly smaller than the corresponding dimension in Ag-free β′ (0.71 nm). The bond overlap population (BOP) was also calculated for the bonding between atoms in the small cluster in the β′-phase by the discrete-variational (DV)-Xa method, suggesting the bonding in β′ with Ag was higher than in the Ag-free β′.
    Download PDF (4315K)
  • N. Afify, A. Gaber, A. M. Abousehly, Y. M. Abou Deif
    2010 Volume 51 Issue 2 Pages 317-320
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    In Al-2.0 at%Cu-1.0 at%Mg alloy, fine-scale precipitates that occur during aging have been investigated by using differential scanning calorimetry (DSC) to search for the phase transition temperatures (formation and dissolution of precipitates). The microhardness measurements (HV) are used to correlate between the developed reaction peaks in DSC and the observed peaks in the microhardness (HV). The scanning electron microscopy (SEM) is utilized to examine the surface microstructure of the precipitated phases and to confirm the obtained results. During the aging treatment the supersaturation is gradually reduced. The strength increases when fine coherent and/or semicoherent precipitates nucleate. The precipitation kinetics can be characterized by analyzing the DSC curves. The kinetics of the early stage precipitates were found to be controlled by the migration of Cu and Mg atoms in the matrix. Whereas, the later precipitates as S″, S′ and S are controlled by diffusion of Mg and Cu in the alloy.
    Download PDF (765K)
  • Koretaka Yuge, Takayuki Ichikawa, Jun Kawai
    2010 Volume 51 Issue 2 Pages 321-324
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Energetic stability and electronic structures of Pt atoms in Pt-Rh nanoparticle is investigated by first-principles calculation. Pt atom energetically prefer surface sites (vertex, edge, and (100)) rather than subsurface and core site, which is attributed to lower Pt surface energy compared with Rh. Vertex of nanoparticle is the most favorable site for Pt atom, which has lowest coordination numbers. Band center of d-state electronic contribution for Pt atom measured from the Fermi energy exhibit negative dependence with respect to Pt coordination number. This can be attributed to positive dependence of second-order moment of density of states for the Pt d-band on the coordination number. Pt segregation to the surface is expected due mainly to contribution from Pt on-site segregation energy compared with weak ordering tendency of Pt-Rh unlike-atom pairs.
    Download PDF (692K)
  • Tetsuya Masuda, Yasuo Takaki, Takeo Sakurai, Shoichi Hirosawa
    2010 Volume 51 Issue 2 Pages 325-332
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The effect of pre-straining in combination with pre-aging on bake-hardening behavior of an Al-0.6 mass%Mg-1.0 mass%Si alloy was investigated by means of Vickers hardness test, electrical conductivity measurement, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Hardness change and DSC analysis revealed that only 3% pre-strain suppresses the formation of clusters; i.e. cluster(1), during single aging below 343 K. On the other hand, by combining with pre-aging at 343 K, pre-straining was found to improve bake-hardening response during final aging at 443 K. TEM observation confirmed that the improvement of bake-hardening response by pre-straining is mainly due to the enhanced precipitation of β″ phase in the matrix. These results are explained by the consideration that dislocations induced by pre-straining reduce the concentration of quenched-in excess vacancies, resulting in both the suppressed clustering of solute atoms during pre-aging and the accelerated precipitation of the β″ phase from more supersaturated solute atoms in final aging.
    Download PDF (677K)
  • Kohei Sato, Yasukazu Murakami, Daisuke Shindo, Satoshi Hirosawa, Akira ...
    2010 Volume 51 Issue 2 Pages 333-340
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The effect of post-sintering heat treatment on the coercivity of Nd–Fe–B based permanent magnets was studied by observing their crystallographic and magnetic microstructures. High-resolution transmission electron microscopy revealed meandering grain boundaries in the as-sintered state, and the smoothness of the boundaries was improved by the post-sintering heat treatment. Electron holography demonstrated that magnetization reversal occurred in a stepwise manner in individual grains in the specimen subjected to the post-sintering heat treatment, whereas reversal was occurred simultaneously in different grains in the as-sintered specimen.
    Download PDF (5647K)
  • Jianzhong Liu, Tianmo Liu, Hanqi Yuan, Xiuling Shi, Zhongchang Wang
    2010 Volume 51 Issue 2 Pages 341-346
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 23, 2009
    JOURNALS FREE ACCESS
    We perform a cold forging and annealing technique on Mg alloy AZ31 and investigate the impact on microstructure evolution and mechanical property. In particular, we focus on how twin and static recrystallization behave during the forging process followed by the annealing. Interestingly, we find that a large number of thick-lenticular {10\\bar12} twins emerge at initial stage of deformation and subsequently evolve into narrow-band {10\\bar11} and {30\\bar32} twins. The transformable twins are found to be crucial for inducing static recrystallization via providing recrystallization sites and refined grains. Moreover, the alloy forged at room temperature and annealed at 623 K is found to have optimal microstructure due to the complete recrystallization and therefore exhibit the highest micro-hardness, largest compressive strength, and most significantly enhanced compressive ratio. The improved mechanical properties are comparable or even superior to those of the alloy deformed using other techniques, rendering the cold forging a promising way for further tailing properties of Mg alloy.
    Download PDF (5442K)
  • Koichi Takasawa, Yoru Wada, Ryoji Ishigaki, Rinzo Kayano
    2010 Volume 51 Issue 2 Pages 347-353
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 14, 2010
    JOURNALS FREE ACCESS
    The effect of grain size on the susceptibility of high-strength low alloy steels to hydrogen environment embrittlement in a 45 MPa gaseous hydrogen atmosphere was examined in term of the hydrogen content penetrating the specimen during the deformation. Notch tensile tests were performed in a 45 MPa hydrogen environment using specimens with different prior austenite grain size numbers varying from 2.5 to 5.4. The hydrogen content was measured by thermal desorption analysis with a quadrupole mass spectrometer before and after the tensile test. The fracture stress of the notch tensile test increased with increasing grain size number; this showed that grain refinement was effective in reducing the susceptibility of the specimens to hydrogen environment embrittlement in a high-pressure hydrogen atmosphere. The addition of nickel did not affect the fracture stress. A remarkable increase in the content of diffusive hydrogen was observed after the notch tensile test. Assuming that part of the diffusive hydrogen desorbed from grain boundaries, it can be inferred that grain refinement can reduce the mass of hydrogen in the unit grain boundary area, and the susceptibility to high-pressure hydrogen environment embrittlement.
    Download PDF (1429K)
  • Jae-sik Yoon, Shoji Goto, Byung Il Kim
    2010 Volume 51 Issue 2 Pages 354-358
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Niobium powder was fabricated by sodiothermic reduction process using K2NbF7 as the raw materials, KCl and KF as the diluents and Na as the reducing agent. The apparatus for the experiment was designed and built specifically for the present study. Varying properties of niobium powder depending on reaction temperature and excess of reducing agent were analyzed. The niobium particle size increased significantly as the reduction temperature increased from 993 to 1093 K. The particle size was fairly uniform at a given reaction temperature, varying from 0.2 μm to 50 nm, depending on the reaction temperature. The yield of niobium powder increased from 58 to 83% with a increasing a reaction temperature. The average particle size of niobium powder is improved from 70 nm to 0.2 μm with a increasing amount of sodium excess. And the yield ratio of Nb powder was 82% in the 5% excess sodium.
    Download PDF (2110K)
  • Rongguang Wang
    2010 Volume 51 Issue 2 Pages 359-365
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 07, 2010
    JOURNALS FREE ACCESS
    The wettability of NaCl solutions on SUS304 stainless steel was investigated under cathodic and anodic current. It was found that the contact angle became small when a cathodic current of 1.0 mA was applied, with a tendency of higher wettability for higher concentrations (between 0.01% and 0.1%). However, the decrease in the contact angle is irreversible even if the current is stopped or anodic current is applied. This phenomenon can be attributed to changes in the electric charge and the passive film at the interface.
    Download PDF (2096K)
  • Mikio Ishikuro, Kazuaki Wagatsuma
    2010 Volume 51 Issue 2 Pages 366-370
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    The method of separation and determination of zirconium carbide in Zr50Al10Ni5Cu30 bulk metallic glass matrix composites containing zirconium carbide particles has been developed.
    The zirconium carbide was not dissolved though the metallic glass specimen was dissolved with 6 kmol·m−3 hydrochloric acid of the room temperature.
    After complete dissolution of the metallic glass matrix specimen with 6 kmol·m−3 hydrochloric acid of the room temperature, the undissolved zirconium carbide was separated by filtration with the membrane filter having the pore size of 0.2 μm. The separated zirconium carbide was fused with the potassium hydrogen sulfate in the platinum crucible. The concentrations of zirconium, copper, aluminum and nickel in the filtrate and the insoluble residue were determined respectively by inductively coupled plasma-optical emission spectrometry.
    The zirconium concentration in the filtrate and the insoluble residue were constant irrespective of the dissolution time. Copper, aluminum and nickel were not detected in the insoluble zirconium carbide.
    It was confirmed that the zirconium carbide in the Zr50Al10Ni5Cu30 bulk metallic glass matrix had been quantitatively separated and determined.
    Download PDF (665K)
  • Shuxin Dong, Yasushi Iwata, Yoshio Sugiyama, Hiroaki Iwahori
    2010 Volume 51 Issue 2 Pages 371-376
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 23, 2009
    JOURNALS FREE ACCESS
    A cold crack criterion for JIS ADC12 aluminum alloy die casting is proposed. Through investigating the temperature dependence of the fracture strain of JIS ADC12 aluminum alloy die casting, it was found that the fracture strain features a turning point at a temperature, Tc (we called “critical temperature to the ductility”, about 573 K for the present composition), i.e. stays low while below Tc, rises rapidly to a high level beyond Tc. Focusing on this character of the fracture strain, we analyzed the equivalent plastic strain (εc) of the castings introduced below Tc in casting processes by thermal stress simulations and compared with the occurrence of cold cracks in the die casting experiments. It was found that the εc of the cracking positions in the castings exceeded, while the εc of the castings without crack were much lower than the fracture strain of JIS ADC12 aluminum alloy die casting below Tc. That is to say, the occurrence of the cold crack in a die casting can be judged by comparing the εc with the fracture strain below Tc. Based on this proposed criterion, it is possible to predict the appearance of the cold cracks in ADC12 die castings by thermal stress simulations.
    Download PDF (1133K)
  • Takeshi Nagase, Takayoshi Nakano, Yukichi Umakoshi, Mitsuo Niinomi
    2010 Volume 51 Issue 2 Pages 377-380
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 23, 2009
    JOURNALS FREE ACCESS
    Beta-Ti-type Ti-30Nb-10Ta-5Zr (TNTZ) wires with high-ductility were developed using the arc-melt-type melt-extraction method. The continuous melt-extracted wire with very smooth surface and small fluctuations in the diameter realizes the high tensile strength and superior bending ductility of TNTZ alloy. The melt-extracted Beta-Ti wire shows the possibility for the use in biomedical applications. The arc-melt-type melt-extraction method is very effective for developing new Beta-Ti-based biomaterials.
    Download PDF (2283K)
  • Nobumitsu Shohoji, Teresa Magalhães, Fernando Almeida Costa Oli ...
    2010 Volume 51 Issue 2 Pages 381-388
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 07, 2010
    JOURNALS FREE ACCESS
    Compositional heterogeneity along the thickness of compacted disc specimens of graphite/tungsten powder mixtures with sub-stoichiometric carbon atom ratios (0.35, 0.50 and 1.00) heated by concentrated solar beam to 1600°C was characterised by X-ray diffraction. Top surface of any examined test piece was consisted purely of mono-carbide WC while the bottom surface showed different constitution depending on the net initial C/W ratio of the test piece; almost pure metallic W for the C/W=0.35 specimen, dominant metallic W associated with small proportion of W2C for the C/W=0.50 and dominant W2C with trivial proportion of WC for the C/W=1.0. In the intermediate zone between the top and the bottom layers, the constitution held virtually constant depending on the nominal C/W ratio of the starting material: co-existing metallic W and W2C for the C/W=0.35, pure W2C for the C/W=0.50 and predominant WC with trace W2C for the C/W=1.00. Unlike for the top surface of the C/W=0.35 test piece heated in a solar furnace to 1900°C reported earlier, no evidence of formation of nano-meter scale WC whisker was detected for the top surface in any sample heated to 1600°C in the present work.
    Download PDF (3637K)
  • Soo-Keun Park, Tae-Woon Nam
    2010 Volume 51 Issue 2 Pages 389-393
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Serious deformation on the pipe transporting hot water for heating was occurred by the cyclic heat impact during trial operation. Non-destructive inspection (RT, UT, MT, PT) and continuous indentation test were carried out to observe the flaw on the pipe and the variation of mechanical property for pipe material respectively. It was newly found by radiographic test that incomplete penetration flaws exist on every welding zone, which had been generated during the process of production. Ultrasonic test showed the length of incomplete penetration flaw reached 2/3 of circumference and its depth reached up to 60% of width. The mechanical property of material was found to be well uniform along the tube by the continuous indentation test. The incomplete penetration flaw was assumed to be a keen notch, and fitness for service was examined to observe the possibility of breakage crack and spread of crack in incomplete penetration area. As a result, it was observed to be usable under current operating condition, considering safety factor.
    Download PDF (546K)
  • Hidekazu Sueyoshi, Yuki Yamano, Yoshikazu Maeda, Kosaku Yamada
    2010 Volume 51 Issue 2 Pages 394-398
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Inventory analyses of manufacturing systems for Pb-bronze (JIS: CAC406), Pb-free bronze produced by Bi addition (JIS: CAC902) and copper sulfide-dispersed Pb-free bronze were assessed from the viewpoint of life cycle assessment. The results show that the manufacturing system of copper sulfide-dispersed Pb-free bronze significantly reduces such environmental impacts as energy consumption, global warming, acidification and resource consumption as compared with that of CAC902.
    Download PDF (146K)
  • Seung-Wook Baek, Don-Hyun Choi, Chang-Yong Lee, Byung-Wook Ahn, Yun-Mo ...
    2010 Volume 51 Issue 2 Pages 399-403
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Low carbon steel plates were joined by friction stir spot welding (FSSW) with lap configuration. The tool penetration depth exerted a strong effect on the failure mode of the joined samples and a weak effect on the joint shear strength. With increasing tool penetration depth, and consequently with increasing depth of the tool shoulder pressing into the top sample, the failure mode in a lap-shear test changed from brittle to ductile and concentrated near the pinhole located away from the weld towards the base metal. No mechanically mixed layer was formed between the top and bottom plates at the weld nugget due to the limited tool penetration and the fact that the pin height of the welding tool was less than the steel plate thickness. The region under the pin exhibited a fully recrystallized microstructure, with grain growth and a different texture.
    Download PDF (2664K)
  • Hideki Hashimoto, Takafumi Kusunose, Tohru Sekino
    2010 Volume 51 Issue 2 Pages 404-407
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: December 23, 2009
    JOURNALS FREE ACCESS
    We prepared Dy1−xSrxCoO3−δ (x=0,0.025) ceramics and evaluated their thermoelectric performances at temperatures up to 873 K. The sample in which x=0.025 showed a higher electrical conductivity and a lower Seebeck coefficient than that in which x=0. Due to phonon scattering, the thermal conductivity of the x=0.025 sample was lower than that of the x=0 sample over the entire range measured although the carrier component of thermal conductivity of the x=0.025 sample was slightly larger than that of the x=0 sample. Due to the effects of an increase of the electrical conductivity and a decrease of the thermal conductivity, the sample in which x=0.025 showed the highest figure of merit, Z=5.7×10−5 K−1, at 773 K in the present system. These results imply that the partial substitution of a larger and lighter divalent cation for the trivalent cation of the A-site effectively enhanced the thermoelectric performance of the RCoO3 system.
    Download PDF (1069K)
  • Duck Young Hwang, Young Gun Ko, Yong Min Kim, Bongyoung Yoo, Dong Hyuk ...
    2010 Volume 51 Issue 2 Pages 408-412
    Published: February 01, 2010
    Released: January 25, 2010
    [Advance publication] Released: January 07, 2010
    JOURNALS FREE ACCESS
    The influence of the post-annealing (PA) treatment on plasma electrolytic oxidation (PEO) treated AZ91 Mg alloy was investigated and the dependence of the dehydration reaction on the PA temperature was also studied. In this study, a series of PA treatments were carried out on the coated samples at four different temperatures, i.e. 373, 423, 473, and 523 K for 10 h. In contrast to the sample without PA treatment, the samples annealed at temperatures higher than 423 K exhibited a significant difference in terms of surface morphology since the MgO content in the oxide layer increased with increasing PA temperature. With increasing PA temperature, the dehydration of Mg(OH)2 led to the increase in the relative amount of the MgO, which was a hard phase. From the nano-indentation results, the applied loads of the samples were seen to increase as PA temperatures increased. Moreover, the corrosion resistance of the sample annealed at 423 K was higher than that of the samples annealed at three different PA temperatures.
    Download PDF (821K)
  • Debabrata Pradhan, Dong Jin Kim, Gautam Roy Chaudhury, Jeong Soo Sohn, ...
    2010 Volume 51 Issue 2 Pages 413-419
    Published: February 01, 2010
    Released: January 25, 2010
    JOURNALS FREE ACCESS
    Bioleaching studies were conducted to evaluate a complex sulfide concentrate using an acidophilic microorganism. The leaching kinetics were found to vary based on pulp density, Fe and pH. In addition, the leaching efficiency increased as the Fe(II) concentration increased up to 20 kg·m−3, after which it decreased due to an increase in iron precipitation. Furthermore, the bacterial activity was good based on observation of the iron oxidation rate and pH and Eh studies. The leaching efficiencies decreased below 2 and 5% (w/v) in the pH and pulp density studies, respectively. Furthermore, the XRD analyses revealed the presence of various product layers, while the SEM-EDX analyses showed partial contact between different sulfide minerals that resulted in formation of a galvanic couple. The dissolution rate followed a product diffusion model. The diffusivity of Fe(III) for chalcopyrite and sphalerite were calculated.
    Download PDF (1541K)
feedback
Top