MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 42 (2001), No. 8

  • Nanostructured Materials from Clusters: Synthesis and Properties

    pp. 1460-1470

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    DOI:10.2320/matertrans.42.1460

    The low energy cluster beam deposition technique (LECBD) is developed to prepare original nanostructured systems from clusters preformed in the gas phase. The nucleation and growth mechanism specific of the cluster deposits is studied in view to control the nanostructured morphology of the cluster assembled films, especially for future applications to high areal density devices. Examples of the synthesis and properties of metallic nanostructures as well as covalent ones are presented. In the first case, systems from noble metal clusters (Ag, Au, and AgxAu1−x) and transition metal based clusters (Co, SmCo5) assemblies are studied for their original optical or magnetic properties, respectively. In the second case, covalent semiconducting films exhibiting specific electronic structures are obtained by Si, C, and SixC1−x cage like clusters (fullerenes and heterofullerenes) depositions.
  • Films as Nanostructured Materials with Characteristic Mechanical Properties

    pp. 1471-1473

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    DOI:10.2320/matertrans.42.1471

    Preparation methods of nanostructured materials are discussed and the main attention is given to the film/coating technique. Short history is also reported on mechanical properties of the thin films. The most interesting result is application of structure and properties of nanostructured films.
  • Size Effect on the Atomistic Structure of Metallic Atom Clusters

    pp. 1474-1479

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    DOI:10.2320/matertrans.42.1474

    The atomistic structure of metallic atom clusters is discussed based on the experimental results with the following conclusions: (1) When ultrafine particles of metals become smaller than the critical sizes corresponding to the nucleus size of the crystals, they behave as atom clusters and their atomistic structure changes as a function of the number of constituent atoms, i.e., the many-body potential. (2) Icosahedrons are formed first and change to the cuboctahedral structure before such atom clusters take the final crystal structures. (3) The phonon mode of these atomistic structures is very much softened, and thus the zigzag atom-chains are formed dynamically around the average position of atoms even in the cuboctahedral structure. (4) The hybrid orbital corresponding to the final crystal structure is formed when atom clusters grow to the critical size. As a result, the binding strength sufficiently increases along a certain crystal axis such as the ⟨110⟩ in the fcc structure and the ⟨111⟩ in the bcc one, so that atomic rearrangement can occur within the ultrafine particles, including disappearance of multi-twin in Au particles, to take the bonding state of crystals.
  • Effects of O2 Gas on the Size and Structure of Cr Clusters Formed by Plasma-Gas-Condensation

    pp. 1480-1484

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    DOI:10.2320/matertrans.42.1480

    Cr clusters have been produced by a plasma-gas-condensation type cluster deposition apparatus, and studied using a time-of-flight mass spectrometer and a transmission electron microscope. The Cr clusters formed in high pressure inert (Ar and/or He) gas atmosphere are of an A15-type structure. When an O2 gas is mixed with the inert gases in the source (sputtering) chamber, a bcc phase is formed together with Cr2O3. The O2 gas introduction leads to an increase in the gas temperature of the source chamber probably due to release of the formation enthalpy of the oxide. The A15 phase is annealed by such excess heat and becomes the equilibrium bcc phase. The sizes of bcc clusters are smaller than those of the A15-clusters, probably due to the heterogeneous nucleation promoted by the oxide formation.
  • Precipitation of Nanoscale Icosahedral Quasicrystalline Phase in Zr-Cu Glassy Alloy Promoted by the Addition of Ir

    pp. 1485-1488

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    DOI:10.2320/matertrans.42.1485

    Zr70Cu30 and Zr70Cu20Ir10 glassy alloys were prepared by a single roller melt-spinning method and their crystallization processes were studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. For the Zr70Cu30 alloy, the glassy state crystallizes through a single exothermic reaction due to the precipitation of the stable Zr2Cu crystalline phase. For the Zr70Cu20Ir10 alloy, a metastable icosahedral quasicrystalline phase precipitates from the glassy matrix in the initial crystallization process, followed by the phase transformation to Zr2Cu, Zr2Ir and unknown crystalline phases upon further annealing. These results illustrate that the partial substitution of Cu by Ir in the Zr70Cu30 glassy alloy is effective in promoting the precipitation of the metastable icosahedral quasicrystalline phase. To explain these experimental results, the existence of icosahedron-like atomic clusters in the Zr70Cu20Ir10 glassy alloy is suggested.
  • Retraction:Nano-Scale Icosahedral Quasicrystals Crystallized from Zr-Nb-Ni-Cu-Al Metallic Glasses

    pp. 1489-1492

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    DOI:10.2320/matertrans.42.1489

    This article was retracted. See the Notification.
  • Nano Icosahedral Quasicrystalline Phase in Zr65Al7.5Ni10Ag17.5 Quaternary Glassy Alloy

    pp. 1493-1496

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    DOI:10.2320/matertrans.42.1493

    A nano icosahedral quasicrystalline phase was confirmed as the primary precipitation phase in the melt-spun Zr65Al7.5Ni10Ag17.5 quaternary glassy alloy with a two-stage crystallization process. The onset temperature of the first exothermic peak is 704 K at a heating rate of 0.67 Ks−1. Although no significant X-ray diffraction peaks were observed in the sample annealed at 705 K, we confirmed the formation of the icosahedral phase by nano beam electron diffraction using FE-TEM . The icosahedral particles have an extremely fine grain size in the diameter range of 2 to 4 nm. In addition to the icosahedral phase, the nano crystalline particles corresponding to Zr2Ag and/or fcc-Zr2Ni structures are also observed in the annealed sample. The second exothermic peak denotes the transition from the nano icosahedral to the crystalline phase of Zr2Ag, fcc-Zr2Ni and Zr4Al3. The formation of the nano icosahedral phase as the primary phase is due to a high nucleation rate and strongly implies the existence of an icosahedral short-range order in the glassy state.
  • Transformation of Nano Icosahedral Phase in Zr65Al7.5Ni10Cu17.5-xPdx (x=0 to 4) Glassy Alloys

    pp. 1497-1501

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    DOI:10.2320/matertrans.42.1497

    We investigated the transformation behavior from glassy to icosahedral and/or fcc Zr2Ni phases in the Zr65Al7.5Ni10Cu17.5−xPdx (x=0 to 4) glassy alloys with low oxygen contents of less than 400 ppm mass%. The primary phase is a metastable single fcc Zr2Ni phase in the x=0 alloy and a single icosahedral quasicrystalline phase in the 2 to 4 at%Pd alloys. The mixture phase of icosahedral and fcc Zr2Ni precipitates at the initial crystallization stage in the x=1 alloy. It is therefore confirmed that the icosahedral phase is formed by the addition of 1 at% Pd to the Zr–Al–Ni–Cu glassy alloy. The icosahedral and Zr2Ni particles have grain sizes in the diameter range of 500 to 1000 nm and are in an isolated state for the sample annealed at a temperature near the crystallization temperature. A significant redistribution leading to the enrichment of Zr in the icosahedral phase is confirmed. Moreover, it is recognized that Ni and Cu are rejected from the icosahedral phase. We also observed the enrichment of Zr and Ni and the rejection of Cu in the Zr2Ni phase. No significant difference in Al content is observed among the icosahedral, Zr2Ni and residual glassy phases. The Pd content in the icosahedral phase is the same as that in the Zr2Ni phase. The difference of Zr, Ni and Cu contents among the icosahedral, Zr2Ni and remaining glassy phases is in the range of 2 to 9 at%. No significant difference in the Pd content is observed between the icosahedral and Zr2Ni phases. Considering that the diameter of the primary phase decreases significantly with increasing Pd content, it is suggested that Pd plays a dominant role in the increase in the number of nucleation sites of the icosahedral phase. Moreover, it is strongly suggested that the icosahedral phase originates from the icosahedral short-range order with an increase of nucleation rate as a result of the addition of noble metal.
  • Effects of Overload and Frequency on Fatigue Crack Propagation in Nanocrystalline Zr-Based Bulk Metallic Glass

    pp. 1502-1508

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    DOI:10.2320/matertrans.42.1502

    A nanocrystalline (NC) bulk glass Zr55Al10Cu30Ni5(at%) containing nano-scale crystals embedded uniformly in a glassy matrix has both high tensile strength of 1.7 GPa and high ductility. The new alloy is therefore expected to have practical applications in machines and structures. The influences of frequency and overload on fatigue crack propagation behavior of the NC bulk glass were examined. The fatigue crack propagation rate dadn less than 3×10−5 mm/cycle was independent of frequency in the frequency range of 0.1 to 50 Hz at the stress ratio of 0.1 under sine and triangular waves. When the overload ratio (overload/baseline load) was large, a complete crack arrest occurred and the ΔK value just before a crack regrowth was three times larger than the threshold stress intensity factor range ΔKth. The reason for the crack arrest was not explained by the crack closure effect. The overloading induced the kinking and branching of the crack. The stress reduction near the crack tip due to the kinking and branching of the crack and the crack closure effect gave an appropriate explanation for the complete crack arrest and the larger threshold stress intensity factor range. When the overload ratio was small, a temporary crack arrest occurred and the kink and branching of cracks occurred intermittently at the crack front.
  • Formation of Nanocrystals by Crystallisation of Zr-Al-Cu-Ni-Fe Metallic Glasses

    pp. 1509-1516

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    DOI:10.2320/matertrans.42.1509

    The influence of iron addition on the crystallisation behaviour of Zr65Al7.5Cu17.5Ni10 bulk metallic glass was investigated by differential scanning calorimetry, (DSC), X-ray diffraction, (XRD), transmission electron microscopy, (TEM) and magnetisation measurements. The amorphous Zr65Al7.5Cu17.5Ni10 alloy crystallises eutectically into CuZr2 and Zr6NiAl2. Addition of iron in amorphous (Zr65Al7.5Cu17.5Ni10)100−xFex (0≤x≤20) leads to a changed crystallisation sequence and to the formation of nanocrystals. The formation of a cubic NiTi2-type phase (S.G. Fd \\bar3m,ao=1.22 nm) is the first step of crystallisation in amorphous alloys with iron contents x≥1. Depending on the iron content the average crystallite size decreases to the nanometer regime. Ultrafine nanoclusters of down to 2 nm in size are formed as the first step of crystallisation for amorphous Zr52Al6Cu14Ni8Fe20 due to a high nucleation rate combined with a low growth velocity. The clusters grow by Ostwald ripening during isothermal annealing up to 5 nm average crystallite size. The magnetic behaviour of the (Zr65Al7.5Cu17.5Ni10)100−xFex alloys is dominated by temperature-independent Pauli paramagnetism for x≤15. For x=20, a small contribution of magnetic clusters is observed. These ferromagnetic clusters are in accordance with statistic composition fluctuations within the homogeneous amorphous phase. With the formation of nanocrystals the size of the magnetic clusters increases to the same order of magnitude.
  • Superplastic Deformation of Supercooled Liquid in Zr-Based Bulk Glassy Alloys Containing Nano-Quasicrystalline Particles

    pp. 1517-1522

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    DOI:10.2320/matertrans.42.1517

    The tensile deformation behavior of the supercooled liquid in the bulk glassy Zr65Al7.5Ni10Cu12.5Ag5 and Zr65Al7.5Ni10Cu12.5Pd5 alloys was investigated in comparison with the glassy Zr65Al7.5Ni10Cu17.5 alloy. An icosahedral phase precipitates as the primary precipitation phase from the supercooled liquid in the Ag- or Pd-containing alloy. The deformation behaviors of both the alloys were similar to that of the Zr65Al7.5Ni10Cu17.5 alloy at relatively high strain rates of about 1×10−2 s−1. While the largest elongation of the Zr65Al7.5Ni10Cu17.5 alloy, 270%, was obtained at 3×10−3 s−1, those of the alloys containing Ag or Pd were about 400% at 1×10−3 s−1. Apparent strain hardening due to the growth of the icosahedral particles was observed during the deformation of both the alloys at lower strain rates. The plastic deformation of the supercooled liquid continues even after the precipitation of the icosahedral particles, while the deformation of the Zr65Al7.5Ni10Cu17.5 alloy is inhibited by the onset of crystallization.
  • Short-Range Order and Micromechanisms Controlling Nanocrystallization of Iron-Cobalt Based Metallic Glasses

    pp. 1523-1529

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    DOI:10.2320/matertrans.42.1523

    Transition from amorphous to nanocrystalline state has been investigated from the viewpoint of rate theory in Fe–Co–Zr–B metallic glass by evaluation of changes of electrical resistivity using a novel method of continuous distribution analysis and by transmission electron microscopy and X-ray diffraction. Ordering process inside α-FeCo nanograins has been observed. The mechanism controlling nanocrystallization is the same throughout the entire reaction. Before the nanocrystallization is over, a new microprocess becomes active. The units active in initial and final stages of transformation may differ in local chemical ordering. The results allow to infer on the character of the original amorphous structure for which we propose two types of internally correlated and chemically ordered regions with different Zr content.
  • Structural Study of Amorphous FE70M10B20 (M=CR, W, NB, ZR and HF) Alloys by X-ray Diffraction

    pp. 1530-1534

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    DOI:10.2320/matertrans.42.1530

    Local atomic structures in amorphous Fe70M10B20 (M=Cr, W, Nb, Zr and Hf) alloys with different ΔTx values were studied by the ordinary X-ray diffraction, anomalous X-ray scattering and EXAFS methods. Their local the atomic structures basically resemble each other, i.e. a random network structure of triangular prisms. Only difference in local atomic structure is a shape of the local structural unit. In the amorphous alloys containing M elements larger than Fe atoms, the prisms show distorted shapes due to a size difference Δr between M and Fe. A linear relation between Δr and ΔTx, and a comparison of their crystallization processes suggest us that their thermal stability is attributed to difficulty in rearranging the irregular structural units because of a non-zero Δr value.
  • Soft Magnetic Properties of Nanocrystalline Fe-Nb-B-P Alloys Produced in the Atmosphere by Melt-Spinning Method

    pp. 1535-1539

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    DOI:10.2320/matertrans.42.1535

    The soft magnetic properties of nanocrystalline Fe–Nb–B and Fe–Nb–B–P alloys produced in the atmosphere by a melt-spinning method have been investigated. The nanocrystalline Fe100−xyNbxBy ternary alloys show good soft magnetic properties, relative permeability (μ) above 35000 at a frequency of 1 kHz and coercive force (Hc) below 5.0 Am−1, as well as high saturation magnetic induction (Bs) above 1.55 T in the compositional range of x=6.5–6.7 and y=9.3–10.0 at%. The soft magnetic properties of the nanocrystalline Fe–Nb–B ternary alloys are improved by 0.5–1.5 at% substitution of P for B, without decreasing their Bs. The magnetostriction (λs) value increases and the mean grain size of bcc-Fe phase (D) decreases slightly by substitution of P for B . The nanocrystalline Fe84Nb6.5B9P0.5 and Fe84Nb6.5B8.5P1 alloys show good soft magnetic properties, μ of 46000–47000 at a frequency of 1 kHz, Hc of 3.6–3.9 Am−1 and the core loss of the 0.09 Wkg−1 at maximum induction (Bm) of 1.33 T and a frequency of 50 Hz as well as high Bs of 1.60 T, suggesting that these nanocrystalline Fe–Nb–B–P alloys are suitable for a core materials for pole transformers.
  • On the Nature of the Hysteresis Loop Shift in Amorphous Soft Magnetic Alloys

    pp. 1540-1542

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    DOI:10.2320/matertrans.42.1540

    The influence of annealing temperature, rate of cooling, magnetic field frequency under thermomagnetic treatment on the hysteresis loop shift field value of Fe5Co70Si15B10 and Fe60Co20Si5B15 amorphous alloys samples has been studied. The relation of the structural state of amorphous alloys with the shift field value of the hysteresis loop has been studied. The physical explanation of this effect is proposed on the basis of obtained data.
  • Hard Magnetic Properties and Nanocrystallized Structure of Fe66.5Co10Pr3.5B20 Glassy Alloy

    pp. 1543-1546

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    DOI:10.2320/matertrans.42.1543

    The value of the supercooled liquid region defined by the difference between the glass transition temperature (Tg) and the crystallization temperature (Tx), ΔTx (=TxTg), was 43 K for an Fe66.5Co10Pr3.5B20 glassy alloy. The crystallized structure consists of Fe3B, Pr2Fe14B, α-Fe and remaining glassy phase after annealing at about 863 K for 420 s and changes to a mixture of Fe3B, Pr2Fe14B and α-Fe phases after annealing at higher temperatures. The grain sizes after annealing at 863 K are about 20 nm for Fe3B, 10 nm for Pr2Fe14B, 20 nm for α-Fe and 5 nm for the remaining glassy phase. The maximum energy product (BH)max was obtained for the alloy containing the residual glassy phase subjected to annealing at 863 K for 420 s. The remanence (Br), coercivity (iHc) and (BH)max of the optimally annealed Fe66.5Co10Pr3.5B20 alloy are 1.35 T, 211 kA/m and 107 kJ/m3, respectively. The hard magnetic properties are interpreted to result from the exchange magnetic coupling among Pr2Fe14B, Fe3B, α-Fe and remaining glassy phase. The formation of the finely mixed structure caused by the residual glassy phase is considered to be responsible for the good hard magnetic properties with (BH)max above 100 kJ/m3 for the new type (Fe, Co)–Pr–B alloy with low rare earth and a high boron contents.
  • Coexistence of Various Nd-Rich and Fe-Rich Fe-Nd Short Range Orderings In Bulk Glassy Nd60Fe30Al10 Hard Magnets

    pp. 1547-1551

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    DOI:10.2320/matertrans.42.1547

    Bulk Nd60Fe30Al10 metallic glasses are found to exhibit a complex magnetic behavior at very low temperatures related to the coexistence of various Nd-rich and Fe-rich magnetic short range orderings, as evidenced by AC-susceptibility studies in combination with hysteretic loops at fields up to 30 T . Above 80 K the magnetic behavior is shown to correlate with Stoner-Wohlfarth hysteresis loops with pronounced thermal activation effects. These observations suggest the existence of an Fe-rich Fe–Nd hard magnetic ’phase’ formed by an ensemble of randomly oriented uniaxial magnetic nanoentities embedded in a Nd-rich matrix. The exchange coupling and development of a large axial crystal field anisotropy at very low temperatures and the uncoupling above 70 K of the Fe-rich Fe–Nd hard magnetic phase to the Nd-rich matrix appears to be at the origin of the observed overall magnetic behavior.
  • Nanometer-Scale Structure of Rapidly Solidified Al92V3Fe3Zr2 Alloy

    pp. 1552-1560

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    DOI:10.2320/matertrans.42.1552

    Nanometer-scale structures were examined for Al92V3Fe3Zr2 ribbons rapidly solidified by a single roller melt-spinning, as a function of a circumferential velocity in the range between 10 and 50 m/s. Deformed scattering patterns along the direction of the ribbons are detected by a pinhole small-angle X-ray instrument for the ribbons rapidly solidified with the circumferential velocities higher than 20 m/s. The deformed patterns can be attributed to the rows of nearly spherical particles into which the elongated particles have disintegrated by shear flow caused by the melt spinning. Size of precipitates decreases with increasing the circumferential velocity, and some change in the precipitation mechanism is suggested to occur at a circumferential velocity of 30 m/s.
  • Nanostructures and Mechanical Properties of Bulk Al-Fe Alloys Prepared by Electron-Beam Deposition

    pp. 1561-1565

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    DOI:10.2320/matertrans.42.1561

    Nanostructure Al-based binary alloys with additions of Fe have been prepared by electron-beam evaporation. The composition dependence of microstructures and mechanical properties has been studied. The deposits up to an Fe content of 4 at% consist of a supersaturated solid solution of Al. At higher Fe contents, the deposits consist of an amorphous and crystalline phase with a grain size below 40 nm. At the content range in which the supersaturated solid solution formed, as the content increased, the crystalline size became finer. The Vickers hardness increases with increasing the content of Fe and reaches values of 200 Hv and 600 Hv for contents of 1 at% and 15 at%, respectively. The tensile strength of the deposit exhibited a high strength of 1000 MPa at the Fe content of 2.5 at% with grain size 40 nm. The strength and hardness followed the Hall-Petch relation up to the grain size of 40 nm.
  • Formation of Supersaturated Single-phase bcc Solid Solutions in Fe-Zn Binary System by Mechanical Alloying

    pp. 1566-1570

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    DOI:10.2320/matertrans.42.1566

    Mechanical alloying (MA) was used in the investigation of the Fe–Zn binary system, which, in the equilibrium state, exhibits negligible mutual solid solubility at room temperature. The formation of single-phase bcc solid solutions with a nanometer-scaled microstructure was achieved by MA in Fe100−xZnx (x≤65) powder mixtures. The nearest neighbor distances of these Fe–Zn solid solutions obey the linear relationship given by the Vegard’s law for ideal solutions, suggesting that the solid solutions formed by MA are homogeneous. The average lattice volume expansion also linearly increases to about 13.4% at 65%Zn. At elevated temperatures the nanostructured solid solutions undergo phase transformations yielding intermetallic compounds. The mechanisms for the phase formation in the Fe–Zn system are discussed.
  • Grain-Size and Alloying Effects on the Pressure-Induced bcc-to-hcp Transition in Nanocrystalline Iron

    pp. 1571-1574

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    DOI:10.2320/matertrans.42.1571

    The pressure-induced bcc-to-hcp phase transformation has been studied by x-ray diffraction for bulk iron as well as nanocrystalline iron and a Fe90Cu10 alloy. The nanocrystalline material has a lower onset pressure and a larger pressure hysteresis than bulk iron. The non-random orientation of the nanocrystals is sensitive to shear stress in the high-pressure cell.
  • Synthesis of Nano-Sized WC-Co Powders by Reduction-Carburization Process

    pp. 1575-1581

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    DOI:10.2320/matertrans.42.1575

    The feasibility of producing nano-sized WC and WC-Co powders by reduction and carburization of WO3 and Co3O4 under hydrogen and methane atmospheres was evaluated. WC powders of 1 \\micron in particle size were obtained from WO3 on reduction and carburization at 950°C. On the other hand, nano-sized WC-Co powders with a particle size of ∼ 100 nm could be produced by a two-step reduction process, using a blend of WO3 and Co3O4. Critical control parameters in this process, such as the gas flow rate, temperature and treatment time, were found.
  • The Liquid-Enhanced Plasticity and Deformation Behavior of Cu-Mg-TiC Nanocrystalline Composite

    pp. 1582-1587

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    DOI:10.2320/matertrans.42.1582

    Cu–Mg–TiC bulk nanocrystalline composites were prepared by mechanical alloying, HIP process and hot-rolling. Tensile tests at constant crosshead speeds were carried out using a universal testing machine at several different temperatures under an argon atmosphere. The elongation drastically increased as the fraction of melt increased, and a maximum nominal elongation of about 200% was obtained at temperature where atomic fraction of liquid phase was about 0.5 and the strain rate sensitivity m was in the range of 0.8 to 1.0 for every composite. After the deformation, nanocrystalline structures with average grain sizes of about 30 nm were retained.
  • Mg-Based Hydrogen Storage Materials with Improved Hydrogen Sorption

    pp. 1588-1592

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    DOI:10.2320/matertrans.42.1588

    Nanocrystalline MgH2/MexOy composite powders were produced by high energy ball milling (MexOy=Sc2O3, TiO2, V2O5, Cr2O3, Mn2O3, Fe3O4, CuO, Al2O3, SiO2). The hydrogen absorption and desorption kinetics were determined in view of a technical application. The addition of selected oxides lead to an enormous catalytic acceleration of hydrogen sorption compared to pure nanocrystalline hydrides. In absorption, the catalytic effect of TiO2, V2O5, Cr2O3, Mn2O3, Fe3O4, and CuO is comparable. Concerning desorption, the composite material containing Fe3O4 shows the fastest kinetics followed by V2O5, Mn2O3, Cr2O3 and TiO2. Only 0.2 mol% of the catalysts is sufficient to provide a fast sorption kinetics. Additionally, Mg absorbs hydrogen already at room temperature by the use of metal oxides as catalysts. Furthermore, it is demonstrated for the first time that MgH2/MexOy-powders release hydrogen at 200°C.
  • Mechanically Alloyed Nanocrystalline Hydrogen Storage Materials

    pp. 1593-1598

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    DOI:10.2320/matertrans.42.1593

    Mechanical alloying and mechanical grinding have been used to synthesize or treat AB, AB2, and AB5 type alloys and Mg-based hydrogen storage materials. A nanocrystalline or an amorphous structure was obtained after milling, depending on the system and its composition. The structure and the hydrogen storage properties of various nanocrystalline alloys were investigated. It was found that the activation and kinetics of hydrogen absorption/desorption were improved. However, a severe loss of storage capacity was observed in the AB, AB2 and AB5 systems, but not much in Mg-based systems. The storage capacity can be recovered by thermal annealing at elevated temperatures. A preliminary explanation is given for the change of absorption/desorption kinetics and storage capacity.
  • Hydrogenation of Benzene over Catalyst Prepared from Amorphous Pt-Zr Alloy

    pp. 1599-1602

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    DOI:10.2320/matertrans.42.1599

    The hydrogenation of benzene in a fixed-bed type reactor operated at atmospheric pressure over amorphous Pt–Zr alloys with different platinum composition (Pt20Zr80, Pt28Zr72, Pt32Zr65) produced by a rapid solidification technique was investigated. Although the catalytic activity of the alloys was very low at virgin state, it gradually increased with increasing number of regeneration (oxidation and reduction)-reaction cycles. The activity approached a constant value after 5 or 6 regenerations. The hydrogenation activity of Pt–Zr alloy is higher than those of Pd–Zr and Ni–Zr alloys with the same composition. Furthermore, the turnover frequency of Pt–Zr defined as the reacting molecule per active site per second is also higher than those of Pd–Zr and Ni–Zr alloys. The hydrogenation order of the turnover frequency in the present study is almost the same as the order of the hydrogenation of olefins over the corresponding catalysts prepared from impregnation method. The characterization of the platinum catalyst prepared from the amorphous alloy revealed that the dispersion of platinum is higher than the impregnated catalysts, even though the platinum content of the former catalyst is much higher than that of latter. It is considered that this is a remarkable feature of the amorphous alloy catalyst.
  • Preparation and Characterization of Gold-Titania Nanoparticles

    pp. 1603-1606

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    DOI:10.2320/matertrans.42.1603

    We prepared gold-titania composite nanoparticles by the gas condensation method, and evaluated their physical and optical characteristics. The structure of obtained particles mainly showed that the gold particles, whose diameter ranged from 10 to 60 nm, were covered with spherical titania particles which were composite phases of anatase and rutile. The effect on the crystal structure and shapes of titania was not clearly observed by compounding with gold.
  • Synthesis and Related Kinetics of Nanocrystalline Ni by Hydrogen Reduction of NiO

    pp. 1607-1612

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    DOI:10.2320/matertrans.42.1607

    The present study has attempted to elucidate the formation mechanism of nanocrystalline (nc) Ni by hydrogen reduction of fine NiO powder in terms of related kinetics aspects. So, the kinetics and related mechanism of hydrogen reduction of NiO were investigated on the basis of structure modification of the NiO powder during reaction. The ball-milled NiO agglomerate powder having 20 nm in grain size and a log-normal pore size distribution was used for study. The non-isothermal reduction study showed that the nano-agglomerate NiO underwent a two-step reduction process which is presumably due to a chemical reaction at lower temperatures and a diffusion controlled process at higher temperatures. The activation energy for the nano-agglomerate NiO was 85.4 kJ/mol for lower temperatures and 105.1 kJ/mol for higher temperatures. The value for lower temperatures is consistent with that of as-received NiO of 85.6 kJ/mol. Such higher activation energy for higher temperatures can be attributed to the retardation of the reduction process by the change in the reduction mechanism from the chemical reaction to the diffusion process. Conclusively, the structure change during the reduction is believed to be responsible for the change in the reduction mechanism.
  • Fabrication of Shallow Silicon Nanoholes and Fixing Nanoparticles

    pp. 1613-1615

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    DOI:10.2320/matertrans.42.1613

    Shallow nanohole structures of uniform size were fabricated on p-type Si by anodizing Si at high applied voltages in a dilute HF solution. The dependence of surface morphology on anodization conditions was investigated and it was found that both HF concentration and ethanol concentration in the electrolyte influenced nanostructures. Nanohole sizes were changed 70–140 nm with increasing applied voltage. Fabricated nanohole structures were used as a substrate for fixing nanoparticles. Nanoparticles, whose sizes were comparable to nanohole sizes, were selectively trapped in nanoholes.
  • Influence of the Particle Size on the Surface Reactivity and Gas Sensing Properties of SnO2 Nanopowders

    pp. 1616-1622

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    DOI:10.2320/matertrans.42.1616

    The surface reactivity of a powder depends on the chemical composition of its surface and on the presence of defects. In the case of nanosized powders, the surface reactivity is enhanced by the increased defect concentration on the surface. On the other hand, the gas sensing properties of a semiconductor material are strongly related to the surface reactivity. In this article, it is shown, by Fourier transform infrared spectrometry, that SnO2 semiconductor nanoparticles are very sensitive toward CO and that the decrease of the particle size greatly enhances this sensitivity. Comparison is made between particles having an average size of 15 and 8 nm. Surface reactions at the origin of the CO detection mechanism are discussed as a function of the particle size.
  • Mechanochemical Synthesis of Niobium Pentoxide Nanoparticles

    pp. 1623-1628

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    DOI:10.2320/matertrans.42.1623

    Synthesis of Nb2O5 nanoparticles by mechanochemical processing has been investigated. The reactions 2NbCl5+5Na2CO3→Nb2O5+10NaCl+5CO2(g) and 2NbCl5+5MgO→Nb2O5+5MgCl2 led to the formation of Nb2O5 aggregates of 100–1000 nm in size. Addition of NaCl in the starting mixture of 2NbCl5+5Na2CO3 prevented the aggregates forming. After heat treatment of the as-milled powder at 300°C, amorphous Nb2O5 having a high surface area of 196 m2/g was obtained. Heat treatment at 550°C resulted in a powder consisting of 10–100 nm single crystal Nb2O5 particles along with a network of ultrafine amorphous particles. Annealing at higher temperature led to the formation of the Na2Nb2O11 phase.
  • Heterogeneously Junctioned Nano-Particles of Hematite and Goethite Formed in a Wet Process

    pp. 1629-1637

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    DOI:10.2320/matertrans.42.1629

    Acicular α-FeOOH particles are formed through aging of ferric oxyhydroxide colloidal solution formed by the neutralization of FeCl3 aqueous solution by NaOH . The effect of foreign ion addition to the colloidal solution on the formation and morphology of α-FeOOH particles has been investigated. The magnetic properties of Fe3O4 particles made from the obtained particles have also been investigated. The rate constant of the formation of α-FeOOH remarkably decreased, but the crystallite size of α-FeOOH particles increased with increasing the quantity of phosphate ion added even with small amounts. These results have been explained as follows: the phosphate ions are selectively adsorbed on the (a) plane of α-FeOOH, cover the (a) plane, and block the crystal growth of the (a) plane of the α-FeOOH . The quantities of the phosphate ion adsorbed on the b and c planes are relatively small. The complex ion of Fe(OH)4 is preferentially deposited on both (b) and (c) planes, and the crystal growth of (b) and (c) planes is greatly accelerated. The relationship between the morphology of the formed α-FeOOH particles and the quantity of phosphate ion added has been investigated. The asterisk type particles: α-FeOOH particles heterogeneously junctioned to α-Fe2O3 particles, were formed when a small amount of phosphate was added to the mother liquid. The α-FeOOH crystal epitaxially grew on the junction interface with the α-Fe2O3 crystal. In the case of the aging at the temperature as high as 80°C, the cross type junctioned particles were stably formed at pH below 12.0. The Fe3O4 particles with screw-like unique three-dimensional morphology were produced from the heterogeneously junctioned particles.
  • Metallic Nanocrystals Formation from Metal-Oxide Nanocrystals via Evaporation Process

    pp. 1638-1640

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    DOI:10.2320/matertrans.42.1638

    Metal or metal-oxide nanocrystals can be formed by the gas deposition method. Here we report a modified gas deposition method, by which nanocrystals of metal oxides are synthesized at first, and transformed into metal nanocrystals by heating the carrying gas. By controlling the heating temperature we can selectively deposit either dielectric films or conductive films in the same deposition process. Demonstrative experiments for transforming Al2O3 nanocrystals into Al nanocrystals are shown.
  • Preparation of Sol-Gel Derived SiO2 and Al2O3 Layers with Designed Nanoporosity

    pp. 1641-1646

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    DOI:10.2320/matertrans.42.1641

    The sol–gel process was used to prepare nanoporous (typically micro and mesoporous) supported layers from silica and alumina sols. The control of aging time for silica gel layers, the investigations of new alumina hydrosols and the general use of removable templating mesophases are crucial parameters to produce layers exhibiting unconventional porosity. Quasidense microporous layers as well as silica layers with a mesoporosity up to 74% were obtained. All these described methods allow the easy preparation of supported crack-free layers with several potential applications.
  • Impedance Spectroscopy Studies of Nanosturctured ZnO Based Varistor Materials

    pp. 1647-1652

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    DOI:10.2320/matertrans.42.1647

    Varistor material with 96 mol%ZnO+4 mol% dopants in oxide form of Bi, Co, Sb, B, Cu and Sn in nanostructured form has been synthesized using colloidal suspension and centrifugal separation method. The synthesized powder sample specimen was compacted into a pellet and sintered in air at 1073 K for 3 h to get a bulk density of 96%. In situ impedance spectroscopy (IS) studies have been carried out for the sintered nanostructured specimen at various temperatures in oxygen and nitrogen atmosphere. The impedance spectroscopy results below 423 K show that the specimen contains three activation energy regions which are attributed to (i) pure ZnO core grain (ii) aliovalent cation diffused layer around the pure ZnO core and (iii) grain boundary (GB). The specimen changes its conducting nature at and above 423 K . The a.c. conductivity was measured at fixed frequencies (106 Hz and 102 Hz) as a function of temperature. The conductivity of bulk grain and grain boundary regions increases with the increase of temperature. Eventhough the conductivity value of bulk grain and grain boundary regions increases with temperature, the rate of change of conductivity in grain boundary region is larger than that in bulk grain. The GB conductivity becomes almost equal to that of bulk grains at high temperatures. The change of grain boundary conductivity with temperature is faster in N2 atmosphere compared to the change in O2 atmosphere. Due to this dominant grain boundary conductivity, the varistor action of the sample is lost at high temperatures in nitrogen atmosphere (air).
  • Sintering of Nanocrystalline ZrO2(3Y) by Hot-Pressing

    pp. 1653-1656

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    DOI:10.2320/matertrans.42.1653

    Processing of synthesising nanocrystalline ZrO2(3Y) by hot-pressing was investigated. Large crack-like pores have been found in the sintered samples. The reason of this phenomenon was that the agglomerate in the powder had not been destroyed efficiently. This agglomerate sintered quickly and turned into aggregate when hot-pressing was applied. Large pores formed as a result of the interaction between the aggregate and the matrix. Since the applied pressure was limited because of the low stress tolerance of the graphite die, no plastic deformation could happen and those large pores could not be “squashed”. As a result, the densities of the samples sintered by hot-pressing were lower than by pressureless sintering at the similar sintering temperature. To overcome this shortage of hot-pressing, sinter forging was applied. Nano Y-TZP materials with grain size of about 85 nm and relative density of 99% could be obtained after sinter-forging at 1100°C for only 30 min.
  • Gas Adsorption Properties of Titania Nanoparticles Coated Piezoelectric Quartz Crystals

    pp. 1657-1660

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    DOI:10.2320/matertrans.42.1657

    In this study, piezoelectric quartz crystals are used as a gas sensor to investigate the detecting properties of titania nanoparticles for carbon monoxide and nitrogen dioxide gases. Titania nanoparticles are deposited on the surface of a piezoelectric quartz crystal by a gas condensation method. It is found that the amount of frequency change is dependent on gas concentrations at constant temperature. The amount of adsorbed carbon monoxide gas at 150°C hardly increases with increasing concentration, and the amount of adsorption is less than which at 200°C. The amount of adsorbed NO2 also indicates similar results. The amount of adsorbed CO at 200°C is more than that of NO2. The results are obtained from this study within one or two order difference in comparison with results in literature.
  • Synthesis of Al2O3/SiC Powders Using Microwave-Induced Combustion Reaction

    pp. 1661-1666

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    DOI:10.2320/matertrans.42.1661

    Nanocomposites Al2O3/SiC powders have been synthesized by a microwave-induced combustion process using aluminium nitrate, β-SiC (powders) and urea. The effect of preheating the solution before the combustion reaction and the effect of the characteristic of the SiC powders, in the crystallization of the alumina, by combustion reaction were evaluated. The preheating of the liquid solution at about 150°C before heating in the microwave oven guaranteed the homogeneity of the solution and modified the characteristics of the products. The mechanism of heating in the microwave oven was favorable to the uniform emission of gases and fast dissipation of heat, promoting formation of different foam and nanocomposites Al2O3/SiC powders with characteristics that were different from those produced conventionally. The direct conversion of liquid solution to the final solid product was assured, and the segregation commonly found in conventional mixing of powders (alumina-SiC) was avoided. The different characteristics of the SiC powders have strong influence in the flame time of the combustion reaction and consequently in the crystallization of the alumina and characteristics of the Al2O3/SiC nanocomposites powders. The SiC particles were not oxidized during the reaction and partial reaction with alumina did not occur; SiC particles remained as a distinct and separate phase.
  • Synthesis and Characterization of Nanocrystalline RuO2-ZrO2

    pp. 1667-1671

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    DOI:10.2320/matertrans.42.1667

    The nanocrystalline samples of zirconium oxide doped with ruthenium oxide (RuO2) have been synthesized from chlorides as precursors by chemical precipitation method. The as-prepared and annealed powder samples were studied by XRD, TEM and Impedance Spectroscopy. With 7.5 mol% of RuO2, only a small percentage of ZrO2 stabilizes in tetragonal form without stabilization in cubic form. With 9 mol% and above, ZrO2 stabilizes in mixed phases having both tetragonal and cubic structure. On annealing, up to 1273 K the proportion of the cubic phase increases; however annealing at temperatures above 1273 K makes the sample to become monoclinic. Average grain size, as determined by Scherrer’s formula using X-ray linewidth, increases with increase of annealing temperature. The same trend is observed in TEM studies. TEM studies show the agglomeration of grains. X-ray diffraction for various concentrations of RuO2 shows the presence of small amount of RuO2 as impurity. This implies that Ru4+ goes to the interstitial position also in addition to its occupation of substitutional position of Zr4+ due to its smaller ionic radius (0.062 nm) compared to that of Zr4+ (0.084 nm). The impedance spectroscopy measurement shows that the conductivity decreases with an increase of grain size. The phase changes in the stabilization process with different concentrations and annealing temperatures, and growth of grain size in RuO2 stabilized ZrO2 will be presented. One of the salient points in this study is stabilization of ZrO2 with RuO2 alone without Y2O3 as reported in the literature.
  • Oriented Arrays of Nanocrystalline Magnetite in Polymer Matrix Produced by Biomimetic Synthesis

    pp. 1672-1675

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    DOI:10.2320/matertrans.42.1672

    Synthesis of nano sized magnetite particles has been carried out following a polymer matrix mediated process. The synthesis route, being akin to bio mineralization, yields elongated magnetite particles of uniform size and morphology. The produced particles were oriented perpendicularly with respect to polymeric tubules and showed a tendency of array formation as happens in magnetotactic bacteria.
  • The Promoting Effect of Sulfate Ions on the Nucleation of TiO2 (Anatase) Nanocrystals

    pp. 1676-1680

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    DOI:10.2320/matertrans.42.1676

    The effect of sulfate ions on the nucleation of anatase nanocrystals during the hydrolysis of TiCl4 solution was investigated. The resulting titania powders were characterized by DSC, FT-Raman spectroscopy, X-ray diffraction and UV-Vis spectroscopy. In the presence of sulfate ions as low as one twentieth to Ti4+, the precipitate prepared at room temperature contained 17.8% anatase nanocrystalline titania. The promoting effect of sulfate ions on the nucleation of anatase at higher temperature was more significant. For example, at 343 K, anatase powder was synthesized in the presence of a small amount of sulfate ions, while mixed-phase (the fraction of rutile was 0.634) powder was prepared in the absence of sulfate ions. Small amount of sulfate ions also modified the pore size distribution effectively and stabilized anatase to convert into rutile during calcining process, and powders with narrow pore size distribution (average pore diameter 3.8 nm) and mesoporous nature were prepared in the presence of sulfate ions.
  • Hydrothermal Processing of Carbon Nanotubes from Dense Fluids: Growth Mechanism

    pp. 1681-1683

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    DOI:10.2320/matertrans.42.1681

    We report in this communication the growth mechanism of multiwall carbon nanotubes during hydrothermal treatment of carbon soot at 800°C and 100 MPa. High-resolution electron microscopy (HRTEM) study reveals the formation of multiwall carbon nanotubes made of a hollow core enclosed in well-ordered concentric graphitic layers after hydrothermal treatment.
  • Metal Nanocrystals Grown by Vacuum Deposition on Aligned Carbon Nanotubes

    pp. 1684-1687

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    DOI:10.2320/matertrans.42.1684

    When the vacuum evaporation method was used to deposit metals, such as Au, Ag, or Cu, on a substrate covered with aligned carbon nanotubes which were fabricated by the microwave-plasma-enhanced chemical vapor deposition method, we found that nanoscale single crystals of the metals with well-defined facets were grown on the surfaces of the carbon nanotubes. Nanocrystals ranging from approximately 50 to 500 nm in diameter were obtained when the deposition time ranged from 1 to 60 min. Whiskerlike crystals with high aspect ratios could also be found frequently in these nanocrystals, which can be applied in field-emission display devices.
  • Synthesis and Characterization of Manganese(II)-Phenanthroline Complex Grafted 3-Methacryloyloxypropyl Functional MCM-41

    pp. 1688-1690

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    DOI:10.2320/matertrans.42.1688

    This paper describes the preparation of manganese(II)-phenanthroline complex functionalized MCM-41 (MCM from Mobil Crystalline Material). The as-synthesized organic group functional MCM-41 and metal-ion-complex functionalized MCM-41 were extensively characterized by powder X-ray diffraction (XRD), TEM, solid-state 29Si and 13C NMR and nitrogen adsorption/desorption isotherms at 77 K, as well as Mn(II) electron spin resonance (ESR) spectroscopy at room temperature. These results indicated that 3-methacryloyloxypropyl group well dispersed in the mesopore of MCM-41, which attached to the silicate walls via Si–O–Si bonds. The mesopore of MCM-41 was tailored by the grafted organic group and the complex, while the coordination state of Mn(II) was unaffected by the process of grafting.
  • An Investigation of the Structure and Corrosion Resistance of Permanganate Conversion Coatings on AZ91D Magnesium Alloy

    pp. 1691-1699

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    DOI:10.2320/matertrans.42.1691

    Conversion coatings for magnesium have traditionally been based on immersion treatment in the solution containing hexavalent chromium compounds. The excellent performance of these coatings as paint bases has been established in a broad range of application. However, the replaceable surface treatment has been strongly emphasized by present environmental needs to eliminate hexavalent chromium. The development of chemical conversion coatings in permanganate bath on magnesium alloys has been studied using mass gain measurements, measurements of corrosion potential, X-ray diffraction, X-ray photoelectron spectroscopy, glow discharge spectroscopy and microscopic examination. Chemical conversion coatings obtained from HF addition in bath consisted of the film that was composed mainly of manganese oxides and magnesium fluoride. It was found that these films formed amorphous composite coating. Corrosion resistances of permanganate chemical conversion coatings were comparable with that for chromating.
  • Effect of Hf on Microstructure and High-Temperature Strength of a Cast NiAl/Cr(Mo) Alloy

    pp. 1700-1704

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    DOI:10.2320/matertrans.42.1700

    A NiAl/Cr(Mo) alloy modified with Hf was fabricated by a vacuum induction melted and drop cast. The alloy was mainly composed of NiAl matrix, Cr(Mo) and Hf-rich phase distributed between NiAl and Cr(Mo) phase boundary and phase transition was also studied. Then it was hot isostically pressed (HIPed) at 1523 K, 200 MPa for 4.5 h. Its high temperature compressive behavior was studied and the deformation features of the alloy could be adequately described by standard power law which is usually used to characterize creep behavior for various metallic material. The stress exponent n as well as the activation energy Q was calculated by fitting the experimental data to the power-law and temperature-compensated power law equation. The possible strengthening mechanism was discussed.
  • Mutual Inductance of Small Solenoid Coil Equipped with Scanning Tunneling Electron Microscope

    pp. 1705-1709

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    DOI:10.2320/matertrans.42.1705

    A small solenoid coil was equipped with a scanning tunneling electron microscope (STM) which has an iron needle core tip as the probe. Mutual inductance of the coil with a thin gold film on a mica plate was investigated in order to profile electrical conductivity. It is important to maintain a small gap between the tip apex and the sample surface. The gap is related to the distribution of electron scattering by induced current. The conductivity mapping was carried out on a large terrace. If the tip is over the step edge, the output signal from the probe coil becomes unstable. Atomically smooth surface of the specimen was in need for the electrical conductivity mapping. The electrical conductivity on the terrace was almost constant. The mutual inductance values with the gold film at various temperatures were investigated by cooling it below 250 K . The mutual inductance is inversely proportional to the temperature to the one-third power, T1⁄3. The relationship between the mutual inductance and the temperature was explained by the electromagnetic theory.
  • Microstructural Stability of Gas-Atomized Al-Based Nanophase Composites

    pp. 1710-1716

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    DOI:10.2320/matertrans.42.1710

    The microstructure evolution and grain growth behavior, of gas-atomized Al88Ni9Ce2Fe1 nanocomposite materials, were studied by means of the X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The results showed that the microstructure of as-atomized powders are affected by the degree of solute supersaturation in matrix, the microstrain contained, the size, distribution and volume fraction of nanophase precipitated, and these are essentially sensitive to the powder particle sizes. Moreover, there appeared to be a two-stage phase transformation during thermal crystallization, i.e., the precipitation of α-Al and the growth of Al3(Ni, Fe) nanophase in preference to Al11Ce3 nanophase, respectively. Finally, the grain growth kinetics of α-Al at temperatures of 250 to 300°C, revealed that the volume-diffusion grain growth mechanism with an activation energy of 1.3 eV is controlling in the nanophase materials.
  • Formation of TiC/Ti2AlC Composite Layer and Improvement on Surface Roughness

    pp. 1717-1722

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    DOI:10.2320/matertrans.42.1717

    In order to improve surface hardness, surface modification of die casting aluminum alloys was carried out by applying a new method called Electrical Discharge Alloying with ultrasonic vibrations, in which a conventional electrical discharge machine can be used. The layer deposited on the substrate consists of TiC and Ti2AlC formed by the reaction between titanium contained in the green compact electrode, the aluminum in the electrode and the substrate and also the carbon decomposed from a working fluid. When the ultrasonic vibration is applied to the substrate, especially at a frequency of 94.2 kHz, the discharged craters are bigger than those obtained when alloying without ultrasonic vibration. Also, for single discharge, the amount of deposited Ti and C increases near the edge of the crater. When the ultrasonic vibration is applied to the electrode for single discharge, many convex-shaped craters are generated on the substrate. The cross-sectional hardness of the alloyed area increases with increase in the concentration of carbon and titanium. The secondary elaboration using the cast Ti–36 mass%Al solid electrode is effective for the improvement of surface roughness of the modified layer. When the green compact electrode is used in the primary Electrical Discharge Alloying and the cast solid electrode is used in the secondary elaboration, surface roughness is not so different between the process with and that without ultrasonic vibration. However, the modified layer’s thickness obtained with ultrasonic vibration is thicker than that without ultrasonic vibration.
  • Effects of Al, Si and Mo on Passivation Characteristics of Fe-10Cr Alloys

    pp. 1723-1730

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    DOI:10.2320/matertrans.42.1723

    A study has been made on the effects of Al, Si and Mo on anodic polarization characteristics of Fe–10Cr alloys in 0.05–1.0 kmol·m−3 H2SO4 and NaCl solutions. Potential decay curves have also been measured in order to evaluate the stability of the passive films formed on Fe–10Cr alloys containing Al, Si and Mo. The analysis of the chemical composition of the passive film has been carried out by AES and XPS . The addition of Mo was very useful to decrease the critical passivation current density of Fe–10Cr alloys which contained Al and Si. The passive current density decreased with addition of 2 mass%Mo to Fe–10Cr–3Si alloy, while it increased in Fe–10Cr–3Al alloy. Pitting potential was moved toward the noble direction by the addition of Mo, except for the case of Fe–10Cr–3Al–3Si–2Mo alloy. It seems that Laves phase (Fe2Mo) was precipitated in this alloy, and Mo-depleted zone was formed locally. The potential decay time of the passive film was increased by the addition of Al, Si and Mo to Fe–10Cr alloys. Two step potential decay curves were obtained in Si-containing alloys, and this behavior of the decay curve was shown more clearly in Fe–10Cr–3Si–2Mo alloy. The results of AES and XPS analysis indicated that Cr and Al concentrated in the passive film of Fe–10Cr–Al alloy. In the case of Fe–10Cr–Si alloy, Si concentrated in the surface region of the film and Cr in the internal region of the film. The confirmation was not possible for the enrichment of Mo in the passive film.
  • Effect of Oxygen in Titanium on Reaction Diffusion between Ti and Al

    pp. 1731-1740

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    DOI:10.2320/matertrans.42.1731

    Reaction diffusion in Ti/Al and Ti–5 mol%O/Al diffusion couples has been investigated by electron-probe microanalysis. Only one intermetallic compound TiAl3 was observed as an intermediate layer in the temperature range from 773 to 903 K in both the diffusion couples. Si, which is an impurity element in aluminum, was concentrated in TiAl3. The growth of the intermediate layer turned out to be diffusion limited; the activation energy was estimated to be 237±15 kJ·mol−1 and the temperature dependence of square of the rate constant, k2, for layer growth can be described with the following equation in the temperature range from 773 to 903 K in the Ti/Al diffusion couples. k_TiAl_3^2=3.5exp[-(237±15) kJ·mol^-1/RT]m^2s^-1In the case of the oxygen doped diffusion couples, the layer growth of TiAl3 was significantly suppressed and the activation energy was 263±7 kJ·mol−1 for temperatures from 773 to 873 K . The suppression is explained by aluminum oxide formed between aluminum and TiAl3. The Kirkendall marker shifted toward the aluminum side, which suggests that diffusion of Al is faster than that of Ti in the intermediate layer.
  • Deformation-Induced Nanocrystal Precipitation in Al-Base Metallic Glasses

    pp. 1741-1747

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    DOI:10.2320/matertrans.42.1741

    Bending and uniaxial tensile tests for Al-base amorphous ribbons were performed at room temperature for a number of compositions. Al-nanocrystal precipitation was observed within vein protrusions on fracture surfaces and along crack propagation paths, as well as within shear bands resulting from bending. A composition dependence of crystallization upon bending was also observed. Effects of local adiabatic heating was observed on fracture surface.
  • Operating Conditions for Hydriding Combustion Synthesis of Pure Mg2NiH4

    pp. 1748-1752

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    DOI:10.2320/matertrans.42.1748

    To study the relationship between hydrogen pressure and holding time for hydrogenation at 680 K, hydriding combustion synthesis of Mg2NiH4 were conducted at different heat patterns and hydrogen pressures. The obtained results were summarized in the form of an operating map, which visualized clearly the possible operating conditions for industrializing the process. Pure Mg2NiH4 can be synthesized at a high pressure of hydrogen and a short holding time at 680 K . At a lower pressure of hydrogen such as 0.5 MPa, 7.2 ks of a holding time at 680 K is enough to obtain 100% pure Mg2NiH4 as a product. The pressure composition isotherm of Mg2NiH4, obtained at 623 K, showed a hydrogen capacity very near the theoretical value of 3.6%, together with a reasonable plateau. The specific surface areas of several samples suggested that the product is a porous material.
  • A Mechanism of Diamond Growth with Carbon Nanotube Nucleation Agent by Hot-Filament Chemical Vapor Deposition

    pp. 1753-1757

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    DOI:10.2320/matertrans.42.1753

    Behaviors of carbon nanotubes (CNTs) in H2 atmosphere or CH4+H2 mixtures, transforming mechanism of CNTs to diamond embryo were investigated. Experimental results show that CNTs could be etched by H2 and transformed to carbon nanoparticles under conditions of hot-filament chemical vapor deposition. The mechanism can be concluded that CNTs were broken down by H2, transformed to carbon nanoparticles or shorter CNTs; on surface of carbon nanoparticles or end caps of CNTs diamond crystals were nucleated and grown up.
  • The Influence of Coherent and Semi-Coherent TiCu Precipitates on the Martensitic Transformation of Melt-Spun Ti50Ni25Cu25 Shape Memory Ribbons

    pp. 1758-1762

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    DOI:10.2320/matertrans.42.1758

    Thin coherent as well as thicker semi-coherent plate-like precipitates of the same type, i.e. TiCu, were generated by different heat treatments of melt-spun Ti50Ni25Cu25 ribbons. Their influence on the martensitic transformation behavior was investigated by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that thin coherent plate-like precipitates lower the temperatures of both martensitic and its reverse transformation and broaden the peak form of the DSC signal. On the other hand, thicker semi-coherent plates act to raise both transformation temperatures. The role of coherency stresses, arrangements of misfit dislocations, and compositional aspects are discussed.
  • Numerical Analysis of Observations on Diffusion Induced Recrystallization in the Ni(Cu) System using A Kinetic Model

    pp. 1763-1770

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    DOI:10.2320/matertrans.42.1763

    Considering the effect of the friction force due to volume diffusion of a solute on the driving force, a new kinetic model has been proposed for diffusion induced recrystallization (DIR) in the A(B) system in which solute B atoms diffuse into a pure A metal or a binary A-B alloy. The energy balance model [M. Kajihara and W. Gust: Scr. Mater. 38 (1998) 1621] has been combined with the columnar geometry and boundary diffusion model [C. Li and M. Hillert: Acta Metall. 29 (1981) 1949] and the extended model [Y. Kawanami et al.: ISIJ Int. 37 (1997) 921] in order to describe mathematically the growth rate of the fine grain region (DIR region) formed by DIR as a function of the reaction time. DIR in the Ni(Cu) system was experimentally observed by Kawanami et al. [Y. Kawanami et al.: Mater. Trans., JIM 39 (1998) 218] at 923 and 1023 K . The new model has been utilized to analyze their observations theoretically. According to the observations, the migration rate v of the moving boundary gradually decreases with increasing reaction time. However, the decrease in the migration rate v is negligible during a small time interval of Δt=1 s at the experimental reaction times. Thus, the value of v was assumed to be constant at each time step with Δt=1 s in order to simplify the analysis. Using the mobility M of the moving boundary as the fitting parameter, the thickness of the DIR region was calculated as a function of the reaction time by a numerical technique. The calculation gives values of M=3.73×10−17 and 1.51×10−15 m4/Js at 923 and 1023 K, respectively, and thus M0=1.03 m4/Js and QM=290 kJ/mol for M=M0exp(−QMRT). The temperature dependence of the mobility indicates that the grain boundary migration may be governed by the solute drag effect for which the volume diffusion of the solute along the moving direction in the untransformed matrix ahead of the moving boundary has the most important role.
  • Effects of Temperature and Strain Rate on Elongation at Elevated Temperature in Al - 4.5Mg Alloy

    pp. 1771-1776

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    DOI:10.2320/matertrans.42.1771

    The effects of temperature and strain rate on elongation of Al–4.5Mg alloy were investigated at 10−4–10−2 s−1 and at 573–773 K . The elongation depended on the temperature and strain rate even in the solute-drag creep region; as a result, a large elongation of 352% was attained at 653 K and at 10−3 s−1. Necking developed due to a decrease in plastic stability arising from apparent strain softening behavior at 10−2 s−1 at 653 K or the low strain rate sensitivity at 10−3 s−1 at 573 K . Also, significant cavitation was caused due to grain boundary sliding at 10−4 s−1 at 653 K and at 10−3 s−1 at 773 K . The development of necking and cavitation is responsible for the temperature and strain rate dependence of elongation.
  • Surface Modification of Magnesium by NaHCO3 and Corrosion Behavior in Hank’s solution for New Biomaterial Applications

    pp. 1777-1780

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    DOI:10.2320/matertrans.42.1777

    The present study was carried out to improve the corrosion resistance of pure magnesium in Hank’s Balanced Salt Solution (HBSS) through the surface modification. Three kinds of alkaline compounds, such as sodium hydrogen carbonate, sodium carbonate, and lithium hydroxide, were used for treatment. Only magnesium treated with aqueous sodium hydrogen carbonate solution gave a good corrosion resistance in HBSS solution at 25°C up to 75 days, while almost no effect in sodium carbonate and lithium hydroxide. It was likely that hydrogen carbonate ions were essential for the surface improvement of magnesium. X-ray diffraction patterns of modified magnesium showed new peaks of magnesium carbonate and others on the surface. New surface structure of needle-shaped crystals was observed by scanning electron microscopy (SEM). Both elemental mapping, and energy dispersive (EDX) techniques in SEM showed the precipitation of calcium magnesium phosphate (low crystallinity whitlockite:(Ca,Mg)3(PO4)2) on the surface of magnesium specimen. It could be concluded that surface modification with sodium hydrogen carbonate made it possible to apply metal magnesium in biomedical, dental, and other industrial usage.
  • High Strain Rate Superplasticity in 6061 Alloy with 1% SiO2 Nano-Particles

    pp. 1781-1789

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    DOI:10.2320/matertrans.42.1781

    Four 6061 aluminum systems were prepared in this study, including the DC cast 6061 alloy processed by TMT and ECAP, the PM modified 6061 alloy added with 1 vol% nano-SiO2, and the commercial 6061/20%SiCw composite. All materials possessed fine grain sizes ∼ 0.3–1 \\micron after processing, but only the latter two could maintain fine grain size upon loading at high temperatures and achieved HSRS over 300% at 570–590°C and 1–5×10−1 s−1. The texture was weaker and the grain boundary misorientation distribution was more random in the 6061/1%nano-SiO2 alloy as compared with the unmodified 6061 alloys. The 1%nanoSiO2 modified alloy exhibited low stresses ∼ 4 MPa, true strain rate sensitivity ∼ 0.5, smooth GBS and a limited amount of liquid phase at high temperatures and strain rates, similar to those observed in HSRS composites. The current results suggest that the addition of a small amount (1 vol%) of SiO2 or Al2O3 nano-particles into commercial Al alloys can effectively suppress grain growth at high temperatures and enhance HSRS.
  • Comparison of the Giant Magnetoimpedance Effect between Ferromagnetic La0.64Ba0.36MnO3-δ and Paramagnetic La0.64Ba0.36Mn0.95Fe0.05O3-δ

    pp. 1790-1793

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    DOI:10.2320/matertrans.42.1790

    In the present paper, ac electric transport behavior of La0.64Ba0.36Mn1−xFexO3−δ with x=0 (the ferromagnetic phase) and x=0.05 (the paramagnetic phase) are comparatively investigated at a temperature of 300 K . The reactance X is positive for the x=0 but negative for the x=0.05. For x=0, the impedance Z increases at first, undergoes a peak and a valley, and finally increases again with increasing ac frequency. On the contrary, for x=0.05, the impedance decreases monotonically with increasing ac frequency. Meanwhile, the giant magnetoimpedance effect has been found in both ferromagnetic x=0 and paramagnetic x=0.05 at 300 K . Results also show that with increasing frequency the change ratio of the magnetoimpedance (Z(0)–Z(5172 A·m−1))⁄Z(0) increases for the sample x=0 but decreases for the sample x=0.05.
  • A Novel Thermic Process for Producing V-Based Solid Solution Type Hydrogen Storage Alloy

    pp. 1794-1799

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    DOI:10.2320/matertrans.42.1794

    The performance of a high hydrogen capacity alloy, V–16%Ti–12%Ni–1.4%Nb–0.96%Co–2.8%Ta, is sensitively influenced by dissolved aluminum and oxygen, both of which can be removed from vanadium by a refining process, but the process currently used is too expensive. It is necessary to develop a process to remove these impurities at a reasonable cost. We propose a new method for production of the alloy. A V–15%Ni–1.8%Nb precursor with a low enough level of aluminum was produced by alumino-thermic reduction from a mixture of V2O5, Nb2O5 and nickel. Subsequently, a V–16%Ti–12%Ni–1.4%Nb–0.96%Co–2.8%Ta alloy was obtained by alloying the precursor and the other constituents of titanium, cobalt and tantalum, and by adding mischmetal as a reducing agent to remove oxygen to a low enough level. It was demonstrated that, by the method described here, the vanadium-based alloy could be produced at a reasonable cost.
  • High-Strength Cu-Based Bulk Glassy Alloys in Cu-Zr-Ti-Be System

    pp. 1800-1804

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    DOI:10.2320/matertrans.42.1800

    New Cu-based bulk glassy alloys with high glass-forming ability and good mechanical properties were formed in Cu–Zr–Ti–Be system. The glass transition temperature (Tg), supercooled liquid region defined by the difference between crystallization temperature (Tx) and Tg, ΔTx(= TxTg) and reduced glass transition temperature (TgTl) are 728 K, 50 K and 0.64, respectively, for the (Cu0.6Zr0.3Ti0.1)92.5Be7.5 and 720 K, 42 K and 0.64, respectively, for the Cu54Zr27Ti9Be10 alloy. The use of the 7.5%Be and 10%Be alloys has enabled us to form glassy alloy rods with diameters up to 5 mm. The bulk glassy 10%Be alloy exhibits high tensile fracture strength of 2450 MPa and Vickers hardness of 710, in combination with Young’s modulus of 146 GPa, compressive fracture strength of 2500 MPa and compressive elongation of 3.5%. The tensile strength level is the highest among all bulk metallic glasses and hence the new Cu-based bulk glassy alloys have significant importance in basic science and engineering aspects.
  • Cu-Based Bulk Glassy Alloys with Good Mechanical Properties in Cu-Zr-Hf-Ti System

    pp. 1805-1812

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    DOI:10.2320/matertrans.42.1805

    High-strength Cu-based bulk glassy alloys were synthesized in Cu–Zr–Ti and Cu–Hf–Ti ternary and Cu–Zr–Hf–Ti quaternary systems by copper mold casting. The critical diameter was 4 mm for the Cu60Zr30Ti10 and Cu60Hf25Ti15 ternary alloys and the Cu60Zr20Hf10Ti10 and Cu60Zr10Hf15Ti15 quaternary alloys. As the substitution amount of Zr or Hf by Ti in Cu60Zr40 and Cu60Hf40 alloys increases, the glass transition temperature (Tg), crystallization temperature (Tx) and temperature interval of supercooled liquid region ΔTx(=TxTg) decrease, while the liquidus temperature (Tl) has a minimum of 1127 K around 20%Ti, resulting in a maximum TgTl of 0.63 in the vicinity of 20%Ti. The high glass-forming ability was obtained at the compositions with high TgTl. The bulk glassy alloys exhibit high fracture strength of 2040–2190 MPa and plastic elongations of 0.3 to 1.9%. The finding of the Cu-based bulk glassy alloys with high TgTl above 0.60, high fracture strength above 2000 MPa and distinct plastic elongation is encouraging for the subsequent development as a new type of bulk glassy alloys which can be used for structural materials.
  • Dry Separation for Rare Earth by Vacuum Distillation of Di and Triiodide Mixture

    pp. 1813-1819

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    DOI:10.2320/matertrans.42.1813

    A basic study on dry separation process for rare earth element by vacuum distillation combined with selective reduction of iodides has been carried out. A possibility for vacuum distillation of di and triiodide mixture is demonstrated. The process is based on large differences in the redox potential of the rare earth iodides and in the vapor pressure of rare earth di and triiodides. Experimental proof of the vacuum distillation is provided for binary iodide systems, neodymium-samarium and samarium-dysprosium. The apparent separation factors, calculated from the compositions of diiodide-enriched and triiodide-enriched deposits, are βSm/Nd>890 and βSm/Dy=2300, respectively. These values are large enough to produce commercial pure metals used in the rare earth magnets. Thermodynamic consideration of the process is made on the basis of data reported in the literature and some thermodynamic assumptions.
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  • (Fe, Co)-(Hf, Nb)-B Glassy Thick Sheet Alloys Prepared by a Melt Clamp Forging Method

    pp. 1820-1822

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    DOI:10.2320/matertrans.42.1820

    Glassy Fe58Co14Hf8B20 and Fe60Co20Hf6Nb2B12 alloys in a thick sheet form were prepared by a meltclamp forging method. Their thickness was 0.78 mm and 0.49 mm, respectively. The glassy sheets have nearly the same values of glass transition temperature (Tg), onset temperature of crystallization (Tx) and Curie temperature (Tc) as those for the melt-spun ribbon samples. The Tg, Tx and Tc were 826 K, 895 K, and 598 K respectively for the Fe58Co14Hf8B20 alloy, and 799 K, 841 K and 638 K respectively for the Fe60Co20Hf6Nb2B12 alloy. The same thermal properties between the forged and the melt-spun samples are presumably due to the formation of a similar glassy structure. The success of manufacturing Fe-based glassy thick sheets by the forging method is encouraging for future progress as a new engineering material.
  • Phase Relationship in a BaO-Bi2O3-TiO2 System and Electrical Properties of BaTiO3 with Addition of Bi4Ti3O12

    pp. 1823-1826

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    DOI:10.2320/matertrans.42.1823

    A phase relationship of the BaO–Bi2O3–TiO2 system at 1273 K was studied using a solid state reaction. A new compound of BaBi6Ti20O50 was found in this ternary system. In the BaTiO3–Bi4Ti3O12 pseudo-binary system, the solid solution of Bi4Ti3O12 into BaTiO3 was observed up to 4 mol%  Bi4Ti3O12. The lattice parameters of tetragonal BaTiO3 varied depending on Bi4Ti3O12 content in the solid solution range. The structure of BaTiO3 became cubic with the addition of more than 4 mol%  Bi4Ti3O12. The temperature dependence of permittivity obeyed the Curie-Weiss-like behavior in the solid solution range. The highest permittivity of BaTiO3 decreased and the peak of permittivity became broader with increasing Bi4Ti3O12 content.
  • Invariant Reaction of Liquid →Solid+Gas — Gas-Evolution Crystallization Reaction —

    pp. 1827-1829

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    DOI:10.2320/matertrans.42.1827

    An invariant reaction of “Liquid(L)→Solid(S)+Gas(G)” was considered as a eutectic reaction in previous literatures. However, since one of the resultant phases is not a solid phase, the invariant reaction of L→S+G should be distinguished from the eutectic reaction. The nomenclature of the L→S+G reaction is suggested to be a gas-evolution crystallization reaction.
  • Structure of One-Dimensional Al-Co-Ni Quasicrystal Studied by Atomic-Scale Transmission Electron Microscopy

    pp. 1830-1833

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    DOI:10.2320/matertrans.42.1830

    The structure of a one-dimensional Al–Co–Ni quasicrystal in an Al71Co19Ni10 alloy annealed at 1100°C for 11 h has been studied by atomic-scale observations of high-angle annular detector scanning transmission electron microscopy and high-resolution transmission electron microscopy. Its structure can be characterized as a two-dimensional aperiodic arrangement of columnar clusters of atoms with a decagonal section of 2.0 nm in diameter and with pentagonal symmetry. In the arrangement of the atomic clusters, pairs of two lattice planes with high density of the atomic clusters are periodically arrayed with an interval of about 3 nm along the one direction. The atomic clusters with two orientations of pentagonal symmetry are randomly arranged with no special ordering manner.

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