• Journal of Powder Materials
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• v.18 no.2
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• pp.149-158
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• 2011

Electro-Discharge Sintering (EDS) employs a high-voltage/high-current-density pulse of electrical energy, discharged from a capacitor bank, to instantaneously consolidate powders. In the present study, a single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical $Ti_{52}Zr_{28}Ni_{20}$ powders in size range of 10~30 and $30\sim50{\mu}m$ consisting of ${\beta}$-(Ti, Zr) and icosahedral phases were applied to examine the structural evolution of icosahedral phase during EDS. Structural investigation reveals that high electrical input energy facilitates complete decomposition of icosahedral phase into C14 laves and ${\beta}$-(Ti, Zr) phases. Moreover, critical input energy inducing decomposition of the icosahedral phase during EDS depends on the size of the powder. Porous Ti and W compacts have been fabricated by EDS using rectangular and spherical powders upon various input energy at a constant capacitance of $450{\mu}F$ in order to verify influence of powder shape on microstructure of porous compacts. Besides, generated heat (${\Delta}H$) during EDS, which is measured by an oscilloscope, is closely correlated with powder size.

• Applied Microscopy
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• v.32 no.1
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• pp.31-37
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• 2002

As-cast microstructure of Mg-rich $Mg_{68}Zn_{28}Y_4$ has been investigated by a detailed transmission electron microscopy. The as-cast $Mg_{68}Zn_{28}Y_4$ alloy consisted of three different types of phases: $10{\sim}20{\mu}m$ size primary solidification phase, dendritic phase grown from the primary phase and a eutectic structure formed at the later stage of solidification. The primary solidification phase has an icosahedral structure with a large degree of phason strain. 1/1 rhombohedral approximant phase with lattice parameters: $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$ is first observed in Mg-Zn-Y system. The rhombohedral structure can be obtained by introducing phason strain in the six dimensional face centered hyper-cubic lattice. The decagonal phase nucleates with orientation relationship with the icosahedral phase, and $Mg_4Zn_7$ nucleates with orientation relationship with the decagonal phase, indicating a close structural similarity between the three phases. Gradual depletion of Y during solidification plays an important role in heterogeneous nucleation of decagonal and $Mg_4Zn_7$ phases from icosahedral and decagonal phases respectively.

• Journal of the Mineralogical Society of Korea
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• v.16 no.1
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• pp.33-47
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• 2003

Various applied-mineralogical characterization including measurements of surface area, size distribution, swelling index, and viscosity were done for some domestic bentonites in order to decipher the rheological properties and their controlling factors. The bentonites, which are Ca-type and relatively low-grade (rnontmorillonite contents: 30 ∼ 75 wt%), occur mostly as subhedral lamellas with the size range of 2 ∼ 4 $\mu\textrm{m}$. The size distribution of mineral fractions in bentonite suspension is dominant in the range of 10 ∼ 100 $\mu\textrm{m}$, and though rather complicated, exhibits roughly bimodal patterns. The feature is more conspicuous in the case of zeolitic bentonite. The bentonites have surface areas ranging 269 ∼ 735 $\m^2$/g, which are measured by EGME adsorption method. The EGME surface areas are nearly proportional to the rnontmorillonite contents, moisture contents, or total CEC. In the surface area measurements, zeolitic bentonites have slightly higher values than those zeolite- free types. The measured swelling index and viscosity of domestic bentonites are comparatively low in values. The swelling values of bentonites were measured to be 250∼500% at maximum by progressively mixing amounts of 2 ∼ 5 wt% Na$_2$CO$_3$, which varies depending on the contents of rnontmorillonite and other impurities, especially zeolite. Much amount of sodium carbonate is required for optimum swelling property of zeolitic bentonited which has usually strong Na- exchanged capacity. The bentonites, which are comparatively feldspar-rich and low in size and crystallinity, tend to be higher in viscosity values. Tn addition, the viscosity is largely higher in case of the bentonites with higher pH in suspension. However, the rheological properties of bentonites such as swelling index and viscosity do not show any obvious relationships with rnontmorillonite contents and mean particle size in suspension. In contrast, roughly speaking, the swelling index of bentonites is reversely proportional to the values of surface area which can be regarded as a collective physico-chemical parameter encompassing all the effects caused by mineral composition, surface charge, particle size, morphological farm, and etc. in bentonites. Thus, the rheological properties in bentonite suspension appear to be rather complicated characteristics which mainly depend on the flocculation of clay particles and the mode of particle association, i.e. quasicrystals, controlled by surface charge, morphology, size, and texture of rnon-tmorillonite, and which partly affected by the finer impurities such as zeolite.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.7-7
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• 2011

Quantum beam technology has been expected to develop breakthroughs for nanotechnology during the third basic plan of science and technology (2006~2010). Recently, Green- or Life Innovations has taken over the national interests in the fourth basic science and technology plan (2011~2015). The NIMS (National Institute for Materials Science) has been conducting the corresponding mid-term research plans, as well as other national projects, such as nano-Green project (Global Research for Environment and Energy based on Nanomaterials science). In this lecture, the research trends in Japan and NIMS are firstly reviewed, and the typical achievements are highlighted over key nanotechnology fields. As one of the key nanotechnologies, the quantum beam research in NIMS focused on synchrotron radiation, neutron beams and ion/atom beams, having complementary attributes. The facilities used are SPring-8, nuclear reactor JRR-3, pulsed neutron source J-PARC and ion-laser-combined beams as well as excited atomic beams. Materials studied are typically fuel cell materials, superconducting/magnetic/multi-ferroic materials, quasicrystals, thermoelectric materials, precipitation-hardened steels, nanoparticle-dispersed materials. Here, we introduce a few topics of neutron scattering and ion beam nanofabrication. For neutron powder diffraction, the NIMS has developed multi-purpose pattern fitting software, post RIETAN2000. An ionic conductor, doped Pr2NiO4, which is a candidate for fuel-cell material, was analyzed by neutron powder diffraction with the software developed. The nuclear-density distribution derived revealed the two-dimensional network of the diffusion paths of oxygen ions at high temperatures. Using the high sensitivity of neutron beams for light elements, hydrogen states in a precipitation-strengthened steel were successfully evaluated. The small-angle neutron scattering (SANS) demonstrated the sensitive detection of hydrogen atoms trapped at the interfaces of nano-sized NbC. This result provides evidence for hydrogen embrittlement due to trapped hydrogen at precipitates. The ion beam technology can give novel functionality on a nano-scale and is targeting applications in plasmonics, ultra-fast optical communications, high-density recording and bio-patterning. The technologies developed are an ion-and-laser combined irradiation method for spatial control of nanoparticles, and a nano-masked ion irradiation method for patterning. Furthermore, we succeeded in implanting a wide-area nanopattern using nano-masks of anodic porous alumina. The patterning of ion implantation will be further applied for controlling protein adhesivity of biopolymers. It has thus been demonstrated that the quantum beam-based nanotechnology will lead the innovations both for nano-characterization and nano-fabrication.

• Journal of Powder Materials
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• v.9 no.6
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.