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  • Title/Summary/Keyword: metallic structure

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High Strength Nanostructured Metastable Alloys

  • Eckert, Jurgen;Bartusch, Birgit;Schurack, Frank;He, Guo;Schultz, Ludwig
    • 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. Mg55Y15Cu30- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% Y2O3 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 Y2O3 additions increase the mechanical strength of the composites compared to the Mg55Y15Cu30 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. Al98xMnxCe2 (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 Al63Cu25Fe12 leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming Al100x(Al0.63Cu0.25Fe0.12)x (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of σy700 MPa and a ductility of εpl5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is σy550 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 Ti3Sn,β-(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.

Design of Plasmonic Slot Waveguide with High Localization and Long Propagation Length

  • Lee, Ki-Sik;Jung, Jae-Hoon
    • Journal of the Optical Society of Korea
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    • v.15 no.3
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    • pp.305-309
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    • 2011
  • We present an efficient design approach for a plasmonic slot waveguide using a genetic algorithm. The analyzed structure consists of a nanometric slot in a thin metallic film embedded within a dielectric. To achieve high confinement without long propagation length, the thickness and width of the slot are optimally designed in order to optimize the figures of merit including mode confinement and propagation length. The optimized design is based on the finite element method and enhances the guiding and focusing of light power propagation.

Study on Influence Strengthening Surface of Concrete by Metallic Lithium (리튬금속이 콘크리트 표면강화에 미치는 영향)

  • Kim, Kwang-Ki;Park, Soon-Jeon;Jung, Sang-Jin
    • Proceedings of the Korea Concrete Institute Conference
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    • 2009.05a
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    • pp.513-514
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    • 2009
  • This study is to determine that lithium-silicate as reinforcement on surface for repairing concrete structure affects adhesive strength of mortar to recover the surface and of the strength for the obverse of concrete. these are focused on applying fields to the study.

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Structure and Oxidation Behavior of the LaCrO3-dispersed Cr alloys (LaCrO3가 분산된 Cr 합금의 구조 및 산화거동)

  • Jeon, Kwang-Sun;Song, Rak-Hyun;Shin, Dong-Ryul;Jo, J.
    • Proceedings of the KIEE Conference
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    • 1998.07d
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    • pp.1303-1305
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    • 1998
  • In order to reduce or avoid oxidation problem at operation the interconnects in SOFCs have so far mostly been made of ceramic material. It has high chemical stability both under cathode and anode condition, relatively thermal expansion coefficient that matchs that of electrolyte material YSZ. But this material shown rather weak in the low oxygen atmosphere and thermal shock, and it has lower mechanical strength than alloys. To avoid these problems one may consider to use metals or alloys as materials for interconnects. Metallic interconnects are advantageous because of their high thermal and electronic conductivities. But it has some problems, Those are high thermal expansion and oxidation at high temperature in air. To solve these problems in the interconnection material in this study, LaCrO3-dispersed Cr alloys for metallic interconnector of SOFC have been investigated as a fuction of LaCrO3 content in the range of 5 to 25 vol.%. The Cr alloy were prepared by mixing Cr and LaCrO3 powders in high-energy ball mill for 48h and by sintering under Ar atmosphere with 5vol.% H2 for 10h at 1500C. The alloys had a relative density of 95% and above. The Cr alloys in composed of two kind of small LaCrO3 and large Cr particles. As the LaCrO3 content increased, the Cr particle size decreased but the LaCrO3 particle size remained contant. Also the oxidation tests show that the LaCrO3-dispersed Cr is very resistant to oxidation in air. These results means that LaCrO3-dispersed Cr is a useful material for metallic interconnect of planar SOFC.

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Measurement of Elastic Constants of Thin Metallic Foil by Guided Wave Dispersion Characteristics (유도초음파 분산 특성을 이용한 박판의 탄성계수 측정)

  • Lee, Dong-Jin;Cho, Youn-Ho;Jang, Kang-Won;Cho, Seung-Hyun;Ahn, Bong-Young
    • Journal of the Korean Society for Nondestructive Testing
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    • v.32 no.1
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    • pp.41-46
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    • 2012
  • As the development of MEMS/NEMS structure and application technology the demand for an assessment of the mechanical properties have increased. The mechanical properties are mainly evaluated by using tensile test or ultrasonic wave measurement. However, the new technology have been developed such as nano-indentation, guided wave method because they have a limitation in case of a thin plate and thin film. In the study, the guided wave velocities are measured by electromagnetic-acoustic transducer(EMAT), the material properties of thin metallic foils are obtained using optimization process of the theoretical and experimental group velocity of guided wave. The Young's modulus obtained by the optimization process(201.6 GPa), nano-indentation(207.0 GPa) and literature value(203.7 GPa) of a 50μm thick nickel thin plate shows good agreement within 3%.

Structural Design based on the Phase Field Design Method to Enhance the Patch Antenna Performance (패치안테나 성능 향상을 위한 페이즈필드 설계법 기반의 형상 설계)

  • Lee, Sangyeub;Shin, Hyundo;Yoo, Jeonghoon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.30 no.1
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    • pp.17-22
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    • 2017
  • In this study, we designed the metallic reception part of a patch antenna using the phase field design method. The design object function is formulated with the S-parameter value which represent the return loss so that it is targeted to maximize radiation efficiency at a target frequency. The initial model of a patch antenna was designed via the ordinary theory based approach and its performance was enhanced by changing the structural configuration of the metallic part using the phase field design method combined with the double well potential functions. The final shape was proposed by removing the gray scale area along the structural boundary by employing a cut-off method. The proposed shape shows that the radiation efficiency at target frequency is significantly improved compared with the initial patch shape. The finite element analysis and optimization precess was performed using the commercial package COMSOL and Matlab programming.

Ceramic Materials for Interconnects in Solid Oxide Fuel Cells - A Review (고체산화물 연료전지 연결재용 세라믹 소재)

  • Park, Beom-Kyeong;Song, Rak-Hyun;Lee, Seung-Bok;Lim, Tak-Hyoung;Park, Seok-Joo;Park, Chong-Ook;Lee, Jong-Won
    • Journal of the Korean Ceramic Society
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    • v.51 no.4
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    • pp.231-242
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    • 2014
  • An interconnect in solid oxide fuel cells (SOFCs) electrically connects unit cells and separates fuel from oxidant in the adjoining cells. The interconnects can be divided broadly into two categories - ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. This paper provides a short review on ceramic materials for SOFC interconnects. After a brief discussion of the key requirements for interconnects, the article describes basic aspects of chromites and titanates with a perovskite structure for ceramic interconnects, followed by the introduction of dual-layer interconnects. Then, the paper presents protective coatings based on spinel-or perovskite-type oxides on metallic interconnects, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation.

CERAMOGRAPHY ANALYSIS OF MOX FUEL RODS AFTER AN IRRADIATION TEST

  • Kim, Han-Soo;Jong, Chang-Yong;Lee, Byung-Ho;Oh, Jae-Yong;Koo, Yang-Hyun
    • Nuclear Engineering and Technology
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    • v.42 no.5
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    • pp.576-581
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    • 2010
  • KAERI (Korea Atomic Energy Research Institute) fabricated MOX (Mixed Oxide) fuel pellets as a cooperation project with PSI (Paul Scherrer Institut) for an irradiation test in the Halden reactor. The MOX pellets were fitted into fuel rods that included instrumentation for measurement in IFE (Institutt for Energiteknikk). The fuel rods were assembled into the test rig and irradiated in the Halden reactor up to 50 MWd/kgHM. The irradiated fuel rods were transported to the IFE, where ceramography was carried out. The fuel rods were cut transversely at the relatively higher burn-up locations and then the radial cross sections were observed. Micrographs were analyzed using an image analysis program and grain sizes along the radial direction were measured by the linear intercept method. Radial cracks in the irradiated MOX were observed that were generally circumferentially closed at the pellet periphery and open in the hot central region. A circumferential crack was formed along the boundary between the dark central and the outer regions. The inner surface of the cladding was covered with an oxide layer. Pu-rich spots were observed in the outer region of the fuel pellets. The spots were surrounded by many small pores and contained some big pores inside. Metallic fission product precipitates were observed mainly in the central region and in the inside of the Pu spots. The average areal fractions of the metallic precipitates at the radial cross section were 0.41% for rod 6 and 0.32% for rod 3. In the periphery, pore density smaller than 2 μm was higher than that of the other regions. The grain growth occurred from 10 μm to 12 μm in the central region of rod 6 during irradiation.