• Title/Summary/Keyword: Nanocrystalline Metals

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MAGNETIC PROPERTIES OF Fe-Al-B-Zr-Cu ALLOYS WITH FINE NANOCRYSTALLINE STRUCTURE

  • Kim, K.J.;Park, J.Y.;Kim, K.Y.;Noh, T.H.;Kang, I.K.
    • Journal of the Korean Magnetics Society
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    • v.5 no.5
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    • pp.491-495
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    • 1995
  • The crystallization behaviors and magnetic properties for $Fe_{81-x}Al_{4}B_{10}Zr_{5}Cu_{x}$ (x=0, 1, 2 at%) alloys is investigated. By the addition of 1~2 Cu, the temperature range, where a single bcc phase exists, expands largely over 200 K and the grain size of bcc phase represents to less than 10 nm. For the optimally annealed Cu-added alloys, the high $\mu_{e}$ (1 kHz) above 20000 combined with the high $B_{10}$ of about 1.4 T is obtained in nanocrystalline state. The low core loss of 95.8 W/kg at 0.1 T and 100 kHz is confirmed for the nanocrystalline $Fe_{80}Al_{4}B_{10}Zr_{5}Cu_{1}$ alloy.

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Temperature-Dependent Thermal and Chemical Stabilities as well as Mechanical Properties of Electrodeposited Nanocrystalline Ni

  • Zheng, Liangfu;Peng, Xiao
    • Metals and materials international
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    • v.24 no.6
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    • pp.1293-1302
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    • 2018
  • Nanocrystalline (NC) Ni electrodeposits (EDs) with a mean grain size of $34{\pm}12nm$ has been investigated, from room temperature to $800^{\circ}C$ under a purge gas of argon, by both non-isothermal and isothermal differential scanning calorimetry measurements, in combination with characterization of temperature-dependent microstructural evolution. A significant exothermic peak resulting from superimposition of recrystallization and surface oxidation occurs between 340 and $745^{\circ}C$ at a heating rate of $10^{\circ}C/min$ for the NC Ni EDs. The temperatures for recrystallization and oxidation increase with increasing the heating rate. In addition, recrystallization leads to a profound brittle-ductile transition of the Ni EDs in a narrow range around the peak temperature for the recrystallization.

A Study on the Grain Size Dependence of Hardness in Nanocrystalline Metals (나노결정금속의 경도의 결정립도의존성에 관한 연구)

  • 김형섭;조성식;원창환
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1997.03a
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    • pp.73-76
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    • 1997
  • Nanocrystalline materials have been modeled as a mixture of the crystallite and the grain boundary phases. The mechanical property has been calculated using the rule of mixtures based on the volume fractions. The critical grain size concept suggested by Nieh and Wadsworth and porous material model suggested by Lee and Kim were applied to the calculation. The theoretical results fit very well with the experimental values

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THE MAGNETIC PROPERTIES OF ULTRATHIN $Fe_{84}B_{9}Nb_{7}$ NANOCRYSTALLINE ALLOY

  • Lee, J.S.;Park, J.Y.;Kim, K.Y.;Noh, T.H.;Kang, I.K.;Yoo, Y.C.
    • Journal of the Korean Magnetics Society
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    • v.5 no.5
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    • pp.500-503
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    • 1995
  • The magnetic properties of ultrathin $Fe_{84}B_{9}Nb_{7}$ nanocrystalline ribbon alloy with the thickness of $7-14\;\mu\textrm{m}$ were investigated. It was found that the effective permeability at the frequency over 100 kHz increased with decreasing ribbon thickness. Moreover the core loss decreased considerably with reduction of the ribbon thickness. The effective permeability at 1 MHz and the core loss at 1 MHz and 0.1 T for $Fe_{84}B_{9}Nb_{7}$ alloy with the thickness of $7\;\mu\textrm{m}$ were 3,700 and 2.7 W/cc, respectively. The reduction of thickness to less than $10\;\mu\textrm{m}$ was found to be very effective in obtaining high permeability and low core loss in the MHz frequency range. It was considered that the improvement of magnetic properties in the high frequency range was due to the reduction of the eddy current.

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Microstructures and Textures of Electrodeposited Ni/Invar Bimetal (전주도금으로 제조된 Ni/Invar 바이메탈의 미세조직과 집합조직)

  • Kang, Ji Hoon;Seo, Jeong Ho;Park, Yong Bum
    • Korean Journal of Metals and Materials
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    • v.46 no.7
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    • pp.420-426
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    • 2008
  • By using electrodeposition, we developed a new method to produce Ni/Invar bimetal sheets, which have been used for the present study to investigate the texture evolution during annealing. The grains of electrodeposited Ni were columnar, while those of electrodeposited Fe-Ni alloy were nanocrystalline. These different parts of the bimetal underwent different evolution of textures and microstructures during annealing. In the nanocrystalline Invar, the as-deposited textures were of fiber-type characterized by strong <100>//ND and weak <111>//ND components, and the occurrence of grain growth resulted in the strong development of the <111>//ND fiber texture with the minor <100> // ND components. On the other hand, in the columnar-structured Ni part, the as-deposited <110>//ND fiber texture transformed to the <112>//ND fiber texture due to recrystallization occurring above $550^{\circ}C$. The development of microtextures which took place during annealing in the Ni/Invar interfacial regions was investigated by using the OIM analysis, and discussed in terms of the effect of atomic diffusion across the interfaces.

Modelling the Tensile Instability of Nanocrystalline Metallic Materials (나노금속재료의 인장불안정에 대한 모델링)

  • Kim H. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.10a
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    • pp.251-254
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    • 2001
  • In this paper, the effect of grain refinement on room temperature ductility of copper was addressed. Recent experimental results have shown that this material, as well as a number of other single-phase metals that are ductile when coarse-grained, loose their ductility with decreasing grain size in the sub micrometer range. A recently developed model in which such materials are considered as effectively two-phase ones (with the grain boundaries treated as a linearly viscous second phase) was applied to analyze stability of Cu against ductile necking. As a basis, Hart's stability analysis that accounts for strain rate sensitivity effects was used. The results confirm the observed trend for reduction of ductility with decreasing grain size. The model can be applied to predicting the grain size dependence of ductility of other metallic materials as well.

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Measurement of WC Grain Size in Nanocrystalline WC-10Co Hardmetal

  • Chenguang, Lin;Guansen, Yuan
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.344-345
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    • 2006
  • The linear intercept (LI) method was used to quantitatively measure the intercepts of WC grains in nano-grained WC-10Co hardmetal. When the surveyed intercept numbers of WC grain exceeded 200, the statistic data for the mean grain size of WC were reproduced. The discriminative minimal grain size of used LI method was 12 nm; the maximum intercept of WC grain was 109 nm; the average intercept of WC grains was 45 nm and the corresponding 3D mean grain size of WC was 70 nm which is agreeable with the XRD outcome.

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Multi-Scale Modelling of a Phase Mixture Model and the Finite Element Method for Nanocrystalline Materials (나노결정 재료의 상혼합모델과 유한요소법을 결합한 멀티스케일 모델링)

  • 윤승채;서민홍;김형섭
    • Transactions of Materials Processing
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    • v.13 no.2
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    • pp.174-179
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    • 2004
  • The effect of grain refinement on the plastic deformation behaviour of nanocrystalline metallic materials is investigated. A phase mixture model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. For the grain interior phase two concurrent mechanisms are considered: dislocation glide and mass transfer by diffusion. The proposed constitutive model was implemented into a finite element code (DEFORM) using a semicoupled approach. The finite element method was applied to simulating room temperature tensile deformation of Cu down to the nanoscale grain size in order to investigate the pre- and post-necking behaviour.

Diffraction Characteristics of Mechanically Alloyed Nanocrystalline FeAl (기계적합금화한 FeAl 나노결정립의 회절특성)

  • Choi, Keun-Seob;Kim, Do-Hyang;Hong, Kyung-Tae
    • Applied Microscopy
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    • v.27 no.4
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    • pp.473-481
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    • 1997
  • Disorder-order transformation of nanocrystalline FeAl have been investigated by a combination of electron and X-ray diffraction analysis including high resolution electron microscopy and differential scanning calorimetry. Fe-50at.%Al powders mechanically alloyed for 90 hours consist of $5\sim10$ nm size grains haying either disordered b.c.c. structure or amorphous structure. X-ray and electron diffraction of mechanically alloyed FeAl powders show that disorder-order transformation occurs at the temperature range of $300^{\circ}C\sim320^{\circ}C$. Such a low-temperature ordering behavior exhibiting an exothermic reaction is attributable to the nm-scale grain structure with a large amount of defects accumulated during mechanical alloying process.

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