• Title, Summary, Keyword: Phase boundary

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A Boundary Diffusion Creep Model for the Plastic Deformation of Grain Boundary Phase of Nanocrystalline Materials (나노재료 입계상의 소성변형에 대한 입계확산크립 모델)

  • 김형섭;오승탁;이재성
    • Transactions of Materials Processing
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    • v.10 no.5
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    • pp.383-388
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    • 2001
  • In describing the plastic deformation behaviour of ultrafine-grained materials, a phase mixture model in which a polycrystalline material is regarded as a mixture of a crystalline phase and a grain boundary phase has been successful. The deformation mechanism for the grain boundary phase, which is necessary for applying the phase mixture model to polycrystalline materials, is modelled as a diffusional flow of matter along the grain boundary. A constitutive equation for the boundary diffusion creep of the boundary phase was proposed, in which the strain rate is proportional to (stress/grain siz $e^{2}$). The upper limit of the stress of the boundary phase was set to equal to the strength to the amorphous phase. The proposed model can explain the strain rate and grain size dependence of the strength of the grain boundary phase. Successful applications of the model compared with published experimental data are described.

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A Boundary diffusion creep model of grain boundary phase of materials (재료결정립계상의 입계확산크립 모델)

  • 김형섭
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.192-195
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    • 2000
  • In describing the plastic deformation behaviour of fine grained materials a phase mixture model in which a polycrystalline material is regarded as a mixture of a crystalline phase and a grain boundary phase has been successful. The deformation mechanism for the grain boundary phase which is necessary for applying the phase mixture model is modelled as a diffusional flow of matter though the grain boundary. The proposed model can explain the strain rate and grain size dependence of the strength of the grain boundary phase.

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Electrical Resistance Tomography: Mesh Grouping and Boundary Estimation Algorithms

  • Kim Sin;Cho Hyo-Sung;Lee Bong-Soo
    • International Journal of Contents
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    • v.1 no.1
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    • pp.1-5
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    • 2005
  • This paper presents the development and application of electrical resistance imaging techniques for the visualization of two-phase flow fields. Two algorithms, the so-called the mesh grouping and the boundary estimation, are described for potential applications of electrical resistance tomography (ERT) and results from extensive numerical simulations are also presented. In the electrical resistance imaging for two-phase flows, numerical meshes fairly belonging to each phase can be grouped to improve the reconstruction performance. In many cases, the detection of phase boundary is a key subject and a mathematical model to estimate phase boundary can be formulated in a different manner. Our results indicated that the mesh grouping algorithm is effective to enhance computational performance and image quality, and boundary estimation algorithm to determine the phase boundary directly.

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Three phase flow simulations using the fractional flow based approach with general initial and boundary conditions

  • Suk, Heejun
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • pp.88-91
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    • 2004
  • The multiphase flow simulator, MPS, is developed based on the fractional flow approach considering tile fully three phase flow with general initial and boundary condition. Most existing fractional flow-based models are limited to two-phase flow and specific boundary conditions. Although there appears a number of three-phase flow models, they were mostly developed using pressure based approaches. As a result, these models require cumbersome variable-switch techniques to deal with phase appearance and disappearance. The use of fractional flow based approach in MPS makes it unnecessary to use variable-switch to handle the change of phase configurations. Also most existing fractional flow based models consider only specific boundary conditions. However, the present model considers general boundary conditions of most possible and plausible cases which consists of ten cases.

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Effect of Impurities in Grain Boundary Phases on Wear Behavior of $Si_3N_4$ (질화규소의 입계상에 존재하는 불순물이 마모에 미치는 영향)

  • 오윤석;임대순;이경호
    • Journal of the Korean Ceramic Society
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    • v.33 no.3
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    • pp.277-284
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    • 1996
  • The water test results indicated that the impurities had detrimetal effect on the wear resistance of silicon nitride and the effects were getting severe as the temperature increased. Especially when Ca existed as an impurity the detrimental effects was the most severe. These results were resulted from the fact that impurities lowered the mechanical properties of the grain boundary phase of silicon nitride. The wear test results of glass/glass-ceramic specimens having a similar composition to the grain boundary phase of silicon nitride revea-led that the specimen containing CaO showed the lowest wear resistance. The existence of Fe and Ca at the grain boundary phase assisted forming a grain boundary phase with relatively low refractoriness. Therefore at a given wear condition the removal of deformed layer would be easier. The results showed that the glass phases could be modified by heat-treatment and this modification improved tribological characteristics of the silicon nitride.

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Antiferromagnetically Exchange-coupled Two Phase Magnets: Co/Co2TiSn

  • Kim, Tae-Wan;Oh, Jung-Keun
    • Journal of Magnetics
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    • v.13 no.2
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    • pp.43-52
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    • 2008
  • The objective of this paper is to review the magnetic and magneto-transport properties of Co/$Co_2TiSn$ consisting of two metallic magnetic phases that are antiferromagnetically exchange-coupled at the phase boundary. The bulk Co/$Co_2TiSn$ system, which has a $Co_2$TiSn Heusler alloy precipitates in the hexagonal Co matrix, showed an unusual coercivity change with a concurrent change in temperature, and was modeled on the basis of a wall formation caused by exchange coupling at the phase boundary. For measurements of magneto-transport properties, Co/$Co_2TiSn$ thin films that had two-magnet phases were deposited using a magnetron sputtering system with a composite target. The magnetization process in the films is also explained on the basis of the model of wall formation at the phase boundary. Annealed Co/$Co_2TiSn$ films showed a 0.12% GMR effect, indicating the scattering of polarized conduction electrons due to the antiparallel exchange coupling at the phase boundary. The scattering process of conduction electrons at the phase boundary was modeled with relation to the magnetization process.

Grain-Boundary Conduction in Solid Oxide Electrolyte (산화물 고체전해질의 입계전도)

  • Lee, Jong-Heun
    • Journal of the Korean Ceramic Society
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    • v.44 no.12
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    • pp.683-689
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    • 2007
  • Grain-boundary conduction in the fluorite-structure solid oxide electrolytes such as acceptor-doped zirconia and ceria were reviewed. The siliceous impurity, even several hundreds ppm, affects the ionic conduction across grain boundary to a great extent. Various approaches to improve grain-boundary conduction in fluorite-structure oxide electrolytes have been investigated, which include (1) the scavenging of siliceous phase by the reaction with second phase, (2) the gathering of intergranular siliceous phase into a discrete configuration and (3) the dewetting of intergranular liquid phase by post-sintering heat treatment.

Current Trend of Second Phase Particle-grain Boundary Interaction Research using Computer Simulations (컴퓨터 시뮬레이션 기법을 이용한 입계면 - 이상 입자 간 상호작용 모사 연구 동향)

  • Chang, Kunok
    • Journal of Korean Powder Metallurgy Institute
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    • v.27 no.4
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    • pp.339-342
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    • 2020
  • Since the interaction between the second-phase particle and grain boundary was theoretically explained by Zener and Smith in the late 1940s, the interaction of the second-phase particle and grain boundary on the microstructure is commonly referred to as Zener pinning. It is known as one of the main mechanisms that can retard grain growth during heat treatment of metallic and ceramic polycrystalline systems. Computer simulation techniques have been applied to the study of microstructure changes since the 1980s, and accordingly, the second-phase particle-grain boundary interaction has been simulated by various simulation techniques, and further diverse developments have been made for more realistic and accurate simulations. In this study, we explore the existing development patterns and discuss future possible development directions.

Effects of Chemical Inhomogeneity on Phase Coexistence in Pb(Zr, Ti))$O_3$ Ceramics at Morphotropic Tetragonal and Rhombohedral Phase Boundary (정방정상과 능면체상의 경계조성 Pb(Zr, Ti)$O_3$ 세라믹스에서 화학조성의 불균일성이 상공존에 미치는 영향)

  • 천채일;김호기
    • Journal of the Korean Ceramic Society
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    • v.27 no.8
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    • pp.1027-1033
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    • 1990
  • In order to identify the origin of phase coexistence at morphotropic tetragonal and rhombohedral boundary in PZT ceramics, the effect of chemical inhomogeneity on phase coexistence region was investigated. Two kinds of PZT ceramics with different chemical homogeneity were prepared by conventional solid state reaction and co-precipitation method. There was coexistence of tetragonal and rhombohedral phase over a wide composition range in PZT ceramics calcined by solid state reaction, and there was also phase coexistence of which region was reduced considerably in sintered samples. And phase coexistence region was not observed in co-precipitated PZT ceramics(within 1 mole%). Therefore compositional fluctuation is considered to be major origin of the phase coexistence at morphotropic phae boundary in PZT ceramics.

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COMPARISON OF NUMERICAL METHODS FOR TERNARY FLUID FLOWS: IMMERSED BOUNDARY, LEVEL-SET, AND PHASE-FIELD METHODS

  • LEE, SEUNGGYU;JEONG, DARAE;CHOI, YONGHO;KIM, JUNSEOK
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.20 no.1
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    • pp.83-106
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    • 2016
  • This paper reviews and compares three different methods for modeling incompressible and immiscible ternary fluid flows: the immersed boundary, level set, and phase-field methods. The immersed boundary method represents the moving interface by tracking the Lagrangian particles. In the level set method, an interface is defined implicitly by using the signed distance function, and its evolution is governed by a transport equation. In the phase-field method, the advective Cahn-Hilliard equation is used as the evolution equation, and its order parameter also implicitly defines an interface. Each method has its merits and demerits. We perform the several simulations under different conditions to examine the merits and demerits of each method. Based on the results, we determine the most suitable method depending on the specific modeling needs of different situations.