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Now showing items 17 - 32 of 72

  • Modified embedded-atom interatomic potential for Fe-Ni,Cr-Ni and Fe-Cr-Ni systems

    Wu, Changjun   Lee, Byeong-Joo   Su, Xuping  

    A semi-empirical interatomic potential formalism, the second-nearest-neighbor modified embedded-atom method (2NN MEAM), has been applied to obtaining interatomic potentials for the Fe-Ni, Cr-Ni and Fe-Cr-Ni systems using previously developed MEAM potentials of Fe and Ni and a newly revised potential of Cr. The potential parameters were determined by fitting the experimental data on the enthalpy of formation or mixing, lattice parameter and elastic constant. The present potentials generally reproduced the fundamental physical properties of the Fe-Ni and Cr-Ni alloys. The enthalpy of formation or mixing of the disordered phase at finite temperature and the enthalpy of mixing of the liquid phase are reasonable in agreements with experiment data and CALPHAD calculations. The potentials can be combined with already-developed MEAM potentials to describe Fe-Cr-Ni-based multicomponent alloys. Moreover, the average diffusivities in the unary, some binary and ternary alloys were simulated based on present potential. Good agreement is obtained in comparison with experimental data.
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  • A modified embedded-atom method interatomic potential for germanium

    Kim, Eun Ha   Shin, Young-Han   Lee, Byeong-Joo  

    A semi-empirical interatomic potential for germanium has been developed based on the modified embedded-atom method (MEAM) formalism. The new potential describes various fundamental physical properties of germanium: elastic, structural, point defect, surface, thermal properties (except melting point), etc., in better agreement with experimental data or first principles calculations than any other empirical potential ever developed. When compared to the previously developed MEAM Ge potential [M.I. Baskes, J.S. Nelson, A.F. Wright, Phys. Rev. B 40 (1989) 6085], certain improvements are made in descriptions of surface relaxations, point defects, thermal expansion and amorphous structure. The potential has the same formalism as already developed MEAM potentials for bcc, fcc and hcp elements, and can be easily extended to describe various metal-silicon multi-component systems. (C) 2007 Elsevier Ltd. All rights reserved.
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  • Intergranular segregation of Cr in Ti-stabilized low-Cr ferritic stainless steel

    Kim, Jeong Kil   Lee, Byeong-Joo   Lee, Bong Ho   Kim, Yeong Ho   Kim, Kyoo Young  

    The precipitation and segregation phenomenon in a type 409L Ti-stabilized 11 wt.% Cr ferritic stainless steel has been investigated using transmission electron microscopy and a laser-assisted three-dimensional atom probe. In solution-treated and aged specimens, a strong segregation and consequent depletion of Cr was observed, as well as segregation of C and Ti atoms along the grain boundary. The reason for the Cr segregation and the way to avoid such segregation is discussed. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • A new strategy for designing immiscible medium-entropy alloys with excellent tensile properties

    Moon, Jongun   Park, Jeong Min   Bae, Jae Wung   Do, Hyeon-Seok   Lee, Byeong-Joo   Kim, Hyoung Seop  

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  • The effect of porosity on the elasticity of pure titanium: An atomistic simulation

    Min, Sung-Yong   Kim, Youngkwang   Lee, Tae Kyung   Seo, Sujin   Jung, Ho Sang   Kim, Duri   Lee, Junho   Lee, Byeong-Joo  

    The effects of the porosity, size, shape and mutual connectivity of pores on the elastic property of pure titanium were investigated using an atomistic simulation (molecular statics). The study concluded that the elasticity of porous Ti is mainly governed by its porosity. The results showed that the size and shape of the pores do not have a significant effect as long as the pores are separated from each other. The interconnection of the pores contributes to further decrease the elasticity than expected from the porosity of samples with isolated pores, and can be thought to be an important factor to further reduce the elasticity of porous load-bearing implant metals. In addition, the atomistic calculation proved to be a successful approach to use with experiments testing the effect of porosity on elastic property, and could be further developed to deal with Ti alloys that have more complex distribution and pore shapes.
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  • A semi-empirical interatomic potential for the Cu-Ti binary system

    Kim, Young-Min   Lee, Byeong-Joo  

    A semi-empirical atomic potential according to the second nearest-neighbor modified embedded-atom method, has been applied to obtain an interatomic potential for the Cu-Ti system based on the previously developed potentials for pure Cu and Ti. The potential describes thermodynamic properties and alloy behaviors of the Cu-Ti binary system fairly well. The procedure for the determination of potential parameter values and the performance of the optimized alloy potential are presented. The possibility and limitations of the potential for application to atomistic studies of Cu-based amorphous alloys are also discussed. (c) 2006 Published by Elsevier B.V.
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  • Thermodynamic Calculations on the Stability of Cu2S in Low Carbon Steels

    Lee, Byeong-Joo   Sundman, Bo   Kim, Sung Il   Chin, Kwang-Geun  

    Thermodynamic stability of Cu2S sulfide in low carbon steels has been investigated using a CALPHAD type thermodynamic calculation method. Thermodynamic properties of the Cu-S binary and Fe-Cu-S ternary systems were critically assessed. By combining the newly assessed thermodynamic parameters to an existing thermodynamic database for steels, a thermodynamic description for low carbon steels involving sulfur and Cu could be obtained and be used to calculate phase equilibria and thermodynamic stability of precipitating phases such as AlN, MnS, and Cu2S. It was predicted that the Cu2S sulfide often observed in low carbon steels is actually a thermodynamically unstable phase and can precipitate when thermodynamic equilibrium state is not reached during steel making processes. Probable reasons and conditions for the formation of this unstable phase are discussed.
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  • Thermodynamic calculations on the stability of Cu2S in low carbon steels

    Lee, Byeong-Joo   Sundman, Bo   Kim, Sung Il   Chin, Kwang-Geun  

    Thermodynamic stability of Cu2S sulfide in low carbon steels has been investigated using a CALPHAD type thermodynamic calculation method. Thermodynamic properties of the Cu-S binary and Fe-Cu-S ternary systems were critically assessed. By combining the newly assessed thermodynamic parameters to an existing thermodynamic database for steels, a thermodynamic description for low carbon steels involving sulfur and Cu could be obtained and be used to calculate phase equilibria and thermodynamic stability of precipitating phases such as AlN, MnS, and Cu2S. It was predicted that the Cu2S sulfide often observed in low carbon steels is actually a thermodynamically unstable phase and can precipitate when thermodynamic equilibrium state is not reached during steel making processes. Probable reasons and conditions for the formation of this unstable phase are discussed.
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  • Thermodynamic calculation of LiH <-> Li3AlH6 <-> LiAlH4 reactions

    Jang, Je-Wook   Shim, Jae-Hyeok   Cho, Young Whan   Lee, Byeong-Joo  

    Thermodynamic properties of hydrides, LiH, Li3AlH6 and LiAlH4 which can be a promising candidate for a hydrogen storage material system, were critically assessed by analyzing available piecewise literature information on thermodynamic properties using the CALPHAD method. The optimized thermodynamic descriptions were used to compute the phase equilibria between Li3AlH6 and LiAlH4 as a function of temperature and hydrogen partial pressure. It was predicted that more than 10(3) bar of hydrogen partial pressure is necessary to induce the hydrogen absorption reaction of Li3AlH6 -> LiAlH4 above room temperature. It could be concluded that a reversible reaction between Li3AlH6 and LiAlH4 is thermodynamically impossible in a practically accessible temperature and hydrogen pressure range for a hydrogen storage material without any attempt to change the thermodynamic properties of the hydrides. (c) 2005 Elsevier B.V. All rights reserved.
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  • Modified embedded-atom method interatomic potentials for Mg-X (X=3DY,Sn,Ca) binary systems

    Kim, Ki-Hyun   Jeon, Jong Bae   Lee, Byeong-Joo  

    Interatomic potentials for pure Ca and Mg-X (X=3DY, Sn, Ca) binary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials can describe various fundamental physical properties of pure Ca (bulk, defect and thermal properties) and the alloy behavior (structural, thermodynamic and defect properties of solid solutions and compounds) of binary systems in reasonable agreement with experimental data or first-principles and other calculations. The applicability of the developed potentials to atomistic investigations of the deformation behavior of Mg and its alloys is discussed together with some challenging points that need further attention. (C) 2014 Elsevier Ltd. All rights reserved.
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  • Modified embedded-atom method interatomic potentials for pure Mn and the Fe-Mn system

    Kim, Young-Min   Shin, Young-Han   Lee, Byeong-Joo  

    Modified embedded-atom method (MEAM) interatomic potentials for pure Mn and the Fe-Mn binary system have been developed using a previously developed MEAM potential for Fe. The potentials can describe various fundamental physical properties of pure M, (cohesive energy, structural energy differences, lattice parameters, elastic constants, vacancy formation energy, surface energy, etc.) and alloy behaviors (enthalpy of mixing in face-centered cubic and liquid phases, composition dependency of lattice parameters in various solid solutions) in reasonable agreement with experimental information or other empirical approaches. The applicability of the potentia to atomistic investigations on a wide range of mechanical or deformation properties of the Fe-Mn alloys is demonstrated. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Thermodynamic calculation on the stability of (Fe,Mn)(3)AlC carbide in high aluminum steels

    Chin, Kwang-Geun   Lee, Hyuk-Joong   Kwak, Jai-Hyun   Kang, Jung-Yoon   Lee, Byeong-Joo  

    A CALPHAD type thermodynamic description for the Fe-Mn-Al-C quaternary system has been constructed by combining a newly assessed Mn-Al-C ternary description and a partly modified Fe-Al-C description to an existing thermodynamic database for steels. A special attention was paid to reproduce experimentally reported phase stability of kappa carbide in high Al and high Mn steels. This paper demonstrates that the proposed thermodynamic description makes it possible to predict phase equilibria in corresponding alloys with a practically acceptable accuracy. The applicability of the thermodynamic calculation is also demonstrated for the interpretation of microstructural and constitutional evolution during industrial processes for high Al steels. (C) 2010 Elsevier B.V. All rights reserved.
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  • Comparative study on graphene growth mechanism using Ni films, Ni/Mo sheets, and Pt substrates

    Lee, Byeong-Joo   Jeong, Goo-Hwan  

    We demonstrate a comparative study on graphene growth mechanism using various catalytic metal substrates such as Ni thin films, Ni-deposited Mo (Ni/Mo) sheets, and Pt sheets during chemical vapor deposition (CVD). Depending on the substrates, two kinds of graphene growth mechanisms that involve either precipitation or surface adsorption of carbon have been reported. We synthesized graphene, focusing especially on the initial growth stage during CVD, by varying synthesis parameters such as synthesis time, amount of feedstock, and cooling rate after synthesis. We concluded that precipitation-driven synthesis is dominant in the case of Ni substrates whereas adsorption-driven growth is dominant in the Ni/Mo system. In the case of the Pt substrate, which is generally believed to grow by carbon precipitation, graphene growth by adsorption was found to be dominant. We believe that our results will contribute to a clearer understanding of the graphene synthesis mechanism, and development of manufacturing routes for controllable synthesis of high-quality graphenes.
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  • An identification scheme of grain boundaries and construction of a grain boundary energy database

    Kim, Hyun-Kyu   Ko, Won-Seok   Lee, Hyuk-Joong   Kim, Seong Gyoon   Lee, Byeong-Joo  

    We have developed a systematic scheme to identify and distinguish individual grain boundaries from one another according to the misorientation and inclination in polycrystalline materials. This allows us to construct a grain boundary energy database in a suitable form for implementation on mesoscale grain growth simulations. The scheme can be equally applied to identify interfaces between two different phase grains, and enables realistic simulations of phase transformations as well as grain growth, assigning real crystallographic orientations to individual grains. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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  • Revealing impact of plasma condition on graphite nanostructures and effective charge doping of graphene

    Lee, Byeong-Joo   Shin, Dong-Hoon   Lee, Sangwook   Jeong, Goo-Hwan  

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  • Structural characterization and stress-relaxation behavior of superlattice Cu5Zr RID E-4584-2011

    Kim, Kyou-Hyun   Ahn, Jae-Pyoung   Kim, Young-Min   Lee, Byeong-Joo   Lee, Jae-Chul  

    A self-organized superlattice containing modulated layers in Cu5Zr was manufactured by casting a Cu-Zr system. Substitutional Zr atoms caused compressive stress in the superlattice so that periodic stress fields were formed with a long-range order along the (110) directions on {111} for stress relaxation. On the other hand, it was demonstrated theoretically by atomistic simulations that a superlattice could form easily due to the large negative enthalpy of formation in the structure (-12.890 kJ/mol of atoms). (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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