Won-Seok Ko
University of Ulsan
Solid solutionDensity functional theoryDislocationComposite materialNickel titaniumMartensiteMetallurgyMaterials scienceCondensed matter physicsInteratomic potentialAlloyMembranePhase (matter)Grain boundaryShape-memory alloyVanadiumHydrogenMolecular dynamicsMicrostructureThermodynamics
48Publications
15H-index
680Citations
Publications 50
Newest
#1Yeonju Oh (SNU: Seoul National University)H-Index: 4
#2Won-Seok Ko (UOU: University of Ulsan)H-Index: 15
Last. Heung Nam Han (SNU: Seoul National University)H-Index: 41
view all 6 authors...
Abstract null null Tungsten as a material exhibits broad and increasingly important applications; however, the characterization of its ductile-to-brittle transition (BDT) is currently limited to large-scale scenarios and destructive testing. In this study, we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure tungsten. In order to predict the failure mode at various temperature ranges, the practical fracture analysi...
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#1Won-Seok Ko (UOU: University of Ulsan)H-Index: 15
#2Ki Beom Park (KITECH)H-Index: 7
Last. Hyung-Ki Park (KITECH)H-Index: 10
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Abstract The role of additional ternary alloying elements on the performance of stationary TiFe-based hydrogen storage alloys was investigated based on first-principles density functional theory calculations. As a basic step for examinations, the site preference of each alloying element in the stoichiometric and non-stoichiometric B2 TiFe compounds was clarified considering possible anti-site defects. Based on the revealed site preference, the effect of various possible ternary elements on the h...
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#1Won-Seok Ko (UOU: University of Ulsan)H-Index: 15
#2Jung Soo Lee (UOU: University of Ulsan)
Last. Dong-Hyun Kim (KITECH)H-Index: 13
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An interatomic potential for the ternary Ag–Cu–Sn system, an important material system related to the applications of lead-free solders, is developed on the basis of the second nearest-neighbor modified embedded-atom-method formalism. Potential parameters for the ternary and related binary systems are determined based on the recently improved unary description of pure Sn and the present improvements to the unary descriptions of pure Ag and Cu. To ensure the sufficient performance of atomistic si...
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#1Ki Beom Park (KITECH)H-Index: 7
#2Julien O. Fadonougbo (KITECH)H-Index: 6
Last. Hyung-Ki Park (KITECH)H-Index: 10
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Abstract null null This study investigated how Fe substitution with Ni, Co, Cu, Mn, and Cr affected the first hydrogenation behavior of air-exposed TiFe-based hydrogen storage alloys. The alloy ingots were crushed into powders and exposed to air for 1 h to analyze the first hydrogenation kinetics. Although Fe was substituted with up to 30% of Ni, Co, and Cu, the alloys had a single TiFe phase. In addition, the TiFe0·7Ni0·2Co0.1 and TiFe0·7Co0·2Ni0.1 alloys also had a single TiFe phase in spite o...
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#1Ki Beom Park (KITECH)H-Index: 7
#3Julien O. Fadonougbo (KITECH)H-Index: 6
Last. Jae Young Park (KITECH)H-Index: 23
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Abstract null null This study investigated how Fe substituted with Mn and Cr affected the microstructure and the first hydrogenation kinetics of a TiFe-based hydrogen storage alloy. Vacuum arc melting was used to prepare TiFe1-xMx ingots (M = Mn, Cr, x = 0.1, 0.2, 0.3). Thermodynamic calculations were performed to predict the phase formation behavior. The TiFe0.9Mn0.1 alloy was expected to form a single TiFe phase, and all other alloys were calculated to have dual-phase microstructures with TiFe...
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#1Hye Ji Im (KAIST)H-Index: 4
#2Wonseok Choi (KAIST)H-Index: 16
Last. Pyuck-Pa Choi (KAIST)H-Index: 56
view all 7 authors...
Abstract We studied the microstructural stability and high-temperature mechanical properties of γ/γ′ Co-Ti-Mo-based alloys of varying compositions (Co-12Ti-4Mo, Co-12Ti-4Mo-2Al, Co-12Ti-4Mo-4Al, Co-10Ti-4Mo-2Al, and Co-8Ti-4Mo-4Al (at.%)) using electron microscopy and density functional theory. The Co-12Ti-4Mo alloy underwent discontinuous precipitation into FCC (γ) and D019 (χ) phases after aging at 800°C for 500 h while the Co-12Ti-4Mo-4Al alloy maintained the γ/γ′ microstructure. Al additions...
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#1Wonseok Choi (MIT: Massachusetts Institute of Technology)H-Index: 16
#2Edward L. Pang (MIT: Massachusetts Institute of Technology)H-Index: 6
Last. Pyuck-Pa Choi (KAIST)H-Index: 56
view all 8 authors...
Abstract Understanding the orientation-dependent deformation behavior of NiTi shape-memory alloys at small length scales is of importance for designing nano- and micro-electromechanical systems. However, a complete understanding of the orientation- and size-dependent competition between the various modes of slip, deformation twinning, and martensitic transformation in NiTi shape-memory alloys is still lacking, especially in micron-scale specimens. In the present study, we perform micro-compressi...
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Abstract Diffusion behaviors in Mg–Sc hcp and bcc solid solutions between 773 and 873 K were investigated using both single-phase and multi-phase diffusion couple techniques. The EPMA detected composition-distance profiles were smoothed and fitted using the error function expansion (ERFEX). The interdiffusion coefficients were extracted using Sauer–Freise integral. The interdiffusion coefficients in hcp phase showed a slightly parabolic composition dependence at the Mg-rich part and the maximum ...
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#1Jing Jiang (Tohoku University)H-Index: 21
#2Won-Seok Ko (UOU: University of Ulsan)H-Index: 15
Last. Dmitri V. Louzguine-Luzgin (Tohoku University)H-Index: 41
view all 7 authors...
Abstract In TiNi-based crystalline/amorphous alloys, superelasticity in crystalline phase coordinating the dislocation sinking in amorphous phase lead to a high ductility and outstanding anti-fatigue properties. We performed cryogenic thermal cycling, between 77K and 303K, on the complex TiNi-based alloys consisting of a major B2 austenite phase, an interdendritic amorphous phase, and a minor B19′ martensite phase in the as-cast state. The critical martensitic phase transformation stress (σm) in...
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