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Now showing items 49 - 64 of 72

  • Effect of alloying elements (Al, Co, Fe, Ni) on the solubility of hydrogen in vanadium: A thermodynamic calculation

    Kim, Ki-Hyun   Shim, Jae-Hyeok   Lee, Byeong-Joo  

    CALPHAD type thermodynamic assessments for the V-M-H (M = Al, Co, Fe, Ni) hydrogen membrane systems have been carried out on the basis of a newly assessed Co H binary description, a partly modified Fe-H description and existing thermodynamic descriptions for the other M-H (V-H, Al-H, Ni-H) and V-M (V-Al, V-Co, V-Fe, V-Ni) binary systems. A special attention was paid to estimate the thermodynamic descriptions for the non-existing bcc Al-H, Co-H and Ni-H alloys. Thermodynamic parameters for those binary alloys were estimated by using a theoretical approach (atomistic computation) and fitting limited amount of experimental data for the hydrogen solubility in V-rich bcc ternary alloys. The proposed thermodynamic descriptions predict phase equilibria, especially the effect of alloying elements on the hydrogen solubility in the V-rich bcc alloys, in good agreement with available experimental data. The present thermodynamic descriptions can be easily extended to higher order alloy systems and can provide useful information for alloy design of metallic hydrogen membranes with well-balanced hydrogen permeability and mechanical properties. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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  • Effect of μ-precipitates on the microstructure and mechanical properties of non-equiatomic CoCrFeNiMo medium-entropy alloys

    Bae, Jae Wung   Park, Jeong Min   Moon, Jongun   Choi, Won Mi   Lee, Byeong-Joo   Kim, Hyoung Seop  

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  • Effect of Tempering Time on Microstructure, Tensile Properties, and Deformation Behavior of a Ferritic Light-Weight Steel

    Han, Seung Youb   Shin, Sang Yong   Lee, Byeong-Joo   Lee, Sunghak   Kim, Nack J.   Kwak, Jai-Hyun  

    In the present study, a ferritic light-weight steel was tempered at 973 K (700 degrees C) for various tempering times, and tensile properties and deformation mechanisms were investigated and correlated to microstructure. kappa-carbides precipitated in the tempered band-shaped martensite and ferrite matrix, and the tempered martensite became more decomposed with increasing tempering time. Tempering times for 3 days or longer led to the formation of austenite as irregular thick-film shapes mostly along boundaries between the tempered martensite and the ferrite matrix. Tensile tests of the 1-day-tempered specimen showed that deformation bands were homogeneously spread throughout the specimen, and that the fine carbides were sufficiently deformed inside these deformation bands resulting in high strength and ductility. The 3-day-tempered specimen showed a small amount of boundary austenite, which readily developed voids or cracks and became sites for fracture. This cracking at boundary austenites became more prominent in the 7- and 15-day-tempered specimens, as the volume fraction of boundary austenites increased with increasing tempering time. These findings suggested that, when the steel was tempered at 973 K (700 degrees C) for an appropriate time, i.e., 1 day, to sufficiently precipitate j-carbides and to prevent the formation of boundary austenites, that the deformation occurred homogeneously, leading to overall higher mechanical properties. DOI: 10.1007/s11661-012-1370-7 (C) The Minerals, Metals & Materials Society and ASM International 2012
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  • Prediction of interface reaction products between Cu and various solder alloys by thermodynamic calculation

    Lee, Byeong-Joo   Hwang, Nong Moon   Lee, Hyuck Mo  

    A new scheme to predict the intermetallic compound which forms first at the substrate/solder interface during the soldering process has been suggested. A local equilibrium was assumed at the interface between the substrate and the liquid solder. By calculating metastable equilibria between the substrate and the liquid solder phases and by comparing the calculated driving forces of formation for individual phases, the compound which forms first at the substrate/solder interface could be successfully predicted. The prediction of interface reactions between Cu substrate and Sn-Pb, Sn-Bi and Sn-Zn binary eutectic solder was in agreement with already known experimental results.
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  • Efficient surface functionalization of vertically-aligned carbon nanotube arrays using an atmospheric pressure plasma jet system

    Lee, Byeong-Joo   Jeong, Goo-Hwan  

    We demonstrate the facile and efficient surface functionalization of vertically-aligned carbon nanotube (VCNT) arrays using an atmospheric pressure plasma jet (APPJ) system. The VCNT arrays were synthesized on Fe-deposited SiO2 wafers using an acetylene carbon source by thermal chemical vapor deposition method. To functionalize the surface of the VCNT arrays, the APPJ system was ignited using nitrogen gas at high voltage of 15kV and frequency of 25kHz. We varied the treatment time of the APPJ and the inter-distance between plasma jet and top surface of the VCNT in order to systematically investigate the optimal conditions of the APPJ system. The hydrophobic nature of the as-grown VCNT arrays was drastically changed to hydrophilic character via the facile APPJ treatment. X-ray photoelectron spectroscopy confirmed the formation of hydrophilic functional groups such as hydroxyl and carboxyl groups, and nitrogen-doping-related functionalities such as amines, in addition to pyrrolic- and pyridinic-bonding. The results prove that the APPJ treatment is a facile and efficient method for the surface modification of nanomaterials.
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  • Effects of intergranular carbide precipitation on delayed fracture behavior in three TWinning Induced Plasticity (TWIP) steels

    Hong, Seokmin   Lee, Junghoon   Lee, Byeong-Joo   Kim, Hyoung Seop   Kim, Sung-Kyu   Chin, Kwang-Geun   Lee, Sunghak  

    The delayed fracture behavior related with intergranular carbide precipitation of three TWinning Induced Plasticity (TWIP) steels was investigated. According to the microstructural analysis, nanosized (Fe,Mn)(3)C cementites were precipitated along grain boundaries in the 0.6C-22Mn and 0.6C-18Mn steels, whereas their precipitation was hardly observed in the 0.6C-18Mn-2Al steel, which was confirmed by equilibrium phase diagrams calculated from a ThermoCalc program. When cup specimens were dipped in the boiled water, the 0.6C-22Mn, 0.6C-18Mn, and 0.6C-18Mn-2Al steel cups were cracked after 5.5, 15, and 169 h, respectively. The delayed fracture regions consisted of intergranular facets, and the tendency of intergranular facture decreased in the order of 0.6C-22Mn, 0.6C-18Mn, and 0.6C-18Mn-2Al steels. Thus, the delayed fracture behavior was closely related with the intergranular fracture mode caused by grain boundary cementites. The addition of Al remarkably increased the resistance to delayed fracture because it suppressed the formation of grain boundary cementites and reduced the residual stresses in the cup specimen. (C) 2013 Elsevier B.V. All rights reserved.
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  • Efficient surface functionalization of vertically-aligned carbon nanotube arrays using an atmospheric pressure plasma jet system

    Lee, Byeong-Joo   Jeong, Goo-Hwan  

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  • Effects of (Cr,Fe)(2)B borides on hardness in powder-injection-molded product fabricated with Fe-based alloy powders

    Do, Jeonghyeon   Jeon, Changwoo   Kim, Choongnyun Paul   Lee, Byeong-Joo   Lee, Sunghak   Lee, Eon-Sik   Yoon, Tae Shik   Shin, Yang Su  

    In the present study, a powder injection molding (PIM) product containing (Cr,Fe)(2)B borides was fabricated with Fe-based alloy powders, and its microstructure and hardness were investigated in relation with volume fraction of (Cr,Fe)(2)B. In the Fe-based alloys designed by the thermodynamic calculation, the volume fractions of (Cr,Fe)(2)B increased with increasing (X-cr+ X-B) value, and were well matched with those obtained from the thermodynamic calculation. The hardness of the Fe-based alloys linearly increased with increasing volume fraction of (Cr,Fe)(2)B. When Fe-based alloy powders were injection-molded and sintered at 1165 degrees C, a densified microstructure with almost no pores was obtained. In the sintered microstructure, 56 vol% of (Cr,Fe)(2)B borides, together with a few pores (porosity; 0.5%), were relatively homogeneously distributed in the tempered martensite matrix, which resulted in the very high hardness over 600 VHN. Such a high hardness suggested that the present Fe-based alloy powders could be readily adopted for fabricating PIM products or for replacing conventional stainless steel PIM products. (c) 2012 Elsevier B.V. All rights reserved.
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  • Evolution of microstructure and tensile properties of cold-drawn hyper-eutectoid steel wires during post-deformation annealing

    Jafari, Majid   Bang, Chan-Woo   Han, Jong-Chan   Kim, Kyeong-Min   Na, Seon-Hyeong   Park, Chan-Gyung   Lee, Byeong-Joo  

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  • Modified embedded-atom method interatomic potentials for the Co-Cr,Co-Fe,Co-Mn,Cr-Mn and Mn-Ni binary systems

    Choi, Won-Mi   Kim, Yongmin   Seol, Donghyuk   Lee, Byeong-Joo  

    Interatomic potentials for the Co-Cr, Co-Fe, Co-Mn, Cr-Mn and Mn-Ni binary systems have been developed in the framework of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials describe various fundamental alloy behaviors (structural, elastic and thermodynamic behavior of solution and compound phases), mostly in reasonable agreements with experimental data or first-principles calculations. The potentials can be utilizdd to complete the interatomic potential for the CoCrFeMnNi alloy and to investigate the atomic scale physical metallurgy of high entropy alloys. (C) 2017 Elsevier B.V. All rights reserved.
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  • Design of cost-effective Fe-based amorphous coating alloys having high amorphous forming ability by thermodynamic calculation

    Jung, Seungmun   Do, Jeonghyeon   Lee, Dong-Geun   Lee, Byeong-Joo   Cha, Gil-up   Lee, Sunghak  

    In this study, new cost-effective Fe-based amorphous coating alloys having high amorphous forming ability were developed by varying the Fe content, while their microstructure, hardness, and corrosion resistance were also evaluated. Chemical compositions that have the lowest driving force of formation of crystalline phases such as Fe3P, Fe3C, and alpha-Fe were obtained from thermodynamically calculated phase diagrams of the representative FexAl2(P10.83C7.47B1.7)(98-x) alloy system at a crystallization temperature of 443 A degrees C. Considering the intersections of driving force curves of Fe3P and Fe3C, Fe3P and alpha-Fe, and Fe3C and alpha-Fe, the Fe contents were found to be 77.8, 76.2, and 75.8 at.%, respectively. The microstructural analysis results of 1.5-mm-diameter suction-cast Fe-based alloys indicated that the Fe76.5Al2(P10.83C7.47B1.7)(21.5) alloy had a fully amorphous microstructure, whereas crystalline phases were formed in other alloys. This alloy showed a better hardness and corrosion resistance than conventional thermal spray coating alloys, and its production cost could also be reduced by using less expensive alloying elements, which could provide a good way to practically apply this alloy to Fe-based amorphous thermal spray coatings.
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  • Effects of annealing temperature on microstructures and tensile properties of a single FCC phase CoCuMnNi high-entropy alloy

    Kim, Dong Geun   Jo, Yong Hee   Park, Jeong Min   Choi, Won-Mi   Kim, Hyoung Seop   Lee, Byeong-Joo   Sohn, Seok Su   Lee, Sunghak  

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  • Ferritin-mixed solution plasma system yielding low-dimensional carbon nanomaterials and their application to flexible conductive paper

    Lee, Byeong-Joo   Jeong, Goo-Hwan  

    We demonstrate the production of low-dimensional carbon nanomaterials using a solution plasma system and their application to flexible conductive paper. The solution plasma system consists of two graphite electrodes and a beaker filled with ferritin-mixed deionized water. Ferritin molecules are used as the growth catalyst of the carbon nanomaterials. A high voltage of 15 kV at a frequency of 25 kHz is supplied to the electrodes using an alternating-current power source. The effects of the graphite rod diameters and the concentration of ferritin molecules are comparatively investigated. The produced carbon nanomaterials are characterized using Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. We confirmed the synthesis of graphitic platelets, onion-like structures, and carbon nanotubes. Finally, we fabricated flexible conductive papers using the produced materials with a good electrical conductance. (C) 2015 Elsevier B.V. All rights reserved.
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  • Ferritin-mixed solution plasma system yielding low-dimensional carbon nanomaterials and their application to flexible conductive paper

    Lee, Byeong-Joo   Jeong, Goo-Hwan  

    Highlights • We construct a ferritin-mixed solution plasma system for low-dimensional carbon nanomaterial synthesis. • We confirm the formation of graphitic plates, carbon nanotubes, and onion-like structures. • The structural quality of the products using the ferritin-mixed solution is greater than that using DI water only. • We also fabricate flexible conductive paper using the produced nanomaterials. Abstract We demonstrate the production of low-dimensional carbon nanomaterials using a solution plasma system and their application to flexible conductive paper. The solution plasma system consists of two graphite electrodes and a beaker filled with ferritin-mixed deionized water. Ferritin molecules are used as the growth catalyst of the carbon nanomaterials. A high voltage of 15 kV at a frequency of 25 kHz is supplied to the electrodes using an alternating-current power source. The effects of the graphite rod diameters and the concentration of ferritin molecules are comparatively investigated. The produced carbon nanomaterials are characterized using Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. We confirmed the synthesis of graphitic platelets, onion-like structures, and carbon nanotubes. Finally, we fabricated flexible conductive papers using the produced materials with a good electrical conductance.
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  • Effects of Cr Reduction on High-Temperature Strength of High-Ni Austenitic Cast Steels Used for High-Performance Turbo-chargers

    Yoo, Jisung   Choi, Won-Mi   Sohn, Seok Su   Lee, Byeong-Joo   Kim, Gi-Yong   Oh, Yong-Jun   Lee, Sunghak  

    Since greater high-temperature strength is required for maintaining high-performance turbo-chargers at higher exhaust gas temperatures, e.g., 1323 K (1050 degrees C), high-Ni (20 wt pct) austenitic steel (ASTM HK40 steel) is presented as an excellent turbo-charger candidate material. To enhance the strength, three types of austenitic cast steel were fabricated in this study by controlling the Cr content in HK40 steel, and high-temperature strength improvement was achieved by detailed microstructural evolution including carbide formation and matrix strengthening. Room temperature and high-temperature strengths were expected to be proportional to the carbide volume fraction, but revealed an opposite trend because the steel containing more Cr (having more carbides) revealed lower strength than the steel containing less Cr (having fewer carbides). This result was associated mainly with the M7C3 to M23C6 decomposition occurring at high temperatures in the less-Cr-steel that beneficially strengthened the austenite matrix and reduced the hardness difference between the carbide and matrix, consequently improving the high-temperature strength. In considering the alloying prices (14 pct cost saving of alloying elements) as well as the high-temperature strength, the steel containing less Cr is promising for new high-performance turbo-charger applications. (C) The Minerals, Metals & Materials Society and ASM International 2018
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  • Effects of strain rate on room- and cryogenic-temperature compressive properties in metastable V10Cr10Fe45Co35 high-entropy alloy

    Song, Hyejin   Kim, Dong Geun   Kim, Dae Woong   Jo, Min Cheol   Jo, Yong Hee   Kim, Wooyeol   Kim, Hyoung Seop   Lee, Byeong-Joo   Lee, Sunghak  

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