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Effects of Alloying Elements on the Microstructures and Mechanical Properties of heavy Section Ductile Cast Iron

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Journal of Materials Science & Technology 2007年第1期23卷 97-101页

作者： G.S.Cho k.h.choe k.W.Lee A.Ikenaga Advanced Material Processing Team Korea Institute of Industrial Technology994-32Dongchun-DongYeonsu-KuIncheon 406-130South Korea Department of Metallurgy and Materials Science Graduate School of EngineeringOsaka Prefecture University1-1Gakuen-ChoSakaiOsaka 599-8531Japan

The effects of alloying elements on the as-cast microstructures and mechanical properties of heavy section ductile cast iron were investigated to develop press die material having high strength and high ductility. Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of alloy amounts within 0.25 to 0.75 wt pct range. hardness is measured on the broken tensile specimens. The small additions of Mo, Cu, Ni and Cr changed the as-cast mechanical properties owing to the different as-cast matrix microstructures. The ferrite matrix of Mo and Ni alloyed cast iron exhibits low strength and hardness as well as high elongation and impact energy. The increase in Mo and Ni contents developed some fractions of pearlite structures near the austenite eutectic cell boundaries, which caused the elongation and impact energy to drop in a small range. Adding Cu and Cr elements rapidly changed the ferrite matrix into pearlite matrix, so strength and hardness were significantly increased. As more Mo and Cr were added, the size and fraction of primary carbides in the eutectic cell boundaries increased through the segregation of these elements into the intercellular boundaries.

关键词： heavy section ductile cast iron Alloying elements As-cast microstructures As-cast mechanical properties

Effect of Applied Pressure on the Joining of Combustion Synthesized Ni_3Al Intermetallics with Al Alloy

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Journal of Materials Science & Technology 2008年第1期24卷 123-126页

作者： G.S.Cho J.h.Yang k.h.choe k.W.Lee A.Ikenaga Advanced Material Processing Team Korea Institute of Industrial Technology 7-47 Songdo-Dong Yeonsu-Ku Incheon 406-840 Korea Department of Metallurgy and Materials Science Graduate School of Engineering Osaka Prefecture University 1-1 Gakuen-Cho Sakai Osaka 599-8531 Japan

We focused on the surface reinforcement of ligth weight casting alloys with Ni-AI intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting *** our previous works,green compact of elemental Ni and Al powders were reacted to form Ni-3Al intermetallic compound by ShS （Self-propagating high temperature synthesis） reaction with the heat of molten Al alloy and simultaneously bonded with Al casting *** some defects such as tiny cracks and porosities were remained in the reacted *** we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting *** compressed Al alloy bonded with the Ni-3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy （SEM）.The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy （EDS） and electron probe micro analysis （EPMA）. Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al *** porosities observed in the reacted Ni-3Al compact were filled up with the liquid AI *** Si particles from the molten Al alloy were detected in the pores of reacted Ni-3Al intermetallic *** Al casting alloy and Ni-3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.

关键词： Joining Combustion synthesis Ni3AI Intermetallic compound Squeeze casting

Study of the Interface between Steel Insert and Aluminum Casting in EPC

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Journal of Materials Science & Technology 2008年第1期24卷 60-64页

作者： k.h.choe k.S.Park B.h.kang G.S.Cho k.Y.kim k.W.Lee M.h.kim A.Ikenaga S.koroyasu Advanced Material Processing Team korea Institute of Industrial Technology IncheonKorea Department of Materials Engineering korea University of Technology and Education ChoongnamKorea Department of Materials Science and Engineering Inha University IncheonKorea Department of Metallurgy and Materials Science Graduate School of Engineering Osaka Prefecture UniversityOsakaJapan Department of Mechanical and Precision Systems Teiko University UtsunomiyaJapan

The effective surface treatment method for steel insert composited with Al base metal by expendable pattern casting （EPC） process and the bonding interface between steel insert and Al base metal were *** was found that Zn plating on steel insert was effective on improving the bonding property between steel insert and Al base metal in EPC *** is thought to promote the formation of diffusion *** almost none content of Zn was observed in the boundary which had been plated on the steel insert.A diffusion layer consisting of Al,Si and Fe was formed at the insert/alloy interface and its hardness was higher than the steel insert as matter of course Al base *** layer turned out to be intermetallic compounds of Al-Si-Fe *** pouring temperature promoted the diffusion of Fe into Al alloy,so Fe content in intermetallic layers increased at higher pouring *** layer nearest to steel disappeared due to applied pressure.

关键词： Expendable pattern casting Insert casting Intermetallic compound Al-Si-Fesystem

Dominant edge direction based fast intra mode decision in the h.264/AVC encoder

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第6期10卷 767-777页

作者： Byeongdu LA Minyoung EOM Yoonsik choe Department of Electrical and Electronic Engineering Yonsei University

The h.264/AVC video coding standard uses an intra prediction mode with 4×4 and 16×16 blocks for luma and 8×8 blocks for chroma. This standard uses the rate distortion optimization (RDO) method to determine the best coding mode based on the compression performance and video quality. This method offers a large improvement in coding efficiency compared to other compression standards, but the computational complexity is greater due to the various intra prediction modes. This paper proposes a fast intra mode decision algorithm for real-time encoding of h.264/AVC based on the dominant edge direction (DED). The DED is extracted using pixel value summation and subtraction in the horizontal and vertical directions. By using the DED, three modes instead of nine are chosen for RDO calculation to decide on the best mode in the 4×4 luma block. For the 16×16 luma and the 8×8 chroma, only two modes are chosen instead of four. Experimental results show that the entire encoding time saving of the proposed algorithm is about 67% compared to the full intra search method with negligible loss of quality.

关键词： h 264 Intra prediction Mode decision Dominant edge direction

Nanostructure and corrosion behaviors of nanotube formed Ti-Zr alloy

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中国有色金属学会会刊：英文版 2009年第4期19卷 1005-1008页

作者： Won-Gi kIM han-Cheol choe Department of Dental Materials & Research Center of Nano-Interface Activation for Biomaterials College of DentistryChosun University

In order to investigate the nanostructures and corrosion behaviors of Ti-Zr alloys,nanotube formed Ti-Zr(10%,20%,30% and 40% in mass fraction) alloys were prepared by arc melting and the condition of controlling nanostructure was at 1 000 ℃ for 24 h in argon atmosphere;formation of nanotubes was conducted by anodizing a Ti-Zr alloy in h3PO4 electrolyte with a small amount of fluoride ions at room *** corrosion properties of specimens were examined through potentiodynamic test(potential range of -1 500-2 000 mV) in 0.9% NaCl solution by using *** of the alloys were observed by optical microscope(OM),field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD).Diameter of nanotube does not depend on Zr content,but interspace of nanotube predominantly depends on Zr content,which confirms that ZrO2 oxides play a role to increase the interspace of nanotube formed on the surface.

关键词：钛锆合金纳米结构腐蚀行为扫描电子显微镜 NaCl溶液阳极氧化光学显微镜 X射线衍射

Carbide Formation Process in Directionally Solidified MAR-M247 LC Superalloy

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Journal of Materials Science & Technology 1999年第1期15卷 48-52页

作者： Chen, Jian huang, Baiyun Lee, J.h. choe, S.J. Lee, Y.T. Cent S Univ Technol Powder Met Res Inst Changsha 410083 Peoples R China Changwon Natl Univ Dept Met & Mat Sci Changwon 641773 South Korea korea Inst Machinery & Mat Changwon 641010 South Korea

Carbide nucleation, growth and trapping behavior in directionally solidified MAR-M247 LC alloy and the corresponding mechanism have been investigated. Carbide forming element enrichment controls the carbide nucleation and the carbide growth behavior. If the carbide forming element enrichment and the nucleation sites are suitable, carbide nucleation can occur both above and below the liquids temperature. heterogeneous carbide nucleation is the preferred nucleation mechanism at low carbide forming element enrichment. Carbide growth occurs mainly at inter-secondary gamma dendrite arm area and lower part of the mushy zone. The carbides are subsequently trapped at these positions after growing to a certain size. Some carbides are only partially trapped by the solid-liquid interface and the carbide growth accelerates after being partially trapped. A critical growth rate exists between 2 multiplied by 10** minus **6 m/s and 5 multiplied by 10** minus **6 m/s. The carbide volume fraction decreases in the directionally solidified part at slow growth rate which is caused by the lack of suitable growth site and the low trapping ability of the solid-liquid interface. (Edited author abstract) 16 Refs.

关键词： Nickel alloys

Characterization of three-dimensional channel reservoirs using ensemble kalman filter assisted by principal component analysis

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Petroleum Science 2020年第1期17卷 182-195页

作者： Byeongcheol kang hyungsik Jung hoonyoung Jeong Jonggeun choe Department of Energy Systems Engineering Seoul National UniversitySeoul 08826South Korea

Ensemble-based analyses are useful to compare equiprobable scenarios of the reservoir ***,they require a large suite of reservoir models to cover high uncertainty in heterogeneous and complex reservoir *** stable convergence in ensemble kalman filter(EnkF),increasing ensemble size can be one of the solutions,but it causes high computational cost in large-scale reservoir *** this paper,we propose a preprocessing of good initial model selection to reduce the ensemble size,and then,EnkF is utilized to predict production performances *** the model selection scheme,representative models are chosen by using principal component analysis(PCA)and clustering *** dimension of initial models is reduced using PCA,and the reduced models are grouped by ***,we choose and simulate representative models from the cluster groups to compare errors of production predictions with historical observation *** representative model with the minimum error is considered as the best model,and we use the ensemble members near the best model in the cluster plane for applying *** demonstrate the proposed scheme for two 3D models that EnkF provides reliable assimilation results with much reduced computation time.

关键词： Channel reservoir characterization Model selection scheme Egg model Principal component analysis(PCA) Ensemble kalman filter(EnkF) history matching

Discovery of Zr-based metal-organic polygon:Unveiling new design opportunities in reticular chemistry

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Nano Research 2021年第2期14卷 392-397页

作者： Jiyeon kim Dongsik Nam hiroshi kitagawa Dae-Woon Lim Wonyoung choe Department of Chemistry Ulsan National Institute of Science and Technology50 UNIST-gilUlsan 44919Republic of Korea Department of Chemistry Graduate School of ScienceKyoto UniversityKitashirakawa Oiwake-choSakyo-kuKyoto 606-8502Japan Department of Chemistry and Medical Chemistry College of Science and TechnologyYonsei University1 Yonseidae-gilWonjuGangwon-do 26493Republic of Korea

Metal-based secondary building unit and the shape of organic ligands are the two crucial factors for determining the final topology of metal-organic materials.A careful choice of organic and inorganic structural building units occasionally produces unexpected structures,facilitating deeper fundamental understanding of coordination-driven self-assembly behind metal-organic ***,we have synthesized a triangular metal-organic polygon(MOT-1),assembled from bulky tetramethyl terephthalate and Zr-based secondary building ***,the Zr-based secondary building unit serves as an unusual ditopic Zr-connector,toform metal-organic polygon MOT-1,proven to be a good candidate for water adsorption with *** study highlights the interplay of the geometrically frustrated ligand and secondary building unit in controlling the connectivity of metal-organic *** a strategy can be further used to unveil a new class of metal-organic materials.

关键词： reticular chem istry Zr-based metal-organic polygon geometrical frustration ditopic secondary building unit

Effects of TiN film coating on electrochemical behaviors of nanotube formed Ti-xhf alloys

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中国有色金属学会会刊：英文版 2009年第4期19卷 857-861页

作者： kang LEE Won-Gi kIM Joo-Young ChO Sang-Won EUN han-Cheol choe Department of Dental Materials & Research Center of Nano-Interface Activation for Biomaterials College of DentistryChosun University Department of Applied Advanced Materials Korea Polytechnic Ⅴ Colleges

Ti-xhf(x=10%,20%,30% and 40%,mass fraction) alloys were prepared by arc melting,and the microstructure was controlled for 24 h at 1 000 ℃ in argon *** formation of nanotube was conducted by anodizing on Ti-hf alloys in 1.0 mol/L h3PO4 electrolytes with small amounts of NaF at room *** then TiN coatings were coated by DC-sputtering on the anodized *** and nanotube morphology of the alloys were examined by field emission scanning electron microscopy(FE-SEM) and X-ray diffractometry(XRD).The corrosion properties of the specimens were examined through potentiodynamic test(potential range from -1 500 to 2 000 mV) in 0.9 % NaCl solution by *** microstructure shows the acicular phase and α' phase with hf *** amorphous oxide surface is transformed to crystalline anatase *** coated nanotube surface has a good corrosion resistance.

关键词：氮化钛涂层合金制备纳米管电化学行为薄膜包衣 0.9%NaCl溶液扫描电子显微镜微观结构