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Enhancement of magnetic properties of hot pressed/die-upset Dy-free Nd-Fe-B magnets with Cu/Nd coating by wet process

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Rare Metals 2020年第1期39卷 48-54页

作者： Jeehye kwon Dajeong Lee Dayoung Yoo Seongkyu Park Hee-Ryoung Cha hae-woong kwon Junggoo Lee Dongyun Lee Department of Advanced Circuit Interconnection Pusan National UniversityBusan46241Republic of Korea Department of Nano Fusion Technology Pusan National UniversityBusan46241Republic of Korea Powder and Ceramics Department Korea Institute of Machinery and MaterialsChangwon51508Republic of Korea Department of Materials Science and Engineering Pukyong National UniversityBusan48513Republic of Korea Department of Nanoenergy Engineering Pusan National UniversityBusan46241Republic of Korea

A grain boundary diffusion process(GBDP)was adopted to improve magnetic properties of Dy-free highly coercive Nd-Fe-B permanent magnet by coating thin layers of Nd and Cu in grain *** GBDP of Nd and Cu,Nd and Cu were coated by wet process,e.g.,electrochemical and electroless on Nd-Fe-B magnets,which was fabricated by hot-deformed/die-upset with meltspun *** treatment was performed for 20 min at 600℃followed by several different cooling *** cooling conditions after heat treatment were varied to understand distribution and micros tructural effects of Nd and Cu species in grain *** coercivity increased from 1.565 to 1.637 T in oil cooling rate but remanence decreased,while remanence jumped with little decrease in coercivity in furnace *** tructure analyses suggested that the coercivity was closely related to the cooling rate as well as distribution of *** mechanism of coercivity enhancement due to the cooling rate was discussed based on the results presented here and those in the literature.

关键词： Magnetic materials Electrochemical deposition Diffusion Scanning electron microscopy Coercivity

Effect of Deformation Temperature on Microstructure and Mechanical Properties of AZ31 Mg Alloy Processed by Differential-Speed Rolling

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Journal of Materials Science & Technology 2015年第5期31卷 498-503页

作者： Mosab Kaseem Bong kwon Chung hae woong Yang Kotiba Hamad Young Gun Ko School of Materials Science and Engineering Yeungnam University

A differential-speed rolling(DSR) was applied to AZ31 magnesium alloy sample at different rolling temperatures of 473,523,573,and 623 K with 1-pass and 2-pass *** microstructural evolution and mechanical properties of the deformed samples were *** rolling temperature was found to be an important parameter affecting the microstructural *** DSR at 473 K,the microstructure was more homogeneous than that obtained after deformation by equal-speed rolling(ESR).The fully recrystallized microstructures were generated after DSR at 573 and 623 *** to mechanical properties,the yield strength(YS) and ultimate tensile strength(UTS) decreased monotonously with increasing rolling *** contrast,the elongation of the DSR-deformed samples was improved as the rolling temperature *** strain hardening exponent(n) calculated by Hollomon equation increased with increasing the rolling temperature,which would explain an increase in the uniform elongation.

关键词： Differential-speed rolling Magnesium alloy Mechani

Effect of Squeeze Cast Process Parameters on Fluidity of Hypereutectic Al-Si Alloy

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Journal of Materials Science & Technology 2008年第1期24卷 7-11页

作者： Jong-Kyu Baek hae-Wook kwon School of Materials Science and Engineering Yeungnam University Gyeongsan 712-749 Korea

The effects of processing variables on the fluidity of hypereutectic Al-Si alloy melt during squeeze casting were *** maximum fluidity of Al-16.0%Si alloy during squeeze casting was obtained under the applied pressure of 30 *** fluidity increased with *** fluidity increased with silicon content in the range from 12.0% to 20.0%.That was decreased respectively by eutectic modification and primary silicon refinement.

关键词： Squeeze casting Al-alloy Fluidity Melt treatment

Plastic anisotropy calculation of severely-deformed Al-Mg-Si alloy considering texture changes in electron backscatter diffraction

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Journal of Materials Science & Technology 2019年第7期35卷 1439-1443页

作者： I Putu Widiantara hae woong Yang Min Jun Kim Young Gun Ko Plasticity Control & Mechanical Modeling Lab. School of Materials Science & Engineering Yeungnam University

The investigation studied the plastic anisotropy of the severely-deformed Al-Mg-Si alloy by considering texture *** sample deformed via asymmetrical rolling under cross-shear condition was annealed at 598 K where recrystallization was in *** is found upon annealing that the intensity of Cube({001})was comparable to those of plane-strain components while the intensities of shear components remained constant despite their instabilities in the recrystallization *** annealing,the average Lankford value(r)of the present sample was close to a unity whereas the in-plane anisotropy(△r)decreased,resulting in nearly isotropic characteristics of Al-Mg-Si alloy.

关键词： Al-Mg-Si alloy Anisotropy Recrystallization Microstructures

Improving the electrochemical stability of AZ31 Mg alloy in a 3.5wt.%NaCl solution via the surface functionalization of plasma electrolytic oxidation coating

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Journal of Magnesium and Alloys 2022年第5期10卷 1311-1325页

作者： Mosab Kaseem Tehseen Zehra Burak Dikici Ali Dafali hae woong Yang Young Gun Ko Department of Nanotechnology and Advanced Materials Engineering Sejong UniversitySeoul 05006Republic of Korea Department of Metallurgical and Materials Engineering Ataturk UniversityErzurum 25240Turkey Faculty of Sciences Oujda Department of ChemistryMohamed the First UniversityOujdaMorocco Pohang Institute of Metal Industry Advancement Pohang 37666Republic of Korea Materials Electrochemistry Group School of Materials Science and EngineeringYeungnam UniversityGyeongsan 38541Republic of Korea

The unique interactions between hexadecanoic acid(HA)and albumin(ALB)molecules on the surface of the porous layer of AZ31 Mg alloy were exploited to fabricate a novel hybrid composite film with excellent electrochemical stability in a 3.5 wt.%Na Cl ***,the inorganic layer(IL)obtained by plasma electrolytic oxidation of AZ31 Mg alloy in an alkaline-phosphate-WO_(3)electrolyte was soaked in an organic solution composed of ALB and HA for 10 and 24 h at 60℃.Although albumin and HA may coexist on the same surface of IL,the higher reactivity of ALB molecules would prevent the formation of a thick layer of *** donor-acceptor complexes formed due to the unique interactions between ALB and/or HA and IL surface would reduce the area exposed to the corrosive species which in turn would efficiently protect the substrate from *** porous structure of the IL would provide preferable sites for the physical and chemical locking triggered by charge-transfer phenomena,leading to the inhomogeneous nucleation and crystal growth of a flowery flakes-like organic *** calculations were performed to reveal the primary bonding modes between the ALB,HA,and IL and to assess the mechanistic insights into the formation of such novel hybrid composites.

关键词： Hybrid composite Coordination bond Albumin Fatty acid Porous layer Corrosion Theoretical approach

Study of material removal behavior on R-plane of sapphire during ultra-precision machining based on modified slip-fracture model

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Nanotechnology and Precision Engineering 2020年第3期3卷 141-155页

作者： Suk Bum kwon Aditya Nagaraj hae-Sung Yoon Sangkee Min Department of Mechanical Engineering University of Wisconsin-Madison1513 University AvenueMadisonWI 53706United States of America School of Aerospace and Mechanical Engineering Korea Aerospace University76 Hanggongdaehak-roDeogyang-guGoyang-siGyeonggi-do 10540Republic of Korea

In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed.

关键词： Ductile-brittle transition Crack morphology Single crystal sapphire Deformation mechanism Orthogonal cutting Ultra-precision machining

Towards high-performance and robust anion exchange membranes(AEMs)for water electrolysis:Super-acid-catalyzed synthesis of AEMs

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Journal of Energy Chemistry 2024年第6期93卷 478-510,I0012页

作者： Geun woong Ryoo Sun Hwa Park Ki Chang kwon Jong Hun Kang Ho Won Jang Min Sang kwon Department of Materials Science and Engineering Research Institute of Advanced Materials(RIAM)Seoul National UniversitySeoul 08826Republic of Korea Interdisciplinary Materials Measurement Institute Korea Research Institute of Standards and Science(KRISS)Daejeon 34113Republic of Korea Department of Chemical and Biological Engineering and Institute of Chemical ProcessSeoul National UniversitySeoul 08826Republic of Korea Department of Applied Measurement Science University of Science and TechnologyDaejeon 34113Republic of Korea

The increasing demand for hydrogen energy to address environmental issues and achieve carbon neutrality has elevated interest in green hydrogen production,which does not rely on fossil *** various hydrogen production technologies,anion exchange membrane water electrolyzer(AEMWE)has emerged as a next-generation technology known for its high hydrogen production efficiency and its ability to use non-metal ***,this technology faces significant challenges,particularly in terms of the membrane durability and low ionic *** address these challenges,research efforts have focused on developing membranes with a new backbone structure and anion exchange groups to enhance durability and ionic ***,the super-acid-catalyzed condensation(SACC)synthesis method stands out due to its user convenience,the ability to create high molecular weight(MW)polymers,and the use of oxygen-tolerant organic *** the synthesis of anion exchange membranes(AEMs)using the SACC method began in 2015,and despite growing interest in this synthesis approach,there remains a scarcity of review papers focusing on AEMs synthesized using the SACC *** review covers the basics of SACC synthesis,presents various polymers synthesized using this method,and summarizes the development of these polymers,particularly their building blocks including aryl,ketone,and anion exchange *** systematically describe the effects of changes in the molecular structure of each polymer component,conducted by various research groups,on the mechanical properties,conductivity,and operational stability of the *** review will provide insights into the development of AEMs with superior performance and operational stability suitable for water electrolysis applications.

关键词： Green hydrogen production Water electrolysis Anion exchange membrane water electrolyzer(AEMWE) Anion exchange membranes(AEMs) Super-acid-catalyzed condensation(SACC)

Velocity Profiles between Two Baffles in a Shell and Tube Heat Exchanger

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Journal of Thermal Science 2015年第4期24卷 356-363页

作者： Tae-Hyun Chang Chang-Hoan Lee hae-Soo Lee kwon-Soo Lee Senior Research Fellow of RESEAT Korea Institute of Science and Technology Information Korea Institute of Science and Technology Information Postdoctoral Research Fellow School of Mechanical Engineering of Kyungnam University International University of Korea

Heat exchangers are extensively utilized for waste heat recovery,oil refining,chemical processing,and steam *** this study,velocity profiles are measured using a 3D particle image velocimetry(PIV)system between two baffles in a shell and tube heat exchanger for parallel and counter *** PIV and computational fluid dynamics results show the occurrence of some strong vectors near the *** vectors are assumed due to the clearance between the inner tubes and the front ***,the major parts of the vectors are moved out through the bottom opening of the rear baffle,and other vectors produce a large circle between the two *** simulations are conducted to investigate the effects of the baffle on the heat exchanger using the Fluent *** k-εturbulence model is employed to calculate the flows along the heat exchanger.

关键词： Baffle P1V Shell and tube heat exchanger Cut off ratio CFD

Diel vertical migration of the copepod Calanus sinicus before and during formation of the Yellow Sea Cold Bottom Water in the Yellow Sea

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Acta Oceanologica Sinica 2013年第9期32卷 99-106页

作者： KANG Jung-Hoon SEO MinHo kwon Oh Youn KIM woong-Seo South Sea Environment Research Division Korea Institute of Ocean Science&Technology (KIOST) Deep-sea and Seabed Resources Research Division

To understand the effects of the Yellow Sea Cold Bottom Water （YSCBW） on the diel vertical migration （D- VM） of the copepod Calanus sinicus, we surveyed vertical distribution of C. sinicus at a fixed station in the Yellow Sea before （spring） and during （summer） formation of the YSCBW. Cold water （〈10℃） was observed in the bottom layer when the water column was thermally stratified in summer, but the water column was thermally well-mixed in spring 2010. Samples were collected from five different layers at 3-h intervals using an opening-closing net. Adult females （1-155 ind./m3） showed a clear normal DVM pattern throughout the entire water column in spring, whereas adult males did not migrate. DVM of copepodite V （CV） individuals was not clear, but the maximum abundance of CI-CIV occurred consistently in the upper 10-20 m layer, where there was a high concentration of chlorophyll-a （Chl-a）（0.49-1.19μg/L）. In summer, weak DVM was limited to cold waters beneath the thermocline for adult females （〈30 ind./m3）, but not for adult males. The maximum abundance of CI-CIV also occurred consistently in the subsurface layer （20-40 m） together with high concentrations of Chl-a （0.81-2.36 μg/L）. CV individuals （1-272 ind./m3） moved slightly upward noc- turnally to the near-surface layer （10-20 m）, where the average temperature was 25.74℃, but they were not found in the surface layer （0-10 m; 28.31℃）. These results indicate that the existence of the YSBCW affected food availability at depth and the vertical temperature distribution, leading to variation in the amplitude and shape of stage-specific vertical distributions （CI to adults） in C. sinicus before and during the formation of cold waters in the Yellow Sea during the study period.

关键词： Yellow Sea Cold Bottom Water (YSCBW) copepod Calanus sinicus developmental stages,diel vertical migration (DVM)