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Effect of Solute Contents of Al-Ni-Sr Alloy on Glass Forming Ability and Thermal Stability

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journal of Rare Earths 2004年第z2期22卷 73-77页

作者： Taek Soo kim j K Lee H j kim j C Bae Advanced Materials R&D Center Korea Institute of Industrial Technology994-32 Dongchun-dongYeonsu-kuIncheon 406-130Korea Advanced Materials R&D CenterKorea Institute of Industrial Technology994-32 Dongchun-dongYeonsu-kuIncheon 406-130Korea Advanced Materials R&D CenterKorea Institute of Industrial Technology994-32 Dongchun-dongYeonsu-kuIncheon 406-130Korea Advanced Materials R&D CenterKorea Institute of Industrial Technology994-32 Dongchun-dongYeonsu-kuIncheon 406-130Korea

Glass forming ability (GFA) and structural characterization of a new amorphous Al-Ni-Sr alloy melt spun were investigated on the theory of the factors for the glass formation. The GFA was varied with the ratio of Ni to Sr in detail and successful amorphous phase dispersed with 2 ～ 5 nm precipitates was prepared from Al-Ni5-Sr3. Thermal stability and crystallization behavior of the amorphous phase were determined by continuous and isothermal heating technique on DCS, resulting that the crystallization occurs by the growth of fcc Al nanocrystals on the preexistent nuclei.

关键词： glass formation crystallization Al base amorphous alloys rapid solidification

Photoluminescence enhancement of red-emitting GdVO_4:Eu and YVO_4:Eu phosphors by adding zinc

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journal of Rare Earths 2013年第1期31卷 13-17页

作者： K.Park j.kim K.Y.kim j.Y.kim Y.kim S.j.Dhoble Faculty of Nanotechnology and Advanced Materials Engineering Sejong University Department of Advanced Materials Engineering Hoseo University Department of Chemistry and Institute of Basic Sciences Dankook University Department of Physics R.T.M. Nagpur University

We synthesized the rare-earth activated Ro.94_xEuo.06ZnxVO4 （R： Gd and Y; 0〈_x〈_0.08） phosphors with a spherical mor- phology and a smooth surface by the ultrasonic spray pyrolysis. The annealed Ro.94_xEuo.06ZnxVO4 crystallized in the tetragonal zircon type structure, belonging to the space group of I41/amd. The incorporation of a small amount of Zn to Ro.94Euo.06VO4 improved the emission characteristics. The emission intensities of the Gdo.88EUo.06Zno.06VO4 and Yo.9Euo.06Zno.04VO4 phosphors at 619 nm were 72% and 2 1% stronger than those of the Gdo,94Euo.06VO4 and Yo.94Euo.06VO4 phosphors, respectively. We demonstrated that the addi- tion of Zn to Ro.94Euo.06VO4 was quite effective for improving the photoluminescent properties.

关键词： rare earths photolurninescence vanadate ultrasonic spray pyrolysis

Strip Casting of High Performance Structural Alloys

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journal of Rare Earths 2004年第z2期22卷 78-84页

作者： S S Park j G Lee Nack j kim Center for Advanced Aerospace Materials Pohang University of Science and TechnologyPohang 790-784Korea Center for Advanced Aerospace MaterialsPohang University of Science and TechnologyPohang 790-784Korea Center for Advanced Aerospace MaterialsPohang University of Science and TechnologyPohang 790-784Korea

There exists a great need for the development of high performance alloys due to increasing demands for energy conservation and environmental protection. Application of strip casting shows a strong potential for the improvement of properties of existing alloys and also for the development of novel alloy systems with superior properties. The present paper reviews our Center's activities in the development of high performance alloys by strip casting. Examples include (1) Al alloys, (2) wrought Mg alloys, and (3) bulk metallic glass (BMG) alloys.

关键词： strip casting 6061 Al alloy AZ Mg alloy bulk metallic glass (BMG) alloy dispersion hardening

Effects of Processing Parameters on Microstructure and Properties of Ultra High Strength Linepipe Steel

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journal of Materials Science & Technology 2012年第10期28卷 889-894页

作者： Xiaodan Wu Hakcheol Lee Young Min kim Nack j.kim University of Pittsburgh Pittsburghl PA 15213USA Pohang University of Science and Technology Pohang 790-784Korea

To examine the effect of processing parameters on microstructural evolution and to obtain the excellent combination of strength and toughness, simulation of thermo-mechanical processing was conducted using the Gleeble machine. Trial production was then conducted under the conditions obtained by Gleeble tests. Based on the results of microstructure analysis and mechanical property evaluation, the relationship between microstructural features and mechanical properties was elucidated. The result shows that the volume fraction of constituted phases can be controlled through adjusting the cooling rate and finish cooling temperature in order to get different strength levels. As cooling rate increases, the volume fraction of upper bainite increases, which leads to the increase of strength. The upper shelf energy （USE） increases with increasing volume fraction of acicular ferrite in bainite base because of the small effective acicular ferrite grain size. Ductile-brittle transition temperature （DBTT） decreases with increasing acicular ferrite volume fraction. High reduction in the rough stage has great influence on grain refinement.

关键词： Linepipe steel Microstructure Gleeble test TMCP (thermomechanicalcontrol process)

Microstructure and tensile properties of magnesium nanocomposites fabricated using magnesium chips and carbon black

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journal of Magnesium and Alloys 2020年第3期8卷 860-872页

作者： T.j.Lee W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

In this study,carbon black(0,0.01,0.03 and 0.08 wt%)and AZ31(Mg-3Al-lZn)magnesium chips were used to fabricate carbon black-reinforced magnesium matrix composites with extrusion or a combination of extrusion and high-ratio differential speed *** hot pressing at 693 K and extrusion at 623 K with an extrusion ratio of 22,the magnesium chips coated with carbon black were soundly bonded into a bulk composite *** grain sizes of the extruded materials were similar with a size of 48.2-51.5|im despite the difference in the amount of carbon *** yield strength and ultimate tensile strength increased from 177 to 191 MPa and from 240 to 265 MPa,respectively,as a result of the addition of 0.01%carbon black;however,a further increase in the strength was marginal with additional carbon *** same trend was observed in the strain hardening *** tensile elongation increased by to the addition of 0.01%carbon black(from 15.8%to 17.4%)due to the increased work hardening effect,but decreased with additional carbon black due to its agglomeration and poor dispersion at higher *** high-ratio differential speed rolling(HRDSR)on the extruded materials and subsequent annealing,the AZ31 and AZ31 composites had a similar fine grain size of 16.3-17.9 *** annealed HRDSR composites showed the best mechanical properties at a higher content of carbon black(0.03%)compared to that(0.01%)for the extruded *** resulted from the enhanced dispersion effect of the carbon black due to the high shear flow induced during the HRDSR *** extruded composites exhibited the three distinct hardening stages(stage II,stage III and stage IV),while the annealed HRDSR composites mainly displayed the stage III *** addition of carbon black increased the strain hardening rate at all the strain hardening stages in both of the extruded and annealed HRDSR *** the initial hardening stage,the strain hardening rates of the extruded comp

关键词： Recycling Magnesium alloys chips Carbon black Nanocomposites Extrusion Differential speed rolling

Power management unit chip design for automobile active-matrix organic light-emitting diode display module

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journal of Central South University 2009年第4期16卷 621-628页

作者： kim j H PARK j H kim j H CAO T V LEE T Y BAN H j YANG K kim H G HA P B kim Y H Department of Electronic Engineering Changwon National University 9 Sarim-Dong Changwon 641-773 Korea Denso PS Electronics Corporation 47 Seongsan-Dong Changwon 641-315 Korea

A power management unit （PMU） chip supplying dual panel supply voltage, which has a low electro-magnetic interference （EMI） characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area. The PMU chip is designed with MagnaChip＇s 0.25 μ high-voltage process. The driving currents of ELVDD and ELVSS are more than 50 mA when a SPICE simulation is done.

关键词： DC-DC converter AMOLED charge pumping power management unit (PMU) dual panel supply voltage

Effect of roll speed ratio on the texture and microstructural evolution of an FCC high-entropy alloy during differential speed rolling

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journal of Materials Science & Technology 2022年第16期111卷 152-166页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

A very coarse-grained(335μm)Fe_(41)Mn_(25)Ni_(24)Co_(8)Cr_(2)high-entropy alloy with a single FCC phase was cold rolling to a 80%reduction in thickness using the differential speed rolling technique with various speed ratios(SRs)ranging between 1 and *** the SR was increased,the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear *** SR=4,the entire thickness of the sheet was covered with micro-shear bands,and ultrafine(sub)grains with a size of1.4μm were uniformly formed along the shear bands.A continuous dynamic recrystallization(CDRX)mechanism occurred during rolling,and a higher SR accelerated the CDRX *** conventional rolling(at SR=1),a brass{110}orientation texture with minor components of S{123}and Cu{112}orientations *** higher SRs,shear texture developed as the main type,while the development of rolling texture was *** microstructure at SR=4 obtained after annealing at973 K showed a fully recrystallized microstructure composed of a five times smaller grain size(4μm)with a higher intensity ofγfiber texture compared with that prepared by conventional *** samples processed with high SRs exhibited better tensile properties compared with the conventionally rolled sample in terms of strength and ductility after *** current results demonstrate that by using differential speed rolling with a high SR,one can achieve a significantly finer and more homogeneous microstructure,stronger shear texture,and superior tensile mechanical properties for an FCC high-entropy alloy compared to that obtained by conventional *** strength of the as-rolled and annealed samples was quantitatively explained by considering the contribution of grain size and dislocation density to strengthening.

关键词： High entropy alloys Differential speed rolling Texture Grain refinement Strength Severe plastic deformation

Grain size and temperature effect on the tensile behavior and deformation mechanisms of non-equiatomic Fe(41)Mn(25)Ni(24)Co8Cr2high entropy alloy

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journal of Materials Science & Technology 2020年第7期42卷 190-202页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul121-791Republic of Korea

The effect of the grain size on the tensile properties and deformation mechanisms of a nonequiatomic Fe(41)Mn(25)Ni(24)Co8 Cr2 high-entropy alloy was studied in the temperature range between 298 and 1173 K by preparing the samples with three different grain sizes through severe plastic deformation and subsequent annealing:ultrafine(sub)grain size(≤0.5μm),8.1μm and 590.2μ*** the temperature between 298 and773 K,the material with the large grain size of 590.2μm exhibited the largest tensile ductility(57%-82%)due to its high strain hardening associated with mechanical twinning,but it exhibited the lowest strength due to its large grain *** material with the ultrafine(sub)grain size exhibited the lowest tensile ductility(3%-7%)due to a greatly reduced strain hardening ability after severe plastic deformation,but it exhibited the highest strength due to the dislocation strengthening and grain refinement *** tensile testing at temperatures above 973 K,recrystallization occurred in the material with the ultrafine(sub)grains during the sample heating and holding stage,leading to the formation of fine and equiaxed grains with the sizes of 6.8-13.5μ*** deformation behavior of the Fe(41)Mn(25)Ni(24)Co8 Cr2 with different grain sizes in the high temperature range between 973 and 1173 K,where pseudosteady-state flow was attained in the stress-strain curves,could be explained by considering the simultaneous contribution of grain boundary sliding and dislocation-climb creep to total plastic *** activation energies for plastic flow for the materials with different grain sizes were similar as^199 kj/*** predicting the deformation mechanism,it was important to consider the change in grain size by rapid grain growth or recrystallization during the sample heating and holding stage because grain boundary sliding is a grain-size-dependent deformation *** sample with the ultrafine(sub)grains exhibited the large tensile elongations of 30%-85%due to it

关键词： High entropy alloys Grain size High temperature deformation mechanism Tensile behavior Grain boundary sliding

Microstructure tailoring of Al_(0.5)CoCrFeMnNi to achieve high strength and high uniform strain using severe plastic deformation and an annealing treatment

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journal of Materials Science & Technology 2021年第12期71卷 228-240页

作者： H.T.jeong W.j.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

Ultrafine-grained alloys fabricated by severe plastic deformation(SPD)have high strength but often poor uniform *** via high-ratio differential speed rolling(HRDSR)followed by an annealing treatment was applied to Al_(0.5)CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be *** optimized microstructure was composed of an ultrafine-grained FCC matrix(1.7-2μm)with a high fraction of high-angle grain boundaries(61%-66%)and ultrafine BCC particles(with a size of 0.6-1μm and a volume fraction of8%-9.3%)distributed uniformly at the grain boundaries of the FCC *** the severely plastically deformed microstructure,the nucleation kinetics of the BCC phase was *** static recrystallization(CSRX)took place during the annealing process at 1273 *** of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC *** precipitation of the hard and brittleσphase was,however,*** annealed sample processed by HRDSR with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14%-20%.These tensile properties are comparable to those of transformation-induced plasticity *** mechanisms of the severely plastically deformed alloy before and after annealing were identified,and each strengthening mechanism contribution was *** calculated results matched well with the experimental results.

关键词： High entropy alloys Severe plastic deformation Uniform ductility High strength Dual phase Annealing