Journal of Powder Materials

Hyoung-Seop Kim

18 Articles

Densification of Copper Powders using High-pressure Torsion Process: Dong-Jun Lee, Eun-Yoo Yoon, Soo-Young Kang, Jung-Hwan Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2012;19(5):333-337.; DOI: https://doi.org/10.4150/KPMI.2012.19.5.333

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In this study, electrolytic copper powders were consolidated by high-pressure torsion process (HPT) which is the most effective process to produce bulk ultrafine grained and nanocrystalline metallic materials among various severe plastic deformation processes. The bulk samples were manufactured by the HPT process at 2.5 GPa and 1/2, 1 and 10 turns. After 10 turns, full densification was achieved by high pressure with shear deformation and ultrafine grained structure (average grain size of 677 nm) was observed by electron backscatter diffraction and a scanning transmission electron microscope.

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Analyses of Densification and Consolidation of Copper Powders during High-Pressure Torsion Process Using Finite Element Method
Dong Jun Lee, Eun Yoo Yoon
Journal of Korean Powder Metallurgy Institute.2015; 22(1): 6. CrossRef
Microstructure Evolution and Mechanical Properties of Al-1080 Processed by a Combination of Equal Channel Angular Pressing and High Pressure Torsion
Mohamed Ibrahim Abd El Aal, Eun Yoo Yoon, Hyoung Seop Kim
Metallurgical and Materials Transactions A.2013; 44(6): 2581. CrossRef

Ultrafine Grained Cu-diamond Composites using High Pressure Torsion: Eun-Yoo Yoon, Dong-Jun Lee, Taek-Soo Kim, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2012;19(3):204-209.; DOI: https://doi.org/10.4150/KPMI.2012.19.3.204

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In this work, powder metallurgy and severe plastic deformation by high-pressure torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. Pure Cu powders were mixed with 5 and 10 vol% diamonds and consolidated into disc-shaped samples at room temperature by HPT at 1.25 GPa and 1 turn, resulting in ultrafine grained metallic matrices embedded with diamonds. Neither heating nor additional sintering was required with the HPT process so that in situ consolidation was successfully achieved at ambient temperature. Significantly refined grain structures of Cu metallic matrices with increasing diamond volume fractions were observed by electron backscatter diffraction (EBSD), which enhanced the microhardness of the Cu-diamond composites.

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Effect of a nano-sized TiC particle addition on the flow-assisted corrosion resistance of SA 106B carbon steel
Jin-Ju Park, Eun-Kwang Park, Gyoung-Ja Lee, Chang-Kyu Rhee, Min-Ku Lee
Applied Surface Science.2017; 415: 143. CrossRef
Analyses of Densification and Consolidation of Copper Powders during High-Pressure Torsion Process Using Finite Element Method
Dong Jun Lee, Eun Yoo Yoon
Journal of Korean Powder Metallurgy Institute.2015; 22(1): 6. CrossRef
Trend in Research of Powder Consolidation Using Severe Plastic Deformation
Eun Yoo Yoon, Dong Jun Lee, Dong-Hyun Ahn, Hyuk Jae Jeong, Hyoung Seop Kim
Journal of Korean Powder Metallurgy Institute.2013; 20(2): 148. CrossRef
Microstructure Evolution and Mechanical Properties of Al-1080 Processed by a Combination of Equal Channel Angular Pressing and High Pressure Torsion
Mohamed Ibrahim Abd El Aal, Eun Yoo Yoon, Hyoung Seop Kim
Metallurgical and Materials Transactions A.2013; 44(6): 2581. CrossRef
Grinding Behaviour of Aluminum Powder for Al/CNTs Nano Composites Fabrication by Dry Grinding Process Using a High Speed Planetary Ball Mill
Heekyu Choi, Jehyun Lee, Seongsoo Kim, Gyungpil Choi, Daehyung Bae, Sungbak Lee, Woong Lee
Korean Journal of Materials Research.2013; 23(2): 89. CrossRef
Densification of Copper Powders using High-pressure Torsion Process
Dong-Jun Lee, Eun-Yoo Yoon, Soo-Young Kang, Jung-Hwan Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(5): 333. CrossRef

Densification and Nanocrystallization of Water-Atomized Pure Iron Powder Using High Pressure Torsion: Eun-Yoo Yoon, Dong-Jun Lee, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2011;18(5):411-416.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.411

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In this study, powder metallurgy and severe plastic deformation by high-pressure torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. Water-atomized pure iron powders were consolidated to disc-shaped samples at room temperature using HPT of 10 GPa up to 3 turns. The resulting microstructural size decreases with increasing strain and reaches a steady-state with nanocrystalline (down to ~250 nm in average grain size) structure. The water-atomized iron powders were deformed plastically as well as fully densified, as high as 99% of relative density by high pressure, resulting in effective grain size refinements and enhanced microhardness values.

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Analyses of Densification and Consolidation of Copper Powders during High-Pressure Torsion Process Using Finite Element Method
Dong Jun Lee, Eun Yoo Yoon
Journal of Korean Powder Metallurgy Institute.2015; 22(1): 6. CrossRef
Microstructure Evolution and Mechanical Properties of Al-1080 Processed by a Combination of Equal Channel Angular Pressing and High Pressure Torsion
Mohamed Ibrahim Abd El Aal, Eun Yoo Yoon, Hyoung Seop Kim
Metallurgical and Materials Transactions A.2013; 44(6): 2581. CrossRef
Trend in Research of Powder Consolidation Using Severe Plastic Deformation
Eun Yoo Yoon, Dong Jun Lee, Dong-Hyun Ahn, Hyuk Jae Jeong, Hyoung Seop Kim
Journal of Korean Powder Metallurgy Institute.2013; 20(2): 148. CrossRef
Ultrafine Grained Cu-diamond Composites using High Pressure Torsion
Eun-Yoo Yoon, Dong-Jun Lee, Taek-Soo Kim, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(3): 204. CrossRef
Densification of Copper Powders using High-pressure Torsion Process
Dong-Jun Lee, Eun-Yoo Yoon, Soo-Young Kang, Jung-Hwan Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(5): 333. CrossRef

Quantitative Analysis of Roughness of Powder Surface Using Three-Dimensional Laser Profiler and its Effect on Green Strength of Powder Compacts: Dong-Jun Lee, Eun-Yoo Yoon, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2011;18(5):406-410.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.406

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Green strength is an important property of powders since high green strength guarantees easy and safe handling before sintering. The green strength of a powder compact is related to mainly mechanical and surface characters, governed by interlocking of the particles. In this study, the effect of powder surface roughness on the green strength of iron powders was investigated using a transverse rupture test. Three-dimensional laser profiler was employed for quantitative analyses of the surface roughness. Two different surface conditions, i.e. surface roughness, of powders were compared. The powders having rough surfaces show higher green strength than the round surface powders since higher roughness leads increasing interlocked area between the contacting powders.

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A Study on the Carbon Composite Briquette Iron Manufacturing Using Fe-containing Process Wastes
Jong Yeong Yu, Dae Young Yang, Hee Dong Shin, Il Sohn
Journal of the Korean Institute of Resources Recycling.2015; 24(3): 34. CrossRef
Obtaining Mechanical Properties of Fe Powder Using a Combined Nanoindentation and the Finite Element Method
Hyeok Jae Jeong, Dong Jun Lee, Eun Yoo Yoon, Eon Sik Lee, Nack Joon Kim, Hyeong Seop Kim
Journal of Korean Powder Metallurgy Institute.2013; 20(4): 280. CrossRef

Effect of Particle Size on Compactibility of Water-atomized Pure Iron Powder: Dong-Jun Lee, Eun-Yoo Yoon, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2011;18(3):221-225.; DOI: https://doi.org/10.4150/KPMI.2011.18.3.221

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In the current study, the effects of particle size on compaction behavior of water-atomized pure iron powders are investigated. The iron powders are assorted into three groups depending on the particle size; 20-45 µM, 75-106 µM, and 150-180 µM for the compaction experiments. The powder compaction procedures are processed with pressure of 200, 400, 600, and 800 MPa in a cylindrical die. After the compaction stage, the group having 150-180 µM of particle size distribution shows the best densification behavior and reaches the highest green density. The reason for these results can be explained by the largest average grain size in the largest particle group, due to the low plastic deformation resistance in large grain sized materials.

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Preparation of high-purity reduced iron powder by Höganäs process from ultra-pure magnetite concentrate
Jin-tian Wu, Bin Xu, Zhong-lin Dong, Yu-juan Zhou, Liang-ping Xu, Guang-hui Li, Tao Jiang
Journal of Central South University.2023; 30(9): 3006. CrossRef
Hydrogen Reduction Behavior of Oxide Scale in Water-atomized Iron Powder
Hea-Min Shin, Kyeong-Ho Baik
Journal of Korean Powder Metallurgy Institute.2014; 21(6): 422. CrossRef
Quantitative Analysis of Roughness of Powder Surface Using Three-Dimensional Laser Profiler and its Effect on Green Strength of Powder Compacts
Dong-Jun Lee, Eun-Yoo Yoon, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 406. CrossRef

Consolidation and Mechanical Behavior of Gas Atomized MgZn_4.3Y_0.7 Alloy Powders using High Pressure Torsion: Eun-Yoo Yoon, Hong-Jun Chae, Taek-Soo Kim, Chong-Soo Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2010;17(3):190-196.; DOI: https://doi.org/10.4150/KPMI.2010.17.3.190

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In this paper, rapid solidified Mg-4.3Zn-0.7Y (at.%) alloy powders were prepared using an inert gas atomizer, followed by a severe plastic deformation technique of high pressure torsion (HPT) for consolidation of the powders. The gas atomized powders were almost spherical in shape, and grain size was as fine as less than 5;µm due to rapid solidification. Plastic deformation responses during HPT were simulated using the finite element method, which shows in good agreement with the analytical solutions of a strain expression in torsion. Varying the HPT processing temperature from ambient to 473 K, the behavior of powder consolidation, matrix microstructural evolution and mechanical properties of the compacts was investigated. The gas atomized powders were deformed plastically as well as fully densified, resulting in effective grain size refinements and enhanced microhardness values.

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Trend in Research of Powder Consolidation Using Severe Plastic Deformation
Eun Yoo Yoon, Dong Jun Lee, Dong-Hyun Ahn, Hyuk Jae Jeong, Hyoung Seop Kim
Journal of Korean Powder Metallurgy Institute.2013; 20(2): 148. CrossRef
Densification of Copper Powders using High-pressure Torsion Process
Dong-Jun Lee, Eun-Yoo Yoon, Soo-Young Kang, Jung-Hwan Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(5): 333. CrossRef
Ultrafine Grained Cu-diamond Composites using High Pressure Torsion
Eun-Yoo Yoon, Dong-Jun Lee, Taek-Soo Kim, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(3): 204. CrossRef
Densification and Nanocrystallization of Water-Atomized Pure Iron Powder Using High Pressure Torsion
Eun-Yoo Yoon, Dong-Jun Lee, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 411. CrossRef

Finite Element Analysis of Densification of Mg Powders during Equal Channel Angular Pressing: Effect of Sheath: Seung-Chae Yoon, Taek-Soo Kim, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2009;16(2):85-90.; DOI: https://doi.org/10.4150/KPMI.2009.16.2.085

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Abstract PDF: Magnesium and its alloys are attractive as light weight structural/functional materials for high performance application in automobile and electronics industries due to their superior physical properties. In order to obtain high quality products manufactured by the magnesium powders, it is important to control and understand the densification behavior of the powders. The effect of the sheath surrounding the magnesium powders on the plastic deformation and densification behavior during equal channel angular pressing was investigated in the study by experimental and the finite element methods. A modified version of Lee-Kim's plastic yield criterion, notably known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders. In addition, a new approach that extracts the mechanical characteristics of both the powder and the matrix was developed. The model was implemented into the finite element method, with which powder compaction under equal channel angular pressing was simulated.

Analysis of Densification Behavior of Magnesium Powders in Extrusion using the Critical Relative Density Model: Seung-Chae Yoon, Hong-Jun Chae, Taek-Soo Kim, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2009;16(1):50-55.; DOI: https://doi.org/10.4150/KPMI.2009.16.1.050

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Abstract PDF: Numerical simulations of the powder extrusion need an appropriate pressure-dependent constitutive model for densification modeling of the magnesium powders. The present research investigated the effect of representative powder yield function of the critical relative density model. We could obtain reasonable physical properties of pure magnesium powders using cold isostatic pressing. The proposed densification model was implemented into the finite element code. The finite element analysis was applied to simulation of powder extrusion of pure magnesium powder in order to investigate the densification and processing load at room temperature.

Analysis of Densification Behavior during Powder Equal Channel Angular Pressing using Critical Relative Density Model: Cheon-Hee Bok, Ji-Hoon Yoo, Seung-Chae Yoon, Taek-Soo Kim, Byong-Sun Chun, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2008;15(5):365-370.; DOI: https://doi.org/10.4150/KPMI.2008.15.5.365

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In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.

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Analysis of Densification Behavior of Magnesium Powders in Extrusion using the Critical Relative Density Model
Seung-Chae Yoon, Hong-Jun Chae, Taek-Soo Kim, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2009; 16(1): 50. CrossRef

Finite Element Analysis on the Impactive Deformation of a Cu Particle in Cold Spraying Processing : Effect of Velocity: Kyu-Jin Cho, Seung-Chae Yoon, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2008;15(3):227-233.; DOI: https://doi.org/10.4150/KPMI.2008.15.3.227

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Abstract PDF: Dynamic plastic deformation behavior of copper particles occurred during the cold spray processing was numerically analyzed using the finite element method. The study was to investigate the impact as well as the heat transfer phenomena, happened due to collision of the copper particle of 20µm in diameter with various initial velocities of 300sim600m/s into the copper matrix. Effective strain, temperature and their distribution were investigated for adiabatic strain and the accompanying adiabatic shear localization at the particle/substrate interface.

Analysis of Aluminum Powder Densification by Continuous Front Extrusion-Equal Channel Angular Pressing: Seung-Chae Yoon, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2008;15(3):204-209.; DOI: https://doi.org/10.4150/KPMI.2008.15.3.204

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Abstract PDF: Aluminum alloys are not only lightweight materials, but also have excellent thermal conductivity, electrical conductivity and workability, hence, they are widely used in industry. It is important to control and enhance the densification behavior of metal powders of aluminum. Investigation on the extrusion processing combined with equal channel angular pressing for densification of aluminum powders was performed in order to develop a continuous production process. The continuous processing achieved high effective strain and full relative density at 200°C. Optimum processing conditions were suggested for good mechanical properties. The results of this simulation helped to understand the distribution of relative density and effective strain.

Consolidation and Mechanical Property of Rapidly Solidified Al-20 wt% Si Alloy Powders by Continuous Equal Channel Multi-Angular Pressing: Seung-Chae Yoon, Cheon-Hee Bok, Min-Hong Seo, Soon-Jik Hong, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2008;15(1):31-36.; DOI: https://doi.org/10.4150/KPMI.2008.15.1.031

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In this study, the bottom-up powder metallurgy and the top-down severe plastic deformation (SPD) techniques for manufacturing bulk nanomaterials were combined in order to achieve both full density and grain refinement without grain growth of rapidly solidified Al-20 wt% Si alloy powders during consolidation processing. Continuous equal channel multi-angular processing (C-ECMAP) was proposed to improve low productivity of conventional ECAP, one of the most promising method in SPD. As a powder consolidation method, C-ECMAP was employed. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructures of the ECMAP processed materials. It was found that effective properties of high strength and full density maintaining nanoscale microstructure are achieved. The proposed SPD processing of powder materials can be a good method to achieve fully density and nanostructured materials.

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X-ray diffraction study on the microstructure of a Mg–Zn–Y alloy consolidated by high-pressure torsion
Péter Jenei, Jenő Gubicza, Eun Yoo Yoon, Hyoung Seop Kim
Journal of Alloys and Compounds.2012; 539: 32. CrossRef
Microstructures and mechanical properties of Mg–Zn–Y alloy consolidated from gas-atomized powders using high-pressure torsion
Eun Yoo Yoon, Dong Jun Lee, Taek-Soo Kim, Hong Jun Chae, P. Jenei, Jeno Gubicza, Tamas Ungár, Milos Janecek, Jitka Vratna, Sunghak Lee, Hyoung Seop Kim
Journal of Materials Science.2012; 47(20): 7117. CrossRef
Synthesis and microstructure control of Mg alloy powder composites by multi-extrusion
Taek-Soo Kim, Hong Jun Chae, Sun-Mi Kim, Hanshin Choi, Hye Sung Kim
Journal of Alloys and Compounds.2011; 509: S247. CrossRef

Densification Behaviour of Magnesium Powders during Cold Isostatic Pressing using the Finite Element Method: Seung-Chae Yoon, Eun-Jeong Kwak, Won-Hyoung Choi, Hyoung-Kun Kim, Taek-Soo Kim, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2007;14(6):362-366.; DOI: https://doi.org/10.4150/KPMI.2007.14.6.362

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Magnesium and magnesium alloys are promising materials for light weight and high strength applications. In order to obtain homogeneous and high quality products in powder compaction and powder forging processes, it is very important to control density and density distributions in powder compacts. In this study, a model for densification of metallic powder is proposed for pure magnesium. The mode] considers the effect of powder characteristics using a pressure-dependent critical density yield criterion. Also with the new model, it was possible to obtain reasonable physical properties of pure magnesium powder using cold iso-state pressing. The proposed densification model was implemented into the finite element method code. The finite element analysis was applied to simulating die compaction of pure magnesium powders in order to investigate the density and effective strain distributions at room temperature.

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Analysis of Densification Behavior of Magnesium Powders in Extrusion using the Critical Relative Density Model
Seung-Chae Yoon, Hong-Jun Chae, Taek-Soo Kim, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2009; 16(1): 50. CrossRef
Finite element analysis of the bending behavior of a workpiece in equal channel angular pressing
Seung Chae Yoon, Anumalasetty Venkata Nagasekhar, Hyoung Seop Kim
Metals and Materials International.2009; 15(2): 215. CrossRef

Finite Element Analysis on the Effect of Die Corner Angle in Equal Channel Angular Pressing Process of Powders: Seung-Chae Yoon, Cheon-Hee Bok, Pham Quang, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2007;14(1):26-31.; DOI: https://doi.org/10.4150/KPMI.2007.14.1.026

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Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both real density and grain refinement of metallic powders. ECAP (Equal Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method. Effects of processing parameters on densification and density distributions were investigated.

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Finite element analysis of the bending behavior of a workpiece in equal channel angular pressing
Seung Chae Yoon, Anumalasetty Venkata Nagasekhar, Hyoung Seop Kim
Metals and Materials International.2009; 15(2): 215. CrossRef

Finite Element Analysis of Densification Behavior during Equal Channel Angular Pressing Process of Powders: Seung-Chae Yoon, Pham Quang, Byong-Sun Chun, Hong-Ro Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2006;13(6):415-420.; DOI: https://doi.org/10.4150/KPMI.2006.13.6.415

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Abstract PDF: Nanostructured metallic materials are synthesized by bottom-up processing which starts with powders for assembling bulk materials or top-down processing starting with a bulk solid. A representative bottom-up and top-down paths for bulk nanostructured/ultrafine grained metallic materials are powder consolidation and severe plastic deformation (SPD) methods, respectively. In this study, the bottom-up powder and top-down SPD approaches were combined in order to achieve both full density and grain refinement without grain growth, which were considered as a bottle neck of the bottom-up method using conventional powder metallurgy of compaction and sintering. For the powder consolidation, equal channel angular pressing (ECAP), one of the most promising method in SPD, was used. The ECAP processing associated with stress developments was investigated. ECAP for powder consolidation were numerically analyzed using the finite element method (FEM) in conjunction with pressure and shear stress.

Equal Channel Angular Pressing of Rapidly Solidified Al-20 wt ％ Si Alloy Powder Extrudates: Seung-Chae Yoon, Soon-Jik Hong, Min-Hong Seo, Pham Quang, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2004;11(2):97-104.; DOI: https://doi.org/10.4150/KPMI.2004.11.2.097

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In this paper processing and mechanical properties of Al-20 wt％ Si alloy was studied. A bulk form of Al-20Si alloy was prepared by gas atomizing powders having the powder size of 106-145 µm and powder extrusion. The powder extrudate was subsequently equal channel angular pressed up to 8 passes in order to refine grain and Si particle. The microstructure of the gas atomized powders, powder extrudates and equal channel angular pressed samples were investigated using a scanning electron microscope and X-ray diffraction. The mechanical properties of the bulk sample were measured by compressive tests and a micro Victors hardness test. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength and hardness of the Al-2OSi alloy without deteriorating ductility in the range of experimental strain of 30％.

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Consolidation of Rapidly Solidified Al-20 wt％ Si Alloy Powders Using Equal Channel Angular Pressing

Journal of Korean Powder Metallurgy Institute.2004; 11(3): 233. CrossRef

Processing of Nano-Sized Metal Alloy Dispersed Al_2O_3 Nanocomposites: Sung-Tag Oh, Namkung Seok, Jai-Sung Lee, Hyoung-Seop Kim, Sekino Tohru; J Korean Powder Metall Inst. 2001;8(3):157-162.

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Abstract PDF: An optimum route to fabricate the ferrous alloy dispersed Al_2O_3 nanocomposites such as Al_2O_3/Fe-Ni and Al_2O_3/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of Al_2O_3 and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded Al_2O_3, forming nanocomposite powder. The sintered Al_2O_3/Fe-Ni composite showed the formation of FeAl_2O_4 phase, while the reaction phases were not observed in Al_2O_3/Fe-Co composite. Hot-pressed Al_2O_3/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

Modelling Strength and Ductility of Nanocrystalline Metallic Materials: Hyoung-Seop Kim; J Korean Powder Metall Inst. 2001;8(3):168-173.

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Abstract PDF: The effect of grain refinement of the strength and ductility of metallic materials is investigated. A model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanisms: dislocation glide and mass transfer by diffusion. The model was exemplified by simulating uniaxial tensile deformation of Cu down to the nanometer grain size. The results confirm the observed strain hardening behaviour and a trend for reduction of ductility with decreasing grain size at room temperature.

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