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윤승채,팜쾅,천병선,이홍로,김형섭,Yoon, Seung-Chae,Quang, Pham,Chun, Byong-Sun,Lee, Hong-Ro,Kim, Hyoung-Seop 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.6
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.
유한요소법을 이용한 등통로각압출 공정의 마그네슘 분말 고형화 거동 해석: 피복재 효과
윤승채,김택수,김형섭,Yoon, Seung-Chae,Kim, Taek-Soo,Kim, Hyoung-Seop 한국분말야금학회 2009 한국분말재료학회지 (KPMI) Vol.16 No.2
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.
분말 ECAP 공정에 미치는 금형 모서리각 효과에 대한 유한요소해석
윤승채,복천희,팜쾅,김형섭,Yoon, Seung-Chae,Bok, Cheon-Hee,Quang, Pham,Kim, Hyoung-Seop 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.1
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.
Finite Element Analysis of the Bending Behavior of a Workpiece in Equal Channel Angular Pressing
윤승채,Anumalasetty Venkata Nagasekhar,김형섭 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.2
For the first time, a detailed and systematic finite element study was carried to identify the parameters which cause the bending of the workpiece in equal channel angular pressing. These simulations were carried out by using commercial finite element code Abaqus with different materials behavior, processing parameters, and die geometries. The results showed that the optimal ways to reduce the bending of strain rate sensitive materials in ECAP without varying the strain homogeneity are the usage of lower processing speed and the increase in length of the die exit-channel. For the first time, a detailed and systematic finite element study was carried to identify the parameters which cause the bending of the workpiece in equal channel angular pressing. These simulations were carried out by using commercial finite element code Abaqus with different materials behavior, processing parameters, and die geometries. The results showed that the optimal ways to reduce the bending of strain rate sensitive materials in ECAP without varying the strain homogeneity are the usage of lower processing speed and the increase in length of the die exit-channel.
등통로각압축이 결합된 압출 공정에 의한 알루미늄 분말의 치밀화 거동
윤승채,김형섭,Yoon, Seung-Chae,Kim, Hyoung-Seop 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.3
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 $200^{\circ}C$. 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.
연속 다단 ECAP 공정을 통한 급속응고 Al-20 wt% Si 합금 분말의 고형화 및 특성 평가
윤승채,복천희,서민홍,홍순직,김형섭,Yoon, Seung-Chae,Bok, Cheon-Hee,Seo, Min-Hong,Hong, Soon-Jik,Kim, Hyoung-Seop 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.1
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.
급속응고 Al-20 wt% Si 합금 분말의 ECAP를 통한 고형화
윤승채,홍순직,서민홍,정영기,김형섭 한국분말야금학회 2004 한국분말재료학회지 (KPMI) Vol.11 No.3
In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of Al-20 wt% Si powders without grain growth, which was considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (Equal channel angular pressing), one of the most promising method in SPD, was used for the powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 passes was conducted for 10$0^{\circ}C$ and 20$0^{\circ}C$ It was found by microhardness, compression tests and micro-structure characterization that high mechanical strength could be achieved effectively as a result of the well bonded powder contact surface during ECAP process. The SPD processing of powders is a viable method to achieve both fully density and nanostructured materials.
윤승채,서민홍,홍순익,김형섭,Yoon Seung-Chae,Seo Min-Hong,Hong Sun-Ig,Kim Hyoung-Seop 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.2
In recent years, equal channel angular pressing (ECAP) has been the subject of intensive study due to its capability of producing fully dense samples having a ultrafine grain size. In this paper, the ECAP process was applied to metallic powders in order to achieve both powder consolidation and grain refinement. In the ECAP process for solid and powder metals, knowledge of the internal stress, strain and strain rate distribution is fundamental to the determination of the optimum process conditions for a given material. The properties of the ECAP processed solid and powder materials are strongly dependent on the shear plastic deformation behavior during ECAP, which is controlled mainly by die geometry, material properties, and process conditions. In this study, we investigated the consolidation, plastic deformation and microstructure evolution behaviour of the powder compact during ECAP.
유한요소법을 이용한 마그네슘 분말의 냉간정수압 공정시 치밀화 거동 해석
윤승채,곽은정,최원형,김형근,김택수,김형섭,Yoon, Seung-Chae,Kwak, Eun-Jeong,Choi, Won-Hyoung,Kim, Hyoung-Kun,Kim, Taek-Soo,Kim, Hyoung-Seop 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.6
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.