• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.827-832
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• 2001

A lot of investigations have been made in recent years on the equal channel angular pressing(ECAP) which produces ultra-fine grains(UFG). Among many process parameters such as channel angles, frictions, die deformations and materials employed, the effects of material properties on the deformation behavior have been investigated. The finite element method(FEM) has been used to investigate this issue.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.189-192
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• 2003

The Electro-thermal Explosion Coating (EEC) technique is a new surface treatment technology emerged in recent years. It uses an electrical discharge (with very high voltage from 5 to 30 kV or more) to produce a pulse current with large density inside the material to be deposited, the metal wire undergo the heating, melting, vaporization, ionization and explosion processes in a very short time (from tens ns to several hundreds ${\mu}s$), and the melted droplets shoot at the substrate with a very high velocity (3000 - 4500 m/s), so that the coating materials can be deposited on the surface of the substrate. Coatings with nano-size grains or ultra- fine grains can be formed because of rapid solidification (cooling rate up to $10^6-10^9\;k/s$). Surface of the substrate (about $1-5{\mu}m$ in depth) can be melted rapidly and coatings with very high bonding strength can be obtained.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.228-230
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• 2004

Samples of the aluminum alloy 3103 sheets were repeatedly deformed by ECAR up to twelve passes. Shear textures developed after the first passage of ECAR. However, the intensity of shear texture components decreased with increasing number of ECAR passages. Observations by TEM and EBSD revealed that the degree of misorientations within the deformed grains increased with increasing number of ECAR passes. Changes in textures and microstructures were hardly observed during recrystallization anneal. Upon subsequent annealing, the samples deformed by a large number of ECAR passes displayed a continuous grain growth. A higher deformation by ECAR resulted in a slower softening, which reflects the stability of ultra-fine grains against the grain growth.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.100-107
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• 1998

Diamond wheels with fine grains and multi-porous structures are newely trial developed for smoothing and mirror finishing materials. Grinding wheel must have performed both to remove tool marks efficienitly and to contact elastically with curved surfaces, that are employed for ultra precision and high performance grinding of difficult-to materials such as tungsten carbide alloy using tool and die materials, Diamond grains are bonded by a melamine resin to prevent the decrease of machining efficiency due to grain sinking within the bond materials. Also, highly foamed structures are developed to increase the flexibility of the grinding wheel, and to induce self-sharpening by increasing contact pressure between the grinding wheel and workpiece surfaces. In this paper, melamine-bonded diamond wheels try to manufacture, then the forming method of grinding wheel are suggested, and the grinding characteristics of melamine-bonded diamond grinding wheel are also illustrated.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.341-344
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• 1999

We reported compositional separation(CS) into Co-enriched and Cri-enriched components inside the grains of Co-Cr based thin films prepared by rf sputtering. CS strongly depends on the sputtering conditions of substrate temperature and target composition. Tuning the microstructure of the Co-Cr films is important in order to employ the CS for high-density magnetic recording. We investigated the origin of CS from thermodynamic viewpoint. We employ a spinodal decomposition-like model to describe the origin of the CS in Co-Cr films. We consider the total free energy of the Co-Cr films as the sum of several free energies of; 1) thermodynamic mixing entropy of a binary solid solution, 2) magnetic ordering interaction(MOI) energy below the Curie temperature, and 3) excess interaction energy(XS) caused by the sputtering process as a function of temperature and composition. Those energies distorted the total free energy like the spinodal decomposition and caused the compositionally separated fine microstructure inside the grains. If the second derivative of the total free energy with respect to Cr composition becomes negative at a given substrate temperature, we may observe a metastable compositional separation inside the Co-Cr alloy films. We expect to exploit the microstructure of CS for ultra-high density magnetic recording.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.381-383
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• 2005

This paper is concerned with the prediction of micro structural changes of Al alloys during cryogenic rolling using an Eulerian finite element analysis. The main objective of cryogenic rolling is to obtain ultra-fine grains by severe plastic deformation at the extremely low temperature. Thereby, this simulation focuses on micro structural developments - the texture development and the changes in the size and shape of grains. The former one may be modeled using a crystal plasticity theory while the other can be predicted by a streamline technique. Applications to three pass rolling are given.

• Journal of the Korean institute of surface engineering
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• v.34 no.6
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• pp.531-536
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• 2001

Co-22 %Cr alloy films are promising for high-density perpendicular magnetic recording media with their perpendicular anisotropy and large coercivity of 3000 Oe. We observed that a self organized nano structure (SONS) of fine ferromagnetic Co-enriched phase and paramagnetic Cr-enriched phase appears inside the grain of Co-Cr magnetic alloy thin films at the elevated substrate temperature after do-sputtering. The periodic fine Co-enriched phase and Cr-enriched phase is the plate shape of 80 (equation omitted)-wide and 1000 (equation omitted)-long. Cr-enriched phases are located at the center of grains. We prepared 5000 (equation omitted) -thick Co-22 %Cr films on polyimide substrate with varying substrate temperature of $ 30^{\circ}C$, $ 150^{\circ}C$ ,200 $^{\circ}C$, $300^{\circ}C$, and $400^{\circ}C$, respectively. A transmission electron microscope equipped with energy dispersive X-ray analyzer is employed to observe the microstructure of each samples after Co-enri-ched phase are etched selectively. The self organized nano structure of Co-enriched and Cr-enriched lamellar is observed above the substrate temperture of $150^{\circ}C$. No compositional change is observed with substrate temperature. The compositional phase separation in self organized structure becomes clear as the substrate temperature increases. Our results implies that the self organized nano structure in Co-22 %Cr film is ideal for ultra high density recording media by recording selectively on Co-enri-ohed phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.7 s.250
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• pp.765-772
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• 2006

Much research efforts have been made on the equal channel angular pressing (ECAP) which produces ultra-fine grains. Along with the experiments, the finite element method has been widely employed to investigate the deformation behavior of specimen during ECAP and the effect of process parameters of ECAP. In this paper, sectional shape change has been investigated during ECAP with the pure-Zr, Zr-702 by using three-dimensional finite element analysis. The results have been compared with experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.661-665
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• 2002

A lot of investigations have been made in recent years on the equal channel angular pressing (ECAP) which produces ultra-fine grains. The finite element method has been used to investigate this issue. In this paper, pure-Zirconium is considered far ECAP process by three dimensional finite element analysis. The effects of fiction on the deformation behavior have been investigated and compared with two dimensional finite element analysis.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.8
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• pp.187-193
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• 2002

Much research efforts have been made on the equal channel angular pressing (ECAP) which produces ultra-fine grains. Among many process parameters such as channel angles, frictions, die deformations and materials employed, the effects of material properties on the deformation behavior have been investigated. The finite element method has been used to investigate this issue.