• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.153.1-153.1
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• 2007

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.124.1-124.1
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• 2007

• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.386-390
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• 2007

In order to, simultaneously, synthesize and control the size of microstructure of amorphous/crystalline composites, a repeated extrusion process was performed using the gas atomized $Cu_{54}Ni_6Zr_{22}Ti_{18}$ metallic glass powders and the crystalline brasses. The size of microstructure in the resultant composites was varied depending on the pass of extrusion as well as on the area reduction ratio. The microstructure could be estimated using an equation of $r_n=r_{n-1}/R^{1/2}$, where R is reduction ratio and $r_n$ is the resultant radius of the extruded bar after n pass. Theory of microstructural refinement as well as the relationship between the resultant microstructures and mechanical properties was discussed.

• Korean Journal of Materials Research
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• v.17 no.6
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• pp.313-317
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• 2007

In-situ micro-channeled multi tubular solid oxide fuel cell(SOFC) was fabricated using multi-pass extrusion process with out side diameter of 2.7 mm and active length of 5 mm that contained 61 individual cells. Cell materials used in this work were NiO-YSZ (50 : 50 vol.%), 8 mol% yttria-stabilized zirconia(8YSZ), $La_{0.8}Sr_{0.2}MnO_3(LSM)$ as anode, electrolyte, and cathode, respectively. The arrangement of each electrode and electrolyte layer in green bodies showed uniformity and integrity after extrusion and sintering. The XRD analysis confirmed that no reaction phases appeared and the microstructure of the electrolyte was fairly dense (relative density > 96%) after sintering.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.44-51
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• 2007

Condenser tubes are mainly produced by precision extrusion with a porthole die and are used in the flow pass of refrigerant cooling systems in automobiles. The recent technical trend of condenser tube requires the tube to be of more multi cellizing, high strength and small size, and to increase the heat transfer area and heat efficiency. Hence, this paper is shown that the results of FE-simulation are in good agreement with the experimental ones. Finally, the extrusion die shape is proposed through analysis of FE-simulation and performance of trial extrusion. Chamber shape dimension and initial temperatures of die is adjusted analysis results. And the possibility of extrusion is estimated that forming load, welding pressure and stress analysis of die in this paper. The validity of simulated results was verified into extrusion experiments on the condenser tubes.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.41.2-41.2
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• 2010

In this work, HAp-(t-ZrO2) ceramic composites of biomimic artificial bone were fabricated by multi-extrusion process in order to replace nature bone. HAp-(t-ZrO2) and graphite powders were mixed separately with ethylene vinyl acetate (EVA) and stearic acid using shear mixer. Extruded HAp-(t-ZrO2) filaments and carbon filaments were arranged in the die to fabricate the first pass filament. The first pass filaments were arranged in the same die with a central carbon core for making the space for spongy bone. Burning out and sintering processes were performed to remove the binder and lubricant. The microstructure channel diameter was researched around $300{\mu}m$. Microstructure analysis was carried out by OM, SEM, and $\mu$-CT. Compressive strength was investigated for the artificial bone. Some preliminary bio-compatibility test was evaluated.

• Journal of the Korean Ceramic Society
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• v.41 no.7
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• pp.560-566
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• 2004

To fabricate the continuously porous alumina bodies by multi-extrusion process, carbon powder and ethylene vinyl acetate were used as a pore forming agent and a binder, respectively. As the change of extrusion pass number, reduction ratio as well as the volume fraction of core and tube, the porous alumina bodies having various kind of pore size and porosity could be obtained. The porous bodies showed continuous pore shape, high specific surface as well as high bending strength, which were compared with those of commercial alumina bodies. In-vitro study was carried out using MG-63 osteoblast cells to investigate of their biocompatibility. As a result, the cells grew well on top and bottom as well as inside surface of pore. From the result of in-vivo study of 3-dimensional porous alumina bodies using rats, it was confirmed that any inflammatory response was not found in the subcutaneous tissue around porous body. Also the porous bodies removed from the rats were fully covered with well-developed fibrous tissues and showed the formation of new capillary blood vessels.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.504-508
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• 2006

Functionally gradient porous $Al_2O_3-(t-ZrO_2)/HAp$ composites consist of 3 layers were fabricated using the multi-pass extrusion process at the various temperatures. The continuous pores were homogeneously formed in the $2^{nd}$ passed samples and their size was about $180{\mu}m$ in diameter. In the porous composites sintered at $1200-1400^{\circ}C$, the relative density and bending strength increased with the sintering temperature. The maximum values of relative density and bending strength in the $2^{nd}$ passed $Al_2O_3-(t-ZrO_2)/HAp$ composites were 62.2% and 107.8 MPa, respectively. In order to investigate the growth behavior of osteogenic cells on the functionally gradient porous $Al_2O_3-(t-ZrO_2)/HAp$ composites, an in vitro test was performed, using human osteoblast-like MG-63 cells. The cells were well attached and grown on the rough surface of the inside of the functionally gradient porous body.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.325-326
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• 2006

Using $6wt%Y_2O_3-2wt%Al_2O_3$ as sintering additives and Si as a raw powder, the continuously porous in-situ $Si_2N_2O-Si_3N_4$ bodies were fabricated by multi-pass extrusion process and their microstructures were investigated depending on the addition of carbon (0-9wt%) in the mixture powder. The introduction of $Si_2N_2O$ fibers observed in the unidirectional continuous pores as well as in the pore-frame regions of the nitrided bodies can be an effective method in increasing the filtration efficiency. In the case of no carbon addition, the network type $Si_2N_2O$ fibers with high aspect ratio appeared in the continuous pores with diameters of 150-200 nm. However, in the case of 9wt% C addition, the fibers were found without any network type and had diameters of 200-250 nm.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.213-218
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• 2003

Fibrous monolithic control of$ Al_2$$O_3$ -$ZrO_2$composite was investigated by multi-pass extrusion process. To obtain sound $Al_2$$O_3$-X $O_2$sintered bodies, burning out and sintering process were carefully carried out. The sintered bodies showed continuous, fibrous monolithic microstructure without any swelling. Many microcracks were observed at the $Al_2$$O_3$-$ZrO_2$interfaces due to the mismatching of thermal expansion coefficient between $Al_2$$O_3$ and $ZrO_2$phase. Most of m- $ZrO_2$grains included twin defects such as (001), (010) and (011) type to accommodate the phase transformation induced stress.