• 한국재료학회:학술대회논문집
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• 한국재료학회 2007년도 추계학술발표대회 및
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• pp.124.1-124.1
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• 2007

• 한국재료학회:학술대회논문집
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• 한국재료학회 2007년도 추계학술발표대회 및
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• pp.153.1-153.1
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• 2007

• 소성∙가공
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• 제16권5호통권95호
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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.

• 한국재료학회지
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• 제17권6호
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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.

• 소성∙가공
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• 제23권3호
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• pp.151-158
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• 2014

Half channel angular extrusion(HCAE) is the integration of equal channel angular extrusion(ECAE), which is a well-known severe plastic deformation(SPD) method, with conventional forward extrusion in order to increase the strain per pass and effectiveness of the grain refinement. In the current study, the effects of processing routes during HCAE(Routes A, B, and C) on the strain distribution of the specimens have been investigated for an AZ61 Mg alloy by using three-dimensional finite element analysis. Comparisons with the results from a multi-pass of ECAE are made.

• 한국정밀공학회지
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• 제24권11호
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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.

• 한국재료학회지
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• 제23권9호
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• pp.531-536
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• 2013

This paper investigates the effect of prolonged high temperature exposure on concentric laminated $Al_2O_3-ZrO_2$ composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was $2-3{\mu}m$ thick. An alternate lamina was composed of 75%$Al_2O_3$-(25%m-$ZrO_2$) and t-$ZrO_2$ ceramics. The composite was sintered at $1500^{\circ}C$ and subjected to $1450^{\circ}C$ temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-$ZrO_2$ layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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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.

• 한국세라믹학회지
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• 제41권7호
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• pp.560-566
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• 2004

다중 압출 공정을 이용하여 알루미나 연속다공질체를 제조하기 위해 기공형성제로서 탄소 분말을 사용하였으며 세라믹 분말의 성형을 용이하게 하기 위하여 에틸렌 비닐 아세테이트 고분자를 바인더로 사용하였다. 압출 횟수, 압출비 및 재료의 부피비를 제어함으로써 균일한 기공의 크기와 기공률을 용이하게 제어하였다. 제조된 소결체는 연속기공을 가질 뿐아니라 우수한 비표면적을 가졌으며, 기존의 공정에 의해 제조된 알루미나 다공질 재료보다 우수한 곡강도 값을 보였다. 생체 친화성 평가를 위해 인간의 뼈모세포인 MG-63 세포를 이용해 In-vitro 실험을 실시한 결과 기공의 아랫면, 윗면, 내부 및 외부에 세포가 잘 생착하여 네트워크 형태로 치밀하게 잘 성장하였다. 또한 이 재료를 이용하여 3차원 다공질체로 제조한 후 생체적합성을 평가하기 위해 쥐의 피하조직에 이식한 결과 어떠한 염증 소견이나 생체 거부반응이 없었으며 섬유조직으로 잘 둘러 쌓인 다공질체 주위로 새로운 모세혈관이 활발히 생성되었다.

• 한국세라믹학회지
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• 제43권8호
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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.