• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.363-368
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2003년도 춘계학술강연 및 발표대회
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• pp.60-60
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• 2003

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2016년도 임시총회 및 하계학술연구발표회
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• pp.5-5
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• 2016

• 한국분말재료학회지
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• 제27권3호
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• pp.219-225
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• 2020

The directed energy deposition (DED) process of metal 3D printing technologies has been treated as an effective method for welding, repairing, and even 3-dimensional building of machinery parts. In this study, stainless steel 316L (STS316L) and Inconel 625 (IN625) alloy powders are additively manufactured using the DED process, and the microstructure of the fabricated STS316L/IN625 sample is investigated. In particular, there are no secondary phases in the interface between STS316L and the IN625 alloy. The EDS and Vickers hardness results clearly show compositionally and mechanically transient layers a few tens of micrometers in thickness. Interestingly, several cracks are only observed in the STS 316L rather than in the IN625 alloy near the interface. In addition, small-sized voids 200-400 nm in diameter that look like trapped pores are present in both materials. The cracks present near the interface are formed by tensile stress in STS316L caused by the difference in the CTE (coefficient of thermal expansion) between the two materials during the DED process. These results can provide fundamental information for the fabrication of machinery parts that require joining of two materials, such as valves.

• 대한기계학회논문집A
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• 제22권4호
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• pp.924-938
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• 1998

Densification behavior of ceramic powder under cold compaction was investigated. Experimental data were obtained for zirconia powder and alumina powder under triaxial compression with various loading conditions. A special form of the Cap model was proposed from experimental data under triaxial compression for a yield function of ceramic powder. The proposed yield function was inplemented into a finite element program (ABAQUS) to study densification behaviors of zirconia and alumina powders under die compaction. The effect of friction between the powder and die wall was also investigated. Density distributions of powder compacts were measured and compared with finite element results.

• 한국세라믹학회지
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• 제55권2호
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• pp.153-159
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• 2018

Porous ceramic plates were prepared from Onggi clay and bamboo charcoal powder at 1100 and $1200^{\circ}C$ and their porous properties and water absorption, and the cooling effect of porous plates, were investigated to produce eco-friendly porous ceramics for a self-cooling system that relies on the evaporation of absorbed water. Porous properties were dependent on the particle size of charcoal powder pore forming additive and the firing temperature; properties were also found to be dependent on the total pore volume, average pore size and porosity, which had values of $0.103-0.243cm^3/g$, 0.81 - 2.56 mm and 20.9 - 38.2%, respectively, at $1100^{\circ}C$ and $0.04-0.18cm^3/g$, 0.33 - 2.03 mm and 10.8 - 30.9%, respectively, at $1200^{\circ}C$. Cooling temperature difference of flowing air parallel to surface of porous ceramic plates fired with two kinds of charcoal powder at $1100^{\circ}C$ was $3.5-3.6^{\circ}C$ at $26^{\circ}C$ and 60% of relative humidity in a closed box. Cooling temperature difference was dependent on the number of porous plates and the distance between porous plates. A simple and eco-friendly cooling system using porous ceramic plates fired from Onggi clay and charcoal powder was proposed.

• 한국세라믹학회지
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• 제32권12호
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• pp.1392-1400
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• 1995

WC-10wt%Co-Al2O3 ceramic composites, using both the SHS (Self-propagating High Temperature Synthesis) synthesized WC powder method and commercial WC powder, were prepared by varing WC-Co/Al2O3 vol% ratio and sintering temperature (1350℃∼1650℃) for 1 hr in Ar atmosphere. Mechanical characterization has been investigated by Instron meterial testing system and Vicker's hardness test. Compositional and structural chracterizations were carried out by energy-dispersive analysis of X-ray (EDAX) data and scanning electron microscope (SEM). Electrical characterization was carried out by the electrical resistivity measurement using 4-point probe method. As sintering period increased and Al2O3 contents decreased in WC-10wt%Co-Al2O3 ceramic composite, shrinkage and relative density increased, resulting in maximum values at 1600℃. Also the major matrix phase changed with increasing Al2O3 content from 0 to 100 vol%. It was also identified by SEM, EDAX, and electrical resistivity measurement. Based on the results of analysis of flexural strength, toughness and hardness, the mechanical properties of WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were better than those WC-10wt%Co-Al2O3 ceramic composites using commercial WC powder because WC-10wt%Co-Al2O3 ceramic composites using the SHS synthesized WC powder were sintered very well due to small initial particle size. By the addition of 40 vol% Al2O3 [60(WC=10wt%Co)-40Al2O3], it was possible to obtain a proper candidate as a superalloy.

• 한국가금학회지
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• 제32권4호
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• pp.261-268
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• 2005

본 연구는 Ceramic분말의 첨가가 산란계의 생산성, 맹장 및 배설물중 병원성 미생물(E. coli, salmolella)의 수, 배설물 중의 악취물질$(NH_3,\;H_2S,\;VFA)$ 및 난황중 지방산 조성에 미치는 영향을 구명하기 위해서 실시하였다. 총 360수의 34주령의 산란계를 120마리씩 3처리구로 구분하여서 Ceramic 분말 $0.0\%$ (대조구), $0.4\%$ 및 $0.8\%$를 첨가한 사료로 6주 동안의 사양시험을 실시하였다. 결론적으로 34에서 40주령의 산란계 사료에 $0.4\%$의 Ceramics 분말의 첨가는 생산성 향상, 장관내 E. coli 및 Salmonella 수가 감소되어 배설물 중의 $NH_3$ 및 VFA의 발생량 감소 및 난황중의 지방산 조성을 개선시킬 가능성이 인정되었다.

• 자원리싸이클링
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• 제26권1호
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• pp.16-21
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• 2017

본 연구는 SiC 결정 성장을 위한 원료 분말 합성법에 관한 것이다. ${\beta}-SiC$ 분말들은 높은 온도 조건(>$1400^{\circ}C$)에서 실리콘 분말과 탄소 분말의 반응에 의해서 합성 된다. 이 반응은 진공 상태(또는 Ar 가스 분위기)에서 실리콘+탄소 혼합물이 반응하고 다결정의 SiC 분말을 형성하기 충분한 횟수를 거쳐 그라파이트 도가니 안에서 진행된다. 최종 결과물의 특성들은 X-ray 회절, SEM/EDS, 입도 분석 및 ICP-OES을 통해 분석되었다. 또한, 최종 결과물의 순도는 the Korean Standard KS L 1612에 의거해서 분석했다.

• 한국분말재료학회지
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• 제24권5호
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• pp.406-413
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• 2017

A Nanosized $WO_3$ and CuO powder mixture is prepared using novel high-energy ball milling in a bead mill to obtain a W-Cu nanocomposite powder, and the effect of milling time on the structural characteristics of $WO_3-CuO$ powder mixtures is investigated. The results show that the ball-milled $WO_3-CuO$ powder mixture reaches at steady state after 10 h milling, characterized by the uniform and narrow particle size distribution with primary crystalline sizes below 50 nm, a specific surface area of $37m^2/g$, and powder mean particle size ($D_{50}$) of $0.57{\mu}m$. The $WO_3-CuO$ powder mixtures milled for 10 h are heat-treated at different temperatures in $H_2$ atmosphere to produce W-Cu powder. The XRD results shows that both the $WO_3$ and CuO phases can be reduced to W and Cu phases at temperatures over $700^{\circ}C$. The reduced W-Cu nanocomposite powder exhibits excellent sinterability, and the ultrafine W-Cu composite can be obtained by the Cu liquid phase sintering process.