• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2000년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.11-11
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• 2000

Large-size ceramic/metal bulk FGMs have been fabricated on a recently developed and the world's largest Spark Plasma Sintering(SPS) systems, As a part of the development program for practical production processes and machines for FGMs by SPS, the processes, mechanical properties, dimensional size and shape effects, and production machine systems were investigated. In the past, $ZrO_{2}$/TiAI, $ZrO_{2}$/Ni, $Al_{2}O_{3}$/Ti, WC/Co, WC/Co/Steel, A1/P, Polymide, Cu/Polymide, nano-composites, porous and other combinations of bulk FGMs have already been processed using SPS. However, most of the specimen sizes were small, in a range of 20 to 30mm in diameter. Recently disk-shape sintered compacts with diameters of 100 and 150 mm, and thickness of approximately 15 and 17 mm, $ZrO_{2}$(3Y)/ stainless steel FGMs were homogenous consolidated in a shorter sintering time, while maintaining high quality and repeatability by utilizing a temperature gradient sintering method. The SPS heating up and holding time totaled less than one hour. Therefore, the SPS process in expected to find increased use in the fabrication of large-size FGMs as a new industrial processing technology. This paper introduces SPS systems, the processing principles, features and the characteristies of ceramic/metal bulk FGM.

• 한국분말재료학회지
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• 제22권3호
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• pp.197-202
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• 2015

In this study, porous stainless steel (STS316L) sintered body was fabricated by powder metallurgy method and its properties such as porosity, compressive yield strength, hardness, and permeability were evaluated. 67.5Fe-17Cr- 13Ni-2.5Mo (wt%) powder was produced by a water atomization. The atomized powder was classified into size with under $45{\mu}m$ and over $180{\mu}m$, and then they were compacted with various pressures and sintered at $1210^{\circ}C$ for 1 h in a vacuum atmosphere. The porosities of sintered bodies could be obtained in range of 20~53% by controlling the compaction pressure. Compressive yield strength and hardness were achieved up to 268 MPa and 94 Shore D, respectively. Air permeability was obtained up to $79l/min{\cdot}cm^2$. As a result, mechanical properties and air permeability of the optimized porous body having a porosity of 25~40% were very superior to that of Al alloy.

• 한국재료학회지
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• 제25권8호
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

• 한국산학기술학회논문지
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• 제6권6호
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• pp.468-472
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• 2005

유리병의 제조에 있어서 유리 융체가 금형 벽면에 부착하는 것을 방지하기 위하여 성형할 때마다 금형 내벽면을 윤활제로 도포하는 공정이 있다. 금형 벽면을 통기성이 있는 다공질 소결체로 제조하면 도포공정을 생략할 수 있다. 따라서 본 연구에서는 스테인리스 중에서 내열${\cdot}$내마모 특성이 가장 우수한 310L계 조대 분말($-150{\mu}m$) 및 420J2 계 미세 분말($40{\~}50{\mu}m$)을 사용, 유리 금형용 내벽면 재로서 가장 적합한 다공질 소결체(소결체의 밀도: $85{\~}90\%$)를 제작하기 위하여 성형압력, 소결 분위기, 소결온도 및 시간을 변화시켜 다음과 같은 결과를 얻었다. (1) 고상 소결로서는 입자 크기가 큰 310L분말을 가지고는 어느 경우에 있어서나, 목적하는 소결 밀도를 얻을 수 없었다. (2) $2ton/cm^2$의 성형압력으로 성형한 실형상 성형체를 양산용 진공($1300^{\circ}C$, 2시간) 소결로에서 소결한 결과, 소결체의 밀도는 $310L+0.03\%B$, 420J2, 420J2+(0.03, 0.06)$\%$B에서 각각 6.2(79$\%$), 6.6(86$\%$), 7.3(95$\%$), $7.6(99\%)g/cm^3$로 나타났다. 따라서, 420J2계 분말(저압성형) 및 310L+0.03$\%$B(고압성형)분말을 사용하여 진공 중 소결하면 목적하는 통기도를 가진 소결체를 제작할 수 있다는 것을 알았다.

• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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• pp.6-10
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• 2003

Silver nano-powder was added to Ma $B_2$ to make (Ag)$_{(x)wt.%}$(Mg $B_2$)$_{(l00-x)wt.%}$ (A $g_{x}$-Mg $B_2$) (10 $\leq$ x $\leq$ 50) composite superconductors to investigate the effect of the Ag nano-powder on the vortex pinning. Pellets made out of the mixed powder were put inside stainless steel tubes, which were sintered at 85$0^{\circ}C$ in Ar atmosphere. No impurity phase was identified for as-rolled samples. However, both the Mg $B_2$ and the A $g_{x}$-Mg $B_2$ composite pellets, when sintered, contain small amount of Mg $B_4$ and MgAg impurity phases. From the magnetization study, it was found that the flux pinning was improved in the high magnetic field region (> 3 T) only when 10w/o Ag was added to Mg $B_2$. The "two step" structures in ZFC M(T) curve gradually increased as the amount of Ag added increased. Pinning centers can be created by adding a suitable amount of Ag nano-powder which is not too large to increase the decoupling between the Mg $B_2$ grains.crease the decoupling between the Mg $B_2$ grains.

• 멤브레인
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• 제20권1호
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• pp.62-68
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• 2010

Cermet 분리막 제조를 위한 혼합 분말은 60 vol.% vanadium과 $Y_2O_3$-stabilized $ZrO_2$ (YSZ)를 기계적으로 혼합하여 준비하였다. 혼합 분말을 원판으로 압축한 후 진공 분위기에서 $1600^{\circ}C$로 2시간동안 소결하였다. 소결 분리막은 치밀하였고, 브레이징 필러를 이용하여 스테인레스 링에 장착되었다. V/YSZ 분리막의 수소 투과량은 100% 수소를 흘려 $200{\sim}350^{\circ}C$ 범위에서 측정되었다. $350^{\circ}C$, 0.5 bar압력에서 분리막의 양 표면에 균열이 형성되었다. 투과실험 동안에 V/YSZ 분리막의 vanadium은 수소와 반응하여 $V_2H$를 생성하였으며, 이로 인해 분리막이 균열되는 것을 알 수 있었다.

• 한국분말재료학회지
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• 제10권2호
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• pp.97-102
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• 2003

The powder-in sheath rolling was applied to the fabrication of $Al/Al_2O_3$ composite. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. Mixture of aluminum powder and $Al/Al_2O_3$ particles of which volume content was varied from 5 to 20 vol.% was filled in the tube by tap filling and then rolled to 75% reduction at ambient temperature. The re]]ed specimen was sintered at 56$0^{\circ}C$ for 0.5 hr. The $Al/Al_2O_3$ composite fabricated by the sheath rolling and subsequent sintering showed the relative density higher than 0.96. The tensile strength of the composite increased with the volume content of $Al_2O_3$ particles, and it reached a maximum of 90 MPa which is 1.5 times higher than unreinforced material. The elongation decreased with the volume content of $Al_2O_3$ particles. It is concluded that the powder-in sheath rolling is an effective method for fabrication of $Al/Al_2O_3$ composite.

• 한국분말재료학회지
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• 제10권2호
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• pp.103-107
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• 2003

Aluminum-based $Al/Al_2O_3$ composites were fabricated by a powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. A mixture of aluminum powder and $Al_2O_3$ particles of which volume content was varied from 5 to 20%, was filled in the tube by tap filling and then rolled by 75% reduction in thickness at ambient temperature. The rolled specimen was then sintered at 56$0^{\circ}C$ for 0.5 h. The mixture of Al powders and $Al_2O_3$ particles was successfully consolidated by the sheath rolling. The $Al/Al_2O_3$ composite fabricated by the sheath rolling showed a recrystallized structure, while unreinforced Al powder compact fabricated by the same procedure showed a deformed structure. The unreinforced Al powder compact was characterized by a deformation (rolling) texture of which main component is {112}<111>, while the $Al/Al_2O_3$ composite showed a mixed texture oi deformation and recrystallization. The sintering resulted in recrystallization in Al powder compact and grain growth in the composite.

• 한국생산제조학회지
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• 제24권6호
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• pp.594-598
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• 2015

The effects of Ni on the mechanical properties of WC-Xwt.%Ni-1.5wt.%Si-1.1wt.%$B_4C$ composite (X = 21.6, 23.6, 25.6 and 27.6 wt.%) were investigated in order to replace Co with Ni as the binder metal for hard materials based on WC-Co system. Using X-ray diffraction, optical microscopy, field-emission scanning electron microscopy results, the microstructure, pore distribution and grain size of the composites sintered at $1,150^{\circ}C$ were examined with different fraction (X = 21.6, 23.6, 25.6 and 27.6 wt.%) of binder metal Ni. The average WC grain size of the $WC-Ni-Si-B_4C$ composites was about $1{\mu}m$. The Rockwell hardness : A (HRA) and transverse rupture strength were about 88HRA and $110kgf/mm^2$, respectively. The obtained sample was bonded with SM45C at a temperature of $1,050^{\circ}C$. The thickness and mechanical properties of the bonded area were investigated with different dwell time at a bonding temperature of $1,050^{\circ}C$.

• 한국분말재료학회지
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• 제11권3호
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• pp.259-264
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• 2004

Aluminum based metal matrix composite reinforced with SiC particles was fabricated by the powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1mm was used as a sheath. Mixture of aluminum powder and SiC particles of which volume content was varied from 5 to 20vol.% was filled in the tube by tap filling and then rolled to 75% reduction at ambient temperature. The rolled specimen was sintered at 56$0^{\circ}C$ for 0.5hr. The tensile strength of the (SiC)$_{p}$/Al composite increased with the volume content of SiC particles, and at 20vol.% it reached a maximum of 100㎫ which is 1.6 times higher than unreinforced material. The elongation decreased with the volume content of $Al_{2}$O$_{3}$ particles. The mechanical properties of the (SiC)$_{p}$/Al composite fabricated by the powder-in sheath rolling is compared with that of (Al$_{2}$O$_{3}$)$_{p}$/Al composite by the same process.ess.