• 한국분말재료학회지
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• 제9권6호
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• pp.455-462
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• 2002

The microstructures and properties of TiC dispersed nickel-base alloy were studied in this work. The alloy prepared by powder metallurgical processing was solution treated, 1st-aged at $880^{\circ}C$ for 16 hours, and then 2nd-aged at $760^{\circ}C$ for 4 hours. Microstucture of sintered specimen showed that TiC particles are uniformly dispersed in Ni base alloy. In the specimen aged at $880^{\circ}C$ for 8 hours, the fine $\gammaNi_3$(Al,Ti) precipitates with round shape are observed and the very fine $\gammaNi_3$(Al,Ti) particles with round shape are precipitated in the specimen aged at $760^{\circ}C$ for 4 hours. The presence of ${\gamma}$precipitates in TiC/Ni base alloy increased the hardness and wear resistance of the specimen. The hardness and wear resistance of the Ni-base with TiC are higher than those of conventional Ni-base superalloy X-750 because of dispersion strengthening of TiC particles. The hardness, transverse rupture strength and resistance of the specimen 2nd-aged at $760^{\circ}C$ for 4 hours are higher than those of 1st-aged specimen due to ultrafine $\gammaNi_3$(Al,Ti) precipitates.

• 한국세라믹학회지
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• 제52권6호
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• pp.395-402
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• 2015

The suspension plasma spray (SPS) technique has been used to obtain dense $Y_2O_3$ coatings and to overcome the drawbacks of the conventional air plasma spray (APS). SPS uses suspensions containing micrometer or sub-micrometer sized powders dispersed in liquid media. In this study, microstructure developments and mechanical properties have been investigated as functions of particle size of source material and plasma processing parameters such as plasma power and stand-off distance. The microstructure of the coating was found to be highly related to the particle size and the plasma processing parameters, and it was directly reflected in the hardness and the adhesion strength. When fine powder (BET $16.4m^2/g$) was used as a raw material in the suspension, there was, with increasing stand-off distance, a change from a dense structure with a slightly bumpy surface to a porous structure with a cauliflower-like surface. On the other hand, when a coarse powder (BET $2.8m^2/g$) was used, the coating density was lower, with microscopic splats on the surface. Using fine $Y_2O_3$ powders, the coating layer with an optimum short stand-off distance showed a high hardness of approximately 90% of that of sintered $Y_2O_3$ and an adhesion strength several times higher than that of the coating by conventional APS.

• 한국결정성장학회지
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• 제1권2호
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• pp.46-58
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• 1991

$Zn(NO_3)_2\cdot6H_2O$ 를 사용하여 출발용액으로 $Zn(NO_3)_2\cdot6H_2O$(aq.)용액을 각각 1M, 0.5M, 0.25M, 0.1M의 농도로 제조하여 초음파 진동자에 의해 액적을 발생시킨후, 2.3cm/sec의 유속으로 건조 및 열분해하여 ZnO분말을 합성하였다. 이때 건조 온도는 $200^{\circ}C$, 열분해 온도는 $600^{\circ}C$였다. 제조된 ZnO분말의 열적특성을 TG-DTA로 측정하였고, IR로 미분해물 및 흡착 가스의 성분을 조사하였다. 결정상 및 crystallite의 크기를 XRD로 분석하였고, 입자의 형태는 SEM과 TEM으로 관찰한 후 입자 크기와 입도분포를 SEM 사진으로부터 측정하였다. 합성 분말은 hexagonal의 결정구조를 갖는 Zinc oxide였다. 입자의 형태는 대부분 구형이고, 약 40nm 크기의 일차입자로 구성된 이차입자였다. 평규 입자 크기는 $0.28-0.61{\mu}m$ 이고 입도 분포도 좁았다.

• Korean Chemical Engineering Research
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• 제45권5호
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• pp.448-454
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• 2007

미세 $BaTiO_3$ 분말의 합성을 위해 함수 티타니아와 수산화바륨을 원료로 수열합성 실험을 수행하여, 반응시간, 온도, 농도 변화에 따른 전화율, 결정구조 및 생성 분말의 물성을 조사하였다. 전화율에 미치는 영향은 시간 < 온도 < 농도 순이었으며, 2.0 M의 원료를 $180^{\circ}C$에서 2 h 수열합성 시킬 때 최대 전화율을 99.5%를 얻을 수 있었다. 낮은 농도(0.25 M)에서는 고온에서도 미반응 $BaCO_3$와 미반응 $TiO_2$ 생성을 피할 수 없었으며, 이 미반응 물질들은 고온에서 $BaTi_2O_5$를 생성시켜 불순물로 존재하였다. 농도를 높일수록 합성 $BaTiO_3$ 분말의 크기는 작아졌으며, 분말의 Ba/Ti 비도 1에 접근하였다. 2.0M 이상의 농도에서는 $180^{\circ}C$, 2 h 반응에서 Ba/Ti 비는 $1{\pm}0.005$ 이였다.

• Journal of Welding and Joining
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• 제15권5호
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• pp.134-143
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• 1997

The formation of thick alloyed layer with high Si content have been investigated on the surface of Al alloy (A5083) plate by PTA process with Si powder. Hardening characteristics and wear resistance of alloyed layer was examined in relation to the microstructure of alloyed layer. Thick hardened layer in mm-order thickness on the surface of A5083 plate can be formed by PTA process with wide range of process condition by using Si powder as alloying element because of eutectic reaction of Al-Si binary alloy. High temperature and rapid solidification rate of molten pool, which are features of PTA process, enable the formation of high Si content alloyed layer with uniform distribution of fine primary Si paticle. High plasma arc current was beneficial to make the alloyed layer with smooth surface appearance in wide range of powder feeding rate, because enough volume of molten pool was necessary make alloyed layer. Uniform dispersion of fine primary Si particle with about 30${\mu}{\textrm}{m}$ in particle size can be obtained in layer with Si content ranging from 30 to 50 mass %. Hardness of alloyed layer increased with increasing Si content, but increasing rate of hardness differed with macrostructure of alloyed layer. Wear resistance of alloyed layer depended on $V_{si}$(volume fraction of primary Si) and was remarkably improved to two times of base metal at 20-30% $V_{si}$ without cracking, but no more improvement was obtained at larger $V_{si}$.

• Metals and materials international
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• 제24권6호
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• pp.1213-1220
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• 2018

The effects of Cr and Fe addition on the mechanical properties of Ti-6Al-4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior ${\beta}$ phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti-6Al-4V resulted in a partially melted Ti-6Al-4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti-33Fe) and the Ti-6Al-4V powder, which induced the formation of a thick liquid layer surrounding Ti-6Al-4V. The ductility of Fe-added Ti-6Al-4V was thus poorer than that of Cr-added Ti-6Al-4V.

• 한국분말재료학회지
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• 제15권5호
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• pp.378-385
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• 2008

This article presents the successful consolidation of the mixed Co and Diamond powders for a drilling segment by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were analyzed. Homogeneous hardness (Hv 220) and density (97%) of sintered bulks fabricated by MPC were obtained by the new technique, where higher pressure has been employed for short period of time than that of general process. A fine microstructure and homogeneous hardness in the consolidated bulk were observed without cracks. Relatively higher drilling speed of 9.61 cm/min and life time of 6.55 m were found to the MPCed specimens, whereas the value of the specimens fabricated by general process was 11.71 cm/min and 7.96 m, respectively. A substantial improvement of mechanical properties of segment was achieved through this study.

• 한국분말재료학회지
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• 제15권5호
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• pp.345-351
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• 2008

The effects of the dopant (Mn) ratio on the microstructure and thermoelectric properties of $FeSi_2$ alloy were studied in this research. The alloy was fabricated by a combination process of ball milling and high pressure pressing. Structural behavior of the sintered bulks were systematically investigated by XRD, SEM, and optical microscopy. With increasing dopan (Mn) ratio, the density and ${\varepsilon}-FeSi$ phase of the sintered bulks increased and maximum density of 94% was obtained in the 0.07% Mn-doped alloy. The sintered bulks showed fine microstructure of ${\alpha}-Fe_{2}Si_{5}$, ${\varepsilon}-FeSi$ and ${\beta}-FeSi_2$ phase. The semiconducting phase of ${\beta}-FeSi_2$ was transformed from ${\alpha}-Fe_{2}Si_{5}+{\varepsilon}-FeSi$ phase by annealing.

• 한국재료학회지
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• 제17권1호
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• pp.50-55
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• 2007

Ultra-fine Copper powder for a conductive paste in electric-electronic field have been synthesized by chemical reduction of aqueous $CuSO_4$ with hydrazine hydrate $(N_2H_4{\cdot}H_2O)$ as a reductor. The effect of reaction conditions such as dispersant and reaction temperature on the particle size and shape for the prepared Cu powders was investigated by means of XRD, SEM, TEM and TGA. Experiments showed that type of dispersant and reaction temperature were affected on the particle size and morphology of the copper powder. When the carboxymethyl cellulose (CMC) was added as a dispersant the relative mono-dispersed and spherical Cu powder was obtained. Cu powders with particle size of approximately 140nm and narrow particle size distribution were obtained from 0.3M $CuSO_4$ with adding of 0.03M CMC and 40ml $N_2H_4{\cdot}H_2O$ at a reaction temperature of $70^{\circ}C$.

• 한국분말재료학회지
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• 제10권6호
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• pp.415-421
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• 2003

The study for producing the flake powders by milling of aluminum foil and gas atomized powders was carried out. The effects of lifter bars on the ball motions and milling of aluminum foils were also investigated. The aluminum foils were laminated each other, elongated, fragmented into small foils and finally formed into the flake powders during the dry ball-milling. The spherical atomized-powders were milled to coarse flake powders with high aspect ratio and then changed to fine flake powders with lower aspect ratio. Even though long times were required for making flake powders by milling of foils, the water covering areas of them were higher than those of powders milled using gas-atomized powders, suggesting aluminum foils were more plastically deformed by micro-forging. On the other hand, as the number of lifter bars increased, the necessary rotation speeds of milling jar for cascading mode and cataracting mode decreased drastically. It was possible to achieve same quality of milled flake powder by using the lifter bars under the lower milling speeds. The painting test showed that the appearance of painted surface was good and optimum content range of aluminum paste in car paint to maximize the degree of gloss was 3-5%.