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저온 분사 공정에서 니켈이 코팅된 다이아몬드 적용을 통한 금속/다이아몬드 복합재료의 코팅성 향상
나현택(Hyuntaek Na),배규열(Gyuyeol Bae),강기철(Kicheol Kang),김형준(Hyungjun Kim),이창희(Changhee Lee) 한국표면공학회 2008 한국표면공학회지 Vol.41 No.6
Generally, deposition mechanism of diamond particle is mainly embedding effect in the kinetic spray process. Accordingly, in spite of high cost, helium gas was employed as process gas to get high diamond fraction in the composite coating. In this study, the deposition behavior of bronze/diamond by kinetic spray process was compared using different process gas (helium and nitrogen). Bare (mean size of 5 ㎛, 20 ㎛) and nickel coated diamond (mean size of 26 ㎛) were deposited on Al 6061-T6 substrate with fixed process temperature and pressure. For comparison with experimental results, plastic deformation behavior of nickel layer was simulated by finite element analysis (using ABAQUS/Explicit 6.7-2). The size, broken ratio, and fraction of diamond in the composite coating were analyzed through scanning electron microscopy and image analysis method. The uniform distribution and deposition efficiency of diamond particles in the coating layer could be achieved by tailoring the physical properties of the feedstock.
Influence of metal powder shape on drag coefficient in a spray jet
S. Kumar,Hyuntaek Na,이창희,V. Selvarajan 한국물리학회 2009 Current Applied Physics Vol.9 No.3
In plasma spraying, particle shape, size, distribution and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. In the present work, nickel, iron and aluminium irregular powders in the size range from 50 to 63 lm were spheroidized using thermal plasma processing. The spheroidization experiments have been carried out at different gas flow rates and plasma torch power levels. The sphericity was analyzed using shape factor. Drag coefficients of the powders were estimated using Reynolds number and sphericity of the powders in plasma. For irregular particles, the drag coefficient is higher than that of the spherical because of its large area of contact with plasma. The temperature dependent on drag coefficient is also discussed. Increasing temperature increases the drag coefficient of the powder particles injected in to the plasma jet. Increasing plasma jet temperature changes the density and viscosity of the plasma which affects the particle’s drag coefficient in the plasma. The results are reported and discussed. In plasma spraying, particle shape, size, distribution and density are the important factors to be considered in order to ensure high spray efficiency and better coating properties. In the present work, nickel, iron and aluminium irregular powders in the size range from 50 to 63 lm were spheroidized using thermal plasma processing. The spheroidization experiments have been carried out at different gas flow rates and plasma torch power levels. The sphericity was analyzed using shape factor. Drag coefficients of the powders were estimated using Reynolds number and sphericity of the powders in plasma. For irregular particles, the drag coefficient is higher than that of the spherical because of its large area of contact with plasma. The temperature dependent on drag coefficient is also discussed. Increasing temperature increases the drag coefficient of the powder particles injected in to the plasma jet. Increasing plasma jet temperature changes the density and viscosity of the plasma which affects the particle’s drag coefficient in the plasma. The results are reported and discussed.
대기 플라즈마 용사공정을 이용한 Fe계 벌크 비정질 금속 코팅의 초기 분말의 화학조성과 크기에 대한 미세 조직 및 마모 특성
김정환(Junghwan Kim),윤상훈(Sanghoon Yoon),나현택(Hyuntaek Na),이창희(Changhee Lee) 한국표면공학회 2008 한국표면공학회지 Vol.41 No.5
In this study, two kinds of Fe-based bulk metallic glasses (BMG) powder were built-up through atmospheric plasma spray (APS) technique. The microstructure of two coatings was analyzed through X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Crystallization and oxidation in coatings were affected by chemical composition and initial powder size. Then, both of them influenced the tribological property.
Oxidation and crystallization mechanisms in plasma-sprayed Cu-based bulk metallic glass coatings
Kim, Junghwan,Kang, Kicheol,Yoon, Sanghoon,Kumar, S.,Na, Hyuntaek,Lee, Changhee Elsevier 2010 Acta materialia Vol.58 No.3
<P><B>Abstract</B></P><P>Cu-based bulk metallic glass (BMG) coatings were built-up by the atmospheric plasma spraying (APS) process at different hydrogen flow rates. As the hydrogen flow rate increased, thermal energy in the plasma jet increased the melting state of the Cu-based BMG particles. Although it was expected that the difference in melting states would quantitatively affect the amorphous fractions in the coatings, both the amorphous fraction and the oxide content of the layers were independent of hydrogen flow rate. However, different melting states resulting from different hydrogen gas flow rates, and the subsequent oxidation which inevitably occurred during spraying, generated different crystallization processes in the coating. In this paper, crystallization mechanisms in plasma-sprayed BMG were studied using their microstructures. Specific analyses of the particles deposited at high travel speed and quenched in cold water also served for further understanding of the melting state and change in composition of the particles undergo during deposition.</P>