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진공상온분사(VKS) 공정에서의 비행입자 가속 기구 및 속도제어를 위한 가스 유량 효과에 관한 연구
박형권,권주혁,이일주,이창희,Park, Hyungkwon,Kwon, Juhyuk,Lee, Illjoo,Lee, Changhee 한국재료학회 2014 한국재료학회지 Vol.24 No.2
Vacuum kinetic spray(VKS) is a relatively advanced process for fabricating thin/thick and dense ceramic coatings via submicron-sized particle impact at room temperature. However, unfortunately, the particle velocity, which is an important value for investigating the deposition mechanism, has not been clarified yet. Thus, in this research, VKS average particle velocities were derived by numerical analysis method(CFD: computational fluid dynamics) connected with an experimental approach(SCM: slit cell method). When the process gas or powder particles are accelerated by a compressive force generated by gas pressure in kinetic spraying, a tensile force generated by the vacuum in the VKS system accelerates the process gas. As a result, the gas is able to reach supersonic speed even though only 0.6MPa gas pressure is used in VKS. In addition, small size powders can be accelerated up to supersonic velocity by means of the drag-force of the low pressure process gas flow. Furthermore, in this process, the increase of gas flow makes the drag-force stronger and gas distribution more homogenized in the pipe, by which the total particle average velocity becomes higher and the difference between max. and min. particle velocity decreases. Consequently, the control of particle size and gas flow rate are important factors in making the velocity of particles high enough for successful deposition in the VKS system.
진공 저온 분사 공정을 통해 형성된 Fe계 비정질 재료의 적층거동 및 미세구조 변화 관찰
권주혁,박형권,이일주,이창희,Kwon, Juhyuk,Park, Hyungkwon,Lee, Illjoo,Lee, Changhee 한국재료학회 2014 한국재료학회지 Vol.24 No.1
Fe-based amorphous coatings were fabricated on a soda-lime glass substrate by the vacuum kinetic spray method. The effect of the gas flow rate, which determines particle velocity, on the deposition behavior of the particle and microstructure of the resultant films was investigated. The as-fabricated microstructure of the film was studied by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). Although the activation energy for transformation from the amorphous phase to crystalline phase was lowered by severe plastic deformation and particle fracturing under a high strain rate, the crystalline phases could not be found in the coating layer. Incompletely fractured and small fragments 100~300 nm in size, which are smaller than initial feedstock material, were found on the coating surface and inside of the coating. Also, some pores and voids occurred between particle-particle interfaces. In the case of brittle Fe-based amorphous alloy, particles fail in fragmentation fracture mode through initiation and propagation of the numerous small cracks rather than shear fracture mode under compressive stress. It could be deduced that amorphous alloy underwent particle fracturing in a vacuum kinetic spray process. Also, it is considered that surface energy caused by the formation of new surfaces and friction energy contributed to the bonding of fragments.
레이저 클래딩 공정 조건이 코발트 합금-텅스텐 카바이드 혼합 코팅층의 균열 발생에 미치는 영향
이창민,박형권,이창희,Lee, Changmin,Park, Hyungkwon,Lee, Changhee 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.6
In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s (WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with ${\gamma}+Cr7C3$ eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.
진공 상온 분사 공정으로 제조된 Al_{2}O_{3} 필름의 광 투과도에 미치는 미세조직 특성의 영향
김진영 ( Jinyoung Kim ),박형권 ( Hyungkwon Park ),남진수 ( Jin Su Nam ),손경수 ( Kyung Soo Son ),임영태 ( Young Tae Im ),이재욱 ( Jae Wook Lee ),정봉근 ( Bong Geun Chung ),이창희 ( Changhee Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.1
Glass materials have been applied in various industrial fields. Research on improvement of mechanical properties has consistently been performed due to this material’s intrinsically vulnerable characteristics. Surface modification is considered as the promising method to supplement the weakness; especially, ceramics are thought of as appropriate materials for film materials because of their outstanding mechanical properties and their chemical stability. However, unfortunately, the optical transmittance of ceramic materials is poor, and can rather restrict this material’s utilization in glass. In this regard, the optical transmittance mechanism of vacuum kinetic sprayed Al_{2}O_{3} film was investigated. To control and analyze the film’s optical property, the gas flow rate, as a main process variable, was controlled; then, post heat-treatment was performed. Consequently, the film’s optical property was determined by three microstructural factors. That is, crystallite size, defects (including lattice distortion), and amorphous phase, generated during particle deposition, were found to strongly affect the transmittance.
고속 화염 용사를 통하여 형성된 다중벽 탄소 나노튜브 알루미늄 복합소재 코팅의 특성 평가
강기철(Kicheol Kang),박형권(Hyungkwon Park),이창희(Changhee Lee) 한국표면공학회 2012 한국표면공학회지 Vol.45 No.1
Multi-walled carbon nanotube (MWCNT) aluminum composite powders were deposited to form coatings using a high velocity oxygen fuel (HVOF) spraying process. High thermal energy and contact with atmospheric oxygen were supplied as the MWCNT aluminum composite particles were exposed to a gas flow field at high temperature (~3.0 × 10<SUP>3</SUP> K) during HVOF spraying. As a result, the particles underwent full or partial melting and rapid solidification due to the high thermal energy, and the exposure to oxygen induced the interfacial reaction of MWCNTs within the particle. The electrical and mechanical properties of MWCNT aluminum composite coatings were evaluated based on microstructure analysis. Electrical resistivity, elastic modulus, and micro-hardness, of the MWCNT aluminum composite coatings were higher than those of pure aluminum coating. The contribution of MWCNTs to the aluminum matrix can be attributed to their high electrical conductivity, dispersion hardening and anchoring effects. The relationship among the properties and the interaction of the MWCNTs with the aluminum matrix is discussed.