• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.55.2-55.2
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• 2010

기존의 thermal spray coating은 분사시 가스와 입자가 높은 열을 동반하여 상대적으로 차가운 기판과의 충돌되는 과정에서 기판과 입자 사이에 열응력이 발생하게 되고, 이것은 코팅 특성을 저하시킨다. 또한 고온의 가연성 가스등의 사용으로 작업 시 안전문제 등의 단점이 있었다. 이러한 단점을 보완하기 위하여 분사 시 운동에너지를 주로 이용하는 cold spray coating 공정이 개발되었다. 이 공정은 코팅 입자를 임계속도 이상으로 가속시켜 입자와 기판이 충돌시 소성 변형을 통해 적층되는 코팅기술이다. Cold spray coating공정은 상온 코팅이 가능하기 때문에 주입입자의 물성이 비교적 그대로 유지되고, 고온의 열로 인한 기판의 변질을 막을 수 있다. Cold Spray coating에서 주로 원형 노즐을 사용하나 본 연구에서는 분사 효율 향상을 위한 광폭노즐을 사용하여 코팅 시간 단축을 기대하고 있다. 임계속도 이상의 입자 확보를 위하여 노즐의 expansion ratio와 노즐 shape의 변화를 주어 그에 따른 노즐내의 유동장을 수치해석을 통해 계산하였다. 분사되는 출구면과 기판 사이의 입자 속도 분포를 해석하였고, 이를 통해 임계속도 이상의 속도를 갖는 유효 입자들의 분포 및 유효 분사 면적을 예측하였다. 또한, 기존의 원형 노즐과 광폭 노즐과의 유동장 비교 및 각 노즐 분사면을 분석하여 cold spray coating공정에서의 효율적인 노즐 형상을 디자인하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1997년도 제26회 추계학술대회
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• pp.183-190
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• 1997

The wear behaviors of $Al_2O_3-40%TiO_2$ deposited on casting aluminum alloy(ASTM A356) by plasma spray against SiC ball have been investigated experimentally. Friction and wear tests are carried out at room temperature. The friction coefficient of $Al_2O_3-40%TiO_2$ coating is lower than that of pure $Al_2O_3$ coating(APS). It is found that low friction correspond to low wear and high friction to high wear in the experimental result. The thickness of $Al_2O_3-40%TiO_2$ coatings indicated the existence of the optimal coating thickness. It is found that a voids and porosities of coating surface result in the crack generated. As the tensile stresses in coating increased with the increased friction coefficient. The columnar grain of coating will be fractured to achieve the critical stress. It is found that the cohesive of splats and the porosity of surface play a role in wear characteristics. It is suggested that the mismatch of thermal expansion of substrate and coating play an important role in wear performance. Tensile and compressire under thermo-mechanical stress may be occurred by the mismatch between thermal expansion of substrate and coating. This crack propagation above interface is observed in SEM.

• 소성∙가공
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• 제24권4호
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• pp.287-292
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• 2015

The possibility of chemical precipitation for recycled ammonium paratungstate (APT) was studied. WO₃ particles were synthesized by chemical precipitation method using a 1:2 weight ratio of APT:DI-water. At the 500℃ sintering temperature, the X-ray diffraction results showed that APT completely decomposed to WO₃. For the granulated powder WC-Co, vacuum heat treatment at proper temperatures increases tap density and flow-ability. Hardness of the WC-Co thermal spray coating layer was measured in the range HV 831~1266. Spray conditions for the best characteristic values were an oxygen flow rate=1500 scfh, a fuel flow rate = 5.25gph and a gun distance = 320mm.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 추계학술대회 초록집
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• pp.245-246
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• 2009

The large and high-speed vessels have been greatly advanced, but ship materials have been caused the problem such as corrosion, cavitation and erosion. Cavitation can produce material damage such as pumps, turbines, valves and ship propellers etc. To solve these problems, the cavitation and electrochemical characteristics for thermal spray coating and the sealing are executed to obtain the excellent corrosion protection characteristics in sea water environment.

• 한국표면공학회지
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• 제49권2호
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• pp.172-177
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• 2016

In this paper, various electrochemical experiments were conducted in seawater solution to evaluate corrosion damage behavior of arc thermal sprayed Inconel 625 coating on SS400 steel in marine environment. As a result, corrosion damages of thermal sprayed Inconel 625 coating preferentially occurred at the defect area, and they were observed as a form of pitting corrosion in the galvanostatic experiments. In Tafel analysis, corrosion current density of Inconel 625 coating was relatively high due to influence of interconnected pores and Cr oxides in the thermal spray coating layer. On the other hand, the result of the potential measurement, thermal sprayed Inconel 625 coating should need the post-treatment which can compensate the defects like pores and cracks because Inconel 625 coating presented a higher potential of about 290 mV than that of the SS400 steel.

• Tribology and Lubricants
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• 제15권1호
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• pp.39-45
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• 1999

The wear behavior of $Al_2$O$_3$-40%TiO$_2$deposited on casted aluminum alloy (ASTM A356) by APS (Air Plasma Spray) against SiC ball has been investigated in this work. Wear tests were carried out at room temperature. The friction coefficient of $Al_2$O$_3$-40%TiO$_2$coating is lower than that of pure $Al_2$O$_3$coating(APS). $Al_2$O$_3$-40%TiO$_2$coating indicated the existence of the optimal coating thickness. It is found that voids and pores of coating surface resulted in the generation of cracks, and the cohesive of splats and the porosity of surface play a role in wear characteristics. It is suggested that the mismatch of thermal expansion of substrate and coating play an important role in wear performance. Tension and compression under thermo-mechanical stress may be occurred by the mismatch between thermal expansion of substrate and coating. The crack propagation above interface is observed in SEM.

• 한국분말재료학회지
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• 제7권2호
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• pp.63-70
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• 2000

Thermal spray coating process has proven to be effective at producing hard, dense, wear resistance coatings on the relatively mild substrates. Among several spraying techniques, HVOF (High Velocity Oxygen Fuel) and plasma coating processes, which are preferentially used for the wear resistance application such as capstans, have been applied in this study. The effects of pre-treatment, it-process and post-treatment parameters on the wear and mechanical properties of WC+12%Co, Cr3C2 and Al2O3 powder coatings have been investigated and correlated with the microstructures. The results indicated that the carbide coating was more preferable to the oxide coatings and the post-treatments consisting of vacuum annealing and sealing on carbide coatings led to significant improvements in wear resistance, adhesive strength and coating phase stabilization over the other processing techniques in this application.

• 해양환경안전학회지
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• 제27권1호
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• pp.187-192
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• 2021

본 연구는 절탄기 튜브의 저온부식 손상을 방지하기 위해 Inconel 625 용사재료를 활용하여 아크 열용사 코팅기술 적용 후 실링처리를 실시하였다. 용사코팅(TSC) 층의 내식성 분석을 위해 0.5 wt% 황산 수용액에서 다양한 전기화학적 실험을 진행하였다. 양극분극 실험 후에는 주사전자현미경과 EDS 성분분석을 통해 부식 손상 정도를 파악하였다. 자연전위 계측 시 TSC+실링처리(TSC+Sealing)의 안정적인 전위 형성을 통해 실링처리 효과를 확인하였다. 양극분극 실험 결과 TSC와 TSC+Sealing에서 부동태 영역이 확인되었으며, 부식 손상 역시 관찰되지 않아 내식성이 개선되었다. 더불어 타펠분석에 의해 산출된 부식전위와 부식전류밀도 분석 결과 TSC+Sealing의 내식성이 가장 우수하게 나타났다.

• 한국세라믹학회지
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• 제45권12호
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• pp.777-781
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• 2008

Experiments were conducted using SUS430 and Crofer 22 APU steels coated by LSM using plasma spray and slurry spray methods, respectively. High-temperature conductivity and oxidation resistance were investigated. For comparison, SUS430 and Crofer 22 APU without LSM coating were also investigated and coefficient of thermal expansion (CTE) was measured. The results show that the materials without LSM coating exhibit almost the same CTE as YSZ electrolyte in a range of temperatures of $550{\sim}850^{\circ}C$. When coated with LSM, the oxidation rate of the steels decreases by $30{\sim}40%$ using slurry spray and by $10{\sim}30%$ using plasma spray whereas the steels using plasma spray have a better high-temperature conductivity than the steels using slurry spray. It is thus concluded that the LSM coating has a limited effect on increasing high-temperature conductivity while it can effectively reduce the oxidation of the steels.

• 한국자동차공학회논문집
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• 제24권3호
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• pp.285-293
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• 2016

The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.