• 한국자기학회지
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• 제15권5호
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• pp.270-275
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• 2005

가스분무법으로 제조한 $35\~180\;{\mu}m$ 크기의 $Fe-6.0wt\%Si$ 합금분말에 대하여 인산염계 절연물질을 피막처리하고 $600\~900^{\circ}C$에서 1시간 동안 열처리한 후 압축성형한 압분자심(분말코아)의 자기적 성질 및 기계적 특성을 조사하였다. 대체적으로 열처리온도가 증가할수록 압축강도가 감소하였으며, 자심손실 또한 낮아졌다. $800^{\circ}C$에서 열처리한 경우 압축성형강도가 15 kgf, 100 kHz에서 실효투자율은 74, 품질계수는 26, 50 Oe의 직류자장 하에서 퍼센트투자율은 78 정도의 값을 나타내었으며, 50 kHz-0.1 T에서 자심손실은 $750\;mW/cm^3$였다. 그리고 투자율-주파수 곡선 상에서의 cut-off 주파수는 거의 200 kHz 이상에 이르는 것으로 나타났다. $Fe-6.0wt\%Si$ 합금 압분자심의 이러한 제반 특성은 인산염 피막의 양호한 전기절연효과와, 고규소농도에 따른 합금의 결정자기이방성 및 포화자기변형의 감소, 전기비저항의 증대 등 기초 물성의 변화에 기인하는 것으로 사료되었다.

• 한국재료학회지
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• 제25권5호
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• pp.226-232
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• 2015

본 연구에서는 손상된 알루미늄 금형의 복원을 위해 고온플라즈마 용사법을 이용하여 금형의 표면에 $Al/Al_2O_3$ 혼합분말을 용사한 후 코팅층과 모재의 증착강도에 대한 평가를 수행하였다. 증착강도의 평가는 분사노즐의 이동속도, 순수한 알루미늄 bond coat 층의 유무에 따라 평가되었으며, bond coat 층을 생성시키지 않았을 때, 코팅층의 두께는 열팽창에 의한 잔류인장응력의 감소를 위해 두껍지 않아야 하지만 일정두께 이상이 되어야 최대의 증착강도를 얻을 수 있음이 나타났다. 또한 순수한 알루미늄 bond coat 층은 내부 결함이 없는 응고된 금속이기 때문에 두께에 따른 증착강도의 영향을 그대로 받아 두께가 두꺼울수록 bond coat 층을 생성시키지 않은 시험편보다 증착강도가 매우 낮게 측정되었다. 반면, 가장 얇게 bond coating 된 시험편 Bc3(3회의 bond coating층과 분사건의 이동속도가 20 cm/sec인 시험편) 는 bond coating을 하지 않은 시험편 중 가장 높은 증착강도를 가지는 시험편 Wbc20(bond coating층이 없고 분사건의 이동속도가 20 cm/sec인 시험편)보다 약 2배 이상증착강도가 향상되었다. 따라서 금형의 복원시에 중간층의 형성이 반드시 필요하며, 이는 코팅층의 잔류 인장응력을 보완시키며 고인성의 순수한 알루미늄과 같은 코팅층과 유사한 층을 코팅하는 것이 필요한 것으로 사료된다.

• 한국광물학회지
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• 제21권3호
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• pp.247-259
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• 2008

카올리나이트(kaolinite) 분말의 티타니아(Titania, $TiO_2$) 포팅을 위한 출발물질로서 인도네시아산 카올리나이트와 티타늄-아이소프로폭사이드(titanium isopropoxidc, TIP)가 사용되었으며, 실험은 졸-겔법(sol-gel method)으로 수행되었다. 또한 강매로서 에탄올이, 가수분해 반응을 위해 물이 사용되었으며 촉매로서 염산을 첨가하였다. 카올리나이트 분말의 소성여부에 따른 영향을 검토하기 위해 카올리나이트와 메타카올리나이트(metakaolinite)를 대상으로 각각 실험하였으며, 반응 혼합물의 몰비, 교반시간, 숙성시간, 결정화 시간과 온도의 변화에 따른 티타니아 결정도를 검토하였다. 실험조건 TIP 0.1 몰(mol), 물 0.15 몰, 염산 0.005 몰, 에탄을 100 ml, 카올리나이트 50 g, 교반 4시간, 숙성 24시간, 결정화온도 $1050^{\circ}C$, 결정화 2시간에서 가장 높은 아나타제 결정도 17.61%를 나타냈다. 결정화온도의 변화에 따른 아나타제 결정도 분석결과, 카올리나이트와 메타카올리나이트 분말에 코팅된 티타니아는 $1050^{\circ}C$와 $1200^{\circ}C$에서 각각 37.61%, 17.39%로 최고의 결정도가 관찰되었다. 즉, 카올리나이트 분말에 코팅된 티타니아가 메타카올리나이트에 비해 더 낮은 온도에서 더 높은 결정도를 나타냈다.

• 대한금속재료학회지
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• 제46권6호
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• pp.351-356
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• 2008

Thermally sprayed tungsten carbide-based powder coatings are being widely used for a variety of wear resistance applications. The coating deposited by high velocity processes such as high velocity oxy-fuel (HVOF) thermal spraying is known to provide improved wear resistant property. In this study, optimal coating process (OCP) is obtained by the study of coating properties such as surface hardness, porosity, surface roughness and microstructure of 9 coatings prepared by Taguchi program for 3 levels of four spray parameters. The Friction and wear behaviors of HVOF WC-CoCr coating prepared by OCP, electrolytic hard chrome (EHC) plating and Inconel718 (In718) are investigated by reciprocating sliding wear test at $25^{\circ}C$, $450^{\circ}C$. Friction coefficients (FC) of all of the 3 samples are decreased as increasing sliding surface temperature from $25^{\circ}C$ to $450^{\circ}C$. FC of WC-CoCr decreases as increasing the surface temperature from $0.33{\pm}0.02$ at $25^{\circ}C$ to $0.26{\pm}0.02$ at $450^{\circ}C$, showing the lowest FC among the 3 samples. Wear trace (WT) and wear depth (WD) of WC-CoCr are smaller than those of EHC and In718 both at $25^{\circ}C$ and $450^{\circ}C$. These show that WC-CoCr is highly recommendable for protective coating on In718 and other metal components.

• 반도체디스플레이기술학회지
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• 제21권3호
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• pp.74-79
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• 2022

In this study, the plasma corrosion resistance and the change in the number of contamination particles generated using the plasma etching process and cleaning process of coating parts for semiconductor plasma etching equipment were investigated. As the coating method, atmospheric plasma spray (APS) was used, and the powder materials were Y₂O₃ and Y₃Al₅O₁₂ (YAG). There was a clear difference in the densities of the coatings due to the difference in solubility due to the melting point of the powdered material. As a plasma environment, a mixed gas of CF₄, O₂, and Ar was used, and the etching process was performed at 200 W for 60 min. After the plasma etching process, a fluorinated film was formed on the surface, and it was confirmed that the plasma resistance was lowered and contaminant particles were generated. We performed a surface cleaning process using piranha solution(H₂SO₄(3):H₂O₂(1)) to remove the defect-causing surface fluorinated film. APS-Y₂O₃ and APS-YAG coatings commonly increased the number of defects (pores, cracks) on the coating surface by plasma etching and cleaning processes. As a result, it was confirmed that the generation of contamination particles increased and the breakdown voltage decreased. In particular, in the case of APS-YAG under the same cleaning process conditions, some of the fluorinated film remained and surface defects increased, which accelerated the increase in the number of contamination particles after cleaning. These results suggest that contaminating particles and the breakdown voltage that causes defects in semiconductor devices can be controlled through the optimization of the APS coating process and cleaning process.

• 한국식품과학회지
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• 제40권6호
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• pp.621-625
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• 2008

오징어 간유 미세캡슐화 분말을 HPMC-FCC, zein-DP로 코팅하여 유동층 코팅 특성을 살펴본 결과, 유동층 코팅 효율은 HPMC-FCC, zein-DP 모두 90%의 효율을 나타내었다. 겉보기 밀도는 zein-DP 코팅분말이 0.6 g/mL로 높게 나타나 코팅 분말의 비중이 커져 흐름성이 개선되었음을 확인할 수 있었다. 인공위액과 인공장액에 대한 용해성을 살펴본 결과, HPMC-FCC는 각각 59.9%와 0%를 나타내었고 zein-DP는 각각 0%와 31.0%를 나타내어 코팅재료에 따라 용해성을 조절할 수 있었다. 저장 안정성은 zein-DP나 HPMC-FCC로 코팅한 분말이 미세캡슐화 분말보다 높은 PUFA/SFA 잔존율을 보여, 유동층 코팅 기술이 유지식품의 안정성을 확보할 수 있는 새로운 기술이 될 수 있음을 확인할 수 있었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.129-129
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• 2018

Hard coating application is effective way of cutting tool for hard-to-machine materials such as Inconel, Ti and composite materials focused on high-tech industries which are widely employed in aerospace, automobile and the medical device industry also Information Technology. In cutting tool for hard-to-machine materials, high hardness is one of necessary condition along with high temperature stability and wear resistance. In recent years, high-entropy alloys (HEAs) which consist of five or more principal elements having an equi-atomic percentage were reported by Yeh. The main features of novel HEAs reveal thermodynamically stable, high strength, corrosion resistance and wear resistance by four characteristic features called high entropy, sluggish diffusion, several-lattice distortion and cocktail effect. It can be possible to significantly extend the field of application such as cutting tool for difficult-to-machine materials in extreme conditions. Base on this understanding, surface coatings using HEAs more recently have been developed with considerable interest due to their useful properties such as high hardness and phase transformation stability of high temperature. In present study, the nanocomposite coating layers with high hardness on WC substrate are investigated using high entropy alloy target made a powder metallurgy. Among the many surface coating methods, reactive magnetron sputtering is considered to be a proper process because of homogeneity of microstructure, improvement of productivity and simplicity of independent control for several critical deposition parameters. The N2 is applied to reactive gas to make nitride system with transition metals which is much harder than only alloy systems. The acceleration voltage from 100W to 300W is controlled by direct current power with various deposition times. The coating layers are systemically investigated by structural identification (XRD), evaluation of microstructure (FE-SEM, TEM) and mechanical properties (Nano-indenter).

• 한국재료학회지
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• 제27권7호
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• pp.374-380
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• 2017

Properties of coatings produced by warm spray were investigated in order to utilize this technique as a repair method for Al tire molds. $Al-(0-10%)Al_2O_3$ composite powder was sprayed on Al substrate by warm spraying, and the microstructure and mechanical properties of the composite coating layer were investigated. For comparative study, the properties of the coating produced by plasma spray, which is a relatively high-temperature spraying process, were also investigated. The composite coating layers produced by the two spray techniques exhibited significantly different morphology, perhaps due to their different process temperatures and velocities of particles. Whereas the $Al_2O_3$ particles in the warm sprayed coating layer maintained their initial shape before the spray, flattened and irregular shape $Al_2O_3$ particles were distributed in the plasma sprayed coating layer. The coating layer produced by warm spray showed significantly higher adhesive strength compared to that produced by plasma spray. Hardness was also higher in the warm sprayed coating layer compared to the plasma sprayed one. Moreover, with increasing the fraction of $Al_2O_3$, hardness gradually increased in both spray coating processes. In conclusion, an $Al-Al_2O_3$ composite coating layer with good mechanical properties was successfully produced by warm spray.

• 한국재료학회지
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• 제24권2호
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• pp.98-104
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• 2014

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.

• 한국세라믹학회지
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• 제53권6호
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• pp.689-699
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• 2016

The effects of composition, structure design, and coating thickness of thermal barrier coating (TBC) on thermal barrier performance were investigated by measuring the temperature differences of TBC samples. TBCs with the thin and thick top coats were used for these studies, including TBCs with rare-earth (Gd, Yb, and La) compositions. The thermal barrier performance was enhanced with increasing the thickness of top coat even for thin TBCs, indicating that the thermal barrier performance was commensurate to the thickness of top coat. On the other hand, the bi-layered TBC, which was prepared with Yb-Gd-YSZ feedstock powder, with the buffer layer of high purity 8YSZ showed a better thermal barrier performance than that of regular purity 8YSZ. The interfaces in the bi-layered TBCs had a decisive effect on the thermal barrier performance, showing the performance enhanced with increasing numbers of interfaces. However, a new structural design and an additional process should be considered to reduce stress concentrations and to ensure interface stability, respectively, for improving thermal durability in the multi-layered TBCs.