• 한국추진공학회지
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• 제19권3호
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• pp.83-88
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• 2015

열차폐 코팅(Thermal Barrier Coating) 기술의 하나로 연구되는 전자빔(EB, Electron Beam) 증착에 사용되는 코팅재료는 증착 공정 중에 고출력의 전자빔이 조사되기 때문에, 균일코팅을 위해서는 증착 중 코팅재료의 형상유지 및 안정한 융탕 형성이 필요하며, 이를 위해 적절한 밀도와 미세구조를 갖춘 잉곳(Ingot) 형태의 코팅소스가 요구된다. 본 연구에서는 8 wt%의 이트리아($Y_2O_3$)가 안정화제로 첨가된 지르코니아(8YSZ) 조성을 활용하여, 고출력 전자빔 조사환경에 사용가능한 잉곳제조를 위해 최적의 원료분말 조건을 확보하고자 하였다. 제조된 잉곳시료들에 대한 전자빔 조사 시, 수십 마이크론과 수십 나노 크기의 입자들로 구성된 혼합형 분말로 제조된 잉곳의 경우, 나노크기의 분말만으로 제조된 경우보다 향상된 열충격 저항성을 보였다.

• 한국표면공학회지
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• 제50권5호
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• pp.352-359
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• 2017

The growth of nanocrystalline diamond films on a p-type poly silicon substrate was studied using microwave plasma chemical vapor deposition method. A 6 mm thick poly silicon plate was mirror polished and scratched in an ultrasonic bath containing slurries made of 30 cc ethanol and 1 gram of diamond powders having different sizes between 5 and 200 nm. Upon diamond deposition, the specimen scratched in a slurry with the smallest size of diamond powder exhibited the highest diamond particle density and, in turn, fastest diamond film growth rate. Diamond deposition was carried out applying different DC bias voltages (0, -50, -100, -150, -200 V) to the substrate. In the early stage of diamond deposition up to 2 h, the effect of voltage bias was not prominent probably because the diamond nucleation was retarded by ion bombardment onto the substrate. After 4 h of deposition, the film growth rate increased with the modest bias of -100 V and -150 V. With a bigger bias condition(-200 V), the growth rate decreased possibly due to the excessive ion bombardment on the substrate. The film grown under -150V bias exhibited the lowest contact angle and the highest surface roughness, which implied the most hydrophilic surface among the prepared samples. The film growth rate increased with the apparent activation energy of 21.04 kJ/mol as the deposition temperature increased in the range of $300{\sim}600^{\circ}C$.

• 대한기계학회논문집A
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• 제41권2호
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• pp.103-109
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• 2017

AMM(Additive Metal Manufacturing)이라 호칭되는 3차원 금속 프린팅(metal 3-D printing) 공정은 금속분말(metal powder)을 적층 재료로 사용하여 기계적부품용 실형상 금속 파트(metallic parts)를 직접 조형하여 제조한다. 한편, 조형 파트형상의 STL모델에 존재하는 기하학적 오류들과 특징형상들의 특이성으로 인하여 조형 작업 중에 내부에 결함들이 포함된 실형상 파트가 조형될 가능성이 존재하게 되며 이로 인해 3차원 금속 프린팅 조형공정 자체의 신뢰성에 문제를 야기할 수 있다. 본 논문에서는 이러한 조형작업 중 발생할 수 있는 결함들을 미리 진단, 분석하고 수정하기 위하여 첫째, 조형 전에 STL 형상모델의 진단분석을 통하여 결함요소를 사전에 탐지하고 둘째, 적층 단면내 조형 공구 경로상에 실제로 포함된 결함들을 분석하고 이를 수정하기 위한 조형 파트 진단 및 조형 공구 경로 검증 연구방법을 제시하였다. 또한 DED(direct energy deposition) 공정을 기준으로 2가지 STL 형상파트 사례들에 대하여 제시한 연구방법의 case study를 수행하였다.

• 한국결정성장학회지
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• 제4권1호
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• pp.92-99
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• 1994

마이크로웨이브 화학 기상 중착법을 이용하여 n 형 Si(100) 기팡위에 다이아몬드 박막을 증착하였다. 다이아몬드의 핵생성 밀도를 향상시키기 위하여 Si 기판을 다이아몬드 분말로 전처리 하거나 negative bias를 인가하여 다이아몬드 박막을 증착하였다. 전처리한 기판에서는 다이아몬드의 순수도가 전체압력이 증가함에 따라 (20~150 Torr)향상되었으며 bias 인가시에는$CH_4$ 농도와 전체압력에 따라 다이아몬드의 생성유무가 결정되었다.플라즈마의 이온에 의해 가판위에 생성되는 전류를 $CH_4$ 농도, bias 전압, 그리고 전체압력에 따라 측정하였으며 그 결과를 다이아몬드 박막의 생성 조건과 관련시켜 검토 하였다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.45-45
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• 2014

The importance of magnesium alloys has significantly increased due to their low density, high strength/weight ratio, very good electromagnetic shielding features and good recyclability. However, unfortunately, Mg alloys are very susceptible to corrosion due to their high chemically activities (= -2.356 V vs. NHE at $25^{\circ}C$), hence, most commercial Mg alloys require corrosion protective coatings. Organic coating such as painting, powder coating and electrophoretic deposition of paint (E-paint) is typically used in the final stages of the coating process of Mg alloys. In this study, effect of pre-immersion time on the deposition of E-paint on AZ31 Mg alloy was investigated. It was found that during pre-immersion time, AZ31 Mg alloy rapidly reacts with E-paint solution and paint can be self-deposited on the AZ31 surface without applying of electric current. The pore size on the E-painted AZ31 Mg alloy increased with increasing pre-immersion time from 0 to 5 min. Both adhesion and corrosion resistance of E-painted AZ31 Mg alloy decreased with increasing pre-immersion time. The best E-paint AZ31 Mg alloy, which showed stronger adhesion after water immersion test and good corrosion resistance, was started to deposit after 5 s of pre-immersion time.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.570-574
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• 1999

In this paper, by using the electrophoresis, preparation of YBCO superconducting wire deposited on metal Ag base wire was studied with its Properties. YBCO Powder could be prepared by solid state reactions with calcining and sintering processes. Superconducting wire prepared on metal Ag wire used as cathode of deposition base could be also fabricated in the YBCO/acetone-dispersed solution to obtain several tens of re thick films. And then it could be used as superconducting wire for measurement after calcination, sintering and oxygen absorption processes. In the process of film deposition, a catalyst I$_2$added into the suspension solution was very useful for preparing thick film of YBCO, and BaF$_2$ of additive material was also necessary for preparing crack-free wire of YBCO superconductor. As a result, YBCO superconducting wire added 2~3wt.% of BaF$_2$\ulcorner with catalyst, 12 had better deposition condition for uniform and dense YBCO wires, and critical current density, Jc was calculated at the value of 1,458A/$\textrm{cm}^2$(more than 10$^{3}$A/$\textrm{cm}^2$ ,77K, o[T]) of 30${\mu}{\textrm}{m}$ thick sample by 4 point prove method.

• 한국방사선학회논문지
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• 제15권5호
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• pp.697-704
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• 2021

3D 프린팅 FDM방식의 재료인 필라멘트 중 차폐성능을 지닌 필라멘트는 국내에 판매되지 않고 있으며 관련 연구도 미비하다. 이에 본 연구는 금속 입자가 함유된 필라멘트의 물성과 방사선의 차폐능력을 평가하여 3D 프린트를 이용한 방사선 차폐체 개발의 기초자료를 제공하고자 한다. 금속입자 강화재가 함유된 금속 필라멘트 5가지를 선정 후 ASTM의 평가방법을 이용하여 인장강도, 밀도, XRD, 무게측정 등 물성을 평가하고 방사선 차폐능력을 알아보기 위하여 한국산업표준의 방호용구류 시험방법에 따라서 방사선 차폐율을 구하였다. 인장강도는 PLA + SS가 가장 높았고 ABS + W가 가장 낮았으며 밀도는 ABS + W 가 3.13 g/cm3으로 가장 높게 나타났다. XRD결과 시편의 표면의 입자의 XRD peak 패턴이 각 입자 강화재 분말 금속의 패턴과 일치함을 확인 할 수 있어 프린트된 시편이 분말금속이 함유 되었음을 확인하였다. 3D 프린트 복합 필라멘트별 차폐효과는 ABS + W, ABS + Bi, PLA + SS, PLA + Cu, PLA + Al의 순서로 실효원자번호와 밀도에 비례하여 차폐율이 높게 나타났다. 본 연구에서는 강화재로 금속 분말이 함유된 금속입자 복합 필라멘트는 방사선의 차폐능력을 가지는 것이 확인되었으며 향후 방사선 차폐용 필라멘트의 사용가능성을 확인하였다.

• 한국세라믹학회지
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• 제47권6호
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• pp.485-490
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• 2010

In our previous studies, continuous SiC fiber-reinforced SiC-matrix composites ($SiC_f$/SiC) had been fabricated by two different slurry infiltration methods: vacuum infiltration and electrophoretic deposition (EPD). 12 wt% of $Al_2O_3-Y_2O_3$-MgO with respect to SiC powder was used as additives for liquid-phase assisted sintering. After hot pressing at $1750^{\circ}C$ under 20 MPa for 2 h in Ar atmosphere, a high composite density could be achieved for both cases, whereas the problems such as large grain size and non-uniform distribution of liquid phase were observed, which was resulted in the relatively poor mechanical properties of composites. Therefore, efforts have been made to reduce the grain growth during the sintering, including the optimization for hot pressing condition and utilization of spark plasma sintering using a SiC monolith. Based on the results, spark plasma sintering was found to be effective method in decreasing the amount of sintering additive, time and grain growth, which will be explained in comparison to the results of hot pressing in this paper.

• 한국분말재료학회지
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• 제31권2호
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• pp.152-162
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• 2024

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150℃ under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10^-2/m²) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

• 한국분말재료학회지
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• 제15권1호
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• pp.1-5
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• 2008

ZnS-$SiO_2$ composite is normally used for sputtering target. In recent years, high sputtering power for higher deposition rate often causes crack formation of the target. Therefore the target material is required that the sintered target material should have high crack resistance, excellent strength and a homogeneous microstructure with high sintered density. In this study, raw ZnS and ZnS-$SiO_2$ powders prepared by a 3-D mixer or high energy ball-milling were successfully densified by spark plasma sintering, the effective densification method of hard-to-sinter materials in a short time. After sintering, the fracture toughness was measured by the indentation fracture (IF) method. Due to the effect of crack deflection by the residual stress occurred by the second phase of fine $SiO_2$, the hardness and fracture toughness reached to 3.031 GPa and $1.014MPa{\cdot}m^{1/2}$, respectively.