• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2006년도 춘계학술발표회 초록집
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• pp.81-81
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• 2006

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1997년도 특별강연 및 추계학술발표 개요집
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• pp.119-121
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• 1997

No Abstract, See Full Text

• 한국표면공학회지
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• 제26권4호
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• pp.192-202
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• 1993

The characteristics of the high-performance ceramic coatings fabricated on the optimum processings con-ditions for the atmospheric plasma spraying are evaluated by various material tests and analyses. The opti-mum processing parameters for the plasma spraying are determined by using the two-level orthogonal arrays of fractional factorial testing method as a statistical approach. Material tests for the coating specimens are carried out to evaluate microstructure, hardness, adhesion strength, and deposition efficiency. The properties of Al2O3-13%TiO2 coating are discussed with regard to the effective processings parameters. The decarburization effects of WC-12%Co coating is examined by XRD analysis in terms of the arc power and the secondary gas species. The hardness of Al2O2-13%TiO2 coating is increased with the arc power and shows the maximum value at around 40 lpm of Ar gas flowrate, which appears to be the most critical parame-ter on the deposition efficiency. For reducing the decarburization of WC-12%Co coating, the injection of inert He gas instead of reactive H2 gas as a secondary gas is more effective than the dropping of arc power to lessen the plasma enthalpy.

• 한국분말재료학회지
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• 제23권5호
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• pp.364-371
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• 2016

This study investigates the thermal shock property of a polycrystalline diamond compact (PDC) produced by a high-pressure, high-temperature (HPHT) sintering process. Three kinds of PDCs are manufactured by the HPHT sintering process using different particle sizes of the initial diamond powders: $8-16{\mu}m$ ($D50=4.3{\mu}m$), $10-20{\mu}m$ ($D50=6.92{\mu}m$), and $12-22{\mu}m$ ($D50=8.94{\mu}m$). The microstructure observation results for the manufactured PDCs reveal that elemental Co and W are present along the interface of the diamond particles. The fractions of Co and WC in the PDC increase as the initial particle size decreases. The manufactured PDCs are subjected to thermal shock tests at two temperatures of $780^{\circ}C$ and $830^{\circ}C$. The results reveal that the PDC with a smaller particle size of diamond easily produces microscale thermal cracks. This is mainly because of the abundant presence of Co and WC phases along the diamond interface and the easy formation of Co-based (CoO, $Co_3O_4$) and W-based ($WO_2$) oxides in the PDC using smaller diamond particles. The microstructural factors for controlling the thermal shock property of PDC material are also discussed.

• 한국재료학회지
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• 제13권12호
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• pp.839-845
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• 2003

The abrasion and impact wear resistance were investigated on the hardfacing weld dispersed with the recycled hard metal(HM). The HM was composed of the tungsten carbide(WC) reinforced metal matrix composite. The cored wire filled with the 25-35wt.% HM and 2-8wt.% of the alloying element, Fe-75Mn- 7C(FeMnC), was used for the gas metal arc(GMA) welding. By using the cored wire of the 25wt.% HM and FeMnC addition, the weld showed mostly constant wear loss for the abrasion as a function of the FeMnC content. This was due to the insufficient amount of the tungsten carbide formed during the GMA welding. The FeMnC addition to the 35wt.% HM did not improve the abrasion wear property since the amount of the tungsten carbide formed was decreased with respect to the FeMnC amount. The 6wt.% FeMnC addition to the 35wt.% HM exhibited the better impact wear resistance than the hardfacing weld by 40wt.% HM.

• 한국재료학회지
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• 제11권11호
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• pp.953-959
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• 2001

Homogeneous spherical W-Co salt powders were made by spray drying of aqueous solution of ammonium $metatungstate(NH_4)_6(H_2W_{12}O_{40}){\cdot}4H_2O,\; AMT)$ and cobalt nitrate $hexahydrate(Co(NO_3)_2{\cdot}6H_2O)$. The thermal decomposition process of spray dried W-Co salt powders was studied by TG, XRD, SEM, TEM and FT-IR. Spray dried W-Co salt powders were calcined for 1 hour in the temperature from$ 350^{\circ}C$ to $800^{\circ}C$ in atmosphere of air. At the temperatures over $600^{\circ}C$, spherical $CoWO_4/WO_3$ composite oxide powders were obtained. The primary particle size of W/Co composite oxide powders increased with increasing thermal decomposition temperature due to the particle growth. The observed crystallite size by TEM was in the range of 60nm and that of $CoWO_4$ calculated by Scherrer's formula at $800^{\circ}C$ was smaller than 55nm. The crystallite site was identified by XRD and TEM.

• 한국표면공학회지
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• 제40권1호
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• pp.23-31
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• 2007

The objective of this study is to investigate the effect of Al addition on the reaction behavior of cobalt with molten zinc. Pure cobalt specimen was immersion tested in the three kinds of molten zinc (pure, 0.12%Al added and 0.24%Al added) baths at $460^{\circ}C,\;490^{\circ}C\;and\;520^{\circ}C$. For the understanding of degradation processes, specimens were analyzed with scanning electron microscope (SEM) and energy dispersive spectrum (EDS), and electrochemical stripping method. When 0.12% and 0.24% Al was added in molten zinc baths, three intermetallic compounds layers of ${\gamma},\;{\gamma}_1,\;and\;{\gamma}_2$ were formed on the Co matrix and ${\beta}_1$ layer was not formed between the Co matrix and the ${\gamma}$ layer. Particles of CoAl intermetallic compound were formed at the interface between the ${\gamma}_2$ layer and zinc melt and they did not adhere to the Co-Zn intermetallic layer. Weight loss of the Co specimen increased as Al content in the molten zinc increased and the relationship of weight loss vs. immersion time followed parabolic rate law. Rate controlling process for the reaction rate of Co with Al added molten zinc was analyzed as the diffusion process of Al atom through a boundary layer between the ${\gamma}_2$ layer and the Al added zinc melt.

• 대한기계학회논문집
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• 제18권12호
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• pp.3175-3184
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• 1994

The high strength and wear-resistant metal bonded diamond wheel was applied to the drilling process of carbon fiber reinforced plastics (CFRP), The helical-feed drilling method was use for the first time to overcome the limit of drilling depth of the conventional drilling process and to improve the dressing of the wheel. The helical-feed drilling method was found effective at high cutting speed without the limit of drilling depth.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.370-370
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• 2010

최근 자연모사를 통한 초저마찰 연구가 활발히 진행되고 있으며 리소그라피, 레이져 가공법 등의 다양한 방법을 통해 표면구조 제어가 시도되고 있다. 본 연구에서는 자장여과 아크 플라즈마 이온 소스를 이용한 WC-Co 및 SCM 415 금속소재의 표면구조 형상제어를 통해 저마찰 특성을 시도하였다. 자장여과 아크 소스는 90도 꺽힘형이며 5개의 자장 코일을 통해 아크 음극에서 발생된 고밀도($10^{13}\;cm^{-3}$ 이상) 플라즈마를 표면처리 대상 기판까지 확산시켰다. 공정 압력은 알곤가스 1 mTorr, 아크 방전 전류는 25 A, 플라즈마 수송 덕트 전압은 10 V이다. 기판 전압은 비대칭 펄스 (-80 %/+5 %)로 -600 V에서 -800 V까지 인가되었으며 -600 V 비대칭 펄스 인가시기판으로 입사하는 알곤 이온 전류 밀도는 약 $4.5\;mA/cm^2$ 이다. WC-Co 시편의 경우 -600 V 전압 인가시, 이온빔 처리 전 46.4 nm(${\pm}12.7\;nm$)의 조도를 갖는 시편이 5분, 10분, 20분동안 이온빔 처리함에 따라 72.8 nm(${\pm}3\;nm$), 108.2 nm(${\pm}5.9\;nm$), 257.8 nm(${\pm}24.4\;nm$)의 조도를 나타내었다. SCM415 시편의 경우 -800 V 인가시, 이온빔 처리 전 20.4 nm(${\pm}2.9\;nm$)의 조도를 갖는 시편이 20분동안 이온빔 처리함에 따라 275.1 nm(${\pm}43\;nm$)의 조도를 나타내었다. 또한 주사전자현미경을 통한 표면 형상 관찰 결과, 이온빔 식각을 통해 생성된 거친 표면에 $3-5\;{\mu}m$ 직경의 돌기들이 산발적으로 생성됨을 확인했다. 마찰계수 측정 결과 SCM415 시편의 경우, 이온빔 처리전 마찰계수 0.65에서 조도 275.1 nm 시편의 경우 0.48로 감소하였다. 본 연구를 통해 이온빔 식각을 이용한 금속표면 제어 및 저마찰 특성 향상의 가능성을 확인하였다.

• 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.