• Corrosion Science and Technology
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• 제18권5호
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• pp.212-219
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• 2019

This paper reviews recent approaches to develop composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE). The features of the unique approaches to form the composite polymer-containing coating on the surface of MA8 magnesium alloy were summarized. Improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of the surface layers and solid lubrication effect of the SPTFE particles. Such multifunctional coatings have high corrosion resistance ($R_p=3.0{\times}10^7{\Omega}cm^2$) and low friction coefficient (0.13) under dry wear conditions. The effect of dispersity and ${\xi}$-potential of the nanoscale materials ($ZrO_2$ and $SiO_2$) used as electrolyte components for the plasma electrolytic oxidation on the composition and properties of the coatings was investigated. Improvement in the protective properties of the coatings with the incorporated nanoparticles was explained by the greater thickness of the protective layer, relatively low porosity, and the presence of narrow non-through pores. The impedance modulus measured at low frequency for the zirconia-containing layer (${\mid}Z{\mid}_{f=0.01Hz}=1.8{\times}10^6{\Omega}{\cdot}cm^2$) was more than one order of magnitude higher than that of the PEO-coating formed in the nanoparticles-free electrolyte (${\mid}Z{\mid}_{f=0.01Hz}=5.4{\times}10^4{\Omega}{\cdot}cm^2$).

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.212-212
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• 2014

0.04% Gd-duplex stainless steels (Gd-DSTSs) for neutron absorbing materials were inert arc-melted and poured into a Y-shape block with the size of $100{\times}100{\times}20[mm]$. The Gd-DSTS was hot rolled at $1200^{\circ}C$ followed by cold rolling to have 33% reduction. The average grain sizes of the rolling (RD), transverse (TD) and short transverse (ST) directions were 6, 7, $11{\mu}m$, respectively. The micro-hardnesses of the RD, TD and ST directions were 258.5, 292.3, 314.7 $H_V$, respectively. Corrosion potential and corrosion rate of the cold rolled Gd-duplex stainless steel in aerated artificial sea water and 0.1M $H_2SO_4$ solution were $0.2216V_{SHE}$, $0.0106A/cm^2$, $-0.0825V_{SHE}$, $0.0168A/cm^2$ for RD, $0.2210V_{SHE}$, $0.0077A/cm^2$, $0.0817V_{SHE}$, $0.0092A/cm^2$ for TD, $0.1056V_{SHE}$, $0.0059A/cm^2$, $0.0475V_{SHE}$, $0.0069A/cm^2$ for ST, respectively. The corrosion behavior depended on the texture, which were due to mainly grain boundary and minorly crystallographic texture. Friction coefficient and wear resistance were 2.07 and 0.48 mm, respectively.

• Journal of Advanced Marine Engineering and Technology
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• 제36권1호
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• pp.78-84
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• 2012

금형의 공정 과정에서 금형과 성형품 사이에서 발생하는 마찰로 인해 발생하는 금형의 마모가공차로 작용하여 성형 품질을 저하시킬 수 있다. 따라서 금형의 내마모성을 향상시키기 위해 질화나 침탄처리, 화염 및 고주파 표면처리 등의 방법들이 적용되어 왔다. 하지만 형상의 제한이나 제품의 변형 등과 같은 문제점을 수반하고 있기 때문에, 이러한 문제점을 해결할 수 있는 표면처리 방법으로써 레이저 표면처리 기술이 검토되고 있다. 따라서 본 연구에서는 고출력 다이오드 레이저를 이용, 금형재료용 주철의 표면처리를 시도하였다. 앞서 제1보와 제2보의 논문에서는 금형의 재료 및 형상의 차이에 따른 열처리 특성을 비교하였다면, 본 논문에서는 열처리 후 생성되는 경화부, 경계부위 및 모재의 조직적 차이를 분석하기 위해 광학 현미경 및 전자 현미경을 이용하여 미세조직을 관찰하고, EDS를 통해 조직의 상태를 파악하였다. 미세조직 관찰 결과, 경화부는 침상의 마르텐사이트 조직이 형성되어 있었다.

• 한국정밀공학회지
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• 제28권9호
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• pp.1078-1085
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• 2011

Prediction of a minimum crack size for growth, which is defined as a crack size that grows fast enough to keep ahead of its removal by contact wear and periodic grinding, is the most demanding work to prevent rail from fatigue failure and develop cost effective railway maintenance strategy In this study, we investigated the wheel load increment due to a rail defect during a train ran over it, and its effect on the minimum crack size for growth. For this purpose, we developed simulation software based on the Fletcher and Kapoor's "2.5D" model and measured wheel load increment during a train passed over a defect. A maximum contact pressure and contact patch size were calculated by 3D FEM and crack growth analyses were performed by varying two of dominant contact contributors; surface friction coefficient(0.1, 0.2, 0.3 and 0.4) and crack aspect ratio. The minimum crack sizes for growth were calculated from 0.29 to 1.44mm depending on the contact conditions. They were decreasing with increasing surface friction coefficient and decreasing with crack aspect ratio(a/b).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.397-397
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• 2007

Diamondlike carbon (DLC) coatings were deposited on alumina ceramic seals using a plasma immersion ion deposition technique (PIID). Then they were subjected to tribological tests using a pin-on-disc tribometer under a high load (1.3 GPa) and under elevated temperatures up to 400C. Coefficients of friction (COFs) were recorded and compared with that of the untreated alumina while the wear tracks were analyzed using SEM with EDS to characterize the DLC films. To enhance the DLC adhesion to the substrate, various interlayers including Si and Cr were deposited using the PIID process or an ion beam assisted deposition (IBAD) method. It was observed that the DLC coating, if adhering well to the substrate, reduced the COFs significantly, from 0.4-0.8 for the uncoated alumina to about 0.05-0.1, within the tested temperature range. The adhesion was determined by the interlayer type and possibly by the application method. Cr interlayer did not perform as well as the Si interlayer. This could also be due to the fact that the Cr interlayer and the subsequent DLC coating had to be done in two different processing systems, while both the Si interlayer and the subsequent DLC film were deposited in one system without breaking the chamber. The coating failure mode was found to be delamination between the Cr and the alumina substrate. In contrast, the Si interlayer with proper DLC deposition procedures resulted in very good adhesion and hence excellent tribological performance. Further study may lead to future DLC applications of ceramic seals.

• 한국산학기술학회논문지
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• 제20권4호
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• pp.510-516
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• 2019

본 논문에서는 사용자의 동작을 측정하고 물리적인 변화를 사용자에게 느끼게 하여 실제 스노우보드를 즐기는 것 같은 스노우보드 시뮬레이터를 개발하였다. 스노우보드는 사용자의 무게중심에 따라 속도와 방향이 결정된다. 개발된 시뮬레이터는 스노우보드 플레이트에 4개의 스프링을 장착하여 사용자의 무게 중심의 변화에 따라 기울기를 변화시켜 스노우보드의 기울기 변화를 직접 느낄 수 있게 하였다. 사용자의 무게중심의 변화에 따른 기울기는 3축 가속도센서를 사용하여 측정하였다. 스노우보드의 회전에 따라 발생하는 슬로프의 마찰을 BLDC 모터를 사용하여 사용자가 느낄 수 있도록 하였고, 스노우보드의 회전은 홀센서를 사용하여 측정하였다. 시뮬레이터의 빠른 데이터 처리를 위해 두 개의 MCU를 사용하여 가속도 센서와 모터를 별도로 사용하여 측정된 데이터를 PC로 전송하였다. 개발된 시뮬레이터는 슬로프의 경사 및 마찰을 직접 경험할 수 있으며, 측정된 데이터와 HMD를 착용하여 보다 현실감이 있는 스노우보드를 즐길 수 있도록 하였다.

• 대한치과보철학회지
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• 제55권3호
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• pp.311-318
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• 2017

임플란트 지지 혹은 유지 피개 의치에서 다양한 종류의 유지 장치가 사용되어 왔다. Locator는 stud type의 유지 장치 중 하나로 널리 사용되어 왔으나 그 matrix는 탄성을 가지며 쉽게 마모되는 경향이 있어, 보철물 장착 후 빈번한 유지 관리가 필요하다. 이러한 문제점을 해결하기 위하여 새로운 유지 장치의 도입이 요구되었다. 본 증례에서는 새로운 ball type 유지 장치인 Air Gap attachment (AGA)를 이용한 피개의치로 수복한 증례를 보고하고자 한다. AGA는 금속으로 제작되어 다른 탄성 유지 장치에 비해 마모 저항성이 높다. 그럼에도 불구하고, 의치가 움직일 때 일정한 간극을 통해 움직임을 허용함으로써 stress breaker로의 역할이 가능하도록 하였다. 또한 기존에 식립된 임플란트와 자연치 모두 AGA와 연결이 용이하여 다른 unsplinted type의 유지 장치를 대체할 수 있다. AGA를 이용한 피개의치에서 기능, 심미 및 유지력의 면에서 만족할 만한 결과를 얻어 이를 보고하는 바이며, 장기간의 경과 관찰을 요한다.

• Transactions on Electrical and Electronic Materials
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• 제8권1호
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• pp.5-10
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• 2007

Using a reference slurry, ammonium dodecyl sulfate (ADS), an anionic and environmentally friendly surfactant, was investigated as an alternative to BTA for its inhibition and lubrication characteristics. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA. Coefficient of friction (COF) was the lowest when the slurry contained ADS. This suggested that adsorbed ADS on the surface provided lubricating action thereby reducing the wear between the contacting surfaces. Temperature results were consistent with the COF and removal rate data. ADS showed the lowest temperature rise again confirming the softening effect of the adsorbed surfactant layer and less energy dissipation due to friction. Spectral analysis of shear force showed that increasing the pad-wafer sliding velocity at constant wafer pressure shifted the high frequency spectral peaks to lower frequencies while increasing the variance of the frictional force. Addition of ADS reduced the fluctuating component of the shear force and the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer. By contrast, in the case of BTA, there were no such observed benefits but instead undesirable effects were seen at some polishing conditions. This work underscored the importance of real-time force spectroscopy in elucidating the adsorption, lubrication and inhibition of additives in slurries in CMP.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권3호
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• pp.149-155
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• 2006

This paper presents a torsional micromirror detached from PZT actuators (TMD), whose rotational motion is achieved by push bars in the PZT actuators detached from the micromirror. The push bar mechanism is intended to reduce the bending, tensile and torsional constraints generated by the conventional bending bar mechanism, where the torsional micromirror is attached to the PZT actuators (TMA). We have designed, fabricated and tested prototypes of TMDs for single-axis and dual-axis rotation, respectively. The single-axis TMD generates the static rotational angle of $6.1^{\circ}$ at 16 VDC, which is 6 times larger than that of single-axis TMA, $0.9^{\circ}$. However, the rotational response curve of TMD shows hysteresis due to the static friction between the cover and the push bar in the PZT actuator. We have shown that 63.2% of the hysteresis is due to the static friction caused by the initial contact force of the PZT actuaor. Without the initial contact force, the rotational response curve of TMD shows linear voltage-angle characteristics. The dual-axis TMD generates the static rotational angles of $5.5^{\circ}$ and $4.7^{\circ}$ in x-axis and y-axis, respectively at 16 VDC. The measured resonant frequencies of dual-axis TMD are $2.1\pm0.1$ kHz in x-axis and $1.7\pm0.1$ kHz in y-axis. The dual-axis TMD shows stable operation without severe wear for 21.6 million cycles driven by 16 Vp-p sinusoidal wave signal at room temperature.

• 대한치과보철학회지
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• 제56권4호
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• pp.368-374
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• 2018

본 증례의 환자는 약 10여년 전 2개의 임플란트를 이용하여 Gold Hader bar 하악 임플란트 피개 의치로 수복하였고, 3년 6개월의 사용으로 인한 bar의 심한 마모로 유지력을 상실하였다. 이를 Locator 부착장치를 이용하여 하악 피개 의치를 수리하였으나, Locator 사용 6년 6개월 후 male 부위가 완전히 닳은 상태로 내원하게 되었다. 다음으로는 하이브리드 이중관(Hybrid telescopic double crown with friction pin)을 사용하여 임플란트 피개 의치를 새로 제작하였고, 이를 2년동안 관찰한 결과 우수한 예후를 보여주고 있다. 여기에서 한 환자에서 2가지(Gold Hader bar, Locator)방법으로 수복한 임플란트 피개 의치에서 각 부착장치의 실패원인에 대해서 알아보고, 이중관 피개 의치의 장단점과 성공을 위한 조건에 대해서 보고하고자 한다.