• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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• pp.660-664
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• 2008

Titanium nitride (TiN) thin films are widely used for hard coatings due to their superior hardness, chemical stability, low friction and good adhesion properties. In this study, we investigated the effect of DC power on the characteristics of TiN thin films deposited on Si and glass substrates by DC magnetron sputtering using TiN target. We made TiN films of 300 nm thickness with various DC powers. The structural properties of films are investigated by x-ray diffractions (XRD) and tribological properties are measured by nano-indentation, nano-scratch tester. The rms roughness was measured by atomic forced microscopy (AFM). In the result, TiN films had the smooth surface and exhibited (111) directions with the increase of DC Power. Also, especially in case of 175 W DC power, TiN film exhibited the maximum hardness about 8 GPa, and the critical load near 25.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.852-858
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• 2007

This paper investigates the dynamic characteristics of a tilted HDD spindle system with fluid dynamic bearings (FDBs). Tilting motion of a HDD spindle system may be caused by improper manufacturing tolerance, such as imperfect cylindricity between shaft and sleeve of FDBs, imperfect perpendicularity between shaft and thrust as well as the gyroscopic moment of the unbalanced mass of the rotating part. Tilting motion may result in the instability of the HDD spindle system and it may increase the disk run-out to limit memory capacity. This research proposes a modified Reynolds equation for the coupled journal and thrust FDBs to include the variable film thickness due to the cylindricity and the perpendicularity. Finite element method is used to solve the Reynolds equation for the pressure distribution. Reaction forces and friction torque are obtained by integrating the pressure and shear stress, respectively. The dynamic behavior is determined by solving the equations of a motion of a HDD spindle system in six degrees of freedom with the Runge-Kutta method to study whirling and tilting motions. This research shows that the cylindricity and the perpendicularity increase the tilting angle and whirl radius of the rotor.

• Tribology and Lubricants
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• v.30 no.1
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• pp.1-8
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• 2014

In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

• Tribology and Lubricants
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• v.24 no.6
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• pp.285-290
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• 2008

The purpose of this paper is to present the case study of tribological failure analysis on the gear damages, oil leakage, and sealant sealing in a manual transmission of front engine and front wheel drive vehicle. The manual transmission is to change the speed range and direction of the engines depending on the driving conditions by friction driving forces with input and output gear system. The material property and surface roughness of the gears are strongly related to the gear noise and micro-vibration, oil leakage and wear, which may decrease the real contact area of the gear and the strength of the oil film thickness between the driving gear and driven one. The O-ring damage of speedometer driven gear and bad sealant sealing of oil pan may produce oil leakage through the contact surfaces, which cause the oil shortage and seizure on the sliding surfaces of the transaxle gears. In the failure case study, the proper repair working and good lubrication are very important for the long life of the transaxle without any tribological failures and oil leakage.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.2
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• pp.91-97
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• 2000

The structure and mechanical properties of TiN and TiCN thin films deposited on STD61 steel substrates by the RF-sputtering methods has been studied by using XPS, XRD, micro-hardness tester, scratch tester, and wear-resistance tester. XPS results showed that the TiCN thin film formed with chemical bonding state. The TiN thin films grew with (111) orientation having the lowest strain energy by compressive stress, whereas the TiCN thin films grew with both (111) and (200) orientation, but (200) orientation having the lowest surface energy becomes dominant as carbon contents increase. The pre-etching treatment of substrate did not affect on the preferred orientation of thin films, but it played an important role in improving mechanical properties of thin films such as the hardness, adhesion and wear- resistance. Especially, the TiCN thin films showed the superior wear resistances due to high hardness and low friction coefficient compared with TiN thin films.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.481-486
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• 1997

The interfacial shear stress is experimentally investigated for co-current air-water stratified flow in inclined rectangular channels having a length of 1854mm, width of 120mm and height of 40mm at almost atmospheric pressure. Experiments are carried out in several inclinations from $0^{\circ}\;up\;to\;10^{\circ}$. The local film thickness and the wave height are measured at three locations, i.e., L/H = 8,23, and 40. According to the inclination angle, the experimental data are categorized into two groups; nearly horizontal data group ($0^{\circ}\;{\leq}\;{\theta}\;{\leq}\;0.7^{\circ}$), and inclined channel data group ($0.7^{\circ}\;{\leq}\;{\theta}\;{\leq}\;10^{\circ}$). Experimental observations for nearly horizontal data group show that the flow is not fully developed due to the water level gradient and the hydraulic jump within the channel. For the inclined channel data group, a dimensionless wave height, $\Delta$h/h, is empirically correlated in terms of $Re_{G}$ and h/H. A modified root-mean-square wave height is proposed to consider the effects of the interfacial and wave propagation velocities. It is found that an equivalent roughness has a linear relationship with the modified root-mean-square wave height and its relationship is independent of the inclination.

• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.375-380
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• 2007

Tribological properties of carbon layers produced by high temperature chlorination of SiC ceramic and DLC (diamond-like carbon) coatings produced by ion plating method were investigated and compared. Carbon coatings were produced by exposure of ball and disc type SiC in chlorine and hydrogen gas mixtures at $1200^{\circ}C$. After treatment for 10 h, dense carbon films up to $180{\mu}m$ in thickness were formed. Tribological behavior of newly developed carbon films were compared with that of DLC films. Wear resistance and frictional coefficient of the surface modified ball and disc type SiC were significantly improved compared to an untreated SiC specimen, and also the modified carbon layer had better performance than DLC coatings. Therefore, in this study, the newly developed carbon films have several advantages over existing carbon coatings such as DLC coatings and showed superior tribological performances.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.2
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• pp.63-67
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• 2018

Recent mold industry uses many roll-to-roll processes that can produce high production speed and precision machining and automation process. In the circular cylinder mold, however, patterns of less than $10{\mu}m$ are difficult to manufacture and maintain. In this study, we fabricated a circular cylindrical mold with a DLC thin film which have high hardness, low coefficient of friction and high releasability by using lithography and lift-off process. The height, line width, and pitch of the fabricated DLC macro pattern are $3.1{\mu}m$, $9.1{\mu}m$ and $20.2{\mu}m$, respectively. The pattern size is finer than the current applied to the aluminum cylinder type, and this shows the possibility of practical use of DLC micro pattern roll mold.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.10a
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• pp.177-178
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• 2009

DLC (Diamond-like Carbon) 코팅막은 저마찰, 고경도, 낮은 표면조도 등의 우수한 특성을 갖는 박막 물질로 다양한 산업분야에서 그 코팅막의 활용을 목적으로 응용연구가 활발하게 이루어지고 있다. 본 연구에서는 플라즈마 화학기상증착(PCVD) 공정을 이용하여 바이어스, 진공도, 공정 온도 등의 코팅 조건 변수를 이용하여 DLC 코팅막을 제작하였다. 또한, 코팅막은 공정 조건에 따라 증착속도, 표면 및 단면 조직, 밀착력, 경도, 마찰계수 등의 특성을 평가하였다. 플라즈마 화학기상증착법을 이용한 DLC 코팅막 제조는 상온과 $175^{\circ}C$에서 이루어졌으며, 저온 중 DLC 코팅막 제조가 가능해짐에 따라 고분자 와 같은 저융점을 갖는 피처리물의 코팅처리가 가능하여 산업적 응용의 확대가 기대된다. SEM 표면 조직 관찰에 따른 DLC 코팅막의 표면조직과 조도는 공정조건에 따라 큰 차이는 보이지 않았지만, 밀착력에 있어서는 매우 큰 차이를 나타내었다. 스크래치 시험 결과 가장 높은 밀착력은 100 N 이상을 나타내었으며, 이 때의 마찰계수는 약 0.02를 나타내었다. 가장 낮은 마찰계수는 약 0.01을 보였으며, 이때의 밀착력은 25 N을 나타내었다. 증착속도는 바이어스 전압의 증가에 따라 증가하는 경향을 나타내었으며, 온도의 증가에 따라 감소하는 경향을 나타내었다.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.445-452
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• 2019

Gel-type biopolymers have recently been introduced as environmentally friendly soil binders and have shown substantial strengthening effects in laboratory experimental programs. Although the strengthening effects of biopolymer-treated sands have been verified in previous direct shear tests and uniaxial compression tests, there has been no attempt to examine shear behavior under different confining stress conditions. This study therefore aimed to investigate the strengthening effects of biopolymer-treated sand using laboratory triaxial testing with a focus on confining pressures. Three representative confining pressure conditions (${\sigma}_3=50kPa$, 100 kPa, and 200 kPa) were tested with varying biopolymer contents ($m_{bp}/m_s$) of 0.5%, 1.0%, and 2.0%, respectively. Based on previous studies, it was assumed that biopolymer-treated sand is susceptible to hydraulic conditions, and therefore, the experiments were conducted in both a hydrated xanthan gum condition and a dehydrated xanthan gum condition. The results indicated that the shear resistance was substantially enhanced and there was a demonstrable increase in cohesion as well as the friction angle when the biopolymer film matrix was comprehensively developed. Accordingly, it can be concluded that the feasibility of the biopolymer treatment will remain valid under the confining pressure conditions used in this study because the resisting force of the biopolymer-treated soil was higher than that in the untreated condition, regardless of the confining pressure.