• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.916-921
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• 2009

In this study, lubrication characteristics of sliding members were compared with the change of the hardness of friction surfaces and the application of nano-oil. The materials of the specimens were gray cast iron (AISI 35, AISI 60) and nickel chromium molybdenum steel (AISI 4320). The Friction coefficients and the temperature variations of on the frictional surfaces were measured by disk-on-disk tribotester under the condition of fixed rotating speed. The friction surfaces were observed by scanning electron microscope (SEM). In the results, the friction coefficients of the disk surface were increased as hardness difference was increased. The friction coefficient lubricated in nano-oil was less than mineral oil. This is because a spherical nano particle plays a tiny ball bearing between the frictional surfaces, improved the lubrication characteristics.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.130-130
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• 2000

타이타늄(CP Ti)과 타？늄합금은 인체의 골격을 구성하고 있는 물질과 가장 흡사한 물리적 성질과 우수한 생체적합성으로 인해 임플란트용 재료로 많이 사용되고 있으며, 최근에 인공관절이나 치근으로의 사용이 증가하고 있다. 그러나 교합면에서의 취약한 마모특성으로 인해 wear debris에 의한 골 흡수 및 이완 등을 야기하는 문제점으로, 이의 개선에 관한 연구가 활발히 진행되어 왔다. 다이아몬드상 카본 (Diamond-Like-Carbon) 박막은, 다이아몬드와 유사한 높은 경도, 내마모성 그리고 화학적 안정성 등의 매우 우수한 물리화학적 특성을 가지고 있는 박막재료로 고체 윤활박막으로서 hard disk나 VCR head drum의 보호막, 우주항공기의 bearing 재료코팅 등으로의 적용이 최근에 급격히 증가하고 있다. 본 연구에서는 이와 같은 특성을 지닌 다이아몬드상 카본 박막의 생체재료로의 적용을 위해, CP Ti과 Ti-6Al-4V에 13.56MHz를 사용하는 r.f PACVD법으로 DLC를 증착하여 생체적합적 특성을 조사하였다. C6H6 가스를 사용하여 1$\mu\textrm{m}$의 두께로 DLC 박막을 증착하였으며, 기판과의 밀찰력 향상을 위해 Si을 증간층으로 합성하였다. 마모특성은 pin-on-disk type wear tester을 사용하였으며 직경 5mm의 ruby ball로 실험을 수행하였다.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.88-93
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• 2005

Ti-AI-Si-N coating layers were deposited on WC-Co substrates by a hybrid system of arc ion plating and sputtering techniques. The coatings were prepared with different Si contents to investigate the effect of Si content on their mechanical properties and microstructures. The dry sliding wear experiments were conducted on Ti-AI-Si-N coated WC-Co discs at constant load, 3N, and sliding speed, 0.1 m/s with two different counterpart materials such as steel ball and zirconia ball using a conventional ball-on-disc sliding wear apparatus. In the case of steel ball, the friction coefficient of Ti-AI-Si-N coating layers became lower than that of Ti-AI­N coating layers. The friction coefficient decreased with increasing of Si content due to adhesive wear behavior between coating layer and steel ball. On the contrary, in the case of zirconia ball, the friction coefficient increased with increasing of Si content, indicating that abrasive wear behavior was more dominant when the coating layers slid against zirconia ball.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.287-293
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• 2006

Diamond-like carbon (DLC) film was deposited using benzene $(C_6H_6)$ by r. f-plasma assisted chemical vapor deposition. The tribological properties of the DLC film were tested by rotating ball-on-disc type tribometer isolated by a chamber. The tribological test was performed in air environment of relative humidity ranging from 0 to 90% in order to observe the tribological behavior of the DLC film with the change of humidity. We used steel ball and DLC coated steel ball to investigate the effect of the counterface material. Using steel ball, the friction coefficient of DLC film increased from 0.025 to 0.2 as the humidity increased from 0% to 90%. In case of DLC coated steel ball which didn't form the Fe-rich debris, the friction coefficient showed much lower dependence of humidity as 0.08 in relative humidity 90%. We confirmed that the high humidity dependence of the friction coefficient using steel ball resulted from the increase of debris size with humidity and the formation of Fe-rich debris by the wear of steel ball. And the friction coefficient was immediately dropped when the relative humidity changed from 90% to 0% during test using steel ball. From this result, we confirmed that the effect of the Fe-rich debris on the friction coefficient was that Fe element in debris formed the highly sensitive graphitic transfer layer to humidity.

• Tribology and Lubricants
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• v.36 no.6
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• pp.365-370
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• 2020

Recently, additive manufacturing (AM) technology has been applied to various industries such as automotive, aviation, medical, and electronics. Most prior studies are limited to the mechanical properties of printed materials, and few studies are being conducted on their tribological characteristics. However, the friction and wear characteristics of the material should be studied in order to utilize the components manufactured using AM technology as mechanical parts. In this study, the friction and wear characteristics of acrylonitrile-butadiene-styrene (ABS)-like resin printed with stereo lithography apparatus (SLA) 3D printing are evaluated according to the viscosity of silicon oil lubricant using a ball-on-disk experiment. Lubricants with a viscosity of 500, 1000, and 2000 cSt are prepared for the experiment. If silicon oil lubricants are used during the ball-on-disk test, the coefficient of friction (COF) and wear rates are significantly reduced, and the higher the viscosity of the lubricant, the lower will be the COF and wear rates. It is also verified that the temperature of the specimen owing to friction also decreases according to the viscosity of the lubricant. This is because of the silicon oil film thickness, and the higher the viscosity of the lubricant, the thicker will be the oil film. More studies on the tribological characteristics of 3D printing materials and suitable lubricants will be required to use 3D printed parts as mechanical elements.

• Tribology and Lubricants
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• v.31 no.1
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• pp.1-5
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• 2015

In this study, we apply an ultrasonic nanocrystal surface modification (UNSM) technique to radial journal bearings (JBs) and disks made of SUJ2 and SCM440, respectively. We investigate frictional properties of untreated and UNSM-treated specimens using a ball-on-disk tester. We construct the Stribeck curve at the boundary, under mixed and full hydrodynamic lubrication conditions for the specimens using friction data obtained from JB tests. The friction at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM-treated specimens is reduced, which improves the service life of JBs. The major effects of this reduction in the three lubrication regimes can be explained in the terms of improved mechanical properties and the presence of micro dimples. Moreover, we estimate the friction and fatigue properties of SCM440 specimens using a ball-on-disk specimen under dry and oil-lubricated conditions. Friction test results reveal that the UNSM-treated specimens show lower friction coefficient than the untreated specimens under both dry and oil-lubricated conditions. We evaluate the fatigue properties of SCM440 specimens by calculating the Hertzian stress with respect to the failure cycles. Fatigue tests results also reveal that the UNSM-treated specimens possess a longer fatigue life than the untreated specimens. The improved properties are effective in increasing the energy efficiency of bearings.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.296-300
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• 2004

Currently. the study on structural ceramic helps to suggest the precise data of friction and wear in accordance with the various conditions in operations. Also, the study helps to predict effective operating conditions by monitoring the occurrence of wear transition. The studies in the Past were mainly concentrated in using identical materials. However, it is highly likely to have unqualified data from the differences of mechanical and chemical properties between ceramic materials. Thus, in this study, through conducting the ball-on-disk type wear testing, the different ceramic materials has been used to consider tribological characteristics between different ceramic materials. We conducted the wear test by using three kinds of specimen which are zirconia, alumina and silicon carbide against zirconia. We have changed the sliding velocity and the loading conditions in this test and found out that there is row friction coefficient and wear rate in the combination of zirconia and silicon carbide.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.538-543
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• 2007

We fabricated the Ni plate by electroforming process and evaluated the microstructure, mechanical properties and wear behavior of the Ni plate. Specifically, the effects of addition of wetting agents, SF 1 and SF 2 solutions, on the microstructure and properties were investigated. The microstructure and surface morphology were characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM), respectively, and friction coefficient was measured by the ball-on-disk method. We found that the microstructure and mechanical properties of Ni plate were changed with kind and amount of wetting agents used. The hardness and tensile strength of Ni plate formed without wetting agents was 228 Hv and 660.7 MPa, respectively, whiled when wetting agent was added, those were improved to be 739 Hv and 1286.3 MPa. These improvements were probably due to the finer grain size and less crystallization of Ni. In addition, when both wetting agents were added, the friction coefficient was reduced from 0.73 to 0.67 which is partially caused by the improved hardness and smooth surface.

• International Journal of Ocean System Engineering
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• v.2 no.2
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• pp.106-115
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• 2012

In the present study, TiN and CrN films were coated by arc ion plating equipment onto aluminum alloy substrate, A2024. The film thickness was about 4.65 ${\mu}m$. TiN and CrN films were analyzed by X-ray diffraction and energy dispersive X-ray equipments. The Young's modulus and the micro-Vickers hardness of aluminum substrate were modified by the ceramic film coatings. The difference in Young's modulus between substrate and coating film would affect on the wear resistance. The critical load, Lc, was 75.8 N for TiN and 85.5 N for CrN. It indicated from the observation of optical micrographs for TiN and CrN films that lots of cracks widely propagated toward the both sides of scratch track in the early stage of MODE I. TiN film began to delaminate completely at MODE II stage. The substrate was finally glittered at MODE III stage. For CrN film, a few crack can be observed at MODE I stage. The delamination of film was not still occurred at MODE II and then was happened at MODE III. This agrees with critical load measurement which the adhesive strength was greater for CrN film than for TiN film. Consequently, it was difficult for CrN to delaminate because the adhesive strength was excellent against Al substrate. The wear process, which the film adheres and the ball transfers, could be enhanced because of the increase in loading. The wear weight of ball was less for CrN than for TiN. This means that the wear damage of ball was greater for TiN than for CrN film. It is also obvious that it was difficult to delaminate because the CrN coating film has high toughness. The coefficient of friction was less for CrN coating film than for TiN film.

• Tribology and Lubricants
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• v.35 no.2
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• pp.106-113
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• 2019

We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to $1586cm^{-1}$, indicating that the $sp^3$ content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.