• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1772-1781
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• 2004

The mechanical as well as tribological characteristics of coating films as thin as a few nm become more crucial as applications in micro-systems grow. Especially, the amorphous carbon film has a potential to be used as a protective layer for micro-systems. In this work, quantitative evaluation of nano-indentation, scratching, and wear tests were performed on the 7nm thick amorphous carbon film using an Atomic Force Microscope (AFM). It was shown that AFM-based nano-indentation using a diamond coated tip can be feasibly utilized for mechanical characterization of ultra-thin films. Also, it was found that the critical load where the failure of the carbon film occurred was about 18${\mu}$N by the ramp load scratch test. Finally, the wear experimental results showed that the quantitative wear rate of the carbon film ranged 10$\^$-9/～10$\^$-8/ ㎣ /N cycle. These experimental methods can be effectively utilized for a better understanding the mechanical and tribological characteristics at the nano-scale.

• Journal of Surface Science and Engineering
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• v.36 no.2
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• pp.116-121
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• 2003

Ti-Si-N coating layers were deposited onto WC-Co substrates by a hybrid system of arc ion plating (AIP) and sputtering techniques. The tribological behaviors of Ti-Si-N coating layers with various Si contents were investigated by the dry sliding wear experiments, which were conducted at three different sliding speeds, 0.1, 0.3, 0.5 m/s, against the steel and alumina balls. In the case of steel ball, the average friction coefficient slightly decreased with increasing the sliding speed regardless of Si content due to adhesive wear behavior between coating layer and steel ball. At constant sliding speed, the average friction coefficient decreased with increase of Si content. On the contrary, in the case of alumina ball, the average friction coefficient increased with increasing the sliding speed regardless of Si content, indicating that the abrasive wear behavior was more dominant when the coating layers slide against alumina ball. Through these experimental results, it was found that the tribological behaviors of Ti-Si-N coating layers were effected by factors such as Si content, sliding speed, and kinds of counterpart materials rather than the hardness of coating layer.

• The Korean Journal of Ceramics
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• v.3 no.1
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• pp.47-51
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• 1997

The dense sintered bodies of Si/SiC composite with various Si contents could be fabricated by changing the green density in the forming process. The Si/SiC/graphite composites with various graphite contents could be also fabricated by changing a graphite content in the starting composition. Their mechanical and tribological properties were characterized and wear mechanism was also studided. The hardness and strength of the Si/SiC and the Si/SiC/graphite were decreased with increasing the contents of free Si and graphite, respectively. However, the friction coefficient and specific wear rate had no specific relations to their hardness and strength. Adhesion of free Si was a main factor to determine a wear resistance of the Si/SiC composite. In the case of the Si/SiC/graphite, solid lubricationl and liquid reservoir of the graphite particles played the main role of the reduction of the friction force. In the torque test to estimate the possibility of practical of practical applications, the value of torque between the Al2O3 disk and Si/SiC/graphite disk was 1/6 lower compared with two $Al_2O_3$ disks on the basis of 100,000 cycles.

• KSTLE International Journal
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• v.2 no.1
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• pp.65-70
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• 2001

The wear debris is fall off the moving surfaces in oil-lubricated systems and its morphology is directly related to the damage and failure to the interacting surfaces. The morphology of the wear particles are therefore directly indicative of wear processes occurring in tribological system. The computer image processing and artificial neural network was applied to shape study and identify wear debris generated from the lubricated moving system. In order to describe the characteristics of various wear particles, four representative parameter (50％ volumetric diameter, aspect, roundness and reflectivity) from computer image analysis for groups of randomly sampled wear particles, are used as inputs to the network and learned the friction condition of five values (material 3, applied load 1, sliding distance 1). It is shown that identification results depend on the ranges of these shape parameters learned. The three kinds of the wear debris had a different pattern characteristics and recognized the friction condition and materials very well by neural network. We discuss how these approach can be applied to condition diagnosis of the oil-lubricated tribological system.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.156-156
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• 2016

The effect of nitrogen doping on the mechanical and tribological performance of single-layer tetrahedral amorphous carbon (ta-C:N) coatings of up to $1{\mu}m$ in thickness was investigated using a custom-made filtered cathode vacuum arc (FCVA). The results obtained revealed that the hardness of the coatings decreased from $65{\pm}4.8GPa$ to $25{\pm}2.4GPa$ with increasing nitrogen gas ratio, which indicates that nitrogen doping occurs through substitution in the $sp^2$ phase. Subsequent AES analysis showed that the N/C ratio in the ta-C:N thick-film coatings ranged from 0.03 to 0.29 and increased with the nitrogen flow rate. Variation in the G-peak positions and I(D)/I(G) ratio exhibit a similar trend. It is concluded from these results that micron-thick ta-C:N films have the potential to be used in a wide range of functional coating applications in electronics. To achieve highly conductive and wear-resistant coatings in system components, the friction and wear performances of the coating were investigated. The tribological behavior of the coating was investigated by sliding an SUJ2 ball over the coating in a ball-on-disk tribo-meter. The experimental results revealed that doping using a high nitrogen gas flow rate improved the wear resistance of the coating, while a low flow rate of 0-10 sccm increased the coefficient of friction (CoF) and wear rate through the generation of hematite (${\alpha}-Fe_2O_3$) phases by tribo-chemical reaction. However, the CoF and wear rate dramatically decreased when the nitrogen flow rate was increased to 30-40 sccm, due to the nitrogen inducing phase transformation that produced a graphite-like structure in the coating. The widths of the wear track and wear scar were also observed to decrease with increasing nitrogen flow rate. Moreover, the G-peaks of the wear scar around the SUJ2 ball on the worn surface increased with increasing nitrogen doping.

• 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.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.181-182
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• 2002

Most recent, Plasma ceramic spray is used on parts of tribosystem, has been investigated on the tribological performance. The application of ceramic coatings by plasma spray has become essential in tribosystems to produce better wear resistance and longer life in various conditions. The purpose of this work was to investigate the wear behavior of $8%Y_2O_3-ZrO_2$ coating due to temperatures of post-spay heat treatment. The plasma-sprayed $8%Y_2O_3--Zirconia$ coating was idiscussed to know the relationship between phase transformations and temperatures of post- spray heat treatment. Wear tests was carried out with ball on disk type on normal load of 50N, 70N and 90N under room temperature. The transformation of phase and the value of residual stress were measured by X-ray diffraction method(XRD). Tribological characteristics and wear mechanisms of coatings was observed by SEM. The tribologieal wear performance was discussed a point of view for residual stress. Consequently. post-spray heat treatment plays an important role in decreasing residual stress. Residual stress in coating system has a significant influence on the wear mechanism of coating.

• Tribology and Lubricants
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• v.37 no.3
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• pp.83-90
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• 2021

In this study, an ultrasonic nanocrystal surface modification (UNSM) was used to improve the mechanical properties, scratch resistance and tribological performance of Cu-based bimetals, which are usually used to manufacture sliding bearings and bushings for internal combustion engines (ICEs). Two different Cu-based bimetals, namely CuPb10Sn10 and CuSn10Bi7, were sintered onto a low carbon steel substrate. The mechanical properties and dry tribological performance using a tensile tester and micro-tribo tester were evaluated, respectively. The scratch resistance was assessed using a micro-scratch tester at an incremental load. The tensile test results showed that the yield strength (YS) and ultimate tensile strength (UTS) of both Cu-based bimetals increased after UNSM. Furthermore, the scratch and tribological tests results revealed that the scratch resistance and tribological performance of both Cu-based bimetals were improved by the application of UNSM. These improvements were mainly attributed to the eliminated pores, increased hardness and reduced roughness after UNSM. CuSn10Bi7 demonstrated better mechanical properties, scratch resistance and tribological performance than CuPb10Sn10. It was found that the presence of Bi in CuSn10Bi7 formed a Cu₁₁Bi₇ intermetallic phase, which is harder than Cu₃Sn. Hence, CuSn10Bi7 demonstrated higher strength and wear resistance than CuPb10Sn10. In addition, a CuSn10Bi7 formed both SnO₂ and Bi₂O₃ that prevented adhesion and improved the tribological performance. It can be expected that under dry tribological conditions, ICEs can utilize UNSM bearings and bushings made of CuSn10Bi7 instead of CuPb10Sn10 under oil-lubricated conditions.

• Tribology and Lubricants
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• v.14 no.2
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• pp.57-62
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• 1998

When lubricants is used under severe running conditions, their tribological characteristics are very important. We have studied the lubricating oil viscosity, kinds of additives and their amounts, and lubricating oil temperatures were changed. In order to study the effect of oil temperature on the wear of the surface, the temperature of the oil was changed for the same sample. Moreover, the temperatures of three kinds of oils which have very different viscosities at room temperature, were varied between 6$0^{\circ}C$ and 115$^{\circ}C$ while the oil viscosity was unchanged. It was shown from the test results that surface wear is not greatly affected by the amount of ZnDTP (Zinc dialkyl dithio phosphate) antiwear agent, but EP (Extreme pressure) additives are less effective against wear than ZnDTP additives. The viscosity of lubricating oil and its temperature greatly affect the wear of the surface. Combining all the wear data with those of the surface strength, it was observed that the higher the load, the wider the scratching of wear, and also in the case of the same running load, the lower the wear, the longer the life of the surface strength.

• Tribology and Lubricants
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• v.23 no.4
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• pp.170-174
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• 2007

Wear and scuffing tests were conducted using friction and wear measurement of piston rings and cylinder blocks in low friction diesel engine. The frictional forces, wear amounts and cycles to scuffing in boundary lubricated sliding condition were measured using the reciprocating wear tester. The cylinder blocks were used as reciprocating specimens, and the piston rings with several coatings were used as fixed pin. Several coatings were used such as DLC, TiN, Cr-ceramic and TiAlN in order to improve the tribological characteristics. From the tests wear volume of piston ring surfaces applied various coatings were compared. During the tests coefficients of friction were monitored. Test results showed that DLC coatings showed good tribological properties. TiN and Cr-ceramic coated rings showed good wear resistance properties but produced high friction.