• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.349-350
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• 2002

The friction and wear behaviors of fluorine-containing compounds such as perfluoropolyethers (PFPE), phosphazenes (X-1P), ionic liquids as lubricants for steel/seel, steel/ceramic, ceramic/ceramic were investigated using a SRV tester and a one-way reciprocating friction tester both in ball-on-disc configuration. It was found that the three fluorine-containing lubricants could reduce friction coefficient and wear volume effectively. The effectiveness of the three lubricants in reducing wear volume could be ranked as ionic liquids>X-1P>PFPE. Tests also showed that aryloxyphosphazene with polar substituent as a lubricant of steel/steel pair gave low wear, while aryloxyphosphazene with nonpolar group on the phenyl pendant led to high wear. The morphology and the tribo-chemical reaction of the worn surfaces were analyzed with a scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). XPS analyses illustrated the formation of iron fluoride in steel/steel system with the lubrication of both phosphazenes and ionic liquids.

• Tribology and Lubricants
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• v.30 no.5
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• pp.291-294
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• 2014

Multiple additives can help improve the performance of generally used lubricants. These additives include MoS2, cadmium, chloride, indium, sulfide, and phosphide, which are harmful to both humans and the environment. Thus, researchers in this industry have been trying to reduce the use of these additives by finding alternatives. Nanodiamonds are one of these candidates. Nanodiamond particles are very hard, chemically stable, and highly heat-conductive. This research involved uniformly dispersing nanodiamond particles in marine engine oils via a matrix synthesis method at various concentrations (0, 0.1, 0.3, 0.5, and 1.0 wt). Friction and wear tests involved constant loads on ball-on-disk specimens, where the ball was AISI 51200 steel, the disk was AISI 1020 steel, and the sliding speed was 0.217 m/s. The lowest wear occurred at a suitable concentration of nanodiamonds (0.3 wt). However, excessive amounts of nanodiamonds caused them to act as abrasive debris because of their hardness, which increased the wear amount. The friction coefficient decreased as the nanodiamond concentration increased because their octagonal, almost spherical shape caused them to act as rolling contact elements between two surfaces.

• Tribology and Lubricants
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• v.28 no.6
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• pp.333-339
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• 2012

Typical magneto-rheological (MR) elastomers consist of silicon-based material. A number of studies have been carried out to evaluate the vibration and tribological characteristics of silicon-based MR e-lastomers. However, these elastomers have quite low strength, so they have low wear resistance. In this study, polyurethane-based MR elastomers with performances better than those of MR elastomers. Experiments have been conducted on different MR elastomers (Pu MR elastomer, Pu-Si MR elastomer, and Pu-wrapped-Si MR elastomer) and different predefined magnetic directions (Non-Direction, Vertical Direction, and Horizontal Directionality) to evaluate the friction and wear performance under a magnetic field. The results show that Pu-wrapped-Si MR elastomer with a horizontal predefined magnetic field has the best performance in terms of wear.

• Tribology and Lubricants
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• v.27 no.2
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• pp.95-100
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• 2011

The brake disc materials for railway vehicle have been mainly used cast-iron. The brake disc and pad should be light, resist to a thermal crack and absorb enough friction energy. In order to satisfy this requirement, aluminum alloy brake disc for railway vehicle has been newly developed. The aluminum itself has not been considered the friction material for railway vehicle. However, in the case of aluminum composite with dispersed ceramic particles, friction characteristics, resistance to wear and heat are much improved. In the present study, aluminum composite brake disc of 20% ceramic particle and three kinds of organic pads have been tested in dynamometer. The results show that Al MMC brake disc and pad have good friction coefficient and wear rate, and thermal cracks in brake disc have not been initiated. Also, the Al MMC brake disc can be applied to railway vehicle of 150 km/h.

• Tribology and Lubricants
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• v.29 no.4
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• pp.235-241
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• 2013

The tribological characteristics of dental metal alloys and zirconia were studied by carrying out a friction and wear performance test. In this study, a pin-on-disk-type tester was used and dead weight was employed as the normal load applied to the test specimen. The friction coefficient of dental metal alloys was investigated in terms of their weight and sliding velocity. Microscopic observations were carried out on worn surfaces of specimens. The results indicated that among all metal alloys, Super-A had the highest friction coefficient. Super-A had the lowest amount of wear among all metal alloys, and the amount of wear increased in the following order: Crown & Bridge, Porcelain, and Partial. Crown & Bridge had the best friction coefficient, but the hardness of Crown & Bridge was lower than that of Porcelain and Partial. Experimental measurement results indicated that the disk weight before and after the experiment was the same.

• Composites Research
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• v.13 no.1
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• pp.78-88
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• 2000

Tribological properties of fiber composite materials were measured and wear resistant hybrid structure was proposed based upon the understanding of tribological behavior of the composite materials. Unidirectional composites with glass fibers, carbon fibers, and aramid fibers were tested for tribological properties in order to propose a wear resistant hybrid structure. Hybrid composites which contain carbon and aramid fibers were prepared, the specimens were sliced by a water-jet cutter, and friction and wear properties were measured. An experimental set-up was designed and built for the friction and wear test of the composite specimens. Unidirectional fiber composite and hybrid composite specimens were tested to evaluated the tribological behavior for biomimetic applications. It is observed that the friction and wear behavior of fiber composites depends upon fiber orientation, sliding speed, and type of reinforcing fibers.

• Tribology and Lubricants
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• v.31 no.4
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• pp.157-162
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• 2015

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si₃N₄) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.50-55
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• 2003

Tribological testing of DLC films was conducted using a rotating type ball on a disk friction tester in a dry chamber. This study made use of four kinds of mating balls that were made with stainless steel but subjected to diverse annealing conditions in order to achieve different levels of hardness. In all load conditions using martensite mating balls, the test results demonstrated that the friction coefficient was lower when the mating materials were harder. The high friction coefficient found in soft martensite balls appeared to be caused by the larger contact areas. The wear track on the mating balls indicated that a certain amount of material transfer occurs from the DLC film to the mating ball during the high friction process. Raman Spectra analysis showed that the transferred materials were a kind of graphite and that the contact surface of the DLC film seemed to undergo a phase transition from carbon to graphite during the high friction process.

• Tribology and Lubricants
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• v.39 no.6
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• pp.262-267
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• 2023

Research to replace metal mechanical elements with polymer materials has recently accelerated. However, polymers exhibit less favorable mechanical properties than metal materials, and are often easily worn-out owing to frictional heat when their mechanical elements contact while in relative motion. Therefore, research on the polymer tribological properties is required to employ polymer materials in mechanical elements operating under harsh conditions. In this study, we examine the effect of mechanical part operating temperatures on the material friction and wear characteristics of polymer materials. We conduct ball-on-disk friction tests under dry conditions at various temperatures, using a metal ball with high hardness and a polymer as the counter surface. Each test is repeated at least three times to ensure the reliability of the test results. Before the friction test, we analyze the surface hardness and roughness of each polymer specimen; after the friction test, we use a three-dimensional confocal microscope to compare and analyze the polymer specimen wear characteristics. Based on this study, we systematically elucidate the polymer material tribological characteristics. This information should be useful for selecting and utilizing polymer materials at various temperatures.

• Tribology and Lubricants
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• v.33 no.5
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• pp.220-227
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• 2017

In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.