• Tribology and Lubricants
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• v.16 no.1
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• pp.1-8
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• 2000

Friction and wear tests have been performed on nylon, acetal resin, and PTFE (polytetrafluoroethylene), in reciprocating dry sliding conditions against steel discs. According to the results, acetal resin showed the lowest wear rates and PTFE exhibited the lowest friction coefficient. The prominent wear mechanisms found were adhesion and abrasion.

• Tribology and Lubricants
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• v.23 no.6
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• pp.288-297
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• 2007

Adhesion and friction tests were carried out in order to investigate the effect of temperature on the tribological characteristics of poly (methylmethacrylate) (PMMA) film using AFM. The pull-off and friction forces on the PMMA film were measured under a high vacuum condition (below $1{\times}10^{-4}$ Pa) as the temperature of the PMMA film was increased from 300 K to 420 K (heating) and decreased to 300K (cooling). Friction tests were also conducted in both high vacuum and air conditions at room temperature. When the temperature was 420 K, which is 25 K higher than the glass transition temperature $(T_g)$ of PMMA, the PMMA film surface became deformable. Subsequently, the pull-off force was proportional to the maximum applied load during the pull-off force measurement. In contrast, when the temperature was under 395 K, the pull-off force showed no correlation to the maximum applied load. The friction force began to increase when the temperature rose above 370 K, which is 25 K lower than the $T_g$ of PMMA, and rapidly increased at 420 K. Decrease of the PMMA film stiffness and plastic deformation of the PMMA film were observed at 420 K in force-displacement curves. After the heating to 420 K, the fiction coefficient was measured under the air condition at room temperature and was found to be lower than that measured before the heating. Additionally, the RMS roughness increased as a result of the heating.

• Transactions of Materials Processing
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• v.24 no.6
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• pp.405-410
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• 2015

Sheet-forming of Mg alloys is conducted at elevated temperatures (250℃) due to the low formability at room temperature. The high-temperature process often gives rise to surface damage on the alloy (i.e. galling.) In the current study, the frictional characteristics of DLC coating slid against an AZ31 Mg alloy at various temperatures were investigated. The coating has been used widely for low-friction processes. Dry-sliding friction and galling characteristics of an AZ31 Mg alloy (disk), which slid against uncoated and a DLC-coated STD-61 steel (pin), were investigated using a reciprocating-sliding tribometer at room temperature and 250℃. To represent the real sliding phenomena during a sheet metal forming process, single-stroke tests were used (10mm stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, and exhibited a low friction coefficient. However, during sliding at 250℃, severe adhesion occurred between the two surfaces, which resulted in a high friction coefficient and galling.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.90-98
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• 2004

Nano/micro-scale studies on friction properties were conducted on Si (100) and three self-assembled monolayers (SAMs) (PFOTC, DMDM, DPDM) coated on Si-wafer by chemical vapor deposition technique. Experiments were conducted at ambient temperature $(24{\pm}1^{\circ}C)$ and humidity $(45{\pm}5\%)$. Nano-friction was evaluated using Atomic Force Microscopy (AFM) in the range of 0-40nN normal loads. In both Si-wafer and SAMs, friction increased linearly as a function of applied normal load. Results showed that friction was affected by the inherent adhesion in Si-wafer, and in the case of SAMs the physical/chemical structures had a major influence. Coefficient of friction of these test samples was also evaluated at the micro-scale using a micro-tribotester. It was observed that SAMs had superior frictional property due to their low interfacial energies. In order to study of the effect of contact area on friction coefficient at the micro-scale, friction was measured for Si-wafer and DPDM against Soda Lime balls (Duke Scientific Corporation) of different radii 0.25 mm, 0.5 mm and 1 mm at different applied normal loads $(1500,\;3000\;and\;4800{\mu}N)$. Results showed that Si-wafer had higher friction coefficient than DPDM. Furthermore, unlike that in the case of DPDM, friction was severely influenced by wear in the case of Si-wafer. SEM evidences showed that solid-solid adhesion to be the wear mechanism in Si-wafer.

• KSTLE International Journal
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• v.5 no.2
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• pp.37-43
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• 2004

Abstract : Nano/micro-scale friction properties were investigated on Si (100) and three self-assembled monolayers (SAMs) (PFOTC, DMDM, DPDM) coated on Si-wafer by chemical vapor deposition technique. Experiments were conducted at ambient temperature(24$pm$1$circ$C) and humidity(45$pm$5%). Friction at nano-scale was measured using Atomic Force Microscopy (AFM) in the range of 0-40nN normal loads. In both Si-wafer and SAMs, friction increased linearly as a function of applied normal load. Results showed that friction was affected by the inherent adhesion in Ssi-wafer, and in the case of SAMs the physical/chemical structures had a major influence. Coefficient of friction of these test samples at the micro-scale was also energies. In order to study the effect of contact area on coefficient of friction at the micro-scale, friction was measured for Si-wafer and DPDM against Soda Lime balls (Duke Scientiffic Corporation) of different radii (0.25 mm, 0.5 mm and 1 mm) at different applied normal loads (1500, 3000 and 4800 mN). Results showed that Si-wafer had higher coefficient of friction than DPDM. Further, unlike that in the case of DPDM, friction in Si-wafer was severely influenced by its wear. SEM evidences showed that solid-solid adhesion was the wear mechanism in Si-wafer.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.2
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• pp.78-83
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• 2007

CrN coatings were deposited by cathodic arc ion plating method on the SKD11 steel substrates. Atmosphere temperature of $350^{\circ}C$, arc current of 90 A, nitrogen partial pressure of 1.0-5.3 Pa, and negative bias voltage of 30-135 V were selected. The characteristics of microstructure were investigated with XRD. Hardness, adhesion and friction coefficient measured by microhardness tester, scratch tester, and ball on disk tribometer. Microstructures depended on nitrogen partial pressure and bias voltage. The preferred orientation of the films was changed from (200) to (111) with decreasing pressure and increasing bias voltage. Adhesion properties related with microstructure, but microstructure changes slightly influenced on hardness and friction properties. The critical load.($Lc_1$) and hardness of CrN films deposited at 5.3 Pa, -30 V condition were 55 N(HF1), $2157{\pm}47\;Hk_{0.025}$. The friction coefficient were about 0.5 under dry condition.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.35-42
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• 2001

Nanotribological characteristics between a Si$_3$N$_4$ AFM tip and hydrophobic thin films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes in various ranges of normal load. Plasma-modified thin polymeric films were deposited on Si-wafer (100). Results showed that wetting angle of plasma-modified thin polymeric film increased with the treating time, which resulted in the hydrophobic surface and the decrease of adhesion and friction. Nanotribological characteristics of these surfaces were compared with those of other hydrophobic surfaces, such as DLC, OTS and IBAD-Ag coated surfaces. Those of OTS coated surface was superior to those of others, though wetting angle of plasma-modified thin polymeric film is higher.

• Journal of Adhesion and Interface
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• v.14 no.3
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• pp.121-127
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• 2013

In this work, the thermoplastic polyurethane (TPU) was melt-blended with EPDM, NBR and BR to form TPU/Rubber blend films, their composition and friction-induced surface fracture relationship was investigated. TPU/EPDM and TPU/BR blends exhibited the improved friction-induced surface fracture, especially the effect of BR was excellent. With addition of more than 10 wt% BR, TPU/BR blends exhibited the improved friction-induced surface fracture. The increase of the soft segment with increasing BR content, which was confirmed by scanning electron microscopy (SEM) analysis enabled us to estimate the improved friction-induced surface fracture.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.383-386
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• 2005

An integrated analytical model which should have essential dynamics on the longitudinal railway vehicle is developed. The model consists of translational movement, rotational movement, brake actuator, adhesion force between rail and wheel, and brake friction force between wheel and pad. Thus, during the deceleration for stopping, a feedback controller controlling the brake cylinder pressure is designed to improve ride quality and to release friction problems. Through the developed model, the feasibility of controlling the cylinder pressure is verified for the better performances during braking.

• Advanced Composite Materials
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• v.17 no.2
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• pp.101-110
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• 2008

Metal nanohoneycomb structures were fabricated by E-beam evaporation and a two-step anodization process in phosphoric acid. Their tribological properties of adhesion and friction were investigated by AFM in relation to the pore size of the nanohoneycomb structures. Variations of the adhesive force are not found with pore size, but formation of the pore greatly reduces the adhesive force compared to the absence of pore structure. The coefficient of friction increased nonlinearly with pore size, due to surface undulation around the pore. Tribological properties do not differ greatly between the original nanohoneycomb structure and the metal nanohoneycomb structure.