Interfacial effect on thermal conductivity of diamond-like carbon films

Kim, Jong Wook; Yang, Ho‐Soon; Jun, Young Ha; Kim, Kyung Chun

doi:10.1007/s12206-010-0416-2

Cited by 9 publications

(7 citation statements)

References 7 publications

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“…These factors make the coatings promising for use in, among others, machine components and cutting tools. Of interest in this study is, however, the low thermal conductivity (in the range of 1-3 W/mK) that has been measured for these thin coatings [20,26,4].…”

Section: Introductionmentioning

confidence: 99%

Friction Reduction in Elastohydrodynamic Contacts by Thin-Layer Thermal Insulation

et al. 2014

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Reducing friction is of utmost importance to improve efficiency and lifetime of many products used in our daily lives. Thin hard coatings like diamond-likecarbon (DLC) have been shown to reduce friction in full film lubricated contacts. In this work, it is shown that, contrarily to common belief, the friction reduction stems mainly from a thermal phenomenon and not only a chemical/surface interaction one. It is shown that a few micrometer thin diamond-like-carbon coating can significantly influence the thermal behavior in a lubricated mechanical system. The presented simulations, validated by experiments, show that applying a thin diamond-like-carbon coating to metal surfaces creates an insulating effect that, due to the increased liquid lubricant film temperature at the center of the contact, locally reduces lubricant viscosity and thus friction. The

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Section: Introductionmentioning

confidence: 99%

Friction Reduction in Elastohydrodynamic Contacts by Thin-Layer Thermal Insulation

et al. 2014

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“…It was thus hypothesized that this, in turn, affects a higher surface-temperature increase, and thus a larger viscosity decrease for a negative SRR than for a positive SRR, where the heat partitioning between the isolating disc and the steel ball is 50:50 [30]. This case is especially relevant for the current study since the reported heat conductivity of the glass was 1.5 J/mK, which is almost the same as a typical DLC coating [31][32][33]. Moreover, a similar hypothesis on the thermal aspects and a reduction of the viscosity, and consequently, a friction reduction due to the DLC isolating effect was also suggested recently by Björling et al [17] for EHL contacts.…”

Section: Discussionmentioning

confidence: 99%

Effect of the Slide-to-Roll Ratio and the Contact Kinematics on the Elastohydrodynamic Friction in Diamond-Like-Carbon Contacts with Different Wetting Behaviours

Kalin

2015

Tribol Lett

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In this paper we show how the slide-to-roll ratio (SRR), the contact kinematics and the surface energy all have important effects on the elastohydrodynamic (EHD) friction. As reported previously, diamond-like-carbon (DLC) contacts of the type DLC/DLC provide the lowest coefficient of friction, in particular those DLC materials with the lowest surface energies (three different DLC coatings were used in this study). A friction reduction of up to 48 %, compared to a steel/steel contact, was obtained. A surprising new finding from this investigation is that the friction in DLC contacts is significantly reduced for high SRRs, i.e., a difference of up to 27 % was measured in the DLC/DLC contacts when the SRR increased from 0.5 (rolling prevails) to 1.8 (sliding prevails). However, even more surprising is the effect of the SRR on the friction in mixed steel/DLC contacts, which is related to the contact design and its kinematics. We found that if the DLC is coated on the slower surface, a high SRR will not reduce the friction to any significant extent, typically about 5 %, and at most 13 %, compared to steel/steel contacts. However, a significant friction reduction is observed This peer reviewed manuscript has been accepted for publications to the Tribology Letters. Cite this article as: M. Polajnar, M. Kalin, Effect of the slide-to-roll ratio and the contact kinematics on the elastohydrodynamic friction in diamond-like-carbon contacts with different wetting behaviours,

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“…A chromium-based interlayer with a thickness of 0.1-0.3 lm deposited by magnetron sputtering was used to improve the adhesion. The thermal conductivities were not measured on these specific coatings, but approximated by the formula obtained by Kim et al [31] that is expressed in Fig. 1.…”

Section: Test Specimens and Lubricantmentioning

confidence: 99%

“…However, the present authors have presented an investigation in which friction reduction with DLC coatings was measured [7] in full film EHL even when the combined RMS roughness of the surfaces was in the range of 155-355 nm. Based on a simplified analytical estimation of the temperature increase in the lubricant film induced by DLC surface coating, the authors proposed that the friction reduction could be a result of thermal insulation due to the low thermal conductivity observed for some DLC coatings [2,31,40]. The temperature increase in the lubricant film would reduce the viscosity and thereby reduce the coefficient of friction.…”

Section: Introductionmentioning

confidence: 99%

The Effect of DLC Coating Thickness on Elstohydrodynamic Friction

2014

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The application of surface coatings has been shown to reduce friction in elastohydrodynamic lubrication (EHL), not only in the mixed and boundary regime when asperity interactions occur, but also in the full film regime. Several studies suggest that the full film friction reduction is due to a violation of the no-slip boundary condition and thus slip is taking place between the solid and the liquid. Another hypothesis proposes that the full film friction reduction is due to the low thermal conductivity of diamond-like carbon (DLC) coatings. In this work, two DLC coatings with the same composition, but different thicknesses, are investigated with uncoated steel specimens as a reference, all with the same surface roughness. Friction tests in a ball-on-disk machine show that both coatings reduce friction compared to the uncoated reference case in full film EHL. The thicker coating is significantly more effective at reducing friction than the thinner one at a maximum friction reduction of 41 % compared to 29 % for the thinner coating. Moreover, contact angle measurements, surface energy measurements, and spreading parameter calculations show no statistically significant differences between the two coatings, suggesting that the friction reduction capabilities of coatings in full film EHL cannot be described by solid-liquid interactions alone. The difference in friction reduction between the specimens in this work is mainly attributed to different thermal properties.

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Interfacial effect on thermal conductivity of diamond-like carbon films

Cited by 9 publications

References 7 publications

Friction Reduction in Elastohydrodynamic Contacts by Thin-Layer Thermal Insulation

Friction Reduction in Elastohydrodynamic Contacts by Thin-Layer Thermal Insulation

Effect of the Slide-to-Roll Ratio and the Contact Kinematics on the Elastohydrodynamic Friction in Diamond-Like-Carbon Contacts with Different Wetting Behaviours

The Effect of DLC Coating Thickness on Elstohydrodynamic Friction

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