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

Published on Sep 9, 2015in Tribology Letters3.106
· DOI :10.1007/S11249-015-0593-3
M. Polajnar5
Estimated H-index: 5
(University of Ljubljana),
Mitjan Kalin40
Estimated H-index: 40
(University of Ljubljana)
Sources
Abstract
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 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 when applying a low-surface-energy DLC coating to the faster surface—on average about 20 % and as high as 33 %. In this case (a high SRR and DLC on the faster surface), mixed steel/DLC surfaces can experience a very similar friction as that seen for DLC/DLC contacts. Qualitatively, the same behaviour was found for both positive and negative SRR values.
References36
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#1Hugh Spikes (Imperial College London)H-Index: 76
#2Zhang Jie (Imperial College London)H-Index: 1
There is currently considerable debate concerning the most appropriate rheological model to describe the behaviour of lubricant films in rolling–sliding, elastohydrodynamic contacts. This is an important issue since an accurate model is required to predict friction in such contacts. This paper reviews the origins of this debate, which primarily concerns a divergence of views between researchers using high pressure, high shear rate viscometry and those concerned with the measurement and analysis ...
Source
#1Aleks Ponjavic (Imperial College London)H-Index: 13
#2Janet S. S. Wong (Imperial College London)H-Index: 16
The effect of interfacial slip on the friction and film thickness in an elastohydrodynamic (EHD) contact was directly evaluated. Experiments showed that the film thickness and friction decrease upon the application of an oleophobic coating given a sufficient pressure, as opposed to bare glass. Direct measurements of the slip velocity enabled the determination of a power law relationship between pressure and slip length. This implied the existence of spatial heterogeneity of the flow in the tribo...
Source
#1Mitjan Kalin (University of Ljubljana)H-Index: 40
#2M. Polajnar (University of Ljubljana)H-Index: 5
Abstract The importance of wetting is becoming increasingly obvious and its control is inevitable in many engineering applications, including tribology and interface nanotechnology. However, the relations between the key parameters affecting surface–liquid wetting behaviour under realistic conditions are not very well understood, especially for typical engineering materials and lubricants (oils), often leading to exceptions and contradictions, which impede their use in engineering models and the...
Source
#1F. Guo (QUT: Qingdao Technological University)H-Index: 9
#2Shuyan Yang (QUT: Qingdao Technological University)H-Index: 2
Last. P.L. Wong (CityU: City University of Hong Kong)H-Index: 20
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This paper describes some experimental studies about the effect of interface wettability on hydrodynamic lubrication film thickness by a custom-made slider bearing tester. The lubricated contact pair consists of a fixed-incline slider and a transparent disc, and a thin lubrication film can be generated when the disc rotates. The film thickness was measured by interferometry. The wettability of different slider surfaces was evaluated by the contact angle of the lubricant on them. The relationship...
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#1Marcus Björling (Luleå University of Technology)H-Index: 14
#2Wassim Habchi (Lebanese American University)H-Index: 16
Last. Pär Marklund (Luleå University of Technology)H-Index: 14
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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-like carbon (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 DLC coating can significantly influence the thermal ...
Source
#1Mitjan Kalin (University of Ljubljana)H-Index: 40
#2M. Polajnar (University of Ljubljana)H-Index: 5
Abstract In this study we investigate the correlation between the wetting, the contact angle, the spreading, the surface energy and the surface tension for five types of DLC coatings (doped, non-doped, hydrogenated and non-hydrogenated) and steel, wetted with synthetic, non-polar, polyalphaolefin (PAO) oils with two distinctly different viscosities. We show how these parameters correlate with each other and how and why they change when different DLC or steel surfaces come into contact with the o...
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#1Marcus Björling (Luleå University of Technology)H-Index: 14
#2Wassim Habchi (Lebanese American University)H-Index: 16
Last. Pär Marklund (Luleå University of Technology)H-Index: 14
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Abstract The capability to predict elastohydrodynamic film-thickness and friction from primary measurements of transport properties of liquid has been an elusive goal for tribologists for 50 years. Most comparisons between predictions and experiments involve some amount of tuning of the model in order to match the experimental results. In true prediction, this cannot be done since there are normally no experimental results to compare to. Primary measurements of lubricant transport properties of ...
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#1Mitjan Kalin (University of Ljubljana)H-Index: 40
#2M. Polajnar (University of Ljubljana)H-Index: 5
This work shows the influence of solid–liquid interactions between engineering surfaces (steel and several types of DLC coatings) and lubricating oil (polyalphaolefin, PAO) on the coefficient of friction in the elastohydrodynamic lubrication (EHL) regime. Specifically, it confirms that the spreading parameter, rather than the contact angle, is the relevant parameter to evaluate the wetting behaviour of these surfaces with oils. Both the spreading parameter and the surface energy correlate very w...
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#1X.M. Li (QUT: Qingdao Technological University)H-Index: 4
#2F. Guo (QUT: Qingdao Technological University)H-Index: 9
Last. P.L. Wong (CityU: City University of Hong Kong)H-Index: 20
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Abstract Boundary slippage has been well confirmed using micro/nano measuring technologies and molecular-dynamic simulations. However, the characteristics of slip behaviour are still open for discussion due to their various behaviors under different conditions. This paper focuses on the boundary slippage under EHL conditions and its dependence on the shear rate and pressure. By tracing the movement of entrapped high molecular polymeric lubricants, boundary slippage was inferred. The slip length ...
Source
#1Mitjan Kalin (University of Ljubljana)H-Index: 40
#2Igor Velkavrh (University of Ljubljana)H-Index: 10
Abstract Due to the specific surface properties of diamond-like-carbon (DLC) coatings their interactions with base oils and additives differ from those of conventional ferrous engineering materials such as steel. This relates not only to their reactions with additives, which were frequently investigated in the past, but also to the effects of base oils and the physical properties of these oils. In order to better understand the physical phenomena of base oils, in this study we analyse the influe...
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Abstract null null The effect of three different film-forming additives mixed in PAO oil on the elasto-hydrodynamic (EHD) friction was investigated and compared to cases with the base oil only. When the boundary films were formed on the surfaces, the organic friction modifier (OFM) decreased the EHL friction by up to 8.7%, the ionic liquid (IL) decreased it by up to 6.4%, while the polymeric organic friction modifier (pOFM) increased it by up to 4.2%. In contrast, if the boundary films were not ...
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Abstract null null The 2,4,6-triamino-1,3,5-triazin-1-ium dibutyl phosphate (NP44) and 2,4,6-triamino-1,3,5-triazin-1-ium diisopentyl phosphate (NP88) were prepared as additives of PEG. In terms of temperature, slip-to-roll ratio and concentration, the effect of additives on tribological performance was explored. Excitingly, PEG with NP44 and NP88 presents outstanding lubricating property because of stable protective films formed in boundary/mixed lubrication. Furthermore, it was found that NP44...
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In this study we present a mechanism for the elastohydrodynamic (EHD) friction reduction in steel/steel contacts, which occurs due to the formation of oleophobic surface boundary layers from common boundary-lubrication additives. Several simple organic additives (amine, alcohol, amide, and fatty acid) with different molecular structures were employed as the model additives. It was found that the stronger chemisorption at 100 °C, rather than the physisorption at 25 °C, is more effective in fricti...
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#2Somayeh AkbariH-Index: 4
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In this work, we evaluated the effect of the counter-body material (the same or dissimilar) and contact configuration (moving or stationary body), at similar contact tribological conditions, on the tribochemical and nanotopography characteristics of adsorbed surface films. Zinc dialkyldithiophosphate (ZDDP), the best performing anti-wear additive, was used in self-mated steel/steel and DLC/DLC contacts, which were compared with mixed steel/DLC and DLC/steel contacts in 1-h and 6-h sliding tests....
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#1Maja Kus (University of Ljubljana)H-Index: 3
#2Mitjan Kalin (University of Ljubljana)H-Index: 40
Abstract In lubrication, additives are added to base oils to form surface layers that crucially improve its performance, particularly at high temperature. However, very little is known about their influence on the wetting behaviour of oil, even at room temperature, while for high-temperature, where the effects of the additives are the most intense, is absent. Accordingly, this work focuses on the additives’ effects on the wetting of oil on steel at 100 °C, which is relevant for the activity of m...
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#1Mitjan Kalin (University of Ljubljana)H-Index: 40
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#1Maja Kus (University of Ljubljana)H-Index: 3
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Abstract The effect of additives, their type and structure on the wetting of oil has received little attention so far and is thus poorly understood. This is despite the fact that a number of additives are present in every lubricating oil. Here, we report on the influence of the addition of some simple organic friction modifiers, namely, fatty acids, amides, alcohols and amines, on the static and dynamic (i.e., the advancing and receding contact angles, and the contact-angle hysteresis) wetting o...
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#1M. Polajnar (University of Ljubljana)H-Index: 5
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High-speed optical imaging is introduced as a visualization method to investigate the film-flow properties of liquids with different surface tensions and viscosities (water, poly-alpha-olefin oil, and glycerol) over free rotating surfaces with different surface energies and polarities (steel, and two different diamond-like-carbon - DLC coatings, i.e. DLC, and F-DLC). It was found that the polar surface energy strongly influences the structural dynamics of the liquid film's flow and the film's sl...
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