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Lubricants, Volume 6, Issue 3 (September 2018)

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Open AccessArticle Meta-Analysis Comparing Wettability Parameters and the Effect of Wettability on Friction Coefficient in Lubrication
Lubricants 2018, 6(3), 70; https://doi.org/10.3390/lubricants6030070 (registering DOI)
Received: 26 June 2018 / Revised: 30 July 2018 / Accepted: 8 August 2018 / Published: 15 August 2018
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Abstract
This work presents a meta-analysis that compares the suitability of various parameters used to characterize wettability in tribological systems. It also examines the relationship between wettability and the friction factor for multiple lubricant-surface pairings. The characterization of wetting behavior was similar when using
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This work presents a meta-analysis that compares the suitability of various parameters used to characterize wettability in tribological systems. It also examines the relationship between wettability and the friction factor for multiple lubricant-surface pairings. The characterization of wetting behavior was similar when using the contact angle between a lubricant and surface and various dimensional and dimensionless formulations of a spreading parameter. It was possible to identify hydrodynamic, boundary, and mixed lubrication regimes by combining a dimensionless wettability parameter with the specific film thickness for a variety of neat ionic liquids and magnetorheological fluids in contact with metallic, thermoplastic, and elastic surfaces. This characterization was possible using multiple dimensionless wettability parameters, but those that can be fully determined using only the contact angle may be preferred by experimentalists. The use of dimensional and dimensionless wettability parameters that included polar and disperse components of surface tension and surface energy did not appear to provide additional insight into the wettability or frictional performance for the tribological system examined here. Full article
(This article belongs to the Special Issue Ionic Liquids: Friction and Lubrication Mechanisms)
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Open AccessArticle Evaluation of Friction Behavior and Surface Interactions of Cyano-Based Ionic Liquids under Different Sliding Contacts and High Vacuum Condition
Received: 29 June 2018 / Revised: 2 August 2018 / Accepted: 8 August 2018 / Published: 9 August 2018
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Abstract
The friction coefficients of ionic liquids were evaluated by many investigations. Most investigations used fluorine-based ionic liquids as lubricants. However, these ionic liquids produce the corrosion wear. This investigation focuses on the use of cyano-based ionic liquids as lubricants. Compared to fluorine-based ionic
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The friction coefficients of ionic liquids were evaluated by many investigations. Most investigations used fluorine-based ionic liquids as lubricants. However, these ionic liquids produce the corrosion wear. This investigation focuses on the use of cyano-based ionic liquids as lubricants. Compared to fluorine-based ionic liquids, cyano-based ionic liquids exhibit high friction coefficients against steel material. This work examines how the friction coefficients of cyano-based ionic liquids are influenced by the type of sliding material used (AISI 52100, TiO2, and tetrahedral amorphous carbon). TiO2 lubricated with 1-ethyl-3-methylimidazolium tricyanomethanide, and ta-C lubricated with 1-butyl-1methylpyrrolidinium tetracyanoborate exhibited very low friction coefficients, smaller than fluorine-based ionic liquids. Time-of-Flight Secondary Ion Mass Spectrometry analysis showed that anions adsorb onto the worn surface, suggesting that anion adsorption is a critical parameter influencing friction coefficients. Quadrupole Mass Spectrometry measurements revealed that cations decompose on the nascent surface, preventing adsorption on the worn surface. These results suggest that low friction coefficients require the decomposition of cations and adsorption of anions. The reactivity of nascent surface changes with the sliding material used due to varying catalytic activity of the nascent surfaces. Full article
(This article belongs to the Special Issue Ionic Liquids: Friction and Lubrication Mechanisms)
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Open AccessReview Common Properties of Lubricants that Affect Vehicle Fuel Efficiency: A North American Historical Perspective
Received: 28 June 2018 / Revised: 28 July 2018 / Accepted: 30 July 2018 / Published: 3 August 2018
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Abstract
The development of advanced lubricants to improve vehicle fuel efficiency can appear to be as simple as lowering the viscosity and frictional properties of a fluid. However, applied research studies have shown that it is quite difficult to quantify the fuel efficiency properties
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The development of advanced lubricants to improve vehicle fuel efficiency can appear to be as simple as lowering the viscosity and frictional properties of a fluid. However, applied research studies have shown that it is quite difficult to quantify the fuel efficiency properties of advanced lubricants in vehicles. A review of the historical research predominantly performed in North America in this area reveals that there are many factors to consider in order to demonstrate the effectiveness of advanced lubricants. First, the methodology used to measure vehicle fuel efficiency will impact the results since there are many factors not related to the lubricant which will influence vehicle fuel efficiency. Second, developing advanced fuel-efficient lubricants under well controlled conditions overlooks the issue that lubricant properties such as viscosity and friction affect the operating conditions encountered by the lubricant in the vehicle. Finally, the physical properties of lubricants that historically control fuel economy do not have the same effect on fuel efficiency in all vehicles. The proper vehicle or system level test needs to be selected to properly assess the benefits of new advanced lubricants. Full article
(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)
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Open AccessArticle Comparative Study of Tribological Behavior of Electroless Ni–B, Ni–B–Mo, and Ni–B–W Coatings at Room and High Temperatures
Received: 6 July 2018 / Revised: 31 July 2018 / Accepted: 31 July 2018 / Published: 2 August 2018
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Abstract
Ni–B alloys deposited by the electroless method are considered to be hard variants of the electroless nickel family. Inclusion of Mo or W to form ternary alloys improves the thermal stability of electroless nickel coatings. Therefore, in the present work, Ni–B, Ni–B–Mo, and
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Ni–B alloys deposited by the electroless method are considered to be hard variants of the electroless nickel family. Inclusion of Mo or W to form ternary alloys improves the thermal stability of electroless nickel coatings. Therefore, in the present work, Ni–B, Ni–B–Mo, and Ni–B–W coatings are deposited; and their tribological behavior at room and high temperatures are investigated. Electroless Ni–B, Ni–B–Mo, and Ni–B–W coatings are deposited on AISI 1040 steel substrates. The coatings are heat treated to improve their mechanical properties and crystallinity. Tribological behavior of the coatings is determined on a pin-on-disc type tribological test setup using various applied normal loads (10–50 N) and sliding speeds (0.25–0.42 m/s) to measure wear and coefficient of friction at different operating temperatures (25 °C–500 °C). Ni–B–W coatings are observed to have higher wear resistance than Ni–B or Ni–B–Mo coatings throughout the temperature range considered. Although for coefficient of friction, no such trend is observed. The worn surface of the coatings at 500 °C is characterized by lubricious oxide glazes, which lead to enhanced tribological behavior compared with that at 100 °C. A study of the coating characteristics such as composition, phase transformations, surface morphology, and microhardness is also carried out prior to tribological tests. Full article
(This article belongs to the Special Issue Tribological Challenges in Extreme Environments)
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Open AccessArticle Study of the Lubricating Ability of Protic Ionic Liquid on an Aluminum–Steel Contact
Received: 6 July 2018 / Revised: 22 July 2018 / Accepted: 26 July 2018 / Published: 28 July 2018
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Abstract
Contact friction between moving components leads to severe wear and failure of engineering parts, resulting in large economic losses. The lubricating ability of the protic ionic liquid, tri-[bis(2-hydroxyethylammonium)] citrate (DCi), was studied as a neat lubricant and as an additive in a mineral
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Contact friction between moving components leads to severe wear and failure of engineering parts, resulting in large economic losses. The lubricating ability of the protic ionic liquid, tri-[bis(2-hydroxyethylammonium)] citrate (DCi), was studied as a neat lubricant and as an additive in a mineral oil (MO) at various sliding velocities and constant load on an aluminum–steel contact using a pin-on-disk tribometer. Tribological tests were also performed at different concentrations of DCi. When DCi was used as an additive in MO, friction coefficient and wear volume were reduced for each sliding velocity, with a maximum friction and wear reduction of 16% and 40%, respectively, when 2 wt % DCi was added to MO at a sliding velocity of 0.15 m/s. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also applied to analyze the wear mechanism of the interface lubricated by MO and DCi as additive. Full article
(This article belongs to the Special Issue Ionic Liquids: Friction and Lubrication Mechanisms)
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Open AccessArticle Evaluation of Wear Phenomena of Journal Bearings by Close to Component Testing and Application of a Numerical Wear Assessment
Received: 23 May 2018 / Revised: 17 July 2018 / Accepted: 23 July 2018 / Published: 26 July 2018
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Abstract
Hydrodynamic journal bearings are subjected to progressively rough loading conditions leading to an increased share of operation in mixed and boundary lubrication. This results in increased frictional losses, additional wear and a higher chance of failure, which calls for the understanding of wear
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Hydrodynamic journal bearings are subjected to progressively rough loading conditions leading to an increased share of operation in mixed and boundary lubrication. This results in increased frictional losses, additional wear and a higher chance of failure, which calls for the understanding of wear processes and the necessity of a numerical assessment. We conducted wear investigations of journal bearings by making use of a close-to-component test setting, and the progress of wear could be linked to the introduced frictional energy and in combination with a comprehensive surface analysis tribological effects could be resolved in detail. Achieved wear coefficients were implemented in a novelly developed numerical framework, which allows for the dynamic numerical evaluation of operation in the fluid and mixed lubrication regime and simultaneously occurring wear processes. By comparing numerical and experimental results, we evaluated the numerical framework’s capability to conduct holistic simulations including aspects like dynamically changing operation conditions, fluid and mixed lubrication as well as wear. Full article
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Open AccessArticle Molecular Mechanisms Underlying Lubrication by Ionic Liquids: Activated Slip and Flow
Received: 19 June 2018 / Revised: 13 July 2018 / Accepted: 17 July 2018 / Published: 20 July 2018
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Abstract
The present study provides molecular insight into the mechanisms underlying energy dissipation and lubrication of a smooth contact lubricated by an ionic liquid. We have performed normal and lateral force measurements with a surface forces apparatus and by colloidal probe atomic force microscopy
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The present study provides molecular insight into the mechanisms underlying energy dissipation and lubrication of a smooth contact lubricated by an ionic liquid. We have performed normal and lateral force measurements with a surface forces apparatus and by colloidal probe atomic force microscopy on the following model systems: 1-ethyl-3-methyl imidazolium bis-(trifluoro-methylsulfonyl) imide, in dry state and in equilibrium with ambient (humid) air; the surface was either bare mica or functionalized with a polymer brush. The velocity-dependence of the friction force reveals two different regimes of lubrication, boundary-film lubrication, with distinct characteristics for each model system, and fluid-film lubrication above a transition velocity V. The underlying mechanisms of energy dissipation are evaluated with molecular models for stress-activated slip and flow, respectively. The stress-activated slip assumes that two boundary layers (composed of ions/water strongly adsorbed to the surface) slide past each other; the dynamics of interionic interactions at the slip plane and the strength of the interaction dictate the change in friction -decreasing, increasing or remaining constant- with velocity in the boundary-film lubrication regime. Above a transition velocity V, friction monotonically increases with velocity in the three model systems. Here, multiple layers of ions slide past each other (“flow”) under a shear stress and friction depends on a shear-activation volume that is significantly affected by confinement. The proposed friction model provides a molecular perspective of the lubrication of smooth contacts by ionic liquids and allows identifying the physical parameters that control friction. Full article
(This article belongs to the Special Issue Ionic Liquids: Friction and Lubrication Mechanisms)
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Open AccessArticle Lubrication Performance of α-Zirconium Phosphates as an Anti-Wear Additive in Vegetable Oil-Based Anhydrous Calcium Grease
Received: 19 June 2018 / Revised: 6 July 2018 / Accepted: 16 July 2018 / Published: 18 July 2018
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Abstract
Vegetable oil has significant potential as a base oil, and substitute for mineral oil in grease formulation due to its biodegradability, low toxicity and excellent lubrication. This paper studied the development of vegetable oil-based greases with α-Zr(HPO4)2·H2O
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Vegetable oil has significant potential as a base oil, and substitute for mineral oil in grease formulation due to its biodegradability, low toxicity and excellent lubrication. This paper studied the development of vegetable oil-based greases with α-Zr(HPO4)2·H2O (α-ZrP) as an additive, exploring base oil influence in tribological behavior. The results demonstrated that the addition of α-ZrP in vegetable-based greases is beneficial to anti-wear property. α-ZrP particles exhibit good performance in anti-wear, friction-reduction and load-carrying capacity, and its tribological performances are better than the normally used molybdenum disulfide and graphite additives. Owing to its superior tribological properties as a vegetable oil-based grease additive, α-ZrP holds great potential for use in environmentally friendly applications in the future. Full article
(This article belongs to the Special Issue Wear Resistant Materials)
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Open AccessArticle Effect of Low Depth Surface Texturing on Friction Reduction in Lubricated Sliding Contact
Received: 30 April 2018 / Revised: 9 July 2018 / Accepted: 11 July 2018 / Published: 17 July 2018
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Abstract
Laser surface texturing is an interesting possibility to tailor materials’ surfaces and thus to improve the friction and wear properties if proper texture feature sizes are selected. In this research work, stainless steel surfaces were laser textured by two different laser techniques, i.e.,
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Laser surface texturing is an interesting possibility to tailor materials’ surfaces and thus to improve the friction and wear properties if proper texture feature sizes are selected. In this research work, stainless steel surfaces were laser textured by two different laser techniques, i.e., the direct laser interference patterning by using a nanosecond pulsed Nd:YAG laser and additionally by an ultrashort pulsed femtosecond Ti:Sa. The as-textured surfaces were then studied regarding their frictional response in a specially designed linear reciprocating test rig under lubricated conditions with a fully formulated 15W40 oil. Results show that dimples with smaller diameter lead to a significant reduction in the coefficient of friction compared to the dimples with a larger diameter and surfaces with a grid-like surface pattern produced by direct laser interference patterning. Full article
(This article belongs to the Special Issue Improvement of Friction and Wear by Laser Surface Texturing)
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Open AccessArticle The Influence of Surface Texturing on the Film Thickness in Starved Lubricated Parallel Sliding Contacts
Received: 27 May 2018 / Revised: 3 July 2018 / Accepted: 4 July 2018 / Published: 11 July 2018
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Abstract
In industrial applications, a starved lubrication condition may occur, leading to a reduction in film thickness; by modifying the surface geometry, the tribological performance of the contact is enhanced. In this paper, the influence of surface texturing as a method for reducing the
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In industrial applications, a starved lubrication condition may occur, leading to a reduction in film thickness; by modifying the surface geometry, the tribological performance of the contact is enhanced. In this paper, the influence of surface texturing as a method for reducing the friction on the film thickness in parallel sliding surfaces for starved lubricated contacts is investigated. The results in this study have shown that surface texturing can improve film formation for starved lubricated contacts and, respectively, the load carrying capacity. The effect of starvation on several texturing patterns with several texturing properties was investigated and the film thickness for these conditions was studied. With the numerical algorithm developed and taking cavitation into consideration, the effect of shape, depth, size, and texture pitch on the film thickness was studied. Full article
(This article belongs to the Special Issue Tribological Performance of Textured Surfaces)
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Open AccessArticle Tribology of Wire Arc Spray Coatings under the Influence of Regenerative Fuels
Received: 2 May 2018 / Revised: 2 July 2018 / Accepted: 3 July 2018 / Published: 9 July 2018
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Abstract
In order to further optimize the efficiency of today’s internal combustion engines, specific coatings are used on functional surfaces to reduce internal engine friction and wear. In the current research project, oxymethylene ether (OME) is discussed because it is CO2 neutral and
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In order to further optimize the efficiency of today’s internal combustion engines, specific coatings are used on functional surfaces to reduce internal engine friction and wear. In the current research project, oxymethylene ether (OME) is discussed because it is CO2 neutral and has a strong soot-reducing effect as a fuel or fuel additive. In some operational regimes of the internal combustion engine a dilution of engine oil by fuel must be assumed. In this paper, the frictional contact between piston ring and cylinder raceway is modelled using a pin-on-disk tribometer and the friction and wear behavior between a diamond-like carbon coating (DLC) and a thermal spray coating is characterized. The wear of the spray layer could be continuously detected by radionuclide technology (RNT). With the aid of photoelectron spectroscopic measurements (XPS), the steel thermal spray coating was chemically analyzed before and after the tribometer tests and the oxidative influence of OME was investigated. In addition, confocal microscopy was used to assess the topographies of the specimens. The measurements showed that the addition of OME to the lubricant reduced the viscosity and load-bearing capacity of the lubricating film, which led to an increase in the coefficient of friction. While almost no wear on the pin could be detected at 10% OME, the first visible material removal occurs at an OME content of 20% and the layer delaminated at 30% OME. The evaluation of the RNT wear tests showed that both the tests with engine oil and with engine oil plus 20% OME achieved very low wear rates. No corrosion of the thermal spray coating could be detected by XPS. Only the proportion of engine oil additives in the friction track increased with increasing OME concentration. Full article
(This article belongs to the Special Issue Applied Nanotribology)
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Open AccessArticle Ultra-Low Friction on Tetrahedral Amorphous Diamond-Like Carbon (ta-C) Lubricated with Ethylene Glycol
Received: 23 May 2018 / Revised: 25 June 2018 / Accepted: 3 July 2018 / Published: 7 July 2018
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Abstract
Lubricated tetrahedral amorphous carbon coatings can show a very complex tribological behavior. In particular, friction regimes with extremely low friction have been observed. In tribological experiments with a ta-C/steel friction pair that was lubricated with ethylene glycol, we observed a sudden and very
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Lubricated tetrahedral amorphous carbon coatings can show a very complex tribological behavior. In particular, friction regimes with extremely low friction have been observed. In tribological experiments with a ta-C/steel friction pair that was lubricated with ethylene glycol, we observed a sudden and very strong decrease in the effective friction coefficient from 0.45 to 0.01 after running-in. By varying different components of the tribological system after this abrupt decrease we investigated the role of the counter-body, the lubricant and the coating. To investigate the surface chemistry, static time-of-flight secondary ion mass spectrometry (ToF-SIMS), dynamic secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS) measurements were performed. Using deuterated lubricants, ToF-SIMS measurements allowed us to distinguish adsorption of hydrogen and hydroxyl-groups from the lubricant from the adsorption from the environment. Deuterated hydroxyl-groups from the lubricant adsorbed to the surface during the experiment. In particular, more adsorbed deuterated hydroxyl-groups were detected prior to the sudden decrease in the friction coefficient. Thus, the sudden decrease in the coefficient of friction was most likely caused by an interplay between the lubricant, the ta-C coating and the counter-body which lead to the formation of transfer and adsorption layers. Full article
(This article belongs to the Special Issue Applied Nanotribology)
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Open AccessReview Electron Microscopy and Spectroscopy in the Analysis of Friction and Wear Mechanisms
Received: 30 May 2018 / Revised: 29 June 2018 / Accepted: 2 July 2018 / Published: 4 July 2018
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Abstract
Friction and wear take place on two solid surfaces in sliding contact as a result of the mechanical, thermal, and chemical interactions with the participation of environmental species. These interactions lead to the formation of a tribo-layer or tribofilm, which attaches on the
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Friction and wear take place on two solid surfaces in sliding contact as a result of the mechanical, thermal, and chemical interactions with the participation of environmental species. These interactions lead to the formation of a tribo-layer or tribofilm, which attaches on the worn surfaces, and consequently, contributes to the variation of the friction and wear behaviour. Electron microscopy and the associated spectroscopic analyses are powerful in probing these matters in spatial resolutions from micro to atomic scale. This article provides a review of the author’s work in the wear and friction mechanisms of physical vapour deposition (PVD) hard coatings, in which various scanning electron microscope (SEM)- and transmission electron microscope (TEM)-based microscopic and spectroscopic techniques were employed. Understanding on the failure mechanisms and the origin of self-adaptive friction has been improved to the nano-scale. Other related issues are also discussed, such as sample preparation techniques for cross-sectional electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy. Full article
(This article belongs to the Special Issue Tribology in Metal Forming)
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Open AccessArticle Performance Evaluation and Lubrication Mechanism of Water-Based Nanolubricants Containing Nano-TiO2 in Hot Steel Rolling
Received: 22 May 2018 / Revised: 27 June 2018 / Accepted: 29 June 2018 / Published: 2 July 2018
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Abstract
Hot rolling tests of a low-alloy steel were conducted at a rolling temperature of 850 °C under different lubrication conditions, including benchmarks (dry condition and water) and water-based nanolubricants containing different concentrations of nano-TiO2 from 1.0 to 8.0 wt%. The effects of
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Hot rolling tests of a low-alloy steel were conducted at a rolling temperature of 850 °C under different lubrication conditions, including benchmarks (dry condition and water) and water-based nanolubricants containing different concentrations of nano-TiO2 from 1.0 to 8.0 wt%. The effects of nanolubricants on rolling force, surface roughness, thickness of oxide scale, and microstructure were systematically investigated through varying nano-TiO2 concentrations. The results show that the application of nanolubricants can decrease the rolling force, surface roughness and oxide scale thickness of rolled steels, and refine ferrite grains. In particular, the nanolubricant containing an optimal concentration (4.0 wt%) of nano-TiO2 demonstrates the best lubrication performance, owing to the synergistic effect of lubricating film, rolling, polishing, and mending generated by nano-TiO2. Full article
(This article belongs to the Special Issue Tribology in Metal Forming)
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