Growing concerns over energy and environmental sustainability have lately sparked worldwide interest in more efficient and cleaner transportation systems and industrial activities. Friction roughly ...consumes one-fifth of all energy used worldwide. One-third of all energy used in transportation goes to overcome friction. At the same time, the fruits of decades of dedicated research on all-electric vehicles powered by advanced batteries are paving the way toward a much cleaner and sustainable transportation future. In this article, we provide a short overview of what are the energy efficiency and environmental impacts of current transportation, industrial, and residential systems and how much of that efficiency is adversely affected by friction and wear losses in moving mechanical parts and components. We also touch upon recent advances in new materials, lubricants, and design changes that could reduce energy losses by 18–40%, mainly resulting from friction and wear. The savings would be up to 8.7% of the total global energy use and 1.4% of the gross national products (GNP). Finally, we calculate the energy consumption and friction losses in battery-powered electric passenger cars and show the benefit of electric cars where the total energy use is in average 3.4 times lower compared to combustion engine powered cars. The CO2 emissions are 4.5 times higher for a combustion engine car compared to an electric car when the electricity comes from renewable energy sources. Moving from fossil to renewable energy sources may cut down the energy losses due to friction in energy production by more than 60%.
•20% (103 EJ) of world total energy consumption goes to overcome friction.•18–40% of that can be saved by applying new technology.•Energy efficiency is 3.4 times lower for ICE passenger cars compared to electric cars.•CO2 emissions are 4.5 times higher for ICE cars than electric cars on renewable electricity.
Calculations of the impact of friction and wear on energy consumption, economic expenditure, and CO
2
emissions are presented on a global scale. This impact study covers the four main energy ...consuming sectors: transportation, manufacturing, power generation, and residential. Previously published four case studies on passenger cars, trucks and buses, paper machines and the mining industry were included in our detailed calculations as reference data in our current analyses. The following can be concluded:
In total, ~23% (119 EJ) of the world’s total energy consumption originates from tribological contacts. Of that 20% (103 EJ) is used to overcome friction and 3% (16 EJ) is used to remanufacture worn parts and spare equipment due to wear and wear-related failures.
By taking advantage of the new surface, materials, and lubrication technologies for friction reduction and wear protection in vehicles, machinery and other equipment worldwide, energy losses due to friction and wear could potentially be reduced by 40% in the long term (15 years)and by 18% in the short term (8 years). On global scale, these savings would amount to 1.4% of the GDP annually and 8.7% of the total energy consumption in the long term.
The largest short term energy savings are envisioned in transportation (25%) and in the power generation (20%) while the potential savings in the manufacturing and residential sectors are estimated to be ~10%. In the longer terms, the savings would be 55%, 40%, 25%, and 20%, respectively.
Implementing advanced tribological technologies can also reduce the CO
2
emissions globally by as much as 1,460 MtCO
2
and result in 450,000 million Euros cost savings in the short term. In the longer term, the reduction can be 3,140 MtCO
2
and the cost savings 970,000 million Euros.
Fifty years ago, wear and wear-related failures were a major concern for UK industry and their mitigation was considered to be the major contributor to potential economic savings by as much as 95% in ten years by the development and deployment of new tribological solutions. The corresponding estimated savings are today still of the same orders but the calculated contribution to cost reduction is about 74% by friction reduction and to 26% from better wear protection. Overall, wear appears to be more critical than friction as it may result in catastrophic failures and operational breakdowns that can adversely impact productivity and hence cost.
H/OH-terminated Diamond Surface Leading to Ultralow Friction and Wear (courtesy of M. Clelia Righi and G. Zilibotti – University of Modena, Italy and Joakim Andersson – Uppsala University, Sweden).
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As the hardest known material, diamond and its coatings continue to generate significant attention for stringent applications involving extreme tribological conditions. Likewise, diamond-like carbon (DLC, especially the tetragonal amorphous carbon, ta-C) coatings have also maintained a high level interest for numerous industrial applications where efficiency, performance, and reliability are of great importance. The strong covalent bonding or sp3-hybridizaiton in diamond and ta-C coatings assures high mechanical hardness, stiffness, chemical and thermal stability that make them well-suited for harsh tribological conditions involving high-speeds, loads, and temperatures. In particular, unique chemical and mechanical nature of diamond and ta-C surfaces plays an important role in their unusual friction and wear behaviors. As with all other tribomaterials, both diamond and ta-C coatings strongly interact with the chemical species in their surroundings during sliding and hence produce a chemically passive top surface layer which ultimately determines the extent of friction and wear. Thick micro-crystalline diamond films are most preferred for tooling applications, while thinner nano/ultranano-crysalline diamond films are well-suited for mechanical devices ranging from nano- (such as NEMS) to micro- (MEMS and AFM tips) as well as macro-scale devices including mechanical pump seals. The ta-C coatings have lately become indispensable for a variety of automotive applications and are used in very large volumes in tappets, piston pins, rings, and a variety of gears and bearings, especially in the Asian market. This paper is intended to provide a comprehensive overview of the recent developments in tribology of super-hard diamond and DLC (ta-C) films with a special emphasis on their friction and wear mechanisms that are key to their extraordinary tribological performance under harsh tribological conditions. Based on the results of recent studies, the paper will also attempt to highlight what lies ahead for these films in tribology and other demanding industrial applications.
We review the most recent advances in tribological studies of 2D materials, with particular focus on the unique mechanisms underlying their novel friction and wear behaviors. Based on the fundamental ...understandings, the impacts of atomic structures of shearing interfaces and environmental factors are summarized and various strategies for achieving friction modulation and superlubricity are discussed. Finally, prospects toward practical applications of 2D materials in engineering mechanical systems are presented.
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Two-dimensional (2D) materials are crystalline materials made of a single or a few layers of atoms. They have been an active research subject in recent years because of their unique physical and chemical properties. In particular, 2D materials such as graphene, hexagonal BN, and MoS2 exhibit some of the lowest friction coefficients and wear rates, making them attractive for enhancing the efficiency, durability, and environmental compatibility of future mechanical systems. This review will focus on recent advances in the tribology of 2D materials. Starting from general physical characteristics, the essential friction and wear behavior of 2D materials together with the associated mechanisms are reviewed for both interlayer and surface sliding. Influences of the atomic structures of the slip interfaces and environmental factors are discussed, with special attention given to various strategies for achieving friction modulation and superlubricity. Finally, the emerging engineering applications of 2D materials, as well as future prospects, are summarized.
Controlling friction and reducing wear of moving mechanical systems is important in many applications, from nanoscale electromechanical systems to large-scale car engines and wind turbines. ...Accordingly, multiple efforts are dedicated to design materials and surfaces for efficient friction and wear manipulation. Recent advances in two-dimensional (2D) materials, such as graphene, hexagonal boron nitride, molybdenum disulfide, and other 2D materials opened an era for conformal, atomically thin solid lubricants. However, the process of effectively incorporating 2D films requires a fundamental understanding of the atomistic origins of friction. In this review, we outline basic mechanisms for frictional energy dissipation during sliding of two surfaces against each other, and the procedures for manipulating friction and wear by introducing 2D materials at the tribological interface. Finally, we highlight recent progress in implementing 2D materials for friction reduction to near-zero valuessuperlubricityacross scales from nano- up to macroscale contacts.
Since their initial discovery, Diamond Like Carbon films have enjoyed an overwhelming interest from both the scientific and industrial community. This book highlights some of the most important ...structural, chemical, mechanical and tribological characteristics of DLC films. It is particularly dedicated to the fundamental tribological issues that impact the performance and durability of these coatings in numerous industrial applications including automotive, microelectronics, aerospace, biomedical, textile, and manufacturing. As a result of numerous systematic studies, there now exist reliable models, computer simulations, and experimental findings that demonstrate some of the lowest friction and wear coefficients for these films. Accordingly, this book covers some of the most important tribological findings on DLC films and emphasizes their application in mechanical systems ranging in size from nano/micro (like MEMS, NEMS) to meso/macro scale devices (like bearings, gears, aerospace mechanisms, liquid/solid lubricated engine parts and components). The book includes contributions from some of the most prominent world experts representing academia, national laboratories, and industrial companies.
This study presents calculations on the global fuel energy consumption used to overcome friction in passenger cars in terms of friction in the engine, transmission, tires, and brakes. Friction in ...tribocontacts was estimated according to prevailing contact mechanisms such as elastohydrodynamic, hydrodynamic, mixed, and boundary lubrication. Coefficients of friction in the tribocontacts were estimated based on available information in the literature on the average passenger car in use today, a car with today’s advanced commercial tribological technology, a car with today’s best advanced technology based upon recent research and development, and a car with the best technology forecasted in the next 10 years. The following conclusions were reached:
•In passenger cars, one-third of the fuel energy is used to overcome friction in the engine, transmission, tires, and brakes. The direct frictional losses, with braking friction excluded, are 28% of the fuel energy. In total, 21.5% of the fuel energy is used to move the car.•Worldwide, 208,000 million liters of fuel (gasoline and diesel) was used in 2009 to overcome friction in passenger cars. This equals 360 million tonne oil equivalent per year (Mtoe/a) or 7.3millionTJ/a. Reductions in frictional losses will lead to a threefold improvement in fuel economy as it will reduce both the exhaust and cooling losses also at the same ratio.•Globally, one passenger car uses on average of 340l of fuel per year to overcome friction, which would cost 510 euros according to the average European gas price in 2011 and corresponds to an average driving distance of 13,000km/a.•By taking advantage of new technology for friction reduction in passenger cars, friction losses could be reduced by 18% in the short term (5–10 years) and by 61% in the long term (15–25 years). This would equal worldwide economic savings of 174,000 million euros and 576,000 million euros, respectively; fuel savings of 117,000 million and 385,000 million liters, respectively; and CO2 emission reduction of 290 million and 960 million tonnes, respectively.•The friction-related energy losses in an electric car are estimated to be only about half those of an internal combustion passenger car.
Potential actions to reduce friction in passenger cars include the use of advanced coatings and surface texturing technology on engine and transmission components, new low-viscosity and low-shear lubricants and additives, and tire designs that reduce rolling friction.
► In passenger cars 1/3 of the fuel is used to overcome friction. ► Worldwide 208,000 million liters fuel was used 2009 to overcome car friction. ► Reduced friction leads to threefold improvement impact in fuel economy. ► Tribology can save 117,000 million liters fuel and 290million t/a CO2 emission. ► Friction losses in electric car are half those of IC passenger car.
During the past two decades, diamond-like carbon (DLC) films have attracted an overwhelming interest from both industry and the research community. These films offer a wide range of exceptional ...physical, mechanical, biomedical and tribological properties that make them scientifically very fascinating and commercially essential for numerous industrial applications. Mechanically, certain DLC films are extremely hard (as hard as 90 GPa) and resilient, while tribologically they provide some of the lowest known friction and wear coefficients. Their optical and electrical properties are also extraordinary and can be tailored to meet the specific requirements of a given application. Because of their excellent chemical inertness, these films are resistant to corrosive and/or oxidative attacks in acidic and saline media. The combination of such a wide range of outstanding properties in one material is rather uncommon, so DLC can be very useful in meeting the multifunctional application needs of advanced mechanical systems. In fact, these films are now used in numerous industrial applications, including razor blades, magnetic hard discs, critical engine parts, mechanical face seals, scratch-resistant glasses, invasive and implantable medical devices and microelectromechanical systems. DLC films are primarily made of carbon atoms that are extracted or derived from carbon-containing sources, such as solid carbon targets and liquid and gaseous forms of hydrocarbons and fullerenes. Depending on the type of carbon source being used during the film deposition, the type of bonds (i.e. sp1, sp2, sp3) that hold carbon atoms together in DLC may vary a great deal and can affect their mechanical, electrical, optical and tribological properties. Recent systematic studies of DLC films have confirmed that the presence or absence of certain elemental species, such as hydrogen, nitrogen, sulfur, silicon, tungsten, titanium and fluorine, in their microstructure can also play significant roles in their properties. The main goal of this review paper is to highlight the most recent developments in the synthesis, characterization and application of DLC films. We will also discuss the progress made in understanding the fundamental mechanisms that control their very unique friction and wear behaviours. Novel design concepts and the principles of superlubricity in DLC films are also presented.
We report that solution-processed graphene layers reduce friction and wear on sliding steel surfaces in air (relative humidity, 30%). In tests with sliding steel surfaces, small amounts of ...graphene-containing ethanol solution decreased wear by almost 4 orders of magnitude and friction coefficients by a factor of 6. A possible explanation for these results is that the graphene layers act as a two-dimensional nanomaterial and form a conformal protective coating on the sliding contact interfaces, and these factors facilitate shear and slow down the tribo-corrosion, thus drastically reducing the wear.
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