Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (MoS2), niobium diselenide, and hexagonal boron nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and MoS2 exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length-dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets' increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates.

http://science.sciencemag.org/content/sci/328/5974/76.full.pdf

Frictional Characteristics of Atomically Thin Sheets

Global energy consumption due to friction in passenger cars

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. sp 1 ,s p 2 ,s p 3 ) 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. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0022-3727/39/18/R01/pdf

Tribology of diamond-like carbon films: recent progress and future prospects

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

Rapid innovation in nanotechnology in recent years enabled development of advanced metal matrix nanocomposites for structural engineering and functional devices. Carbonous materials, such as graphite, carbon nanotubes (CNT's), and graphene possess unique electrical, mechanical, and thermal properties. Owe to their lubricious nature, these carbonous materials have attracted researchers to synthesize lightweight self-lubricating metal matrix nanocomposites with superior mechanical and tribological properties for several applications in automotive and aerospace industries. This review focuses on the recent development in mechanical and tribological behavior of self-lubricating metallic nanocomposites reinforced by carbonous nanomaterials such as CNT and graphene. The review includes development of self-lubricating nanocomposites, related issues in their processing, their characterization, and investigation of their tribological behavior. The results reveal that adding CNT and graphene to metals decreases both coefficient of friction and wear rate as well as increases the tensile strength. The mechanisms involved for the improved mechanical and tribological behavior is discussed.

Mechanical and tribological properties of self-lubricating metal matrix nanocomposites reinforced by carbon nanotubes (CNTs) and graphene – A review

In recent years, several new solid lubricant and modern lubrication concepts have been developed to achieve better lubricity and longer wear life in demanding tribological applications. Most of the traditional solid lubricants were prepared in the form of metal, ceramic and polymer-matrix composites. They have been used successfully in various engineering applications. Recent progress in thin-film deposition technologies has led to the synthesis of new generations of adaptative, self-lubricating coatings with composite or multilayered architectures, by using duplex/multiplex surface treatments. These modern self-lubricating coatings progressively make their way into the commercial marketplace and meet the ever-increasing performance demands of more severe applications. The present paper reviews our recent understanding of the lubrication mechanisms of both traditional and new solid lubricants, with particular emphasis on solid lubricant methods and practices.

Historical developments and new trends in tribological and solid lubricant coatings.

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. The book provides reliable and up-to-date information on available industrial DLC coatings and includes clear definitions and descriptions of various DLC films and their properties.

/pdf/tribology-of-diamond-like-carbon-films-56s5jlmbp8.pdf

Tribology of diamond-like carbon films

Tribology of Diamond-like Carbon Films discusses important structural, chemical, mechanical and tribological characteristics of DLC films. Particularly dedicated to the fundamental tribological issues that impact performance and durability, this discription covers a variety of industrial applications, including automotive, microelectronics, aerospace, biomedical, textile, and manufacturing. This overview provides current tribological findings on DLC films and emphasizes their application in mechanical systems ranging in size from nano/micro (MEMS, NEMS) to meso/macro scale devices (bearings, gears, aerospace mechanisms, liquid/solid lubricated engine parts and components). Researchers and engineers involved in microelectronics and manufacturing will find contributions from prominent world experts representing academia, national laboratories and industrial companies. Contents: Classification of DLC Films.- Nondestructive Characterization of Carbon Films.- Mechanical Characterization and Properties of DLC Films.- Residual Stresses in DLC Films and Adhesion to Various Substrates.- Fundamentals of the Tribology of DLC Coatings.- Environmental and Thermal Effects on the Tribological Performance of DLC Coatings.- Third Bodies and Tribochemistry of DLC Coatings.- An Overview of Superlubricity in Diamond-like Carbon Films.- Hard DLC Growth and Inclusion in Nano-Structured Wear Protective Coatings.- Environmental and Surface Chemical Effects on Tribological Properties of Carbon-Based Coatings.- Triboemission and Triboplasma Generation with DLC Films.- Doping and Alloying Effects on DLC Coatings.- Tribology of DLC Films under Fretting Conditions.- Tribology of DLC Films Under Slip-Rolling Conditions.- Tribological Behavior of DLC Films in Various Lubrication Regimes.- Industrial Production of DLC Coatings.- DLC Films in Mechanical and Manufacturing Industry.- Wear Resistance of Amorphous DLC and Metal Containing DLC in Industrial Applications.- Nanotribology of Ultrathin and Hard Amorphous Carbon Films.- Laser Processing of Tribological DLC Films: An Overview.- New Trends in Boundary Lubrication of DLC Coatings.- Fullerene-like Carbon Nitride: A New Carbon-Based Tribological Coating.

Tribology of diamond-like carbon films : fundamentals and applications

In recent years, great strides have been made in the formulation of solid lubricant coatings for a wide range of industrial applications These coatings are now available in nano-structured and/or -composite forms to provide better performance and durability even under very severe sliding conditions By coupling these coatings with smart surface engineering strategies (such as micro-texturing and/or -patterning), researchers have achieved higher levels of performance and durability in demanding tribological applications Some of these advanced coatings are now commercially available and can meet the ever-increasing performance and durability requirements of severe tribological applications This paper will provide a historical overview of recent developments in solid lubricant coatings and will expand on the lubrication mechanisms of both traditional and new solid lubricants Special emphasis will be placed on modern practices that are aimed at enhancing the properties of these coatings and expanding their uses in practical applications

C. Donnet

Papers

Tribology of diamond-like carbon films: recent progress and future prospects

Historical developments and new trends in tribological and solid lubricant coatings.

Tribology of diamond-like carbon films

Tribology of diamond-like carbon films : fundamentals and applications

Solid Lubricant Coatings: Recent Developments and Future Trends