Molybdenum disulfide (MoS2) is one of the most broadly utilized solid lubricants with a wide range of applications, including but not limited to those in the aerospace/space industry. Here we present a focused review of solid lubrication with MoS2 by highlighting its structure, synthesis, applications and the fundamental mechanisms underlying its lubricative properties, together with a discussion of their environmental and temperature dependence. The review also includes an extensive overview of the structure and tribological properties of doped MoS2, followed by a discussion of potential future research directions.

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Solid Lubrication with MoS2: A Review

This review provides an overview of recent advances that have been achieved in understanding the basic physics of friction and energy dissipation in molecularly thin adsorbed films and the associated impact on friction at microscopic and macroscopic length scales. Topics covered include a historical overview of the fundamental understanding of macroscopic friction, theoretical treatments of phononic and electronic energy dissipation mechanisms in thin films, and current experimental methods capable of probing such phenomena. Measurements performed on adsorbates sliding in unconfined geometries with the quartz crystal microbalance technique receive particular attention. The final sections review the experimental literature of how measurements of sliding friction in thin films reveal energy dissipation mechanisms and how the results can be linked to film-spreading behavior, lubrication, film phase transitions, superconductivity-dependent friction, and microelectromechanical systems applications. Materials s...

Friction and energy dissipation mechanisms in adsorbed molecules and molecularly thin films

Progress in the design and exploration of hard coatings with high temperature adaptive behavior in tribological contacts is reviewed. When coupled with most recent surface engineering strategies for high temperature contact thermal management, this progress opens a huge opportunity for adaptive coating applications on machine parts, where oils and coolants are commonly used. The adaptive mechanisms discussed here include metal diffusion and formation of lubricant phases at worn surfaces, thermally- and mechanically-induced phase transitions in hexagonal solids, contact surface tribo-chemical evolutions to form phases with low melting point, formation of easy to shear solid oxides, and others. All of these adaptive mechanisms are combined in nanocomposite coatings with synergistic self-adaptation of surface structure and chemistry to lubricate from ambient temperatures to 1000 °C and provide surface chemical and structural reversibility during temperature cycling to maintain low friction coefficients. The review also highlights emerging surface adaptive concepts, where advances with ab initio modeling of intrinsically layered solids point to new compositions for thermally stable, easy to shear ceramic coatings, load- and temperature-adaptive surfaces with arrays of compliant carbon and boron nitride nanotubes as well as low friction two-dimensional structures. Approaches for self-regulation of coating thermal conductivity, heat flow, and thermal spike mitigations are discussed in the context of surface structure evolution and phase transitions. Future progress is linked to the development of in situ exploration techniques, capable of identifying adaptive surface chemistry and structural evolutions in broad temperature regimes. When combined with predictive modeling, such approaches drastically accelerate adaptive coating developments. The review identifies opportunities, strategies, and challenges for designs and applications of hard coatings with high temperature adaptive lubrication and contact thermal management.

Hard coatings with high temperature adaptive lubrication and contact thermal management: review

Self-lubricating composites containing MoS2: A review

The field of friction is usually associated with its obvious practical importance. This tends to emphasize the engineering aspects of friction and thereby hides the fact that there is a wealth of interesting physics involved, part of which cannot be regarded as fully understood at present. New techniques, such as friction force microscopy, have started to provide access to the phenomenon of friction on the atomic scale. This has given a strong impulse to the field of tribology, pushing it significantly beyond the engineering level and into the regime of the fundamental aspects of frictional energy dissipation. This article reflects the authors’ personal view on matters of interest in the field of atomic-scale friction. Rather than to review important contributions in this field, we have chosen to summarize what has been learned and identify phenomena that may seem familiar to tribologists but actually should be regarded as non-trivial from a physical point of view.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pssb.201350154

The physics of atomic‐scale friction: Basic considerations and open questions

https://www.physics.uci.edu/~taborek/publications/Dunckle-TriInter-2011.pdf

Friction of molybdenum disulfide–titanium films under cryogenic vacuum conditions

A variable temperature, ultrahigh vacuum atomic force microscope (AFM) was used to characterize interfacial friction for a single-asperity diamond contact on a diamondlike carbon (DLC) substrate over a nominal substrate temperature range of 90 to 275 K. Calibrated friction force measurements were obtained by analyzing lateral force hysteresis loops as a function of normal force. For sufficiently large normal forces, the lateral force was proportional to the normal force, and a friction coefficient μ could be identified. μ varied approximately linearly with substrate temperature, with μ=0.28 at T=90 K and μ=0.38 at 275 K. These results are compared to other recent variable temperature AFM friction measurements and to theoretical calculations based on the Tomlinson model. This comparison is obscured by large, experimentally uncontrolled temperature differences between the tip and the substrate which inevitably exist in conventional, variable temperature AFMs. A thermal model which can be used to quantitativ...

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Temperature dependence of single-asperity friction for a diamond on diamondlike carbon interface

A Comment on the Letter by Xueying Zhao et al. Phys. Rev. Lett. 102, 186102 (2009). The authors of the Letter offer a Reply.

C. G. Dunckle

Papers

Friction of molybdenum disulfide–titanium films under cryogenic vacuum conditions

Temperature dependence of single-asperity friction for a diamond on diamondlike carbon interface

Comment on "Transition from thermal to athermal friction under cryogenic conditions".