Abstract
Diamond-like carbon (DLC) coatings have proven to be an excellent thin film solution for reducing friction of tribological systems as well as providing resistance to wear. These characteristics yield greater efficiency and longer lifetimes of tribological contacts with respect to surface solutions targeting for example automotive applications. However, the route from discovery to deployment of DLC films has taken its time and still the design of these solutions is largely done on a trial-and-error basis. This results in challenges both in designing and optimizing DLC films for specific applications and limits the understanding, and subsequently exploitation, of many of the underlying physical mechanisms responsible for its favorable frictional response and high resistance to various types of wear. In current work multiscale modeling is utilized to study the friction and wear response of DLC thin films in dry and lubricated contacts. Atomic scale mechanisms responsible for friction due to interactions between the sliding surfaces and shearing of the amorphous carbon surface are utilized to establish frictional response for microstructure scale modeling of DLC to DLC surface contacts under dry and graphene lubricated conditions. Then at the coarser microstructural scale both structure of the multilayer, substrate and surface topography of the DLC coating are incorporated in studying of the behavior of the tribosystem. A fracture model is included to evaluate the nucleation and growth of wear damage leading either to loss of adhesion or failure of one of the film constituents. The results demonstrate the dependency of atomistic scale friction on film characteristics, particularly hybridization of bonding and tribochemistry. The microstructure scale modeling signifies the behavior of the film as a tribosystem, the various material properties and the surface topography interact to produce the explicitly modeled failure response. Ultimately, the work contributes towards establishing multiscale modeling capabilities to better understand and design novel DLC material solutions for various tribological applications.
Highlights
Diamond-like carbon (DLC) is the name commonly used for hard carbon coatings, which have similar mechanical, optical, electrical and chemical properties to natural diamond, but which do not have a dominant crystalline lattice structure
This especially with respect to conditions, which lead to superlubricity-like conditions, surface shearing and formation of the respective tribolayers and triboreactivity leading to covalent bond formation and subsequently to elevated values of coefficient of friction
The outcome from Molecular dynamics (MD) simulations is the input to FE modeling, which focuses on quantifying the significance of different surface frictional behaviors with respect to coating system performance and integrity
Summary
Diamond-like carbon (DLC) is the name commonly used for hard carbon coatings, which have similar mechanical, optical, electrical and chemical properties to natural diamond, but which do not have a dominant crystalline lattice structure. They are amorphous and consist of a mixture of sp and sp carbon structures with sp2 -bonded graphite-like clusters embedded in an amorphous sp3 -bonded carbon matrix [1,2]. Diamond-like carbon coatings have excellent tribological properties, very similar to the diamond coatings; they are chemically inert and have excellent biocompatibility. Molecular dynamics (MD) simulations have shown that the three dimensional structure, not just the sp3 /sp ratio, is important in determining the mechanical properties of the coatings
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