Features of self-organization in ion modified nanocrystalline plasma vapor deposited AlTiN coatings under severe tribological conditions

2010

Entropy

Abstract:The paper discusses the concept of entropy as applied to friction and wear. Friction and wear are classical examples of irreversible dissipative processes, and it is widely recognized that entropy generation is their important quantitative measure. On the other hand, the use of thermodynamic methods in tribology remains controversial and questions about the practical usefulness of these methods are often asked. A significant part of entropic tribological research was conducted in Russia since the 1970s. Surprisingly, many of these studies are not available in English and still not well known in the West. The paper reviews various views on the role of entropy and self-organization in tribology and it discusses modern approaches to wear and friction, which use the thermodynamic entropic method as well as the application of the mathematical concept of entropy to the dynamic friction effects (e.g., the running-in transient process, stick-slip motion, etc.) and a possible connection between the thermodynamic and information approach. The paper also discusses non-equilibrium thermodynamic approach to friction, wear, and self-healing. In general, the objective of this paper is to answer the frequently asked question -is there any practical application of the thermodynamics in the study of friction and wear?‖ and to show that the thermodynamic methods have potential for both fundamental study of friction and wear and for the development of new (e.g., self-lubricating) materials.

“…Note that S in Equation 10 is entropy per unit surface area and thus it is measured in JK −1 m −2 , unlike the total entropy in Equation 6, which is measured in JK −1 [22,25].…”

Section: Friction and Dissipationmentioning

confidence: 99%

Entropy in Tribology: in the Search for Applications

2010

Entropy

“…The stability condition given by equation (2.15) takes the form of It is known from non-equilibrium thermodynamics that, when the secondary structure is formed, the rate of entropy production reduces (Fox-Rabinovich et al 2007). Therefore, if equation (2.20) is satisfied, the frictional force and wear can reduce.…”

Section: (Iii) Criterion For Self-organizationmentioning

confidence: 99%

“…This includes polymer composites (White et al 2001), polymer-nanoparticle mixtures (Lee et al 2003), nanocomposite hard coatings for severe tribological conditions (Fox-Rabinovich et al 2007) and others.…”

Section: (B ) Biomimetic Applicationsmentioning

confidence: 99%

Thermodynamics of surface degradation, self-organization and self-healing for biomimetic surfaces

Phil. Trans. R. Soc. A.

Bhushan

2009

Friction is a dissipative irreversible process; therefore, entropy is produced during frictional contact. The rate of entropy production can serve as a measure of degradation (e.g. wear). However, in many cases friction leads to self-organization at the surface. This is because the excess entropy is either driven away from the surface, or it is released at the nanoscale, while the mesoscale entropy decreases. As a result, the orderliness at the surface grows. Selforganization leads to surface secondary structures either due to the mutual adjustment of the contacting surfaces (e.g. by wear) or due to the formation of regular deformation patterns, such as friction-induced slip waves caused by dynamic instabilities. The effect has practical applications, since self-organization is usually beneficial because it leads to friction and wear reduction (minimum entropy production rate at the self-organized state). Self-organization is common in biological systems, including self-healing and self-cleaning surfaces. Therefore, designing a successful biomimetic surface requires an understanding of the thermodynamics of frictional self-organization. We suggest a multiscale decomposition of entropy and formulate a thermodynamic framework for irreversible degradation and for self-organization during friction. The criteria for self-organization due to dynamic instabilities are discussed, as well as the principles of biomimetic self-cleaning, selflubricating and self-repairing surfaces by encapsulation and micro/nanopatterning.

“…The model suggested in this section can easily be generalized for the case of several parameters j k and f k . In addition, if heat conduction is taken into account, the rate of entropy production per unit interface area is given by (Fox-Rabinovich et al 2007…”

Section: Friction-induced Self-organizationmentioning

confidence: 99%

“…where d 2Ṡ is the second variation of entropy production rate (Fox-Rabinovich et al 2007;Nosonovsky & Bhushan 2009) and k is the number of generalized forces and flows. Equation (2.1) states that the energy dissipation per unit time in the steady state should be at its minimum, or the variations of the flow and the force should be of the same sign.…”

Section: Friction-induced Self-organizationmentioning

confidence: 99%

Self-organization at the frictional interface for green tribology

Phil. Trans. R. Soc. A.

2010

Despite the fact that self-organization during friction has received relatively little attention from tribologists so far, it has the potential for the creation of self-healing and self-lubricating materials, which are important for green or environment-friendly tribology. The principles of the thermodynamics of irreversible processes and of the nonlinear theory of dynamical systems are used to investigate the formation of spatial and temporal structures during friction. The transition to the self-organized state with low friction and wear occurs through destabilization of steady-state (stationary) sliding. The criterion for destabilization is formulated and several examples are discussed: the formation of a protective film, microtopography evolution and slip waves. The pattern formation may involve self-organized criticality and reaction-diffusion systems. A special self-healing mechanism may be embedded into the material by coupling the corresponding required forces. The analysis provides the structure-property relationship, which can be applied for the design optimization of composite self-lubricating and self-healing materials for various ecologically friendly applications and green tribology.