Complex Behavior of Nano-Scale Tribo-Ceramic Films in Adaptive PVD Coatings under Extreme Tribological Conditions

Abstract

Experimental investigations of nano-scale spatio-temporal effects that occur on the friction surface under extreme tribological stimuli, in combination with thermodynamic modeling of the self-organization process, are presented in this paper. The study was performed on adaptive PVD (physical vapor deposited) coatings represented by the TiAlCrSiYN/TiAlCrN nano-multilayer PVD coating. A detailed analysis of the worn surface was conducted using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) methods. It was demonstrated that the coating studied exhibits a very fast adaptive response to the extreme external stimuli through the formation of an increased amount of protective surface tribo-films at the very beginning of the running-in stage of wear. Analysis performed on the friction surface indicates that all of the tribo-film formation processes occur in the nanoscopic scale. The tribo-films form as thermal barrier tribo-ceramics with a complex composition and very low thermal conductivity under high operating temperatures, thus demonstrating reduced friction which results in low cutting forces and wear values. This process presents an opportunity for the surface layer to attain a strong non-equilibrium state. This leads to the stabilization of the exchanging interactions between the tool and environment at a low wear level. This effect is the consequence of the synergistic behavior of complex matter represented by the dynamically formed nano-scale tribo-film layer.

Thin-Film PVD Coating Metamaterials Exhibiting Similarities to Natural Processes under Extreme Tribological Conditions

“…The adaptive of hard thin-film PVD coatings [ 46 ], as well as self-lubricating hard coatings [ 47 ], had been developed more than a decade ago [ 48 ]. The adaptive features progress in time through the permanent regeneration of surface nanoscale tribo-films caused by the interaction of the coating material with the external environment [ 49 ]. This is directly related to the process of self-organization during friction [ 48 ].…”

“…Such structures determine the adaptive behavior of the studied complex adaptive tribo-system. During friction, these tribo-films are produced on the base surface of the engineered material through structural modification and interaction with the environment (mostly with surrounding oxygen, Figure 1 ) [ 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ].…”

Relationship of Secondary Structures and Wear Resistance of Antifriction Aluminum Alloys for Journal Bearings from the Point of View of Self-Organization During Friction

“…Those run-in results are achieved due to formation of the relevant secondary structures. However, on the initial run-in stage when the equilibrium oxide films are destructed, the coefficient of friction, wear rate, seizure area, temperature in the contact, and thermal conductivity of the surface layers increase [36]. On the initial run-in stage, the following conditions are observed:…”

“…In [36] it is shown that the compositions of the secondary structures formed on the initial run-in stage undergo only minor subsequent changes, in spite of changes in sizes and surface layer structures.…”

The Effect of Elements of Secondary Structures on the Wear Resistance of Steel in Friction against Experimental Aluminum Alloys for Monometallic Journal Bearings

“…During the running-in stage, not only an increase in the contact area and a decrease in the contact load but also the formation of secondary structures occurs. Furthermore, it has been shown [17] that the elemental composition of the SSs was formed at the initial stage of friction.…”