Tribofilms: aspects of formation, stability and removal

Abstract

There has been much attention paid to the lubricant additives zinc dialkyldithiphosphate and molybdenum dialkyldithiocarbamate as the most commonly used antiwear/antioxidant and friction modifiers. The mechanism by which they function has been the subject of much research work. As a result of these efforts the tribofilms formed from the above additives are fully chemically characterized but understanding the physical properties and the dynamics of their formation, stability and removal is still not satisfactory and needs more research. This paper reviews the general characteristics of tribofilms formed from these additives in single component systems and also on their interactions as well as the current understanding of the dynamics of their formation. Experimental work is then presented alongside discussion of the literature to present a current status of understanding of the stability and the removal of tribofilms. The effect of temperature and additive interactions on the thickness of the steady state tribofilms, and consequently the effect on friction performance, is evaluated. The results of this study show that temperature and additive interactions play a significant role on the dynamic process of tribofilm formation as well as its chemical properties. This study also highlights the areas in which further development is needed to ensure progress in understanding of the tribofilm's formation and removal processes.

A new insight into the interfacial mechanisms of the tribofilm formed by zinc dialkyl dithiophosphate

“…It is clear that the tribofilm is more resistant to rubbing and only a few nanometres of the film are removed. These results are in agreement with [22,32] that report a durable ZDDP tribofilm once fully formed. XPS analysis was carried out to differentiate the chemical properties of the tribofilm formed on the surfaces at two different stages.…”

“…All these studies give good insights of mechanical characteristics of ZDDP tribofilms under severe conditions. It was suggested by Morina et al [22] that the durability of tribofilm can be evaluated by the chemistry of the tribofilm formed on the surface. The experiments were based on investigating the formation, stability and removal of the tribofilm by changing the oils during the tests and monitoring the friction coefficient.…”

“…Testing the model in different conditions suggests that the removal of the tribofilm is time dependent [22,32].…”

Tribofilm Formation As a Result of Complex Interaction at the Tool/Chip Interface during Cutting

“…Comprehensive reviews on tribofilms have been previously published [1,2]. As stressed in these articles, the importance of tribofilms is frequently underestimated.…”

“…Tribofilms, being self-organized patterns [3][4][5], form as a result of (1) the transformation (structural/chemical) of an existing surface layer through interaction with the environment [2][3][4][5][6][7]; or (2) material transfer from the counter body (due to chips sticking to the tool rake surface) with the further formation of a modified layer on top of the original surface [1]. Tribofilms carry out protective, thermal barrier and lubricating functions.…”