Film-Forming Properties of Zinc-Based and Ashless Antiwear Additives

The evolution of hardness and tribofilm growth during running-in of case carburized steel under boundary lubrication

“…Evaluation Since the formation of these tribofilms initiates in rolling-sliding contact applications, some researchers believed it was caused by increased surface roughness [53,54]. Other work suggested the growth of the films can be additionally attributed to the high, localized contact pressures caused by the asperity contact between surfaces [55,56].…”

Volatility of phosphorus-containing anti-wear agents for motor oils

“…The formation of such films can be measured by the minitraction machine (MTM). 3 In this report the kinetics of the formation of the film was measured. Here, we only show the stabilized effect of two additives after 3 hours (Figure 8).…”

The correlation between ZDDP tribofilm morphology and the microstructure of steel

“…Such patchiness is generally undesirable since it significantly increases surface roughness, especially for initially smooth surfaces [11,12,13,14,15,1,16,17,18,19] and consequently leads to higher asperity stresses with the associated risk of surface damage. AW additives have been observed to cause an increase in coe cient of friction in mixed lubrication regime [5,20,17,16]. This was initially thought to be related to increased surface roughness and tribofilm directionality [5,17], although more detailed studies performed by Spikes and Taylor [16,21] suggest that e↵ects other than surface roughness may also play a role in the mechanism through which ZDDP increases the coe cient of friction.…”

“…AW additives have been observed to cause an increase in coe cient of friction in mixed lubrication regime [5,20,17,16]. This was initially thought to be related to increased surface roughness and tribofilm directionality [5,17], although more detailed studies performed by Spikes and Taylor [16,21] suggest that e↵ects other than surface roughness may also play a role in the mechanism through which ZDDP increases the coe cient of friction. As the formation of AW films is tribologically triggered, some researchers have attributed the morphology of anti-wear tribofilms to asperities present initially on tested specimens with preferential tribofilm formation in such regions resulting from increased local contact pressure [22,23,7].…”

“…Zinc dialkyl dithiophosphates (ZDDPs) are the most popular representatives of this group of additives, due to excellent AW performance and a relatively low cost, as well as some additional beneficial properties such as their extreme-pressure (EP) and anti-oxidant functionalities [1,2,3]. As an alternative to ZDDPs, ashless phosphorus-containing AW additives are often employed in applications where the ZDDP content has to be limited due to environmental concerns [4,5]. In tribochemical tests ZDDP is known to form tribofilms that on the micro-scale exhibit a patch-like morphology [1,6,7,8].…”