Influence of Additive Chemistry on the Tribological Behavior of Steel/Copper Friction Pairs

The tribological behavior of boundary lubrication is largely dominated by the anti-wear additives. Here five different anti-wear additives were selected and their tribological properties for a steel-copper contact were investigated. It was found that the tribological performance are highly depending on the anti-wear additive chemistry which determines activity, element compositions of the additive. An amine phosphate anti-wear additive AW 316 exhibit best tribological performance with the lowest mean friction coefficient of 0.082 and smallest wear volume which is more than one order of magnitude smaller than base oil. The friction-reducing order of the tested anti-wear additives are AW 316 > ZDDP > 353 > TCP > [P 8888 ][DEHP] while anti-wear showed similar trend. In addition, the tribological mechanism of AW 316 were also discussed based on surface analysis results, and it was found that an even boundary lubrication film of 10–15 nm which was composed of copper oxides, phosphates, amines was formed on the copper disc and is responsible for its outstanding tribological performances. This study provides fundamental insights of the compatibilities among steel-copper friction pairs and suitable anti-wear additives, which can be beneficial for the development of high performance used for steel-copper friction pairs.