Effect of dispersant on nano-PTFE based lubricants on tribo-performance in fretting wear mode

Abstract

Very recently nano-PTFE particles have shown great promise as anti-friction (AF), anti-wear (AW) and extreme-pressure (EP) additives. However, their stability in oil in suspension form was limited and the issue needed immediate attention. Hence, a proper dispersant was required to be tried, which could avoid the sedimentation and agglomeration problem of nano-particles NPs for a longer time. Hence polyisobutylene succinimide (PIBSI) was selected as a dispersant in this work. This paper describes the effect of nano-PTFE-PIBSI additive interaction in a lubricant system. Initially few oils were prepared containing various amounts (1, 5 and 10%) of PIBSI to investigate its influence on the extent of stability and influence on the tribo-properties leading to selection of an optimum amount for the best possible combination of properties. Oils with PIBSI in a fixed amount (1%) and varying amount of nano-PTFE particles (0 to 6 wt%) were then prepared. The oils were characterized for their physical properties such as density, viscosity, pour point and flash point. The friction and wear studies performed in the oscillating wear mode indicated that PIBSI 1% (wt) was an optimum amount. However, the PIBSI-NP combination clearly showed competition as an AF and AW additive, with a film-forming tendency of the counterface, and hence it showed antagonistic behaviour. With an increase in the amount of NPs, the dominance of the NPs increased and finally the combination of PIBSI and NPs (6 wt%) could significantly improve the AF property (35%) as well as the AW property (25%) of the virgin oil besides improving the stability of the suspension significantly. The topography and surface chemistry of the specimens were examined using scanning electron microscopy/atomic force microscopy to establish the nature of the protective surface film formed on the steel surfaces.