Synergistic effect of diisopropyl phosphite and ashless organic ammonium phosphate salt additives on tribological properties of AISI 52100 steel/Al2O3 ceramics

Abstract

The friction-reducing and antiwear effects of the 500SN base oil containing diisopropyl phosphite (T451) and ashless organic ammonium phosphate salt (KT139) on AISI 52100 steel/Al2O3 ceramic were investigated with a ball-on-disc tribometer at a light load of 200 N and a high load of 400 N. The results indicate that the 500SN base oil containing T451 and KT139 appears with a synergistic effect on AISI 52100 steel/Al2O3 ceramic. Under a single additive, increasing percentage of T451 or KT139 can decrease the friction coefficient and the wear rate of the pair monotonously. However, under the compound system, the tribological behaviour of the pair is strongly dependent of the concentrations of additives. Within the experimental data, the most effective compositions for the loads 200 and 400 N are 2 wt%T451 + 2 wt%KT139 and 1 wt%T451 + 3 wt%KT139, respectively. The scanning electron microscopic images showed that plowed grooves, spalling, and corrosion are the dominant wear modes for the pair. The energy dispersive spectroscopy analysis shows that a protective tribochemical film containing both S and P forms on the steel ball worn surface. Nevertheless, the atom concentrations of P and S are too low to be referred for further analysis of the tribochemical reaction mechanism.