Abstract: The additives of zinc dialkyldithiophosphate (ZDDP) and molybdenum dialkyldithiocarbamate (MoDTC) was respectively added into samples of poly alpha olefin (PAO), PAO with dispersant and PAO with ester. The sensitivities of ZDDP and MoDTC in different samples were investigated by the grinding test of four-ball machine. In other test, the two additives were mixed and added into the samples and tested by scanning electron microscopy to observe the wear scar on the surface. The results indicated that the ester oil with a mass fraction of 5%-10% improved well the anti-wear performance of PAO base oil. For the PAO with dispersant T154B，the increase of ZDDP could not effectively reduce the diameter of the wear scar, while the increase of MoDTC could. In the ester-containing PAO base oil sample，the diameter of the wear scar was decreased when the ZDDP increased, indicating that the anti-wear effect of ZDDP was better than the MoDTC. No obvious synergistic effect was found for the composite additives compared with the single one. The analysis of wear scar morphology showed that the surface was flat, showing that the MoDTC had better effect on the repair of the worn surface. When ZDDP and MoDTC coexisted in the sample, the surface of the wear scar was irregular, indicating a competitive relationship between the two additives.

Key words: zinc dialkyldithiophosphate, Molybdenum dialkyldithiocarbamate, ester base oil, anti-wear performance