Deagglomeration of Transfer Film in Metal Contacts Using Nanolubricants

Experimental results presented in this article reveal the ability of nanoparticle-dispersed engine oil (nanolubricant) to deagglomerate metallic transfer films under extreme pressures. Specifically, metallic transfer films were formed and accumulated on the upper AISI 52100 ball in a four-ball tester, which resulted in negative wear—that is, weight gain—under Hertzian contact pressures ranging from 3.4 to 5.5 GPa. When molybdenum disulfide nanoparticles were dispersed in the engine oil, the AISI 52100 upper balls exhibited wear as expected. Scanning electron microscope examination of worn surfaces indicated large patches of metallic transfer films on the ring-shaped wear track of AISI 52100 upper balls tested with the engine oil. Such large patches of transfer films could not be found on the surfaces tested with the nanoparticle-modified engine oil. The experimental results and the mechanism of transfer film deagglomeration are discussed.