Deagglomeration of Transfer Film in Metal Contacts Using Nanolubricants

Abstract

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.

KEY WORDS:

• Boundary Lubrication (General)
• Molybdenum Disulfide
• Internal Combustion Engine Oils
• Transfer Film
• Solid Lubricant Additives

ACKNOWLEDGEMENT

This work was partially supported by The Boeing Company under contract TBC-HU-GTA-1 (RA-4). We thank John H. Belk and Orval M. Nobles for their help. The authors also acknowledge James Griffin of the Howard University Nanoscience Facility (HNF) for his assistance in using the surface characterization facilities.

Review led by C. Fred Higgs