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Title: Atom Probe Tomography Unveils Formation Mechanisms of Wear-Protective Tribofilms by ZDDP, Ionic Liquid, and Their Combination

The development of advanced lubricant additives has been a critical component in paving the way for increasing energy efficiency and durability for numerous industry applications. However, the formation mechanisms of additive-induced protective tribofilms are not yet fully understood because of the complex chemomechanical interactions at the contact interface and the limited spatial resolution of many characterizing techniques currently used. In this paper, the tribofilms on a gray cast iron surface formed by three antiwear additives are systematically studied; a phosphonium-phosphate ionic liquid (IL), a zinc dialkyldithiophosphate (ZDDP), and an IL+ZDDP combination. All three additives provide excellent wear protection, with the IL+ZDDP combination exhibiting a synergetic effect, resulting in further reduced friction and wear. Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) were used to interrogate the subnm chemistry and bonding states for each of the tribofilms of interest. The IL tribofilm appeared amorphous and was Fe, P, and O rich. Wear debris particles having an Fe-rich core and an oxide shell were present in this tribofilm and a transitional oxide (Fe 2O 3)-containing layer was identified at the interface between the tribofilm and the cast iron substrate. The ZDDP+IL tribofilm sharedmore » some of the characteristics found in the IL and ZDDP tribofilms. Finally, tribofilm formation mechanisms are proposed on the basis of the observations made at the atomic level.« less
ORCiD logo [1] ;  [2] ; ORCiD logo [1] ;  [2] ; ORCiD logo [2] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 9; Journal Issue: 27; Journal ID: ISSN 1944-8244
American Chemical Society (ACS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
Country of Publication:
United States
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; atom probe tomography; ionic liquid; lubricant; STEM-EELS; tribofilm; ZDDP
OSTI Identifier: