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

Journal Article · · ACS Applied Materials and Interfaces

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 (Fe2O3)-containing layer was identified at the interface between the tribofilm and the cast iron substrate. The ZDDP+IL tribofilm shared 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.

Research Organization:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1376428
Journal Information:
ACS Applied Materials and Interfaces, Vol. 9, Issue 27; ISSN 1944-8244
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 28 works
Citation information provided by
Web of Science

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Cited By (5)

Engine Oils in the Field: A Comprehensive Chemical Assessment of Engine Oil Degradation in a Passenger Car journal May 2019
Five-Stage Selection Procedure of Ionic Liquids for Lubrication of Steel–Steel Contacts in Space Mechanisms journal May 2019
Material‐Dependent Antagonistic Effects between Soot and ZDDP journal February 2020
High lubricity and electrical responsiveness of solvent-free ionic SiO 2 nanofluids journal January 2018
Correlation Between Engine Oil Degradation, Tribochemistry, and Tribological Behavior with Focus on ZDDP Deterioration journal May 2019