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New Functionality of Ionic Liquids as Lubricant Additives: Mitigating Rolling Contact Fatigue
Benjamin C Stump, Yan Zhou, Huimin Luo
1Research & Development Center, General Motors , 30470 Harley Earl Boulevard , Warren , Michigan 48092-2031 , United States.
ACS Applied Materials & Interfaces
|July 31, 2019
Summary
Ionic liquids (ILs) show promise as lubricant additives for mitigating rolling contact fatigue (RCF). Specific phosphonium-phosphate ILs significantly improved RCF protection in low-viscosity oils, outperforming commercial gear oils.
Area of Science:
- Tribology
- Materials Science
- Mechanical Engineering
Background:
- Oil-soluble ionic liquids (ILs) are known lubricant additives for reducing friction and wear in sliding contacts.
- Their effectiveness in mitigating rolling contact fatigue (RCF) remains largely unexplored.
- Distinct damage mechanisms in sliding versus rolling contacts necessitate different additive functionalities.
Purpose of the Study:
- To investigate the potential of phosphonium-phosphate, ammonium-phosphate, and phosphonium-carboxylate ionic liquids as additives for rolling-sliding boundary lubrication.
- To evaluate their impact on rolling contact fatigue (RCF) performance.
- To understand the chemical basis for ILs' beneficial or detrimental effects on RCF.
Main Methods:
- Evaluation of phosphonium-phosphate, ammonium-phosphate, and phosphonium-carboxylate ionic liquids as additives in a low-viscosity base oil.
- Testing under rolling-sliding boundary lubrication conditions.
- Comparison of performance against a commercial gear oil and analysis of generated tribofilm characteristics.
Main Results:
- Ionic liquid performance in RCF mitigation is chemistry-dependent, with some being beneficial and others detrimental.
- A specific phosphonium-phosphate IL at 2% addition significantly reduced RCF surface damage and vibration noise.
- This superior performance was attributed to the formation of a thicker, smoother, and more homogeneous tribofilm compared to commercial additives.
- The IL-treated low-viscosity oil outperformed a higher-viscosity commercial gear oil.
Conclusions:
- Appropriate ionic liquid additives hold significant potential for enhancing the durability and efficiency of low-viscosity gear and axle fluids.
- The findings suggest a pathway for developing advanced lubricants that can mitigate rolling contact fatigue effectively.
- Tailoring IL chemistry is crucial for optimizing RCF protection in lubrication applications.
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