Abstract
Friction, wear and tribofilm growth of organic friction modifiers (glycerol monooleate and oleamide), anti-wear additive (ZDDP) and binary additive system comprising the organic friction modifiers and ZDDP were studied in polyalphaolefin (PAO) and ester oil. The mechanisms underlying base oil polarity-dependent frictional performance of the OFM and AW additives at high temperature (140 ℃), either singly or in combination, were investigated in the light of chemical composition analysis of the tribofilms post friction measurements using energy dispersive X-ray spectroscopy (EDX), static and dynamic time-of-flight secondary ion mass spectrometry (ToF–SIMS). Depending on the rubbing conditions, the boundary friction coefficient of the binary additive systems was found to be either lower than that of individual additives or to lay between the values for the individual additives. Chemical composition analysis of the tribofilms indicated that the nature of base oil controlled interactions between ZDDP and OFM and consequently adsorption and reactive tribofilm formation in the boundary lubrication layer. Surface roughness and wear scar width measured post tribological tests using 3D surface profiler showed improved wear performance in both PAO and ester-based additive formulations.
Highlights
The use of lubricants dates back to thousands of years and has played a pivotal role in enhancing the durability and efficiency of mechanical components
Chemical composition analysis of the tribofilms indicated that the nature of base oil controlled interactions between zinc dialkyldithiophosphate (ZDDP) and organic friction modifiers (OFMs) and adsorption and reactive tribofilm formation in the boundary lubrication layer
As precipitates from thermal degradation can lead to such deposition, absorption mode Fourier Transform Infrared Spectroscopy (FT-IR) and viscosity measurements of tribo-tested oils were carried out to study the likelihood of oxidative degradation
Summary
The use of lubricants dates back to thousands of years and has played a pivotal role in enhancing the durability and efficiency of mechanical components. Lubricants used today have complex chemical makeup where a variety of bulk and surface active additives are added to the base oil. Lubricant additives enhance the inherent properties of the base oil and impart new characteristics to improve the performance [1]. The need for improved energy efficiency has led to the shift towards low viscosity lubricants [3]. Even though low viscosity lubricants contribute to improved energy efficiency by reducing fluid friction, they are likely to cause a break in oil film. The decrease in base oil viscosity will lead to a decrease in film thickness eventually reaching that of composite surface roughness resulting in high friction and wear in boundary/ mixed lubrication regimes. Friction modifiers and anti-wear additives are used in commercial systems to enhance engine oil performance and to meet ever-rising automotive industry demands
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