Effect of alpha olefins as additives on the friction performance of a-C/PAO composite systems under variable load conditions

Abstract

The tribological performance of amorphous carbon (a-C) and PAO oil composites is critical for mechanical system. However, the impact of unsaturated AO molecules in PAO oil on the a-C/PAO system under variable loads complicating experimental characterization and understanding of friction mechanisms. Herein, reactive molecular dynamics simulations were employed to systematically examine the influence of AO molecules on the friction behavior of a-C/PAO composite systems under variable load conditions. Results reveal distinct pressure-dependent mechanisms governing the tribological behavior, highlighting the interplay between hydrodynamic lubrication and interfacial passivation. At low contact pressure, friction behavior is primarily governed by hydrodynamic lubrication, where an increase in AO chain length reduces lubricant mobility. Upon increasing contact pressure to 50 GPa, the friction interface transitions to a regime dominated by the competitive interplay between hydrocarbon passivation and C–C bond formation, but the degree of interfacial passivation induced by AO molecules results in variations in friction performance. As pressure further reverts to 5 from 50 GPa, the fracture of long-chain AO molecules into shorter fragments weakens the difference in interfacial structures between systems. These results deepen the understanding of friction mechanisms involving AO molecules in a-C/PAO systems and provide theoretical guidance for designing high-performance lubrication systems.