On the Friction and Wear Mechanisms of Electrified Steel Contacts in CO2: Unveiling the Role of Carbon-Rich Tribofilms Under Dry Sliding Conditions

This study examines the friction and wear mechanisms of dry sliding steel interfaces in a CO2 atmosphere, with and without contact electrification. Comparative tests were also performed in ambient air and dry N2 atmospheres to differentiate the extent and nature of interfacial phenomena and better understand the underlying friction and wear mechanisms. Experimental results show that contact electrification significantly increases friction and wear in test pairs in air and dry N2, whereas in CO2 the coefficient of friction (CoF) decreases by approximately 30% and wear by nearly 85%. Surface analyses indicate that this improved performance is mainly due to the formation of a stable, highly protective carbon-rich tribofilm on rubbing surfaces in CO2. Additionally, high-resolution TEM and EELS spectra, along with reactive molecular dynamics (MD) simulations, helped elucidate the lubrication mechanisms during sliding in CO2, particularly the pressure-dependent lubrication process. The combined experimental, analytical, and computational results demonstrate that CO2 can tribochemically interact with steel surfaces during sliding, forming a highly protective tribofilm. Therefore, CO2-rich environments can strongly influence tribofilm formation and tribo-oxidation mechanisms at electrified steel interfaces under dry sliding conditions, providing insights that can be used in future studies involving lubricated contacts under electrification to control friction and wear.