Mechanism of contact pressure-induced friction at the amorphous carbon/alpha olefin interface

Abstract

Combining an amorphous carbon (a-C) film with a lubricating oil can significantly improve the friction performance and lifetime of moving mechanical components. However, the friction mechanism is not well understood owing to a lack of information regarding the structure of the interface when exposed to high contact pressure. Here, we select linear alpha olefin, C 5 H 10 , as a lubricant and study the evolution of the structure of the a-C/C 5 H 10 /a-C sliding interface under contact pressure via reactive molecular dynamics simulation. Our results suggest that introducing C 5 H 10 into the a-C/a-C interface reduces the friction coefficient by up to 93% compared with no lubricant, although the lubricating efficiency strongly depends on the contact pressure. In particular, increasing the contact pressure not only induces the binding of the lubricant with a-C, but also facilitates the dissociation of the C 5 H 10 carboncarbon skeleton by specific scissions, which governs the friction behavior. These results disclose the underlying lubrication mechanism and could enable the development of new and effective lubricating systems with long lifetimes.

Tribo‐Induced Structural Transformation and Lubricant Dissociation at Amorphous Carbon–Alpha Olefin Interface

“…Especially, the friction coefficient at 50 GPa shows lower sensitivity to lubricant variety than that at 5 GPa, which is a typical feature for the boundary lubrication state . Hence, on the one hand, introducing C 5 H 10 , C 8 H 16 , or C 12 H 24 into the a‐C–a‐C sliding interface decreases the friction coefficient, but it works more effectively at the low contact pressure, which is similar to previous study, and the increase of friction coefficient with contact pressure may be related to the strong friction‐induced tribochemical reaction at the interface. On the other hand, the selection of lubricant is essential to optimize the friction property, and a lubricant with high viscosity is suggested for systems working at high contact pressure conditions.…”

“…Note that at the same contact pressure, there is no significant difference in the morphologies when the lubricant changes from C 5 H 10 to C 8 H 16 and C 12 H 24 , while there is a strong dependence on the contact pressure. At the contact pressure of 5 GPa, the AO molecules are uniformly distributed at the interface after the sliding process and two a‐C–AO interfaces can be clearly distinguished . With an increase of contact pressure to 50 GPa, compared to the cases before the sliding process, the mixing and interaction between the a‐C and AOs enhance drastically after the sliding process, and some AO molecules even bond with C atoms located at the deeper position of a‐C structures, suggesting the existence of lubricant dissociation and significant reconstruction of sliding interface, as will be discussed later.…”

“…Figure shows the morphologies of a‐C–C 8 H 16 –a‐C friction system before and after the sliding process, while those for C 5 H 10 and C 12 H 24 lubricants can be found in Figure S1, Supporting Information. Note that at the same contact pressure, there is no significant difference in the morphologies when the lubricant changes from C 5 H 10 to C 8 H 16 and C 12 H 24 , while there is a strong dependence on the contact pressure.…”

“…Friction results including average friction force, average load, and friction coefficient in a‐C–AO–a‐C systems with different lubricants at contact pressures of a) 5 and b) 50 GPa, respectively. Those for the pure a‐C–a‐C system without lubricant and with C 5 H 10 are also presented for comparison.…”

Atomistic Insights into the Tunable Transition from Cavitation to Crazing in Diamond Nanothread-Reinforced Polymer Composites

“…Model Construction. Using the coarse-grained method, the CG models which maintain a lot of atomistic details of the nanoscale systems are advantageous for solving complex physical problems [47,48]. At the beginning, a PMMA polymer chain containing 10 monomers and a DNT reinforcement whose structural configuration is a hydronated CNT with chirality of (3, 0) are constructed.…”