Formation and Nature of Carbon-Containing Tribofilms

TLDR

Minimizing friction and wear at rubbing interfaces remains a challenge, prompting the use of coatings such as diamond‑like carbon, whose limited wear life drives the search for alternatives. The authors present a lubrication strategy that generates self‑replenishing, wear‑protective carbon‑containing tribofilms without requiring surface pretreatment. The films form under modest sliding conditions in a polyalphaolefin base oil containing cyclopropanecarboxylic acid as an additive. Raman spectroscopy and reactive molecular‑dynamics simulations reveal that the tribofilms are high‑molecular‑weight hydrocarbons with graphite‑ or DLC‑like signatures that function as solid lubricants.

Abstract

Minimizing friction and wear at a rubbing interface continues to be a challenge and has resulted in the recent surge toward the use of coatings such as diamond-like carbon (DLC) on machine components. The problem with the coating approach is the limitation of coating wear life. Here, we report a lubrication approach in which lubricious, wear-protective carbon-containing tribofilms can be self-generated and replenishable, without any surface pretreatment. Such carbon-containing films were formed under modest sliding conditions in a lubricant consisting of cyclopropanecarboxylic acid as an additive dissolved in polyalphaolefin base oil. These tribofilms show the same Raman D and G signatures that have been interpreted to be due to the presence of graphite- or DLC films. Our experimental measurements and reactive molecular dynamics simulations demonstrate that these tribofilms are in fact high-molecular weight hydrocarbons acting as a solid lubricant.