Dopant-dependent interactions of organic friction-modifying species with diamond-like carbon coatings: A pathway-based review

This is the authors' abstract. We don't add key points for this paper.

Diamond-like carbon (DLC) coatings are widely used in boundary-lubricated contacts because of their high hardness, chemical stability, and low friction. However, their lubricated performance is not governed only by the carbon matrix. Dopants can modify surface chemistry, defect structure, reactivity, and the tendency to form boundary films, tribofilms, or transfer layers, thereby changing how DLC interacts with organic friction-modifying species. This review synthesizes a manually curated corpus of 31 source papers, represented by 307 condition-level extraction rows. The corpus includes low-molecular adsorbates, ester-rich and bio-derived lubricants, polymeric organic friction modifiers, and selected reaction-active additive systems. The evidence does not show that dopants universally improve additive performance. Instead, dopants redirect interfacial response. Si-containing DLC is most consistently associated with adsorption-sensitive behavior toward polar oxygenated and nitrogen-containing species, including fatty acids, alcohols, ethyl lactate, and functionalized copolymers. W/WC-containing DLC systems are more often linked to tribofilm- or transfer-layer-mediated behavior, although their response depends strongly on formulation and counterface. For Ti- and Cr-containing systems, the available data are not only sparse but partly contradictory, and no clear dopant-family pattern can be stated at present. These trends indicate that the key question is how specific dopants redirect adsorption, tribochemistry, and film stability, rather than whether doping is inherently beneficial. The review therefore proposes a pathway-based framework for interpreting doped-DLC/organic-species compatibility and for identifying under-resolved systems as targets for future study.