Friction‐induced two‐dimensional solid films from lubricant additives

Abstract

Abstract Tribochemical interactions between some lubricant additives, namely zinc dithiophosphate (ZnDTP), an antiwear additive, molybdenum dithiocarbamate (MoDTC), a friction modifier, and overbased calcium borate (OCaB) detergent, have been investigated. The nature of the tribofilms formed was studied by combining high‐resolution transmission electron microscopy of wear fragments and inside wear scars with micro‐spot X‐ray photoelectron spectroscopy at the same location of the wear track (‘dual’ analysis). The OCaB/ZnDTP/MoDTC ternary system provides both a low wear rate and ultralow friction, while adding detergent and anti‐corrosion properties to the formulation. The analytical data indicate that such a synergistic effect can be attributed to an outstanding feature of the tribofilm nanostructure: it is composed of perfectly oriented MoS 2 single sheets embedded in a single‐phase calcium and zinc borophosphate glass. Compared to phosphate alone, MoS 2 sheets are oriented by the borophosphate phase. This could be related to a template effect of friction‐aligned planar molecules of the glassy borate polymer.