Macroscale Superlubricity with High Pressure Enabled by Partially Oxidized Violet Phosphorus for Engineering Steel

As a novel cross-structured 2D material, violet phosphorus (VP) promises to further develop the dynamic performance, energy efficiency, and service lifetime of mechanical components owing to its high strength and toughness, large carrier mobility, wide bandgap, and good friction-reducing properties. In this work, the partially oxidized violet phosphorus nanosheets (oVP) are synthesized and employed as the lubricating additives in the poly alpha olefin (PAO) oil environment with less oleic acid (OA) improver, which can trigger the macroscale superlubricity on the diamond-like carbon (DLC) film deposited steel surface at high loading pressures (>800 MPa) and sliding speeds (>0.1 m s(-1)). The friction coefficient (COF) of the steel-DLC tribopair lubricated by the oVP-PAO oil can reduce down to 0.0064 with little wear. At the high-pressure sliding interface, the force-thermal coupling action during the running-in process promotes the cleavage and recombination of oVP nanosheets and OA molecules to form a reliable chemical adsorption tribofilm mainly composed of phosphorus oxides and amorphous carbon, which prevents the original asperities from direct contact and provides an ultralow shear strength. These findings suggest a new method to achieve macroscale oil-based high-pressure superlubricity for engineering steel through the lubrication and catalyzation effects of oVP.