Solid lubrication performance of multi-layered V₂CT_x coatings

MXenes induce excellent wear resistance under solid lubrication due to their distinctive surface chemistry, easy-to-shear ability, and capability to form low-friction and wear-resistant tribofilms. However, beyond the extensively studied Ti₃C₂T_x, other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V₂CT_x) coatings (thickness ∼10.8 μm) on steel substrates and studied their tribological performance for prolonged times (10,000 cycles) using a reciprocating ball-on-disk tribometer with acting contact pressure of 445 MPa in ambient conditions. Results show that V₂CT_x-coated substrates demonstrate an 8-fold reduction in friction (COF of 0.11) and a 10-fold wear rate reduction (1.405 × 10⁻⁶ mm³ N⁻¹ m⁻¹). High-resolution materials characterization confirmed that the remarkable tribological performance of these coatings can be traced back to the formation of protective films on the substrate (tribofilm) and counterbody (transferfilm) consisting of contact pressure and frictional heat-induced degraded, deformed, exfoliated V₂CT_x nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V₂CT_x, which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V₂CT_x (M₂XT_x) due to its remarkable thermal stability, low molecular weight, good mechanical properties, and high interlayer spacing, thus serving as an entry point into diverse MXene compositions, including M₄X₃T_x (V₄C₃T_x).