A flexible and tough Ti₃C₂T_x nanocomposite coating for remarkable ultralow friction and wear

Solid lubricants that deliver simultaneously low friction and low wear are central to improving the efficiency and durability of mechanical systems. Inspired by the low-resistance locomotion of earthworms, an “soft-yet-tough” Ti₃C₂T_x MXene/polysiloxane (PS) nanocomposite coating was fabricated by incorporating few-layer Ti₃C₂T_x nanosheets into a cross-linked polysiloxane adhesive matrix and depositing the mixture on the substrate via spin coating. The MXene nanosheets are homogeneously dispersed within the PS network and the resulting coatings exhibit strong adhesion to the metallic substrate. Under reciprocating dry sliding against a Si₃N₄ ball at room temperature and 20% relative humidity, the Ti₃C₂T_x-0.5 coating achieves an ultralow coefficient of friction (COF) of 0.057 with negligible wear, outperforming the uncoated substrate and the substrate lubricated by PAO4 oil. Mechanistic analyses indicate that tribological loading induces a friction-responsive redistribution of Ti₃C₂T_x within the wear track: MXene enrichment near the surface provides a low-shear sliding interface, while subsurface nanosheets reinforce the matrix and improve load-bearing capacity. When combined with conventional oils, the coating further enables solid–liquid composite lubrication, reducing COF to 0.01–0.035 depending on the lubricant, with the minimum value of 0.01 achieved in silicone oil. These results demonstrate a bioinspired design strategy for durable, ultralow-friction coatings and highlight their potential as a complementary technology to liquid lubrication in demanding tribological contacts.