Superior Wear-Resistance of Ti3C2Tx Multilayer Coatings

Owing to MXenes' tunable mechanical properties induced by their structural and chemical diversity, MXenes are believed to compete with state-of-the-art 2D nanomaterials such as graphene regarding their tribological performance. Their nanolaminate structure offers weak interlayer interactions and an easy-to-shear ability to render them excellent candidates for solid lubrication. However, the acting friction and wear mechanisms are yet to be explored. To elucidate these mechanisms, 100-nm-thick homogeneous multilayer Ti3C2Tx coatings are deposited on technologically relevant stainless steel by electro-spraying. Using ball-on-disk tribometry (Si3N4 counterbody) with acting contact pressures of about 300 MPa, their long-term friction and wear of performance under dry conditions are studied. MXene-coated specimens demonstrate a 6-fold friction reduction and an ultralow wear rate (4 x 10(-9) mm(3) N-1 m(-1)) over 100 000 sliding cycles, outperforming state-of-the-art 2D nanomaterials by at least 200% regarding their wear life. High-resolution characterization verified the formation of a beneficial tribolayer consisting of thermally/mechanically degraded MXenes and amorphous/nanocrystalline iron oxides. The transfer of this tribolayer to the counterbody transforms the initial steel/Si3N4 contact to tribolayer/tribolayer contact with low shear resistance. MXene pileups at the wear track's reversal points continuously supply the tribological contact with fresh, lubricious nanosheets, thus enabling an ultra-wear-resistant and low-friction performance.