Solid Lubrication Performance of Multilayer Ti₃CNT_x Carbonitrides

2D MXene nanosheets have gained increasing attention in tribology due to their excellent wear resistance and solid lubrication capabilities. While carbide-based MXenes have been extensively studied, the tribological performance of carbonitride MXenes, especially under dry conditions, has yet to be assessed. Therefore, we studied the mechanical and tribological performance of multilayer Ti₃CNT_x coatings, revealing their load-dependent tribochemical response. Using linear-reciprocating ball-on-disk tribometry combined with advanced structural and surface characterization, we demonstrate that Ti3CNTx coatings provide excellent friction reduction and wear resistance at low loads due to the formation of compact, aligned, and protective tribofilms. Under higher loads, however, the coatings undergo a transition to severe wear dominated by the formation of rutile TiO₂, a behavior not previously observed in carbide-based MXenes (anatase TiO₂). Our findings highlight the critical role of X-site chemistry (C, N, or CN) in governing tribo-oxidation pathways and tribolayer stability, underscoring the influence of carbonitride composition on the long-term performance of MXene coatings in solid lubrication applications, which are essential for aerospace applications, electrical contacts, or dry-running bearings.

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