Effect of Stoichiometry in Mo-Based Ordered Double Transition Metal Carbide MXenes on Solid Lubrication and Tribo-Film Formation
Darío Zambrano, Bo Wang, Beichen Duan, Javier Marqués Henríquez, Paulina Valenzuela, William Gacitúa, Markus Varga, Manel Rodríguez-Ripoll, Krutarth Kiran Kamath, Brian C. Wyatt, Babak Anasori, Andreas Rosenkranz
Abstract
MXenes have emerged as promising solid lubricants due to their layered structure, tunable chemistry, and ability to form mechanically robust, wear-resistant tribo-films. However, most studies have focused on single-metal MXenes such as Ti 3 C 2 T x, Ti 3 CNT x, or V 2 CT x, leaving multimetal MXenes largely unexplored. Here, we present a comprehensive tribological and mechanochemical evaluation of ordered double-transition metal Mo 2 TiC 2 T x and Mo 2 Ti 2 C 3 T x coatings under dry sliding in ambient conditions. Using nanoindentation mapping, X-ray photoelectron spectroscopy, Raman spectroscopy, and electron microscopy, we demonstrate that Mo 2 Ti 2 C 3 T x tends to form dense, chemically stabilized, and mechanically robust tribo-layers thus maintaining a low and stable coefficient of friction (∼0.1) and wear rate (∼0.1 × 10 –3 mm 3 /N·m) under a contact pressure of 0.55 GPa. These tribolayers exhibit improved mechanical properties (hardness ∼ 4.2 GPa; Young’s modulus ∼ 103 GPa), along with increased carbide retention and reduced surface oxidation. In contrast, Mo 2 TiC 2 T x coatings display a less favorable behavior, resulting in a higher COF (∼0.5), greater wear rate (∼1.3 × 10 –3 mm 3 /N·m), and the formation of thinner, chemically degraded tribo-layers under comparable conditions. Mo 2 Ti 2 C 3 T x exhibited the best tribological and mechanical performance under comparable conditions, clearly outperforming Ti 3 C 2 T x, Ti 3 CNT x, and Mo 2 TiC 2 T x . Our study introduces Mo-based MXenes as an emerging frontier in solid lubrication and the importance of MXene structure and composition in their tribo-layer evolution and stress accommodation mechanisms.