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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 Ti 3 C 2 T x , other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V 2 CT 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 V 2 CT 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 V 2 CT x nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V 2 CT x , which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V 2 CT x (M 2 XT 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 M 4 X 3 T x (V 4 C 3 T x). [Display omitted] [ABSTRACT FROM AUTHOR]

MXene research in tribology has predominantly focused on Ti 3 C 2 T x , overlooking the untapped potential of other promising MXenes with equally intriguing properties. Thus, to enhance tribological reliability in industrial applications, Ti 2 CT x coatings were applied to 316 stainless steel as a solid lubricant. Using a linear ball-on-disk tribometer under 460 MPa pressure, we found that Ti 2 CT x coatings reduced friction by 82% and wear rate by 70% compared to uncoated steel. Advanced characterizations showed that this improved tribology is linked to nanostructured carbon-rich protective tribofilms resulting from the contact pressure-induced graphitization of Ti 2 CT x MXenes sheets. Our research comprehensively elucidates the tribological effectiveness of multi-layer Ti 2 CT x , which is pivotal to design advanced lubricants for contemporary mechanical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to the long-standing use of MAX phase materials since the 1960s and the emergence of MXenes in 2011, both are celebrated for their extraordinary mechano-tribological properties, including layered structures, high mechanical strength, and thermal conductivity. Nevertheless, there remains a crucial research gap in comprehensively comparing their tribological performance under solid lubrication, underscoring the need for an in-depth investigation. To close this research gap, we deposited MAX phase and MXene coatings by spray-coating on stainless-steel substrates. Subsequently, we evaluated their tribological properties, deciphered the underlying mechanisms using linear-reciprocating tribometry and high-resolution material characterizations. Our results demonstrated that the MXene coatings surpass the MAX phase coating in friction reduction by 81.82 %. In terms of wear depth, MXene coating has shown a notably reduced depth compared to both the reference steel sample and the MAX phase coating. Advanced tribochemical analysis indicates that MXenes' superior tribological performance is endorsed by their ability to form a thick, patchy-like transferlayer on the counterbody, which results from their ability to shear and delaminate under acting contact stress. Our study offers a framework for future investigations into utilizing MXene-based materials in tribological applications. [ABSTRACT FROM AUTHOR]