Vacuum tribology of multi-layer Ti3C2Tx and Ti3C2Tx/MoS2 hybrid coatings

Under vacuum conditions, MoS2 is an excellent 2D solid lubricant with remarkable tribological properties. However, its beneficial performance rapidly deteriorates when wear occurs. Within this context, MXene nano-sheets provide a potential alternative to MoS2 due to their superior wear resistance verified under ambient conditions. However, their vacuum performance is completely unexplored. Therefore, this paper aims at scrutinizing the frictional and wear performance of multi-layer Ti3C2Tx and Ti3C2Tx/MoS2 hybrid coatings used as solid lubricants under vacuum by reciprocating sliding tests using a pin-on-disc vacuum tribometer having MoS2 coatings as reference. To understand the involved friction and wear mechanisms as well as to elucidate the involved tribolayer formation, the wear tracks were analysed post-mortem by scanning electron microscopy and X-ray photoelectron spectroscopy. Our results evidenced that multi-layer Ti3C2Tx are not a suitable solid lubricant under vacuum conditions (friction higher than MoS2 coatings). In contrast, MXene/MoS2 hybrid coatings outperformed the pure MoS2 coatings thus displaying the best tribological performance, experiencing low friction for the entire test duration and reduced wear. Therefore, MXene/MoS2 hybrid coatings proved immense potential as anti-friction and wear resistance coatings for future work and prospective space applications.