Achieving superlubricity with 2D transition metal carbides (MXenes) and MXene/graphene coatings

Two-dimensional (2D) materials have demonstrated unique friction and antiwear properties unmatched by their bulk (3D) counterparts. A relatively new, large and quickly growing family of two-dimensional early transition metal carbides and nitrides (MXenes) present a great potential in different applications. There is a growing interest in understanding the mechanical and tribological properties of MXenes, however, no report of MXene superlubricity in a solid lubrication process at the macroscale has been presented. Here we investigate the tribological properties of two-dimensional titanium carbide (Ti3C2) MXene deposited on SiO2-coated silicon (Si) substrates subjected to wear by sliding against a diamond-like carbon (DLC)-coated steel ball counterbody using a ball-on-disc tribometer. We have observed that a reduction of the friction coefficient to the superlubric regime (0.0067 ± 0.0017) can be achieved with Ti3C2 MXene in dry nitrogen environment. Moreover, the addition of graphene to Ti3C2 further reduced the friction by 37.3% and wear by the factor of 2 as compared to Ti3C2 alone, while the superlubricity behavior of the MXene remains unchanged. These results open up new possibilities for exploring the family of MXenes in various tribological applications.