Load-dependent sliding behavior of WSe2-x solid lubricant coating

Transition-metal dichalcogenides (TMDs) are commonly used as solid lubricants in various environments. Molybdenum disulfide is the most studied and applied TMD solid lubricant, but other members may have similar or even better sliding properties. Tungsten diselenide is one of the materials that has rarely been investigated in terms of tribological properties. This paper provides a comprehensive tribological characterization of substoichiometric tungsten diselenide and molybdenum disulfide coatings deposited by magnetron sputtering. We focused on tribological properties at a macroscopic scale, particularly friction and wear dependence on applied load; however, a nanoscale frictional assessment of worn surfaces was performed as well to identify the major wear mechanisms. Substoichiometric tungsten diselenide outperformed traditional molybdenum disulfide, exhibiting much lower friction in humid air, suggesting lower coating sensitivity to the humid atmosphere. Moreover, a combination of nanotribological experiments in the wear tracks with sliding under different environmental conditions suggests that the key factor causing frictional load-dependence (deviation from Amonton's law) is frictional heating of the surface.