Evolution of damage in MoS2-based dry film lubricants (DFLs) in fretting wear-The effect of DFL thickness and contact geometry

Dry film lubricant (DFL) coatings are widely used to reduce coefficients of friction and damage in highly loaded contacts. This work investigates the behaviour of a commercially available MoS2-based DFL in a cylinder-on-flat contact geometry with a fretting amplitude of 300 μm with a range of cylinder radii and DFL thicknesses. Three stages in the lifetime of the system were identified. In the first stage, the DFL wore with a volumetric rate that was proportional to the number of cycles (under a given load), until the thickness of the DFL was reached; in the second stage, a thin low friction surface layer existed, with its durability being proportional to the contact pressure; in the third stage, metal-metal contact resulted in short-term instabilities in the coefficient of friction and the DFL system was said to have failed.