Micro-tribological performance of MoS2 lubricants with varying Au content

Microtribological testing with a spherical diamond tip (radius = 100 μm) was conducted on two Au–MoS2 coatings with 32 at.% and 84 at.% Au. For lower loads (0.2 to 2.0 mN), the performance of both coatings was similar, with minimal wear (< 50 nm depth) and relatively stable friction coefficients. At higher loads (3.0–5.0 mN), similar trends were found for the 84 at.% Au specimen, but the 32 at.% Au sample wore severely and the friction became unstable. Non-linear curve fitting of friction coefficient versus normal load was conducted using a model containing an elastic (Hertzian) term and a plastic (plowing) term. Changes in the two contributions to the friction with time were used to explain the differences in performance observed between the two coatings.