Low-Friction MoSx Coatings Resistant to Wear in Ambient Air of Low and High Relative Humidity

The investigation of the tribological performance of MoS2-based coatings in air of high humidity is critical for the future use of such low-friction and high-wear-resistant coatings in ambient air. Sulfur-deficient MoSx coatings with a basal plane (x = 1.3) and a random (x = 1.8) crystallographic orientation were produced by planar magnetron sputtering. The coefficient of friction and the wear loss of MoSx coatings in comparison with TiN and amorphous TiB2 coatings were investigated in bi-directional sliding fretting tests performed in ambient air of different relative humidity. The wear rate expressed as a volumetric loss per unit of dissipated energy was determined. From these results, the best friction and wear performance was achieved with basal-plane-oriented MoSx coatings tested at a relative humidity in the range of 10-50%. A coefficent of friction of 0.06-0.08 and a wear rate of 4 × 103μm3J-1, at a normal load of 1 N and a fretting frequency of 10 Hz, were recorded for that type of MoSx coatings.