Structure and tribological properties of MoSx coatings prepared by bipolarDC magnetron sputtering

MoSx coatings were prepared by bipolar pulse DC (balanced and unbalanced) m agnetron-sputtering systems. Deposition parameters, cathode current density , argon pressure, bias voltage and magnetron sputtering conditions, were va ried in order to obtain low friction and wear-resistant coatings. Compositi on and surface morphology were determined by energy dispersive X-rays and s canning electron microscopy, while the structure was investigated by X-ray diffraction. The friction and wear properties were investigated by fretting tests in ambient air of < 10% and 50% relative humidity. On proper selecti on of the argon pressure and the cathode current density, MoSx coatings cha racterised by a strong (002) basal plane orientation parallel to the substr ate were obtained in a reproducible way. Such coatings deposited under opti mised conditions exhibit very good lubricity and high wear-resistance, even in ambient air with a relative humidity of 50%. Conversely, when depositio n parameters such as higher argon pressure and larger cathode current densi ty result in the deposition of a MoSx coatings with a needle-like structure and preferential (100) and (110) plane orientations, a lower wear resistan ce is achieved especially in air of 50% relative humidity. Ion bombardment, achieved by applying a negative voltage bias or unbalanced sputtering cond itions, improves the friction and wear performance. Conversely, a positive bias voltage deteriorates the tribological performance of the coatings. Exp erimental data on the friction and sliding wear resistance for MoSx coating s indicate that the best tribological properties are obtained with low sulf ur and featureless MoSx coatings. <(c)> 2001 Elsevier Science B.V. All righ ts reserved.