Effect of crystallographic orientation on fretting wear behaviour of MoSx coatings in dry and humid air

The tribological behaviour of MoS2 coatings in air of high humidity is crit ical for their application in air. An improved friction and wear resistance of sulfur-deficient MoSx coatings in humid air is reported based on fretti ng wear tests. For random-oriented MoSx coatings, the coefficient of fricti on and the wear volume are still significantly dependent on the relative hu midity. On the contrary, basal-oriented MoSx coatings show an interesting l ow sensitivity to humidity. MoO3 and SO42- have been detected in the wear t rack and the debris. The amount of MoO3 and SO42- is related to the crystal lographic orientation of the coatings and the relative humidity in the fret ting wear tests. However, them structure and grain size of the MoO3 debris are not dependent on the relative humidity and the crystal orientation of t he coatings. The effect of humidity on the friction and wear of these sulfu r-deficient MoSx coatings with different crystallographic orientations is d iscussed. (C) 2001 Elsevier Science B.V. All rights reserved.