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

Abstract

The tribological behaviour of MoS 2 coatings in air of high humidity is critical for their application in air. An improved friction and wear resistance of sulfur-deficient MoS x coatings in humid air is reported based on fretting wear tests. For random- oriented MoS x coatings, the coefficient of friction and the wear volume are still significantly dependent on the relative humidity. On the contrary, basal- oriented MoS x coatings show an interesting low sensitivity to humidity. MoO 3 and SO 4 2− have been detected in the wear track and the debris. The amount of MoO 3 and SO 4 2− is related to the crystallographic orientation of the coatings and the relative humidity in the fretting wear tests. However, the structure and grain size of the MoO 3 debris are not dependent on the relative humidity and the crystal orientation of the coatings. The effect of humidity on the friction and wear of these sulfur-deficient MoS x coatings with different crystallographic orientations is discussed.