Reorientation of Randomly Oriented MoSx Coatings During Fretting Wear Tests

The reorientation of as-deposited randomly oriented sulphur-deficient MoS_x coatings during fretting wear tests has been investigated by X-ray diffraction (XRD), Scanning Electron Microscope and Transmission Electron Microscope. The driving force for the reorientation seems to be the plastic deformation induced by the tangential friction force during fretting tests. The evolution from an as-deposited randomly orientation into a basal one occurs above a threshold normal load and fretting frequency. This reorientation results in a lowering of the coefficient of friction as well as in a high resistance to humidity, but unfortunately a high wear rate is noticed. The effect of normal load and fretting frequency on that reorientation process in MoS_x coatings is discussed.