Nanostructural, electrical, and tribological properties of composite Au–MoS 2 coatings

Abstract

Considerable research has been done on the tribological properties of cosputtered metal/MoS 2 solid lubricant films with low metal content (< 20 at.%) because of their usefulness in applications at high Hertzian contact stress (around 1 GPa). However, cosputtered Au–MoS 2 coatings with a much higher range of metal contents up to (95 at.%) have shown surprisingly good performance at low contact stresses (as low as 0.1 MPa). In the present study, transmission electron microscopy, X-ray diffraction and electrical resistance measurements of cosputtered Au–MoS 2 coatings reveal them to be composites of nanocrystalline Au particles within an amorphous MoS 2 matrix. Electrical conductivity images of the coatings displayed metallic (Au) and semi-conducting (MoS 2) domains of nanometer dimensions. Auger Nanoprobe analyses confirmed that sliding on the coatings causes the formation of a pure MoS 2 layer about a nanometer thick on top of the bulk of the coatings. Lattice resolution atomic force microscopy revealed that this nanometer-thick MoS 2 layer is crystalline, and oriented with the basal plane (0001) parallel to the coating surface. Electrical resistance obtained during sliding and pull-off force measurements was consistent with the structure of the coatings. Sliding friction data on the coatings support previous results showing that performance at different Hertzian contact stresses correlated strongly with Au content.