Microstructural and tribological characterization of MoSx coatings produced by high-energy ion-beam-assisted deposition

Thin (0.1-1 μm) MoSx (x = 1.2) films were deposited onto 440C steel by ion beam sputtering of an MoS2 target with (or without) high-energy (160 keV) Ar+ ion beam assistance. The coatings were analyses for microstructure by transmission electron microscopy and grazing incidence X-ray diffraction and their tribological performance was evaluated using a pin-on-disc machine operating under argon environment. The sputter-deposited MoSx films were amorphous with short-range order in the form of layered clusters parallel to the substrate, whereas the high-energy ion-beam-assisted deposition (high-energy IBAD) films were partially crystallized with no preferential orientation of the layered structure with respect to the surface. In all cases, the initial friction coefficient was low (less than 0.05) but the wear-life (number of revolutions to reach a friction coefficient of 0.2) was much better for the sputter-deposited films (30 000 revolutions for a thickness of 0.5 μm) than for the high-energy IBAD coatings (a few revolutions for a thickness of 0.5 μm). Diffusion processes enhanced by the defects created during the high-energy ion bombardment of the deposit can explain the disappearance of the preferential parallel-to-the-surface orientation of the layered microstructure and, as a consequence, the poor performance of the high-energy IBAD coatings. © 1993.