Surface texturing for adaptive solid lubrication

The production of surface micro-patterns in steel substrates for solid lubricant (SL) reservoirs was previously shown to provide improved wear and frictional properties in sliding contact. We report on the fabrication of micrometer-sized dimple patterns of different sizes on TiAlCN hard coatings produced by cathodic arc vacuum evaporation. These dimples were produced by reactive ion etching in a mixed Ar/CF4 plasma. An overlayer of MoS2 or Mo/MoS2/Ag SLs was deposited on the micro-textured surfaces using unbalanced magnetron sputtering. The tribological properties of the coatings were investigated against Si3N4 in dry sliding at 25 °C and in air at 570 °C. The coatings and respective wear tracks were examined using scanning electron microscopy (SEM), optical microscopy (OM), optical profilometry (OP), energy dispersive x-ray spectroscopy (EDX), and micro-Raman spectroscopy. The frictional and wear properties of textured and flat surfaces were compared. A significant decrease in friction and wear coefficients was achieved at 25 °C and 570 °C for the textured films because the dimples acted as reservoirs that provided a new supply of SLs to the contact surfaces. The chemistry and phase analysis of the coating wear tracks showed temperature adaptive behavior with the lubrication being provided primarily by MoS2 at 25 °C and by silver and silver molybdate compounds at high temperature.