Molybdenum disulfide as a lubricant and catalyst in adaptive nanocomposite coatings

Nanocomposite YSZ–Ag–Mo–MoS2 coatings with different MoS2 additions (0–100 at.%) were deposited with a hybrid pulsed laser/magnetron sputtering/filtered cathodic arc process. Wear testing was performed from 25 to 700 °C for each of the coatings. Electron microscopy and other characterization techniques were used to examine the surfaces and wear tracks of the coatings and to determine the mechanisms resulting in the measured tribological properties. Adaptive coatings containing 8 at.% MoS2 demonstrated a friction coefficient of 0.2 throughout the temperature range examined here, compared to 0.4 for YSZ–Ag–Mo with no MoS2. Characterization of the YSZ–Ag–Mo–8% MoS2 coating revealed that MoS2 and silver provided lubrication at temperatures ≤ 300 °C, while silver molybdate phases and MoO3 were effective lubricants at higher temperatures. Silver molybdate was not observed in the coatings containing 0% MoS2. The role of sulfur in the formation of silver molybdate is briefly discussed.