Reactive Pulsed Laser Deposition of Clustered-Type MoSx (x ~ 2, 3, and 4) Films and Their Solid Lubricant Properties at Low Temperature

We studied the tribological properties of amorphous molybdenum sulfide (MoS<i>_x</i>) thin-film coatings during sliding friction in an oxidizing environment at a low temperature (-100 °C). To obtain films with different sulfur contents (<i>x</i> ~ 2, 3, and 4), we used reactive pulsed laser deposition, where laser ablation of the Mo target was performed in H₂S at various pressures. The lowest coefficient of friction (0.08) was observed during tribo-testing of the MoS₃ coating. This coating had good ductility and low wear; the wear of a steel counterbody was minimal. The MoS₂ coating had the best wear resistance, due to the tribo-film adhering well to the coating in the wear track. Tribo-modification of the MoS₂ coating, however, caused a higher coefficient of friction (0.16) and the most intensive wear of the counterbody. The MoS₄ coating had inferior tribological properties. This study explored the mechanisms of possible tribo-chemical changes and structural rearrangements in MoS<i>_x</i> coatings upon contact with a counterbody when exposed to oxygen and water. The properties of the tribo-film and the efficiency of its transfer onto the coating and/or the counterbody largely depended on local atomic packing of the nanoclusters that formed the structure of the amorphous MoS<i>_x</i> films.