A revised interpretation of the mechanisms governing low friction tribolayer formation in alloyed-TMD self-lubricating coatings

Enhanced Tribological Performance of Low-Friction Nanocomposite WSexSy/NP-W Coatings Prepared by Reactive PLD

A novel laser-based method for producing nanocomposite coatings consisting of a tungsten sulfoselenide (WSe_xS_y) matrix and W nanoparticles (NP-W) was developed. Pulsed laser ablation of WSe₂ was carried out in H₂S gas under appropriate laser fluence and reactive gas pressure. It was found that moderate sulfur doping (S/Se ~0.2-0.3) leads to significant improvement in the tribological properties of WSe_xS_y/NP-W coatings at room temperature. Changes in the coatings during tribotesting depended on the load on the counter body. The lowest coefficient of friction (~0.02) with a high wear resistance was observed in a N₂ environment at an increased load (5 N), resulting from certain structural and chemical changes in the coatings. A tribofilm with a layered atomic packing was observed in the surface layer of the coating. The incorporation of nanoparticles into the coating increased its hardness, which may have influenced the formation of the tribofilm. The initial matrix composition, which had a higher content of chalcogen atoms ((Se + S)/W~2.6-3.5), was altered in the tribofilm to a composition close to the stoichiometric one ((Se + S)/W~1.9). W nanoparticles were ground and retained under the tribofilm, which impacted the effective contact area with the counter body. Changes in the tribotesting conditions-lowering the temperature in a N₂ environment-resulted in considerable deterioration of the tribological properties of these coatings. Only coating with a higher S content that was obtained at increased H₂S pressure exhibited remarkable wear resistance and a low coefficient of friction, measuring 0.06, even under complicated conditions.