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Effects of Nitrogen Modification of Porous PVD–MoS<sub>2</sub> Coatings on the Tribological Behavior under Rolling–Sliding Conditions in Vacuum
oleh: Armin Seynstahl, Markus Polzer, Marcel Bartz, Sandro Wartzack, Stephan Tremmel
| Format: | Article |
|---|---|
| Diterbitkan: | MDPI AG 2023-08-01 |
Deskripsi
In order to improve the tribological performance of PVD–MoS<sub>2</sub> coatings, which are frequently used as a solid lubricant for operating in challenging environments, e.g., in a vacuum, they can be modified with nitrogen. This work evaluates the tribological behavior and a possible compaction occurring during the initial tribological load in the rolling contact for pure and nitrogen-modified PVD–MoS<sub>2</sub> coatings in a vacuum. Short-running tests (1000 cycles) of coated steel discs paired with uncoated steel discs made from 100Cr6 (1.3505, AISI 52100) were conducted on a two-disc tribometer. The slide-to-roll ratio of 10.5% was kept constant, while the load was varied in two steps from 1.1 GPa to 1.6 GPa. Subsequently, a comparison was made between the worn and the pristine coatings by means of nanoindentation and an optical analysis of the wear track. The formation of a load-bearing solid lubrication was achieved for both MoS<sub>2</sub>-variants. The main differences affected the material transfer and wear mechanisms. The worn coatings reached a similar wear coefficient of 4 × 10<sup>−6</sup> mm<sup>3</sup>N<sup>−1</sup>m<sup>−1</sup> and a possible compaction of the coatings was found, indicated through an increased indentation hardness (for MoS<sub>2</sub> 1158% and MoS<sub>2</sub>:N 96% at a 1.1 GPa load). The assumed tribological mechanism changed with nitrogen modification, but scales with increasing load. The nitrogen-modified MoS<sub>2</sub> coating showed less compaction than pure MoS<sub>2</sub>, while the frictional behavior was improved by a 17% reduction of the coefficient of friction.