An insight on the MoS2 tribo-film formation to determine the friction performance of Mo-S-N sputtered coatings

Kaushik Hebbar Kannur*, Teodor Huminiuc, Talha Bin Yaqub, Tomas Polcar, Christophe Pupier, Christophe Héau, Albano Cavaleiro

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Amorphous Mo-S-N coatings are known to provide excellent tribological properties in diverse environments due to easy sliding under the influence of MoS2 tribo-films. However, the role of nitrogen incorporation, the formation mechanism of MoS2 tribo-film at the sliding interface and the changes in the friction behaviour under different environments are not fully understood. In this study, an amorphous coating with 30 at. % N was deposited in a semi-industrial reactive direct current magnetron sputtering (DCMS) system, using a single MoS2 target in combination with a secondary plasma source. The coating was predicted to have either a Mo-S-N phase with N filling some of the S sites or a MoS2(N2) structure where the gas molecules prevent the formation of a crystalline lamellar structure. Tribological studies performed in vacuum and ambient air resulted in steady-state COF values of 0.03 and 0.15, respectively. High-resolution transmission electron microscopy (HRTEM) analysis performed on the wear-tracks revealed that the low coefficient of friction (COF) in vacuum was attributed to the formation of a thick and continuous lamellar tribo-film with a low amount of nitrogen. Contrarily, in ambient air, the surface oxidation disturbed the formation of a continuous MoS2 tribo-film from the amorphous coatings, leading to an increase in the COF and wear rate. This study shows through indirect measurements of the chemical composition of the as-deposited coating and wear debris that nitrogen is stored in gaseous form (N2) within the amorphous matrix and is released from the contact during sliding.

Original languageEnglish
Article number126791
Number of pages6
JournalSurface and Coatings Technology
Early online date10 Jan 2021
Publication statusPublished - 25 Feb 2021


  • Direct current magnetron sputtering
  • Mo-S-N coatings
  • Molybdenum disulfide
  • Nitrogen-alloying mechanism
  • Solid lubricant coatings
  • Transition metal dichalcogenides


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