Structure, mechanical and tribological properties of MoSe2 and Mo-Se-N solid lubricant coatings

Mo-Se-N films were prepared by pulsed direct current (DC) High Target Utilisation Sputtering (HiTUS) in reactive Ar + N-2 atmosphere. Here, the effect of nitrogen doping was studied. MoSex film with Se/Mo atomic ratio similar to 2 exhibited polycrystalline structure and the lowest coefficients of friction (COFs) in humid air from 0.025 to 0.1 for loads in the range 2-45 N. Mo-Se-N coatings were deposited with N concentrations ranging from 1 to 40 at.%, whereas Se/Mo ratio varied from 0.6 to 2. Mo-Se-N coatings formed amorphous structures for the N contents above 7 at.% and increased hardness proportional with the N content up to 9 GPa. The addition of nitrogen also resulted in a general decrease in wear rate of two orders of magnitude when compared to pristine films while retaining a reasonably low coefficient of friction. Mo-Se-N films showed notable COF values in humid environment ranging from 0.22 to 0.015 when tested using loads from 2 to 45 N. The excellent friction properties of Mo-Se-N films were associated to the crystallisation of a MoSe2 tribofilm in the wear scar. Moreover, we showed that modern pulsed DC HiTUS technology represents a suitable way of producing thin films with a variety of elemental compositions and desired mechanical and tribological properties, even from sensitive, semiconducting and extremely low thermally conductive MoSe2 targets.

Automated summary

By preparing Mo-Se-N films in reactive atmospheres and controlling the nitrogen doping, films with excellent friction properties, increased hardness, and reduced wear rates can be obtained. Additionally, the use of modern technology allows for the production of films with a variety of elemental compositions and desired properties.