Correlation of nitrogen gas processing level to structural and tribological properties of MoS2/Ti/N solid lubricated coatings

There has been much interest recently in PVD deposited solid lubricants consisting of MoS2 doped with a metal such as Ti. Coatings have been deposited for this study by unbalanced magnetron co-sputtering of MoS2 and Ti targets in Ar and Ar/N-2 low pressure plasmas. This study examines the effect of nitrogen gas processing level on compositional and structural properties of the coatings and on tribological behavior of coatings during extensive wear testing. It is shown that the presence of nitrogen resulted in microstructural densification, amorphization, and hardening (up to 40% harder), but at the cost of poorer adhesion and increased friction during wear testing. Physical testing methods used included: scratch testing, multi-pass wear testing, and environmental (elevated humidity) pin-on-disc testing. A Hiden EQP quadrupole mass spectrometer was also used to analyze plasma species and energies of ions present during deposition to determine the effect of the nitrogen gas processing level on plasma conditions. These probe data indicate that molecular nitrogen incorporation could be a significant cause of coating embrittlement for high nitrogen gas processing levels. Finally, wear rates of the coatings are compared to Teer Coatings' commercially available MoST (R).