Physicochemical, structural, mechanical, and tribological characteristics of Si3N4-MoS2 thin films deposited by reactive magnetron sputtering

Si3N4 coatings show outstanding performance in wear and corrosion resistance of cutting tools at high temperatures, up to 1000 °C and above. In addition, the incorporation of minor concentrations of MoS2 in Si3N4 could reduce the friction coefficient and preserve sufficiently high hardness values. In the present work, Si3N4-MoS2 thin films were deposited on C and Si (001) substrates by RF and DC reactive deposition magnetron sputtering from Si and MoS2 targets in a Ar/N2 plasma, with different low MoS2 amounts. The thin films were characterized by nanoindentation at different temperatures from 23 °C to 400 °C and sliding friction and nanoscratch tests at a constant temperature of 23 °C. Several different analytical techniques were also employed to characterize the thin films. In the whole layer both Si3N4 and MoS2 compounds are stoichiometric and the structure is amorphous and homogenous. Although the hardness is roughly constant in the here investigated MoS2 concentration range at constant temperature, the lowest amount of MoS2 (0.2 at.%) increases substantially the hardness of Si3N4-MoS2 thin films at 23 °C. The hardness of Si3N4-MoS2 thin films decreases with the increase of temperature. The friction coefficient decreases substantially for MoS2 concentrations between 0.2 and 0.3 at.% and the annealing process does not modify such behavior. The 24 h annealing performed during hardness measurements, up to 400 °C, induced thermally-activated processes in the thin films, which modify the critical load, hardness, and reduced elastic modulus of the thin film when measured at 23 °C.