Tribological characterization of tungsten nitride coatings deposited by reactive magnetron sputtering

The coatings exhibited different phases as a function of the nitrogen content: films with low N content exhibited the α-W phase; β-W phase was dominant for nitrogen contents from 12 to 15 at.% and β-W2N was observed for nitrogen content higher that 30 at.%. The mechanical and tribological properties of the tungsten nitride coatings were strongly influenced by the structure. The hardness and the Young's modulus values were in the ranges (29-39 GPa) and (300-390 GPa), respectively; the lowest values correspond to the coatings with the highest nitrogen content. Generally, the friction and wear rate of tungsten nitride coatings sliding against ceramic balls increased with nitrogen content reaching a maximum at 12 at.%; further increase of the nitrogen content led to a decrease of the friction and wear. The sliding with the steel balls did not wear the coatings under the selected testing conditions.