High-temperature tribological behaviour of sputtered NbNx thin films

The crystal structure of the films changes from hexagonal Nb2N for coatings deposited at 6% N2 to hexagonal NbN for higher nitrogen partial pressures, and reaches a cubic phase for 40% N2. The hardness and Young's modulus strongly depend on the crystal structure. The friction coefficient decreases slightly with increasing temperature, presumably due to niobium oxide formation on the surface during the heating step.