Influence of Cu additions on the mechanical and wear properties of NbN coatings

Abstract The influences of increasing copper content in the NbN–Cu coatings on mechanical and tribological properties were studied. The coatings were deposited on an M2 tool steel by using reactive magnetron sputtering. The copper content of NbN–Cu coatings was adjusted by controlling both the applied current to the Cu target and the dwell time of the substrate in front of the Nb and Cu targets. The copper content of the coatings was varied from 1 to 24 at.%. The microstructure, microhardness and wear properties of the coatings were also examined. The addition of 1 and 5 at.% Cu into NbN coatings modified the grain size and morphology. With the addition of 24 at.% Cu, the coating structure changed into a multilayered one. Mechanically, the microhardness of the coatings except for NbN–24 at.% Cu was increased by the addition of Cu. The hardness of the films reached the maximum level, 40 GPa, at 1 at.% copper content, while the hardness of the coatings decreased to 8 GPa with the addition of 24 at.% Cu. The addition of 1 at.% Cu into niobium nitride showed a beneficial effect on the abrasive character of the coatings. The wear of the counter material has increased in these coatings without the occurrence of any wear damage on the coating side. Higher Cu content multilayer coatings showed very severe wear damage.