The improvement of toughness and tribological properties of niobium nitride film by addition of copper

NbN/Cu composite films with different copper contents were synthesized by pulsed bias ion plating and the influence of copper contents on the crystal structure, toughness and tribological properties at room temperature was investigated. The results showed that three-phase of face-centered cubic (fcc) NbN, hexagonal close-packed (hcp) NbN and fcc-copper coexisted in the films. Addition of copper enhanced toughness from 0.14 MPa m1/2 at 0 at.% copper to 0.73 MPa m1/2 at 25.1 at.% copper due to the appearance a large volume of grain boundaries, while the hardness decreased gradually with the increase of copper contents. The average friction coefficient dropped from 0.81 at 0 at.% copper to 0.58 at 25.1 at.% copper, and the wear rate (WR) first decreased until a minimum, but a further increase in copper content led to the increase of the WR. The minimum value of WR was 1.2 × 10−8 mm3/N·mm at 5.2 at.% copper.