Improvement of tribological properties of niobium nitride films via copper addition

Niobium nitride and copper (NbN-Cu) composite films with different copper content (Cu/(Nb+Cu) = 0.6 at.%-24.8 at.%) were deposited using magnetron sputtering, and the microstructure and tribological properties of the films were investigated. The results showed that the films exhibited a mixture phase of face-centered cubic (fcc) NbN, hexagonal close-packed (hcp)NbN and fcc-Cu. The addition of copper below 6.0 at.% dropped both friction coefficient (μ) and wear rate (WR) sharply. A further increase in copper content decreased the μ furtherly, while the decreasing in μ took sacrifice of WR. The addition copper of 6.0 at.% into the niobium nitride matrix could broaden the niobium nitride film's effective service temperature to 400 °C. The lubricating copper (<200 °C) and the tribo-phases of copper oxide and niobium oxide remained the value of μ at ∼0.55 regardless of temperatures at the cost of the increase of WR.