Mechanical and tribological properties of CNx films deposited by reactive magnetron sputtering

• Published in: Wear 2001-03, Vol.248 (1-2), p.55-64
• Main Authors: Broitman, E., Hellgren, N., Wänstrand, O., Johansson, M.P., Berlind, T., Sjöström, H., Sundgren, J.-E., Larsson, M., Hultman, L.
• Format: Article
• Language: English
• Subjects: Magnetron sputtering; Mechanical properties; TECHNOLOGY; TEKNIKVETENSKAP; Tribological properties
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/S0043-1648(00)00519-6

The hardness, elasticity, wear rate and friction coefficient of carbon nitride (CNx) films of defined microstructure and composition are presented. CNx films were deposited by dc reactive magnetron sputtering from a C target in N2/Ar plasma. Films were grown on Si (001), Ni, and HSS substrates to thickness of ~0.5 µm at a total pressure of 3 mTorr with the N2 fraction varied from 0 to 1, and the substrate temperature Ts, varied from ambient to 350°C. The mechanical and tribological properties of the coatings were evaluated by nanoindentation and dry ball-on-disk test. For CNx (0 = x = 0.35) films deposited below 200°C (amorphous structure), the elastic recovery and hardness do not change significantly with increasing N concentration, however, the friction coefficient increases from 0.19 to 0.45, while the coating wear rate is low. For CNx (0 = x = 0.15) films grown at Ts = 350°C, where a transition from a graphite-like to a "fullerene-like" phase occurs, a dramatic increase in hardness and elasticity is observed. Furthermore, the rms surface roughness decreases from 15.0 to 0.4 nm. For 0.15 = x = 0.20, CNx films deposited at Ts = 350°C (fullerene-like phase) exhibit a smooth surface, high hardness and elasticity (~90% recovery), and a coefficient of friction against hard steel of ~0.25. For all substrates, film friction coefficient tends to increase as the nitrogen content in the film is increased. Results also indicate the formation of a transfer layer which improves the tribological properties of the films. © 2001 Elsevier Science B.V. All rights reserved.