Mechanical and tribological properties of CN x films deposited by reactive magnetron sputtering

Abstract

The hardness, elasticity, wear rate and friction coefficient of carbon nitride (CN x ) films of defined microstructure and composition are presented. CN x films were deposited by dc reactive magnetron sputtering from a C target in N 2/Ar plasma. Films were grown on Si (0 0 1), Ni, and HSS substrates to thickness of ∼0.5 μm at a total pressure of 3 mTorr with the N 2 fraction varied from 0 to 1, and the substrate temperature T S, 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 CN x (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 CN x (0≤ x≤0.15) films grown at T S=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, CN x films deposited at T S=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.