Deposition and characterization of magnetron sputtered amorphous Cr–C films

Thin films in the Cr–C system with carbon content of 25–85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 °C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrCx phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young’s modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp2/sp3 ratio of the a-C phase.

► Amorphous, sputtered Cr–C coatings consist of two amorphous phases, CrCx and a-C.
► The relative amounts of amorphous phases influence the properties of the films.
► The resistivity decreases rapidly with increased amount of a-CrCx phase.