Nano-structured CrN/CNx multilayer films deposited by magnetron sputtering

CrN/CNx nano-scale multilayered films have been grown on both Si(1 0 0) and high speed steel substrates (HSS) by closed-field unbalanced magnetron sputtering. Designed experimental parameters enabled an evaluation of the effects of negative substrate bias voltage (Vb), and bi-layer thickness λ (by changing substrate rotation rate) during deposition on the structural and mechanical properties of reactively sputtered CrN/CNx multilayer thin films. In all cases, the CNx layers prepared at OEM = 55% were amorphous independent of Vb, while the microstructures of the CrN layers were dependent primarily on Vb. The CrN layers showed a mixed structure phase consisting of CrN, Cr2N, and Cr at Vb = −(40–120) V. At higher Vb values (−140 V or above), the Cr2N phase was dominant along with low CrN phase content. AFM measurements revealed that the root-mean-square (rms) surface roughness of the CrN/CNx film was 2.5 nm at Vb = −200 V whereas the rms values were about 9.5–3.3 2 nm for lower Vb values of −(40–180 V). By nanoindentation measurements, a maximum hardness of ∼36 GPa was observed in a film prepared at Vb = −140 V. The improved mechanical properties of the CrN/CNx multilayer films are correlated to the phase formation during deposition.