The effect of nitrogen pressure on cathodic arc deposited NbN thin films

NbN thin films were deposited on non-standard grade high speed steel (HSS) (79.90 wt.% Fe, 0.71 wt.% C, 6.09 wt.% W, 4.52 wt.% Mo, 3.95 wt.% Cr, 1.82 wt.% Co, 1.75 wt.% V and a hardness of 65 HRC) using cathodic arc deposition at 0.125, 0.5, 1.0 and 1.5 Pa nitrogen pressures (PN2), with a bias voltage of − 150 V. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Nanoindentation and Rockwell C analysis were used to characterize the thin films in order to identify the NbN phases and to investigate the influence of PN2 on mechanical properties. Hexagonal β-Nb2N, ε-NbN and δ′-NbN0.95 are identified in XRD analysis. Hardness values derived by nanoindentation technique are 20 GPa for β-Nb2N, ε-NbN and 40 GPa for δ'-NbN0.95. Due to the complexity of phase system special attention was focused on identification of NbN phases by deconvolating the XRD peaks especially at 0.5 Pa in which both ε-NbN and β-Nb2N were found. Rockwell C analysis revealed that the film adhesion is found to be poor at lower PN2, due to the brittle nature of β-Nb2N.