Optical emission diagnostics of cathodic arc plasmas used for deposition of TiN and Ti(C, N) coatings

The interelectrode region of titanium arc discharge in various atmospheres (N2, C2H2, mixtures of N2+C2H2 and vacuum) has been investigated by optical emission spectroscopy. A multi-source, industrial arc vacuum device was used to generate the discharges. It was found that the temperatures determined by applying the Boltzmann and coupled Saha–Boltzmann equations for lines of Ti I, Ti II and Ti III were very close together, with exception of those connected with low-lying energy levels of Ti I. The temperatures were dependent on the atmosphere composition. The interelectrode plasma was observed to be in a partial local thermodynamic equilibrium (p-LTE) state. The N2 pressure (between 0.2 and 2 Pa) and the N2/C2H2 ratio (between 5 and 30%) changed the relative abundance of various excited species in the plasma. The electron impact processes were suggested to be here mainly responsible for the excitation and ionization of plasma components in the interelectrode area. The effect of plasma cooling in the presence of higher C2H2 concentration was observed.