Growth mechanism for Ti(C_xN_1-x) thick films prepared by plasma electrolytic carbonitriding

Ti(C_xN_1-x) thick films were obtained on Ti ₆A_l4V substrate by plasma electrolytic carbonitriding(PECN). The vapor envelope compositon in PECN was investigated by IR, and the growth mechanism of the Ti(C_xN_1-x) films was analyzed. The results show that the gas products in PECN are mainly composed of CH₄, NH₃, C₂H₂, CO, C0₂ and H₂O. The gas products are derived from the decomposition of the organic solvent and there is an interaction between gases. With the extension of the discharge time, the carbon and nitrogen potential in vapor envelope change with the variations of the gases concentrations, so do the ratios of C/N of Ti(C_xN_1-x) films. The Ti(C_xN_1-x) film grows as a result of the following stages during PECN process: (i) the formation of the vapor envelope due to the liberation of gaseous hydrogen and the decomposition of organic solvent, (ii) the dissociation and ionization of gas products under the action of plasma to produce active carbon-and nitrogen-containing radicals, (iii) the diffusion of active carbon-and nitrogen-containing radicals into the titanium under the action of strong electric field, (iv) the absorption of active species and the reaction of the active species with the titanium surface to promote the formation of the Ti(C_xN_1-x) film.