Corrosion protection study of nanocrystalline plasma-electrolytic carbonitriding process for CP-Ti

The effect of various nanocrystalline plasma-electrolytic carbonitriding of a commercially pure titanium in a glycerol bath with various additives, such as carbamide, sodium nitrate, and triethanolamine, was studied. Effects of the bath composition on chemical composition and corrosion resistance of the PEC/N films were examined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in Ringer solution. The results showed that the films obtained in solutions with triethanolamine (T-film) had better corrosion resistance. A design of experiment (DOE) technique according to the Taguchi method, was used to optimize the process. The design was constituted of four factors, namely, triethanolamine concentration, electric conductivity of the bath, applied voltage, and duration of the process), each containing three levels. An analysis of the mean of signal-to-noise (S/N) ratio indicated that the corrosion resistance of plasma-electrolytically carbonitrided (commercially pure) Titanium was influenced significantly by the levels in the Taguchi orthogonal array. The optimized coating parameters for corrosion resistance are 1060 g/l for triethanolamine concentration, 360 mS/Cm for electric conductivity of the electrolyte, 260 Volts for applied voltage, and 9 minutes for treatment time. The percentage of contribution for each factor was determined by the analysis of variance (ANOVA). The results showed that the applied voltage is the most significant factor affecting the corrosion resistance of the coatings.