Effect of sodium carbonate additive on corrosion behavior of nitrocarburized coating by cathodic plasma electrolytic

In this research, nitrocarburized coating by cathodic plasma electrolytic process were deposited on CK45 steel substrate in an electrolyte consisted of Urea and Sodium Carbonate. In order to study the effect of sodium carbonate concentrations on structural characteristic and properties of produced layer, XRD and SEM were used. Moreover, corrosion behavior of these coatings were calculated by two different methods of polarization and EIS in 3. 5 % NaCl. The results showed that an increase in concentration of sodium carbonate from 10 to 30 g/l caused a decrease of 150 volts in discharge inception voltage and coarser pores were observed on the surface of coating. Due to this increase in concentration, the surface roughness of these coatings increased about 1. 5 time. Moreover, ε-Fe2-3N, γ'-Fe4N، Fe3C و Fe[Fe (CN) 6]3 phases were detected in XRD pattern of these coatings. The results of both corrosion tests also revealed that the coating prepared in 20 g/l sodium carbonate had the lowest value of icorr (2. 25×10-6 A/cm2) and the highest value of polarization resistance (33000 Ω. cm2) among all other samples.