Morphological and Electrochemical Study of Sulfide/Nitride Nanostructure Deposited Through Pulsed Plasma Electrolysis

This study investigated the feasibility of coating a steel St12 substrate with a sulfide/nitride layer. The coating process was conducted through a plasma electrolysis technique with a pulsed regime applied at frequencies of 100, 500, and 1000 Hz. It was found that the use of higher frequencies in the mentioned process provides better control over workpiece surface temperature and leads to reduced extent of voltage variations required to achieve a fixed temperature. The coating deposited at the frequency of 1000 Hz and voltage of about 235 V exhibited a nanostructure composed of 50 nm particles. The deposited coating consisted of an outer porous layer and an inner relatively dense layer. The x-ray studies identified the phases of the coating as γ′-Fe4N, Fe2-3N and FeS. The presence of FeS phase reduces the friction coefficient of the surface to about half the value obtainable in its absence. Studying the electrochemical impedance of the layer revealed that using a higher frequency in the deposition process increases the stability of resulting layer against seven days of immersion in the corrosive solution.