Development of Multi-Functional Coating for Ferritic Steels Using Cathodic Plasma Electrolytic Nitriding

Cathodic plasma electrolytic nitriding (c-PEN) technique has been utilized to modify a low-alloy ferritic steel (2.25Cr-1Mo) surface and assess the effect of the c-PEN layer on corrosion, hydrogen permeation, and tribological behavior of the steel. The surface morphology and phase composition of the c-PEN-treated surface were analyzed, and it was found that the surface exhibits a globular network morphology of iron nitride and expanded ferrite. The potentiodynamic polarization results showed that the c-PEN treatment created an electrochemically noble surface compared to the untreated steel. Next, electrochemical hydrogen permeation experiments carried out on the nitrided surface exhibited a noticeable drop in hydrogen permeability, diffusivity, and reversible trap density of the steel. Furthermore, based on nanomechanical and tribological characterization, the c-PEN treatment was found to create a noticeably harder and wear-resistant surface. Overall, these findings demonstrate the applicability of c-PEN treatment to create a multi-functional coating for low-alloy steels that can assist in mitigating the effect of various harsh environments.