Enhancement of corrosion resistance of AISI 420 stainless steels by nitrogen and silicon plasma immersion ion implantation

The effects of nitrogen and silicon plasma immersion ion implantation (PIII) on the surface corrosion resistance of martensitic stainless steel AISI 420 were investigated. Nitrogen was plasma-implanted at elevated temperature and diffused to form a thick and continuous nitrided surface layer, followed by silicon cathodic arc plasma implantation to produce an additional Si-rich oxynitride region near the stainless steel surface. X-ray photoelectron spectroscopy was used to delineate the elemental depth distribution and determine the layer composition and structure. Surface microhardness and corrosion measurements were performed using Vicker indentation and potentiodynamic polarization in a NaCl solution, respectively. The experimental results demonstrate the passivation behavior and dramatic reduction of the corrosion current after nitrogen and silicon PIII. Scanning electron microscopy results reveal differences in the pitting distribution and appearance suggesting that the improvement in the corrosion resistance arises from the change in the surface chemical composition due to the formation of a Si-rich region and oxynitride layer. The mechanism of the enhancement is discussed.