Electrochemical corrosion properties of AISI 304 SS treated by low, intermediate and high temperature plasma immersion ion implantation in a toroidal vessel

Significant improvements in the surface properties of austenitic AISI 304 stainless steel by the use of PIII technology in nitrogen plasmas have been demonstrated. Yet, such treatments, often focused on the development of microhardness, can affect adversely the corrosion performance of the samples. Several results in this direction are presented in this work which have been obtained from the PIII processing of stainless steel plates in a nitrogen plasma within a toroidal chamber. This geometry presents a potential for turbulence which, in turn, should enhance the collisional effects and better the plasma densities. The main relevant structural, mechanical and corrosion wise properties of the samples were analyzed by XRD, SEM, Vickers microhardness, surface profilometry and electrochemical methods. The results indicate that at a low temperature range (below some 250 °C) both microhardness and corrosion resistance improve. At middle temperature ranges (in the order of 250–400 °C) chromium nitride tends to precipitate affecting the austenitic phase and therefore leading to a decline in the tolerance to corrosion albeit to a substantial increase in the sample microhardness. Finally, at higher temperatures, microhardness grows dramatically along with the implantation depth while a significant reduction in the corrosion performance is observed.