Corrosion resistance of AISI 316L stainless steel nitrided by three different plasma assisted techniques

Abstract

Plasma assisted surface modification methods have been used to nitride stainless steels in order to enhance and therefore the lifetime of industrial components. Nevertheless, the corrosion resistance is not always preserved since it is very sensitive to the process parameters, either in implantation or in thermochemical diffusion techniques. AISI 316L stainless steel was plasma nitrided using three different techniques: low energy ion implantation (LEII), plasma immersion implantation (PI3) and convencional DC pulsed plasma nitriding (DCPN). For each method sveral parameters were tested and some of them were selectedto achieve the so called S phase of about 3 um thickness and no nitrides precipitation. The nitrided layer was characterized with OM and SEM. Hardness wass assessed on the surface with Vickers indenter and 25 g load. XRD was performed to characterize The S phase and to detect other phases if present and electrochemical corrosion tests were carried out in 3.5% NaCI solution. Although the S phase thickness in the three groups of samples was comparable, hardness was not and neither wasthe corrosion resistance. The PI3 samples were he hardest with the best performance in corrosion experiments, resulting in a higher breakdown potencial and lower currents.