Corrosion performance of the plasma nitrided 316L stainless steel

The AISI 316L stainless steel has been widely used in artificial knee or hip joints, as well as internal fixation devices. It is well known that this material has a good corrosion resistance and acceptable biocompatibility properties. Ion nitriding is a well established process for steel hardening that can also be applied to this kind of steels with the aim of enhancing its hardness but without reducing its corrosion resistance. In this work, the effects of ion nitriding on the corrosion performance of a 3l6L stainless steel was evaluated in a 0.9% sodium chloride solution by using electrochemical tests such as potentiodynamic polarization and linear polarization in both nitrided and untreated AISI 316L steel condition. Surface characterization before and after corrosion testing was performed using scanning electron microscopy (SEM) with an energy dispersive X-ray analysis (EDS). It was shown that an ion nitriding treatment in a 25% N2–75% H2 atmosphere performed at a temperature of 410 °C improves the surface hardness of the AISI 316L stainless steel. However, under the experimental conditions carried out in this research, the nitrided steel is as prone to localized corrosion as the untreated one. It is considered that this behavior is mainly due to the presence of CrN, which precipitates during processing, contributing to the depletion of chromium from the adjacent matrix and leading to a galvanic corrosion mechanism.