Surface Modification Of AISI316L Austenitic Stainless Steel By Plasma Nitriding At Anodic Potential

Plasma nitriding is a successfully and widely used technique to improve the surface hardness and wear resistance of stainless steels, especially of the relatively soft austenitic ones. In the DC plasma nitriding, the components to be nitrided are subject to a high cathode potential. For the components with complex geometry, electric field distortions occur around the true edges, known as "edges effects". Low-temperature plasma nitriding can improve the hardness and wear resistance of austenitic stainless steels without losing corrosion resistance by producing a metastable phase supersaturating nitrogen atoms which is usually called'expanded austenite'γN and S-phase.Previous authors' work has demonstrated that the anodic plasma nitriding is possible to achieve a similar hardening effect as general plasma nitriding. A series of plasma nitriding experiments has been carried out on AISI316L austenitic stainless steel in ammonia atmosphere at anodic potential. The phase composition, the compound layer thickness and the surface morphology of the nitrided layer, as well as its surface hardness, were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and microhardness tester. The corrosion properties of the untreated and plasma nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The results showed that, for the samples nitrided with anodic potential at temperatures employed in this study the surface hardness as well as the corrosion resistance was improved substantially.