Oxygen-induced nickel segregation in nitrogen plasma implanted AISI 304 stainless steel

Austenite stainless steel is widely used commercially due to its superior c orrosion resistance. Plasma surface treatment has been shown to improve the wear resistance of the materials without degrading the corrosion resistanc e. Plasma immersion ion implantation (PIII) is a special form of plasma tre atment in which the ion energy can be adjusted easily and its non-line-of-s ight characteristic makes it suitable for large industrial components posse ssing an irregular geometry. We observe nickel segregation beneath the top surface in nitrogen plasma immersion ion implanted AISI 304 stainless steel . The amount of segregated nickel and the location depend on the implantati on conditions. The phenomenon can be attributed to oxygen-induced surface s egregation despite the use of high-purity (99.999%) nitrogen in our experim ents. The Auger results indicate that the sample surface has been unexpecte dly oxidized in spite of a very small amount of oxygen in the residual vacu um, This is due to the non-UHV (ultra-high vacuum) nature of PIII instrumen ts and the reactive plasma environment. It is believed that the movement of the nickel atoms away from the surface is due to the higher affinity of ox ygen to Cr or Fe than Ni. Our investigation also shows that the phenomenon is not related to nitrogen incorporation. As the properties of the treated sample depend on many factors, nickel segregation must be considered in des igning PIII experiments. (C) 2001 Elsevier Science B.V. All rights reserved .