Microstructure, corrosion and tribological behaviour of plasma immersion ion-implanted austenitic stainless steel

The surface modification of AISI 316 stainless steel by plasma immersion ion implantation (PI "SUP 3" ) has been investigated over a range of treatment temperatures. Below 250 degrees C the results are similar to those obtained by conventional ion beam implantation of nitrogen, but the depth of nitrogen penetration increases dramatically with temperature. Up to 450 degrees C a nitrogen-expanded austenite phase is formed which is shown to have improved corrosion performance over the untreated material. At 520 degrees C chromium nitride is precipitated and the expanded austenite transforms to martensite, leading to a reduction in corrosion resistance. Pin-on-disc testing indicates improved wear resistance at all temperatures, with reduction in the wear volume by factors of several hundred at high loads. This can be attributed to the formation of an oxide layer which prevents the initiation of severe metallic wear