Wear Resistance and Non-Magnetic Layer Formation on 316L Implant Material with Plasma Nitriding

In this study, the applicability of plasma nitriding treatment in the production of non-magnetic and corrosion resistant layer on 316L stainless steel implant material was investigated. 316L stainless steel substrates were plasma nitrided at temperatures of 350 °C, 375 °C, 400 °C, 425 °C and 450 °C for 2 h in a gas mixture of 50% N₂–50% H₂, respectively. It was determined that the treatment temperature is the most important factor on the properties of the corrosion resistant layer of 316L stainless steel. The results show that s-phase formed at the temperatures under 400 °C, and at the temperatures above 400 °C, instead of s-phase, CrN and γ′-Fe₄N phases were observed in the modified layer. The electrical resistivity and surface roughness of the modified layer increase with treatment temperature. Under 400 °C the corrosion resistance increased with the temperature, above 400 °C it decreased with the increase in treatment temperature. It was analyzed that the electrical resistivity and the soft (ideal) ferromagnetic properties of 316L stainless steel increased with treatment temperature during nitriding treatment. Also, plasma nitriding at low temperatures provided magnetic behavior close to the ideal untreated 316L stainless steel.