A comparative study of beam ion implantation, plasma ion implantation and nitriding of AISI 304 stainless steel

This paper presents the results of a comparative study using beam ion implantation (BII), plasma ion implantation (PII), ion nitriding and gas nitriding of AISI 304 stainless steel. We have demonstrated that under controlled conditions (the same treatment times of 30 and 60 min, and the same treatment temperature of 400 degrees C), the microstructures produced by all four techniques are similar, being mainly the formation of nitrogen in solid solution (gamma(N) phase). However, the concentrations of nitrogen and the detectable depths of the nitrogen-enriched layers are significantly different, depending on the process. Both BII and PII produce thick nitrogen-enriched layers (greater than 1 mu m) at high concentrations (20-30 at.%) compared with either ion nitriding or gas nitriding (layers less than 1 mu m thick with low nitrogen concentrations). As a result, the load-bearing capacity after either BII or PII is much greater than after either ion or gas nitriding. It has also been found that high current density implantation is crucial for the formation of the thick N-enriched layers.