Nitriding of austenitic stainless steel using pulsed low energy Ion implantation

Using a pulse low energy ion implantation with an electronic beam switch operating in the kHz regime, a more efficient nitriding process is possible than with either pulsed plasma immersion ion implantation (PIII) or continuous low energy ion implantation (LEII). Besides the pulsed mode, a fast and precise external heating system for controlling the substrate temperature is necessary. Using such an experimental setup, it is shown that the duty cycle itself does not influence the diffusion and phase formation, as long as the exact same substrate temperature is maintained, thus nitrogen uptake and diffusion are decoupled. Optimal nitriding efficiency was observed for a duty cycle between 20 and 35%. At lower duty cycles (below 15% duty cycle), not enough nitrogen was available to allow the formation of expanded austenite, while higher duty cycles led to a reduced layer thickness caused by higher sputtering induced by the increased ion bombardment itself.