Nitriding of tool steel using dual DC/RFICP plasma process

•Nitriding of tool steel can be accomplished at relatively low power using combined effect of DC and RFICP plasma.•Surface hardness of treated tool steel significantly increases up to more than 1000 HV after only 9 h of nitriding time.

The nitriding process of AISI H13 tool steel samples using dual DC/RFICP source is reported. The aim was to explore the advantages of the process in improving the surface hardness of the material. The reactor incorporated a weakly ionized DC plasma source that provides continuous surface cleaning of the sample and a RFICP discharge source that supplies a highly reactive environment to enhance the kinetics of nitriding process. The gas mixture of Ar, H2 and N2 was used as plasma medium. The samples were nitrided for times ranging between 1 and 20 h by keeping the DC source at 300 V, RF power at 100 W and substrate temperature at 300 °C. The hardness profiles obtained revealed a significant improvement of the present method over conventional nitriding and some advantage over other plasma-assisted methods, especially in the comparatively lower process temperature. The evolution of the hardness could be related to the formation of CrN and Fe4N as confirmed by XRD and EPMA analysis.Abstract code: AO4