Plasma source ion nitriding: A new low temperature, low-pressure nitriding approach

Plasma source ion nitriding is a new approach for surface modification of steel with certain advantages over conventional plasma nitriding and plasma-based nitrogen ion implantation. A nitriding apparatus based on an electron cyclotron resonance (ECR) microwave plasma source has been developed. Nitrogen ions are accelerated from the ECR microwave plasma by a low-pulsed negative bias (typically −2 kV) which is applied directly to the workpiece, implanted, and finally diffused into the steel at elevated temperatures that are regulated up to 550 °C by an auxiliary heater. An application of plasma source ion nitriding into 1Cr18Ni9Ti austenitic stainless steel is described. The nitriding layer thicknesses are varied continuously from 0.8 to 10 μm at various process temperatures from 230 to 480 °C for a nitriding time of 4 h. A dramatic increase in microhardness has been observed. Glancing angle x-ray diffraction has been used to determine the structural changes that occur in the nitrided surface layer.