Abstract
The feasibility of a rapid plasma ion nitriding process assisted by hollow cathode discharge has been examined for austenitic stainless steel (SUS304), ferritic stainless steel (SUS340) and Ni base heat resistant alloys (Inconel 625 and Udimet 500).
Hollow cathode discharge was easily realized by arranging two specimens on a cathode plate, so that their treating faces were set parallel at an optimum distance, which was different depending on the pressure of N2+H2 mixed gas as 3 mm for 800 and 1330Pa, 5 mm for 270Pa or 15 mm for 80Pa. At these optimum conditions, the nitriding speed was increased to about 2 times as fast as that for a conventional plasma ion nitriding process at the same nitriding temperature and time without any decrease in the hardness of nitrided layer. This increase in nitriding speed was considered to be due to the high ionization rate of hollow cathode discharge in comparison with conventional glow discharge.
