For investigating plasma ion nitriding process , we used two kinds of metals as an objective material ; titanium and an austenitic stainless steel (SUS304) . We observed the D.C. glow discharge morphology and also investigated the nitriding situation of metal surface with X-ray diffraction analyses. We measured Vickers hardness of nitrided surfaces . Titanium was able to be nitrided if we only elevated the temperature of specimen and wherever we placed it (as cathode or anode) or exposed it

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... positive column of the glow plasma. On the other hand, SUS304 was nitrided only when we placed it as a cathode. It is necessary for SUS304 to remove oxide film from the surface. It is concluded that role of plasma in nitriding process is to facilitate removal of the oxide film by means of sputtering.