Influence of microwave plasma parameters on the nitriding of T-304 stainless steel

A microwave (f = omega/2 pi = 2.45 GHz) electron cyclotron resonance (ECR) plasma source was employed to carry out the nitriding of T-304 stainless steel at low pressures (similar to 10(-4) torr.) with samples at the plasma floating potential. Even for nitriding times as short as 40 min the surface hardness was found to increase up to 6x the initial value; the nitrogen concentration and penetration depth were typically up to 27 at. % and 15 mu m, respectively. These quantifies were determined by measurements of the nitrogen concentration profiles obtained by Nuclear Reaction Analysis (NRA) and by means of energy dispersion X-ray spectroscopy (EDX) analysis of surface perpendicular to that which received the nitrogen flux. Three different mixtures of N-2/H-2 were used as working gases with an electron plasma density which was greater than the critical value. This density was achieved by lowering the external magnetic field to almost half of its resonant value (B-r = 875 G-resonant magnetic field); in this way the samples received enhanced surface ion bombardment during the treatment. The plasma specifications were determined using electric probes. (C) 1998 Elsevier Science Ltd. All rights reserved.