DIAGNOSTIC OF ARC DISCHARGES FOR PLASMA NITRIDING BY OPTICAL-EMISSIONSPECTROSCOPY

A new high current (100-300 A), low voltage (25-45 V) and low pressure (0.4-1 Pa) are discharge plasma used for steel nitriding is presented and characterized by optical emission spectroscopy (OES), In this pro cess, the nitriding rate is high even if the workpieces are nitrided a t floating potential without hydrogen in Ar-N-2 gas mixtures. With H-2 , there is no appreciable gain in nitrogen content or in growth rate o f the diffusion layer. In this paper, the OES diagnostic technique has been used to characterize the different excitation processes of both neutral and ionic argon species in Ar-N-2, Ar-H-2 and Ar-N-2-H-2 gas m ixtures. The reactivity of this process is evaluated by using AISI 316 L austenitic stainless steel substrates nitrided for different treatm ent times at 690 K. (C) 1998 Elsevier Science S.A.