Effects of pulse frequency and temperature on the nitride layer and surface characteristics of plasma nitrided stainless steel

This work was initiated to examine the effects of pulse frequency and treat ment temperature on the formation of nitrided layers and surface characteri stics during plasma nitriding. Plasma nitriding experiments were performed with 316L austenitic stainless steel at the temperatures of 400 and 500 deg reesC using a pulsed d.c. plasma with various frequencies in an atmosphere of N-2-H-2 gas mixture. The microstructure and thickness of the nitrided la yers and morphology of the nitrided surfaces were investigated using optica l microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (X RD), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). XRD patterns revealed that the surface layer formed at 400 degreesC consisted of S-phase only and CrN + Fe4N nitrides at 500 degreesC, and no change of phase composition with frequency was observed. The compound layer thickened slightly with increased frequency. In addition, the surface roug hness also increased as the frequency of the pulsed plasma was increased fr om 50 to 5000 Hz. (C) 2001 Elsevier Science B.V. All rights reserved.