On plasma nitriding of steels

With the aim of optimizing the nitriding process, experimental studies of t he plasma nitriding of four selected steels were carried out, using a d.c. glow discharge. The process parameters were varied systematically. By means of transmission and scanning electron microscopy and X-ray diffraction, th e microstructures, including the thicknesses of the compound zones and the diffusion zones of the nitrided steels, were obtained. Using cross-sectiona l samples and a micro-Vickers indenter, hardness depth profiles were also o btained. From the time and temperature dependences of the hardness profiles , effective diffusion constants and corresponding activation enthalpies wer e obtained. Furthermore, in an attempt to shed some light on the atomistic nitriding mechanisms, the glow discharges were studied by measuring energy spectra of the energetic ions hitting the cathode (the steel test specimens ). It was shown that an increase of the mean energy of the ions bombarding the steel significantly increases the number of N atoms taken up by the ste el. (C) 2000 published by Elsevier Science S.A. All rights reserved.