COMPARISON OF DIRECT CURRENT AND CATHODIC CAGE PLASMA NITRIDING TECHNIQUES1

摘要

Over the last decade, various plasma nitriding techniques exploring shielding of parts were used in order to eliminate problems in the conventional nitriding technique as edge effects and non-uniformity heating. The cathodic cage plasma nitriding (CCPN) is a technique that uses a same shielding as active screen but with better efficiency and control of process because multi hollow cathodes formation. In this work, the CCPN technique was compared with conventional technique called direct current plasma nitriding (DCPN) during nitriding of both AISI 316 and AISI 1020 steels. Rods with 8.0 mm in diameter were cut to various heights: 1, 3, 5, 8 and 10 mm and nitrided at temperature of 773K, 723K and 673 K using both (DCPN) and (CCPN). Influence of parameters as pressure, position and time of treatment were also evaluated. Unlike of the DCPN, the samples nitrided by CCPN did not have restriction rings in the layer and the hardness on surface is independent of the height of the samples. Further it was observed that the CCPN has a nitriding rate higher than the DCPN when the pressure for the occurrence of the effect of hollow cathode is properly used. These results shows a better efficiency of the CCPN when compared with the conventional technique, evidencing also that the application of such a new technique eliminates problem as thermal gradient and edge effect.