Cathode sputtering as a pre-treatment for gas nitriding

The authors present the results of studying the influence of cathode sputtering used as a pre-treatment on the kinetics of surface layer formation. The samples made of alpha -iron were cathode sputtered before nitriding. The cathode sputtering process was performed in a separate chamber in argon or nitrogen atmosphere. The following parameters of cathode sputtering were applied: voltage; 700-1350V, current density; 1-4A/cm(2), time 10min. The sample was connected as a cathode and immediately after sputtering it was introduced into the reaction zone of the furnace. Gaseous nitriding was carried out in two types of atmospheres: 50%NH3 + NH3dys and 15% NH3 + NH3dys. The time of the nitriding process was 1 h and the temperature 843 K. The results show that sputtering process has a very important influence on increasing the kinetics of nitride layer formation. This influence also depends on the parameters of the sputtering. The higher the current density and voltage, the thicker the nitride layer obtained. Both the gases used for sputtering have the same influence on the nitriding kinetics. Only small changes of surface roughness were observed. The results were controlled by metallographic testings (scanning and light microscopy) and roughness measurements. The structure investigation of the upper surface after sputtering was evaluated by X-ray diffraction (GID). (C) 2001 Elsevier Science Ltd. All rights reserved.