Increasing of gas nitriding kinetics via surface pre-treatment

The possibility of an increase of gas nitriding kinetics was studied. The duration of the first stage of the nitride layer formation, plays a significant role in the overall treatment time. To shorten this time surface activation techniques are used. In the present work cathode sputtering was investigated as a surface activation technique. The investigation was carried out on iron. The cathode sputtering process was performed in a separate chamber under argon atmosphere with the following parameters: voltage 700–1350 V, current density 1–4 mA/cm2 and time 10–60 min. The sample was connected as a cathode and after exposition was introduced into the furnace reaction zone where gas nitriding was carried out in an ammonia atmosphere. The thickness of the compound case and internal diffusion zone were compared for specimens pre-treated and non-pre-treated before gas nitriding. Moreover, changes in the upper surface of iron after cathode sputtering were investigated. It has been stated that cathode sputtering increases the kinetics of nitride layer formation even if the neutral gas is used for sputtering. Also, some mathematical relationships between thickness of nitride layer and cathode sputtering parameters were found.