Glow-discharge plasma nitriding is carried out in nitrogen-hydrogen atmospheres at pressures in the range of 100 to 1000. At pressures below 10 Pa, the glow-discharge technique is not used, but plasma can still be generated by radio-frequency (RF) excitation, microwave energy, or electrons produced by a heated filament. These low-pressure plasmas diffuse through the treatment chamber with a large number of active species, which increases the nitriding efficiency. The uncoupling of plasma generation from the part being treated allows independent control of the energy and flux of ions against the substrate surface, and the temperature can be kept low.
In the RF plasma process, plasma is generated by high frequency, in the range of 13.56 MHz, is applied to an inductive antenna inside the vacuum chamber. The part is heated by heating the chamber and the working table with standard electrical resistance. One of the limiting factors for the commercial exploitation of the process is the high vacuum required, and the subsequent cost. The diagram shows a schematic of RF plasma equipment.
Volume 4D, Heat Treating of Irons and Steels ⇒ Nitriding of Stainless Steels ⇒ Thermochemical Nitriding Treatments
