Recent progress in plasma nitriding

The paper reports on a new system for plasma nitriding combined with a hollow cathode discharge sputtering at high pressures (about 1000 Pa), a new way of producing duplex coatings, and on a low-pressure (0.1–0.3 Pa) plasma nitriding using microwave discharges. It has been shown that an addition of an auxiliary cathode into a conventional high-pressure nitriding system can improve properties of the nitrided surfaces by incorporation of the elements sputtered from the auxiliary cathode. A converse duplex coating technique consisting of plasma nitriding or vacuum heat treatment of pre-coated substrates has been successfully tested for the protection of aluminium. It has been shown that a low-alloy steel nitriding can be effective not only inside the low-pressure electron cyclotron resonance discharges, i.e. for a standard distance of the substrate from an output of the plasma source, d =250 mm, but also outside these discharges, i.e. for a large distance d =750 mm.