Control of plasma nitriding using oxygen probes

It has been shown by experiments, that a recently developed vacuum-tight ox ygen probe enables the direct control of the oxidising action of plasma nit riding atmospheres. In connection with this, the 'oxygen-sensitivity' of st eels with different chromium content has been investigated according to the variation of the hydrogen and amount of oxygen in the nitriding atmosphere . Threshold oxygen partial pressures for the transition from nitriding to o xidising were evaluated. These critical partial pressures decrease with inc reasing chromium content. The oxygen probe measurements confirm the influen ce of further parameters like temperature, pumping time, leakage and histor y of the facility (time interval under atmospheric pressure) on the oxygen partial pressure and thus on the nitriding results. Measuring the oxidising potential by an oxygen probe offers new possibilities in controlling and o ptimising plasma nitriding in commercial facilities. This is of special imp ortance for the treatment of high alloyed steels and non-ferrous materials like aluminium. (C) 2001 Elsevier Science B.V. All rights reserved.