Gas nitriding – process control and nitriding non-ferrous alloys

Abstract

This paper, based on the Second Lakhtin Memorial Lecture, gives an overview of the developments in the process control of gas nitriding and describes the current status of nitriding of non-ferrous alloys. Control of the nitriding process involves both thermodynamic and kinetic factors. On this basis, Lakhtin developed concepts that provide the foundations for controlled gas nitriding processes. The progress in the development of sensors in the last few years offers new possibilities for gas nitriding and nitrocarburising process control. The control of the reaction gas composition leads to higher quality assurance. Adjusting defined nitriding and oxidation potentials enables surface activation of components which allows, for example, a uniform nitriding of stainless steels at temperatures of 300°C. There are significant differences between the nitriding behaviour of aluminium, titanium, and iron alloys owing to the different solubilities of nitrogen in the base metal, the differences between the nitriding and solidus temperatures, and the different oxygen affinities of the base metals. Considerable progress has been made in the field of plasma nitriding of aluminium alloys in recent years. An essential part of this is the evidence that commercial plants can be used for the plasma nitriding of aluminium alloys. New possibilities for the production of load specific nitrided layers on titanium alloys allow the nitriding process to be intensified and combined with solution treatment and subsequent aging.