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.
Der geringe VerschleilJwiderstand voii Titanwerkstoffen kann mittels thermochemischer Randschichtbehandlung durch Nitrieren erhiiht werden. Im Ergebnis von vergleichenden Untersuchungen zum Gas-und Plasmanitrieren wird die Miiglichkeit einer gezielten Veranderung der Eigenschaften iin beanspruchten Randbereich durch beide Verfahren am Beispiel der (a+p)-Legierung TiA16V4 aufgezeigt. Der Gas-und PlasmanitrierprozeB erfolgte im Temperaturbereich von 650 bis 800 "C iiber 4 bis 48 h in den verschiedenen Gasatmosphiren 100 % NH, (Gas). 100 % N, (Gas und Plasma), 20 9 H2 + 80 % N2 und 20 9% Ar + 20 %I H2 (Plasma). Es wurden Temperaturen im mittleren (a+P)-Gebiet gewiihlt, da sich die Kerneigenschaften bei einer Behandlung im Bereich der S-Transustemperatur verschlechtern. Die Beziehungen zwischen den angewandten Nitrierteclinologien, dem Schichtaufbau (chemisch, phasenmiiUig, geometrisch) und ausgewiihlten Schichteigenschaften (Mikrorauheit, Mikrohirte, Bruch-und Verschleilherhalten) werden beschrieben.The usually low wear resistance of titanium materials can be increased by the thermochemical surface treatment nitriding. In result of comparative investigations of gas and plasma nitriding it will be shown that it is possible to obtain a specific variation of the properties in the highly stressed case by means of these both technologies on example of the (a+p) alloy Ti-6A1-4V. Gas and plasma nitriding was cart-ied out in the temperature range from 650 to 800 "C over 4 to 48 h in different gas atmospheres, i. e. 100 9% NH, (gas), 100 % N2 (gas and plasma), 20 % H, + 80 % N, and 20 % Ar + 20 % H2 (plasma). The temperature range was fixed in the middle of (a+P) region, because the core properties are influenced negative in the field of p-transustemperature. The relations between the applied ni triding technologies, the layer structure (chemical, phases, geometrical) and selected layer properties (microroughness, microhardness, fracture and wear behaviour) are described.
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