The paper presents the results of nitriding in partially dissociated ammonia of the pure technical iron, respectively 34CrAlMo5 steel after titanaliting in powdery solid medium, with direct reference on the growth kinetics of the layers, the phase composition and the morphology of the resulting layers. Thermodynamics was anticipated and experimentally demonstrated that the layers of titanium aluminide formed on the surfaces of the two metallic materials considered do not constitute barriers to nitrogen diffusion during the nitriding process, but actively participate in the formation of simple or complex nitrides of the two elements, titanium and aluminum. On the other hand, in the presence of these layers, the flux of nitrogen atoms is slightly diminished with repercussions on the dimensions of the structural components of the layer. The conclusion of the experimental research was that the role of titanaliting prior to nitriding is to increase the proportion of the hardening phases in the surface layers of thermochemically processed metal products after nitriding.

This paper discusses the issue of the effects of modifying the activity of nitriding media by diluting ammonia with nitrogen and the concomitant variation in the degree of ammonia dissociation on the layer’s growth kinetics and their phase composition. To understand and quantify the effects of the variation in the main parameters that influence the layer growth kinetics, the experimental programming method was used and mathematical models of interactions between influence and kinetics parameters were obtained for two metallic materials: Fe-ARMCO and 34CrAlMo5 nitralloy steel. It was concluded that the nitriding operating temperature and the degree of nitrogen dilution of the ammonia have statistically significant influences on the kinetics of the nitrided layer. In the same context, it was analytically proved and experimentally confirmed that the ammonia degree dissociation from the gaseous ammonia-nitrogen mixture, along with the dilution degree of the medium with nitrogen, significantly influences the nitrogen potential of the gaseous mixture used for nitriding and thus the concentration of nitrogen in balance at the medium thermochemically processed metal product interface.

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The paper addresses aspects of nitriding in ammonia-nitrogen gaseous mixtures, after simultaneous saturation with Ti and Al using solid powdery media. The effects quantification of the nitriding conditions variation, i.e., temperature, the ammonia dissociation degree and dilution degree with nitrogen, on the layer's growth kinetics, simultaneous saturated with Ti and Al and subsequently nitrided, in the case of two metallic materials, Fe-ARMCO and 34CrAlMo5 steel, could be ensured using the second-order non-compositional experimental programming method. It was concluded that, in the case of ammonia dilution with nitrogen, the variation of the ammonia dissociation degree in the range 20÷70%, in the context of simultaneous dilution of ammonia with nitrogen, statistically significantly influences the layers growth kinetics with increasing nitriding temperature. On the other hand, for a dilution degree of ammonia with about 30% nitrogen and an ammonia dissociation degree of about 45%, the most intense layers growth kinetics was highlighted if the nitrided layer has been previously saturated simultaneously with Ti and Al.

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