MESSAOUDI Salim University of Biskra

Spoluautoři TEYSSANDIER Francis

Among the various processes that are available to nitride iron alloys, the thermal active nitriding process, which uses NH3-H2 gas mixtures, is extremely attractive because it allows controlling the nature of the phases. However, this process still encounters many problems of control and reproducibility. In this work, we used a thermodynamic approach to predict, under the equilibrium conditions, the nature of the phases which can be obtained according to the potential nitriding rN. We traced the phase diagram of Fe-N and build two new diagrams. The diagram: Pressure-Temperature makes it possible to establish the pressures with which nitriding with pure nitrogen gas is possible. And diagram: Temperature-Nitriding Potential allows us to determine the experimental parameters of the nitriding with NH3-H2 gas mixtures. These thermodynamic predictions were confronted with the experimental results. It highlighted the formation of phases under the conditions of thermodynamic equilibrium. And showed that the composition (configuration) of the nitrided layer can be controlled by the nitriding potential as predicted by the model. The nitrided layers are composed by: the diffusion layer  alone, or the diffusion layer  with the nitride ' or the three phases  and ' and . We also noted that the relationship between the thicknesses of the phases ,  ' and  is also function of the value of the nitriding potential.

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