Structural Characterization of Fine γ′-Fe4N Nitrides Formed by Active Screen Plasma Nitriding

The paper presents the structural characterization of &gamma
&prime
Fe4N nitrides produced by active screen plasma nitriding (ASPN) processes. Experiments were performed on the Fe-Armco model material at 693, 773, and 853 K for 6 h. Investigation of the properties of the substrate was realized using scanning electron microscopy (SEM, SEM&ndash
EBSD/Kikuchi lines), energy-filtered transmission electron microscopy (TEM-EFTEM), X-ray diffraction (GID, grazing incidence diffraction, micro-XRD), and secondary ion mass spectroscopy (SIMS). Results have confirmed that the &gamma
Fe4N nitrides&rsquo
structure and morphology depend considerably on the nitriding process&rsquo
s plasma conditions and cooling rate. In addition to that, &gamma
formation can be correlated with the surface layer saturation mechanism and recombination effect. It has been shown that the &gamma
Fe4N structure depends considerably on several phenomena that occur in the diffusive layer (e.g., top layer decomposition, nitrogen, and carbon atoms&rsquo
migration). Our research proves that the nitrogen concentration gradient is a driving force of nitrogen migration atoms during the recombination of &gamma
Fe4N nitrides. Finally, realized processes have allowed us to optimize active screen plasma nitriding to produce a surface layer of fine nitrides.