Nitriding of surface Mo-enriched sintered iron: Structure and morphology of compound layer

In this work a pulse glow discharge was used to enrich a superficial layer with molybdenum (Mo) and then the nitriding treatment was conducted at high nitrogen concentration for the development of a compound layer. The present study involves an analysis of a compound layer formed on powder metallurgy (PM) parts, sintered with simultaneous surface enrichment and then, nitrided. Both the treatments were assisted by plasma technology. In particular, whether the alloying element Mo is incorporated (dissolved) into the iron nitrides that were formed was investigated. The different microstructures of the Mo-enriched surface layer in sintered iron after plasma nitriding have been investigated by employing light; scanning and transmission electron microscopy (SEM and TEM); X-ray diffraction (XRD); and hardness measurements. Analysis of the entire enriched layer and of the surface of samples demonstrated that Mo is present in the surface as γ-Mo2N fine precipitates and is incorporated into the iron nitrides in the compound layer.