저널

The interfacial structure of duplex treated AISI 4140 consisting of iron nitride and TiN layer was characterized by optical microscope, SEM and XRD. A black layer was formed from the decomposition of iron nitride during Ti ion bombardment. The black layer was characterized as an a-Fe phase transformed from the iron nitride by XRD. In order to identify the formation mechanism of the black layer, a thermal analysis of iron nitride undertaken by DSC method. As an iron nitride was mostly consisted of ${gamma}$`-Fe$_4$N and $varepsilon$-$Fe_3$N phase after plasma nitriding, in this study, a ${gamma}$`$-Fe_4$N and $varepsilon$-$Fe_3$N powders were separately prepared by the different processing conditions of gas nitriding of iron powder in the fluidized bed. From the DSC thermal analysis, the phase transformation of ${gamma}$`$-Fe_4$N, $varepsilon$-$Fe_3$N was followed the path of transformation; $ Upsilon{`}-Fe_4$Nlongrightarrow${gamma}$-Felongrightarrowa-Fe and of $varepsilon$-$Fe_3$Nlongrightarrow$varepsilon$-$Fe_{2.5}$ /N+${gamma}$`$-Fe_4$Nlongrightarrow${gamma}$`-Fe$_4$Nlongrightarrow${gamma}$longrightarrowFelongrightarrowalongrightarrowFe, respectively. It explains the reason why the $varepsilon$ $-Fe_3$N phase disappeared in the first time and then ${gamma}$`-Fe$_4$N in the formation of the black layer in the duplex coating.

black layer;duplex coating;hard coating;TiN;nitride;