New method for low temperature gaseous nitriding of iron

Abstract

A new method for obtaining nitride layers in iron at low temperatures is presented. In this method, bulk iron is coated with a thin layer of nickel and is then treated in an NH3/H2 atmosphere at a temperature of 325°C. Analysis by elastic recoil detection, X-ray diffraction, and Rutherford backscattering spectrometry shows that nitride layers are formed in Fe which is covered with a Ni layer, while uncovered Fe is oxidised by impurities in the gas. The influence of the Ni layer is discussed. It is shown that it is possible to obtain pore free iron nitride layers at low temperatures.

Phase transformations in epitaxial Ni/Fe bilayers upon low-temperature gaseous nitriding

“…In polycrystalline Fe samples covered with a Ni layer the formation of ͑nearly 100%͒ of the phase was observed at the conditions used here. 9,8 However, the nitride in our sample consists for more than 95% of the ␥Ј-Fe 4 N phase. The delay observed in the phase formation is probably due to a lack of nucleation sites ͑such as lattice defects or grain boundaries͒ in the epitaxial Fe layer, which causes high energy barriers for phase transitions.…”

“…9,10 The role of Ni is twofold. On the one hand, it protects the underlying Fe from oxidation while allowing transport of N. On the other hand, it serves as a catalyst promoting decomposition of NH 3 .…”

Low-Temperature Nitridation of Iron Layers in NH3-H2 Mixtures

“…Other authors calculated values of %170 C or even %20 C [11]. A new nitriding method is applied [8,9] in which the iron is covered first with a thin layer of nickel. The role of the Ni layer in this process is twofold.…”

Low-temperature gaseous nitriding and subsequent oxidation of epitaxial Ni/Fe bilayers

“…Recently, we have found a method allowing fabrication of Fe-N phases in a mixture of NH 3 ϩH 2 at relatively low temperatures (275-350°C) by using a Ni cap layer as a catalyst. 4,5 With this method pore-free Fe-nitride layers can be obtained. The role of the Ni cap layer has been found to be twofold: ͑i͒ it promotes decomposition of the NH 3 molecules into atomic N and H; ͑ii͒ it protects the underlying Fe layer from possible oxidation by a small amount of H 2 O often present in the system.…”