Ion beam synthesis of nitride layers in iron

Abstract

Stoichiometric iron nitride layers have been synthesized by high dose, high energy nitrogen implantation into Fe using a two-step implantation process. First, a nitrogen preimplantation at ~100 °C is used to form nitride precipitates. A low temperature is necessary to restrict the nitrogen mobility. Second, 1 MeV implantation at ~300 °C leads to the formation of a stoichiometric γ′–Fe4N layer at the position of the preimplanted N atoms. Growth of this nitride layer proceeds by diffusion of the implanted N through either the α–Fe matrix (for 200 or 500 keV preimplantations) or the nitride layer itself (for 1 MeV preimplantation). During annealing above 350 °C the γ′ layers dissolve in a planar fashion, characterized by an activation energy of 2.3 eV. Phase formation during preimplantation and phase transformations during subsequent annealing or hot implantation can be understood from the thermodynamics for the Fe–N system, while the kinetics of layer growth is influenced by the beam-induced defects. The experiment and model suggest that γ′ is not a thermodynamically stable phase below 310 ± 10 °C and should decompose into α (ferrite) and ∊ nitride.

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

“…Below such a triple point the g H -phase would be unstable with respect to both the e-phase and the a-phase. From ion implantation experiments and thermodynamical calculations this point was suggested to lie at % 300 C [6,7]. Other authors calculated values of %170 C or even %20 C [11].…”

Phase transformations in the Fe-N system induced by the concomitant use of ion irradiation and temperature

“…Alternatively, the ion implantation technique has been used in recent years to produce nitride precipitates (Principi et al 1980) or to synthesize nitride layers (Vredenberg et al 1992) by implanting N into Fe under different conditions. The aspects studied include the influence of the N implantation fluence, fluence rate, energy of implantation and temperature of the matrix during the implantation.…”

Nitrogen Vacancy Complexes in Nitrogen Irradiated Metals

“…A good example is nitrogen irradiation of metals to improve wear resistance and hardness [ 1,2]. The very early stages of the nucleation and agglomeration of nitrogen defects is not fiequently studied [3].…”