In-situ X-ray investigations of phase formation and diffusion during low energy nitrogen ion implantation into austenitic stainless steel

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Nitrogen insertion into transition metals is in general associated with nitride formation, e.g. CrN or Fe3N. However, the fcc phase austenitic stainless steel incorporates nitrogen in solid solution with up to 30 at.% at temperatures between 350 and 400 °C, accompanied by an anisotropic lattice expansion of 5 – 15%. At the same time, a rapid diffusion of nitrogen from the surface into the bulk – following a d(t) α t1/2 law – is observed. Numerous exsitu experiments show diverging results with competing models for the phase formation proposed by different groups. In this project, in-situ X-ray diffraction experiments for low energy nitrogen ion implantation into fcc austenitic stainless steel (and related materials) for varying process temperatures, ion energy and ion current density are proposed to obtain a better understanding of the underlying processes. The existing models will be verified against the experimental results and modified and refined. Beside insights into radiation enhanced diffusion, additional information on the phase formation and stability of high nitrogen phases for transition metals of the iron group will be obtained.