Orrientation dependant nitrogen diffusion in single crystalline austenitic stainless steel during ion beam nitriding

Nitrogen diffusion in single crystalline stainless steel during ion beam nitrding is investigated. Single crystalline [orientations (001), (110) and (111)] AISI 316L austenitic stainless steel was ion beam nitrided at 400 °C using a Kaufman-type ion source with ion energy and flux of 1.2 keV and 0.5 mA cm−2, respectively. Phase structure was determined by X-ray diffraction (XRD) while nitrogen distribution profiles were obtained by nuclear reaction analysis (NRA). XRD analysis shows the presence of the phase usually called “expanded” austenite or γN phase. The NRA nitrogen depth distribution can be depicted by an initial quasilinear decrease followed by a sharp leading edge. It is observed that nitrogen penetration depth depends on the orientation: the fastest diffusion is observed in single crystalline samples with orientation (001) than in (011) or (111), while the orientations (110) and (111) showed similar penetration depth. The NRA profiles were compared with theoretical calculated employing ‘trapping-detrapping’ model. This comparison shows that the full experimental profile shape can be theoretically reproduced. In addition, this allows extracting diffusion coefficient values for different orientations.