Development of CrN precipitates during the initial stages of PIII nitriding of stainless steel thin films

Abstract

Stainless steel thin films produced by ion beam sputtering (IBS) were used as a model system to investigate the nitrogen diffusion and CrN formation after 10min of nitrogen plasma immersion ion implantation (PIII) at 350°C and 450°C. At 350°C, a thin nitrided layer of 70nm is formed, with additional diffusion of nitrogen along grain boundaries and the growth of CrN precipitates along these grain boundaries. For 450°C, a complete nitriding of the whole 400nm thick layer was observed, with the lower 75nm consisting of an expanded phase and the upper 330nm of a decomposed phase with CrN precipitates formed inside the original grains. Such a layered structure capturing the transformation process has not been observed before. A determination of time–temperature dependencies of this process and the transfer of these results for bulk material should be possible.