Anisotropic ion-enhanced diffusion during ion nitriding of single-crystalline austenitic stainless steel

Nitrogen diffusion is investigated in single crystalline austenitic stainless steel AISI 316L (ASS) during ion beam nitriding and subsequent annealing at different crystalline orientations. After nitriding at 400ºC and ion energy of 1 keV, the N penetration depth depends significantly on the crystalline orientation, with the highest penetration depth for (001) orientation. The experimental observations are quantitatively reproduced by fitting using the model of diffusion under the influence of traps. During subsequent isothermal annealing, the N diffusion becomes significantly slower than during nitriding and independent of the orientation. Possible mechanisms of the anisotropic ion enhanced N diffusion are discussed.