Microstructure of expanded austenite in ion-nitrided AISI 316L single crystals

Single crystalline AISI 316L austenitic stainless steel (ASS) samples of different orientations (001), (110), (310) were implanted at 400 °C with 1.2 keV nitrogen ions using a high current density of 0.5 mA˙cm− 2. Quantitative nitrogen distribution profiles were determined using nuclear reaction analysis (NRA), while the structure of the nitrided layer was analyzed using X-ray diffraction mapping of the reciprocal space. For identical nitriding conditions it is observed that surface N concentration does not depend on the orientation (∼23-24 at%), on contrary to the N penetration depth which is larger for the (001) and (310) orientations than for the (110) one. In each single crystal, lattice expansion in the nitrided layer is similar for all the studied crystallographic planes but it increases with the thickness of the nitrided layer. In addition, it is shown that during nitriding a simultaneous lattice rotation of a few degrees (< 5°) of the nitrided layer accompanies the lattice expansion with an increased mosaïcity.