SMAT (Surface Mechanical Attrition Treatment) and plasma nitriding are surface treatments that enhance the mechanical properties of surface layers by inducing superficial nanostructures and formation of hard phases, respectively. By combining the two, the nanocrystalline layer generated by SMAT is thought to enhance the atomic diffusion of nitrogen into the material during the nitriding step. In this paper, a series of SMAT and nitriding experiments has been carried out at temperatures of 425°C for 20 h. Several observations (Transmission Electron Microscopy (TEM), scanning electron microscopy (SEM), crosssectional optical micrographs, micro-hardness profiles) show that polishing away a very thin layer after SMAT and before nitriding significantly improves nitrogen diffusion into the substrate, yielding a 50% thicker nitrided layer with respect to nitrided only. Furthermore, it improves the friction behaviour of the 316L steel. Additional chemical analyses by Energy Dispersive X-ray spectrometry (EDS) were performed to try to understand the effect of SMAT on the nitrogen diffusion.
