Ion implantation as a surface modification technique to improve localised corrosion of different stainless steels

The effect of silicon and argon implantation on the corrosion behaviour of different stainless steels (AISI 304, AISI 316L, AISI 317L and AISI 430) is discussed in this work. Silicon was implanted in order to generate an Si-rich region near the surface. Argon, as an inert gas, is supposed to have no chemical effects on the material. Different implantation doses (1×1014, 5×1014, 1×1015 ions/cm2) at an energy of 80 keV have been tested to optimise the implantation dose for each steel. Theoretical simulations using TRIM 96 computer code have been performed in order to estimate the depth profiles and to optimise the implantation parameters. The corrosion measurements were carried out in NaCl solution by using electrochemical impedance spectroscopy (EIS). The surfaces have been characterised by SEM and AES. The experimental results showed that the effect of Si and Ar implantation mainly depends on the microstructure and/or composition of the stainless steels. Less compact structures and/or less amount of alloying elements (as occurs with the body centred cubic, ferritic AISI 430) achieve bigger changes with this modification, whereas on stainless steels with a larger amount of alloying elements and/or more compact structures (like the face centred cubic, austenitic AISI 317L) ion implantation slightly modifies the corrosion behaviour.