Comparative Study Of The Effect Of Silicon As An Alloying Element And As An Implanted Element In Austenitic Stainless Steels

摘要

The addition of Silicon into stainless steels is known to enhance the corrosion resistance to localised corrosion in chloride media. In this work, a comparison between Silicon as an alloying element and as an implanted element is studied. Ion implantation is a surface modification technique in which a graded alloy can be produced from the surface to the unchanged underlying bulk alloy, so that they can be independently optimised. This technique is known to produce chemical effects when interacting with the host material, and some physical effects during the process, generating a high number of defects inside the material. To study the first effect, a comparison between a Si-implanted, commercial stainless steel (AISI 304) and a silicon-rich stainless steel (MA153) is made. In addition, in order to obtain information about the radiation damage, Argon implantation has been carried out in the same material. The untreated AISI 304 was also studied for comparison purposes. The implantation dose used in this work is 1×10~(15) ions/cm~2 at an energy of 80keV. 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 0.5M NaCl solution for 5 weeks by using Electrochemical Impedance Spectroscopy (EIS). The surfaces have been characterised by Scanning Electron Microscopy (SEM). The results showed that Si-implantation produced some changes on the corrosion behaviour of AISI 304. During the first stages of the experiments, the physical modifications introduced during the process are more evident, whereas the chemical effect is more important for longer exposure periods, showing an intermediate response between the untreated material and the Si-rich one.