Electrochemical study of multiple-energy nitrogen-ion-implanted aluminium alloys

Abstract

Nitrogen-implanted aluminium is reported to show a better pitting corrosion resistance. However, the corrosion behaviour depends on the number of nitrogen atoms available on the surface and the thickness of the implanted layer. In single-energy implantations the number of nitrogen atoms available on the surface is less than that in the bulk because of the Gaussian nature of the depth profile obtained. To overcome this difficulty, we decided to obtain a thick implanted layer and a flat depth profile by using multiple-energy implantations. Aluminium specimens were implanted with N + ions in energy steps of 80, 35 and 15 keV to a total dose of 4.6×10 17 N + cm −2 to obtain a layer of implanted surface 2000 Å thick. The implanted specimens were tested for corrosion resistance in Na 2SO 4 solutions at different pH values ranging from acidic to basic conditions. Cathodic and anodic polarization curves, corrosion potential and polarization resistance vs. time plots were obtained for implanted and unimplanted specimens. The samples were also characterized by scanning electron microscopy and Auger electron spectroscopy before and after the corrosion test. The electrochemical behaviour of the implanted samples appears quite different with respect to the unimplanted ones and the corrosion resistance improves in the acidic environment.