Formation of corrosion-resistant surface alloys by metal ion implantation

Abstract

Surface alloys were fabricated by the implantation of 25 keV chromium and nickel ions into polycrystalline iron in doses ranging from 1.0 × 10 16 to 4.0 × 10 16 ions cm -2. The alloy distribution as a function of depth (depth profile) was determined for the Fe-Cr and Fe-Ni surface alloys, and the results were compared with theoretical predictions. The resistance of the surface alloys to environmental attack was evaluated both by determining their anodic polarization behavior under potentiostatic conditions in a buffered boric acid solution and by determining their gaseous oxidation characteristics. The results of the electrochemical studies showed that the general corrosion resistances of the surface alloys are comparable with those of nominally equivalent bulk alloys and that the pitting-corrosion resistances of the surface alloys are superior to that of iron, although generally they are not as good as those of most equivalent bulk alloys. The gaseous oxidation studies showed that surface and bulk Fe-Cr alloys exhibit essentially identical oxidation kinetics, with a much higher rate of oxidation being observed for iron. In both the aqueous corrosion and the gaseous oxidation studies the quantity of the alloying element in the surface alloys was six to seven orders of magnitude less than that in the equivalent bulk alloys.