ELECTROCHEMICAL CORROSION BEHAVIOR OF ION-IMPLANTED HSLA-80 STEEL

A high-strength low-alloy steel (HSLA-80), designated for naval structural applications and containing copper as a major precipitation-hardening element, was implanted with 52Cr+, 48Ti+, 27Al+, and 63Cu+ ions at 125 keV to different doses and subsequently investigated by the potentiodynamic technique for electrochemical corrosion behavior in electrolytes, viz., sodium acetate/acetic acid, pH 5.0, and 0.01 N sodium chloride, pH 6.0. The resistance was enhanced by reducing the critical corrosion current (icrit) by several order of magnitude over an unimplanted surface. Of these four ions, chromium had the most beneficial effect. Sample implanted with the four different ions responded differently in 0.01 N NaCl solution, which is often used as a pitting medium. In this case, chromium and aluminum ions improve the corrosion properties by reducing the general corrosion current and shifting the corrosion potential towards more noble values. Surface analysis by x-ray photoelectron spectroscopy and Auger electron spectroscopy confirmed the passivation of chromium and its enrichment on the surface in sodium acetate/acetic solution, while in NaCl it is the copper and iron that enriches and may take part in passivation. Chlorine deep inside an etch pit was also observed.