Combined Effects of pH and γ-Irradiation on the Corrosion of Co-Cr Alloy Stellite-6

The effects of gamma-radiation on the corrosion of a cobalt-based alloy, Stellite-6, were studied at pH 6.0, 8.4 and 10.6 at room temperature. The type and thickness of the oxide formed and the dissolved cobalt content were analyzed following 3-d long corrosion tests using coupons in sealed vials. Oxidation kinetics were studied by monitoring the corrosion potential as a function of test conditions and by performing potentiostatic polarization tests as a function of applied potential. The results of this work show that gamma-irradiation increases the cobalt oxidation rate but the consequence of this increase varies with pH. This is due to the fact that pH influences the relative rates of two competing reactions, oxide growth and dissolution, differently. The increased cobalt oxidation rate at pH 6.0 leads mostly to an increase in the rate of cobalt dissolution, whereas the increased oxidation rate at pH 10.6 mostly increases the rate of oxide growth. At an intermediate pH (8.4) both dissolution and oxide growth are modestly enhanced. (C) 2014 Elsevier Ltd. All rights reserved.