Corrosion of Cu-Au in acid sulfate solution under electrochemical and mechanical perturbation

Potentiostatic electrochemical noise measurements are performed on polycrystalline Cu0,75Au0,25 in aqueous sulfuric acid solutions, in the "passive" region below critical dealloying (V-c). Well detectable metastable events are observed on two types of Au enriched surfaces, obtained either by initially stepping the electrode potential in the dealloying region, or by preparing the surface so as to keep the initial Au segregation profile resulting from the annealing treatment. In contrast, when loading mechanically Cu0,75Au0,25, one observes successive silent or active electrochemical regions, which can be associated with the various stages of the mechanical test. Semi-quantitative signal analysis using low dimensional chaos theory reveals that : -i) the elastic - plastic transition is characterized by an increase in the local maximum Lyapunov exponent, ii) brittle cracking is announced by a net decrease of the local maximum Lyapunov exponent.