Study of respective roles of anodic and cathodic reactions in acoustic emission recorded during crevice corrosion of 304L austenitic stainless steel

Abstract

The contributions of anodic and cathodic reactions to the acoustic emission recorded during crevice corrosion of 304L austenitic stainless steel have been investigated. During the experiments, crevice propagation was localised on an anodic sample, whereas the cathodic reactions were isolated on a separate specimen. The application of shot-peening to the anodic and/or cathodic sample surfaces allowed control over the distribution of anodic and cathodic reactions on both specimens. The shot-peening treatment led to an increased crevice propagation rate, due to an increase in the cathodic current density. It has been established that the most energetic acoustic emissions originate from cathodic reactions, whereas anodic processes are associated with more numerous but shorter AE signals. During crevice development, the cathodic reactions begin with the reduction of O₂ and/or H₂O₂ on the cathodic specimen, but later involve H⁺ reduction in the so-called ‘anodic’ confined area. The involvement of proton reduction within the crevice as a driving force for crevice propagation has been confirmed by analysis of the acoustic emission data.