Detection of SCC by the simultaneous use of electrochemical noise and acoustic emission measurements

Abstract

Electrochemical noise (EN) signals are recorded simultaneously with acoustic emission (AE) when tensile specimens made of a sensitized AISI 304 austenitic stainless steel are tested under a constant load. Specimen elongation is also measured. In order to obtain different types of cracking, various load levels and two electrolytes are used. In the case of transgranular stress corrosion cracking (SCC), several simultaneous EN and AE transients, accompanied by the “jumps” of specimen elongation, are detected. It is assumed that electrochemical events follow the mechanical events. In the case of intergranular SCC, some specific fluctuations of measured EN signals are observed, but neither related AE events nor specimen elongation jumps are found. At the same time, an increase in the direct current (DC) component of the measured electrochemical current is observed. It seems that the shift of the current in the anodic direction is originated by an increase in the dissolution surface area due to the growth of cracks. The simultaneous use of EN and AE techniques may, in certain cases, detect certain single events during SCC and provide valuable information on the nature of SCC processes.