Cracking of Zircaloy-4 in acidic solution under controlled potentials

The susceptibility of Zircaloy-4 (Zr-4), a leading cladding material for nuclear fuels, to stress corrosion cracking (SCC) has been determined in an acidic solution at ambient and elevated temperatures by using constant-load and slow-strain-rate (SSR) testing techniques. Since the cracking susceptibility of Zr-4 may be influenced by electrochemical potential resulting from the repository environment, SCC testing has been performed under anodic and cathodic controlled potentials (Econt). While no failures were observed at constant load, the results of SSR testing exhibited enhanced ductility but reduced failure stress at elevated temperatures. The corrosion potential, determined by the cyclic potentiodynamic polarization technique, became more active at the elevated temperature. The SCC testing under anodic Econt showed brittle failure, characterized by transgranular cracking, as determined by scanning electron microscopy. The specimens tested with or without cathodic Econt showed dimpled microstructures, indicating ductile failure.