The role of applied potential on environment-assisted cracking of zirconium alloys

Zircaloy-2 and Zircaloy-4 have been tested by the slow-strain-rate technique at ambient and elevated temperatures in an acidic environment relevant to the proposed geologic repository at the Yucca Mountain site. Tests were performed with and without cathodic and anodic applied potentials. The results of stress corrosion cracking testing without applied potentials indicate that the ductility of both alloys was enhanced in terms of percent elongation, percent reduction in area, failure strain, and the time-to-failure with increasing temperature indicating improved ductility. However, the magnitude of true failure stress was gradually reduced at higher testing temperatures. The application of anodic and cathodic controlled potentials during slow-strain-rate testing enhanced the cracking susceptibility of both alloys showing more pronounced effect at anodic applied potentials. The corrosion potential for both alloys, became more active at the elevated temperature. The morphology of failure at cathodic potentials was ductile, showing dimpled microstructure. However, transgranular brittle failure was observed with both alloys at anodic controlled potentials.