Three types of recrystallized Zircaloy-4 plates have been studied at room temperature in a methyl alcohol solution of iodine (iodine concentration = 10^-3) and in dry air as a reference medium. Crack growth rates have been measured using double cantilever beam (DCB) and center notched (CN) specimens, depending on plate thickness. Fatigue life was obtained on smooth tensile type specimens.

Experimental data show that a corrosion fatigue phenomenon exists for Zircaloy in an iodine methyl alcohol solution; it is characterized by the following results: For fatigue life, a reduction in numbers of cycles to failure has been observed at intermediate stress levels, about a factor of 8, while there was no reduction of the fatigue strength. For crack growth rate, an increase has been found, by a factor of about 4, which had slight frequency and orientation dependence.

Extensive scanning electron microscope (SEM) fractography showed that the mechanism of corrosion fatigue of Zircaloy is rather unique: in contrast to classical corrosion fatigue, for which the increase in crack growth rate is due to the chemical enhancement of crack opening along the entire crack front, leading to wider striations, it was found in Zr-4 that the fracture surface consists of grains fractured by pseudo-cleavage as seen during stress corrosion cracking (SCC) crack growth, and other grains fractured by fatigue with striation spacings similar to those obtained in dry air at the same Delta K. For the initiation step, it was found that only intergranular cracking occurred on the free surface, until the stress intensity factor reached the threshold level for SCC or dry fatigue crack propagation, or both, at which point corrosion-fatigue started.