Characterisation of Zircaloy corrosion fatigue phenomena in an iodine environment. Pt. 1

After work on SCC of Zry-4 in an iodine environment, the present authors have studied elastic corrosion fatigue in the same environment. Three types of recrystallized Zry-4 plates have been tested at room temperature in a methyl alcohol solution of iodine, with a load frequency of 10, 1, and 0.1 Hz. Crack growth rates have been measured on notched specimens in air and in an iodine environment. An increase of the crack growth rate - by a factor of about 4 - has been found in the latter environment. It was slightly frequency- and orientation dependent. SEM fracture surface examination showed that the mechanism of corrosion fatigue crack growth is rather unique: the fracture surface consists of a mixture of grains, some broken by pseudo-cleavage as seen during SCC crack growth, and the others broken by fatigue with striation spacing similar to those obtained in dry air. However, depending on the microstructure, cyclic work hardening masks the texture effects and makes the influence of stress frequency and loading direction more complex than in SCC. (orig.)