In two WASPALOY specimens, the orientations of grains that initiated fatigue cracks and adjacent grains were measured using electron backscattered diffraction patterns (EBSP). Crystallographic relationships were found for crack initiating regions that resulted in slip transmission across areas larger than the initiating grain, and the initiating grain was usually larger than average. A similar evaluation of control areas on each specimen found that there was much less likelihood of slip transmission across grain boundaries. Schmid factors (SFs) were also evaluated. It is concluded that the reason that fatigue cracks formed at these locations was due to the lower stress required for slip initiation in these clusters of grains oriented for slip transmission across grain boundaries. Many of the cracks initiated within grain boundaries. A detailed crystallographic analysis of the adjacent grains suggests criteria for intergranular (IG) crack initiation.

A three-dimensional (3-D) granular model that has the capability of predicting time-dependent intergranular corrosion (IGC) damage propagation depths in AA5083-H131 exposed to 0.6 M NaCl solution under potential control is presented. The geometry of grains and degree of sensitization (DoS) of grain boundaries were utilized as inputs, organized in a database, which informed the model to produce IGC depth distributions. The dependencies of IGC depth with exposure time, DoS, and orientation of propagation, both in terms of propagation kinetics and damage morphology, are outputs from the model. The model was calibrated by comparing outputted damage depths to IGC depth data from experiments. Model validation was achieved by comparing the predicted to experimental IGC depths based on image analyses of metallographic cross-section of AA5083-H131 exposed under the same conditions. The relevance and limitations of the current version of the model are discussed.