CRYSTALLOGRAPHIC ORIENTATION ANALYSIS OF FATIGUE CRACK SURFACE FROM AA7050 SAMPLES WITH MULTI-STAGE AGING TREATMENTS
André CarvalhoGrand Ballroom B
The retrogression and re-aging (RRA) and interrupted aging heat treatments (T6I4 conditions) lead to a bimodal microstructure feature within the 7050-aluminum alloy. Microstructural effects have a strong influence on fatigue crack nucleation and short crack growth via the activation of competing mechanisms operating during fatigue crack nucleation. Electron Back Scatter Diffraction (EBSD) technique permits the study of the effects of fatigue-induced crystal defects on the crack path and the pre-existing defect structure. Furthermore, few studies have explored the potential of multi-stage aging treatments on the fatigue crack nucleation paths using the EBSD technique. The purpose of this study is to elucidate the role of the microstructure on small fatigue crack crystallography in samples of RRA, T6I4-65 and T7451 conditions made from AA 7050. Fatigue crack surface crystallography will be determined near the vicinity of crack initiation sites and within the early crack growth regime using focused ion beam (FIB) surface preparation combined with electron back-scattered diffraction (EBSD). All the small fatigue cracks were initiated at the bore-hole surfaces on the gage length of specimen geometry, i.e., double-edge notches with two 4.8 mm diameters. The bore-hole surfaces of samples were electropolished prior to fatigue loading to remove bore-hole surface machining damage.