In-situ TEM investigation of fracture process in an Al-Cu-Mg alloy

The deformation and fracture process in Al-Cu-Mg alloy were investigated by using the in situ straining transmission electron microscopy (TEM) method. Some major aspects of the fracture process, including dislocation emission and migration, thinning of dislocation free zone (DFZ), crack propagation (both in continuous and discontinuous manners) and slipping/twinning deformation, can be observed. The rod-like T dispersoids, which may increase the microcrack initiation sensitivity, also can effectively prevent the fast and continuous propagation of the crack. DFZ ahead of crack tip can be thinned in a mixed mode characterized by tearing and shear deformation, while nanovoids, which are typical characteristics in DFZ during discontinuous crack propagation, may originate from the enrichment of defects such as dislocations and vacancies. Deformation twinning at crack tip can slow down crack propagation and change crack propagation path, thus may be beneficial to the fracture toughness of the alloy.